RIETER CARDING TECHNOLOGY

The card

Introduction

Two maxims of the experts - ‘The card is the heart of the spinning mill’ and ‘Well carded is half spun’ – demonstrate the immense significance of carding for the final result of the spinning operation. According to Dr. Artzt of the Research Institute in Denkendorf, Germany, the operation of the card shows:

• the highest correlation to quality;
• and also to productivity.

The importance of carding is even greater where new spinning systems are concerned. The considerable influence of the card on yarn quality arises from the very complex series of events in the process itself, and also from the pressure to adopt an extremely high production rate on economic grounds. This high production rate causes problems, since there is a close relationship between increases in production and reductions in quality:

• the higher the performance, the more sensitive the carding operation becomes
• and the greater the danger of a negative influence on quality.

One of several causes is that we are still operating according to a concept dating from 1770 and with a type of machine dating from 1850. On the other hand, since 1965 production rates have increased from about 5 kg/h to about 220 kg/h – a rate of increase not matched by any other textile machine except the drawframe.

When dealing with cards it has to be kept in mind that nowadays cards and  blowroom form an integral, homogeneous, inseparable unit, coordinated to complement one another.

While in the case of an easy-to-clean cotton, for example, the blowroom line might assume most of the working load required, for hard-to-clean cotton this might be done by the card.

Opening into individual fibers

Whereas the  blowroom only opens the raw material into tufts, the card must open to the stage of individual fibers. This is essential to enable  impurities to be  eliminated and the other operations to be performed.

Elimination of impurities

Elimination of foreign matter occurs mainly but not exclusively in the region of the  licker-in. Only a small part of the contaminants is carried along with the flat strippings, or falls out at other positions. The  degree of cleaning achieved by the modern card is very high, in the range of 80 - 95%. Thus, the overall degree of cleaning achieved by the  blowroom and the carding room together is as high as 95 - 99%. But carded sliver still contains 0.05 - 0.3% of foreign matter.

Elimination of dust

In addition to free dust, which can be directly extracted by suction as in the  blowroom, the card also removes a large proportion of the microparticles that are bound to the fibers. Significant fiber/metal or fiber/fiber friction is needed in order to loosen such particles. Both are available on the card to a considerable degree, i.e. the card is a good  dust removing machine.

Disentangling neps

While the number of neps increases from machine to machine in the  blowroom, the card reduces the remaining number to a small fraction. It is often falsely assumed that neps are eliminated at the card; in fact, they are mostly opened out. Only a fraction of the neps leaves the machine unopened via the flat strippings. Fig. 87 shows the approximate change in the number of neps in the process.

An improvement in the disentangling of neps is obtained by:

• reducing fiber density on the cylinder by using larger cylinder widths;
• closer spacing between the clothing surfaces;
• sharper clothing;
• optimal (not too low) licker-in speeds;
• low doffer speeds;
• lower throughput.

Fig. 87 – Change in the number of neps in the cotton when passing blowroom and cards

Elimination of short fibers

Short fibers can only be eliminated if they are pressed into and retained in the  clothing. Since that is not possible with metallic clothing, only the  flats can be considered in this context. The ability to select short as opposed to long fibers is based on the fact that long fibers have more contact with the clothing of the  main cylinder than the short fibers. Thus longer fibers are continually caught and carried along by the main cylinder. Short fibers, on the other hand, offer less surface to the clothing of the main cylinder; they therefore remain caught in the flats clothing, are pressed into it and leave the machine in the flat strippings. Elimination of short fibers in the card must, however, be viewed in proportion. It is actually very small, as can be readily demonstrated. The card eliminates 1 - 2% flat strippings. Approximately half of the strippings are made up of short fibers. The card therefore eliminates fewer than 1% short fibers. In the staple diagram this is scarcely noticeable – the inaccuracy of the staple measurement procedure is greater than the change in value.

Fiber blending

The card scarcely improves long-term blending, since the time spent by the material in the machine is too short. However, it improves transverse blending and fiber-to-fiber blending because, apart from the OE spinner, the card is the only machine to process individual fibers. Intimate fiber-to-fiber mixing is achieved in the formation of the web.

Fiber orientation

Parallelizing action is often attributed to the card. This is not completely justified, since the fibers in the web are not parallel, although they do have, for the first time, a certain degree of longitudinal order. It is true that a parallel condition is achieved on the  main cylinder, but it disappears during formation of the web between the cylinder and the  doffer. Thus, the card can be given the task of creating partial longitudinal orientation of the fibers, but not that of creating parallelization.

Sliver formation

In order to be able to deposit the fiber material, transport it and process it further, an appropriate intermediate product must be formed. This is the sliver. In extreme cases, card sliver has a count of 3 ktex (new spinning processes) to 9 ktex. Generally the count lies between 4 and 7 ktex (for direct feeding of drawframes up to 20 ktex) in the short-staple spinning mill.

It also has to be kept in mind that all these operations must be performed:

• at very high output;
• with very careful treatment of the fibers; and
• very high utilization of the raw material.

Operating principle

Fig. 88 – Modern high-performance card

In modern installations, raw material is supplied via pipe ducting (Fig. 88, 1) into the  feed chute (of different designs) (2) of the card. An evenly compressed batt of about 500 - 900 ktex is formed in the chute. A transport roller (3) forwards this batt to the feed arrangement (4). This consists of a feed roller and a feeder plate designed to push the sheet of fiber slowly into the operating range of the licker-in (5) while maintaining optimal clamping.
The portion of the sheet projecting from the feed roller must be combed through and opened into tufts by the licker-in. These tufts are passed over grid equipment (6) and transferred to the  main cylinder (8). In moving past mote knives, grids, carding segments (6), etc., the material loses the majority of its impurities. Suction ducts (7) carry away the waste. The tufts themselves are carried along with the main cylinder and opened up into individual fibers between the cylinder and the flats in the actual carding process.
The flats (10) comprise 80 - 116 individual carding bars combined into a belt moving on an endless path. Nowadays some 30 - 46 (modern cards about 27) of the flats are located in the carding position relative to the main cylinder; the rest are on the return run. During this return, a cleaning unit (11) strips fibers, neps and foreign matter from the bars. Fixed  carding bars (9) and (12) are designed to assist the operation of the card.  Grids or cover plates (13) enclose the underside of the main cylinder. After the carding operation has been completed, the main cylinder carries along the fibers that are loose and lie parallel without hooks. However, in this condition the fibers do not form a transportable intermediate product. An additional cylinder, the doffer (14), is required for this purpose. The doffer combines the fibers into a web because of its substantially lower peripheral speed relative to the main cylinder.
A stripping device (15) draws the web from the  doffer. After calender rolls (16) have compressed the sliver to some extent, the coiler (18) deposits it in cans (17). The working rollers, cylinder and  flats are provided with clothing, which becomes worn during fiber processing, and these parts must be reground at regular intervals.

Varying types of design

Basic considerations

Fig. 89 – The Rieter C 60 card with a width of 1 500 mm compared with a standard card

Carding engines are basically designed for processing either relatively long fibers (wool cards with carding rollers) or relatively short fibers such as those found in the usual short-staple spinning mill. Since machines of the latter type have flats circulating on an endless path, they are referred to as revolving flat cards.

The name card is derived from the Latin ‘carduus’, meaning thistle, the spiked fruit of which was used in earlier times for plucking fibers apart. The working width was usually 1 000 mm or 40 inches; Rieter recently increased it to 1 500 mm on its new  C 60 card.

This is one of the reasons (out of a dozent others) for the extremely large increase in production from usually 5 kg/h to max. 120 kg/h (the last but one generation) and to about 220 kg/h for the latest generation.

Although the card used today is still the same type as that designed in 1850, its performance has been improved tremendously, mainly by some design details. The target was first of all to provide:

• better opening of the material in front of the main cylinder;
• far better and more even spread of fibers on the surface of the cylinder.

This was achieved by installing more opening and carding devices in front of and around the main cylinder, e.g.:

• an opening device in the feed chute;
• new feeding arrangement (directional feed) at the licker-in;
• a second and a third licker-in;
• carding bars in front of the flats and behind the flats at the cylinder.

Another means for achieving these improvements was the former Crosrol  tandem card (no longer available), which will be described in the following chapter.

Duo or tandem cards

As the name implies, tandem cards consist of two individual cards joined together to make up a unit, in which the doffer of the first card feeds fiber material to the  licker-in of the second card. Double carding of the raw material has a positive effect on quality and on  blending. However, these advantages are purchased at the cost of expense in hardware and maintenance, and additional space is required. Modern cards of the latest generation give the same and better quality as tandem cards. Therefore tandem cards are not necessary and are no longer available (Fig. 90).

Fig. 90 – Crosrol tandem card

The operating zones of the card

Material feed

Requirements

In modern spinning installations the card is the first machine to deliver a cohesive intermediate product. Among other requirements, the product is expected to be very even and as far as possible free of faults. Irregularities in the sliver can be traced through into the yarn, at least in the spinning of carded yarns; that is, they diminish yarn quality.
A fault-free sliver cannot be obtained unless the feedstock is in an adequate condition, since every irregularity in the feedstock is transmitted completely into the sliver – in an elongated form owing to the draft. The time spent by the material in the machine is too short for total compensation. In spinning, as in any other type of manufacturing process, the rule must be that faults should not be corrected and hidden but their occurrence should be prevented from the start. It follows that the feed to the card must be very even. Where lap feed was used, this represented only a minor problem, since the scutcher formed even laps, each of which was checked for accuracy of count. Tuft feed systems react much more sensitively.
The tufts must be transported pneumatically from a distributor unit into the chutes of several cards. One of the cards is always located very close to the fan of the distributing system, whereas the others are located at steadily increasing distances from the fan. To obtain even feeding, the batts in the individual feed chutes of all cards must be equally thick, evenly distributed over the whole width of the chute and of equal density. This requirement cannot be fulfilled continuously without the expenditure of some effort. An additional requirement for the feedstock of high-performance cards is a high degree of openness. This very good openness in turn is the reason for the large increase in performance of this card in comparison with conventional machines. Higher loading of the clothing (600 to 900 ktex) permits greater throughput of material. Correspondingly finely opened material is therefore essential.

Basic concept of tuft feed

Fig. 91 – Material feed at the card

Fig. 92 – Tuft feed with a one-piece chute

Fig. 93 – Tuft feed with a two-piece chute

The two-piece chute system

Raw material, delivered by a fan between the  UNIflex B 60 and the chutes or by the  UNIstore A 78, travels via the transport duct, which extends over all integrated machines within a unit, into the reserve chutes (upper half of the chute) of the individual cards. The transport air escapes via a perforated sheet and is carried away by a suction duct. In this part of the chute (upper half) an electronic pressure regulator ensures an approximately constant height of material. ´
The feed roller, which seals the upper half of the chute, pushes the stock into the region of the opening roller, and this roller in turn plucks out fine tufts and discharges them into the actual feed chute (lower part). Here, controlled condensing is carried out by a metered supply of compressed air from a fan. A perforated sheet that is part of the rear wall permits the air to escape. It then flows back to the fan.
An electronic pressure switch ensures constant filling and density of material in the chute; this is obtained by adjusting the speed of the feed roll (above the opening roller).
The airflow in the chute continually carries the tufts to the zone in which the perforated sheet is currently least covered by fibers. Even distribution of tufts over the whole chute width is thus obtained.

Fine cleaning integrated in the card chute

With this solution, fine cleaning has been transferred to the  card chute. The existing opening position is supplemented with a mote knife.

The result is:

• a card chute with integrated fine cleaning;
• the high production load of the blowroom is now distributed over several cards;
• fine cleaning is performed very gently at considerably lower production rates compared to the blowroom;
• yarn quality is improved; for example, imperfections (thick places, thin places and neps) are usually reduced and short fiber content improves.

Mode of operation (Fig. 94):

1. Fiber tufts are fed uniformly to the card chute with integrated fine cleaning.
2. The fiber tufts are separated from the transport air in the upper section of the card chute (1, 2) and form  an initial homogeneous batt.
3. A feed roller with a feed trough (4) and a needled cylinder (3) produces small tufts and thus a large tuft surface.
4. The integrated mote knife immediately eliminates the exposed trash particles.
5. The released tufts are blown into the lower section (5) of the shaft by means of an additional controlled air current and condensed there into a homogeneous batt.
6. The perforated rear wall at this point permits additional dedusting of the tufts.

Fig. 94 – Fine cleaning in the card chute

Feed device to the lickerin

Conventional system

A well designed feed device is expected to perform the following tasks:

• clamp the batt securely over its full width;
• be able to hold the material back against the action of the licker-in;
• present the batt to the licker-in in such a manner that opening can be carried out gently.

The conventional feed assembly (Fig. 95) comprises a stationary feed table with a feed plate (1) and a feed roller (2) pressed against the plate. The feed plate is formed as a special extension of the feed table and is adapted to the curvature of the cylinder.
The plate is formed at its upper edge with a nose-like deflector (b, Fig. 96) to hold the batt. Facing the licker-in, the plate has a fairly long guide surface (a). The deflector nose and guide surface have a significant influence on quality and on the quantity of waste eliminated. A sharp deflector nose gives good retention of the fibers and hence an intensive, but unfortunately not very gentle, opening effect. On the other hand, an over-rounded curve results in poor retention and poor opening. In this case, the  licker-in often tears out whole clumps of fibers. The length of the guide surface (Fig. 96 a) also influences waste elimination. If it is too short, the fibers can escape the action of the licker-in.
They are scraped off by the mote knives and are lost in the waste receiver. If this surface is too long, it presses the fibers into the clothing. This gives better take-up of the fibers, but at the same time better take-up of impurities. The result is a reduction in the cleaning effect. The length of the guide surface is dependent on the staple length, at least within a wide range.
The feed roller has a diameter of 80 - 100 mm and is usually clothed with saw-tooth wire, the teeth being directed against the flow of material. This gives good retention of the batt, which ensures that the licker-in does not tear whole lumps out of the batt. The opening effect of the licker-in is thus more in the nature of combing.

Fig. 95 – Conventional feed device

Fig. 96 – The shape of the feed plate

Feed in the same direction as licker-in rotation (unidirectional feed)

Fig. 97 – Feed in the same direction as drum rotation (Rieter)

When the conventional system is examined, it is observed that the material is pushed forward, illogically, against the direction of rotation of the  licker-in. The batt must undergo a sharp bend so that the licker-in can sweep through it. This diversion certainly does not contribute to gentle fiber treatment. Rieter has therefore converted the feed system to enable material to be fed in the direction of rotation of the licker-in (Fig. 97). The arrangement of the two feed devices is opposite to that of the conventional system, i.e. feed roller (2) is located below and plate (1) is pressed against the roller by spring pressure.
Owing to the rotation of the feed roller in the same direction as the licker-in, the batt runs downward without diversion directly into the teeth of the licker-in. In order to give perfect operating conditions in the conventional feed system, the spacing between the feed plate and the licker-in must be adapted precisely to the material. Where the direction of rotation of the feed roller and the drum is the same, the distance from the clamping zone (the exit from the plate) to the feed roller/licker-in clamping point (distance b/a) is adjustable.

The licker-in

This is a cast roller with a diameter usually of around 250 mm. Saw-tooth clothing is applied to it. Beneath the licker-in there is an enclosure of grid elements or  carding segments; above it is a protective casing of sheet metal. The purpose of the licker-in is to pluck finely opened tufts out of the feed batt, lead them over the dirt-eliminating parts under the roller and then deliver them to the main cylinder. In high-performance cards, rotation speeds are in the range of 800 - 2 000 rpm for cotton and about 600 rpm for synthetics.

The operation of the licker-in

By far the greatest part of opening and cleaning is performed by the licker-in. In machines with only one licker-in, opening is performed to an extent where more than 50% of all fibers pass onto the surface of the  main cylinder in the form of tufts, and slightly less than 50% in the form of individual fibers. Treatment imparted by the licker-in is therefore very intensive, but unfortunately not very gentle. The licker-in combs through a fairly thick fiber fringe at a rotation speed of 1 600 rpm (approximately 600 000 wire points per second), a circumferential speed of around 21 m/sec (approximately 76 km/h) and a draft of more than 1 600. Even without sophisticated mathematical computation, it will be clear that fiber deterioration is very likely to occur at the opening point. Only the degree of deterioration can and must be precisely controlled by adjustment of:

• the thickness of the batt;
• the degree of openness of the raw material in the feedstock;
• the spacing between the operating devices;
• the degree of orientation of the fibers in the feedstock;
• the aggressiveness of the clothing;
• the rotation speed of the licker-in;
• the material throughput.

Opening itself involves the tearing away of the feed batt on a wedge shape by means of the licker-in; 'wedge shape' refers to the fact that the projecting fiber fringe becomes steadily thinner where it faces away from the clamping point owing to the plucking-out of fibers. The type and intensity of the opening process influences the final yarn, primarily as regards neppiness, imperfections, evenness and strength.

Elimination of waste

Waste elimination is very intensive and takes place under the licker-in by means of special devices. The classic cleaning assembly consisted of 1 - 2 mote knives and a grid, one half of which was made of slotted sheet and another half of perforated sheet. In this arrangement, elimination of foreign matter took place exclusively by scraping off on the mote knives. The grid sheets tend to serve as devices for guiding and holding-back fibers, i.e. they prevent additional fiber losses that could arise from ejection.

High-performance cards require alternative assemblies in order to be able to deal with the high material throughput. Accordingly, the lickers-in of such cards no longer operate with grids but with carding segments (4, Fig. 99).

In the last but one generation of the Rieter card, for example, the tufts are first guided over a mote knife (2), then over a carding plate (3), then again over a mote knife and again over a carding plate, before they finally pass to the main cylinder. The carding plates are fitted with special clothing (3a).

A trash mote knife with suction unit is assigned to the licker-in. With the effective opening in the chute the  C 60 card with single licker-in provides much better opening than the C 51. The single licker-in opens the material tufts even more with absolutely minimal loss of sound fibers, and extracts coarse trash and dust gently.

Fig. 99 – Carding segments under the licker-in of the Rieter C 51 card

Fig. 100 – Single licker-in, Rieter C 60 card

Transfer of fibers to the main cylinder

Between licker-in and  main cylinder the clothing is configured for doffing. It follows that the opening effect at this position cannot be very strong. Nevertheless, it exerts an influence on sliver quality and also on the improvement in the longitudinal orientation of the fibers that occurs here. The effect depends on the ratio of the speeds of the two devices. According to various investigations, this ratio should be about 1:2; i.e., the draft between the licker-in and the main cylinder should be slightly more than 2 (this refers to a card with one licker-in, not to a machine with several). The optimum ratio depends upon the raw material; in any event, when speeds are to be altered, this interdependence should be borne in mind.

Auxiliary carding device

Need for such assemblies

The so-called combing rate was used previously in order to indicate the opening effect of the card. This was the ratio of the  main cylinder’s rotation speed (rpm) to the infeed speed (inches/min.). This number can no longer be used under modern production conditions. The opening effect can now be represented only by the number of points per fiber, i.e. average of total fibers fed in per unit of time over the number of points available in the same time. At the licker-in there may be, for example, 0.3 points per fiber (three fibers per point) and at the main cylinder perhaps 10 - 15 points per fiber.

If a given quality of yarn is required, a corresponding degree of opening at the card is needed. However, an increase in production at the card such as we have experienced in recent years means quite simply that more fibers must be passed through the machine.

In order to obtain the same carding effect (i.e. the same number of points per fiber), the number of points per unit of time must also be increased. This can be achieved by:

• more points per unit area (finer clothing);
• higher roller and cylinder speeds;
• more carding surface or carding positions;
• finer opening of the fibers before feeding to the cylinder.

Little can now be done to increase the number of points, since the mass of fiber also has to be accommodated between the clothing: coarse fibers and a high throughput demand coarser  clothing; fine fibers and a lower throughput permit the use of finer clothing.

Much has already been achieved by increasing speeds, but further increases will prove steadily more difficult, as an example will demonstrate. If, for example, the production of a card is increased from 25 kg/h to 60 kg/h with the same number of points per fiber, the main cylinder speed must be raised from 300 rpm to 750 rpm (according to P. Artzt). This cannot be achieved from either the design or the technological standpoint. One effect, among many, would be severe deterioration of the fibers.

There remain only the third and fourth approach – insertion of additional carding surface or additional carding positions and/or installing more  lickers-in. Here also, there are two possibilities:

• increase in the number of lickers-in;
• fitting of additional carding plates.

Both have been put into practice.

Increase in the number of lickerin

The standard card has only one  licker-in; for a long time attempts have been made to increase this number and thereby to increase the opening effect. With the introduction of modern high-production cards, several manufacturers again saw this approach as one way to improve performance. Various card designs therefore now incorporate multiple lickers-in, e.g. Rieter (Fig. 101), Trützschler or Marzoli.

They are optionally available. The clothing surfaces are in the doffing configuration relative to each other, and speeds must be increased in the throughflow direction, for example from 600 rpm (first licker-in) via 1 200 rpm to 1 800 rpm (third licker-in) (or the velocity by increasing the diameter). Instead of grids, the lickers-in are encapsulated in casings.

Within these casings there are a few small openings including sharp-edged grid blades to scrap off the impurities. The latter fall into a pipe and are sucked away to the waste collecting devices. For fine, long fibers mostly only one licker-in is used.

Fig. 101 – Three lickers-in on the Rieter C 60 card

Carding plates or carding bars

The other or additional method of intensifying the carding effect is the insertion of  carding elements at special positions.

Today, carding aids can be applied at three positions:

• under the licker-in;
• between the licker-in and the flats;
• between the flats and the doffer.

These aids are in the form of carding plates or carding bars.
Carding plates have already been illustrated in Fig. 99 at the licker-in, while carding bars are shown in Fig. 102 and Fig. 103.
Plates are usually used in the licker-in zone, while bars are being located increasingly in the region of the main cylinder (Fig. 102 and Fig. 103).
An aluminium carding profile (1) consists of 2 carding bars (2). One of the advantages of bars is that they can be provided in different finenesses, e.g. they can become finer in the through-flow direction. Different manufacturers use differing numbers of elements (between one and four) per position. Special clothing is required that must not be allowed to choke. Most modern high-performance cards are already fitted with these carding aids as integral equipment; all other machines can be retrofitted by, for example, Graf of Switzerland or Wolters of Germany.
In use are also other carding devices of different design and with different components, e.g. mote knives (4) with guiding element (5) and suction tubes (3), etc.

Fig. 102 – Carding bars at the infeed

Fig. 103 – Different carding segments at the delivery

Purpose and effect of carding elements

If carding elements or additional  lickers-in are not used, the licker-in delivers mostly tufts, if not whole lumps, to the main cylinder.

These are compact and relatively poorly distributed across the licker-in. If they pass into the space between the cylinder and the flats in this form, fiber-to-fiber separation becomes very difficult and imposes considerable loading on the clothing. The whole carding operation suffers.

That is why high-performance cards presuppose unconditionally individual fibers to be spread evenly over the whole surface of the cylinder, and this again can be obtained only by increasing the number of lickers-in and the inclusion of carding elements, since they ensure further opening, thinning out and primarily spreading out and improved distribution of the fibers over the total surface area.

In the final analysis, these additional devices reduce the loading on the carding zone cylinder/flats, among other things. Two diagrams (Fig. 104 and Fig. 105) by Schmolke and Schneider  [10] illustrate loading of the  flats with and without carding segments; in addition, it is clear from these diagrams that the main opening work is done at the first flats after entry of the material. Carding segments bring the following advantages:

• improved dirt and dust elimination;
• improved untangling of neps;
• the possibility of a speed increase and hence a production increase;
• preservation of the clothing;

and hence

• longer life of the clothing, especially on the flats;
• the possibility of using finer clothing;
• better yarn quality;
• less damage to the clothing;
• cleaner clothing.

Even  carding elements following the  flats exert a considerable influence on yarn quality – although the main carding work has been completed at that stage. This is shown in a diagram by Artzt, Abt and Maidel in Fig. 106  [11]. The segments create an additional fine carding zone as the fibers rotate 5 to 10 times with the cylinder before they pass to the doffer. This additional treatment of 5 to 10 times at the segments also improves both fiber orientation and transfer of fibers to the doffer.

Fig. 104 – Carding effect in the flats in cards without additional carding segments: A, carding effect (carding force); B, number of the flat starting from the entry point.

Fig. 105 – Carding effect in the flats in cards with additional carding segments over the licker-in; A, carding effect; B, number of the flat starting from the entry point.

Fig. 106 – Improvement in yarn properties through the use of carding segments following the flatsA, comparison values related to cards without carding segments (100%); I, neps; II, thick places; III, thin places; IV, yarn evenness; V, tenacity; a, main cylinder clothing: 430 points per square inch; b, main cylinder clothing: 660 points per square inch; c, main cylinder clothing: 760 points per square inch.

The cylinder

The cylinder is usually manufactured from cast iron, but is now sometimes made of steel. Most  cylinders have a diameter of 1 280 - 1 300 mm (Rieter C 60 card 814 mm, speed up to 900 rpm) and rotate at speeds between 250 and 500 (to 600) rpm. The roundness tolerance must be maintained within extremely tight limits – the narrowest setting distance (between the cylinder and the doffer) is only about 0.1 mm. The cylinder is generally supported in roller bearings.

The casing of the cylinder

Beneath the cylinder, and fully enclosing it, is a grid made of sheet metal provided with transverse slots. This is designed to remove impurities and maintain constant airflow conditions. However, since the cleaning effect is extremely small, some manufacturers, such as Rieter, have replaced the grid with a closed sheet metal casing. This enables the multitude of small air vortexes that tend to arise at the slots to be prevented. A closed sheet gives better fiber orientation on the cylinder surface and often reduces the number of neps at high cylinder speeds. Covering of the cylinder between the  licker-in and the  flats, and between these and the  doffer, takes the form of protective casing. One of these protective sheets, near the flats at the front of the machine, is specially formed as a knife blade. The level and quality of the flat waste can be influenced by adjusting the distance between this blade and the cylinder. Narrow spacing produces little waste and wide spacing produces more strippings.This setting option is, however, not suitable for use as a means of adjusting the waste extraction effect of the flats. If, for example, an attempt is made to eliminate more short fibers by raising the flat waste level, it will not succeed. More long fibers rather than short fibers will be eliminated in the flat strippings. Fiber loss will be increased. Once an optimum has been established (mostly by the manufacturer), the setting should not be altered without excellent reasons.

Flats

Function

Together with the cylinder (Fig. 107, 1), the flats form the main carding zone. Here, the following effects should be achieved:

• opening of tufts into individual fibers;
• elimination of remaining impurities;
• elimination of some of the short fibers;
• untangling neps (possibly their elimination);
• dust removal (3);
• high degree of longitudinal orientation of the fibers.

In order to fulfill all these requirements, a large continuous carding surface is needed. The surface is created by a large number of individual clothing strips secured to the bars of the flats (2) and arranged in succession. 40 to 46 such strips are commonly used (30 in Trützschler machines) to make up the carding surface in the operating position. Since elimination of waste can be carried out only by filling the  clothing, the flats must be cleaned continuously. They must therefore be moved past a cleaning device (4) (hence the name 'revolving flat cards'). The bars of the flats must be joined together to form an endless, circulating belt, for which purpose they are fixed to chains or toothed belts. In addition to the 40 - 46 flats (2) (Rieter  C 60 card: 27 flats) that interact with the cylinder (1), further flats are needed for the return movement on the endless path, so that altogether 100 - 120 flats (Rieter 79) are fitted to the rotating chains.

Fig. 107 – Carding zone between cylinder and flats

Construction of the flats

The bars of the flats are made of cast iron (nowadays aluminum profiles, Fig. 109) and are somewhat longer than the operating width of the card, since they rest on adjustable (so-called flexible) bends to the left and right of the main cylinder and must slide on these guide surfaces. Each bar is approximately 32 - 35 mm wide (might change to smaller widths). The bars are given a ribbed form (T-shape) in order to prevent longitudinal bending. A clothing strip (108 b) of the same width is stretched over each bar and secured by clamping, using clips (c) pushed onto the left- and right-hand sides of the assembly. Since some space is taken up by the upper edge of each clip, only a strip about 22 mm wide remains for the clothing (hooks or teeth). For this reason, the flats do not enable an absolutely continuous carding surface to be formed above the cylinder; there are gaps between the clothing strips.

The bars are thickened at their left- and right-hand ends in order to take fixing screws corresponding with screw holes in the chains; the individual bars can thus be secured to respective links of the circulating chains (Fig. 110).

The slide surfaces on the bars are not ground level but are slightly inclined (Fig. 111). Therefore, as the flats move over the cylinder, they have a slight tilt, i.e. viewed in the direction of material flow the leading edge of each bar is spaced further from the cylinder clothing than the trailing edge (1). The result is that the fibers are not pushed along in front of the flats, but can pass underneath them.

Fig. 108 – Mounting of the clothing strips (b) on the flat bars (a) using clips (c)

Fig. 109 – A modern flat construction

Fig. 110 – Securing the flat bars to the endless chain by means of screws

Fig. 111 – Inclined gap between flat clothing and main cylinder clothing

Movement of the flats

The bars of the flats mesh individually, like an internally toothed wheel, with the recesses in a sprocket gear, and are carried along by rotation of the sprocket. The ends of the bars of the operative flats slide over a continuous bend – with metal-to-metal friction.

As the flats move at a very low speed compared with that of the  cylinder in principle, the flats can be moved forward or backward, i.e. in the same direction as or in opposition to the cylinder. If the flats move with the cylinder (forward), the cylinder assists in driving the flats and the removal of strippings is easier. Forward movement therefore gives design advantages. On the other hand, reverse movement (against the cylinder) brings technological advantages. In this system, 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 toward the licker-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 that position, above the licker-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 (directly at the point where the flats leave the machine).

A diagram by Rieter (Fig. 112) shows that this is not simply an abstract principle, demonstrating clearly that the greater part of the dirt is flung into the first flats directly above the licker-in. Rieter and Trützschler offer cards with backward movement of the flats.

Fig. 112 – Dirt take-up of the flats from the entry point A, dirt; B, flat number 1...40

Carding plates instead of flats

Stationary carding plates were used for a short time as carding elements in place of traveling flats (Fig. 113). For example, the former Hollingsworth company fitted four such plates above the main cylinder where the flats would otherwise be located. The plates were in the form of curved plates of aluminum, provided with special steel wire clothing on their internal surfaces. The plates were adjustable and replaceable. This latter feature is advantageous because the first plate, which wears faster than the others, can be exchanged with one of the others after a certain period and thus continues in service. This system has some striking advantages but also very serious disadvantages. It is therefore no longer available.

Fig. 113 – Carding plates instead of flats. C1; C2; C3; C4

Cleaning positions in front of the flats

Illustrated by the Rieter TREX system

The remaining impurities in the material on the  cylinder, and a large proportion of the dust, can be removed only by way of total opening of the raw material, i.e. absolute separation of the fibers.

This degree of opening is achieved practically only once in the spinning process, namely on the card cylinder (similarly also in rotor spinning within the spinning unit). This position is therefore ideal for the finest cleaning.

The slotted grid beneath the cylinder that has been used formerly is not suited to this purpose. Mote knives are better. They have been in use for a long time at the cylinder (above the doffer) in the form of stripping blades for the flats, but they have never been properly exploited for cleaning.

For several years now, the manufacturers of cards have used assemblies better suited to this purpose, e.g. the Rieter company’s TREX system (Fig. 114). Beneath the flats cover is a mote knife, set close to the cylinder; this knife is associated with a suction tube. Foreign matter stripped from the cylinder surface passes into the tube and is carried away.

Nowadays it is nearly standard to have assemblies comprising carding plates and mote knives (behind each other) above the doffer.

Fig. 114 – Rieter TREX system a) above the licker-in; b) above the doffer

The doffer

The cylinder is followed by the doffer, which is designed to take the individual fibers from the cylinder and condense them to a web. The doffer is mostly formed as a cast iron (or steel) drum with a diameter of about 600 - 707 mm. (680 mm on Rieter machines) . It is fitted with metallic  clothing and runs at speeds up to about 300 m/min.

The doffing operation

It would appear logical to arrange the  clothing of the  cylinder and doffer in the  doffing configuration relative to each other. In practice, however, they are actually arranged in the carding configuration (Fig. 115). This clothing arrangement is essential because the web that is finally delivered must be cohesive and therefore the fibers must be interlaced with each other and condensed. Compared with the doffing configuration, the carding configuration at this point is disadvantageous in some respects. One disadvantage is that the desired fiber parallelization achieved on the main cylinder largely disappears again, since a degree of random orientation is necessary to form a web and to doff it.

Another is the undesirable bending of the fiber ends which occurs here, because the cylinder has to give up the fibers to the doffer clothing, during which a certain degree of sweeping through the fiber fleece takes place. In the course of this step, the fibers are caught as hooks on the points of the clothing. Accordingly

• over 50% of the fibers in the web exhibit trailing hooks(at the rear end as viewed in the direction of material flow);
• about 15% have leading hooks;
• another 15% have double hooks and
• only a small proportion are delivered without hook deformation of any kind.

A third disadvantage, namely the poor efficiency of fiber transfer from the cylinder to the doffer, is in practice more an advantage than a disadvantage. Of course, it is a fact that the fibers rotate with the main cylinder about 5 to 10 (15) times (!) before passing to the doffer, but it is also a fact that this results in some important improvements:

• it is an additional carding point;
• the fiber-to-fiber blending effect increases, i.e.
• a high degree of intermingling results there, which is important, e.g. for man-made fiber/cotton blending);
• it produces good diagonal and short-term regularity.

The carding configuration implies that it is more or less a matter of chance which of the two clothing surfaces will finally carry along any individual fiber. However, this operation favors the cylinder clothing, as the flats push the fibers vigorously into the cylinder clothing, and as the cylinder clothing has more points, both facts increase the retaining effect.

As mentioned above, the result is a poor transfer factor. However, certain provisions can influence the latter positively, mainly by:

• coordinating the clothing of both assemblies accordingly;
• the choice of a proper relationship of the peripheral speeds;
• providing for small distances between cylinder and doffer.

A reduction of the spacing between the two assemblies, e.g. from 0.18 mm to 0.08 mm results, for example, in a 100% improvement in the transfer factor.

Fig. 115 – Clothing configuration between main cylinder and doffer

The detaching apparatus

Fig. 116 – Web detaching using detaching rollers and transverse belts

On old cards, a fly-comb (a rapidly oscillating comb) oscillating at up to 2 500 strokes per minute takes the web from the  doffer. In modern high-performance cards, a fly-comb would be unable to perform this task because the stroke rate would have to be significantly higher (above the mechanical limit). A roller (Fig. 116, 1) now has the task of separating the web from the doffer. In old cards, the web is guided into a funnel, while being freely suspended over a distance of 30 - 50 cm and running together in a wedge shape.
This arrangement is also no longer possible at the high speeds of modern high-performance cards, since the web would fall apart.
Now, the web must be condensed into a sliver while still located within the detaching device.
This can be achieved in a number of ways; for example, with web guide plates upstream from the detaching device, with several transversely arranged guide rollers (Marzoli), or with a transverse sliver condenser (3). In the latter, either two counter-rotating belts carry the web into the center or one circulating belt carries the web to one side of the card.

Crushing rollers (web crushing)

Fig. 117 – Web crushing

Between take-off roller (1) and transverse sliver condenser (3), some manufacturers include two smooth steel rollers, arranged one above the other (Fig. 117). They can run without loading, in which case they serve simply as guide rollers, or they can be loaded with a pressure of about 15 N/cm and are thus converted into crushing rollers. Where cotton with medium to high dirt content is being processed, additional cleaning can be carried out here by squashing the foreign particles (the fragments fall away immediately after the rollers or in the subsequent machines).
In some models, the rollers are ground with a barrel shape. With this arrangement their central sections cannot escape the pressure – the pressing effect is the same over the full width. Clean fiber material should not be crushed. Owing to the absence of dirt particles, the full roller pressure would be exerted on the fibers, resulting in fiber damage.
This would show up directly in the breaking strength of the yarn. Sticky cotton (honeydew) should also be carded without crushing, as should cotton with a high proportion of seed particles, because of the danger of lap formation at the rollers (again sticky effect).
With the high cleaning efficiency in high performance cards this arrangement is out-dated.

Coiling in cans

The sliver must be  coiled in cans for storage and transport. As described in  "Technology of Short-staple Spinning", this is performed cycloidally, with large windings when working with smaller cans and small windings when working with larger cans. Can diameters now lie in the 600 to 1 200 mm range and can heights are between 1 000 and 1 220 mm. If the cans are supplied directly to the rotor spinning machine, they must be smaller because less space is available (better suited as round cans are rectangular cans).

The can diameter in this case is only about 350 to 400 mm. Fig. 118 gives Trützschler data on the capacity of cans with a height of 1 200 mm.

Most manufacturers offer cards with can changers as either standard equipment or an option. These permit efficient operation since they enable the need for attendance by mill personnel to be reduced substantially.

Fig. 118 – Capacity of cans (A) in kg; can diameter (B) in mm

The machine drive

Fig. 119 – Drive of a modern card (Trützschler)

Old cards had only one drive motor. This drove the  licker-in and  main cylinder directly via belts and the other moving parts indirectly via belts and gear transmissions. Modern high-performance cards differ in that they include several drive motors so that the individual zones of the card are driven independently of each other as shown in Fig. 119 by Trützschler:

• A, main drive for the cylinder, licker-in and flats;
• B, drive for the infeed;
• C, drive for the delivery, i.e. doffer, detaching rollers and coiler;
• D, drive for the cleaning roller of the detaching roller;
• E, drive for the cleaning roller of the flats via the stripping roller;
• F, fan.

Several manufacturers, e.g. Rieter, also provide a separate drive for the  flats. Individual drives have the advantage that transmission of the forces is better, and adjustments can be performed more quickly and conveniently. They are also better suited to operation with control equipment.

Choice of clothing

Of all the individual components of the card, the clothing has the greatest influence on quality and productivity. The development of new clothing enabled, for example, the production rate of the card to be increased from 5 kg/h to the current level of up to 220 kg/h. New clothing was not, of course, the only factor involved in this increase, but it made a major contribution to it. Unfortunately, a price has to be paid for this development in the form of a steadily increasing departure from any possibility of universal clothing, which was formerly aimed at. Mills now have to make a difficult choice between hundreds of available clothing types, a choice of the utmost importance. Selection criteria are:

• type and design of card;
• rotation speed of the cylinder;
• production rate;
• material throughput;
• raw material type (natural or man-made fibers);
• fiber characteristics (mainly fineness, length, bulk, dirt content);
• overall quality requirements;
• price of the clothing;
• service offered by the clothing supplier.

Operating conditions not only differ between mills – they can alter within a single mill. Compromises are therefore unavoidable.

Classification

If we consider not only the short-staple spinning mill, but all fields in which card clothing is used, thousands of variations are currently on offer. They can be divided into three groups.

Flexible clothing

This features hooks of round or oval wire set into elastic, multi-ply cloth backing. Each hook is bent into a U-shape and is formed with a knee that flexes under bending load and returns to its original position when the load is removed. In short-staple spinning mills this clothing is now found, if at all, only on the  card flats (Fig. 120).

Semi-rigid clothing

In this, wires with square or round cross-sections and sharp points are set in backing which is less elastic than that of flexible clothing. This backing is a multi-ply structure with more plies than the backing of flexible clothing, comprising layers of both cloth and plastics. Flat wires are not formed with a knee, but round wires may have one. The wires cannot bend and are set so deeply in layers of cloth, and possibly foamed material, that they are practically immovable. When subjected to bending loads, they are therefore much less capable of yielding than flexible clothing types. They are also found only on the flats (Fig. 121).

Metallic clothing

These are continuous, self-supporting, square wire structures in which teeth are cut at the smallest possible spacings by a process resembling a punching operation. If the teeth are relatively large, for example as in the  licker-in, the clothing is referred to as saw-tooth clothing. (The terms saw-tooth clothing and metallic clothing refer to the same thing.) Nowadays, the licker-in, main cylinder and doffer use metallic clothing without exception (Fig. 123).

Flexible clothing in detail

The substrate is formed as a continuous narrow band (51 mm for the main cylinder) or as a broad band (equal to the length of the  flats) comprising five (flexible clothing), seven (semi-rigid clothing) or even more plies of cloth joined together by vulcanizing. Double hooks of round or oval wire are embedded in the substrate; each has a knee in the leg and a cross-bar at the foot. The knee is required so that the hook does not project too far outward when the leg is bent back; it is thus possible to operate with small spacings between the clothing surfaces. In order to make the clothing more aggressive, the points are mostly ground on both sides (lateral sharpening), and they are also hardened. In the flats, the point density is in the range of 240 - 500 points per square inch.

Fig. 120 – Flexible clothing

Semi-rigid clothing

This clothing is similar in structure to the flexible types. However, it has more cloth layers (possibly also foamed material) and has hooks of wire with squared cross-sections without a knee, or of reinforced round wire with or without a knee. Compared with flexible clothing, it has the advantage that it does not choke with fiber and thus eliminate less flat strippings. In addition, it does not need sharpening as often as flexible clothing types. At least in respect to flat wires, it should be mentioned that each sharpening removes material from the tip so that the working surface becomes steadily broader and the aggressiveness of the clothing declines over time. This wire clothing without lateral sharpening can be re-sharpened only once or twice; with lateral sharpening up to four times.

 Fig. 121 – Semi-rigid clothing

Manufacture of metallic clothing

The starting material is round wire, which is rolled in several stages to give the desired profile (Fig. 122). This profiled stock is passed through a cutting machine. Here, a high-precision cutting tool, corresponding exactly to the shape of the gap between two teeth, punches (cuts) the wire away piece by piece between the teeth, which remain after the cutting operation. It is of the utmost importance that the dimensions are held within the finest tolerance limits. Hardening immediately follows cutting, i.e. the wire is passed through a flame and a quenching bath. Here also a high degree of uniformity is required, this time in the hardness achieved. The required ‘feel’ for this operation can only be appreciated when it is realized that in fine clothing the tip of the tooth has a thickness of only 0.05 - 0.06 mm.

Fig. 122 – Forming the wire profile for metallic clothing

The geometry of the clothing

No.	Name	Symbol or formula	Comment
1	Base width	a1	in mm
2	Tooth thickness at the root	a2	in mm
3	Tooth thickness at  the tip	a3	in mm
4	Overall height	h1	in mm
5	Height of the base	h2	in mm
6	Depth of the tooth	h3	in mm
7	Tooth pitch	T	spacing between successive tooth tips measured with the wire stretched out
8	Carding angle		angle between a line at right angles to the base of the tooth and the leading edge of the tooth, measured with the wire stretched out
9	Tooth apex angle		angle between the leading and trailing edges of the tooth

Fig. 123 – Angle and other dimensions of metallic clothing

The most important operating parameters of the clothing

Point density (Number of points per unit surface area)

The point (or tip) density has a significant influence on the carding operation. However, the number of points and the speed of rotation of the cylinder must be considered together. It is not simply the total number that is significant, but also the number available per unit of time, i.e. the product of the point density and the speed of movement of the surface. Thus, low point populations can be partially compensated by higher  cylinder speeds. (This is not always possible, since the overall result may be deterioration in some quality parameters.)
It must also be kept in mind that the populations of the main cylinder and doffer clothing have to be adapted to each other. In general, the higher the point population, the better the carding effect – up to a certain optimum. Above that optimum, the positive influence becomes a negative one. This optimum is very dependent upon the material. Coarse fibers need fewer points, as they need more space in the card clothing; finer fibers must be processed with more points, since more fibers are present if the material throughput is the same. Point density is specified in terms of points per square inch or per square centimeter, and can be calculated as follows:

Base width (a1)

This influences the point density. The narrower the base, the greater the number of turns that can be wound on the cylinder and, correspondingly, the higher the point population.

Height of the clothing (h1)

The height of metallic clothing on the cylinder today varies between 2 mm and 3.8 mm. The height must be very uniform. It can also exert an influence on the population, since shorter teeth – for a given tooth carding angle – leave space for more teeth. Where shorter teeth are used, the fibers are less able to escape into the clothing during carding and better carding over the total surface is obtained. Clothing with smaller teeth is also less inclined to choke with dirt particles.

Tooth pitch (T)

The population is also determined by the tip-to-tip spacing.

Carding Angle ()

This is the most important angle of the tooth:

• the aggressiveness of the clothing; and
• the hold on the fibers

are determined by this parameter. The angle specifies the inclination of the leading face of the tooth to the vertical. It is described as positive (a, Fig. 124), negative (b) or neutral. The angle is neutral if the leading edge of the tooth lies in the vertical (0°). Clothing with negative angles is used only in the  licker-in, when processing some man-made fibers. Since the fibers are held less firmly by this form of tooth, they are transferred more easily to the cylinder and the clothing is less inclined to choke. Carding angles normally fall into the following ranges:     

licker-in	+5° to -10°
Cylinder	+12° to +27°
Doffer	+20° to +40°

The tooth point

Carding is performed at the tips of the teeth and the formation of the point is therefore important (Fig. 125). For optimum operating conditions the point should have a surface or land (b) at its upper end rather than a needle form. This land should be as small as possible. To provide retaining power, the land should terminate in a sharp edge (a) at the front. Unfortunately, during processing of material this edge becomes steadily more rounded; the tooth point must therefore be re-sharpened from time to time. Formation of a burr at the edge (a) must be avoided during re-sharpening. The tooth must only be ground down to a given depth, otherwise land (b) becomes too large and satisfactory carding is impossible – the clothing has to be replaced.

The base of the tooth

The base is broader than the point in order to give the tooth adequate strength, and also to hold the individual windings apart. Various forms can be distinguished (Fig. 126). In order to mount the wire, the normal profile ((a) for the licker-in, (b) for the cylinder) is either pressed into a groove milled into the surface of the licker-in (a) or is simply wound under high tension onto the plain cylindrical surface of the main cylinder (b). (d) represents a locked wire and (c) a chained wire. Both can be applied to a smooth surface on the licker-in; in this case a milled groove is no longer necessary.

Tooth hardness

In order to be able to process as much material as possible with one clothing, the tooth point must not wear away rapidly. Accordingly, a very hard point is needed, although it cannot be too hard because otherwise it tends to break off. On the other hand, to enable winding of the wire on a round body, the base must remain flexible. Each tooth therefore has to be hard at the tip and soft at the base. A modern tooth has hardness structures as shown in Fig. 127 (Graf).

Fig. 124 – Positive (a) and negative (b) carding angle

Fig. 125 – The thoot point

Fig. 126 – Formation of the tooth base and mounting on the drum

Fig. 127 – Metal hardness at various heights in the wire: A, hardness (A1 = Rockwell, A2 = Vickers); B, tooth height from the tip to the base

Clothing suggestions

Autoleveling equipment

Basic

As already mentioned, the general aim of manufacturing everywhere is to create durable, faultless products, i.e. primarily: not to correct errors but rather to prevent them, especially and as far as possible at the start of the process. In the spinning mill, the card is the effective start of the process, since the first intermediate product, the sliver, is produced here. A relatively high degree of evenness is required in this product. For various reasons, the card cannot always operate absolutely evenly, for example, owing to uneven material feed. Spinning mills are therefore forced to use autoleveling equipment under highly varying circumstances. Different principles for autoleveling can be selected depending upon the quality requirements and the operating conditions in the individual mill.

Classification

Fig. 128 – Rieter card leveling system

Irregularities can actually be compensated:

• in the material supply system;
• at the feed;
• at the delivery

as shown in Fig. 128 of the Rieter card leveling system.
The material supply should operate with the greatest possible degree of accuracy in any case, since this has a direct effect on sliver evenness. It is therefore not surprising that more and more card manufacturers offer the double-chute system with a degree of coarse regulation in the lower chute section. However, the main regulating position is the feed; adjusting the feed roller speed (5) usually performs autoleveling. Virtually all autoleveling devices exploit this possibility; adjustment of the delivery speed is hardly ever used. A distinction should also be drawn between:

• short-term leveling systems, regulating lengths of product from 10 - 12 cm (rarely used in carding);
• medium-term leveling systems, for lengths above about 3 m;
• long-term leveling, for lengths above about 20 m (maintaining count).

In addition, regulating can be performed by open-loop or closed-loop control systems (see  Technology of Short-staple Spinning).

The principle of short term leveling

Regulation at the delivery

 Fig. 129 – Short-term leveling by Trützschler

If this is used, it calls for a drafting arrangement before coiling.
In the open-loop control system illustrated in Fig. 129, a measuring point (2) is provided upstream from this drafting arrangement to sense the volume of the incoming sliver and transmit corresponding pulse signals to an electronic control unit. The control signal generated by this unit is passed to a regulating device that can be of various design, and which adapts the speed of the delivery drafting rollers to the measured sliver volume. If the measuring point is located downstream from the drafting arrangement, or if the delivery roller pair itself provides the measuring point, then the system is operating on the closed-loop control principle. If the open-loop principle is used in a short-term autoleveler, short lengths can certainly be made even, but it is not always possible to hold the average sliver count constant. On the other hand, closed-loop control is not suited for regulating short-wave variation because of the dead time inherent in the system. Finally, the drive to the delivery can present problems, since in this system the delivery speed must be continually varied, and in very small ranges. There are two possible applications for assemblies of this type, namely in processing comber noil and where card sliver is fed directly to the rotor spinning machine.

Autoleveling in the infeed

Rieter card leveling operates as medium-term to long-term leveling (closed-loop, produced by a proportional-integral regulator) and is performed by a microprocessor. In the feed of the card the feed measuring device records the fluctuations in the cross-section of the batt feed. The speed of the feed roller of the card is changed electronically so that these fluctuations in the cross-section are leveled out. The  chute is also included in the control loop. However, the filling level is not used for regulating the feed rollers in the chute but is considered as an additional control parameter. In the delivery of the card a pair of disc rollers scan the cross-section of the carded sliver as it emerges. These readings are compared electronically with the preselected set value. Deviations in the set value are corrected electronically by altering the speed of the feed roller in the card (Fig. 130).

Fig. 130 – Autoleveling with sensing at the feed roller

The principle of medium-term autoleveling

In former Zellweger equipment a medium-term autoleveler was provided as an addition to the long-term autoleveler. An optical measuring device (see Fig. 131) detects relative variations in the cross-section of the fiber layer on the main cylinder over the whole width of the cylinder. The measuring device is built into the protective cover above the doffer. The device measures reflection of infrared light from the fibers.

After comparison with the set value, a difference signal is generated and passed to an electronic regulating unit. This operates via a regulating drive to adjust the infeed speed of the card so that the depth of the fiber layer on the main cylinder is held constant.

Fig. 131 – Medium-term leveling (Zellweger, Uster)

The principle of long-term leveling

This is the most commonly used principle of card autoleveling and serves to keep the sliver count constant. Measuring is performed by a sensor in the delivery (at the delivery roller). The pulses derived in this way are processed electronically so that the speed of the infeed roller can be adapted to the delivered sliver weight via mechanical or electronic regulating devices (see Fig. 132).

Long-term autoleveling is an integral part of modern cards, and in any case used in production of carded yarns and in the rotor spinning mill.

Fig. 132 – Long-term leveling (Zellweger, Uster)

Measuring device

The active pneumatic system

In a normal card, a funnel is provided before the calender rollers (2, Fig. 133) in order to collect the web into a sliver. In Zellweger equipment, this funnel is developed to form a measuring device based on a simple physical principle. When fiber material enters the funnel (3), it carries along quite an amount of air held between the fibers. Owing to the continuous convergence of the funnel, air is squeezed out as the material passes through.
This generates air pressure in excess of atmospheric pressure, which is a function of the sliver cross-section if the sliver speed is kept constant. If all fiber characteristics also remain constant, this pressure is proportional to the volume. A lateral bore (5) in the funnel, and corresponding leads, transmit the pressure into the chamber of a pneumatic-electrical pressure transducer, using electrical induction to convert the pressure into an electrical signal.
Comparison of the signal with a set value enables pulses to be generated to control the electronic units in the regulator equipment. The advantage of active pneumatic measurement lies in the simplicity of the system, which does not require additional and/or sensitive moving parts. The disadvantage is that measurement is affected by the fiber count and hence count variation can lead to errors.

Fig. 133 – Active pneumatic measuring system (Zellweger, Uster)

 

The mechanical principle

Fig. 134 – Mechanical measuring system

This is the most common system for deriving a measured value. Usually, two material-forwarding rollers are used. One of these rollers must be movable (up and down) relative to the other. The relative movement, corresponding to the volume of the material passing through (a, Fig. 134) gives the instantaneous value required for the regulation operation.
The rollers can be smooth or grooved, b and c. The latter arrangement prevents lateral escape of the fibers and thus gives more precise measurement. However, it must be so designed and must operate in such a manner that the fibers are not crushed at the roller edges.
The advantage of the mechanical principle lies in its insensitivity to variations in the characteristics of the raw material, with the possible exception of bulk.

Maintenance

Stripping the clothing

If at all, metallic  clothing should not be cleaned out with a revolving brush, but rather with a hand scraper while the  cylinder is rotated manually (not by the motor drive). Rapidly rotating brushes create considerable metal-to-metal friction (brush on saw-tooth wire) and cause more wear on the clothing points than do the fibers. The life of the clothing is markedly reduced.

Burnishing the clothing

Burnishing should be avoided for reasons already explained under cleaning out. A single burnish wears down the teeth more than processing tens of thousands of kilograms of material. Nevertheless, burnishing sometimes becomes unavoidable, for example if the teeth were ground too intensively in re-sharpening and the raw material is released relatively poorly from the clothing.
Occasionally, this proves necessary on the doffer. In that case, however, burnishing must be carried out in the direction of the teeth and not against them. Rotation of the brush with a stationary cylinder is to be avoided. Cleaning out with a hand scraper is often enough, without burnishing.

Grinding the clothing

Intervals between grinding

The operating life of clothing is quoted in terms of the total throughput of material. For the cylinder it normally lies between 300 000 and 600 000 kg, but it can be higher in some circumstances.

Such quantities of material represent a huge number of fibers, which have to be processed by the individual tooth points. Processing therefore considerably wears down the teeth – they become rounded at the top and lose their aggressiveness. The direct result is a continuous increase in the nep content of the sliver (b).

The points must therefore be sharpened from time to time, in order to give a better shape to the edges by grinding them. Each new grinding operation reduces the number of neps, but the level never returns to that prior to the previous grinding. As Fig. 135 illustrates, the lower nep limit increases noticeably from “a” to “b”.

The deterioration in quality from one grinding interval to the next arises from the fact that the teeth are ground down to successively lower heights, the lands at the teeth points become steadily larger, and softer metal layers are gradually exposed. The following grinding intervals are currently in use: 

	Cylinder	Doffer
First grinding after [kg]	80 000 - 150 000	80 000 - 150 000
Each additional grinding after [kg]	80 000 - 120 000	80 000 - 120 000

The interval is best selected depending on the mills nep limit (c). Since the doffer clothing works much less than that of the cylinder, it should be ground only half as often, or even less frequently, except when man-made fibers are being processed: grinding should then be carried out more often but more lightly. The clothing on the licker-in should not be ground; it should be renewed after a throughput of 100 000 - 200 000 kg.

Fig. 135 – Increase in neps between grinding periods: A, number of neps in the web; B, grinding interval; b, general rise of the lower nep level; c, mills limit for neps

Grinding depth

Fig. 136 – Correct grinding of the tooth point (a) and incorrect (b, c)

Grinding is carried out with the  cylinder rotating in its normal direction at normal speed, so that the grinding roller moves with (not against) the teeth of the clothing. The grinding depth is such that a plane surface with a sharp edge is produced at the point of the tooth (a, Fig. 136). Satisfactory carding will not be achieved if too little material is ground away so that the front edge stays rounded (b), or if the grinding operation is too harsh (too much pressure on the grinding roller) so that a burr is formed at the tooth edge (c).

Grinding the flat

There are two possibilities, namely grinding in the card by installing the grinding roller on the machine for a short time under normal production conditions, or grinding the flats in a special grinding machine after removing them from the card. This machine comprises mainly a full-width grinding roller with moveable carriages mounted over it to receive 1 - 4  flats. During grinding, the carriages move the flats repeatedly back and forth over the grinding roller until they have been ground down to the precisely set height. Each of these two methods has its advantages and disadvantages. Grinding on the card is more efficient and demands significantly less effort; grinding in a flat grinding machine is somewhat more exact. It may prove advantageous to grind as often as possible on the card, but occasionally to put the flats on a flat grinding machine to level up.

The grinding tools

Fig. 137 – The full-width grinding roller

Fig. 138 – The traversing grinding disc

The full-width grinding roller

This has a drum with an abrasive sheet or, more generally nowadays, a coating of carborundum abrasive (Al2O3). The drum can be driven externally by a disc or internally by a motor within the drum. In the latter case, the tubular body of the roll forms the rotor. The grinding roller, in the form of the abrasive-coated drum, extends over the full width of the machine. Thus, the full width of the clothing on the operating elements of the card is treated simultaneously, which is very economical. On the other hand, if maintenance is poor, the drum can bend in the middle while revolving on the card. If this happens, the central portions of the main cylinder and doffer may be ground more than the edge zones. With modern grinding rollers the danger of this is minimal.

The traversing grinding disc

The grinding head (S), in the form of an abrasive disc 90 mm wide, can slide and is seated on a guide tube. It is driven back and forth over the clothing by a worm spindle in the interior of the tube. At any time it treats only a small portion of the total surface of the cylinder. Grinding takes far longer than with a full-width roller, but there is practically no danger of bending in the middle. In some equipment, the back-and-forth movement is not effected by a worm spindle but by specially driven belts. Drive is by individual motors.

Highperformence maintenance systems

Requirements

Card maintenance is a very demanding, uneconomical operation. Considerable effort is required to keep conventional cards running, and it is even greater for high-performance cards. It was therefore inevitable for manufacturers to equip their new types of cards with maintenance systems of different designs (depending on the manufacturer) that:

• are modern;
• ergonomic;
• save time and effort; and
• relieve personnel.

Rieter’s solution (on the modular design principle) will be explained briefly by way of an example within next chapters.

Easy exchange of modules

To improve the accessibility and exchangeability of all parts of the card, Rieter designed its card on modular principles. The only fixed parts are the feed chute and the main cylinder; all other modules can be removed. As a result,

• cleaning;
• setting;
• wire mounting;
• exchanging (licker-in, flats);

can be performed easily by taking the modules out of the machine, e.g.:

• the licker-in module (Fig. 140);
• the flat assembly (Fig. 141);
• the doffer module (Fig. 142).

These systems not only facilitate maintenance, they also improve quality, as shown by Rieter’s  IGS device.

Fig. 139 – The modules of the C 60 card

Fig. 140 – Licker-in module

Fig. 141 – Flat assembly

Fig. 142 – Doffer module

Rieter’s automatic grinding system (IGS)

IGS stands for Integrated Grinding System.

With IGS-classic a grindstone is moved over the  cylinder  clothing by the automatic control during production. This procedure takes place 400 times during the expected service life of the clothing, not every 80 - 100 tons, as is the case with laborintensive manual grinding. There is absolutely no risk of damage to the clothing due to improper handling of the grinding system when using IGS-classic. The service life of the cylinder clothing has been prolonged by over 30% thanks to IGS-classic. In addition, the savings made on maintenance are obvious. Also there are no downtimes where the machine is idle while manual grinding takes place.

The IGS-classic cylinder grinding system (Fig. 143)

consists of an aluminum profile as carrier and a linear-directed grindstone stabilized by spring pressure. In the parked position (right-hand side of the machine) the flat belt is pushed upwards by clamp profiles so that no dust or particles of fibers can get inside the profile. The parameters necessary for the grinding operation can be entered on the card. The program calculates the grinding schedule, distributing the fixed grinding cycles optimally over the lifetime of the cylinder clothing (270 and/or 400, to and fro = 1 cycle ). The time between cycles is longer at the beginning of the schedule than at the end. On the way to the left-hand side of the machine the grindstone is lowered. Grinding occurs when the grindstone moves from the left to the right-hand side of the machine. This means a sharp wire all the time and thus constant quality (Fig. 144).

 Fig. 143 – IGS-classic

Fig. 144 – Grinding without (left) and with IGS (right)

IGS-top integrated grinding system

A grinding brush is permanently installed behind the flat cleaning device (Fig. 145). Under the grinding brush and the one flat in contact with this brush a spring is provided that presses the flat bar against the brush. The flats are thus raised one by one and ground at this point. With the IGS grinding device grinding takes place for more than 100 cycles during the lifetime of the clothing.

Fig. 145 – IGS-top grinding system

The sharp edge makes all the difference

IGS-classic and  IGS-top feature considerably more frequent but less aggressive grinding than takes place in manual clothing maintenance. This prolongs the service life of the clothing, and at the same time the tips always stay sharp. The success of this approach is reflected in the card sliver through high consistency in purity and low nep content.

Fig. 146 – Graph of quality improvement using the IGS system

Settings

Basics

The card comprises a large number of individual parts that guide the material, open it and clean it. Optimal, gentle treatment is only possible if these parts have the correct form and the right relative positions and spacings. The socalled settings of the card are of the greatest importance. For example, too narrow spacing of the operating elements leads to fiber damage (loss of breaking strength); too wide a setting produces more neps.

 Table of settings shows the most common settings for conventional cards. The  licker-in on these conventional cards calls for special treatment: the licker-in has to be removed and replaced by a gauge in the form of a pendulum (Fig. 147). The radius of the gauge has to correspond exactly to that of the licker-in. It should be realized that the settings vary from one make of machine to another – the setting instructions of the individual manufacturer must be followed. This applies especially to modern, high-performance cards. That is why no instructions for these cards can be given here.

Fig. 147 – Template for setting the licker-in grid

Table of settings

For conventional cards (see Fig. 148)

Fig. 148 – Setting positions on the card

Auxiliary equipment

Dust extraction on high-performance cards

More and more countries are enacting rigorous regulations governing permissible dust concentrations in the atmospheres of workrooms. The card releases enormous quantities of dust and it is essential to ensure comprehensive and immediate removal of this waste. For this purpose, modern cards are fully enclosed and subjected to permanent partial vacuum, so that dust and fly can no longer escape from the machine. Within the casing, suction removal systems are provided at some or all of the following positions:

• in the infeed region;
• at the entrance to the flats;
• within the flats;
• at the exit from the flats;
• between the main cylinder and the doffer;
• at the web detaching point;
• beneath the main cylinder;
• in the coiler.

The suction removal systems operate continuously to maintain constant conditions on the card. In modern plants the fly- and dust-laden air passes to the air-conditioning equipment. The quantity of suction air per card lies in the range from about 4 000 to 5 000 m³/h.

Waste disposal

The card eliminates on an average 4% of waste. In a carding room processing 500 kg/h of material, about 500 kg of waste is produced per day in three-shift operation.

The waste falls mainly into two categories:

• droppings from below the licker-in;
• flats and filter strippings.

Filter waste can be removed manually, but nowadays the attendants cannot be asked to perform manual removal of licker-in droppings. Modern cards are therefore fitted with suction waste-removal systems. These can operate either continuously or intermittently. An intermittent system, for example, empties the waste chambers under the lickers-in – individually in succession or simultaneously for two cards; in a second cycle, the waste chambers for flat stripping and filters are emptied. It continues with the next two cards a.s.o. The waste material is passed via piping to central bale presses (described in chapter  Blowroom). Handling of dirty material is therefore confined to removal of the pressed bales.

Technical data of three high performance cards

References

[1] Tamas, H. Optimal use of preparation machines and effects on yarn quality. Melliand Textilberichte 9/77; 701 - 705.
[2] Artzt, P., Schenek, A. and Al Ali, R. Methods of achieving better exploitation of raw material in the cotton spinning mill. Textilpraxis International 5/80; 530 - 537.
[3] Siersch, E. Ways of improving raw material utilization in cotton prespinning. International Textile Bulletin 4/81; 413 - 420.
[4] Mandl, G. Control of dust in the cotton spinning mill. Melliand Textilberichte 4/80; 305 - 308.
[5] Binder, R. Preparation and recycling of cotton waste in the spinning mill. Swiss Association of Textile Specialists (SV T), instruction course.
[6] Gilhaus, K. F. Technological reserves in the cotton spinning mill. Textilbetrieb 12/82; 25 - 28.
[7] Wirth, W. The influence of opening of cotton flocks on cleaning in the blowroom process. Textilpraxis International 2/66.
[8] Frey, M. Recycling of spinning waste and influence on yarn quality due to re-blending. Mittex 9/82.
[9] Abt, C. and Topf, W. High-performance cards and quality of combed cotton yarns. Melliand Textilberichte 4/84.
[10] Schmolke, K. H. and Schneider, U. Advances in carding of cotton from the viewpoint of the manufacturer of card clothing. Textilpraxis International 10/82; 1021 - 1025.
[11] Artzt, P., Abt, C. and Maidel, H. Carding of fine titer polyester fibers. Textilpraxis International 9/84.
[12] Wolf, B. Metallic clothing in operation in the mill. International Textile Bulletin 11/74.