Carding Technological Functions, Carding Opening the fiber tufts, Carding Neps reduction,

 

CARDING TECHNOLOGICAL FUNCTIONS

 The complex functions of the card will be described in detail in the following sections.

    Opening the fiber tufts

 Opening the fiber tufts into their individual fibers is the primary purpose of the card. As a result of the actions of the ginning process, the cleaning steps in the blow room and the fans used to transport fibers between machines, entangled and knotted fiber bundles are created. These bundles are frequently referred to as – horseshoes, starfish, buttons, slubs and neps.

 If these bundles are not eliminated, the spinning process will be limited to coarse counts and the yarn quality will be low.

     Neps reduction

 A distinction is made between two basic types of neps:

• Fiber neps: small knots of entangled fibers, often with immature fibers at their core
•  Husk or seed coat neps: consist of tangled fibers attached to a fragment of seed coat.

 In general, cotton neps are associated with fine fibers, but in particular with immature low micronaire cotton. The susceptibility to neps is typically:

 micronaire cotton. The susceptibility to neps is typically:

With micronaire 5.0  = 1

With micronaire 4.5 = 5

With micronaire 2.5 = 40

Investigations of causes of neps in general showed that:

60% due to immature fibers, 35% due to normal fibers, 5% due to seed coat fragments.  

However it should be pointed out that certain cotton varieties and growing regions produce a cotton seed that has a relatively fragile coat. The coat breaks off with the cotton fiber during the ginning operation.

  Owing to the design of blowroom machinery and the nature of fibers, the nep count progressively increases up to the card and is then reduced considerably. During the rest of the preparation processes the nep count increases slightly with the exception of the combing process in which again the neps are removed.

  It is normal for the nep count in the card matt to be double the count in the raw cotton. The card nep removal rate can be between 80 and 90 percent of the neps in the matt, i.e.

 Very good / medium / low grade cotton Manual count AFIS – VFM

•  Neps in raw cotton 10/30  /50  per 100 mg
•  Neps in card matt-15/40  /80  per 100 mg
•  Neps in card sliver 4/9  /16  per 100 mg

A decisive factor is not only the number of neps but also the size. Small neps are

 often not visible in rotor yarn or in coarse ring yarns, but are of major concern in

 fine-combed yarns. Small neps are difficult to remove even by the comber.

 Neps may be reduced in two ways: by removing them or by opening them. It has demonstrated that 75% of all neps can be opened, but normally it is no more than 60%.

 The majority of the unopened neps either passes into the sliver or is removed by the flats. A small percentage is removed in the waste.

 Opening / removing of neps at the card is primarily accomplished by:

 •   Close settings of the clothing,

 •   Sharp clothing

 •   Low doffer speeds

 •   Light sliver weight

  Increasing production rate increases the nep level in the sliver. Reducing production rate reduces the nep level.

 Every plant should establish upper tolerable nep levels. When these levels are approached the cylinder and flats should be re-ground.

 All points on the cylinder should be sharpened,

 90% of the flat points should be touched up.

 The frequency between grindings is dependent upon the amount of material processed, the abrasive nature of the fiber dust or finish and the requirements of the end product.

    Separating short fibers by using flats.

 The mean staple length of the fibers in the flat strips is much shorter than that of the delivered card sliver. That there are many more short fibers in the flat strips is explained by the fact that the cylinder easily holds the longer fibers that pass into the sliver. The short fibers tend to float into the flats and some become pressed into the clothing and are ultimately stripped. This can possibly be seen as performing a valuable function of the card, i.e. eliminating short fibers. This is only partially correct:

 •   Approximately 50% of the fibers in the flats are short fibers,

 •   The short fiber removed by the flats is 0.5 to 1.0% of the total fiber processed.

 •   The carding action breaks some fibers and creates short fibers that amount to as much if not more than the flats remove.

 •   Driving the flats at a higher speed can increase the amount of flat strips. While this increases the quantity of the flat strips, considerably more good fibers are removed. Each spinning plant has to determine the value of increasing the rate of flat strip removal.

 •   NOTE: The primary functions of the flats are to remove and open up neps plus eliminate foreign matter.

Separating short fiber by suction

High pressure points are generated by the various rotating surfaces. When these pressure zones are released by applying a slight suction there is a tendency for the dust and short fibers to be withdrawn.

 Suction plenums are located throughout the card, some primarily for dust / air control and others to perform a cleaning function.

 •   Flat strips can be in the range of 1 to 2% of the fiber processed.

•   Suction over the licker-in and at the licker-in / cylinder transfer zone remove dust and fly,

 •   Suction at the TREX and TREXplus is applied to remove trash and short fibers. The design, incorporating the fiber-guiding segment, minimizes the loss of good fiber while allowing the trash and very short fiber to be extracted.

 •   Suction inside the flats encourages the collection of dust and fly released at the cylinder / flats pressure zone.

 •   At the cylinder / doffer zone a suction duct is provided to extract short fibers, fiber fragments and dust.

 The suction levels have to be correctly controlled to enable the devices such as the TREX and TREXplus to perform their functions.