89. Textile Goods Industry
Chapter Editors: A. Lee Ivester and John D. Neefus
The Textile Industry: History and Health and Safety
Leon J. Warshaw
Global Trends in the Textile Industry
Production and Ginning of Cotton
W. Stanley Anthony
Cotton Yarn Manufacturing
Phillip J. Wakelyn
M.M. El Attal
A.E. Quinn and R. Mattiusi
Natural Felt Products
Jerzy A. Sokal
Dyeing, Printing and Finishing
J.M. Strother and A.K. Niyogi
Nonwoven Textile Fabrics
William Blackburn and Subhash K. Batra
Weaving and Knitting
Carpets And Rugs
The Carpet and Rug Institute
Hand-woven and Hand-tufted Carpets
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The Textile Industry
The term textile industry (from the Latin texere, to weave) was originally applied to the weaving of fabrics from fibres, but now it includes a broad range of other processes such as knitting, tufting, felting and so on. It has also been extended to include the making of yarn from natural or synthetic fibres as well as the finishing and dyeing of fabrics.
In prehistoric eras, animal hair, plants and seeds were used to make fibres. Silk was introduced in China around 2600 BC, and in the middle of the 18th century AD, the first synthetic fibres were created. While synthetic fibres made from cellulose or petrochemicals, either alone or in varied combinations with other synthetic and/or natural fibres, have seen increasingly widening use, they have not been able to totally eclipse fabrics made of natural fibres such as wool, cotton, flax and silk.
Silk is the only natural fibre formed in filaments which can be twisted together to make yarn. The other natural fibres must first be straightened, made parallel by combing and then drawn into a continuous yarn by spinning. The spindle is the earliest spinning tool; it was first mechanized in Europe around 1400 AD by the invention of the spinning wheel. The late 17th century saw the invention of the spinning jenny, which could operate a number of spindles simultaneously. Then, thanks to Richard Arkwright’s invention of the spinning frame in 1769 and Samuel Crompton’s introduction of the mule, which allowed one worker to operate 1,000 spindles at one time, yarn-making moved from being a cottage industry into the mills.
Making of fabric
The making of fabric had a similar history. Ever since its origins in antiquity, the hand loom has been the basic weaving machine. Mechanical improvements began in ancient times with the development of the heddle, to which alternate warp threads are tied; in the 13th century AD, the foot treadle, which could operate several sets of heddles, was introduced. With the addition of the frame-mounted batten, which beats the weft or filling yarns into place, the “mechanized” loom became the predominant weaving instrument in Europe and, except for traditional cultures where the original hand looms persisted, around the world.
John Kay’s invention of the flying shuttle in 1733, which allowed the weaver to send the shuttle across the width of the loom automatically, was the first step in mechanization of weaving. Edmund Cartwright developed the steam-powered loom and in 1788, with James Watt, built the first steam-driven textile mill in England. This freed the mills from their dependence on water-driven machinery and allowed them to be constructed anywhere. Another significant development was the punch-card system, developed in France in 1801 by Joseph Marie Jacquard; this allowed automated weaving of patterns. The earlier power looms made of wood were gradually replaced by looms made of steel and other metals. Since then, technological changes have focused on making them larger, faster and more highly automated.
Dyeing and printing
Natural dyes were originally used to impart colour to yarns and fabrics, but with the 19th-century discovery of coal-tar dyes and the 20th-century development of synthetic fibres, dyeing processes have become more complicated. Block printing was originally used to colour fabrics (silk-screen printing of fabrics was developed in the mid-1800s), but it soon was replaced by roller printing. Engraved copper rollers were first used in England in 1785, followed by rapid improvements that allowed roller printing in six colours all in perfect register. Modern roller printing can produce over 180 m of fabric printed in 16 or more colours in 1 minute.
Early on, fabrics were finished by brushing or shearing the nap of the fabric, filling or sizing the cloth, or passing it through calender rolls to produce a glazed effect. Today, fabrics are pre-shrunk, mercerized (cotton yarns and fabrics are treated with caustic solutions to improve their strength and lustre) and treated by a variety of finishing processes that, for example, increase crease resistance, crease holding and resistance to water, flame and mildew.
Special treatments produce high-performance fibres, so called because of their extraordinary strength and extremely high temperature resistance. Thus, Aramid, a fibre similar to nylon, is stronger than steel, and Kevlar, a fibre made from Aramid, is used to make bullet-proof fabrics and clothing that is resistant both to heat and chemicals. Other synthetic fibres combined with carbon, boron, silicon, aluminium and other materials are used to produce the lightweight, superstrong structural materials used in airplanes, spacecraft, chemical resistant filters and membranes, and protective sports gear.
From hand craft to industry
Textile manufacture was originally a hand craft practised by cottage spinners and weavers and small groups of skilled artisans. With the technological developments, large and economically important textile enterprises emerged, primarily in the United Kingdom and the Western European countries. Early settlers in North America brought cloth mills to New England (Samuel Slater, who had been a mill supervisor in England, constructed from memory a spinning frame in Providence, Rhode Island, in 1790), and the invention of Eli Whitney’s cotton gin, which could clean harvested cotton with great speed, created a new demand for cotton fabrics.
This was accelerated by the commercialization of the sewing machine. In the early 18th century, a number of inventors produced machines that would stitch cloth. In France in 1830, Barthelemy Thimonnier received a patent for his sewing machine; in 1841, when 80 of his machines were busy sewing uniforms for the French army, his factory was destroyed by tailors who saw his machines as a threat to their livelihood. At about that time in England, Walter Hunt devised an improved machine but abandoned the project because he felt that it would throw poor seamstresses out of work. In 1848, Elias Howe received a US patent for a machine much like Hunt’s, but became embroiled in legal battles, which he ultimately won, charging many manufacturers with infringement of his patent. The invention of the modern sewing machine is credited to Isaac Merritt Singer, who devised the overhanging arm, the presser foot to hold down the cloth, a wheel to feed the fabric to the needle and a foot treadle instead of a hand crank, leaving both hands free to manoeuvre the fabric. In addition to designing and manufacturing the machine, he created the first large-scale consumer-appliance enterprise, which featured such innovations as an advertising campaign, selling the machines on the installment plan, and providing a service contract.
Thus, the technological advances during the 18th century were not only the impetus for the modern textile industry but they can be credited with the creation of the factory system and the profound changes in family and community life that have been labelled the Industrial Revolution. The changes continue today as large textile establishments move from the old industrialized areas to new regions that promise cheaper labour and sources of energy, while competition fosters continuing technological developments such as computer-controlled automation to reduce labour needs and improve quality. Meanwhile, politicians debate quotas, tariffs and other economic barriers to provide and/or retain competitive advantages for their countries. Thus, the textile industry not only provides products essential for the world’s growing population; it also has a profound influence on international trade and the economies of nations.
Safety and Health Concerns
As machines became larger, speedier and more complicated, they also introduced new potential hazards. As materials and processes became more complex, they infused the workplace with potential health hazards. And as workers had to cope with mechanization and the demand for increasing productivity, work stress, largely unrecognized or ignored, exerted an increasing influence on their well-being. Perhaps the greatest effect of the Industrial Revolution was on community life, as workers moved from the country to cities, where they had to contend with all of the ills of urbanization. These effects are being seen today as the textile and other industries move to developing countries and regions, except that the changes are more rapid.
The hazards encountered in different segments of the industry are summarized in the other articles in this chapter. They emphasize the importance of good housekeeping and proper maintenance of machines and equipment, the installation of effective guards and fences to prevent contact with moving parts, the use of local exhaust ventilation (LEV) as a supplement to good general ventilation and temperature control, and the provision of appropriate personal protective equipment (PPE) and clothing whenever a hazard cannot be completely controlled or prevented by design engineering and/or substitution of less hazardous materials. Repeated education and training of workers on all levels and effective supervision are recurrent themes.
Environmental concerns raised by the textile industry stem from two sources: the processes involved in textile manufacture and hazards associated with the way the products are used.
The chief environmental problems created by textile manufacturing plants are toxic substances released into the atmosphere and into wastewater. In addition to potentially toxic agents, unpleasant odours are often a problem, especially where dyeing and printing plants are located near residential areas. Ventilation exhausts may contain vapours of solvents, formaldehyde, hydrocarbons, hydrogen sulphide and metallic compounds. Solvents may sometimes be captured and distilled for reuse. Particulates may be removed by filtration. Scrubbing is effective for water-soluble volatile compounds such as methanol, but it does not work in pigment printing, where hydrocarbons make up most of the emissions. Flammables may be burned off, although this is relatively expensive. The ultimate solution, however, is the use of materials that are as close to being emission-free as possible. This refers not only to the dyes, binders and cross-linking agents used in the printing, but also to the formaldehyde and residual monomer content of fabrics.
Contamination of wastewater by unfixed dyes is a serious environmental problem not only because of the potential health hazards to human and animal life, but also because of the discolouration that makes it highly visible. In ordinary dyeing, fixation of over 90% of the dyestuff can be achieved, but fixation levels of only 60% or less are common in printing with reactive dyes. This means that more than one-third of the reactive dye enters the wastewater during the washing-off of the printed fabric. Additional amounts of dyes are introduced into the wastewater during the washing of screens, printing blankets and drums.
Limits on wastewater discolouration have been set in a number of countries, but it is often very difficult to heed them without an expensive wastewater purification system. A solution is found in the use of dyestuffs with a lesser contaminating effect and the development of dyes and synthetic thickening agents that increase the degree of dye fixation, thereby reducing the amounts of the excess to be washed away (Grund 1995).
Environmental concerns in textile use
Residues of formaldehyde and some heavy-metal complexes (most of these are inert) may be sufficient to cause skin irritation and sensitization in persons wearing the dyed fabrics.
Formaldehyde and residual solvents in carpets and fabrics used for upholstery and curtains will continue to vaporize gradually for some time. In buildings that are sealed, where the air-conditioning system recirculates most of the air rather than exhausting it to the outside environment, these substances may reach levels high enough to produce symptoms in the occupants of the building, as discussed elsewhere in this Encyclopaedia.
To ensure the safety of fabrics, Marks and Spencer, the British/Canadian clothing retailer, led the way by setting limits for formaldehyde in garments they would purchase. Since then, other garment manufacturers, notably Levi Strauss in the United States, have followed suit. In a number of countries, these limits have been formalized in laws (e.g., Denmark, Finland, Germany and Japan), and, in response to consumer education, fabric manufacturers have been voluntarily adhering to such limits in order to be able to use eco labels (see figure 1).
Figure 1. Ecological labels used for textiles
Technological developments are continuing to enhance the range of fabrics produced by the textile industry and to increase its productivity. It is most important, however, that these developments be guided also by the imperative of enhancing the health, safety and well-being of the workers. But even then, there is the problem of implementing these developments in older enterprises that are marginally financially viable and unable to make the necessary investments, as well as in developing areas eager to have new industries even at the expense of the health and safety of the workers. Even under these circumstances, however, much can be achieved by education and training of the workers to minimize the risks to which they may be exposed.
Human beings have relied on clothing and food to survive ever since they appeared on earth. The clothing or textile industry thus began very early in human history. While early people used their hands to weave and knit cotton or wool into fabric or cloth, it was not until the late 18th and early 19th centuries that the Industrial Revolution changed the way of making clothes. People started to use various kinds of energy to supply power. Nevertheless, cotton, wool and cellulose fibres remained the major raw materials. Since the Second World War, the production of synthetic fibres developed by the petrochemical industry has increased tremendously. The consumption volume of synthetic fibres of world textile products in 1994 was 17.7 million tons, 48.2% of all fibres, and it is expected to exceed 50% after 2000 (see figure 1).
Figure 1. Change in fibre supply in the textile industry before 1994 and projected through 2004.
According to the world apparel fibre consumption survey by the Food and Agricultural Organization (FAO), the average annual rates of growth for textile consumption during 1969–89, 1979–89 and 1984–89 were 2.9%, 2.3% and 3.7% respectively. Based on the previous consumption trend, population growth, per capita GDP (gross domestic product) growth, and the increase of consumption of each textile product with rising income, the demand for textile products in 2000 and 2005 will be 42.2 million tons and 46.9 million tons, respectively, as shown in figure 1. The trend indicates that there is a consistent growing demand for textile products, and that the industry will still employ a large workforce.
Another major change is the progressive automation of weaving and knitting, which, combined with rising labour costs, has shifted the industry from the developed to the developing countries. Although the production of yarn and fabric products, as well as some upstream synthetic fibres, has remained in more developed countries, a large proportion of the labour-intensive downstream apparel industry has already moved to the developing countries. The Asia-Pacific region’s textile and clothing industry now accounts for approximately 70% of the world production; table 1 indicates a shifting trend of employment in this region. Thus, the occupational safety and health of textile workers has become a major issue in developing countries; figure 2, figure 3, figure 4 and figure 5, illustrate some textile industry processes as they are carried out in the developing world.
Table 1. Numbers of enterprises and employees in textile and apparel industries of selected countries and territories in the Asia-Pacific area in 1985 and 1995.
Korea, Republic of
Wilawan Juengprasert, Ministry of Public Health, Thailand
Wilawan Juengprasert, Ministry of Public Health, Thailand
Wilawan Juengprasert, Ministry of Public Health, Thailand
Wilawan Juengprasert, Ministry of Public Health, Thailand
Cotton production practices begin after the previous crop is harvested. The first operations usually include shredding stalks, ripping out roots and disking the soil. Fertilizer and herbicides generally are applied and incorporated into the soil before the land is bedded in preparation for needed irrigation or planting. Since soil characteristics and past fertilization and cropping practices can cause a wide range of fertility levels in cotton soils, fertility programmes should be based on soil test analyses. Control of weeds is essential to obtain high lint yield and quality. Cotton yields and harvesting efficiency can be reduced by as much as 30% by weeds. Herbicides have been widely used in many countries for weed control since the early 1960s. Application methods include pre-planting treatment to foliage of existing weeds, incorporation into pre-plant soil and treatment at pre-emergence and post-emergence stages.
Several factors that play an important role in achieving a good stand of cotton plants include seed-bed preparation, soil moisture, soil temperature, seed quality, seedling disease infestation, fungicides and soil salinity. Planting high-quality seed in a well-prepared seed-bed is a key factor in achieving early, uniform stands of vigorous seedlings. High-quality planting seed should have a germination rate of 50% or higher in a cool test. In a cool/warm test, the seed vigour index should be 140 or higher. Seeding rates of 12 to 18 seeds/metre of row are recommended to obtain a plant population of 14,000 to 20,000 plants/hectare. A suitable planter metering system should be used to ensure uniform spacing of seed regardless of seed size. Seed germination and seedling emergence rates are closely associated with a temperature range of 15 to 38 ºC.
Early-season seedling diseases can hamper uniform stands and result in the need to replant. Important seedling disease pathogens such as Pythium, Rhizoctonia, Fusarium and Thielaviopsis can reduce plant stands and cause long skips between seedlings. Only seed that has been properly treated with one or more fungicides should be planted.
Cotton is similar to other crops with respect to water use during different plant developmental stages. Water use is generally less than 0.25 cm/day from emergence to the first square. During this period, loss of soil moisture by evaporation may exceed the amount of water transpired by the plant. Water use increases sharply as the first blooms appear and reaches a maximum level of 1 cm/day during the peak bloom stage. Water requirement refers to the total amount of water (rainfall and irrigation) needed to produce a crop of cotton.
Insect populations can have an important impact on cotton quality and yield. Early-season population management is important in promoting balanced fruiting/vegetative development of the crop. Protecting early fruit positions is essential to achieving a profitable crop. Over 80% of the yield is set in the first 3 to 4 weeks of fruiting. During the fruiting period, producers should scout their cotton at least twice a week to monitor insect activity and damage.
A well-managed defoliation programme reduces leaf trash that can adversely affect the grade of the harvested cotton. Growth regulators such as PIX are useful defoliators because they control vegetative growth and contribute to earlier fruiting.
Two types of mechanical harvesting equipment are used to harvest cotton: the spindle picker and the cotton stripper. The spindle picker is a selective-type harvester that uses tapered, barbed spindles to remove seed cotton from bolls. This harvester can be used on a field more than once to provide stratified harvests. On the other hand, the cotton stripper is a nonselective or once-over harvester that removes not only the well-opened bolls but also the cracked and unopened bolls along with the burs and other foreign matter.
Agronomic practices that produce a high-quality uniform crop will generally contribute to good harvesting efficiency. The field should be well drained and rows laid out for effective use of machinery. Row ends should be free of weeds and grass, and should have a field border of 7.6 to 9 m for turning and aligning the harvesters with the rows. The border also should be free of weeds and grass. Disking creates adverse conditions in rainy weather, so chemical weed control or mowing should be used instead. Plant height should not exceed about 1.2 m for cotton that is to be picked, and about 0.9 m for cotton that is to be stripped. Plant height can be controlled to some extent by using chemical growth regulators at the proper growth stage. Production practices that set the bottom boll at least 10 cm above the ground should be used. Culturing practices such as fertilization, cultivation and irrigation during the growing season should be carefully managed to produce a uniform crop of well-developed cotton.
Chemical defoliation is a culturing practice that induces abscission (shedding) of foliage. Defoliants may be applied to help minimize green-leaf-trash contamination and promote faster drying of early morning dew on the lint. Defoliants should not be applied until at least 60% of the bolls are open. After a defoliant is applied, the crop should not be harvested for at least 7 to 14 days (the period will vary depending on chemicals used and weather conditions). Chemical desiccants may also be used to prepare plants for harvest. Desiccation is the rapid loss of water from the plant tissue and subsequent death of the tissue. The dead foliage remains attached to the plant.
The current trend in cotton production is toward a shorter season and one-time harvest. Chemicals that accelerate the boll opening process are applied with the defoliant or soon after the leaves drop. These chemicals allow earlier harvests and increase the percentage of bolls that are ready to be harvested during the first harvest. Because these chemicals have the ability to open or partially open immature bolls, the quality of the crop may be severely impacted (i.e., the micronaire may be low) if the chemicals are applied too early.
The moisture content of cotton before and during storage is critical; excess moisture causes stored cotton to overheat, resulting in lint discolouration, lower seed germination and possibly spontaneous combustion. Seed cotton with a moisture content above 12% should not be stored. Also, the internal temperature of newly built modules should be monitored for the first 5 to 7 days of cotton storage; modules that experience a 11 ºC rise or are above 49 ºC should be ginned immediately to avoid the possibility of major loss.
Several variables affect seed and fibre quality during seed cotton storage. Moisture content is the most important. Other variables include length of storage, amount of high-moisture foreign matter, variation in moisture content throughout the stored mass, initial temperature of the seed cotton, temperature of the seed cotton during storage, weather factors during storage (temperature, relative humidity, rainfall) and protection of the cotton from rain and wet ground. Yellowing is accelerated at high temperatures. Both temperature rise and maximum temperature are important. Temperature rise is directly related to the heat generated by biological activity.
About 80 million bales of cotton are produced annually worldwide, of which about 20 million are produced by about 1,300 gins in the United States. The principal function of the cotton gin is to separate lint from seed, but the gin must also be equipped to remove a large percentage of the foreign matter from the cotton that would significantly reduce the value of the ginned lint. A ginner must have two objectives: (1) to produce lint of satisfactory quality for the grower’s market and (2) to gin the cotton with minimum reduction in fibre spinning quality, so that the cotton will meet the demands of its ultimate users, the spinner and the consumer. Accordingly, quality preservation during ginning requires the proper selection and operation of each machine in a ginning system. Mechanical handling and drying may modify the natural quality characteristics of cotton. At best, a ginner can only preserve the quality characteristics inherent in the cotton when it enters the gin. The following paragraphs briefly discuss the function of the major mechanical equipment and processes in the gin.
Cotton is transported from a trailer or module into a green-boll trap in the gin, where green bolls, rocks and other heavy foreign matter are removed. The automatic feed control provides an even, well-dispersed flow of cotton so that the gin’s cleaning and drying system will operate more efficiently. Cotton that is not well dispersed can travel through the drying system in clumps, and only the surface of that cotton will be dried.
In the first stage of drying, heated air conveys the cotton through the shelves for 10 to 15 seconds. The temperature of the conveying air is regulated to control the amount of drying. To prevent fibre damage, the temperature to which the cotton is exposed during normal operation should never exceed 177 ºC. Temperatures above 150 ºC can cause permanent physical changes in cotton fibres. Dryer-temperature sensors should be located as near as possible to the point where cotton and heated air come together. If the temperature sensor is located near the exit of the tower dryer, the mixpoint temperature could actually be 55 to 110 ºC higher than the temperature at the downstream sensor. The temperature drop downstream results from the cooling effect of evaporation and from heat loss through the walls of machinery and piping. The drying continues as the warm air moves the seed cotton to the cylinder cleaner, which consists of 6 or 7 revolving spiked cylinders that rotate at 400 to 500 rpm. These cylinders scrub the cotton over a series of grid rods or screens, agitate the cotton and allow fine foreign materials, such as leaves, trash and dirt, to pass through the openings for disposal. Cylinder cleaners break up large wads and generally condition the cotton for additional cleaning and drying. Processing rates of about 6 bales per hour per metre of cylinder length are common.
The stick machine removes larger foreign matter, such as burs and sticks, from the cotton. Stick machines use the centrifugal force created by saw cylinders rotating at 300 to 400 rpm to “sling off” foreign material while the fibre is held by the saw. The foreign matter that is slung off the reclaimer feeds into the trash-handling system. Processing rates of 4.9 to 6.6 bales/hr/m of cylinder length are common.
Ginning (lint-seed separation)
After going through another stage of drying and cylinder cleaning, cotton is distributed to each gin stand by the conveyor-distributor. Located above the gin stand, the extractor-feeder meters seed cotton uniformly to the gin stand at controllable rates, and cleans seed cotton as a secondary function. The moisture content of cotton fibre at the extractor-feeder apron is critical. The moisture must be low enough that foreign matter can be easily removed in the gin stand. However, the moisture must not be so low (below 5%) as to result in the breakage of individual fibres as they are separated from the seed. This breakage causes an appreciable reduction both in fibre length and lint turnout. From a quality standpoint, cotton with a higher content of short fibres produces excessive waste at the textile mill and is less desirable. Excessive breakage of fibres can be avoided by maintaining a fibre moisture content of 6 to 7% at the extractor-feeder apron.
Two types of gins are in common use—the saw gin and the roller gin. In 1794, Eli Whitney invented a gin that removed fibre from the seed by means of spikes or saws on a cylinder. In 1796, Henry Ogden Holmes invented a gin having saws and ribs; this gin replaced Whitney’s gin and made ginning a continuous-flow process rather than a batch process. Cotton (usually Gossypium hirsutum) enters the saw gin stand through a huller front. The saws grasp the cotton and draw it through widely spaced ribs known as huller ribs. The locks of cotton are drawn from the huller ribs into the bottom of the roll box. The actual ginning process—separation of lint and seed—takes place in the roll box of the gin stand. The ginning action is caused by a set of saws rotating between ginning ribs. The saw teeth pass between the ribs at the ginning point. Here the leading edge of the teeth is approximately parallel to the rib, and the teeth pull the fibres from the seed, which are too large to pass between the ribs. Ginning at rates above those recommended by the manufacturer can cause fibre quality reduction, seed damage and choke-ups. Gin stand saw speeds are also important. High speeds tend to increase the fibre damage done during ginning.
Roller-type gins provided the first mechanically aided means of separating extra-long staple cotton (Gossypium barbadense) lint from seed. The Churka gin, which has an unknown origin, consisted of two hard rollers that ran together at the same surface speed, pinching the fibre from the seed and producing about 1 kg of lint/day. In 1840, Fones McCarthy invented a more efficient roller gin that consisted of a leather ginning roller, a stationary knife held tightly against the roller and a reciprocating knife that pulled the seed from the lint as the lint was held by the roller and stationary knife. In the late 1950s, a rotary-knife roller gin was developed by the US Department of Agriculture (USDA) Agricultural Research Service’s Southwestern Cotton Ginning Research Laboratory, US gin manufacturers and private ginneries. This gin is currently the only roller-type gin used in the United States.
Cotton is conveyed from the gin stand through lint ducts to condensers and formed again into a batt. The batt is removed from the condenser drum and fed into the saw-type lint cleaner. Inside the lint cleaner, cotton passes through the feed rollers and over the feed plate, which applies the fibres to the lint cleaner saw. The saw carries cotton under grid bars, which are aided by centrifugal force and remove immature seeds and foreign matter. It is important that the clearance between the saw tips and grid bars be properly set. The grid bars must be straight with a sharp leading edge to avoid reducing cleaning efficiency and increasing lint loss. Increasing the lint cleaner’s feed rate above the manufacturer’s recommended rate will decrease cleaning efficiency and increase loss of good fibre. Roller-ginned cotton is usually cleaned with non-aggressive, non-saw-type cleaners to minimize fibre damage.
Lint cleaners can improve the grade of cotton by removing foreign matter. In some cases, lint cleaners may improve the colour of a lightly spotted cotton by blending to produce a white grade. They may also improve the colour grade of a spotted cotton to light spotted or perhaps white colour grade.
The cleaned cotton is compressed into bales, which must then be covered to protect them from contamination during transportation and storage. Three types of bales are produced: modified flat, compress universal density and gin universal density. These bales are packaged at densities of 224 and 449 kg/m3 for the modified flat and universal density bales, respectively. In most gins cotton is packaged in a “double-box” press wherein the lint is initially compacted in one press box by a mechanical or hydraulic tramper; then the press box is rotated, and the lint is further compressed to about 320 or 641 kg/m3 by modified flat or gin universal density presses, respectively. Modified flat bales are recompressed to become compress universal density bales in a later operation to achieve optimum freight rates. In 1995, about 98% of the bales in the United States were gin universal density bales.
Cotton quality is affected by every production step, including selecting the variety, harvesting and ginning. Certain quality characteristics are highly influenced by genetics, while others are determined mainly by environmental conditions or by harvesting and ginning practices. Problems during any step of production or processing can cause irreversible damage to fibre quality and reduce profits for the producer as well as the textile manufacturer.
Fibre quality is highest the day a cotton boll opens. Weathering, mechanical harvesting, handling, ginning and manufacturing can diminish the natural quality. There are many factors that indicate the overall quality of cotton fibre. The most important ones include strength, fibre length, short fibre content (fibres shorter than 1.27 cm), length uniformity, maturity, fineness, trash content, colour, seedcoat fragment and nep content, and stickiness. The market generally recognizes these factors even though not all are measured on each bale.
The ginning process can significantly affect fibre length, uniformity and the content of seedcoat fragments, trash, short fibres and neps. The two ginning practices that have the most impact on quality are the regulation of fibre moisture during ginning and cleaning and the degree of saw-type lint cleaning used.
The recommended lint moisture range for ginning is 6 to 7%. Gin cleaners remove more trash at low moisture but not without more fibre damage. Higher fibre moisture preserves fibre length but results in ginning problems and poor cleaning, as illustrated in figure 1. If drying is increased to improve trash removal, yarn quality is reduced. Although yarn appearance improves with drying up to a point, because of increased foreign-matter removal, the effect of increased short-fibre content outweighs the benefits of foreign-matter removal.
Figure 1. Moisture-ginning cleaning compromise for cotton
Cleaning does little to change the true colour of the fibre, but combing the fibres and removing trash changes the perceived colour. Lint cleaning can sometimes blend fibre so that fewer bales are classified as spotted or light spotted. Ginning does not affect fineness and maturity. Each mechanical or pneumatic device used during cleaning and ginning increases the nep content, but lint cleaners have the most pronounced influence. The number of seedcoat fragments in ginned lint is affected by the seed condition and ginning action. Lint cleaners decrease the size but not the number of fragments. Yarn strength, yarn appearance and spinning-end breakage are three important spinning quality elements. All are affected by length uniformity and, therefore, by the proportion of short or broken fibres. These three elements are usually preserved best when cotton is ginned with minimum drying and cleaning machinery.
Recommendations for the sequence and amount of gin machinery to dry and clean spindle-harvested cotton were designed to achieve satisfactory bale value and to preserve the inherent quality of cotton. They have generally been followed and thus confirmed in the US cotton industry for several decades. The recommendations consider marketing-system premiums and discounts as well as the cleaning efficiency and fibre damage resulting from various gin machines. Some variation from these recommendations is necessary for special harvesting conditions.
When gin machinery is used in the recommended sequence, 75 to 85% of the foreign matter is usually removed from cotton. Unfortunately, this machinery also removes small quantities of good-quality cotton in the process of removing foreign matter, so the quantity of marketable cotton is reduced during cleaning. Cleaning cotton is therefore a compromise between foreign matter level and fibre loss and damage.
Safety and Health Concerns
The cotton ginning industry, like other processing industries, has many hazards. Information from workers’ compensation claims indicates that the number of injuries is highest for the hand/fingers, followed by back/spine, eye, foot/toes, arm/shoulder, leg, trunk and head injuries. While the industry has been active in hazard reduction and safety education, gin safety remains a major concern. The reasons for the concern include the high frequency of accidents and workers’ compensation claims, the large number of lost work days and the severity of the accidents. Total economic costs for gin injuries and health disorders include direct costs (medical and other compensation) and indirect costs (time lost from work, downtime, loss in earning power, higher insurance costs for workers’ compensation, loss of productivity and many other loss factors). Direct costs are easier to determine and much less expensive than indirect costs.
Many international safety and health regulations affecting cotton ginning are derived from US legislation administered by the Occupational Safety and Health Administration (OSHA) and the Environmental Protection Agency (EPA), which promulgates pesticides regulations.
Other agricultural regulations may also apply to a gin, including requirements for slow-moving vehicle emblems on trailers/tractors operating on public roadways, provisions for rollover protective structures on tractors operated by employees and provisions for proper living facilities for temporary labour. While gins are considered agricultural enterprises and are not specifically covered by many regulations, ginners will likely want to conform to other regulations, such as OSHA’s “Standards for General Industry, Part 1910”. There are three specific OSHA standards that ginners should consider: those for fire and other emergency plans (29 CFR 1910.38a), exits (29 CFR 1910.35-40) and occupational noise exposure (29 CFR 1910.95). Major exit requirements are given in 29 CFR 1910.36 and 29 CFR 1910.37. In other countries, where agricultural workers are included in mandatory coverage, such compliance will be compulsory. Compliance with noise and other safety and health standards is discussed elsewhere in this Encyclopaedia.
Employee participation in safety programmes
The most effective loss control programmes are those in which management motivates employees to be safety conscious. This motivation can be accomplished by establishing a safety policy that gets the employees involved in each element of the programme, by participating in safety training, by setting a good example and by providing employees with appropriate incentives.
Occupational health disorders are lessened by requiring that PPE be used in designated areas and that employees observe acceptable work practices. Hearing (plugs or muffs) and respiratory (dust mask) PPE should be used whenever working in areas having high noise or dust levels. Some people are more susceptible to noise and respiratory problems than others, and even with PPE should be reassigned to work areas with lower noise or dust levels. Health hazards associated with heavy lifting and excessive heat can be handled by training, use of materials-handling equipment, proper dress, ventilation and breaks from the heat.
All persons throughout the gin operation must be involved in gin safety. A safe work atmosphere can be established when everyone is motivated to participate fully in the loss control programme.
Cotton accounts for almost 50% of the worldwide consumption of textile fibre. China, the United States, the Russian Federation, India and Japan are the major cotton-consuming countries. Consumption is measured by the amount of raw cotton fibre purchased and used to manufacture textile materials. Worldwide cotton production is annually about 80 to 90 million bales (17.4 to 19.6 billion kg). China, the United States, India, Pakistan and Uzbekistan are the major cotton-producing countries, accounting for over 70% of world cotton production. The rest is produced by about 75 other countries. Raw cotton is exported from about 57 countries and cotton textiles from about 65 countries. Many countries emphasize domestic production to reduce their reliance on imports.
Yarn manufacturing is a sequence of processes that convert raw cotton fibres into yarn suitable for use in various end-products. A number of processes are required to obtain the clean, strong, uniform yarns required in modern textile markets. Beginning with a dense package of tangled fibres (cotton bale) containing varying amounts of non-lint materials and unusable fibre (foreign matter, plant trash, motes and so on), continuous operations of opening, blending, mixing, cleaning, carding, drawing, roving and spinning are performed to transform the cotton fibres into yarn.
Even though the current manufacturing processes are highly developed, competitive pressure continues to spur industry groups and individuals to seek new, more efficient methods and machines for processing cotton which, one day, may supplant today’s systems. However, for the foreseeable future, the current conventional systems of blending, carding, drawing, roving and spinning will continue to be used. Only the cotton picking process seems clearly destined for elimination in the near future.
Yarn manufacturing produces yarns for various woven or knitted end-products (e.g., apparel or industrial fabrics) and for sewing thread and cordage. Yarns are produced with different diameters and different weights per unit length. While the basic yarn manufacturing process has remained unchanged for a number of years, processing speeds, control technology and package sizes have increased. Yarn properties and processing efficiency are related to the properties of the cotton fibres processed. End-use properties of the yarn are also a function of processing conditions.
Yarn Manufacturing Processes
Opening, blending, mixing and cleaning
Typically, mills select bale mixes with the properties needed to produce yarn for a specific end-use. The number of bales used by different mills in each mix ranges from 6 or 12 to over 50. Processing begins when the bales to be mixed are brought to the opening room, where bagging and ties are removed. Layers of cotton are removed from the bales by hand and placed in feeders equipped with conveyors studded with spiked teeth, or entire bales are placed on platforms which move them back and forth under or over a plucking mechanism. The aim is to begin the sequential production process by converting the compacted layers of baled cotton into small, light, fluffy tufts that will facilitate the removal of foreign matter. This initial process is referred to as “opening”. Since bales arrive at the mill in various degrees of density, it is common for bale ties to be cut approximately 24 hours before the bales are to be processed, in order to allow them to “bloom”. This enhances opening and helps regulate the feeding rate. The cleaning machines in mills perform the functions of opening and first-level cleaning.
Carding and combing
The card is the most important machine in the yarn manufacturing process. It performs second- and final-level cleaning functions in an overwhelming majority of cotton textile mills. The card is composed of a system of three wire-covered cylinders and a series of flat, wire-covered bars that successively work small clumps and tufts of fibres into a high degree of separation or openness, remove a very high percentage of trash and other foreign matter, collect the fibres into a rope-like form called a “sliver” and deliver this sliver in a container for use in the subsequent process (see figure 1).
Figure 1. Carding
Wilawan Juengprasert, Ministry of Public Health, Thailand
Historically, cotton has been fed to the card in the form of a “picker lap”, which is formed on a “picker”, a combination of feed rolls and beaters with a mechanism made up of cylindrical screens on which opened tufts of cotton are collected and rolled into a batt (see figure 2). The batt is removed from the screens in an even, flat sheet and then is rolled into a lap. However, labour requirements and the availability of automated handling systems with the potential for improved quality are contributing to the obsolescence of the picker.
Figure 2. A modern picker
Wilawan Juengprasert, Ministry of Public Health, Thailand
The elimination of the picking process has been made possible by the installation of more efficient opening and cleaning equipment and chute-feed systems on the cards. The latter distribute opened and cleaned tufts of fibres to cards pneumatically through ducts. This action contributes to processing consistency and improved quality and reduces the number of workers required.
A small number of mills produce combed yarn, the cleanest and most uniform cotton yarn. Combing provides more extensive cleaning than is provided by the card. The purpose of combing is to remove short fibres, neps and trash so that the resulting sliver is very clean and lustrous. The comber is a complicated machine composed of grooved feed rolls and a cylinder that is partially covered with needles to comb out short fibres (see figure 3).
Figure 3. Combing
Wilawan Juengprasert, Ministry of Public Health, Thailand
Drawing and roving
Drawing is the first process in yarn manufacturing that employs roller drafting. In drawing, practically all draft results from the action of rollers. Containers of sliver from the carding process are staked in the creel of the drawing frame. Drafting occurs when a sliver is fed into a system of paired rollers moving at different speeds. Drawing straightens the fibres in the sliver by drafting to make more of the fibres parallel to the axis of the sliver. Parallelization is necessary to obtain the properties desired when the fibres are subsequently twisted into yarn. Drawing also produces a sliver that is more uniform in weight per unit of length and helps to achieve greater blending capabilities. The fibres that are produced by the final drawing process, called finisher drawing, are nearly straight and parallel to the axis of the sliver. Weight per unit length of a finisher-drawing sliver is too high to permit drafting into yarn on conventional ring-spinning systems.
The roving process reduces the weight of the sliver to a suitable size for spinning into yarn and inserting twist, which maintains the integrity of the draft strands. Cans of slivers from finisher drawing or combing are placed in the creel, and individual slivers are fed through two sets of rollers, the second of which rotates faster, thus reducing the size of the sliver from about 2.5 cm in diameter to that of the diameter of a standard pencil. Twist is imparted to the fibres by passing the bundle of fibres through a roving “flyer”. The product is now called “roving”, which is packaged on a bobbin about 37.5 cm long with a diameter of about 14 cm.
Spinning is the single most costly step in converting cotton fibres to yarn. Currently, over 85% of the world’s yarn is produced on ring-spinning frames, which are designed to draft the roving into the desired yarn size, or count, and to impart the desired amount of twist. The amount of twist is proportional to the strength of the yarn. The ratio of the length to the length fed can vary on the order of 10 to 50. Bobbins of roving are placed onto holders that allow the roving to feed freely into the drafting roller of the ring-spinning frame. Following the drafting zone, the yarn passes through a “traveller” onto a spinning bobbin. The spindle holding this bobbin rotates at high speed, causing the yarn to balloon as twist is imparted. The lengths of yarn on the bobbins are too short for use in subsequent processes and are doffed into “spinning boxes” and delivered to the next process, which may be spooling or winding.
In the modern production of heavier or coarse yarns, open-end spinning is replacing ring spinning. A sliver of fibres is fed into a high-speed rotor. Here the centrifugal force converts the fibres into yarns. There is no need for the bobbin, and the yarn is taken up on the package required by the next step in the process.
Considerable research and development efforts are being devoted to radical new methods of yarn production. A number of new spinning systems currently under development may revolutionize yarn manufacturing and could cause changes in the relative importance of fibre properties as they are now perceived. In general, four of the different approaches used in the new systems appear practical for use on cotton. Core-spun systems are currently in use to produce a variety of specialty yarns and sewing threads. Twistless yarns have been produced commercially on a limited basis by a system that bonds the fibres together with a polyvinyl alcohol or some other bonding agent. The twistless yarn system offers potentially high production rates and very uniform yarns. Knit and other apparel fabrics from twistless yarn have excellent appearance. In air-vortex spinning, currently under study by several machinery manufacturers, drawing sliver is presented to an opening roller, similar to rotor spinning. Air-vortex spinning is capable of very high production speeds, but prototype models are particularly sensitive to fibre length variations and foreign matter content such as trash particles.
Winding and spooling
Once the yarn is spun, the manufacturers must prepare a correct package. The type of package depends on whether the yarn will be used for weaving or knitting. Winding, spooling, twisting and quilling are considered preparatory steps for weaving and knitting yarn. In general, the product of spooling will be used as warp yarns (the yarns that run lengthwise in woven fabric) and the product of winding will be used as filling yarns, or weft yarns (the yarns that run across the fabric). The products from open-end spinning by-pass these steps and are packaged for either the filling or warp. Twisting produces ply yarns, where two or more yarns are twisted together before further processing. In the quilling process yarn is wound onto small bobbins, small enough to fit inside the shuttle of a box loom. Sometimes the quilling process takes place at the loom. (See also the article “Weaving and knitting” in this chapter.)
In modern textile mills where control of dust is important, the handling of waste is given greater emphasis. In classical textile operations, waste was collected manually and delivered to a “wastehouse” if it could not be recycled into the system. Here it was accumulated until there was enough of one type to make a bale. In the present state of the art, central vacuum systems automatically return waste from opening, picking, carding, drawing and roving. The central vacuum system is used for cleaning of machinery, automatically collecting waste from under machinery such as fly and motes from carding, and for returning unusable floor sweeps and wastes from filter condensers. The classical baler is a vertical upstroke press which still forms a typical 227-kg bale. In modern wastehouse technology, wastes are accumulated from the central vacuum system in a receiving tank which feeds a horizontal bale press. The various waste products of the yarn manufacturing industry can be recycled or reused by other industries. For example, spinning can be used in the waste spinning industry to make mop yarns, garnetting can be used in the cotton batting industry to make batting for mattresses or upholstered furniture.
Safety and Health Concerns
Accidents may occur on all types of cotton textile machinery, though the frequency rate is not high. Effective guarding of the multiplicity of moving parts presents many problems and needs constant attention. Training of operators in safe practices is also essential, in particular to avoid attempting repairs while the machinery is in motion, the cause of many of the accidents.
Each piece of machinery may have sources of energy (electrical, mechanical, pneumatic, hydraulic, inertial and so on) that need to be controlled before any repair or maintenance work is attempted. The facility should identify energy sources, provide necessary equipment and train personnel to ensure that all hazardous energy sources are turned off while working on equipment. An inspection should be performed on a regular basis to ensure that all lockout/tagout procedures are being followed and correctly applied.
Cotton dust inhalation (byssinosis)
Inhalation of the dust generated where cotton fibre is converted into yarn and fabric has been shown to cause an occupational lung disease, byssinosis, in a small number of textile workers. It usually takes 15 to 20 years of exposure to higher levels of dust (above 0.5 to 1.0 mg/m3) for workers to become reactors. OSHA and the American Conference of Governmental Industrial Hygienists (ACGIH) standards set 0.2 mg/m3 respirable cotton dust as measured by the vertical elutriator as the limit for occupational exposure to cotton dust in textile yarn manufacturing. The dust, an airborne particulate released into the atmosphere as cotton is handled or processed, is a heterogeneous, complex mixture of botanical trash, soil and microbiological material (i.e., bacteria and fungi), which varies in composition and biological activity. The aetiological agent and pathogenesis of byssinosis are not known. Cotton plant trash associated with the fibre and the endotoxin from gram-negative bacteria on the fibre and plant trash are thought to be the cause or to contain the causative agent. The cotton fibre itself, which is mainly cellulose, is not the cause, since cellulose is an inert dust that does not cause respiratory disease. Appropriate engineering controls in cotton textile processing areas (see figure 4) along with work practices, medical surveillance and PPE can, for the most part, eliminate the byssinosis. A mild water washing of cotton by batch kier washing systems and continuous batt systems reduces the residual level of endotoxin in both lint and airborne dust to levels below those associated with the acute reduction in pulmonary function as measured by the 1-second forced expiratory volume.
Figure 4. Dust extraction system for a carding machine
Noise can be a problem in some processes in yarn manufacturing, but in a few modern textile mills the levels are below 90 dBA, which is the US standard but which exceeds noise exposure standards in many countries. Thanks to the abatement efforts of machinery manufacturers and industrial noise engineers, noise levels are continuing to decrease as machinery speeds increase. The solution for high noise levels is the introduction of more modern, quieter equipment. In the United States, a hearing conservation programme is required when noise levels exceed 85 dBA; this would include noise-level monitoring, audiometric testing and making hearing protection available to all employees when noise levels cannot be engineered below 90 dBA.
Since spinning sometimes requires high temperatures and artificial humidificaton of the air, careful monitoring attention is always necessary to ensure that permissible limits are not exceeded. Well designed and maintained air-conditioning plants are increasingly used in place of more primitive methods of temperature and humidity regulation.
Occupational safety and health management systems
Many of the more modern textile yarn manufacturing mills find it useful to have some type of occupational safety and health management system in place to control the workplace hazards that workers may encounter. This can be a voluntary programme like the “Quest for the Best in Health and Safety” developed by the American Textile Manufacturers Institute, or one that is mandated by regulations such as the US State of California Occupational Injury and Illness Prevention Program (Title 8, California Code of Regulations, Section 3203). When a safety and health management system is used, it should be flexible and adaptable enough to allow the mill to tailor it to its own needs.
Adapted from 3rd edition, Encyclopaedia of Occupational Health and Safety.
The origins of the wool industry are lost in antiquity. Sheep were easily domesticated by our remote ancestors and were important in satisfying their basic needs for food and clothing. Early human societies rubbed together the fibres collected from the sheep to form a yarn, and from this basic principle the processes of manipulating the fibre have increased in complexity. The wool textile industry has been in the forefront in developing and adapting mechanical methods and was therefore one of the early industries in the development of the factory system of production.
The length of fibre when taken from the animal is the dominant, but not the only, factor determining how it is processed. The type of wool available may be broadly classified into (a) merino or botany, (b) crossbreds—fine, medium or coarse and (c) carpet wools. Within each group, however, there are various grades. Merino usually has the finest diameter and a short length, while the carpet wools are long-fibred, with a coarser diameter. Today, increasing quantities of synthetic fibres simulating wool are blended with the natural fibre and are processed in the same manner. Hair from other animals—for example, mohair (goat), alpaca (llama), cashmere (goat, camel), angora (goat) and vicuña (wild llama)—also plays an important, although subsidiary, role in the industry; it is relatively expensive and is usually processed by specialized firms.
The industry has two distinctive processing systems—woollen and the worsted. The machinery is in many ways similar, but the purposes are distinct. In essence, the worsted system uses the longer stapled wools and in the carding, preparing, gilling and combing processes the fibres are kept parallel and the shorter fibres are rejected. Spinning produces a strong yarn of fine diameter, which then is woven to yield a light fabric with the familiar smooth and firm appearance of men’s suits. In the woollen system, the aim is to intermingle and intertwine the fibres to form a soft and fluffy yarn, which is woven to give a cloth of full and bulky character with a “woolly” surface—for example, tweeds, blankets and heavy overcoatings. Since uniformity of fibre is not necessary in the woollen system, the manufacturer can blend together new wool, shorter fibres rejected by the worsted process, wools recovered from tearing up old wool garments and so on; “shoddy” is obtained from soft, and “mungo” from hard waste material.
It should be borne in mind, however, that the industry is particularly complex and that the condition and type of the raw material used and the specification for the finished cloth will influence the method of processing at each stage and the sequence of those stages. For example, wool may be dyed before processing, at the yarn stage or towards the end of the process when in the woven piece. Moreover, some of the processes may be carried on in separate establishments.
Hazards and Their Prevention
As in every section of the textile industry, large machines with rapidly moving parts pose both noise and mechanical injury hazards. Dust can also be a problem. The highest practicable form of guarding or enclosure should be provided for such generic parts of the equipment as spur gear wheels, chains and sprockets, revolving shafting, belts and pulleys, and for the following parts of machinery used specifically in the wool textile trade:
The guarding of such dangerous parts presents practical problems. The design of the guard should take into account the working practices connected with the particular process and particularly should preclude possible removal of the guard when the operator is at the greatest risk (e.g., lockout arrangements). Special training and close supervision are required to prevent waste removal and cleaning while machinery is in motion. Much of the responsibility devolves on machinery manufacturers, who should ensure that such safety features are incorporated into new machines at the design stage, and on supervisory personnel, who should ensure that workers are adequately trained in safe handling of equipment.
Spacing of machinery
The risk of accidents is increased if insufficient space is allowed between the machines. Many older premises squeezed the maximum number of machines into the available floor area, thereby reducing the space available for aisles and passageways and for the temporary storage of raw and finished materials within the workroom. In some old mills, the gangways between the carding machines are so narrow that enclosure of the driving belts within a guard is impracticable and recourse has to be made to “wedge” guarding between the belt and the pulley at the in-running point; a well-made and smooth belt fastener is particularly important in these circumstances. Minimum spacing standards, as recommended by a British Government committee for certain wool textile machinery, are required.
When modern mechanical load-handling methods are not employed, there remains the risk of injury from the lifting of heavy loads. Materials handling should be mechanized to the fullest extent possible. Where this is not available, the precautions discussed elsewhere in this Encyclopaedia should be employed. Proper lifting technique is particularly important for workers who manipulate heavy beams into and out of looms or who handle heavy and cumbersome bales of wool in the early preparatory processes. Wherever possible, hand-trucks and movable carts or skids should be used to move such bulky and heavy loads.
Fire is a serious hazard, especially in old multistorey mills. The mill structure and layout should conform to local regulations governing unobstructed gangways and exits, fire-alarm systems, fire extinguishers and hoses, emergency lights and so on. Cleanliness and good housekeeping will prevent accumulations of dust and fluff, which encourage the spread of fire. No repairs involving the use of flame cutting or flame-burning equipment should be carried on during working hours. Training of all staff in procedures in case of fire are necessary; fire drills, conducted if possible in concert with local fire, police and emergency medical services, should be practised at appropriate intervals.
Emphasis has been placed on those accident situations which are especially to be found in the wool textile industry. However, it should be noted that the majority of accidents in mills occur in circumstances that are common to all factories—for example, falls of persons and objects, handling of goods, use of hand tools and so on—and that the relevant fundamental safety principles to be followed apply no less in the wool industry than in most other industries.
The industrial disease usually associated with wool textiles is anthrax. It was at one time a great danger, particularly to wool sorters, but has been almost completely controlled in the wool textile industry as a result of:
Besides anthrax fungal spores, it is known that spores of the fungus Coccidiodes immitis can be found in wool, especially from the southwestern United States. This fungus can cause the disease known as coccidioidomycosis, which, along with the respiratory disease from anthrax, usually has a poor prognosis. Anthrax has the added hazard of causing a malignant ulcer or carbuncle with a black centre when entering the body through a break in the skin barrier.
Various chemicals are used—for example, for degreasing (diethylene dioxide, synthetic detergents, trichloroethylene and, in the past, carbon tetrachloride), disinfection (formaldehyde), bleaching (sulphur dioxide, chlorine) and dyeing (potassium chlorate, anilines). The risks include gassing, poisoning, irritation of the eyes, mucous membranes and lungs, and skin conditions. In general, prevention relies on:
Noise, inadequate lighting, and the high temperatures and humidity levels required for wool processing may have a deleterious effect on general health unless they are strictly controlled. In many countries, standards are prescribed. Steam and condensation may be difficult to control effectively in dyeing sheds, and expert engineering advice is often needed. In weaving sheds, noise control presents a serious problem on which much work remains to be done. A high standard of lighting is necessary everywhere, particularly where dark fabrics are being manufactured.
As well as the specific risk of anthrax spores in the dust produced in the earlier processes, dust in high quantities sufficient to induce irritation of the respiratory tract mucosae is produced at many machines, especially those with a tearing or carding action, and should be removed by effective LEV.
With all the moving parts in the machinery, particularly the looms, woollen mills are often very noisy places. While attenuation can be achieved by proper lubrication, the introduction of sound baffles and other engineering approaches should be considered as well. By and large, prevention of occupational hearing loss depends on the workers’ use of ear plugs or muffs. It is essential that workers be trained in the proper use of such protective equipment and supervised to verify that they are using it. A hearing conservation programme with periodic audiograms is required in many countries. As equipment is replaced or repaired, appropriate noise-reduction steps should be taken.
Work stress, with its attendant effects on workers’ health and well-being, is a common problem in this industry. Since many of the mills operate around the clock, shift work is frequently required. To meet the production quotas, the machines operate continuously, with each worker being “tied” to one or more pieces of equipment and unable to leave it for bathroom or rest breaks until a “floater” has taken his or her place. Coupled with the ambient noise and use of noise protectors, their heavily routinized, repetitive activity makes for de facto isolation of the workers and a lack of social interaction that many find stressful. The quality of supervision and the availability of workplace amenities have a great influence on workers’ job stress levels.
While larger enterprises are able to invest in new technological developments, many smaller and older mills continue to operate in old plants with out-dated but still functioning equipment. Economic imperatives dictate less rather than greater attention to workers’ safety and health. Indeed, in many developed areas, mills are being abandoned in favour of new plants in developing countries and areas where cheaper labour is readily available and where health and safety regulations are either non-existent or are generally ignored. Worldwide, this is an important labour-intensive industry in which reasonable investments to workers’ health and well-being can bring significant dividends to both the enterprise and its workforce.
Adapted from 3rd edition, Encyclopaedia of Occupational Health and Safety.
Silk is a lustrous, tough, elastic fibre produced by the larvae of silkworms; the term also covers the thread or cloth made from this fibre. The silk industry originated in China, as early as 2640 BC according to tradition. Towards the 3rd century AD, knowledge of the silkworm and its product reached Japan through Korea; it probably spread to India a little later. From there silk production was slowly carried westward through Europe to the New World.
The production process involves a sequence of steps not necessarily carried out in a single enterprise or plant. They include:
Health and Safety Hazards
Symptoms of carbon monoxide toxicity consisting of headache, vertigo and sometimes nausea and vomiting, usually not severe, have been reported in Japan, where sericulture is a common home industry, as a result of the use of charcoal fires in poorly ventilated rearing rooms.
Mal des bassines, a dermatitis of the hands of female workers reeling raw silk, was quite common, particularly in Japan, where, in the 1920s, a morbidity rate of 30 to 50% among reeling workers was reported. Fourteen per cent of the affected workers lost an average of three working days each year. The skin lesions, localized mainly on fingers, wrists and forearms, were characterized by erythema covered with small vesicles which became chronic, pustular or eczematous and extremely painful. The cause of this condition was usually attributed to the decomposition products of the dead chrysalis and to a parasite in the cocoon.
More recently, however, Japanese observations have showed that it is probably related to the temperature of the reeling bath: until 1960 almost all reeling baths were kept at 65 °C, but, since the introduction of new installations with a bath temperature of 30 to 45 °C, there have been no reports of the typical skin lesions among reel workers.
The handling of raw silk may produce allergic skin reactions in some reel workers. Facial swelling and ocular inflammation have been observed where there was no direct local contact with the reeling bath. Similarly, dermatitis has been found among silk throwers.
Respiratory tract problems
In the former Soviet Union, an unusual outbreak of tonsillitis among silk spinners was traced to bacteria in the water of reeling basins and in the ambient air of the cocoon department. Disinfection and frequent replacement of reel bath water, combined with exhaust ventilation at the cocoon reels, brought about a swift improvement.
Extensive long-term epidemiological observations also carried out in the former USSR have shown that workers in the natural silk industry may develop respiratory allergy featuring bronchial asthma, asthmatiform bronchitis and/or allergic rhinitis. It appears that natural silk can cause sensitization during all stages of production.
A situation causing respiratory distress among spinning-frame workers when packaging or repackaging silk on a spinning or winding frame has also been reported. Depending upon the speed of the machinery, it is possible to aerosolize the proteinaceous substance surrounding the silk filament. This aerosol, when respirable in size, will cause a lung reaction very similar to that of the byssinotic reaction to cotton dust.
Noise exposure can reach harmful levels for workers at machines spinning and winding the silk threads, and at looms where fabric is woven. Adequate lubrication of the equipment and the interposition of sound baffles may reduce the noise level somewhat, but the continuing exposure throughout the working day can have a cumulative effect. If effective abatement is not obtained, resort will have to be made to personal protective devices. As with all workers exposed to noise, a hearing protection programme featuring periodic audiograms is desirable.
Safety and Health Measures
Control of temperature, humidity and ventilation are important at all stages of the silk industry. Home workers should not escape supervision. Adequate ventilation of rearing rooms should be ensured, and charcoal or kerosene stoves should be replaced by electric heaters or other warming devices.
Lowering the temperature of reeling baths may be effective in preventing dermatitis. The water should be replaced frequently, and exhaust ventilation is desirable. Direct skin contact with raw silk immersed in reeling baths should be avoided as far as possible.
The provision of good sanitary facilities and attention to personal hygiene are essential. Hand washing with a 3% acetic acid solution has been found effective in Japan.
The medical examination of new entrants and medical supervision thereafter are desirable.
The hazards from machinery in silk manufacture are similar to those in the textile industry in general. Accident prevention is best achieved by good housekeeping, adequate guarding of moving parts, continuing worker training and effective supervision. Power looms should be provided with guards to prevent accidents from flying shuttles. Very good lighting is required for the yarn preparation and weaving processes.
Adapted from 3rd edition, Encyclopaedia of Occupational Health and Safety.
Rayon is a synthetic fibre produced from cellulose (wood pulp) that has been chemically treated. It is used alone or in blends with other synthetic or natural fibres to make fabrics that are strong, highly absorbent and soft, and which can be dyed in brilliant, long-lasting colours.
The manufacture of rayon had its origins in the quest for an artificial silk. In 1664, Robert Hooke, a British scientist noted for his observations of plant cells, predicted the possibility of duplicating silk by artificial means; almost two centuries later, in 1855, fibres were made from a mixture of mulberry twigs and nitric acid. The first successful commercial process was developed in 1884 by the French inventor Hilaire de Chardonnet, and in 1891, the British scientists Cross and Bevan perfected the viscose process. By 1895, rayon was being produced commercially on a rather small scale, and its use grew rapidly.
Rayon is made by a number of processes, depending on its intended use.
In the viscose process, cellulose derived from wood pulp is steeped in a sodium hydroxide solution, and the excess liquid is squeezed out by compression to form alkali cellulose. Impurities are removed and, after being torn into shreds similar to white crumbs that are allowed to age for several days at a controlled temperature, the shredded alkali cellulose is transferred to another tank where it is treated with carbon disulphide to form golden-orange crumbs of cellulose xanthate. These are dissolved in dilute sodium hydroxide to form a viscous orange liquid called viscose. Different batches of viscose are blended to obtain uniform quality. The mixture is filtered and ripened by several days of storage at rigidly controlled temperature and humidity. It is then extruded through metal nozzles with fine holes (spinnerets) into a bath of about 10% sulphuric acid. It can be wound as a continuous filament (cakes) or cut into the required lengths and spun like cotton or wool. Viscose rayon is used to make wearing apparel and heavy fabrics.
In the cuprammonium process, used to make silk-like fabrics and sheer hosiery, the cellulose pulp dissolved in the sodium hydroxide solution is treated with copper oxide and ammonia. The filaments come out of the spinnerets into a spinning funnel and are then stretched to the required fineness by the action of a jet stream of water.
In the viscose and cuprammonium processes, the cellulose is reconstituted, but acetate and triacetate are esters of the cellulose and are considered by some to be a separate class of fibre. Acetate fabrics are known for their ability to take brilliant colours and to drape well, features that make them particularly desirable for apparel. Short fibres of acetate are used as fillers in pillows, mattress pads and quilts. Triacetate yarns have many of the same properties as acetate but are particularly favoured for their ability to retain creases and pleats in garments.
Hazards and Their Prevention
The principal hazards in the viscose process are the exposures to carbon disulphide and hydrogen sulphide. Both have a variety of toxic effects depending on the intensity and duration of the exposure and the organ(s) affected; they range from fatigue and giddiness, respiratory irritation and gastrointestinal symptoms to profound neuropsychiatric disturbances, auditory and visual disorders, deep unconsciousness and death.
Moreover, with a flashpoint below –30 °C and explosive limits between 1.0 and 50%, carbon disulphide has a high risk of fire and explosion.
The acids and alkalis used in the process are fairly dilute, but there is always danger from the preparing of the proper dilutions and splashes into the eyes. The alkaline crumbs produced during the shredding process may irritate workers’ hands and eyes, while the acid fumes and hydrogen sulphide gas emanating from the spinning bath may cause a kerato-conjunctivitis characterized by excessive lachrimation, photophobia and severe ocular pain.
Keeping the concentrations of carbon disulphide and hydrogen sulphide below the safe exposure limits requires diligent monitoring such as may be provided by an automatic continuous recording apparatus. Complete enclosure of the machinery with efficient LEV (with intakes at floor levels since these gases are heavier than air) is advisable. Workers must be trained in emergency responses in the event of leaks, and, in addition to being provided with proper personal protective equipment, maintenance and repair workers must be carefully schooled and supervised to avoid unnecessary levels of exposure.
Rest rooms and washing up facilities are necessities rather than mere amenities. Medical surveillance through preplacement and periodic medical examinations is desirable.
Adapted from 3rd edition, Encyclopaedia of Occupational Health and Safety.
Synthetic fibres are made from polymers that have been synthetically produced from chemical elements or compounds developed by the petrochemical industry. Unlike natural fibres (wool, cotton and silk), which date back to antiquity, synthetic fibres have a relatively short history dating back to the perfection of the viscose process in 1891 by Cross and Bevan, two British scientists. A few years later, rayon production started on a limited basis, and by the early 1900s, it was being produced commercially. Since then, a large variety of synthetic fibres has been developed, each designed with special characteristics that make it suitable for a particular kind of fabric, either alone or in combination with other fibres. Keeping track of them is made difficult by the fact that the same fibre may have different trade names in different countries.
The fibres are made by forcing liquid polymers through the holes of a spinneret to produce a continuous filament. The filament can be directly woven into cloth or, to give it the characteristics of natural fibres, it can, for example, be textured to add bulkiness, or it can be chopped into staple and spun.
Classes of Synthetic Fibres
The main classes of synthetic fibres used commercially include:
Silk is the only natural fibre that comes in a continuous filament; other natural fibres come in short lengths or “staples”. Cotton has a staple of about 2.6 cm, wool of 6 to 10 cm and flax from 30 to 50 cm. The continuous synthetic filaments are sometimes passed through a cutting or stapling machine to produce short staples like the natural fibres. They can then be re-spun on cotton or wool spinning machines in order to produce a finish free of the glassy appearance of some synthetic fibres. During the spinning, combinations of synthetic and natural fibres or mixtures of synthetic fibres may be made.
To give synthetic fibres the look and feel of wool, the twisted and tangled cut or stapled fibres are crimped by one of a number of methods. They may be passed through a crimping machine, in which hot, fluted rollers impart a permanent crimp. Crimping can also be done chemically, by controlling the coagulation of the filament so as to produce a fibre with an asymmetrical cross section (i.e., one side being thick-skinned and the other thin). When this fibre is wet, the thick side tends to curl, producing a crimp. To make crinkled yarn, known in the United States as non-torque yarn, the synthetic yarn is knitted into a fabric, set and then wound from the fabric by back-winding. The newest method passes two nylon threads through a heater, which raises their temperature to 180 °C and then passes them through a high-speed revolving spindle to impart the crimp. The spindles in the first machine ran at 60,000 revolutions per minute (rpm), but newer models have speeds of the order of 1.5 million rpm.
Synthetic Fibres for Work Clothes
The chemical resistance of polyester cloth makes the fabric particularly suitable for protective clothing for acid-handling operations. Polyolefin fabrics are suitable for protection against long exposures to both acids and alkalis. High-temperature-resistant nylon is well adapted for clothing to protect against fire and heat; it has good resistance at room temperature to solvents such as benzene, acetone, trichlorethylene and carbon tetrachloride. The resistance of certain propylene fabrics to a wide range of corrosive substances makes them suitable for work and laboratory clothing.
The light weight of these synthetic fabrics makes them preferable to the heavy rubberized or plastic-coated fabrics that would otherwise be required for comparable protection. They are also much more comfortable to wear in hot and humid atmospheres. In selecting protective clothing made from synthetic fibres, care should be taken to determine the generic name of the fibre and to verify such properties as shrinkage; sensitivity to light, dry-cleaning agents and detergents; resistance to oil, corrosive chemicals and common solvents; resistance to heat; and susceptibility to electrostatic charging.
Hazards and Their Prevention
In addition to good housekeeping, which means keeping floors and passageways clean and dry to minimize slips and falls (vats must be leak proof and, where possible, have baffles to contain splashes), machines, drive belts, pulleys and shaftings must be properly guarded. Machines for spinning, carding, winding and warping operations should be fenced to keep materials and parts from flying out and to prevent workers’ hands from entering the dangerous zones. Lockout devices must be in place to prevent restart of machines while they are being cleaned or serviced.
Fire and explosion
The synthetic-fibres industry uses large amounts of toxic and flammable materials. Storage facilities for flammable substances should be out in the open or in a special fire-resistant structure, and they should be enclosed in bunds or dykes to localize spills. Automation of the delivery of toxic, flammable substances by a well-maintained system of pumps and pipes will reduce the hazard of moving and emptying containers. Appropriate fire-fighting equipment and clothing should be readily available and workers trained in their use through periodic drills, preferably conducted in concert with or under the observation of local fire-fighting authorities.
As the filaments emerge from the spinnerets to be dried in air or by means of spinning, large amounts of solvent vapours are released. These constitute a considerable toxic and explosion hazard and must be removed by LEV. Their concentration must be monitored to be sure that it remains below the solvent’s explosive limits. The exhausted vapours may be distilled and recovered for further use or they may be burned off; on no account should they be released into the general environmental atmosphere.
Where flammable solvents are used, smoking should be prohibited and open lights, flames and sparks eliminated. Electrical equipment should be of certified flameproof construction, and machines should be earthed (grounded) to prevent the build-up of static electricity, which might lead to catastrophic sparks.
Exposures to potentially toxic solvents and chemicals should be maintained below the relevant maximum allowable concentrations by adequate LEV. Respiratory protective equipment should be available for use by maintenance and repair crews and by workers charged with responding to emergencies caused by leaks, spillage and/or fire.
Felt is a fibrous material made by interlocking fibres of fur, hair or wool through the application of heat, moisture, friction and other processes into an unwoven, densely matted fabric. There are also needleloom felts, in which the felt is attached to a loosely woven backing fabric, usually made of wool or jute.
Fur Felt Processing
Fur felt, used most frequently in hats, is usually made from the fur of rodents (e.g., rabbits, hares, muskrats, coypus and beavers), with other animals used less frequently. After sorting, the skins are carroted using hydrogen peroxide and sulphuric acid, and then the following processes are performed: cutting of hair, hardening and dyeing. For dyeing, synthetic dyestuffs are usually used (e.g., acid dyes or dyes containing complex metal compounds). The dyed felt is weighted using a shellac or vinyl polyacetate.
Wool Felt Processing
Wool used for felt manufacture may be unused or reclaimed. Jute, generally obtained from old sacks, is used for certain needlefelts, and other fibres such as cotton, silk and synthetic fibres may be added.
The wool is sorted and selected. To separate the fibres, it is ragged in a rag-grinding machine, a spiked cylinder that rotates and tears up the fabric, and then garnetted in a machine that has rollers and cylinders covered with fine saw-toothed wires. The fibres are carbonized in an 18% sulphuric acid solution and, after drying at a temperature of 100 ºC, they are blended and, when necessary, oiled with mineral oil with emulsifier. After teasing and carding, which further blends the fibres and arranges them more or less parallel to one another, the material is deposited on a moving belt as layers of a fine web that are wound up on poles to form batts. The loose batts are taken to the hardening room, where they are sprinkled with water and pressed between two heavy plates, the top one of which vibrates, causing the fibres to curl and cling together.
To complete the felting, the material is placed in bowls of dilute sulphuric acid and pounded by heavy wooden hammers. It is washed (with the addition of tetrachloroethylene), dewatered and dyed, usually with synthetic dyestuffs. Chemicals may be added to make the felt rot-resistant. The final steps include drying (at 65 °C for soft felts, 112 °C for hard felts), shearing, sanding, brushing, pressing and trimming.
Safety and Health Hazards
The machines used in felt manufacturing have driving belts, chain and sprocket drives, rotating shafts, spiked drums and rollers used in garnetting and teasing, heavy presses, rollers and hammers, and so on, all of which must be properly guarded and have lockout/tagout systems to prevent injuries when they are being serviced or cleaned. Good housekeeping is also necessary to avoid slips and falls.
Many of the operations are noisy; when safe noise levels cannot be maintained by enclosures, baffles and proper lubrication, personal hearing protection must be made available. A hearing conservation programme featuring periodic audiograms is required in many countries.
Felt workplaces are dusty and are not recommended for persons with chronic respiratory diseases. While, fortunately, the dust is not associated with any specific disease, adequate exhaust ventilation is necessary. Animal hair can evoke allergic reactions in sensitive individuals, but bronchial asthma appears to be infrequent. Dust also can be a fire hazard.
The sulphuric acid solution used in felt making is usually dilute, but care is needed when diluting the supply of concentrated acid to the desired level. The danger of splashes and spills requires that eyewash facilities be nearby and that workers be fitted with protective clothing (e.g., goggles, aprons, gloves and shoes).
Tanning of certain papermakers’ felts may involve the use of quinone, which can cause severe damage to skin and mucous membranes. The dust or vapour of this compound can cause staining of the conjunctivae and cornea of the eye and, with prolonged or repeated exposures, may affect vision. Quinone powder should be dampened to prevent dusting, and it should be handled in enclosed hoods or chambers fitted with LEV, by workers fitted with hand, arm, face and eye protection.
Heat and fire
The high temperature of the material (60 °C) involved in the manual hat-shaping process dictates the use of hand skin protection by the workers.
Fire is a common hazard during the early, dusty stages of felt manufacture. It may be caused by matches or sparks from metallic objects left in the waste wool, hot-running bearings or faulty electrical connections. It may also occur in finishing operations, when vapours of flammable solvents may collect in the drying ovens. Because it damages the material and corrodes the equipment, water is less popular for fire extinguishing than dry-powder extinguishers. Modern equipment is fitted with vents through which the extinguishing material can be sprayed, or with an automatic carbon dioxide releasing device.
Although rare, cases of anthrax have occurred as a result of exposure to contaminated wool imported from areas where this bacillus is endemic.
The section on dyeing is adapted from A.K. Niyogi’s contribution to the 3rd edition of the Encyclopaedia of Occupational Health and Safety.
Dyeing involves a chemical combination or a powerful physical affinity between the dye and the fibre of the fabric. An extensive variety of dyes and processes is used, depending on the type of fabric and the end-product desired.
Classes of dyes
Acid or basic dyes are used in a weak acid bath for wool, silk or cotton. Some acid dyes are used after mordanting the fibres with metallic oxide, tannic acid or dichromates. Direct dyes, which are not fast, are used for the dyeing of wool, rayon and cotton; they are dyed at the boil. For dyeing cotton fabrics with sulphur dyes, the dyebath is prepared by pasting the dye with soda ash and sodium sulphide and hot water. This dyeing is also carried out at the boil. For dyeing cotton with azo dyes, naphthol is dissolved in aqueous caustic soda. The cotton is impregnated with the solution of the sodium naphthoxide that is formed, and it is then treated with a solution of a diazo compound to develop the dye in the material. Vat dyes are made into leuco-compounds with sodium hydroxide and sodium hydrosulphite; this dyeing is done at 30 to 60 ºC. Disperse dyes are used for the dyeing of all synthetic fibres which are hydrophobic. Swelling agents or carriers which are phenolic in nature must be used to enable the disperse dyes to act. Mineral dyes are inorganic pigments which are salts of iron and chromium. After impregnation, they are precipitated by addition of hot alkaline solution. Reactive dyes for cotton are used in a hot or a cold bath of soda ash and common salt.
Preparing fabrics for dyeing
The preparatory processes before dyeing cotton fabrics consist of the following sequence of steps: The cloth is passed through a shearing machine to cut the loosely adhering fibres and then, to complete the trimming process, it is passed rapidly over a row of gas flames and the sparks are extinguished by passing the material through a water box. Desizing is carried out by passing the cloth through a diastase solution which removes the size completely. To remove other impurities, it is scoured in a kier with dilute sodium hydroxide, sodium carbonate or turkey red oil for 8 to 12 hours at high temperature and pressure.
For coloured woven material, an open kier is used and sodium hydroxide is avoided. The natural colouring in the cloth is removed by hypochlorite solution in the bleaching pits, after which the cloth is aired, washed, dechlorinated by means of a sodium bisulphite solution, washed again and scoured with dilute hydrochloric or sulphuric acid. After a final, thorough washing, the cloth is ready for the dyeing or printing process.
Dyeing is carried out in a jig or padding machine, in which the cloth is moved through a stationary dye solution prepared by dissolving the dyestuff powder in a suitable chemical and then diluting with water. After dyeing, the cloth is subjected to a finishing process.
The preparation of polyamide (nylon) fibres for dyeing involves scouring, some form of setting treatment and, in some cases, bleaching. The treatment adopted for the scouring of woven polyamide fabrics depends mainly on the composition of the size used. Water-soluble sizes based on polyvinyl alcohol or polyacrylic acid can be removed by scouring in a liquor containing soap and ammonia or Lissapol N or similar detergent and soda ash. After scouring, the material is rinsed thoroughly and is then ready for dyeing or printing, usually in a jigger or winch dyeing machine.
The raw wool is first scoured by the emulsification process, in which soap and a soda ash solution are used. The operation is carried out in a washing machine which consists of a long trough provided with rakes, a false bottom and, at the exit, wringers. After thorough washing, the wool is bleached with hydrogen peroxide or with sulphur dioxide. If the latter is used, the damp goods are left exposed to the sulphur dioxide gas overnight. The acid gas is neutralized by passing the fabric through a sodium carbonate bath, and then it is thoroughly washed. After dyeing, the goods are rinsed, hydroextracted and dried.
Hazards in Dyeing and Their Prevention
Fire and explosion
The fire hazards found in a dye works are the flammable solvents used in the processes and certain flammable dyestuffs. Safe storage facilities should be provided for both: properly designed storerooms constructed of fire-resisting materials with a raised and ramped sill at the doorway so that escaping liquid is contained within the room and prevented from flowing to a place where it may be ignited. It is preferable that stores of this nature be located outside the main factory building. If large quantities of flammable liquids are kept in tanks outside the building, the tank area should be mounded to contain escaping liquid.
Similar arrangements should be made when the gaseous fuel used on the singeing machines is obtained from a light petroleum fraction. The gas-making plant and the storage facilities for the volatile petroleum spirit should preferably be outside the building.
Many factories use hypochlorite solution for bleaching; in others, the bleaching agent is gaseous chlorine or bleaching powder which releases chlorine when it is charged into the tank. In either case, workers may be exposed to dangerous levels of chlorine, a skin and eye irritant and a dangerous pulmonary tissue irritant causing delayed lung oedema. To limit the escape of chlorine into the workers’ atmosphere, bleaching vats should be designed as closed vessels provided with vents that limit the escape of chlorine so that the relevant recommended maximum exposure levels are not exceeded. Atmospheric chlorine levels should be checked periodically to ensure that the exposure limit is not being exceeded.
The valves and other controls of the tank from which the liquid chlorine is supplied to the dyeworks should be controlled by a competent operator, since the possibilities of an uncontrolled leak could well be disastrous. When a vessel that has contained chlorine or any other dangerous gas or vapour has to be entered, all of the precautions advised for work in confined places should be taken.
The use of corrosive alkalis and acids and the treatment of cloth with boiling liquor expose the workers to the risk of burns and scalds. Both hydrochloric acid and sulphuric acid are used extensively in dyeing processes. Caustic soda is used in bleaching, mercerizing and dyeing. Chips from the solid material fly and create hazards for the workers. Sulphur dioxide, which is used in bleaching, and carbon disulphide, which is used as a solvent in the viscose process, can also pollute the workroom. Aromatic hydrocarbons such as benzol, toluol and xylol, solvent naphthas and aromatic amines such as aniline dyes are dangerous chemicals to which workers are likely to be exposed. Dichlorobenzene is emulsified with water with the help of an emulsifying agent, and is used for dyeing of polyester fibres. LEV is essential.
Many dyestuffs are skin irritants that cause dermatitis; in addition, workers are tempted to use harmful mixtures of abrasive, alkali and bleaching agents to remove dye stains from their hands.
Organic solvents used in the processes and for the cleaning of machines may themselves cause dermatitis or render the skin vulnerable to the irritant action of the other harmful substances that are used. Furthermore, they may be the cause of peripheral neuropathy—for example, methyl butyl ketone (MBK). Certain dyes, such as rhodamine B, magenta, β-naphthylamine and certain bases such as dianisidine, have been found to be carcinogenic. The use of β-naphthylamine has generally been abandoned in dyestuffs, which are discussed more fully elsewhere in this Encyclopaedia.
In addition to the fibre materials and their contaminants, allergy may be caused by the sizing and even by the enzymes used to remove the sizing.
Suitable PPE, including eye-protective equipment, should be provided to prevent contact with these hazards. In certain circumstances when barrier creams have to be used, care should be taken to ensure that they are effective for the purpose and that they can be removed by washing. At best, however, the protection they provide is rarely as reliable as that afforded by properly designed gloves. Protective clothing should be cleaned at regular intervals, and when splashed or contaminated by dyestuffs, it should be replaced by clean clothing at the earliest opportunity. Sanitary facilities for washing, bathing and changing should be provided, and the workers should be encouraged to use them; personal hygiene is particularly important for dye workers. Unfortunately, even when all protective measures have been taken, some workers are found to be so sensitive to the effects of these substances that transfer to other work is the only alternative.
Serious scalding accidents have occurred when hot liquor has been accidentally admitted to a kier in which a worker has been arranging the cloth to be treated. This can occur when a valve is accidentally opened or when hot liquor is discharged into a common discharge duct from another kier on the range and enters the occupied kier through an open outlet. When a worker is inside a kier for any purpose, the inlet and outlet should be closed, isolating that kier from the other kiers on the range. If the locking device is operated by a key, it should be retained by the worker who might be injured by an accidental admission of hot liquid until he or she leaves the vessel.
Printing is carried out on a roller printing machine. The dye or pigment is thickened with starch or made into emulsion which, in the case of pigment colours, is prepared with an organic solvent. This paste or emulsion is taken up by the engraved rollers which print the material, and the colour is subsequently fixed in the ager or curing machine. The printed cloth then receives the appropriate finishing treatment.
Wet printing is performed with dyeing systems similar to those used in dyeing, such as vat printing and fibre-reactive printing. These printing methods are used only for 100% cotton fabric and for rayon. The health hazards associated with this type of printing are the same as those discussed above.
Solvent-based pigment printing
Solvent-based printing systems use large amounts of solvents such as mineral spirits in the thickening system. The major hazards are:
Aqueous-based pigment printing
None of the health hazards for solvent-based pigment printing apply to the aqueous-based printing systems. Although some solvents are used, the amounts are so small that they are not significant. The primary health hazard is the presence of formaldehyde.
Pigment printing requires the use of a cross-linker to assist in the bonding of the pigments to the fabric. These cross-linkers exist as stand-alone products (e.g., melamine) or as part of other chemicals such as binders, antiwicks, and even in the pigments themselves. Formaldehyde plays a necessary role in the function of the cross-linkers.
Formaldehyde is a sensitizer and an irritant that may produce reactions, sometimes violent, in workers who are exposed to it either by inhaling the air around the printing machine as it is operating or by coming into contact with the printed fabric. These reactions may range from simple eye irritation to welts on the skin and severe difficulty with breathing. Formaldehyde has been found to be carcinogenic in mice but it has not yet been conclusively associated with cancer in humans. It is classified as a Group 2A Carcinogen, “Probably Carcinogenic to Humans”, by the International Agency for Research on Cancer (IARC).
To protect the local environment, emissions from the plant have to be monitored to ensure that levels of formaldehyde do not exceed those stipulated by applicable regulations.
Another potential hazard is ammonia. Since the print paste is pH (acidity) sensitive, ammonia is often used as a print-paste thickener. Care should be taken to handle ammonia in a well-ventilated area and to wear respiratory protection if necessary.
Since all dyes and pigments used in printing are usually in a liquid form, dust exposure is not a hazard in printing as it is in dyeing.
Finishing is a term applied to a very broad range of treatments that are usually performed during the last manufacturing process before fabrication. Some finishing can also be performed after fabrication.
This type of finishing involves processes that change the texture or appearance of a fabric without the use of chemicals. They include:
The principal hazards are the presence of heat, the very high temperatures being applied and nip points in the moving machine parts. Care should be taken to properly guard the machinery to prevent accidents and physical injury.
Chemical finishing is performed on a variety of types of equipment (e.g., pads, jigs, jet dye machines, becks, spray bars, kiers, paddle machines, kiss roll applicators and foamers).
One type of chemical finishing does not involve a chemical reaction: the application of a softener or a hand builder to modify the feel and texture of the fabric, or to improve its sewability. This presents no significant hazards except for the possibility of irritation from skin and eye contact, which can be prevented by the use of proper gloves and eye protection.
The other type of chemical finishing involves a chemical reaction: resin finishing of cotton fabric to produce desired physical properties in the fabric such as low shrinkage and a good smoothness appearance. For cotton fabric, for example, a dimethyldihydroxyethylene urea (DMDHEU) resin is catalysed and bonds with the cotton molecules of the fabric to create a permanent change in the fabric. The primary hazard associated with this type of finishing is that most resins release formaldehyde as part of their reaction.
As in the rest of the textile industry, dyeing, printing and finishing operations present a mixture of old, generally small establishments in which worker safety, health and welfare are given little if any attention, and newer, larger establishments with ever-improving technology in which, to the extent possible, hazard control is built into the design of the machinery. In addition to the specific hazards outlined above, such problems as substandard lighting, noise, incompletely guarded machinery, lifting and carrying of heavy and/or bulky objects, poor housekeeping and so on remain ubiquitous. Therefore, a well-formulated and implemented safety and health programme that includes the training and effective supervision of workers is a necessity.
The nonwoven textile fabric industry had an exploratory beginning in the late 1940s which entered into a development phase in the 1950s followed by commercial expansion in the 1960s. During the next 35 years, the nonwoven industry matured and established markets for nonwoven fabrics by either providing cost-effective performance as alternatives to conventional textiles or providing products specifically developed for targeted end-uses. The industry has survived recessions better than conventional textiles and has grown at a faster rate. Its health and safety problems are similar to those of the rest of the textile industry (i.e., noise, airborne fibres, chemicals used in bonding fibres, safe working surfaces, pinch points, burns from thermal exposures, back injuries and so on).
The industry generally has a good safety record, and the number of injuries per standard work unit is low. The industry has responded to challenges associated with clean water and clean air acts. In the United States, the Occupational Safety and Health Administration (OSHA) has promulgated a number of worker protection rules which require safety training and manufacturing practices that have improved worker protection significantly. Responsible companies throughout the world are adopting similar practices.
The raw materials used by the industry are generally similar to those used in conventional textiles. The industry has been estimated to use almost 1 billion kg of a mix of raw materials annually. The natural fibres used are predominately cotton and wood pulp. The manufactured fibres include rayon, polyolefins (both polyethylene and polypropylene), polyesters and, to a smaller degree, nylons, acrylics, aramids and others.
There was an early growth in the number of nonwoven processes to approximately ten. These include; spunbond, melt blown, air-laid pulp and blends, wet laid, dry laid (bonded by either needlepunching, thermal bonding or chemical bonding) and stitch bonding processes. In the United States, the industry has saturated many of its end-use markets and is currently searching for new ones. A major growth area for nonwovens is developing in the area of composites. Laminates of nonwovens with films and other coatings are broadening markets for nonwoven materials. The storage of nonwoven roll goods has recently come under scrutiny because of the flammability of some products that have very low densities and high surface areas. Rolls whose volume-to-weight ratio is greater than a certain roll loft factor are considered to pose storage problems.
The volume of bleached cotton used in nonwoven fabrics has been steadily increasing, and cotton-polyester and rayon-polyester blends in nonwoven fabrics, bonded by hydroentangling, have become attractive combinations for medical and feminine hygiene applications. There has been an interest in using unbleached cotton in nonwoven processes, and some attractive experimental fabrics have been produced through the use of the hydroentangling process.
Rayon has encountered some pressure from environmentalists who are concerned about the impact that by-products of the process have on the environment. Some rayon-producing companies in the United States abandoned the industry rather than face the cost of complying with regulatory requirements imposed by the clean water and air acts. Those companies that chose to meet the requirements now appear to be comfortable with their modified processes.
Wood pulp fibres are a major component of disposable diapers, incontinence products and other absorbent products. Fibres from hardwood and kraft fibres are employed. In the United States alone, use of pulp fibres totals more than 1 billion kg annually. A small percentage is used in air-laid nonwoven processes. The products are popular as towels in applications which range from the kitchen to sports.
The two most popular polyolefin fibres are polyethylene and polypropylene. These polymers are either converted into staple-length fibres which are subsequently converted into nonwoven fabrics, or else converted into spunbonded nonwoven fabrics by extruding the polymers to form filaments which are formed into webs and bonded by thermal processes. Some of the fabrics produced are converted into protective apparel, and by 1995, more than 400,000,000 coveralls had been made using a popular spunbonded polyethylene fabric.
The largest single use for a nonwoven fabric in the United States (approximately 10 billion square metres) is as the cover sheet in disposable diapers. This is the fabric which contacts the baby’s skin and separates the baby from the other diaper components. Fabrics from these fibres are also used in durable products and in some geotextile applications where they are expected to last indefinitely. The fabrics will degrade in ultraviolet light or some other types of radiation.
Thermoplastic fibres from polyester polymers and copolymers are widely used in nonwovens in both staple fibre and spunbonded processes. The combined volume of polyester and polyolefin polymers used in the United States in nonwoven fabrics has been estimated to be more than 250 million kg annually. Blends of polyester fibres with wood pulp which are wet laid and then bonded by hydroentangling and subsequently treated with a repellent coating are widely used in disposable surgical gowns and drapes. By 1995, the use of disposable medical nonwovens in the United States alone exceeded 2 billion square metres annually.
Nylon fibres are used only sparingly in the form of staple fibres and in a limited volume in spunbonded nonwovens. One of the largest uses for spundbonded nylon nonwovens is in the reinforcement of carpet pads and in fibreglass filters. The fabrics provide a low friction surface to carpet pads that facilitates the installation of carpets. In fibreglass filters, the fabric helps retain the fibreglass in the filter and prevents glass fibres from entering the filtered air stream. Other specialty nonwovens, such as aramids, are used in niche markets where their properties, such as low flammability, recommend their use. Some of these nonwovens are used in the furniture industry as flame blockers, to reduce the flammability of sofas and chairs.
Spunbonded and meltblown
In the spunbonded and meltblown processes, suitable synthetic polymers are melted, filtered, extruded, drawn, charged electrostatically, laid down in web form, bonded and taken up as rolls. The process requires good safety practices common to working with hot extruders, filters, spinnerets and heated rolls used for bonding.
Workers should wear proper eye protection and avoid wearing loose clothing, neckties, rings or other jewellery that may be caught in moving equipment. Also, these processes almost always involve the use of large volumes of air, and special precautions must be taken to avoid designs that might lead to fires, such as placing light ballasts in an air duct. Extinguishing a fire in an air duct is difficult. It is important to maintain safe working-floor surfaces, and the floors around any nonwoven equipment should be free of contamination that can lead to unsafe footing.
Spunbonded and meltblown processes call for cleaning some of the process equipment by burning away any accumulated polymer residue. This usually involves the use of very hot ovens for both cleaning and storing the cleaned parts. Obviously, these operations require proper gloves and other thermal protection, as well as appropriate ventilation to reduce heat and exhaust fumes.
Spunbonded processes owe their economic advantages in part to the fact that they are relatively fast and the take-up rolls can be changed while the process continues to run. The design of the roll-changing equipment and the training of the operators should provide for an adequate margin of safety to handle these changeovers.
Processes that involve opening of bales of fibres, blending the fibres to provide a uniform feed to a carding machine, carding to form webs, cross-lapping the webs to provide optimum strength in all directions and then forwarding the web to some bonding process are similar in their safety requirements to conventional textile processes. All exposed points that could trap a worker’s hands in roll interfaces need protection. Some dry-laid processes involve the generation of small amounts of airborne fibres. The worker should be provided with adequate respiratory PPE in order to avoid inhalation of any respirable part of these fibres.
If the webs formed are to be bonded thermally, there will normally be a small amount (on the order of 10% by weight) of a lower-melting fibre or powder that has been blended into the web. This material is melted by exposure to a hot air oven or to heated rollers and then cooled to form the fabric’s bonds. Protection against exposure to the heated environments should be provided. In the United States, approximately 100 million kg of thermally bonded nonwovens are produced annually.
If the webs are bonded by needle punching, a needle loom is used. An array of needles is mounted in needle boards, and the needles are driven through the web. Needles capture surface fibres, carry them from the top to the bottom of the fabric and then release the fibres on the return stroke. The number of penetrations per unit area can range from a small number (in the case of high-loft fabrics) to a large number (in the case of needled felts). A loom may be used for needling from both the top and bottom sides of the web and for use with multiple boards. Broken needles must be replaced. Safety-locking the looms is required in order to prevent accidents during such maintenance. As in the case of carding, some small fibres may be generated by these processes, and ventilation and respirators are recommended. In addition, eye protection is advised to protect against flying debris from broken needles. In the United States, approximately 100 million kg of needlepunched nonwovens are manufactured annually.
If the webs are bonded by chemical adhesive, the process normally calls for spraying the adhesive on one side of the web and passing it through a curing area, normally a through-air oven. The web direction is then reversed, another application of the adhesive is made and the web is sent back through the oven. A third pass through the oven is sometimes used if needed to complete the curing process. Obviously, the area must exhaust the oven gases and it is necessary to capture and remove any toxic effluents (in the United States, this is required by various state and federal clean air acts). In the case of adhesive bonding, there has been worldwide pressure to reduce the release of formaldehyde into the environment. In the United States, the EPA has recently tightened limits on the release of formaldehyde to one tenth of the previously acceptable limits. There are concerns that the new limits challenge the precision of currently available laboratory methods. The adhesive industry has responded by offering new binders which are formaldehyde free.
There is some nomenclature confusion in regard to air-laid nonwovens. One of the variations of carding processes includes a card that includes a section that randomizes the fibres being processed in an air stream. This process is often referred to as an “air-laid nonwoven process”. Another, very different, process, also called air laid, involves the dispersion of fibres in an air stream, usually using a hammer mill, and directing the airborne fibre dispersion to a device that deposits the fibres on a moving belt. The web formed is then spray bonded and cured. The laydown process may be repeated in line with different types of fibres to produce nonwoven fabrics from layers with different fibre compositions. The fibres used in this case can be very short, and protection to prevent exposure to such airborne fibres must be taken.
The wet laid nonwoven process borrows technology developed for making paper and calls for the formation of webs from dispersions of fibres in water. This process is assisted by the use of dispersion aids that help avoid non-uniform clumps of fibres. The fibre dispersion is filtered through moving belts and dewatered by pressing between felts. At some point in the process a binder is often added which bonds the web during the heat of drying. Alternatively, in a newer method, the web is bonded by hydroentangling using high-pressure jets of water. The final step involves drying and may include steps to soften the fabric by microcreping or some other similar technique. There are no known major hazards associated with this process, and the safety programmes normally are based on common good manufacturing practices.
This process is often excluded from some definitions of nonwovens because it can involve the use of yarns to stitch webs into fabrics. Some definitions of nonwovens exclude any fabrics which contain “yarn”. In this process a web is presented to conventional stitchbonding machines to produce knit-like structures that offer a wide variety of combinations including the use of elastic yarns to produce fabrics with attractive stretch and recovery properties. Again, no exceptional hazards are associated with this process.
Finishes for nonwoven fabrics include flame retardant, fluid repellent, antistatic, softeners, anti-bacterial, fusible, lubricants and other surface treatments. Finishes for nonwovens are applied either on-line or as off-line, post-manufacturing treatments, depending on the process and the type of finish. Frequently, antistatic finishes are added on-line, and surface treatment such as corona etching is normally an on-line process. Flame-retardant and -repellent finishes are often applied off-line. Some specialized fabric treatments include exposing the web to a high-energy plasma treatment to influence the polarity of fabrics and improve their performance in filtration applications. The safety of these chemical and physical processes varies with each application and must be considered separately.
Weaving and knitting are the two primary textile processes for manufacturing fabrics. In the modern textile industry, these processes take place on electrically powered automated machines, and the resulting fabrics find their way into a wide range of end-uses, including wearing apparel, home furnishings and industrial applications.
The weaving process consists of interlacing straight yarns at right angles to one another. It is the oldest technology of manufacturing fabric: hand-powered looms were used in pre-Biblical times. The basic concept of interlacing the yarns is still followed today.
Warp yarns are supplied from a large reel, called a warp beam, mounted at the back of the weaving machine. Each warp yarn end is threaded through a heddles harness. The harness is used to lift or depress the warp yarns to allow the weaving to be done. The simplest weaving requires two harnesses, and more intricate woven fabrics require as many as six harnesses. Jacquard weaving equipment is used to manufacture the most decorative fabrics and has features to enable each individual warp yarn to be lifted or depressed. Each yarn end then is threaded through a reed of closely spaced thin parallel metal pieces mounted on the machine’s lay, or sley. The lay is designed to move in a reciprocating arc around a pivotal anchor point. The yarn ends are attached to the take-up roll. The woven fabric is wound on this roll.
The oldest technology for feeding the filling yarn across the width of the warp yarns is the shuttle, which is propelled in a free-flight fashion from one side of the warp yarn to the other side and pays out the filling yarn from a small bobbin mounted in it. New and faster technology, shown in figure 1, called shuttleless weaving, uses air jets, water jets, small projectiles that ride in a guidetrack, or small, sword-like devices called rapiers to carry the filling yarn.
Figure 1. Air-jet weaving machines
Employees in weaving are typically grouped into one of four job functions:
Weaving presents only a moderate worker safety risk. However, there are a number of typical safety hazards and minimization measures.
Objects on the floor that cause worker falls include machine parts and oil, grease and water spots. Good housekeeping is particularly important in weaving, since many of the process workers spend most of their workday patrolling the area with eyes directed to the production process rather than toward objects on the floor.
Power transmission devices and most other pinch points are typically guarded. The machine lay, harnesses and other parts that must be frequently accessed by weavers, however, are only partially enclosed. Ample walking and working space must be provided around the machines, and good work procedures help workers avoid these exposures. In shuttle weaving, guards mounted on the lay are needed to prevent the shuttle from being thrown out, or to deflect it in a downward direction. Lockouts, mechanical blocks and so on are also required in order to prevent the introduction of hazardous energy into areas when technicians or others are performing job duties on stopped machines.
These can include lifting and moving heavy cloth rolls, warp beams and so on. Hand-trucks to help unload, or doff, and transport small cloth rolls from take-ups on the weaving machine reduce the risk of worker strain injuries by alleviating the need to lift the full weight of the roll. Powered industrial trucks can be used to doff and transport large cloth rolls from bulk take-ups placed at the front of the weaving machine. Wheeled trucks with powered or manual hydraulic assists can be used to handle warp beams, which usually weigh several hundred kg. Warp-handling workers should wear safety shoes.
Fires and ignition
Weaving creates a fair amount of lint, dust and fibre flyings which can represent fire hazards if the fibres are combustible. Controls include dust-collection systems (located under the machines in modern facilities), regular machine cleanings by service workers and use of electrical equipment designed to prevent sparking (e.g., Class III, Division 1, Hazardous Locations).
Health risks in modern weaving are generally limited to noise-induced hearing loss and to pulmonary disorders associated with some types of fibres used in the yarn.
Most weaving machines, operating in the numbers found in a typical production facility, produce noise levels that generally exceed 90 dBA. In some shuttle and high-speed shuttleless weaving, levels may even exceed 100 dBA. Appropriate hearing protectors and a hearing conservation programme are nearly always necessary for weaving workers.
Pulmonary disorders (byssinosis) have long been linked with dusts associated with the processing of raw cotton and flax fibres, and are discussed elsewhere in this chapter and this Encyclopaedia. Generally, ventilation and room air filtration cleaning systems with dust collection points under the weaving machines and at other points in the weaving area maintain dusts at or below required maximum levels (e.g., 750 mg/m3 of air in the OSHA cotton dust standard) in modern facilities. Additionally, dust respirators are needed for temporary protection during cleaning activities. A worker medical surveillance programme should be in place to identify workers who might be especially sensitive to the effects of these dusts.
There is a major cottage industry for the production of hand-knitted items. There are inadequate data on numbers of workers, generally women, thus engaged. The reader is referred to the chapter Entertainment and the arts for an overview of likely hazards. Editor.
The mechanical knitting process consists of interconnecting loops of yarn on powered automated machines (see figure 2). The machines are equipped with rows of small, hooked needles to draw formed yarn loops through previously formed loops. The hooked needles have a unique latch feature that closes the hook to easily allow the loop drawing and then opens to allow the yarn loop to slide off the needle.
Figure 2. Circular-knitting machine
Circular-knitting machines have needles arranged in a circle, and the fabric produced on them comes off the machine in the shape of a large tube that is wound onto a take-up roll. Flat-knitting machines and warp-knitting machines, on the other hand, have needles arranged in a straight row, and fabric comes off the machine in a flat sheet for roll take-up. Circular- and flat-knitting machines are generally fed from yarn cones, and warp-knitting machines are generally fed from warp beams that are smaller but similar to those used in weaving.
Employees in knitting are grouped into job functions with duties similar to those in weaving. Job titles appropriately parallel the process name.
Safety risks in knitting are similar to those in weaving though generally of a lesser degree. Oil on the floor often is a little more prevalent in knitting due to the high lubrication needs of the knitting needles. Machine entrapment risks are less in knitting since there are fewer pinch points on the machines than those found in weaving, and much of the machinery lends itself well to enclosure guarding. Energy-control lockout procedures remain a must.
Cloth roll handling still presents a worker strain injury risk, but the heavy warp-beam handling risks are not present except in warp knitting. Risk control measures are similar to those in weaving. Knitting does not produce the levels of lint, flyings and dust that are found in weaving, but the oil from the process helps keep the fire fuel load at a level that needs attention. Controls are similar to those in weaving.
Health risks in knitting are also generally lower than those in weaving. Noise levels range in the mid-80-dBA to low-90-dBA levels. Respiratory disorders for knitting workers processing raw cotton and flax do not appear to be especially prevalent, and regulatory standards for these materials are often not applicable in knitting.
The Carpet and Rug Institute
Hand-woven or hand-knotted carpets originated several centuries BC in Persia. The first US woven carpet mill was built in 1791 in Philadelphia. In 1839, the industry was reshaped with Erastus Bigelow’s invention of the power loom. The majority of carpet is machine-made in modern mills by one of two processes: tufted or woven.
Tufted carpet is now the predominant method of carpet production. In the United States, for example, approximately 96% of all carpet is machine tufted, a process that developed from tufted bedspread manufacturing centred in northwest Georgia. Tufted carpet is made by inserting a pile yarn into a primary backing fabric (usually polypropylene) and then attaching a secondary backing fabric with a synthetic latex to hold the yarns in place and attach the backings to each other, adding stability to the carpet.
The tufting machine is comprised of hundreds of needles (up to 2,400) in a horizontal bar across the width of the machine (see figure 1). The creel, or yarn on cones arranged in racks, are passed overhead through small-diameter guide tubes to the machine needles on a jerker bar. Generally, two yarn spools are provided for each needle. The yarn end of the first spool is spliced together with the leading end of the second one, so that when yarn from the first spool has been used, yarn is supplied from the second without stopping the machine. A guide tube is provided for each yarn end, in order to prevent the yarns from becoming entangled. The yarns pass through a series of vertically aligned, fixed guides attached to the machine body and a guide located on the end of an arm extending from the moving needle bar of the machine. When the needle bar moves up and down, the relationship between the two guides is changed. Tufted product used for residential carpet is shown in figure 2.
Figure 1. Tufting machine
Carpet and Rug Institute
Carpet and Rug Institute
The jerker bar takes up the slack yarn delivered during the upward stroke of the needles. The yarns are threaded through their respective needles in the needle bar. The needles are operated simultaneously at 500 or more strokes per minute in a vertical, reciprocating motion. A tufting machine can produce 1,000 to 2,000 square metres of carpet in 8 hours of operation.
The primary backing into which the yarns are inserted is supplied from a roll located in front of the machine. The speed of the roll of carpet backing controls the stitch length and the number of stitches per inch. The number of needles in the width per inch or cm of the machine determines the gauge of the fabric, such as 3/16 gauge or 5/32 gauge.
Located below the needle plate of the tufting machine are loopers or looper-and-knife combinations, which pick up and hold momentarily the yarns carried by the needles. When forming loop pile, loopers shaped like inverted hockey sticks are positioned in the machine so that the formed pile loops move away from the loopers as the backing is advanced through the machine.
Loopers for cut pile are a reversed “C” shape, with a cutting surface on the top inside edge of the crescent shape. They are used in combination with knives having a ground cutting edge on one end. As the backing advances through the machine toward the cut pile loopers, the yarns picked up from the needles are cut with a scissor-like action between the looper and knife cutting edge. Figure 3 and figure 4 show the tufts on a backing and the kinds of loops available.
Figure 3. Commercial carpet profile
Carpet and Rug Institute
Carpet and Rug Institute
Woven carpet has a pile surface yarn woven simultaneously with warp and weft threads that form the integrated backing. Backing yarns are usually jute, cotton or polypropylene. Pile yarns can be wool, cotton or any of the synthetic fibres, such as nylon, polyester, polypropylene, acrylic and so on. A back coating is applied to add stability; however, a secondary back is unnecessary and is rarely applied. Variations of woven carpet include velvet, Wilton and Axminster.
There are other methods of making carpet—knitted, needlepunched, fusion bonded—but those methods are used less often and for more specialized markets.
Fibre and Yarn Production
Carpet is manufactured primarily from synthetic yarns—nylon, polypropylene (olefin) and polyester—with lesser quantities of acrylic, wool, cotton and blends of any of these yarns. In the 1960s, synthetic fibres became predominant because they provide a durable, quality product in an affordable price range.
Synthetic yarns are formed by the extrusion of a molten polymer forced through the tiny holes of a metal plate, or spinneret. Additives to the molten polymer may provide solution-dyed colour or less transparent, whiter, more durable fibres and various other performance attributes. After the filaments emerge from the spinneret, they are cooled, drawn and texturized.
Synthetic fibres can be extruded in different shapes or cross-sections, such as round, trilobal, pentalobal, octalobal or square, depending upon the design and shape of the spinneret holes. These cross-sectional shapes can affect many properties of carpet, including lustre, bulkiness, texture retention, and soil-hiding abilities.
After fibre extrusion, post-treatments, such as drawing and annealing (heating/cooling), increase tensile strength and generally enhance the fibre’s physical properties. The filament bundle then goes through a crimping or texturing process, which converts straight filaments to fibres with a repeating kinked, curled or sawtooth configuration.
Yarn can be produced as either bulked continuous filament (BCF) or staple. The BCF is continuous strands of synthetic fibre formed into yarn bundles. Extruded yarn is made by winding the proper number of filaments for the desired yarn denier directly onto “take-up” packages.
Staple fibres are converted into spun yarns by textile yarn spinning processes. When staple fibre is produced, large bundles of fibre called “tow” are extruded. After the crimping process, the tow is cut into fibre lengths of 10 to 20 cm. There are three critical preparation steps—blending, carding and drafting—before the staple fibres are spun. Blending carefully mixes bales of staple fibre to ensure that the fibres intermingle in a way so that yarn streaking will not occur in subsequent dyeing operations. Carding straightens the fibres and puts them in a continuous sliver (rope-like) configuration. Drafting has three main functions: it blends fibres, places them in a parallel form and continues to decrease the weight per unit length of the total fibre bundle to make it easy to spin into the final yarn.
After spinning, which draws the sliver down to the desired yarn size, the yarn is plied and twisted to provide various effects. The yarn is then wound onto yarn cones to prepare it for the heat-setting and yarn-twisting processes.
Because the synthetic fibres have various shapes, they take dyestuffs differently and may have varying colouration performance characteristics. Fibres of the same generic type can be treated or modified so that their affinity for certain dyes is changed, producing a multicolour or two-toned effect.
Colouration for carpet can be achieved at two possible times in the manufacturing process—either by dyeing the fibre or yarn before the fabric is tufted (pre-dyeing) or by dyeing the tufted fabric (post-dyeing of greige goods) before the application of the secondary backing and the finishing process. Methods of pre-dyeing include solution dyeing, stock dyeing and yarn dyeing. Post-dyeing methods include piece dyeing, the application of colour from an aqueous dye bath onto unfinished carpet; beck dyeing, which handles batches of greige goods of approximately 150 running metres; and continuous dyeing, a continuous process of dyeing almost unlimited quantities by distributing dye with an injection applicator across the full width of the carpet as it moves in open-width form under the applicator. Carpet printing uses machinery that is essentially enlarged, modified textile printing equipment. Both flat-bed and rotary-screen printers are used.
Carpet finishing has three separate purposes: to anchor the individual tufts into the primary backing, to adhere the tufted primary backing to a secondary backing and to shear and clean the surface pile to give an attractive surface appearance. Adding a secondary backing material, such as woven polypropylene, jute or attached cushion material, adds dimensional stability to the carpet.
First, the back of the carpet is coated, usually by means of a roller rotating in a synthetic latex mix, and the latex is spread by a doctor blade. The latex is a viscous solution, usually from 8,000 to 15,000 centipose viscosity. Normally, between 22 and 28 ounces (625–795 g) of latex per square yard is applied.
A separate roll of secondary backing is positioned carefully onto the latex coating. The two materials are then carefully pressed together by a marriage roller. This laminate, remaining flat and unflexed, then passes through a long oven, usually 24 to 49 m long, where it is dried and cured at temperatures from 115 to 150 C for 2 to 5 minutes through three zones of heating. A high rate of evaporation is important for carpet drying, with forced hot air moving along precisely controlled heating zones.
In order to clean the surface yarns that may have developed fuzzing on the tips of the fibre during the dyeing and finishing stages, the carpet is lightly sheared. The shear is a unit that heavily brushes the carpet pile to make it both erect and uniform; it passes the carpet through a series of rotary knives or blades that shear or cut off the fibre tips at a precise, adjustable height. Two or four shear blades operate in tandem. The “double shear” has a double set of hard bristle or nylon brushes and two shear blade heads per unit, used in tandem.
The carpet goes through an intense inspection process and is packaged and stored, or cut, packaged and shipped.
Safe Practices in Carpet Mills
Modern carpet and yarn mills provide safety policies, monitoring of safety performance and, when necessary, prompt and thorough accident investigation. Carpet manufacturing machinery is well guarded to protect employees. Keeping the equipment serviced and safe is of primary importance for enhancing quality and productivity and for protection of the workers.
Workers should be trained in the safe use of electrical equipment and work practices to avoid injuries resulting from the unexpected start-up of machines. They need training to recognize hazardous energy sources, the type and magnitude of the energy available and the methods necessary for energy isolation and control. They also should be trained to distinguish exposed live parts from other parts of electrical equipment; to determine the nominal voltage of exposed, energized parts; and to know the required clearance distances and corresponding voltages. In areas where lockout/tagout will be in effect, employees are instructed in the prohibition against restarting or re-energizing equipment.
Where older equipment is in use, careful inspections should be frequent and upgrades made when advisable. Rotating shafts, v-belts and pulley drives, chain and sprocket drives, and overhead hoists and rigging should be periodically inspected, and guards installed whenever possible.
Because hand-pushed yarn buggies are used to move material in a yarn mill, and because yarn fly waste or lint (the scrap from yarn production) accumulates on the floor, the wheels of the yarn buggies must be kept clean and free to roll.
Employees should be trained in the safe use of compressed air, which is frequently used in clean-up procedures.
Fork-lift trucks, either electric- or propane-powered, are used throughout the carpet manufacturing and warehouse facilities. Proper maintenance and attention to safe refuelling, battery changing and so on are essential. Because fork-lift trucks are used where other personnel are working, various ways may be employed to avoid accidents (e.g., walkways reserved exclusively for workers, in which the trucks are prohibited); portable stop signs where employees are required to work in aisles with heavy fork-lift truck traffic; limiting the warehouse/shipping-dock areas to fork-lift truck operators and shipping personnel; and/or instituting a one-way traffic system.
Redesign of machines to minimize repetitive motions should help to reduce the incidence of repetitive-motion injuries. Encouraging workers to regularly practise simple hand and wrist exercises along with adequate work breaks and frequent changes in work tasks may also be helpful.
Musculoskeletal injuries from lifting and carrying may be reduced by the use of mechanical lifting devices, hand-trucks and rolling carts, and by stacking materials on platforms or tables and, where possible, keeping their bulk and weight to more easily manageable dimensions. Training in proper lifting techniques and muscle strengthening exercises can also be helpful, especially for workers returning after an episode of back pain.
A hearing conservation programme is advisable to avoid injury from the noise levels created in some mill operations. Sound-level surveys of the manufacturing equipment will identify those areas in which engineering controls are not sufficiently effective and in which workers may be required to wear hearing-protection equipment and have annual audiometric testing.
Contemporary standards of ventilation and exhaust of heat, lint and dust should be met by the mills.
Adapted from 3rd edition, Encyclopaedia of Occupational Health and Safety.
All “oriental” carpets are hand woven. Many are made in family workplaces, with all the members of the household, often including very small children, working long days and often into the night on the loom. In some cases it is only a part-time occupation of the family, and in some areas the carpet weaving has been moved from the home into factories that are usually small.
The processes involved in the manufacture of a carpet are: yarn preparation, consisting of wool sorting, washing, spinning and dyeing; designing; and the actual weaving.
In some cases the yarn is received at the weaving place already spun and dyed. In others, the raw fibre, usually wool, is prepared, spun and dyed at the weaving place. After the sorting of the wool fibre into grades, usually done by women sitting on the floor, it is washed and spun by hand. The dyeing is carried out in open vessels using mostly aniline-based or alizarine dyestuffs; natural dyestuffs are no longer being used.
Designing and weaving
In handicraft weaving (or tribal weaving, as it is sometimes called), the designs are traditional, and no new designs need to be made. In industrial establishments employing a number of workers, however, there may be a designer who first sketches the design of a new carpet on a sheet of paper and then transfers it in colours onto squared paper from which the weaver can ascertain the number and arrangement of the various knots to be woven into the carpet.
In most cases the loom consists of two horizontal wooden rollers supported on uprights, one about 10 to 30 cm above floor level and the other about 3 m above it. The warp yarn passes from the top roller to the bottom roller in a vertical plane. There is usually one weaver working at the loom, but for wide carpets there may be as many as six weavers working side by side. In about 50% of the cases, the weavers squat on the floor in front of the bottom roller. In other cases, they may have a narrow horizontal plank on which to sit, which is raised up to 4 m above the floor as weaving proceeds. The weaver has to tie short pieces of woollen or silk yarn into knots around pairs of warp threads and then move the thread by hand across the whole length of the carpet. Picks of weft are beaten up into the fibre of the carpet by means of a beater or hand comb. The tufts of yarn protruding from the fibre are trimmed or cut down by scissors.
As the carpet is woven, it is usually wound onto the lower roller, which increases its diameter. When the workers squat on the floor, the position of the lower roller prevents them from stretching their legs, and as the diameter of the rolled-up carpet increases, they have to sit further back but must still lean forward to reach the position in which they tie in the knots of yarn (see figure 1). This is avoided when the weavers sit or squat on the plank, which may be raised as high as 4 m above the floor, but there may still not be enough room for their legs, and they are often forced into uncomfortable positions. In some instances, however, the weaver is provided with a back rest and a pillow (in effect, a legless chair), which may be moved horizontally along the plank as the work progresses. Recently, improved types of elevated looms have been developed that allow the weaver to sit on a chair, with ample room for his or her legs.
Figure 1. Squat loom
In some parts of the Islamic Republic of Iran, the warp in the carpet loom is horizontal instead of being vertical, and the worker sits on the carpet itself whilst working; this makes the task even more difficult.
Hazards of Carpet Weaving
As a largely cottage industry, carpet weaving is fraught with the hazards imposed by impoverished homes with small, crowded rooms that have poor lighting and inadequate ventilation. The equipment and processes are passed along from generation to generation with little or no opportunity for the education and training that might spark a break with the traditional methods. Carpet weavers are subject to skeletal deformations, eyesight disorders and mechanical and toxic hazards.
The squatting position that the weavers must occupy on the old type of loom, and the need for them to lean forward to reach the place into which they knot the yarn, may, over time, lead to some very serious skeletal problems. These are often compounded by the nutritional deficiencies associated with poverty. Especially among those who start as young children, the legs may become deformed (genu valgum), or a crippling arthritis of the knee may develop. The constriction of the pelvis that sometimes occurs in females may make it necessary for them to have a Cesarean delivery when giving birth. Lateral curvature of the spinal column (scoliosis) and lordosis are also common maladies.
The constant close focus on the point of weaving or knotting may cause considerable eyestrain, particularly when the lighting is inadequate. It should be noted that electric lighting is not available in many home workplaces, and the work, which is often continued into the night, must be performed by the light of oil lamps. There have been cases of almost total blindness occurring after only about 12 years of employment at this work.
Hand and finger disorders
The constant tying of small knots and the threading of the weft yarn through the warp threads may result in swollen finger joints, arthritis and neuralgia causing permanent disabilities of the fingers.
The high degree of skill and constant attention to detail over long hours are potent psychosocial stressors, which may be compounded by exploitation and harsh discipline. Children are often “robbed of their childhood”, while adults, who often lack the social contacts essential for emotional balance, may develop nervous illness manifested by trembling of the hands (which may hamper their work performance) and sometimes mental troubles.
As no power machinery is used, there are practically no mechanical hazards. If the looms are not properly maintained, the wooden lever tensioning the warp may break and strike the weaver as it falls. This hazard may be avoided by using special thread tensioning gears.
The dyestuffs used, particularly if they contain potassium or sodium bichromate, may cause skin infections or dermatitis. There is also the risk from the use of ammonia, strong acids and alkalis. Lead pigments are sometimes used by designers, and there have been cases of lead poisoning due to their practice of smoothing the tip of the paintbrush by placing it between the lips; lead pigments should be replaced by non-toxic colours.
There is a danger of anthrax infection from contaminated raw wool from areas where the bacillus is endemic. The appropriate governmental authority should ensure that such wool is properly sterilized before it is delivered to any workshops or factories.
The sorting of the raw material—wool, camel hair, goat hair and so on—should be done over a metal grid fitted with exhaust ventilation to draw any dust into a dust collector located outside the workplace.
The rooms in which the wool-washing and dyeing processes take place should be adequately ventilated, and the workers provided with rubber gloves and waterproof aprons. All waste liquors should be neutralized before being discharged into waterways or sewers.
Good lighting is required for the designing room and for weaving work. As noted above, inadequate light is a serious problem where there is no electricity and when the work is continued after sundown.
Perhaps the most important mechanical improvement would be mechanisms that raise the lower roller of the loom. This would obviate the necessity of weavers having to squat on the floor in an unhealthy and uncomfortable fashion and allow them to sit in a comfortable chair. Such an ergonomic improvement will not only improve the health of the workers but, once adopted, will increase their efficiency and productivity.
The workrooms should be kept clean and well ventilated, and properly boarded or covered floors substituted for earth floors. Adequate heating is required during cold weather. Manual manipulation of the warp places great strain on the fingers and may cause arthritis; wherever possible, hooked knives should be used for holding and weaving operations. Pre-employment and annual medical examinations of all workers are highly desirable.
The manufacture of carpets by the tying of knots of yarn by hand is a very slow process. The number of knots varies from 2 to 360 per square centimetre according to the quality of the carpet. A very large carpet with an intricate design may take over a year to make and involve the tying of hundreds of thousands of knots.
Hand tufting is an alternative method of rug manufacture. It uses a special kind of hand tool fitted with a needle through which the yarn is threaded. A sheet of coarse cotton cloth on which the design of the carpet has been traced is suspended vertically, and when the weaver places the tool against the cloth and presses a button, the needle is forced through the cloth and retracts, leaving a loop of yarn about 10 mm deep on the reverse side. The tool is moved horizontally about 2 or 3 mm, leaving a loop on the face of the cloth, and the trigger button is pressed again to form another loop on the reverse side. With acquired dexterity, as many as 30 loops on each side can be made in 1 minute. Depending on the design, the weaver has to stop from time to time to change the colour of yarn as called for in different parts of the pattern. When the looping operation has been finished, the carpet is taken down and placed reverse side up on the floor. A rubber solution is applied to the back and a covering or backing of stout jute canvas placed over it. The carpet is then placed face upwards and the protruding loops of yarn are trimmed by portable electric clippers. In some cases the design of the carpet is made by cutting or trimming the loops to varying depths.
Hazards in this type of carpet making are considerably less than in the manufacture of hand-knotted carpets. The operator usually sits on a plank in front of the canvas and has plenty of leg room. The plank is raised as the work proceeds. The weaver would be made more comfortable by provision of a backrest and a cushioned seat which could be moved horizontally along the plank as work proceeds. There is less visual strain, and no hand or finger movements that are likely to cause trouble.
The rubber solution used for this carpet usually contains a solvent which is both toxic and highly flammable. The backing process should be carried out in a separate workroom with good exhaust ventilation, at least two fire exits, and with no open flames or lights. Any electrical connections and equipment in this room should be certified as meeting sparkproof/flameproof standards. No more than a minimum amount of the flammable solution should be kept in this room, and appropriate fire extinguishers should be provided. A fire-resistant storage facility for the flammable solutions should not be situated inside any occupied building, but preferably in an open yard.
In most countries, the general provisions of factory legislation cover the necessary standards required for the safety and health of workers in this industry. They may not be applicable, however, to family undertakings and/or home work, and they are difficult to enforce in the scattered small enterprises which, in the aggregate, employ many workers. The industry is notorious for the exploitation of its workers and for its use of child labour, often in defiance of existing regulations. A nascent worldwide trend (mid-1990s) among purchasers of hand-woven and tufted carpets to refrain from buying products produced by illegal or overly exploited workers will, it is hoped by many, eliminate such servitude.