Abstract

Neps are "blemishes" in the yarn. They adverselyaffect the appearance of yarn and fabrics. Sometimes immature neps appear as "Specks"in certain shades after dyeing. Even mercerizing cannot overcome such "specks"in certain shades. Basically, quality of cotton has great influence onoccurrence of neps in yarn. In the present article, the influence of blendingtechnique on neps have been studied by taking trials on the shop floor. Processparameters specially in mixing, blow room, cards, combing operations influencethe occurrences of such neps in yarn. In the present article it is observedthat neps are influenced by the method by which mixing is prepared and howmaterial is fed to the blow room with chute feed system.

Keywords: Blow Room, Draw frame, Blending, Neps, Mill Practices

1. Introduction

Every stage of processing influences the occurrence of nepin yarn as under:

• Blow Room increases the neps.
• Carding reduces the neps.
• Combing reduces the neps.
• Drawing increases the neps.
• Winding increases the neps on wound yarn compared to ring spun yarn.

In competitive environment, mill management has to play animportant role in "cost reduction". Nowadays some technologist areadvocating for blending of lap bits with polyester fiber at mixing stage, so asto reduce cost of conversion and product. Blending at blow room, or at drawinghas it's own merit and demerit.

1.1 Blending

There are different practices of blending of cotton withpolyester as under:

1.1.1 Stock Blending isadopted for blending in the blow room either at the beginning or atintermediate stage.

1.1.2 Lap Blending isused for blending at breaker scutcher and thus demands the use of double blowroom process.

1.1.3 Sliver blending isdone at draw frame stage, by feeding the required number of sliver at breakerdraw frame according to the blend ratio.

1.1.4 Fleece blending isaccomplished on blending draw frame specifically designed for this purpose.

1.1.5 The blending of stock/ comber sliver blending is done at blow room by adding combed cotton sliverin the required proportion to the unprocessed polyester stock.

The major advantages of comber sliver blending are:

• Produces a very intimate blend.
• Trouble free running and higher productivity at the cards.
• Less yarn imperfection due to better fiber individualization because of reprocessing of cotton component.
• Reduced number of draw frame passage.
• Lower end breaks due to fewer slubs.
• Better uniformity of dyeing due to more intimate blend.

Though there are disadvantages in this method like requirement of additional blow room and carding capacity, extra space in blow room for stock mixing and slightly higher waste in blow room and carding, this method is preferred owing to its homogeneity of blending and for dyed piece good varieties.

1.1.6 General Considerations of blending

• There are basically two stages in the spinning sequence where fiber blending is normally effected i.e. at blow room and draw frame.
• As a general rule, it can be stated that the earlier the fibres are blended, the better is the blending. Other things remaining same, the blow room blending will therefore give a more intimate, homogeneous blend and blend irregularity is less.
• Earlier the mills were invariably using combed cotton sliver for blending either at blow room or at drawing frame. Subsequently under cost reduction program, mills resorted to use carded sliver for blending.

2. Practices followed by mills

The present practices followed by mills for PC blend are as under:

2.1 Practice 1

Process cotton up to draw frames, take fleece at draw frame instead of sliver and add at blow room to the polyester according to the blend ratio required.

2.2 Practice 2

Alternatively, some mills are processing cotton up to card and take out fleece and this card fleece of cotton is added to polyester fiber as per the required blend.

2.3 Practice 3

Another practice is to process cotton fiber up to card and this card sliver itself is added to the polyester fiber at blow room as per requirement.

3. Methodology

Controlled studies were conducted to compare the properties of yarn produced by:

1. Adding drawing fleece of cotton to the polyester in the blow room.
2. Adding toppled carded sliver of cotton to the polyester as per blend requirement to the blow room.

Under this experiment two separate sandwich mixings were prepared as under:

• By adding carded and drawn cotton fleece with polyester (sample No.1)
• Another by adding carded toppled cotton sliver to polyester by sandwiching.
• Polyester and cotton lots were kept same while taking controlled trials, so that effect of fibre properties is eliminated.

4. Results

The results are tabulated below:

It is observed from the test result that:

1. There is considerable reduction in thick place and thin place in the yarn when toppled card sliver is added to the polyester for blending as compared to using drawing fleece of cotton to the polyester for blending. This trend was noticed in all the three trials undertaken.

2. There is significant reduction in neps in yarn sample with toppled card sliver (Sample No.2) against the fleece sample. The main reason for this reduction is due to the fact that the fleece cotton which is in open and loose form, curls while passing through pipeline along with air. This may be resulting in formation of small beads that is not removed at card and show up as neps in the yarn.

3. Yarn sample with card sliver blending shows lower U %. Thus it can be observed that the main yarn property that is influenced by blending technique is only neps.

4. This indicates that the way by which mixing is prepared and fed to chute feed system has critical bearing on carding quality and imperfections. This shows that there could be optimum size of tufts which should be fed to blow room chute-feed arrangement.

The above study has helped the mills in curtailing extra drawing passage and related labor and power cost.

Such practice of blending is also adapted by fibre dyed PV manufacturers of yarn wherein dyed viscose fibre is first carded and this carded sliver is broken by hand into pieces. These broken pieces are mixed with opened polyester.

5. Conclusion

From the above study, it can be inferred that there could be optimum size of tuft for feeding to blow room even in case of polyester blend varieties to obtain better results. For 100% cotton yarn spinning, use of Blendomat is in practice, while such machine is not available for PCIPV blended yarn manufacturing.

Acknowledgement

Authors are thankful to Mr. B. Nataraja of Technical Division, NTC (WR) and to Mr. Dhanpal, Mr. Singh and management of Podar mills for the help in conducting the above study.

Reference

• Spinning of manmade fibres (K.R. Salhotra) - TAl Publication.

About the Authors

The authors are Manager (Tech/R&D) NTC Ltd. (WR), Mumbai and Chief General Manager (T/P&D) NTC Ltd. (WR) Mumbai; respectively.

The article was originally published in "Journal of the Textile Association"; Jan -Feb: 2009 Vol 69, No. 5