By: – T.Sureshram
Junior Scientific Officer, Department of Textile Physics,
The South India Textile Research Association, Coimbatore-14
Combination of textile technology and medical sciences has resulted into a new field called medical textiles. Medical textiles are one of the most rapidly expanding sectors in the technical textile market. Textile materials in the medical textile field gradually have taken on more important roles. The wide range of textile products used in the medical industry are classified in to four major segments namely non-implantable materials, implantable materials, extracorporeal devices and healthcare & hygiene products. This paper deals with the specifications/properties required and different types of test methods involved for evaluating the characteristics of the medical textile products.
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Geotextiles are made from polypropylene, polyester, polyethylene, polyamide (nylon), polyvinylidene chloride, and fiberglass. Polypropylene and polyester are the most used. Sewing thread for geotextiles is made from KevlarL or any of the above polymers. The physical properties of these materials can be varied by the use of additives in the composition and by changing the processing methods used to form the molten material into filaments. Yarns are formed from fibers which have been bundled and twisted together, a process also referred to as spinning. (This reference is different from the term spinning as used to denote the process of extruding filaments from a molten material.) Yarns may be composed of very long fibers (filaments) or relatively short pieces cut from filaments (staple fibers).
In woven construction, the warp yarns, which run parallel with the length of the geotextile panel (machine direction), are interlaced with yarns called fill or filling yarns, which run perpendicular to the length of the panel (cross direction as shown in fig 1-1). Woven construction produces geotextiles with high strengths and moduli in the warp and fill directions and low elongations at rupture. The modulus varies depending on the rate and the direction in which the geotextile is loaded. When woven geotextiles are pulled on a bias, the modulus decreases, although the ultimate breaking strength may increase. The construction can be varied so that the finished geotextile has equal or different strengths in the warp and fill directions.
Woven construction produces geotextiles with a simple pore structure and narrow range of pore sizes or openings between fibers. Woven geotextiles are commonly plain woven, but are sometimes made by twill weave or leno weave (a very open type of weave). Woven geotextiles can be composed of monofilaments (fig l-2) or multifilament yarns (fig 1-3). Multifilament woven construction produces the highest strength and modulus of all the constructions but are also the highest cost. A monofilament variant is the slit-film or ribbon filament woven geotextile (fig l-4). The fibers are thin and flat and made by cutting sheets of plastic into narrow strips. This type of woven geotextile is relatively inexpensive and is used for separation, i.e., the prevention of intermixing of two materials such as aggregate and fine-grained soil.
Nonwoven geotextiles are formed by a process other than weaving or knitting, and they are generally thicker than woven products. These geotextiles may be made either from continuous filaments or from staple fibers. The fibers are generally oriented randomly within the plane of the geotextile but can be given preferential orientation. In the spunbonding process, filaments are extruded, and laid directly on a moving belt to form the mat, which is then bonded by one of the processes described below.
(a) Needle punching. Bonding by needle punching involves pushing many barbed needles through one or several layers of a fiber mat normal to the plane of the geotextile. The process causes the fibers to be mechanically entangled (fig l-5). The resulting geotextile has the appearance of a felt mat.
(b) Heat bonding. This is done by incorpo-rating fibers of the same polymer type but having different melting points in the mat, or by using hetero filaments, that is, fibers composed of one type of polymer on the inside and covered or sheathed with a polymer having a lower melting point. A heat-bonded geotextile is shown in figure l-6.
(c) Resin bonding. Resin is introduced into the fiber mat, coating the fibers and bonding the contacts between fibers.
(d) Combination bonding. Sometimes a combination of bonding techniques is used to facilitate manufacturing or obtain desired properties.
Composite geotextiles are materials which combine two or more of the fabrication techniques. The most common composite geotextile is a nonwoven mat that has been bonded by needle punching to one or both sides of a woven scrim.
Exposure to sunlight degrades the physical properties of polymers. The rate of degradation is reduced by the addition of carbon black but not eliminated. Hot asphalt can approach the melting point of some polymers. Polymer materials become brittle in very cold temperatures. Chemicals in the groundwater can react with polymers. All polymers gain water with time if water is present. High pH water can be harsh on polyesters while low pH water can be harsh on polyamides. Where chemically unusual environment exists, laboratory test data on effects of exposure of the geotextile to this environment should be sought. Experience with geotextiles in place spans only about 30 years. All of these factors should be considered in selecting or specifying acceptable geotextile materials. Where long duration integrity of the material is critical to life safety and where the in-place material cannot easily be periodically inspected or easily replaced if it should become degraded (for example filtration and/or drainage functions within an earth dam), current practice is to use only geologic materials (which are orders of magnitude more resistant to these weathering effects than polyesters).
a. Joining Panels. Geotextile sections can be joined by sewing, stapling, heat welding, tying, and gluing. Simple overlapping and staking or nailing to the underlying soil may be all that is necessary where the primary purpose is to hold the material in place during installation. However, where two sections are joined and must withstand tensile stress or where the security of the connection is of prime importance, sewing is the most reliable joining method.
b. Sewn Seams. More secure seams can be produced in a manufacturing plant than in the field. The types of sewn seams which can be produced in the field by portable sewing machines are presented in figure 1-7. The seam type designations are from Federal Standard 751. The SSa seam is referred to as a “prayer” seam, the SSn seam as a “J” seam, and the SSd as a “butterfly” seam. The double-sewn seam, SSa-2, is the preferred method for salvageable geotextiles. However, where the edges of the geotextile are subject to unravelling, SSd or SSn seams are preferred.
c. Stitch Type. The portable sewing machines used for field sewing of geotextiles were designed as bag closing machines. These machines can produce either the single-thread or two-thread chain stitches as shown in figure l-8. Both of these stitches are subject to unravelling, but the single-thread stitch is much more susceptible and must be tied at the end of each stitching. Two rows of stitches are preferred for field seaming, two rows of stitches are absolutely essential for secure seams when using the type 101 stitch. since, with this stitch, skipped stitches lead to complete unravelling of the seam. Field sewing should be conducted so all stitching is exposed forinspection. Any skipped stitches should be over sewn.
d. Sewing Thread. The composition of the thread should meet the same compositional performance requirements as the geotextile itself, although it may be desirable to permit the thread to be made of a material different from the geotextile and being sewn. Sewing thread for geotextiles is usually made from Kevlar, polyester, polypropylene, or nylon with the first two recommended despite their greater expense. Where strong seams are required, Kevlar sewing thread provides very high-strength with relative ease of sewing.
Geotextile Functions and Applications
a. Functions. Geotextiles perform one or more basic functions: filtration, drainage, separation, erosion control, sediment control, reinforcement, and (when impregnated with sphalt) moisture barrier. In any one application, a geotextile may be performing several of these functions.
b. Filtration. The use of geotextiles in filter applications is probably the oldest, the most widely known, and the most used function of geotextiles. In this application, the geotextile is placed in contact with and down gradient of soil to be drained. The plane of the geotextile is normal to the expected direction of water flow. The capacity for flow of water normal to the plane of the geotextile is referred to as permittivity. Water and any particles suspended in the water which are smaller than a given size flow through the geotextile. Those soil particles larger than that size are stopped and prevented from being carried away. The geotextile openings should be sized to prevent soil particle movement. The geotextiles substitute for and serve the same function as the traditional granular filter. Both the granular filter and the geotextile filter must allow water (or gas) to pass without significant buildup of hydrostatic pressure. A geotextile-lined drainage trench along the edge of a road pavement is an example using a geotextile as a filter. Most geotextiles are capable of performing this function. Slit film geotextiles are not preferred because opening sizes are unpredictable. Long term clogging is a concern when geotextiles are used for filtration.
c. Drainage. When functioning as a drain, a geotextile acts as a conduit for the movement of liquids or gases in the plane of the geotextile. Examples are geotextiles used as wick drains and blanket drains. The relatively thick nonwoven geotextiles are the products most commonly used. Selection should be based on transmissivity, which is the capacity for in-plane flow. Questions exist as to long term clogging potential of geotextile drains. They are known to be effective in short duration applications.
d. Erosion Control. In erosion control, the geotextile protects soil surfaces from the tractive forces of moving water or wind and rainfall erosion. Geotextiles can be used in ditch linings to protect erodible fine sands or cohesionless silts. The geotextile is placed in the ditch and is secured in place by stakes or is covered with rock or gravel to secure the geotextile, shield it from ultraviolet light, and dissipate the energy of the flowing water. Geotextiles are also used for temporary protection against erosion on newly seeded slopes. After the slope has been seeded, the geotextile is anchored to the slope holding the soil and seed in-place until the seeds germinate and vegetative cover is established. The erosion control function can be thought of as a special case of the combination of the filtration and separation functions.
e. Sediment Control. A geotextile serves to control sediment when it stops particles suspended in surface fluid flow while allowing the fluid to pass through. After some period of time, particles accumulate against the geotextile, reducing the flow of fluid and increasing the pressure against the geotextile. Examples of this application are silt fences placed to reduce the amount of sediment carried off construction sites and into nearby water courses. The sediment control function is actually a filtration function.
f. Reinforcement. In the most common reinforcement application, the geotextile interacts with soil through frictional or adhesion forces to resist tensile or shear forces. To provide reinforcement, a geotextile must have sufficient strength and embedment length to resist the tensile forces generated, and the strength must be developed at sufficiently small strains (i.e. high modulus) to prevent excessive movement of the reinforced structure. To reinforce embankments and retaining structures, a woven geotextile is recommended
because it can provide high strength at small strains.
g. Separation. Separation is the process of preventing two dissimilar materials from mixing. In this function, a geotextile is most often required to prevent the undesirable mixing of fill and natural soils or two different types of fills. A geotextile can be placed between a railroad subgrade and track ballast to prevent contamination and resulting strength loss of the ballast by intrusion of the subgrade soil. In construction of roads over soft soil, a geotextile can be placed over the soft subgrade, and then gravel or crushed stone placed on the geotextile. The geotextile prevents mixing of the two materials.
h. Moisture Barrier. Both woven and nonwoven geotextiles can serve as moisture barriers when impregnated with bituminous, rubber-bitumen, or polymeric mixtures. Such impregnation reduces both the cross-plane and in-plane flow capacity of the geotextiles to a minimum. This function plays an important role in the use of geotextiles in paving overlay systems. In such systems, the impregnated material seals the existing pavement and reduces the amount of surface water entering the base and subgrade. This prevents a reduction in strength of these components and improves the performance of the pavement system.
Yarns are continuous strands of fibers that can be woven or knitted into fabrics. The term, “spinning” refers both to the final yarn-making operation that puts a twist in the yarn and also to the entire sequence of operations that convert raw fibers into usable yarns. Yarn making from staple fibers involves picking (opening, sorting, cleaning, blending), carding and combing (separating and aligning), drawing (re-blending), drafting (drawing into a long strand) and spinning (further drawing and twisting)3. Silk and synthetic filaments are produced by a less extensive procedure. Current high-production yarn-making operations are performed on integrated machines that perform this entire sequence as one combined operation.
Includes the separation of the raw fibers from unwanted material: leaves, twigs, dirt, any remaining seeds, and other foreign items. The fibers are first blended with fibers from different lots or other sources to provide uniformity. (They also may be blended with different fibers to provide improved properties in the final fabric.) When cotton fibers are processed, the raw cotton is run through a cotton ginning operation and then undergoes a cleaning sequence before it is pressed into rectangular bales for shipment to the textile mill. There, the picking starts with a blending machine operation. Bales are opened and cotton from several lots is fed to the machine. The cotton then proceeds to an opening machine that opens tufts of cotton with spiked teeth that pull the fibers apart. Up to three stages of picking follow, after which the cotton is often in the form of a lay, a roll of cotton fiber about 40 in (1 m) wide, 1 n (25 mm) thick and weighing about 40 lb. (18 kg)1. Figs. 1a, 1b and 1c show the lending, opening and picking operations.
Figure 1a: Blending and feeding cotton fibers. Cotton from bales (1), is dropped onto an apron conveyor (2), and moves to another apron conveyor (3), whose surface is covered with spikes. The spikes carry the cotton upward where some of it is knocked off by a ribbed roller(4). The cotton knocked back mixes with cotton carried by the spiked apron. Cotton that passes the knock-back roller is stripped off by another roll (5) and falls (6) to a conveyor that carries it to the next operation. (Illustration used with permission, Dan River Inc.).
Figure 1b: Opening cotton fibers—Cotton from the blending operation falls on an apron conveyor (1) and passes between feeder rolls (2) to a beater cylinder (3). The beater cylinder has rapidly rotating blades that take small tufts of cotton from the feeder rolls, loosen the bunches, remove trash, and move the cotton to the pair of screen rolls (4). The surfaces of these rolls are covered with a screen material. Air is drawn through the screens by a fan (5),pulling the cotton against the screens and forming a web. Small rolls (6), pull the cotton from the screen rolls and deposit it on another conveyor (7), that carries it to another beater (8), that removes more trash. The cotton then moves to the picker operation. (Illustration used with permission, Dan River Inc.)
Figure 1c: Picking cotton fibers—Cotton from the opening operation falls on an apron conveyor (1) which moves it to the first of a series of beaters (2), and screen rolls (3). The beaters and screen rolls in the series are all similar but are progressively more refined as the bottom moves through the equipment. Each beater removes more trash from the cotton. When it reaches the output section (4), the cotton is in the form of a web or lap that is wound into lap roll (5) by winding rolls (6). The lap roll in then ready to be transported to the carding equipment. (Illustration used with permission, Dan River Inc.)
Is a process similar to combing and brushing. It disentangles bunches and locks of fibers and arranges them in a parallel direction. It also further eliminates burrs and other foreign materials and fibers that are too short. The operation is performed on cotton, wool, waste silk,and synthetic staple fibers by a carding machine that consists of a moving conveyor belt with fine wire brushes and a revolving cylinder, also with fine wire hooks or brushes. The fibers from the picking operation are called “picker lap”, and are fed between the belt and the cylinder whose motions pull the fibers in the same direction to form a thin web. The web is
fed into a funnel-like tube that forms it into a round rope-like body about 3/4 in (2 cm) in diameter. This is called a sliver or card sliver. The carding operation is illustrated in Fig.
Figure:Carding cotton fibers—The lap (1) from the picking operation is unrolled and fed by the feed roll (2), to the lickerin roll (3), which has wire shaped like saw teeth. The lickerin roll moves the lap against cleaner bars (4), that remove trash, and passes it to the large cylinder (5). The surface of the large cylinder holds the cotton with thousands of fine wires.The flats (6), with more fine wires, move in the direction opposite to that of the large cylinder.The cotton remains on the large cylinder until it reaches the doffer cylinder (7), which removes it from the large cylinder. A doffer comb (8), vibrates against the doffer cylinder and removes the cotton from it. The cotton, in a filmy web, passes through condenser rolls (9),and into a can through a coiler head (10). The subsequent operation is either combing or drawing. (Illustration used with permission, Dan River Inc.)
Is an additional fiber alignment operation performed on very fine yarns intended for finer fabrics. (Inexpensive and coarser fabrics are made from slivers processed without this further refining.) Fine-tooth combs are applied to the sliver from carding, separating out the shorter fibers, called noils, and aligning the longer fibers to a higher level of parallelism. The resulting strand is called a comb sliver. With its long fibers, the comb sliver provides a smoother, more even yarn.
Drawing (Drafting), (Re-Blending)
After carding and, if performed, combing, several slivers are combined into one strand that is drawn to be longer and thinner. Drawing frames have several pairs of rollers through which he slivers pass. Each successive pair of rollers runs at a higher speed than the preceding pairso that the sliver is pulled longer and thinner as it moves through the drawing frame. The operation is repeated through several stages. The drawing operations produce a product called roving which has less irregularities than the original sliver. Afterward, the finer sliver is given a slight twist and is wound on bobbins. Fig. 10B4 illustrates the drawing operation.Figure
Figure : Drawing—Cans (1), filled with slivers from the carding operation, feed the slivers to the drawing frame. The slivers pass through spoons (2), that guide the slivers and stop the equipment if any should break. The rollers (3), turn successively faster as the slivers move through them, reducing the size of the slivers and increasing their length approximately six fold. At this point, the slivers are combined into one which is deposited into a can (4), by coiler head. The sliver fibers are much more parallel, and the combined sliver is much more uniform after the operation, which is usually repeated for further improvement of the cotton slivers. (Based on an illustration from Dan River, Inc. Used with permission.)
Further draws out and twists fibers to join them together in a continuous yarn or thread. The work is performed on a spinning frame after drawing. The twist is important in providing sufficient strength to the yarn because twisting causes the filaments to interlock further with one another. The roving passes first through another set of drafting rolls, resulting in lengthened yarn of the desired thickness.
There are three kinds of spinning frames: ring spinning, open-end (rotor) spinning, and air-jet spinning. With the common ring spinner, the lengthened yarn is fed onto a bobbin or spool on rotating spindle. The winding is controlled by a traveller feed that moves on a ring around the spindle but at a slower speed than that of the spindle. The result is a twisting of the yarn.The yarn guide oscillates axially during winding to distribute the yarn neatly on the bobbin.The yarn can then be used to weave or knit textile fabrics or to make thread, cord or rope.Staple yarns, made from shorter fibers require more twist to provide a sufficiently strong yarn;filaments have less need to be tightly twisted. For any fiber, yarns with a smaller amount of twist produce fabrics with a softer surface; yarns with considerable twist, hard-twisted yarns,provide a fabric with a more wear resistant surface and better resistance to wrinkles and dirt,but with a greater tendency to shrinkage. Hosiery and crepe fabrics are made from hard twisted
yarns. Fig. illustrates ring spinning.
Figure : Ring spinning. Spun sliver from the drawing operations, which is then called roving, and is wound on bobbins (1), and is fed through another series of drawing rollers (2),that further draw the strand to its final desired thickness. A larger bobbin (4) on a rotating spindle (3), turns at a constant speed. The speed of the final pair of drawing rollers is set a the speed that delivers the yarn so that it is twisted by the desired amount as it is wound on the bobbin. The yarn is guided by the traveller (5), which slides around the bobbin on the ring (6).Because of some drag on the traveller, the yarn winds on the bobbin at the same rate of speed as it is delivered by the final pair of rollers. (Illustration used with permission, Dan RiverInc.)
Spinning Synthetic Fibers
The term “spinning” is also used to refer to the extrusion process of making synthetic fibbers forcing a liquid or semi-liquid polymer (or modified polymer, e.g., rayon) through small holes in an extrusion die, called a spinneret, and then cooling, drying or coagulating the resulting filaments. The fibers are then drawn to a greater length to align the molecules. This increases their strength. The monofilament fibres may be used directly as-is, or may be cut into shorter lengths, crimped into irregular shapes and spun with methods similar to thoseused with natural fibers. These steps are taken to give the synthetic yarns the same feel and
appearance as natural yarns when they are made into thread, garments and other textile products. (Section A2, above, describes wet and dry spinning methods of making rayon and acetate fibers.)
Manipulation of fiber perimeter has a potential to impact the length, micronaire, and strength of cotton fibers. The perimeter of the fiber is regulated by biological mechanisms that control the expansion characteristic of the cell wall and establish cell diameter.
mprovements in fiber quality can take many different forms. Changes in length, strength, uniformity, and fineness In one recent analysis, fiber perimeter was shown to be the single quantitative trait of the fiber that affects all other traits . Fiber perimeter is the variable that has the greatest affect on fiber elongation and strength properties. While mature dead fibers have an elliptical morphology, living fibers have a cylindrical morphology during growth and development. Geometrically, perimeter is directly determined by diameter (perimeter = diameter × p). Thus, fiber diameter is the only variable that directly affects perimeter. For this reason, understanding the biological mechanisms that regulate fiber diameter is important for the long-term improvement of cotton.
A review of the literature indicates that many researchers believe diameter is established at fiber initiation and is maintained throughout the duration of fiber development . A few studies have examined, either directly or indirectly, changes in fiber diameter during development. Some studies indicate that diameter remains constant ; while others indicate that fiber diameter increases as the fiber develops.
The first three stages occur while the fiber is alive and actively growing. Fiber initiation involves the initial isodiametric expansion of the epidermal cell above the surface of the ovule. This stage may last only a day or so for each fiber. Because there are several waves of fiber initiation across the surface of the ovule , one may find fiber initials at any time during the first 5 or 6 d post anthesis. The elongation phase encompasses the major expansion growth phase of the fiber. Depending on genotype, this stage may last for several weeks post anthesis. During this stage of development the fiber deposits a thin, expandable primary cell wall composed of a variety of carbohydrate polymers . As the fiber approaches the end of elongation, the major phase of secondary wall synthesis starts. In cotton fiber, the secondary cell wall is composed almost exclusively of cellulose. During this stage, which lasts until the boll opens (50 to 60 d post anthesis), the cell wall becomes progressively thicker and the living protoplast decreases in volume. There is a significant overlap in the timing of the elongation and secondary wall synthesis stages. Thus, fibers are simultaneously elongating and depositing secondary cell wall.
The establishment of fiber diameter is a complex process that is governed, to a certain extent, by the overall mechanism by which fibers expand. The expansion of fiber cells is governed by the same related mechanisms occurring in other walled plant cells. Most cells exhibit diffuse cell growth, in which new wall and membrane materials are added throughout the surface area of the cell. Specialized, highly elongated cells, such as root hairs and pollen tubes, expand via tip synthesis where new wall and membrane materials are added only at a specific location that becomes the growing tip of the cell. While the growth mechanisms for cotton fiber have not been fully documented, recent evidence indicates that throughout the initiation and early elongation phases of development, cotton fiber expands primarily via diffuse growth . Later in fiber development, late in cell elongation, and well into secondary cell wall synthesis (35 d post anthesis), the organization of cellular organelles is consistent with continued diffuse growth . Many cells that expand via diffuse growth exhibit increases in both cell length and diameter; but cells that exhibit tip synthesis do not exhibit increases in cell diameter . If cotton fiber expands by diffuse growth, then it is reasonable to suggest that cell diameter might increase during the cell elongation phase of development.
Cell expansion is also regulated by the extensibility of the cell wall. For this reason, cell expansion most commonly occurs in cells that have only a primary cell wall . Primary cell walls contain low levels of cellulose. Production of the more rigid secondary cell wall usually signals the cessation of cell expansion. Secondary cell wall formation is often indicated by the development of wall birefringence.
Analyses of fiber diameter and cell wall birefringence show that fiber diameter significantly increased as fibers grew and developed secondary cell walls. Both cotton species and all the genotypes tested exhibited similar increases in diameter; however, the specific rates of change differed. Fibers continued to increase in diameter during the secondary wall synthesis stage of development, indicating that the synthesis of secondary cell wall does not coincide with the cessation of cell expansion.
The generally recommended machinery sequence at gins for spindle-picked cotton is rock and green-boll trap, feed control, tower drier, cylinder cleaner, stick machine, tower drier, cylinder cleaner, extractor feeder, gin stand, lint cleaner, lint cleaner, and press.
Cylinder cleaners use rotating spiked drums that open and clean the seedcotton by scrubbing it across a grid-rod or wire mesh screen that allows the trash to sift through. The stick machine utilizes the sling-off action of channel-type saw cylinders to extract foreign matter from the seedcotton by centrifugal force. In addition to feeding seedcotton to the gin stand, the extractor feeder cleans the cotton using the stick machine’s sling-off principle.
In some cases the extractor-feeder is a combination of a cylinder cleaner and an extractor. Sometimes an impact or revolving screen cleaner is used in addition to the second cylinder cleaner. In the impact cleaner, seedcotton is conveyed across a series of revolving, serrated disks instead of the grid-rod or wire mesh screen.
Lint cleaners at gins are mostly of the controlled-batt, saw type. In this cleaner a saw cylinder combs the fibers and extracts trash from the lint cotton by a combination of centrifugal force, scrubbing action between saw cylinder and grid bars, and gravity assisted by an air current
Seedcotton-type cleaners extract the large trash components from cotton. However, they have only a small influence on the cotton’s grade index, visible liint foreign-matter content, and fiber length distribution when compared with the lint cleaning effects. Also, the number of neps created by the entire seedcotton cleaning process is about the same as the increase caused by one saw-cylinder lint cleaner.
Most cotton gins today use one or two stages of saw-type lint cleaners. The use of too many stages of lint cleaning can reduce the market value of the bale, because the weight loss may offset any gain from grade improvement. Increasing the number of saw lint cleaners at gins, in addition to increasing the nep count and short-fiber content of the raw lint, causes problems at the spinning mill. These show up as more neps in the card web and reduced yarn strength and appearance .
Pima cotton, extra-long-staple cotton, is roller ginned to preserve its length and to minimize neps. To maintain the highest possible quality bale of pima cotton, mill-type lint cleaners were for a long time the predominant cleaner used by the roller-ginning industry. Today, various combinations of impacts, incline, and pneumatic cleaners are used in most roller-ginning plants to increase lint-cleaning capacity.
COTTON FIBER QUALITY:
Two simple words, fiber quality, mean quite different things to cotton growers and to cotton processors. No after-harvest mechanisms are available to either growers or processors that can improve intrinsic fiber quality.
Most cotton production research by physiologists and agronomists has been directed toward improving yields, so the few cultural-input strategies suggested for improving fiber quality during the production season are of limited validity. Thus, producers have limited alternatives in production practices that might result in fibers of acceptable quality and yield without increased production costs.
Fiber processors seek to acquire the highest quality cotton at the lowest price, and attempt to meet processing requirements by blending bales with different average fiber properties. Of course, bale averages for fiber properties do not describe the fiber-quality ranges that can occur within the bales or the resulting blends. Further, the natural variability among cotton fibers unpredictably reduces the processing success for blends made up of low-priced, lower-quality fibers and high-priced, higher-quality fibers.
Blends that fail to meet processing specifications show marked increases in processing disruptions and product defects that cut into the profits of the yarn and textile manufacturers. Mill owners do not have sufficient knowledge of the role classing-office fiber properties play in determining the outcome of cotton spinning and dyeing processes.
Even when a processor is able to make the connection between yarn and fabric defects and increased proportions of low-quality fibers, producers have no way of explaining why the rejected bales failed to meet processing specifications when the bale averages for important fiber properties fell within the acceptable ranges.
If, on the other hand, the causes of a processing defect are unknown, neither the producer nor the processor will be able to prevent or avoid that defect in the future. Any future research that is designed to predict, prevent, or avoid low-quality cotton fibers that cause processing defects in yarn and fabric must address the interface between cotton production and cotton processing.
Every bale of cotton produced in the USA crosses that interface via the USDA-AMS classing offices, which report bale averages of quantified fiber properties. Indeed, fiber-quality data reports from classing offices are designed as a common quantitative language that can be interpreted and understood by both producers and processors. But the meaning and utility of classing-office reports can vary, depending on the instrument used to evaluate.
Fiber maturity is a composite of factors, including inherent genetic fineness compared with the perimeter or cross section achieved under prevailing growing conditions and the relative fiber cell-wall thickness and the primary -to- secondary fiber cell-wall ratio, and the time elapsed between flowering and boll opening or harvest. While all the above traits are important to varying degrees in determining processing success, none of them appear in classing-office reports.
Micronaire, which is often treated as the fiber maturity measurement in classing-office data, provides an empirical composite of fiber cross section and relative wall thickening. But laydown blends that are based solely on bale-average micronaire will vary greatly in processing properties and outcomes.
Cotton physiologists who follow fiber development can discuss fiber chronological maturity in terms of days after floral anthesis. But, they must quantify the corresponding fiber physical maturity as micronaire readings for samples pooled across several plants, because valid micronaire determinations require at least 10 g of individualized fiber.
Some fiber properties, like length and single fiber strength, appear to be simple and easily understood terms. But the bale average length reported by the classing office does not describe the range or variability of fiber lengths that must be handled by the spinning equipment processing each individual fiber from the highly variable fiber population found in that bale.
Even when a processing problem can be linked directly to a substandard fiber property, surprisingly little is known about the causes of variability in fiber shape and maturity. For example:
Spinners can see the results of excessive variability in fiber length or strength when manifested as yarn breaks and production halts.Knitters and weavers can see the knots and slubs or holes that reduce the value of fabrics made from defective yarns that were spun from poor-quality fibre
Inspectors of dyed fabrics can see the unacceptable color streaks and specks associated with variations in fiber maturity and the relative dye-uptake success.
The grower, ginner, and buyer can see variations in color or trash content of ginned and baled cotton.
But there are no inspectors or instruments that can see or predict any of the above quality traits of fibers while they are developing in the boll. There is no definitive reference source, model, or database to which a producer can turn for information on how cultural inputs could be adapted to the prevailing growth conditions of soil fertility, water availability, and weather (temperature, for example) to produce higher quality fiber.
The scattered research publications that address fiber quality, usually in conjunction with yield improvement, are confusing because their measurement protocols are not standardized and results are not reported in terms that are meaningful to either producers or processors. Thus, physiological and agronomic studies of fiber quality frequently widen, rather than bridge, the communication gap between cotton producers and processors.
This overview assembles and assesses current literature citations regarding the quantitation of fiber quality and the manner in which irrigation, soil fertility, weather, and cotton genetic potential interact to modulate fiber quality. The ultimate goal is to provide access to the best answers currently available to the question of what causes the annual and regional fiber quality variations
From the physiologist’s perspective, the fiber quality of a specific cotton genotype is a composite of fiber shape and maturity properties that depend on complex interactions among the genetics and physiology of the plants producing the fibers and the growth environment prevailing during the cotton production season.
Fiber shape properties, particularly length and diameter, are largely dependent on genetics. Fiber maturity properties, which are dependent on deposition of photosynthate in the fiber cell wall, are more sensitive to changes in the growth environment. The effects of the growth environment on the genetic potential of a genotype modulate both shape and maturity properties to varying degrees.
Anatomically, a cotton fiber is a seed hair, a single hyperelongated cell arising from the protodermal cells of the outer integument layer of the seed coat. Like all living plant cells, developing cotton fibers respond individually to fluctuations in the macro- and microenvironments. Thus, the fibers on a single seed constitute continua of fiber length, shape, cell-wall thickness, and physical maturity .
Environmental variations within the plant canopy, among the individual plants, and within and among fields ensure that the fiber population in each boll, indeed on each seed, encompasses a broad range of fiber properties and that every bale of cotton contains a highly variable population of fibers.
Successful processing of cotton lint depends on appropriate management during and after harvest of those highly variable fiber properties that have been shown to affect finished-product quality and manufacturing efficiency . If fiber-blending strategies and subsequent spinning and dyeing processes are to be optimized for specific end-uses and profitability, production managers in textile mills need accurate and effective descriptive and predictive quantitative measures of both the means and the ranges of these highly variable fiber properties .
In the USA, the components of cotton fiber quality are usually defined as those properties reported for every bale by the classing offices of the USDA-AMS, which currently include length, length uniformity index, strength, micronaire, color as reflectance (Rd) and yellowness (+b), and trash content, all quantified by the High Volume Instrument (HVI) line. The classing offices also provide each bale with the more qualitative classers’ color and leaf grades and with estimates of preparation (degree of roughness of ginned lint) and content of extraneous matter.
The naturally wide variations in fiber quality, in combination with differences in end-use requirements, result in significant variability in the value of the cotton lint to the processor. Therefore, a system of premiums and discounts has been established to denote a specified base quality. In general, cotton fiber value increases as the bulk-averaged fibers increase in whiteness (+Rd), length, strength, and micronaire; and discounts are made for both low mike (micronaire less than 3.5) and high mike (micronaire more than 4.9).
Ideal fiber-quality specifications favored by processors traditionally have been summarized thusly: “as white as snow, as long as wool, as strong as steel, as fine as silk, and as cheap as hell.” These specifications are extremely difficult to incorporate into a breeding program or to set as goals for cotton producers. Fiber-classing technologies in use and being tested allow quantitation of fiber properties, improvement of standards for end-product quality, and, perhaps most importantly, creation of a fiber-quality language and system of fiber-quality measurements that can be meaningful and useful to producers and processors alike.
GENE AND ENVIRONMENTAL VARIABILITY:
Improvements in textile processing, particularly advances in spinning technology, have led to increased emphasis on breeding cotton for both improved yield and improved fiber properties Studies of gene action suggest that, within upland cotton genotypes there is little non-additive gene action in fiber length, strength, and fineness ; that is, genes determine those fiber properties. However, large interactions between combined annual environmental factors (primarily weather) and fiber strength suggest that environmental variability can prevent full realization of the fiber-quality potential of a cotton genotype.
More recently, statistical comparisons of the relative genetic and environmental influences upon fiber strength suggest that fiber strength is determined by a few major genes, rather than by variations in the growth environment . Indeed, spatial variations of single fertility factors in the edaphic environment were found to be unrelated to fiber strength and only weakly correlated with fiber length .
Genetic potential of a specific genotype is defined as the level of fiber yield or quality that could be attained under optimal growing conditions. The degree to which genetic potential is realized changes in response to environmental fluctuations such as application of water or fertilizer and the inevitable seasonal shifts such as temperature, day length, and insolation.
In addition to environment-related modulations of fiber quality at the crop and whole-plant levels, significant differences in fiber properties also can be traced to variations among the shapes and maturities of fibers on a single seed and, consequently, within a given boll.
EFFECT ON FIBER LENGTH:
Comparisons of the fiber-length arrays from different regions on a single seed have revealed that markedly different patterns in fiber length can be found in the micropylar, middle, and chalazal regions of a cotton seed – at either end and around the middle . Mean fiber lengths were shortest at the micropylar (upper, pointed end of the seed) . The most mature fibers and the fibers having the largest perimeters also were found in the micropylar region of the seed. After hand ginning, the percentage of short fibers less than 0.5 inch or 12.7 mm long on a cotton seed was extremely low.
It has been reported that, in ginned and baled cotton, the short fibers with small perimeters did not originate in the micropylar region of the seed . MEasurements of fibers from micropylar and chalazal regions of seeds revealed that the location of a seed within the boll was related to the magnitude of the differences in the properties of fibers from the micropylar and chalazal regions.
Significant variations in fiber maturity also can be related to the seed position (apical, medial, or due to the variability inherent in cotton fiber, there is no absolute value for fiber length within a genotype or within a test sample . Even on a single seed, fiber lengths vary significantly because the longer fibers occur at the chalazal (cup-shaped, lower) end of the seed and the shorter fibers are found at the micropylar (pointed) end. Coefficients of fiber-length variation, which also vary significantly from sample to sample, are on the order of 40% for upland cotton.
Variations in fiber length attributable to genotype and fiber location on the seed are modulated by factors in the micro- and macroenvironment . Environmental changes occurring around the time of floral anthesis may limit fiber initiation or retard the onset of fiber elongation. Suboptimal environmental conditions during the fiber elongation phase may decrease the rate of elongation or shorten the elongation period so that the genotypic potential for fiber length is not fully realized . Further, the results of environmental stresses and the corresponding physiological responses to the growth environment may become evident at a stage in fiber development that is offset in time from the occurrence of the stressful conditions.
Fiber lengths on individual seeds can be determined while the fibers are still attached to the seed , by hand stapling or by photoelectric measurement after ginning. Traditionally, staple lengths have been measured and reported to the nearest 32nd of an inch or to the nearest millimeter. The four upland staple classes are: short (<21 mm), medium (22-25 mm), medium-long (26-28 mm) and long (29-34 mm). Pimastaple length is classed as long (29-34 mm) and extra-long (>34 mm). Additionally, short fiber content is defined as the percentage of fiber less than 12.7 mm.
Cotton buyers and processors used the term staple length long before development of quantitative methods for measuring fiber properties. Consequently, staple length has never been formally defined in terms of a statistically valid length distribution.
In Fibrograph testing, fibers are randomly caught on combs, and the beard formed by the captured fibers is scanned photoelectrically from base to tip . The amount of light passing through the beard is a measure of the number of fibers that extend various distances from the combs. Data are recorded as span length (the distance spanned by a specific percentage of fibers in the test beard). Span lengths are usually reported as 2.5 and 50%. The 2.5% span length is the basis for machine settings at various stages during fiber processing.
The uniformity ratio is the ratio between the two span lengths expressed as a percentage of the longer length. The Fibrograph provides a relatively fast method for reproducibility in measuring the length and length uniformity of fiber samples. Fibrograph test data are used in research studies, in qualitative surveys such as those checking commercial staple-length classifications, and in assembling cotton bales into uniform lots.
Since 1980, USDA-AMS classing offices have relied almost entirely on high-volume instrumentation (HVI) for measuring fiber length and other fiber properties (Moore, 1996). The HVI length analyzer determines length parameters by photoelectrically scanning a test beard that is selected by a specimen loader and prepared by a comber/brusher attachment
The fibers in the test beard are assumed to be uniform in cross-section, but this is a false assumption because the cross section of each individual fiber in the beard varies significantly from tip to tip. The HVI fiber-length data are converted into the percentage of the total number of fibers present at each length value and into other length parameters, such as mean length, upper-half mean length, and length uniformity . This test method for determining cotton fiber length is considered acceptable for testing commercial shipments when the testing services use the same reference standard cotton samples.
All fiber-length methods discussed above require a minimum of 5 g of ginned fibers and were developed for rapid classing of relatively large, bulk fiber samples. For analyses of small fiber samples , fiber property measurements with an electron-optical particle-sizer, the Zellweger Uster AFIS-A2 have been found to be acceptably sensitive, rapid, and reproducible. The AFIS-A2 Length and Diameter module generates values for mean fiber length by weight and mean fiber length by number, fiber length histograms, and values for upper quartile length, and for short-fiber contents by weight and by number (the percentages of fibers shorter than 12.7 mm). The AFIS-A2 Length and Diameter module also quantifies mean fiber diameter by number .
Although short-fiber content is not currently included in official USDA-AMS classing office reports, short-fiber content is increasingly recognized as a fiber property comparable in importance to fiber fineness, strength, and length . The importance of short-fiber content in determining fiber-processing success, yarn properties, and fabric performance has led the post-harvest sector of the U.S. cotton industry to assign top priority to minimizing short-fiber content, whatever the causes .
The perceived importance of short-fiber content to processors has led to increased demands for development and approval of a standard short-fiber content measurement that would be added to classing office HVI systems . This accepted classing office-measurement would allow inclusion of short-fiber content in the cotton valuation system. Documentation of post-ginning short-fiber content at the bale level is expected to reduce the cost of textile processing and to increase the value of the raw fiber . However, modulation of short-fiber content before harvest cannot be accomplished until the causes of increased short-fiber content are better understood.
Fiber length is primarily a genetic trait, but short-fiber content is dependent upon genotype, growing conditions, and harvesting, ginning, and processing methods. Further, little is known about the levels or sources of pre-harvest short-fiber content .
It is essential that geneticists and physiologists understand the underlying concepts and the practical limitations of the methods for measuring fiber length and short-fiber content so that the strong genetic component in fiber length can be separated from environmental components introduced by excessive temperatures and water or nutrient deficiencies. Genetic improvement of fiber length is fruitless if the responses of the new genotypes to the growth environment prevent full realization of the enhanced genetic potential or if the fibers produced by the new genotypes break more easily during harvesting or processing. The reported effects of several environmental factors on fiber length and short-fiber content, which are assumed to be primarily genotype-dependent, are discussed in the subsections that follow. FIBER LENGTH AND TEMPERATURE:
Maximum cotton fiber lengths were reached when night temperatures were around 19 to 20 °C, depending on the genotype . Early-stage fiber elongation was highly temperature dependent; late fiber elongation was temperature independent . Fiber length (upper-half mean length) was negatively correlated with the difference between maximum and minimum temperature.
Modifications of fiber length by growth temperatures also have been observed in planting-date studies in which the later planting dates were associated with small increases in 2.5 and 50% span lengths . If the growing season is long enough and other inhibitory factors do not interfere with fiber development, early-season delays in fiber initiation and elongation may be counteracted by an extension of the elongation period .
Variations in fiber length and the elongation period also were associated with relative heat-unit accumulations. Regression analyses showed that genotypes that produced longer fibers were more responsive to heat-unit accumulation levels than were genotypes that produced shorter fibers . However, the earliness of the genotype was also a factor in the relationship between fiber length (and short-fiber content by weight) and accumulated heat units .
As temperature increased, the number of small motes per boll also increased. Fertilization efficiency, which was negatively correlated with small-mote frequency, also decreased. Although fiber length did not change significantly with increasing temperature, the percentage of short-fibers was lower when temperatures were higher. The apparent improvement in fiber length uniformity may be related to increased assimilate availability to the fibers because there were fewer seeds per boll. FIBER LENGTH AND WATER:
Cotton water relationships and irrigation traditionally have been studied with respect to yield . Fiber length was not affected unless the water deficit was great enough to lower the yield to 700 kg ha-1. Fiber elongation was inhibited when the midday water potential was -2.5 to -2.8 mPa. Occurrence of moisture deficits during the early flowering period did not alter fiber length. However, when drought occurred later in the flowering period, fiber length was decreased .
Severe water deficits during the fiber elongation stage reduce fiber length , apparently due simply to the direct mechanical and physiological processes of cell expansion. However, water availability and the duration and timing of flowering and boll set can result in complex physiological interactions between water deficits and fiber properties including length.
FIBRE LENGTH AND LIGHT:
Changes in the growth environment also alter canopy structure and the photon flux environment within the canopy. For example, loss of leaves and bolls from unfavorable weather (wind, hail), disease, or herbivory and compensatory regrowth can greatly affect both fiber yield and quality . The amount of light within the crop canopy is an important determinant of photosynthetic activity and, therefore, of the source-to-sink relationships that allocate photoassimilate within the canopy . Eaton and Ergle (1954) observed that reduced-light treatments increased fiber length. Shading during the first 7 d after floral anthesis resulted in a 2% increase in the 2.5% span length .
Shading (or prolonged periods of cloudy weather) and seasonal shifts in day length also modulate temperature, which modifies fiber properties, including length.
Commercial cotton genotypes are considered to be day-length neutral with respect to both flowering and fruiting . However, incorporation of day-length data in upland and pima fiber-quality models, based on accumulated heat units, increased the coefficients of determination for the length predictors from 30 to 54% for the upland model and from 44 to 57% for the pima model .
It was found that the light wavelengths reflected from red and green mulches increased fiber length, even though plants grown under those mulches received less reflected photosynthetic flux than did plants grown with white mulches. The longest fiber was harvested from plants that received the highest far red/red ratios.
FIBER LENGTH AND MINERAL NUTRITION:
Studies of the mineral nutrition of cotton and the related soil chemistry usually have emphasized increased yield and fruiting efficiency . More recently, the effects of nutrient stress on boll shedding have been examined . Also, several mineral-nutrition studies have been extended to include fiber quality .
Reports of fiber property trends following nutrient additions are often contradictory due to the interactive effects of genotype, climate, and soil conditions. Potassium added at the rate of 112 kg K ha-1yr-1 did not affect the 2.5% span length , when genotype was a significant factor in determining both 2.5 and 50% span lengths . Genotype was not a significant factor in Acala fiber length, but an additional 480 kg K ha-1yr-1 increased the mean fiber length . K ha-1yr-1 increased the length uniformity ratio and increased 50%, but not 2.5% span length. Genotype and the interaction, genotype-by-environment, determined the 2.5% span length.
As mentioned above, fiber length is assumed to be genotype-dependent, but growth-environment fluctuations – both those resulting from seasonal and annual variability in weather conditions and those induced by cultural practices and inputs – modulate the range and mean of the fiber length population at the test sample, bale, and crop levels.
Quantitation of fiber length is relatively straightforward and reproducible, and fiber length (along with micronaire) is one of the most likely fiber properties to be included when cotton production research is extended beyond yield determinations. Other fiber properties are less readily quantified, and the resulting data are not so easily understood or analyzed statistically. This is particularly true of fiber-breaking strength, which has become a crucial fiber property due to changes in spinning techniques.
The inherent breaking strength of individual cotton fibers is considered to be the most important factor in determining the strength of the yarn spun from those fibers . Recent developments in high-speed yarn spinning technology, specifically open-end rotor spinning systems, have shifted the fiber-quality requirements of the textile industry toward higher-strength fibers that can compensate for the decrease in yarn strength associated with open-end rotor spinning techniques.
Compared with conventional ring spinning, open-end rotor-spun yarn production capacity is five times greater and, consequently, more economical. Rotor-spun yarn is more even than the ring-spun, but is 15 to 20% weaker than ring-spun yarn of the same thickness. Thus, mills using open-end rotor and friction spinning have given improved fiber strength highest priority. Length and length uniformity, followed by fiber strength and fineness, remain the most important fiber properties in determining ring-spun yarn strength.
Historically, two instruments have been used to measure fiber tensile strength, the Pressley apparatus and the Stelometer . In both of these flat-bundle methods, a bundle of fibers is combed parallel and secured between two clamps. A force to try to separate the clamps is applied and gradually increased until the fiber bundle breaks. Fiber tensile strength is calculated from the ratio of the breaking load to bundle mass. Due to the natural lack of homogeneity within a population of cotton fibers, bundle fiber selection, bundle construction and, therefore, bundle mass measurements, are subject to considerable experimental error .
Fiber strength, that is, the force required to break a fiber, varies along the length of the fiber, as does fiber fineness measured as perimeter, diameter, or cross section Further, the inherent variability within and among cotton fibers ensures that two fiber bundles of the same weight will not contain the same number of fibers. Also, the within-sample variability guarantees that the clamps of the strength testing apparatus will not grasp the various fibers in the bundle at precisely equivalent positions along the lengths. Thus, a normalizing length-weight factor is included in bundle strength calculations.
In the textile literature, fiber strength is reported as breaking tenacity or grams of breaking load per tex, where tex is the fiber linear density in grams per kilometer . Both Pressley and stelometer breaking tenacities are reported as 1/8 in. gauge tests, the 1/8 in. (or 3.2 mm) referring to the distance between the two Pressley clamps. Flat-bundle measurements of fiber strength are considered satisfactory for acceptance testing and for research studies of the influence of genotype, environment, and processing on fiber (bundle) strength and elongation.
The relationships between fiber strength and elongation and processing success also have been examined using flat-bundle strength testing methods . However cotton fiber testing today requires that procedures be rapid, reproducible, automated, and without significant operator bias. Consequently, the HVI systems used for length measurements in USDA-AMS classing offices are also used to measure the breaking strength of the same fiber bundles (beards) formed during length measurement.
Originally, HVI strength tests were calibrated against the 1/8-in. gauge Pressley measurement, but the bundle-strengths of reference cottons are now established by Stelometer tests that also provide bundle elongation-percent data. Fiber bundle elongation is measured directly from the displacement of the jaws during the bundle-breaking process, and the fiber bundle strength and elongation data usually are reported together (ASTM, 1994, D 4604-86). The HVI bundle-strength measurements are reported in grams-force tex-1 and can range from 30 and above (very strong) to 20 or below (very weak). In agronomic papers, fiber strengths are normally reported as kN m kg-1, where one Newton equals 9.81 kg-force .
The HVI bundle-strength and elongation-percent testing methods are satisfactory for acceptance testing and research studies when 3.0 to 3.3 g of blended fibers are available and the relative humidity of the testing room is adequately controlled. A 1% increase in relative humidity and the accompanying increase in fiber moisture content will increase the strength value by 0.2 to 0.3 g tex-1, depending on the fiber genotype and maturity.
Further, classing-office HVI measurements of fiber strength do not adequately describe the variations of fiber strength along the length of the individual fibers or within the test bundle. Thus, predictions of yarn strength based on HVI bundle-strength data can be inadequate and misleading . The problem of fiber-strength variability is being addressed by improved HVI calibration methods and by computer simulations of bundle-break tests in which the simulations are based on large single-fiber strength databases of more than 20 000 single fiber long-elongation curves obtained with MANTIS .
Fiber Strength, Environment, and Genotype:
Reports of stelometer measurements of fiber bundle strength are relatively rare in the refereed agronomic literature. Consequently, the interactions of environment and genotype in determining fiber strength are not as well documented as the corresponding interactions that modulate fiber length. Growth environment, and genotype response to that environment, play a part in determining fiber strength and strength variability .
Early studies showed fiber strength to be significantly and positively correlated with maximum or mean growth temperature, maximum minus minimum growth temperature, and potential insolation . Increased strength was correlated with a decrease in precipitation. Minimum temperature did not affect fiber strength. All environmental variables were interrelated, and a close general association between fiber strength and environment was interpreted as indicating that fiber strength is more responsive to the growth environment than are fiber length and fineness. Other investigators reported that fiber strength was correlated with genotype only.
Square removal did not affect either fiber elongation or fiber strength . Shading, leaf-pruning, and partial fruit removal decreased fiber strength . Selective square removal had no effect on fiber strength in bolls at the first, second, or third position on a fruiting branch . Fiber strength was slightly greater in bolls from the first 4 to 6 wk of flowering, compared with fibers from bolls produced by flowers opening during the last 2 wk of the flowering period .
In that study, fiber strength was positively correlated with heat unit accumulation during boll development, but genotype, competition among bolls, assimilatory capacity, and variations in light environment also helped determine fiber strength. Early defoliation, at 20% open bolls, increased fiber strength and length, but the yield loss due to earlier defoliation offset any potential improvement in fiber quality .
Of the fiber properties reported by USDA-AMS classing offices for use by the textile industry, fiber maturity is probably the least well-defined and most misunderstood. The term, fiber maturity, used in cotton marketing and processing is not an estimate of the time elapsed between floral anthesis and fiber harvest . However, such chronological maturity can be a useful concept in studies that follow fiber development and maturation with time . On the physiological and the physical bases, fiber maturity is generally accepted to be the degree (amount) of fiber cell-wall thickening relative to the diameter or fineness of the fiber .
Classically, a mature fiber is a fiber in which two times the cell wall thickness equals or exceeds the diameter of the fiber cell lumen, the space enclosed by the fiber cell walls . However, this simple definition of fiber maturity is complicated by the fact that the cross section of a cotton fiber is never a perfect circle; the fiber diameter is primarily a genetic characteristic.
Further, both the fiber diameter and the cell-wall thickness vary significantly along the length of the fiber. Thus, attempting to differentiate, on the basis of wall thickness, between naturally thin-walled or genetically fine fibers and truly immature fibers with thin walls greatly complicates maturity comparisons among and within genotypes.
Within a single fiber sample examined by image analysis, cell-wall thickness ranged from 3.4 to 4.9 µm when lumen diameters ranged from 2.4 to 5.2 µm . Based on the cited definition of a mature fiber having a cell-wall thickness two times the lumen diameter, 90% of the 40 fibers in that sample were mature, assuming that here had been no fiber-selection bias in the measurements.
Unfortunately, none of the available methods for quantifying cell-wall thickness is sufficiently rapid and reproducible to be used by agronomists, the classing offices, or fiber processors. Fiber diameter can be quantified, but diameter data are of limited use in determining fiber maturity without estimates of the relationship between lumen width and wall thickness. Instead, processors have attempted to relate fiber fineness to processing outcome. Estimating Fiber Fineness:
Fiber fineness has long been recognized as an important factor in yarn strength and uniformity, properties that depend largely on the average number of fibers in the yarn cross section. Spinning larger numbers of finer fibers together results in stronger, more uniform yarns than if they had been made up of fewer, thicker fibers . However, direct determinations of biological fineness in terms of fiber or lumen diameter and cell-wall thickness are precluded by the high costs in both time and labor, the noncircular cross sections of dry cotton fibers, and the high degree of variation in fiber fineness.
Advances in image analysis have improved determinations of fiber biological fineness and maturity , but fiber image analyses remain too slow and limited with respect to sample size for inclusion in the HVI-based cotton-classing process.
Originally, the textile industry adopted gravimetric fiber fineness or linear density as an indicator of the fiber-spinning properties that depend on fiber fineness and maturity combined . This gravimetric fineness testing method was discontinued in 1989, but the textile linear density unit of tex persists. Tex is measured as grams per kilometer of fiber or yarn, and fiber fineness is usually expressed as millitex or micrograms per meter . Earlier, direct measurements of fiber fineness (either biological or gravimetric) subsequently were replaced by indirect fineness measurements based on the resistance of a bundle of fibers to airflow.
The first indirect test method approved by ASTM for measurement of fiber maturity, lineardensity, and maturity index was the causticaire method. In that test, the resistance of a plug of cotton to airflow was measured before and after a cell-wall swelling treatment with an 18% (4.5 M) solution of NaOH (ASTM, 1991, D 2480-82). The ratio between the rate of airflow through an untreated and then treated fiber plug was taken as indication of the degree of fiber wall development. The airflow reading for the treated sample was squared and corrected for maturity to serve as an indirect estimate of linear density. Causticaire method results were found to be highly variable among laboratories, and the method never was recommended for acceptance testing before it was discontinued in 1992.
The arealometer was the first dual-compression airflow instrument for estimating both fiber fineness and fiber maturity from airflow rates through untreated raw cotton (ASTM, 1976, D 1449-58; Lord and Heap, 1988). The arealometer provides an indirect measurement of the specific surface area of loose cotton fibers, that is, the external area of fibers per unit volume (approximately 200-mg samples in four to five replicates). Empirical formulae were developed for calculating the approximate maturity ratio and the average perimeter, wall thickness, and weight per inch from the specific surface area data. The precision and accuracy of arealometer determinations were sensitive to variations in sample preparation, to repeated sample handling, and to previous mechanical treatment of the fibers, e.g., conditions during harvesting, blending, and opening. The arealometer was never approved for acceptance testing, and the ASTM method was withdrawn in 1977 without replacement.
The variations in biological fineness and relative maturity of cotton fibers that were described earlier cause the porous plugs used in air-compression measurements to respond differently to compression and, consequently, to airflow . The IIC-Shirley Fineness/Maturity Tester (Shirley FMT), a dual-compression instrument, was developed to compensate for this plug-variation effect (ASTM, 1994, D 3818-92). The Shirley FMT is considered suitable for research, but is not used for acceptance testing due to low precision and accuracy. Instead, micronaire has become the standard estimate of both fineness and maturity in the USDA-AMS classing offices.
Fiber Maturity and Environment:
Whatever the direct or indirect method used for estimating fiber maturity, the fiber property being as sayed remains the thickness of the cell wall. The primary cell wall and cuticle (together »0.1 µm thick) make up about 2.4% of the total wall thickness ( »4.1 µm of the cotton fiber thickness at harvest) . The rest of the fiber cell wall (»98%) is the cellulosic secondary wall, which thickens significantly as polymerized photosynthate is deposited during fiber maturation. Therefore, any environmental factor that affects photosynthetic C fixation and cellulose synthesis will also modulate cotton fiber wall thickening and, consequently, fiber physiological maturation
Fiber Maturity and Temperature and Planting Date:
The dilution, on a weight basis, of the chemically complex primary cell wall by secondary-wall cellulose has been followed with X-ray fluorescence spectroscopy. This technique determines the decrease, with time, in the relative weight ratio of the Ca associated with the pectin-rich primary wall . Growth-environment differences between the two years of the studies cited significantly altered maturation rates, which were quantified as rate of Ca weight-dilution, of both upland and pima genotypes. The rates of secondary wall deposition in both upland and pima genotypes were closely correlated with growth temperature; that is, heat-unit accumulation .
Micronaire (micronAFIS) also was found to increase linearly with time for upland and pima genotypes . The rates of micronaire increase were correlated with heat-unit accumulations . Rates of increase in fiber cross-sectional area were less linear than the corresponding micronaire-increase rates, and rates of upland and pima fiber cell-wall thickening were linear and without significant genotypic effect .
Environmental modulation of fiber maturity (micronaire) by temperature was most often identified in planting- and flowering-date studies . The effects of planting date on micronaire, Shirley FMT fiber maturity ratio, and fiber fineness (in millitex) were highly significant in a South African study (Greef and Human, 1983). Although genotypic differences were detected among the three years of that study, delayed planting generally resulted in lower micronaire. The effect on fiber maturity of late planting was repeated in the Shirley FMT maturity ratio and fiber fineness data.
Planting date significantly modified degree of thickening, immature fiber fraction, cross-sectional area, and micronaire (micronAFIS) of four upland genotypes that also were grown in South Carolina . In general, micronaire decreased with later planting, but early planting also reduced micronaire of Deltapine 5490, a long-season genotype, in a year when temperatures were suboptimal during the early part of the season.
Harvest dates in this study also were staggered so that the length of the growing season was held constant within each year. Therefore, season-length should not have been an important factor in the relationships found between planting date and fiber maturity. Fiber Maturity and Source-Sink Manipulation:
Variations in fiber maturity were linked with source-sink modulations related to flowering date , and seed position within the bolls . However, manipulation of source-sink relationships by early-season square (floral bud) removal had no consistently significant effect on upland cotton micronaire in one study . However, selective square removal at the first, second, and third fruiting sites along the branches increased micronaire, compared with controls from which no squares had been removed beyond natural square shedding . The increases in micronaire after selective square removals were associated with increased fiber wall thickness, but not with increased strength of elongation percent. Early-season square removal did not affect fiber perimeter or wall thickness (measured by arealometer) . Partial defruiting increased micronaire and had no consistent effect on upland fiber perimeter in bolls from August flowers.
Fiber Maturity and Water:
Generous water availability can delay fiber maturation (cellulose deposition) by stimulating competition for assimilates between early-season bolls and vegetative growth . Adequate water also can increase the maturity of fibers from mid-season flowers by supporting photosynthetic C fixation. In a year with insufficient rainfall, initiating irrigation when the first-set bolls were 20-d old increased micronaire, but irrigation initiation at first bloom had no effect on fiber maturity. Irrigation and water-conservation effects on fiber fineness (millitex) were inconsistent between years, but both added water and mulching tended to increase fiber fineness. Aberrations in cell-wall synthesis that were correlated with drought stress have been detected and characterized by glycoconjugate analysis .
An adequate water supply during the growing season allowed maturation of more bolls at upper and outer fruiting positions, but the mote counts tended to be higher in those extra bolls and the fibers within those bolls tended to be less mature . Rainfall and the associated reduction in insolation levels during the blooming period resulted in reduced fiber maturity . Irrigation method also modified micronaire levels and distributions among fruiting sites.
Early-season drought resulted in fibers of greater maturity and higher micronaire in bolls at branch positions 1 and 2 on the lower branches of rainfed plants. However, reduced insolation and heavy rain reduced micronaire and increased immature fiber fractions in bolls from flowers that opened during the prolonged rain incident. Soil water deficit as well as excess may reduce micronaire if the water stress is severe or prolonged . Fiber Maturity and Genetic Improvement:
Micronaire or maturity data now appear in most cotton improvement reports . In a five-parent half-diallel mating design, environment had no effect on HVI micronaire . However, a significant genotypic effect was found to be associated with differences between parents and the F1 generation and with differences among the F1 generation. The micronaire means for the parents were not significantly different, although HVI micronaire means were significantly different for the F1 generation as a group. The HVI was judged to be insufficiently sensitive for detection of the small difference in fiber maturity resulting from the crosses.
In another study, F2 hybrids had finer fibers (lower micronaire) than did the parents, but the improvements were deemed too small to be of commercial value. Unlike the effects of environment on the genetic components of other fiber properties, variance in micronaire due to the genotype-by-environment interaction can reach levels expected for genetic variance in length and strength . Significant interactions were found between genetic additive variance and environmental variability for micronaire, strength, and span length in a study of 64 F2 hybrids .
The strong environmental components in micronaire and fiber maturity limit the usefulness of these fiber properties in studies of genotypic differences in response to growth environment. Based on micronaire, fiber maturity, cell-wall thickness, fiber perimeter, or fiber fineness data, row spacing had either no or minimal effect on okra-leaf or normal-leaf genotypes . Early planting reduced micronaire, wall-thickness, and fiber fineness of the okra-leaf genotype in one year of that study. In another study of leaf pubescence, nectaried vs. no nectaries, and leaf shape, interactions with environment were significant but of much smaller magnitude than the interactions among traits .
Micronaire means for Bt transgenic lines were higher than the micronaire means of Coker 312 and MD51ne when those genotypes were grown in Arizona . In two years out of three, micronaire means of all genotypes in this study, including the controls, exceeded 4.9; in other words, were penalty grade. This apparent undesirable environmental effect on micronaire may have been caused by a change in fiber testing methods in the one year of the three for which micronaire readings were below the upper penalty limit. Genotypic differences in bulk micronaire may either be emphasized or minimized, depending on the measurement method used . GRADE:
In U.S. cotton classing, nonmandatory grade standards were first established in 1909, but compulsory upland grade standards were not set until 1915 . Official pima standards were first set in 1918. Grade is a composite assessment of three factors – color, leaf, and preparation . Color and trash (leaf and stem residues) can be quantified instrumentally, but traditional, manual cotton grade classification is still provided by USDA-AMS in addition to the instrumental HVI trash and color values. Thus, cotton grade reports are still made in terms of traditional color and leaf grades; for example, light spotted, tinged, strict low middling. Preparation:
There is no approved instrumental measure of preparation – the degree of roughness/smoothness of the ginned lint. Methods of harvesting, handling, and ginning the cotton fibers produce differences in roughness that are apparent during manual inspection; but no clear correlations have been found between degree of preparation and spinning success. The frequency of tangled knots or mats of fiber (neps) may be higher in high-prep lint, and both the growth and processing environments can modulate nep frequency . However, abnormal preparation occurs in less than 0.5% of the U.S. crop during harvesting and ginning.
Trash or Leaf Grade:
Even under ideal field conditions, cotton lint becomes contaminated with leaf residues and other trash . Although most foreign matter is removed by cleaning processes during ginning, total trash extraction is impractical and can lower the quality of ginned fiber. In HVI cotton classing, a video scanner measures trash in raw cotton, and the trash data are reported in terms of the total trash area and trash particle counts (ASTM, D 4604-86, D 4605-86). Trash content data may be used for acceptance testing. In 1993, classer’s grade was split into color grade and leaf grade . Other factors being equal, cotton fibers mixed with the smallest amount of foreign matter have the highest value. Therefore, recent research efforts have been directed toward the development of a computer vision system that measures detailed trash and color attributes of raw cotton .
The term leaf includes dried, broken plant foliage, bark, and stem particles and can be divided into two general categories: large-leaf and pin or pepper trash . Pepper trash significantly lowers the value of the cotton to the manufacturer, and is more difficult and expensive to remove than the larger pieces of trash.Other trash found in ginned cotton can include stems, burs, bark, whole seeds, seed fragments, motes (underdeveloped seeds), grass, sand, oil, and dust. The growth environment obviously affects the amount of wind-borne contaminants trapped among the fibers. Environmental factors that affect pollination and seed development determine the frequency of undersized seeds and motes.
Reductions in the frequencies of motes and small-leaf trash also have been correlated with semi-smooth and super-okra leaf traits . Environment (crop year), harvest system, genotype, and second order interactions between those factors all had significant effects on leaf grade . Delayed harvest resulted in lower-grade fiber. The presence of trash particles also may affect negatively the color grade.
Raw fiber stock color measurements are used in controlling the color of manufactured gray, bleached, or dyed yarns and fabrics . Of the three components of cotton grade, fiber color is most directly linked to growth environment. Color measurements also are correlated with overall fiber quality so that bright (reflective, high Rd), creamy-white fibers are more mature and of higher quality than the dull, gray or yellowish fibers associated with field weathering and generally lower fiber quality . Although upland cotton fibers are naturally white to creamy-white, pre-harvest exposure to weathering and microbial action can cause fibers to darken and to lose brightness.
Premature termination of fiber maturation by applications of growth regulators, frost, or drought characteristically increases the saturation of the yellow (+b) fiber-color component. Other conditions, including insect damage and foreign matter contamination, also modify fiber color.
The ultimate acceptance test for fiber color, as well as for finished yarns and fabrics, is the human eye. Therefore, instrumental color measurements must be correlated closely with visual judgment. In the HVI classing system, color is quantified as the degrees of reflectance (Rd) and yellowness (+b), two of the three tri-stimulus color scales of the Nickerson-Hunter colorimeter.
Fiber maturity has been associated with dye-uptake variability in finished yarn and fabric, but the color grades of raw fibers seldom have been linked to environmental factors or agronomic practices during production. Other Environmental Effects on Cotton Fiber Quality:
Although not yet included in the USDA-AMS cotton fiber classing system, cotton stickiness is becoming an increasingly important problem . Two major causes of cotton stickiness are insect honeydew from whiteflies and aphids and abnormally high levels of natural plant sugars, which are often related to premature crop termination by frost or drought. Insect honeydew contamination is randomly deposited on the lint in heavy droplets and has a devastating production-halting effect on fiber processing.
The cost of clearing and cleaning processing equipment halted by sticky cotton is so high that buyers have included honeydew free clauses in purchase contracts and have refused cotton from regions known to have insect-control problems. Rapid methods for instrumental detection of honeydew are under development for use in classing offices and mills .
FIBER QUALITY OR FIBER YIELD?
Like all agricultural commodities, the value of cotton lint responds to fluctuations in the supply-and-demand forces of the marketplace. In addition, pressure toward specific improvements in cotton fiber quality – for example, the higher fiber strength needed for today’s high-speed spinning – has been intensified as a result of technological advances in textile production and imposition of increasingly stringent quality standards for finished cotton products.
Changes in fiber-quality requirements and increases in economic competition on the domestic and international levels have resulted in fiber quality becoming a value determinant equal to fiber yield . Indeed, it is the quality, not the quantity, of fibers ginned from the cotton seeds that decides the end use and economic value of a cotton crop and, consequently, determines the profit returned to both the producers and processors.
Wide differences in cotton fiber quality and shifts in demand for particular fiber properties, based on end-use processing requirements, have resulted in the creation of a price schedule, specific to each crop year, that includes premiums and discounts for grade, staple length, micronaire, and strength . This price schedule is made possible by the development of rapid, quantitative methods for measuring those fiber properties considered most important for successful textile production . With the wide availability of fiber-quality data from HVI, predictive models for ginning, bale-mix selection, and fiber-processing success could be developed for textile mills .
Price-analysis systems based on HVI fiber-quality data also became feasible . Quantitation, predictive modeling, and statistical analyses of what had been subjective and qualitative fiber properties are now both practical and common in textile processing and marketing.
Field-production and breeding researchers, for various reasons, have failed to take full advantage of the fiber-quality quantitation methods developed for the textile industry. Most field and genetic improvement studies still focus on yield improvement while devoting little attention to fiber quality beyond obtaining bulk fiber length, strength, and micronaire averages for each treatment . Indeed, cotton crop simulation and mapping models of the effects of growth environment on cotton have been limited almost entirely to yield prediction and cultural-input management.
Plant physiological studies and textile-processing models suggest that bulk fiber-property averages at the bale, module, or crop level do not describe fiber quality with sufficient precision for use in a vertical integration of cotton production and processing. More importantly, bulk fiber-property means do not adequately and quantitatively describe the variation in the fiber populations or plant metabolic responses to environmental factors during the growing season. Such pooled or averaged descriptors cannot accurately predict how the highly variable fiber populations might perform during processing.
Meaningful descriptors of the effects of environment on cotton fiber quality await high-resolution examinations of the variabilities, induced and natural, in fiber-quality averages. Only then can the genetic and environmental sources of fiber-quality variability be quantified, predicted, and modulated to produce the high-quality cotton lint demanded by today’s textile industry and, ultimately, the consumer.
Increased understanding of the physiological responses to the environment that interactively determine cotton fiber quality is essential. Only with such knowledge can real progress be made toward producing high yields of cotton fibers that are white as snow, as strong as steel, as fine as silk, and as uniform as genotypic responses to the environment will allow.
Modern mills now a day’s uses automatic bale openers or feeders in place of conventional hopper bale openers for more accurate mixing/ blending and also helps to eliminate mane power.
Modern bale pluckers can be mainly classified into two categories viz.
1. Moving bale type
The first generation bale opening machines were mostly stationary. Only the bales were moved either backward or forward or in a circle. The examples of these types of machines are Trutzschler multi-bale plucker, karousel-beater type opener by Rieter, etc.
2. Moving beater type
The second generation machines are of the travelling type i.e. they move past the bales of the layout and extract material from top to bottom. Travelling machines have the advantages that more bales can be processed as an overall unit, and thus better long-term blend is achieved. It should be noted however that these machines extract material only in batches, i.e. they can process only one, two or maximum three bales simultaneously. If long term blend is needed to be achieved, then mixing machines must be included downstream from the bale opener. These machines are completely electrically controlled and extract material evenly from all bales evenly, independently of varying bale density.
In concept, these machines are most commonly utilized now a day. Machines similar to uni-floc by Rieter are developed by various other manufactures viz. Optimix by Hargeth Hollingsworth, B12 by marzoli and blendomat by Trutzschler. The latest uni-floc provided in modern Rieter blow room line in place of the hopper bale opener is UNI-FLOCA-11.
· OPERATIONAL PRINCIPLE
The A 11 UNI-floc processes cotton from all sources and manmade fibres in staple lengths of up to 65 mm. The bales being opened are placed lengthwise or crosswise on both sides of the bale opener, and the take-off unit can process up to four different assortments.
Reduction of the raw material into micro-tufts is assured by the patented double teeth on the take-off roller and the grid with closely set clamping rails. The unique geometry of the double teeth ensures the uniform treatment of the entire bale surface. Retaining rollers travelling with the take-off unit prevent bale layers from sloughing and ensure precise, controlled operation over the entire height of the bale. The A 11 UNI-floc still produces small tufts, even at maximum output of 1400 kg/h.
The take-off unit is lowered by a preselected or computed distance at each pass. Running-in and running-out programs compensate for the differing hardness of the bales over their cross section and ensure a uniform level of production. The fan incorporated in the swivelling tower extracts the opened tufts and feeds them into the tuft channel running between the guide rails. Transport to the following machine is pneumatic.
Figure 1 OPERATIONAL PRINCIPLE OF UNI-FLOC A-11
· DISTINGUISHING FEATURES OF UNI-FLOC A-11
The UNI-floc is basically one type of opening which is most commonly utilized in place of “hopper bale openers”. The distinguishing features of UNI-floc are:
1. Bale opening into micro-tufts for effective cleaning and dust extraction.
Figure narrow grid gauge for micro-tufts
Micro tufts are the basic requirement for the production of yarn quality. Trash and dust can only be removed from natural fibres gently and efficiently on the surface of the tufts.
The take-off unit of the UNI-floc is considered to be the “heart” of the system as it is responsible for micro tuft formation. The patented take-off roller and the grid design with small gaps between the clamping rails enables small fibre tufts ( micro tufts ) to be extracted. The twin-tooth profile ensures uniform, gentle and efficient extraction of the tufts, also irrespective of the take-off roller’s direction of rotation.
Figure comparison of output and tuft size in modern machine(UNI-floc A-11) to conventional bale opener
2. Uniform take-off of bale lay-down by means of “BALE PROFILEING”
Bale Profiling guarantees totally uniform bale take-off. The height profile of the bale lay-down is precisely detected by light barriers and memorized. Scanning is performed at a constant speed of 9 m/min. Tufts are already taken off in the profiling phase. Continuous feeding of the subsequent machines is thus ensured from the outset.
Figure uniform take-off of bale lay-down by means of bale profiling
During the subsequent passes the bales are opened at the preselected speed of travel and take-off depth. In the process the system automatically compensates for differences in height in the bale profile. Labour-intensive manual levelling is eliminated. After the required height range, take-off depth and speed of travel have been entered for each group of bales, take-off proceeds fully automatically.
3. Simultaneous processing of up to 4 assortment
We can lay down as many as 130 bales in four groups on each side of the machine. This means that four assortments can be processed automatically at the preselected take-off speed and with the required production volume.
4. Patented, individually interchangeable double teeth on the opening roller
The double teeth enable maintenance intervals to be halved. The teeth are mounted individually. They can easily and quickly be replaced if required, without removing the take-off roller. This explains the exceptionally high operational readiness of the A 11Uni-floc
5. Processing of cotton from all sources and man-made fibres in staple lengths of up to 65 mm
6. Output of up to 1 400 kg/h (carded sliver)
7. Bale lay-down over a length of 7.2 to 47.2 meters
A bale lay-down of overall lengths of 7.2 to 47.2 meters and two take-off of unit lengths of 1 700 mm and 2 300 mm. The maximum version is capable of accommodating raw material up to 40 000 kg. This ensures flexible, economical and largely autonomous processing on UNI-floc A-11.
8. Take-off width selectable between 1 700 mm and 2 300 mm
9. Graphic interface for easy, intuitive operation at the control panel
The control panel is placed facing the extraction duct, providing a clear view and safety for operating the machine. Setting and control of the A 11 UNI-floc can easily be performed at the screen.
10. Interface to higher-level control and information systems available
In the interests of optimum monitoring of the installation as a whole, this modern machine control unit can be connected to the UNI-control or UNI-command control system. UNI-control and NI command also provide the interface to Reiter’s higher-level SPIDER web mill monitoring system.
This class of weave will form cut effect or dice effect with the implementation of herringbone twill. This effect is used in ornamentation, shirting, etc.
Principle of Construction:
Ø The simplest weaves of this type are produced as a further development of the herringbone twill, in which the principle of opposing a warp float on the one side of the design by a weft float on the other is extended in both directions, i.e. horizontally and vertically.
Ø In this manner a design is formed in which the typical herringbone cut splits the design into four quarters, the diagonally opposite caters being similar.
Ø These structures are frequently employed as they are capable of forming large design repeats with considerable economy in the number of heald to be used.
v Diapers can also be constructed on the herringbone draft basis provided that the twills from which they were originated fall into a certain specific category the characteristic of such twills are:-
o They are even sided
o Their repeat splits in two halves each of which is symmetrical within itself.
o The lifts in each of the two halves are diametrically opposite
v Even sided twill containing more than two lines of float which do not split in the manner indicae than two lines of float which do not split in the mannner self.
v twills from which they were originated falll ted above cannot be woven with the economical herring bone draft.
v Warp and weft faced twills can also be used to produce diapers on the herring bone reversal but owing to the very prominent quartering of the repeat a distinct check effect is produced and for this reason, such effects are frequently termed as “dice checks”.
v In additional to the herring bone based diapers many other diaper forms can be constructed without a preconceived base.
Advanced Fibre Information System is based on the single fibre testing. There are two modules, one for testing the number of neps and the size of neps, while the other one is used for testing the length and the diameter. Both modules can be applied separately or together.
Among all physical properties of the cotton, fiber length varies the most within any one sample. There are two sources of variability;
1) Variability that comes from mixing cottons of various lengths
2) Variability that is biological in nature and exists within a sample of the same origin.
The same variety grown under different conditions, with lower or higher fertilizer doses, irrigation, or pest control, can produce various lengths. This is why fibre length is tested as an average of many fibres. Fibres also break during handling and processing thus, emphasizing the need for measurement of magnitude of the length variation. There are many different measurements of fibre length, including staple length, model length, mean length (aver-age length), 2.5% span length, effective length, upper quartile length, upper-half mean length, length uniformity index, length uniformity ratio, span length, short fibre contents and floating fibre length.
The AFIS test provides several length parameters deduced from individual fibre measurements. The main measurements include: the mean length, the length upper percentiles, the length CV%, and the Short Fibre Content (defined as the percentage of fibres less than 12.7 mm in length). Fibre length information is provided as a number or as weight-based data (by number/by weight). The length distribution by weight is determined by the weight-frequency of fibres in the different length categories, that is the proportion of the total weight of fibres in a given length category. The length distribution by number is given by the proportion of the total number of fibres in different length categories. The length parameters by weight and by number are computed from the two distributions accordingly. Once the AFIS machine determines the length distribution, the machine computes the length distribution by weight assuming that all fibres have the same fineness. Samples do not require any preparation and a result is obtained in 2-3 minutes. The results generally show a good correlation with other methods.
With the introduction of AFIS, it is possible to determine the average properties for a sample, and also the variation from the fibre to fibre. The information content in the AFIS is more. The spinning mill is dependent on the AFIS testing method, to achieve the optimum conditions with the available raw material and processing machinery. The AFIS-N module is dealt here and it is basically used for counting the number of neps and the size of neps. The testing time per sample is 3 minutes in AFIS-.N module.
This system is quick, purpose oriented and reproducible counting of neps in raw material and at all process stages of short staple spinning mill. It is thus possible, based on forecasts supervisory measures and early warning information to practically eliminate subsequent complaints with respect to finished product. The lab personnel are freed from the time consuming, delicate and unpopular, proceeding of nep counting. Personnel turnover and job rotation no more affects the results of the nep counting. The personnel responsible for quality can now at least deal with the unpopular neps in a more purpose-oriented manner than ever before.
AFIS -Working principle:-
A fibre sample of approximately 500 mg is inserted between the feed roller and the feed plate of the AFIS-N instrument Opening rollers open the fibre assembly and separate off the fibres, neps, trash and dust. The trash particles and dust are suctioned off to extraction. On their way through the transportation and acceleration channels, the fibres and neps pass through the optical sensor, which determines the number and size of the neps.
The corresponding impulses are converted into electrical signals, which are then transmitted to a microcomputer for evaluation purposes. According to these analyses, a distinction is made between the single fibres and the neps. The statistical data are calculated and printed out through a printer. The measuring process can be controlled through a PC-keyboard and a screen.
Uster AFIS PRO- application report
Various HVI models available in market in present date are:-
· USTER® AFIS PRO 2
• Length and Maturity (L&M) Module to measure cotton fiber length and maturity, integrating results into the USTERÒ AFIS PRO 2.
• Trash (T) Module to measure the dust and trash content in cotton, integrating results into the USTERÒ AFIS PRO 2.
• USTERÒ AFIS AUTOJET (AJ) Module to measure up to 30 samples automatically, reducing idle operating time.
Moisture in atmosphere has a great impact on the physical properties of textile fibres and yarns.Relative humidity and temperature will decide the amount of moisture in the atmosphere. High relative humidity in different departments of spinning is not desirable. It will result in major problems. But on the other hand, a high degree of moisture improves the physical properties of yarn. Moreover it helps the yarn to attain the standard moisture regain value of the fibre. Yarns sold with lower moisture content than the standard value will result in monetary loss. Therefore the aim of CONDITIONING is to provide an economical device for supplying the necessary moisture in a short time, in order to achieve a lasting improvement in quality.
In these days there is a dramatic change in the production level of weaving and knitting machines, because of the sophisticated manufacturing techniques. Yarn quality required to run on these machines is extremely high. In order to satisfy these demands without altering the raw material, it was decided to make use of the physical properties inherent in the cotton fibres. Cotton fibre is hygroscopic material and has the ability to absorb water in the form of steam. It is quite evident that the hygroscopic property of cotton fibres depends on the relative humidity. The higher the humidity, more the moisture absorption. The increase in the relative atmospheric humidity causes a rise in the moisture content of the cotton fibre, following an S-shaped curve.
The relative humidity in turn affects the properties of the fibre via the moisture content of the cotton fibre. The fibre strength and elasticity increase proportionately with the increase in humidity. If the water content of the cotton fibre is increased the fibre is able to swell, resulting in increased fibre to fibre friction in the twisted yarn structure. This positive alteration in the properties of the fibre will again have a positive effect on the strength and elasticity of the yarn.
CONTEXXOR CONDITIONING PROCESS BY XORELLA:
The standard conventional steaming treatment for yarn is chiefly used for twist setting to avoid snarling in further processing. It does not result in lasting improvement in yarn quality. The steaming process may fail to ensure even distribution of the moisture, especially on cross-wound bobbins(cheeses) with medium to high compactness. The thermal conditioning process of the yarn according to the CONTEXXOR process developed by XORELLA is a new type of system for supplying the yarn package.
The absence of Vacuum in conventional conditioning chambers, prevents homogeneous penetration. The outer layers of the package are also too moist and the transition from moist to dry yarn gives rise to substantial variations in downstream processing of the package, both with regard to friction data and strength.
Since the moisture is applied superficially in the wet steam zone or by misting with water jets, it has a tendency to become re-adjusted immediately to the ambient humidity level owing to the large surface area. Equipment of this king also prevents the optimum flow of goods and takes up too much space.
PRINCIPLE OF WORKING:
Thermal conditioning uses low-temperature saturated steam in vacuum. With the vacuum principle and indirect steam, the yarn is treated very gently in an absolutely saturated steam atmosphere. The vacuum first removes the air pockets from the yarn package to ensure accelerated steam penetration and also removes the atmospheric oxygen in order to prevent oxidation. The conditioning process makes use of the physical properties of saturated steam or wet steam (100% moisture in gas-state). The yarn is uniformly moistened by the gas. The great advantage of this process is that the moisture in the form of gas is very finely distributed throughout the yarn package and does not cling to the yarn in the form of drops. This is achieved in any cross-wound bobbins, whether the yarn packages are packed on open pallets or in cardboard boxes.
pic: XORELLA CONDITIONING SYSTEM
ADVANTAGES OF CONTEXXOR PROCESS:
saturated steam throughout the process
even penetration of steam and distribution of moister
absolute saturated steam atmosphere of 50 degree C to 150 degreees C.
no additional boiler required, the steam is generated in the system
minimum energy consumption(approx. 25 KWh for 1000 kgs of yarn)No tube buckling in case of mad-made yarns
treatment of all natural yarns, blends, synthetics and microfibre yarns.
low installation and maintenance cost
preheating for trollys and plastic tubes to avoid drops (Wool)
length up to 20 meters (66 feet) and max. temperature deviation of 1°C
various loading and unloading facilities
no contamination of the treated packages
energy recovery option offered by indirect heating system using steam or hot water
no special location required, the systems can be operated next to the production machines.
BENEFITS ACHIEVED OUT OF CONDITIONING:
The treatment temperature for knitting yarn is held below the melting point of the wax. Temperatures for unwaxed
yarn are coordinated to the compatibility fo each individual type of yarn
Upto 20% greater efficiency due to a reduction in the unwinding tension
fewer needle breaks
uniform moisture content and friction values
regular stitch formation
no change in size of finished articles
no extra dampening required
free from electrostatic
less fly hence less problems. It helps if the yarn is running on a closer gauge machines
NOTE: Please note that the wax applied should be able to withstand min 60 degree centigrade. If low quality wax is used, it will result in major problem. Conditioning should be done at 55 to 60 degree centigrade.
upto 15% fewer yarn breaks due to greater elongation
less fly, resulting in a better weaving quality
increased take-up of size, enhanced level of efficiency in the weaving plant
Pic: improved strength Pic: improved elongation
Conditioning and fixing of the twist at the same time in a single process.
better dye affinity
Pic: dye pick up of conditioned and unconditioned yarn
It is better to review the basics concepts, costing methods and techniques and elements of costing before we work out a costing for a spinning mill.
Cost accounting is a system of determining the costs of products or services. It has primarily developed to meet the needs of management. It provides detailed cost information to various levels of management for efficient performance of their functions.
Financial accounting provides information about profit , loss, cost etc., of the collective activities of the business as a whole. It does not give the data regarding costs by departments, products, processes and sales territories etc. Financial accounting does not fully analyse the losses due to idle time, idle plant capacity, inefficient labour, sub-standard materials, etc. Cost accounting is not restricted to past. It is concerned with the ascertainment of past, present and expected future costs of products manufactured or services supplied. Cost accounting provides detailed cost information to various levels of management for efficient performance of their functions.
“A cost is the value of economic resources used as a result of producing or doing the things costed”
Cost is ascertained by cost centres or cost units or by both.
For the purpose of ascertaining cost, the whole organisation is divided into small parts of sections. Each small section is treated as a cost centre of which cost is ascertained. A cost centre is defined as ” a location, person, or item of equipment(or group of these) for which costs may be ascertained and used for the purpose of control. A cost accountant sets up cost centres to enable him to ascertain the costs he needs to know. A cost centre is charged with all the costs that relate to it. The purpose of ascertaining the cost of cost centre is cost control. The person in charge of a cost centre is held responsible for the control of cost of that centre.
Cost unit breaks up the cost into smaller sub-divisions and helps in ascertaining the cost of saleable products or services. A cost unit is defined as a ” unit of product , service or time in relation to which cost may be ascertained or expressed.” For example in a spinning mill the cost per kg of yarn may be ascertained. Kg of yarn is cost unit. In short Cost unit is unit of measurement of cost.
Method of costing refers to the techniques and processes employed in the ascertainment of costs. The method of costing to be applied in a particular concern depends upon the type and nature of manufacturing activity. Basically there are two methods of costing
1.Job costing: Cost unit in job order costing is taken to be a job or work order for which costs are separately collected and computed.
2.Process costing: This is used in mass production industries manufacturing standardised products in continuous processes of manufacturing. Cost are accumulated for each process or department. For spinning mills , process costing is employed.
TECHNIQUES OF COSTING:
These techniques may be used for special purpose of control and policy in any business irrespective of the method of costing being used there.
Standard costing: This is the valuable technique to control the cost. In this technique, standard cost is predetermined as target of performance and actual performance is measured against the standard. The difference between standard and actual costs are analysed to know the reasons for the difference so that corrective actions may be taken.
Marginal costing: In this technique, cost is divided into fixed and variable and the variable is of special interest and importance. This is because, marginal costing regards only variable costs as the costs of products. Fixed cost is treated as period cost and no attempt is made to allocate or apportion this cost to individual cost centres or cost units.
Cost Ascertainment is concerned with computation of actual costs. Ascertainment of actual costs reveals unprofitable activities losses and inefficiencies .
Cost Estimation is the process of predetermining costs of goods or services. The costs are determined in advance of production and precede the operations. Estimated costs are definitely the future costs and are based on teh average of the past actual costs adjusted for future anticipated changes in future. Cost estimates are used in the preparation of the budgets. It helps in evaluating performance. It is used in preparing projected financial statements. Cost estimates may serve as targets in controlling the costs.
CLASSIFICATION OF COSTS:
Costs are classified into direct costs and indirect costs on the basis of their identifiability with cost units or processes or cost centres.
DIRECT COST: These are the costs which are incurred for and conveniently identified with a particular cost unit, process or equipment. For a spinning mill, costs of raw material used, packing material, freight etc are direct costs
INDIRECT COST: These are general costs and are incurred for the benefit of a number of cost units, processes or departments. These costs cannot be conveniently identified with a particular cost unit or cost centre. In a spinning mill, power cost, administrative wages, managerial salaries, materials used in repairs etc. are indirect costs.
The terms direct and indirect should be used in relation to the object of costing. An item of cost may be direct cost in one case and the same may be indirect in the other case.It is the nature of business and the cost unit chosen that will determine whether a particular cost is direct or indirect.
FIXED AND VARIABLE COSTS; Costs behave differently when level of production rises or falls. Certain costs change in sympathy with production level while other costs remain unchanged. As such on the basis of behaviour or variability, costs are classified into fixed, variable and sem-variable.
FIXEDCOSTS; These costs remain constant in “total” amount over a wide range of activity for a specified period of time. They do not increase or decrease when the volume of production changes.
VARIABLE COSTS: These costs tend to vary in direct proportion to the volume of output. In other words, when volume of output increases, total variable cost also increases and vice-versa.
ELEMENTS OF COST: A cost is composed of three elements i.e. material , labour and expense. Each of these elements may be direct or indirect.
DIRECT MATERIAL is that which can be conveniently identified with and allocated to cost units. Direct materials generally become a part of the finished product. For example, cotton used in a spinning mill is a direct material.
INDIRECT MATERIAL is that which can not be conveniently identified with individual cost units. In a spinning mill, engineering department spares, maintenance spares, lubricating oils, greases, ring travellers etc
DIRECT LABOUR cost consists of wages paid to workers directly engaged in converting raw materials into finished products. These wages can be conveniently identified with a particular product, job or process.
INDIRECT LABOUR is of general character and cannot be conveniently identified with a particular cost unit. In other words, indirect labour is not directly engaged in the production operations but only to assist or help in production operations. For example in a spinning mill, the number of maintenance workers, no of workers in utility department etc
EXPENSES; All costs other than material and labour are termed as expenses.
DIRECT EXPENSES are those expenses which are specifically incurred in connection with a particular job or cost unit. Direct expenses are also known as chargeable expenses.
INDIRECT EXPENSES can not be directly identified with a particular job, process and are common to cost units and cost centres.
PRIME COST = Direct material +Direct labour + Direct expenses
OVERHEAD = Indirect material + Indirect labour + Indirect expenses
TOTAL COST = PRIME COST + OVERHEAD
ADVANTAGES OF COST ACCOUNTING:
It reveals profitabale and unprofitable activities.
It helps in controlling costs with special techniques like standard costing and budgetary control
It supplies suitable cost data and other related information for managerial decision making such as introduction of a new product, replacement of machinery with an automatic plant etc
It helps in deciding the selling prices, particularly during depression period when prices may have to be fixed below cost
It helps in inventory control
It helps in the introduction of a cost reduction programme and finding out new and improved ways to reduce costs
Cost audit system which is a part of cost accountancy helps in preventing manipulation and frauds and thus reliable cost can be furnished to management
ESSENTIALS OF A GOOD COST ACCOUNTING SYSTEM:
The method of costing adopted. It should be suitable to the industry
It should be tailor made according to the requirements of a business. A ready made system can not be suitable
It must be fully supported by executives of various departments and every one should participate in it
In order to derive maximum benefits from a costing system, well defined cost centres and responsibility centres should be built within the organisation
controllable and uncontrollable costs of each responsiblity centre should be separately shown
cost and financial accounts may be integrated in order to avoid duplication of accounts
well trained and educated staff should be employed to operte the system
It should prepare an accurate reports and promptly submit teh same to appropriate level of management so that action may be taken without delay
resources should not be wasted on collecting and compiling cost data not required. Only useful cost information should be compiled and used whenever required.
CASE 1. Project costing for a POLY/COTTON PLANT with autodoffing and link to autoconer:(IN INDONESIA)
Following information is required to work out a costing for a new plant:
The average count of the plant
Capacity of the plant – No of spindles to be installed and the number of back process and winding machines required
Investment on machineries
Investment on land
Investment on building
working capital required
product lay out, the count pattern
Selling price of individual counts
rawmaterial cost(including freight, duty etc)
packing cost per kg of yarn
freight per kg of yarn
direct labour cost
indirect labour cost
fixed power cost
variable power cost
Let us work out a project cost:
For this , i have used the details of the modern mill which is running in Indonesia from year 2000
STEP NO.1: Contribution to be calculated. In general for a spinning mill ,contribution per kg of particular count is calculated to work out the economics for a new project as well as for a running mill.
Cotribution = selling price – direct cost
Direct cost for a spinning mill includes rawmaterial price, packing cost, freight. All other costs are either fixed costs or semi variable costs. The other costs can not be conveniently allocated to per kg of a particular count.
The basic idea of a new project or a running plant is to maximise this contribution. Because once the plant is designed, spares cost, power cost, administration cost,labour cost etc almost remain constant. There will not be significant changes in these costs for different count patterns if the plant is utilisation is same.
The following table gives the details of count pattern, selling price, rawmaterial price, packing cost and contribution per kg of different counts for a particular period ( year 2000). This is just an example , one should understand that the selling price, rawmaterial price and all other costs keep changing. This is the reason why costing is important for a running mill. All the costs are changing. Some costs change every month, some once in a year. Therefore costing plays a major role to run the plant efficiently.
no. of spls
no of mcs
raw material cost/kg
packing cost /kg
freight per kg
common 2% on selling price
selling price / kg
contribn per kg
In the above table, all the costs are in US$. The ringframes are with 1120 spindles per machine with automatic doffing and link to autoconer. Packing cost is based on indonesian packing material prices for carton packing.
The ultimate aim of the project is to maximise the contribution. Looking into the cotribution per kg of yarn, the project should produce only 36s TC. But in this project they have considered 5 different counts. Because
yarn market is not stable. It needs a lot flexibility
customers are not same, the price depends on the customers
the end uses are not same, the price depends on the end use.
this unit exports 80% of the yarn, it can not depend on one country, eg. 36sTc is only for Philippines market, it can not be sold in Malaysia, even though the quality is good
the count pattern depends upon the market requirement and the major counts in the market, not only on the contribution
A linear programming technique can be used to maximise the contribution, considering all market constraints, and production constraints.
flexibility needs more investment and more day to day expenses, if a project has to be more flexible, it has to invest more money on infrastructure
the major factor which will make the project feasible with less flexibility is YARN QUALITY in a spinning mill
Since this is a critical step for a new project, management should be clear about their Yarn quality , Flexibility required for marketing and should make use of Linear Programming Techniques to find out the best product mix to maximise the contribution.
STEP NO. 2: To work out the Total Investment cost ( machineries, accessories, land and building, humidification and electrical instruments)
The following table gives the requirement of production machines. To calculate the number of back process and winding drums required, a detailed spin plan should be worked out with speeds and efficiencies to be achieved in each machine.
While calculating the no of machines required, m/c utilisation, m/c efficiency , waste percentage, twist multipliers, delivery speeds etc should be considered properly. These factors should be decided based on yarn quality required, end breakage rates and the capacity of machine.
INVESTMENT ON MACHINERY
NO. OF MCS
RATE / MC
Trutzschler Blowrrom line for cotton
Trutschler Blowrrom line for Polyester
Trutshcler DK-903 cards
Rieter RSB-D30 draw frames (with autoleveller)
Rieter double delivery drawframe
Rieter E62 combers
Howa speed frames with overhead blower
Ring frames with autodoffer
winding machines ( 26 drums per mc)
Roving transport ( manual)
Argus fire system
Some of the following points can be considered while deciding the machines.
From the above table it is clear that, 23 ringframes with 1120 spindles are working with auto doffing and with link to autoconer. The major advantage of this automation is to reduce labour and to reduce the problems related to material handling. One has to really work out the benefits achieved because of this and the pay back for the extra investment.
Drawframe contributes a lot to the yarn quality and the ringframe and winding machine working. It is always better to go in for the best drawframes like RSB-D30 drawframes with autoleveller. It is not wise to buy a cheaper drawframe and save money.
It is always better to keep excess carding and autoleveller drawframes, so that flexibility of the project is also maintained. If the coarser counts contributes more and the market is good, overall production can be increased. If the market is for finer count, both the machines (carding and drawframes)can be run at slower speeds, which will surely contribute to yarn quality.
Speeds of speedframe , combers and ringframes do not affect the yarn quality as it is affected by card and drawframe speeds.
Blow room capacity should be utilised to the maximum, as it consumes a lot of power ,space and money.
Ringframe specification should be perfect, because the working performance and power consumption of the ringframe depends on the specifications like, lift, ring dia, no of spindles etc. Ring frame specification should be decided to get the maximum production per spindle and to reduce the power consumed per kg of yarn produced by that spindle. Because the investment cost and the power consumption for the ringframe is the highest in a spinning mill.
INVESTMENT ON ACCESSORIES:
The following table gives the details of the accessories like cans for carding, drawframe, bobbins, trollies etc
NO. OF MCS
RATE / MC
Carding cans 36″ x 48″
comber cans 24″ x 48″
Drawframe cans 20″ x 48″
Identification bands 20″
Identification bands 24″
Roving and spinning bobbins
SERVICE AND MAINTENANCE EQUIPMENTS:
The following table gives the details about the investments required on service and maintenance equipment’s
SERVICE AND MAINTENANCE EQUIPEMENTS
NO OF MCS
Cots buffing machine and accessories
Card room accessories
Spindle oil lubricator
Clearer roller cleaning machine
Premier uster tester
Premier strength tester
premier fiber testing
Card service machines like Flat tops clipping machine and flats grinding machine are very important for yarn quality. One should not look for cheaper machine. It is always better to go for reputed manufacturers like GRAF, HOLLINGSWORTH etc.
Rubber cots contributes a lot to yarn quality. Bad buffing in ring frame can increase the imperfections by 15%. Poor quality of buffing in drawframe and speedframes can affect both production and quality. It is better to go for the best cots mounting machine and cots buffing machine.
HUMIDIFICATION AND ELECTRICAL EQUIPMENTS:
The following table gives the details about the investments required on humidification and electrical instrument’s
Electrical installation including transformer, incoming and outgoing panels, bus duct, capacitor, etc for 3800 KVA
Compressor, Dryer and pipe lines
Ducting and installation for humidification system
workshops, hydrant and other equipments
In Indonesia, most of the units use PLN power and some of the spinning mills use Gensets. A detailed costing has to be done to compare the cost per unit to decide, Whether to use the PLN power or to go in for Gensets. while working out the costing finance cost on investment , overhauling cost, running cost, efficiency of the machine should be considered for cost calculation in the case of Genset. In case of PLN power, the losses due to power interruption( based on the area data), finance cost on initial investment, md charges, unit charges to be considered. It is better to use 50% PLN and 50 % own generation.
The following table gives the details about land and building investments
Factory building Including Service ally 192 x 62 meters11,712 Square meter @ 120 usd/sq meter
Road and others
STEP NO.3: To calculate the expenses ( labour, power, stores,working capital, insurance etc)
Working capital = 3,000,000
LABOUR:The following table gives the details about labour requirement
No of people required
administration and personal dept
Total no of people required per day
wages at 50 usd/month including bonus and insurance
other facilities at 35 %
salaries for managerial staff
Other facilities at 35 %
Total labour cost / month
POWER: The following table gives the details about the power
Total units(KWH) produced (consumed)per day
Unit cost (cost / KWH)
Total production in Kgs
KWH/ Kg of yarn
TOTAL POWER COST /DAY
SPARES:The following table shows the spares cost, repair , and insurance
spares cost at usd 8/1000 spindle shift
repairs and other overheads
Insurance at 0.175% on investment and working capital
Roving machine is complicated, liable to faults, causes defects, adds to production costs and delivers a product that is sensitive in both winding and unwinding. This machine is forced to use by the spinner for the following two reasons.
Sliver is thick, untwisted strand that tends to be hairy and to create fly. The draft needed to convert this is around 300 to 500. Drafting arrangements of ring frames are not capable of processing
this strand in a single drafting operation to create a yarn that meets all the normal demands on such yarns.
Drawframe cans represent the worst conceivable mode of transport and presentation of feed material to the ring spinning frame.
· Fibre to fibre cohesion is less for combed slivers. Rollers in the creel can easily create false drafts.Care must be taken to ensure that the slivers are passed to the drafting arrangement without disturbance.
Therefore, a perfect drive to the creel rollers is very important.
· The drafting arrangement drafts the material with a draft between 5 and 15.The delivered strand is too thin to hold itself together at the exit of the front bottom roller.
· Bobbin and flyer are driven separately, so that winding of the twisted strand is carried out by running the bobbin at a higher peripheral speed than the flyer.
· The bobbin rail is moving up and down continuously, so that the coils must be wound closely and parallel to one another to ensure that as much as material is wound on the bobbin.
· Since the diameter of the packages increases with each layer, the length of the roving per coil also will increase. Therefore the speed of movement of bobbin rail must be reduced by a small amount after
each completed layer
· Length delivered by the front roller is always constant. Owing to the increase in the diameter of the package for every up and down movement, the peripheral speed of package should keep on changing , to maintain the same difference in peripheral speeds between package and flyer.
· There are two types of drafting systems.
3/3 drafting system
4/4 drafting system
In general 3/3 drafting system is used, but for higher draft applications 4/4 drafting system is used.
· The draft often has limits not only at the upper limit (15 to 20), but also at lower limit. It is around 5 for cotton and 6 for synthetic fibers. If drafts below these lower limits are attempted, then the fibre masses to be moved are too large, the drafting resistance becomes too high and the drafting operation is difficult to control.
It is advisable to keep the break draft (predarft) as low as possible, because lower break draft always improves roving evenness.
· In general two condensers are used in the drafting arrangement. The purpose of these condensers is to bring the fibre strands together. It is difficult to control, Spread fibre masses in the drafting zone and they cause unevenness. In addion, a widely spread strand leaving the drafting arrangement leads to high fly levels and to high hairiness in the roving. The size of condensers should be selected according to the volume of the fibre sliver.
· Flyer inserts twist. Each flyer rotation creates one turn in the roving. Twist per unit length of roving depends upon the delivery rate.
Turns per metre = (flyer rpm)/(delivery speed (m/min))
Higher levels of roving twist, therefore, always represent production losses in Roving frame and possible draft problems in the ring spinning machine. But very low twist levels will cause false drafts and roving breaks in the roving frame.
· Centrifugal tension is created at the bobbin surface as the layers are being wound and is created by the rotation of the package. Each coil of roving can be considered as a high-speed rotating hool of roving on which centrifugal tension increases with increasing diameter of the package. centrifugal tension in the roving is proportional to the square of the winding surface velocity.In this context, centrifugal force acts in such a manner as to lift the top roving strand from the surface of the package so that the radial forces within the strand that hold the fibres together are reduced and the roving can be stressed to the point of rupture. Breaks of this type may occur at the winding-on Point of the presser or in strands that have just been wound on the top surface of the package. This phenomenon is known as “bobbin-bursting”. This phenomenon will be prominent if the twist per inch is less or the spindle speed is extremely high when the bobbin is big.
· Apart from inserting twist, the flyer has to lead the very sensitive strand from the flyer top to the package without introducing false drafts. Latest flyers have a very smooth guide tube set into one flyer leg
and the other flyer leg serves to balance the flyer. The strand is completely protected against air flows and the roving is no longer pressed with considerable force against the metal of the leg, as it is in
the previous designs. Frictional resistance is considerably reduced, so that the strand can be pulled through with much less force.
· False twisters are used on the flyers to add false twist when the roving is being twisted between the front roller and the flyer.Because of this additional twist, the roving is strongly twisted and this reduces the breakage rate. Spinning triangle is also reduced which will reduce the fibre fly and lap formation on
the front bottom roller.
· Because of the false twister, the roving becomes compact which helps to increase the length wound on the bobbin. This compactness helps to increase the flyer speed also.
· Roving strength is a major factor in determining winding limitations. It must be high enough for the fibres to hold together in a cohesive strand and low enough for satisfactory drafting at the spinning machine. The factors affecting roving strength are as follows:
the length, fineness, and parallelisation of fibres
the amount of twist and compactness of the roving
the uniformity of twist and linear density.
· BUILDER MOTION: This device has to perform the following tasks
to shift the belt according to the bobbin diameter increase
to reverse the bobbin rail direction at top and bottom
to shorten the lift after each layer to form tapered ends
· Shifting of the belt is under the control of the ratchet wheel. The ratchet wheel is permitted to rotate by a half tooth. The bobbin diameter increases more or less rapidly depending upon roving hank. The belt must be shifted through corresponding steps. The amount of shifting, which depends upon the thickness of the roving, is modified by replacement of the ratchet wheel or by other gears.If a ratchet wheel with fewer teeth is inserted, then the belt is shifted through larger steps, i.e. it moves more rapidly, and vice versa.
· To form a package, the layer must be laid next to its neighbours. For that the lay-on point must continually be moved. The shift of the winding point is effected by moving the bobbin rail. This raising and lowering is done by rails.Since the package diameter is steadily increasing, the lift speed must be reduced by a small amount after each completed layer.
· During winding of a package, the ratchet is rotated at every change-over.Reversal of the bobbin layer occurs little earlier for every reversal.This gives a continuous reduction in the lift of the rail . Thus bobbins are built with taper.