Short Staple Processing


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.

Picking (Including Opening and Blending)

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.).

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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.)

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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.)

Carding

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.

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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.)

Combing

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

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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.)

Spinning (Twisting)

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.

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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.)

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Fibre Dynamics in the Revolving-Flats Card


Over the last 30 years numerous developments have taken place with the cotton card. The production rate has risen by a factor of 5 with the main rotating components running at significantly higher speeds. Triple taker-in rollers and modified feed systems are in use, additional carding segments are fitted for more effective fibre opening, and improved wire clothing profiles have been developed for a better carding action. Advances in electronics have provided much improved monitoring and process control. Most of these developments have resulted in enhanced cleaning of cotton fibres, reduced neppiness of the card web and better sliver uniformity.

Despite the various improvements made to the card a commonly held view is that more is known about the cleaning processes on the card than about the carding process itself . For instance, modern cards can achieve an overall cleaning efficiency of 95%. It is well established that the cleaning efficiency of modern taker-in systems is a round 30%, that the cylinder/flats action with the latest wire clothing profiles gives 90% cleaning efficiency and that effective cleaning is associated with lower neps in the card web ……

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Carding


  • 19th c. ox powered double carding machine
    Image via Wikipedia

    INTRODUCTION

“Card is the heart of the spinning mill” and “Well carded is half spun” are two proverbs of the experts.These proverbs inform the immense significance of carding in the spinning process.High production in carding to economise the process leads to reduction in yarn quality.Higher the production, the more sensitive becomes the carding operation and the greater danger of a negative influence on quality.The technological changes that has taken place in the process of carding is remarkable. Latest machines achieve the production rate of 60 – 100 kgs / hr, which used to be 5 – 10 kgs / hr, upto 1970.

THE PURPOSE OF CARDING:

  1. to open the flocks into individual fibres
  2. cleaning or elimination of impurities
  3. reduction of neps
  4. elimination of dust
  5. elimination of short fibres
  6. fibre blending
  7. fibre orientation or alignment
  8. sliver formation
  • TECHNOLOGICAL POINTS IN CARDING

· There are two types of feeding to the cards

  1. feeding material in the form of scutcher lap
  2. flock feed system (flocks are transported pneumatically)

· lap feeding

  1. linear density of the lap is very good and it is easier to maintain(uniformity)
  2. the whole installation is very flexible
  3. deviations in card output will be nil, as laps can be rejected
  4. autolevellers are not required, hence investment cost and maintenance cost is less
  5. transportation of lap needs more manual efforts( more labour)
  6. lap run out is an additional source of fault, as it should be replaced by a new lap
  7. more good fibre loss during lap change
  8. more load on the taker-in, as laps are heavily compressed

· flock feeding

  1. high performance in carding due to high degree of openness of feed web
  2. labour requirement is less due to no lap transportation and lap change in cards
  3. flock feeding is the only solution for high production cards
  4. linear density of the web fed to the card is not as good as lap
  5. installation is not flexible
  6. autoleveller is a must, hence investment cost and maintenance cost is more

· Type of flock feed(chute feed)

  1. there are two basic concepts of flock feed
    1. one piece chute without an opening device
    2. two piece chute with an opening system
  2. one piece chute is simple, economical and requires little maintenance
  3. two piece chute is complex, expensive, but delivers a uniform batt.
  4. One piece chute is a closed system, i.e.excess flock returns to the distributor, if too much material is present, neps can be increased
  5. one piece chute is not flexible to run different mixings
  6. layout restrictions are more with one piece chute

· A feeding device is a must to feed the web to the Taker-in region and it should perform the following tasks

  1. to clamp the batt securely throughout its width
  2. to grip the fibres tightly without slippage during the action of taker-in
  3. to present the fibres in such a manner that opening can be carried out gently· The diverter nose(sharp or round) and the length of the nose(guide surface) have a significant influence on quality and quantity of waste removed. Short nose diverter avoids fibre slippage but the opening action is not gentle.If the length of the guide surface is too short, the fibres can escape the action of the taker-in. They are scraped off by the mote knives and are lost in the waste receiver.

· Feed roller clothed with sawtooth is always better , because it gives good batt retention. Thus the opening effect of the taker-in is more as it is in combing

· Rieter has developed a “unidirectional feed system” where the two feed devices(feed roller and feed plate are oppositely arranged when compared with the conventional system. i.e. the cylinder is located below and  the plate is pressed against the cylinder by spring force. Owing to the direction of feed roller, the fibre batt runs downwards without diversion directly into the teeth of the taker-in(licker-in) which results in gentle fibre treatment. This helps to reduce faults in the yarn.

· of The purpose the taker-in is to pluck finely opened flocks out of the feed batt, to lead them over the dirt eliminating parts like mote knives, combing segment and waste plates, and then to deliver the fibres to the main cylinder. In high production cards the rotational speed ranges from 700-1400

· The treatment for opening and cleaning imparted by Taker-in is very intensive, but unfortunately not very gentle.Remember that around 60% of the fibres fed to the main cylinder is in the form of individual fibres.

· The circumferential speed of Taker-in is around 13 to 15 m/sec and the draft is more than 1000.It clearly shows that fibre gets deteriorated at this opening point. Only the degree of deterioration can be controlled
by adjusting the following

  1. the thickness of the batt
  2. the degree of openness of the raw material
  3. the degree of orientation of the fibres
  4. the aggressiveness of the clothing
  5. the distance between the devices
  6. the rotational velocity of the taker-in
  7. the material throughput

· Latest TRUTZSCHLER cards work with three licker-ins compared to one liker-in.The first one is constructed as needle roll. This results in very gentle opening and an extremely long clothing life for this roll. The other two rollers are with finer clothing and higher speeds, which results in feeding more %of individual fibres and smallest tufts compared to single lickerin, to the main cylinder. This allows the maing cylinder to go high in speeds and reduce the load on cylinder and flat tops. There by higher productivity is achieved with good quality. But the performance may vary for different materials and different waste levels.

· between the taker-in and main cylinder , the clothings are in the doffing disposition. It exerts an influence on the sliver quality and also on the improvement in fibres longitudinal orientation that occurs here. The effect depends on the draft between main cylinder and taker-in.The draft between main cylinder and taker-in should be slightly more than 2.0.

· The opening effect is directly proportional to the number of wire points per fibre. At the Taker-in perhaps 0.3 points/ fibre and at the main cylinder 10-15 points /fibre.If a given quality of yarn is required, a corresponding degree of opening at the card is needed. To increase production in carding, the number of points per unit time must also be increased. this can be achieved by

  1. more points per unit area(finer clothing)
  2. higher roller and cylinder speeds
  3. more carding surface or carding position

speeds and wire population has reached the maximum, further increase will result in design and technological problems. Hence the best way is to add carding surface (stationary flats). Carding plates can be applied at

  1. under the liker-in
  2. between the licker-in and flats
  3. between flats and doffer

· Taker-in does not deliver 100% individual fibres to main cylinder. It delivers around 70% as small flocks to main cylinder. If carding segments are not used, the load on cylinder and flats will be very high and carding
action also suffers. If carding segemets are used, they ensure further opening, thinning out and primarily, spreading out and improved distribution of the flocks over the total surface area.carding segments bring the following advantages

  1. improved dirt and dust elimination
  2. improved disentanglement of neps
  3. possibility of speed increase (production increase)
  4. preservation of the clothing
  5. possibility of using finer clothings on the flats and cylinder
  6. better yarn quality
  7. less damage to the clothing
  8. cleaner clothing

· In an indepth analysis, all operating elements of the card were therefore checked in regard to their influence on carding intensity. It showed that the “CYLINDER-FLATS” area is by far the most effective region of the card for.

  1. opening of flocks to individual fibres
  2. elimination of remaining impurities(trash particles)
  3. elimination of short fibres( neps also removed with short fibres)
  4. untangling the neps
  5. dust removal
  6. high degree of longitudinal orientation of the fibres

· The main work of the card, separation to individual fibres is done between the main cylinder and the flats Only by means of this fibre separation, it is possible to eliminate the fine dirt particles and dust. When a flat enters the working zone, it gets filled up very quickly. Once it gets filled, after few seconds, thereafter , hardly any further take-up of fibres occurs, only carding.Accordingly, if a fibre bundle does not find place at the first few flats, then it can be opened only with difficulty.It will be rolled between the working surfaces and usually leads to nep formation

· In principle, the flats can be moved forwards or backwards, i.e. in the same direction as or in opposition to the cylinder.In reverse movement, the flats come into operative relationship with the cylinder clothing on the doffer side. At this stage, the flats are in a clean condition. They then move towards the taker-in and fill up during this movement.Part of their receiving capacity is thus lost, but sufficient remains for elimination of dirt, since this step takes place where the material first enters the flats. At this position, above the taker-in, the cylinder carries the material to be cleaned into the flats. The latter take up the dirt but do not transport it through the whole machine as in the forward movement system. Instead , the dirt is immediately removed from the machine. Rieter studies show clearly that the greater part of the dirt is hurled into the first flats directly above the taker-in.

· Kaufmann indicates that 75% of all neps can be disentangled, and of these about 60% are in fact disentangled. Of the remaining 40% disentaglable nep

  1. 30-33% pas on with the sliver
  2. 5-6% are removed with the flat strips
  3. 2-4%are eliminated with the waste

The intensity of nep separation depends on

  1. the sharpness of the clothing
  2. the space setting between the main cylinder and the flats
  3. tooth density of the clothing
  4. speed of the main cylinder
  5. speed of the flat tops
  6. direction of flats with reference to cylinder
  7. the profile of the cylinder wire

· The arrangement of the clothing between the cylinder and the doffer is not meant for stripping action, It is for CARDING ACTION.This is the only way to obtain a condensing action and finally to form a web. It has both advantages and disadvantages.The advantage is that additional carding action is obtained here and it differs somewhat from processing at the flats.A disadvantage is that leading hooks and trailing hooks are formed in the fibres , because the fibres remain caught at one end of the main cylinder(leading hook) and some times on the doffer clothing(trailing hook).

· There are two rules of carding

  1. The fibre must enter the carding machine, be efficiently carded and taken from it in as little time as possible.
  2. The fibre must be under control from entry to exit

· Carding effect is taking place between cylinder and doffer because, either the main cylinder clothing rakes through the fibres caught in the doffer clothing, or the doffer clothing rakes thro the fibres on the main cylinder. Neps can still be disentangled here, or non-separated fibre bundles can be opened a bit in this area and can be separated during the next passage through the flats

· A disadvantage of web-formation at the card is the formation of hooks. According to an investigation by Morton and Yen in Manchester, it can be assumed that

  1. 50% of the fibres have trailing hooks
  2. 15% have leading hooks
  3. 15% have both ends hooked
  4. 20% without hooks

· Leading hooks must be presented to the comber and trailing hooks to the ring spinning frame. There must be even number of passages between card and comber and odd number between the card and ring frame.

 

Metallic Card Clothing


INTRODUCTION:

As Carding machine design improved in 1950’s and 60’s, it became apparent that card clothing was a limiting factor Much time and effort was spent in the development of metallic card clothing.

· There are two rules of carding

  1. The fibre must enter the carding machine, be efficiently carded and taken from it in as little time as possible
  2. The fibre must be under control from entry to exit

· Control of fibres in a carding machine is the responsibility of the card clothing

· Following are the five types of clothing’s used in a Carding machine

  1. Cylinder wire
  2. Doffer wire
  3. Flat tops
  4. Licker-in wire
  5. Stationary flats

CYLINDER WIRE:

The main parameters of CYLINDER Card clothing

  1. Tooth depth
  2. Carding angle
  3. Rib width
  4. Wire height
  5. Tooth pitch
  6. Tooth point dimensions
  1. Shallowness of tooth depth reduces fibre loading and holds the fibre on the cylinder in the ideal position under the carding action of the tops. The space a fibre needs within the cylinder wire depends upon
    its Micronaire/denier value and staple length.
  2. The recent cylinder wires have a profile called “NO SPACE FOR LOADING PROFILE”(NSL). With this new profile, the tooth depth is shallower than the standard one and the overall wire height is reduced to 2mm , which eliminates the free blade in the wire. This free blade is responsible for fibre loading.Once the fibre lodges between the free blade of two adjacent teeth it is difficult to remove it.In order to eliminate the free blade, the wire is made with a larger rib width
  1. Front angle not only affects the carding action but controls the lift of the fibre under the action of centrifugal force. The higher the cylinder speed , the lower the angle for a given fibre. Different fibres have different co-efficient of friction values which also determine the front angle of the wire.
  2. If the front angle is more, then it is insufficient to overcome the centrifugal lift of the fibre created by cylinder speed. Therefore the fibre control is lost, this will result in increasing flat waste and more neps in the sliver.
  3. If the front angle is less, then it will hold the fibres and create excessive recycling within the carding machine with resulting over carding and therefore increased fibre damage and nep generation.
  4. Lack of parallelisation, fibre damage, nep generation, more flat waste etc. etc., are all consequences of the wrong choice of front angle.
  1. Each fibre has a linear density determined by its diameter to length ratio. Fine fibres and long fibres necessitates more control during the carding process. This control is obtained by selecting the tooth pitch which gives the correct contact ratio of the number of teeth to fibre length.
  2. Exceptionally short fibres too require more control, in this case , it is not because of the stiffness but because it is more difficult to parallelise the fibres with an open tooth pitch giving a low contact ratio.
  • RIB THICKNESS:
  1. The rib thickness of the cylinder wire controls the carding “front” and thus the carding power. Generally the finer the fibre, the finer the rib width. The number of points across the carding machine is determined by the carding machine’s design, production rate and the fibre dimensions. General trend is towards finer rib thicknesses, especially for high and very low production machines.
  2. Rib thickness should be selected properly, if there are too many wire points across the machine for a given cylinder speed, production rate and fibre fineness, “BLOCKAGE” takes place with disastrous results
    from the point of view of carding quality. In such cases, either the cylinder speed has to be increased or most likely the production rate has to be reduced to improve the sliver quality
  • POINT POPULATION:
    The population of a wire is the product of the rib thickness and tooth pitch per unit area. The general rule higher populations for higher production rates, but it is not true always. It depends upon other factors
    like production rate, fineness, frictional properties etc.
  • TOOTH POINT:
    The tooth point is important from a fibre penetration point of view. It also affects the maintenance and consistency of performance. Most of the recent cylinder wires have the smallest land or cut-to-point.
    Sharp points penetrate the fibre more easily and thus reduce friction, which in turn reduces wear on the wire and extends wire life.
  • BLADE THICKNESS:
    Blade thickness affects the fibre penetration. The blade thickness is limited by practical considerations,but the finer the blade the better the penetration of fibres. Wires with thin blade thickness penetrate the more easily and thus reduce friction, which in turn reduces wear on the wire and extends wire life.
  • BACK ANGLE:
    A lower back angle reduces fibre loading, but a higher value of back angle assists fibre penetration. Between the two extremes is an angle which facilitates both the reduction in loading and assists fibre penetration and at the same time gives the tooth sufficient strength to do the job for which it was designed.
  • HARDNESS OF WIRE:
    The cylinder wire needs to be hard at the tip of the tooth where the carding action takes place.The hardness is graded from the hard tip to the soft rib. High carbon alloy steel is used to manufacture a cylinder wire and it is flame hardened. Rib should not be hardened, otherwise, it will lead to mounting problems.

The design or type of clothing, selected for the fibre to be carded is important,but it is fair to state that within reason, an incorrect design of clothing in perfect condition can give acceptable carding quality whereas a correct clothing design in poor condition will never give acceptable carding quality. There is no doubt that the condition of the clothing’s is the most important single factor affecting quality at high rates of production. Wire condition and selection of wire are considered to be the two most important factors which influence the performance of modern high production carding machines.

· The condition of the clothing may be defined as the collective ability of the individual teeth of the clothing to hold on to the fibre against the opposing carding force exerted by other teeth acting in the carding
direction. For a given design of clothing the condition of the teeth determines the maximum acceptable production rate that can be achieved at the card.

· The speed of the main cylinder of card provides the dynamic force required to work on separating the fibres fed to the card but it is the ability of the carding teeth on the cylinder to carry the fibre forward against the opposing force offered by the teeth of the tops which determines the performance of the card. Increasing cylinder speed increases the dynamic forces acting upon the carding teeth and thus the condition of teeth becomes more important with increased speed.If the condition and design of the cylinder wire is poor, the teeth will not be able to hold onto the fibre through the carding zone, thus allowing some of the freed fibre to roll itself into nep.

DOFFER WIRE:

  1. The doffer is a collector and it needs to have a sharp tooth to pickup the condensed mass of fibres circulating on the cylinder. It also requires sufficient space between the teeth to be efficient in fibre transfer from the cylinder, consistent in the transfer rate and capable of holding the fibre under control until the doffer’s stripping motion takes control.
  2. A standard doffer wire has an overall height of approx. 4.0 mm to facilitate the deeper tooth which must have sufficient capacity to collect all the fibre being transferred from the cylinder to meet production requirements. Heavier webs require a deeper doffer tooth with additional collecting capacity to handle the increased fibre mass.
  3. The doffer wire’s front angle plays a very important part in releasing the fibre from the cylinder wire’s influence. A smaller angle has a better chance of enabling the doffer wire’s teeth to find their way under
    the fibres and to secure the fibre’s release from the cylinder with greater efficiency. A 60 degree front angle for Doffer has been found to give the optimum performance under normal carding conditions. Too small an angle results in cloudy web and uneven sliver whilst too large an angle results in fibre recirculation and nep generation.
  4. Having collected the fibre, it is important for the doffer to retain it until it is stripped in a controlled manner by the doffer stripping motion. The tooth depth, tooth pitch and rib width combine to create the space available for fibre retention within the doffer wire. Thus they directly influence the collecting capacity. If the space is insufficient, fibre will fill the space and any surplus fibre will be rejected. When
    the surplus fibre is left to recirculate on the cylinder, cylinder loading can take place. Unacceptable nep levels and fibre damage will also result. In severe cases pilling of the fibre will take place.
  5. The point of the doffer wire normally has a small land which helps to strengthen the tooth. The extremely small land of around 0.05 mm ensures that the doffer wire height is consistent, has no adverse effect on fibre penetration and is considered essential for efficient fibre transfer from the cylinder. The land has microscopic striations which are created during manufacturing or grinding. The striations help to collect the fibres from the cylinder and keep them under control during the doffing process.
  6. It has been found that a cut-to-point doffer wire penetrates the fibre better than does the landed point wire but is less likely to keep the fibre under control during the doffing process. Sometimes a cut-to-point doffer wire is accompanied by striations along one side of the tooth for this reason. Until recently 0.9mm rib thickness is standardised for doffer wire, regardless of production and fibre characteristics.This rib thickness has been found to give optimum results. However doffer wires with a 0.8mm rib thickness have been introduced for applications involving finer fibres.
  7. In general 300 to 400 PPSI(points per square inch) has been found to perform extremely well under most conditions. Doffer wire point population is limited by the wire angle and tooth geometry. Higher
    population for doffer does not help in improving the fibre transfer.
  8. As the production rate rises, the doffer speed also increases. The doffer is also influenced by the centrifugal force, as is the cylinder.But cylinder wire front angle can become closer to counter the effect
    of centrifugal force, to close the front angle on a doffer wire would reduce its collecting capacity and result in a lowering of the production rate. The solution is to use the wire with striations, which will hold the fibre until the doffer is stripped.
  9. The hardness of the doffer wire is a degree lower than that of the cylinder but sufficiently hard to withstand the forces generated in doffing and the resultant wear of the wire. The reason for this slightly lower hardness requirement is the longer and slimmer tooth form of the differ wire.
  10. The fibres which are not able to enter the wire will lay on top, i.e.completely out of control. There fore instead of being carded by the tops the fibres will be rolled. Similarly a fibre buried too deep
    within the cylinder wire will load the cylinder with fibre, weaken the carding action and limit the quantity of new fibres the cylinder can accept. Therefore, the production rate would have to be reduced.

LICKER-IN WIRE:

  1. Licker-in with its comparatively small surface area and small number of carding teeth, suffers the hardest wear of all in opening the tangled mass of material fed to it.
  2. Successful action of the Licker-in depends upon a penetrating sharp point rather than a sharp leading edge as with the cylinder wire. Therefore the licker-in wire cannot be successfully restored to optimum performance by grinding.
  3. The most satisfactory system to adopt to ensure consistent performance is to replace the licker-in wire at regular intervals before sufficient wear has taken place to affect carding quality.
  4. The angles most widely used are 5 degrees negative or 10 degrees.
  5. There is no evidence to suggest recommendation of a tooth pitch outside the range of 3 to 6 points per inch.
  6. It is better to use Licker-in roller without groove. Interlocking wires are used for such type of licker-ins. This avoids producing the eight precise grooves and to maintain them throughout its life. Interlocking wire is almost unbreakable and thus no threat to the cylinder, tops and doffer in the event of foreign bodies entering the machine.

FLAT TOPS:

  1. The flat tops are an equal and opposite carding force to the cylinder wire and it should be sharp,
    well maintained and of the correct design.
  2. The selection of flexible tops is very much related to the choice of cylinder wire, which in turn is related
    to the cylinder speed, production rate and fibre charactersitics, as previously stated.
  3. The modern top is of the semi-rigid type, having flexible foundation and sectoral wire. The points are
    well backed-off and side-ground to give the necessary degree of fineness. The strength of the top from a carding
    point of view is in the foundation and is affected by the number of plies and the type of material used.
    The position of the bend in the wire is determined by stress factors, at around 2:1 ratio along the length of the wire protrusion.
  4. The modern top is made from hardened and tempered wire to increase wear resistance , thus improving
    the life of the flat top.

· Life of the cylinder wire depends upon

  1. Material being processed
  2. production rate
  3. cylinder speed
  4. settings

· Wear is the natural and unavoidable side effect of the work done by the vital leading edge of the metallic wire tooth in coping with the opposing forces needed to obtain the carding action which separates fibre from fibre. When the leading edge becomes rounded due to wear, there is a loss of carding power because the point condition has deteriorated to an extent where the leading edge can no longer hold on to the fibre against the carding resistance of the flats. This ultimately leads to fibres becoming rolled into nep with consequent degradation of carding quality. Therefore it is important to recognise that, due to the inevitable wear which takes place during carding, metallic wire must be reground at regular intervals with the object of correctly resharpening the leading edge of each tooth.

· GRINDING:

  1. GRINDING A CUT-TO-POINT CYLINDER WIRE:
    1. Wire points of cylinder have become finer and the tip is cut-to-point.Because of this new profile, it has become necessary to recommend a little or no grinding of the cylinder wire following mounting.
      TSG grinding machine of GRAF(wire manufacturer) can be used to sharpen these modern wires. TSG grinding is a safe method of grinding.
    2. Before grinding , the wire should be inspected with a portable microscope to ascertain the wear. Based on this and the wire point land width, no of traverse for TSG grinding should be decided. If the width of the wire point tip is bigger and the wear out is more, the number of traverse during grinding should be more. For a new wire, 3 or 4 traverses may be enough. But it may require 10 to 30 traverses for the last grinding before changing the wire, depending upon the maintenance of the wire.
  2. GRINDING A NORMAL CYLINDER AND DOFFER WIRE:
    1. The first grinding of the metallic wire on the cylinder and doffer is the final and most important step leading up to providing the card with a cylinder in the best possible condition for carding well at maximum production rate.Grinding the lands of the teeth provides the leading edge of each tooth with the final sharpness required for maximum carding power.
    2. The first grinding should be allowed to continue until at least 80% (for cylinder) and 100% (for doffer) of the lands of the teeth have been ground sufficient to sharpen the leading edge of the tooth.
    3. To ascertain this stage of grinding, it is necessary to stop the cylinder regularly and use a simple microscope to examine the teeth at random across and round the cylinder.
    4. If the wire on the cylinder is of good quality and has been correctly mounted, the initial grinding period should be completed with in 20 min.
    5. It is essential to avoid over-working the wire before taking corrective action. The regrinding cycle must be determined accurately for the conditions applying in the individual mill, by using the microscope.
    6. If regrinding is done properly, there are several advantages
      1. carding quality will remain consistent
      2. There is no risk of overworking the wire
      3. Time required for regrinding is very short
      4. The exact condition of the clothing is known
      5. The working life of the wire is likely to be longer because the points are never allowed to become worn
        beyond recovery
    7. To obtain acceptable grinding conditions at the low grinding speed, the grindstone must always be SHARP, CLEAN and CONCENTRIC. If the grinding stone is gradually allowed to become dull and glazed
      through constant use, the limited cutting action available will eventually disappear, resulting in burning and hooking of the carding teeth.
    8. Due to the low peripheral speed of the grindstone which has to be used, it is most important that the speed of the wire to be ground is as high as is practicable to provide a high relative speed between
      the grindstone surface and the cardig teeth.If wire speed is low, the individual carding tooth spends too long a time in passing under the grindstone, thereby increasing the risk of hooking and burning the tooth, which is usually irreparable.
    9. With cylinder grinding, speed is no problem because the normal operating speed of the cylinder is more than sufficient. The speed of the doffer for grinding is more commonly a problem and this should be driven at a minimum speed of 250 m/min, to avoid damage when grinding the wire, the design which is particularly susceptible to hooking due to the long fine, low angled teeth needed on the doffer.
    10. The directions of rotation for metallic wire grinding are normally arranged so that the back edge of the tooth is first to pass u nder the grindstone. This is termed grinding “back of point”
  3. GRINDING FLAT TOPS:
    1. Flat tops provide the opposing carding force against the cylinder wire and hence can equally effect
      carding quality.It is essential to ensure that the tops are kept in good condition to maintain maximum
      carding power with the cylinder.Again, the only reliable approach is to examine the tops with the
      microscope and decide whether grinding is required or not.
    2. For cards fitted with regrindable tops, it is good practice to regrind the flats at regular intervals
      thus ensuring that the conditions of the two principal carding surfaces are always complementary one to other.

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