As nowadays good winding is the mirror of spinning mills, it is necessary that this process is understood very well by all the personnel handling the department. Yarn winding can thus be viewed as simply being a packaging process, forming a link between the last few elements of yarn manufacturing and the first element of fabric manufacturing process. Improper utilisation of the features of the winding machine can not only cost heavily to the spinning mills, but it can also lead to loss of good customers permanently. Quality of the output material largely depends on the quality of the feed material in any process. This article briefly encompasses the quality requirements of ring cop in terms of yarn as well as package, which is to be fed to cone winding.

1. To remove objectionable faults from yarn, and

2. To build packages of dimensions compatible with requirements of the subsequent processes, which are equally important both for high speed warping and shuttleless weaving.

In today’s competitive market, the customers are becoming more and more sensitive with regard to quality. So, every parameter regarding yarn and package quality is of prime importance and must be met out in a close tolerance. To meet both qualitative and quantitative demands, one has to exploit all the available features of winding machine in a judicious manner. The quality criteria of a spun yarn to be efficiently converted into a woven or knitted cloth, and its customer acceptability in terms of the cloth into which it is woven or knitted. The control of the quality characteristics of a yarn during winding can be done by off-line or on-line testing.

Flow Chart: 1

New generation of high speed looms and knitting machines places increasingly more stringent demands on the quality and processability of the yarn. Companies, which are best able to respond to the challenge of economically improving the quality of the yarn to effectively meet the requirements of high-speed fabric producing machines are going to be successful in a competitive market.

The type of defects that result in yarn breakage during cone winding and contribution of each category of fault as a percentage of total faults are summarised as shown in Table 1.

The spun-in fly is originated from the spinning frame and the various causes for this could be listed as below:

· Improper maintenance of spinning frame

· Higher short fibre content in the mixing

· Low humidity level in the department

· Spinning of coarse count in the adjacent frame

Irregularity can adversely affect many of the properties of textile materials. There is deterioration in terms of U% & IPI values and hairiness from ring frame bobbin to cone due to abrasion of yarn with various contact points in yarn path. The average deterioration can be as shown in Table 2:

Thus, a yarn with higher unevenness directly affects the costs of production, the likelihood of rejection of a product and the profit. Keeping the deterioration in mind, one has to decide winding parameters, eg, winding speed, auto speed, tension, etc in such a manner that the final yarn would attain the satisfactory quality.

A bobbin change occurs when yarn on the bobbin is fully exhausted during winding. But if a bobbin is changed with yarn still left on it, we call it ‘Rejected Bobbin’. The quantity of yarn on the bobbin may vary from full bobbin to only few layers of yarn.

The various reasons of bobbin rejection are as follows:

· Long Tail End

· Kirchi/Lapetta

· Deshaped Bobbin

· Overfilled Bobbin

· Bottom Spoiled Bobbin

· Ring Cut Bobbin

· Soft Bobbin

· Sick Bobbin

· Presence of under-winding and back-winding while feeding the bobbins in the magazine leads to rejection.

· Top bunch position is lower wrt bobbin tip.

· Blowing device does not come down to concentrate blow at the bobbin tip.

· Very few numbers of coils at the bobbin tip.

· Removal of top bunch due to fault in cutter at the bobbin preparatory or any other reason.

· Very few numbers of coils at the top bunch.

· High degree of objectionable fault

· Count variation

·High Hairiness Bobbin

Whenever there is a count change in ring frame, the cop quality should be checked. Proper quality of cop ensures higher winding efficiency. The cop quality is checked as per the following parameters:

 2. Cop content:
Depending on the spindle lift and ring diameter, the cop content (in gms) should be as follows:

Table 4

3. Diameter of the Cop:
The ‘Actual cop diameter’ must be checked against ‘Standard cop diameter’. The standard cop diameter depends on the ring diameter.
Standard Cop Diameter = Ring Diameter – 3mm.


4. Back Winding:
The number of back winding coils should be around 1.5 to 2.5 and the maximum length of back winding should not be more than 80cms.

5. Under Winding:
The number of under winding coils should be around 2 to 3 and the maximum length of back winding should not be more than 20cm. As the under winding and back winding increases, more time is wasted to open them up before feeding in the magazine and also hard waste is increased.

6. Top Clearance:
The clearance from bobbin tip to yarn body of a full cop should be approx 10 mm. If the top clearance is too less, it may cause slough off at the start of the bobbin unwinding

7. Bottom Clearance:
The clearance from bobbin bottom to yarn body of should be approx. 10mm. If the bottom clearance is too less, it may cause bottom spoiled bobbin.

8. Yarn length per chase:
The length of yarn per chase should be around 3.5 to 5.5 m. If the length is too long, it may lead to slough of during high speed unwinding.

9. Bobbin hardness:
The bobbin hardness should be around 50° to 55°. Soft bobbins results slough off.
Besides the above mentioned points, the cops should be also checked for long tail end, deshaped bobbin, kirchi & lapetta, ring cut, overfilled and bottom spoiled bobbin to ensure high production efficiency in winding.

Conclusion

Due to the ever-increasing emphasis on better quality of yarn for the competitive market and process performance, the normal parameters of yarn tenacity, unevenness and imperfections are not adequate to completely define today’s quality. Besides the above mentioned traditional parameters, so many factors influence the performance of the yarn in the subsequent process such as process parameters in ring spinning & cone winding, work procedures in ring spinning & cone winding and ambient conditions. So to attain the expected quality for any applications such as weaving or knitting, one should focus mainly on the fault free feed material preparation because it contributes more than any other factor. Best winding capabilities can be achieved through best bobbin quality.

References
1. Schlafhorst Autoconer 338 Manual.
2. Yarn Winding –Edited by P K Banerjee & R Alagirusamy, NCUTE Publication.
3. Allan Ormerod & Walter S.Sondhelm: Weaving --Technology and Operations.
4.W.Klein: The Technology of Short Staple Spinning.

Note: For detailed version of this article please refer the print version of The Indian Textile Journal May 2008 issue.

R Senthil Kumar
Department of Textile Technology,
Indian Institute of Technology,
New Delhi 110 016.
Email: sen29iit@yahoo.co.in