FACTORS INFLUENCING YARN QUALITY DURING HIGH SPEED WINDING

FACTORS INFLUENCING  YARN QUALITY DURING HIGH SPEED WINDING:

Textile materials are known for their visco-elastic behaviour.  They loose strength and elasticity when subjected to stresses and strains, the loss being dependent on the amount of stress and the duration for which it is applied.  During winding the combination of operational conditions such as yarn speed, yarn tension and humidity levels influence the stresses and strains put on the yarn as well as the degree of abrasion of the yarn with different parts of the machine.  This in turn, may affect yarn properties like imperfections, hairiness and tenacity.  The effect of process variables during winding on the  yarn quality is discussed in the following sections:-

1) High winding speed

2) Pulling tension on the yarn

3) Abrasion of the yarn with the rough surface

4) Yarn quality on imperfection rise

5) Yarn quality during winding

6) Humidity condition

High Winding Speed

High winding speed affects adversely both yarn imperfections and hairiness.  Studies  conducted by SITRA  in some popular counts have shown that when winding speed is increased from 1000-1400 mpm the yarn imperfections increase steeply by 40-50% in combed counts and 60-85% in carded counts.   In the case of blended yarns, the increase is somewhat lower at 35-45% possibly due to the lower level of basic yarn imperfections and hairiness.  As far as yarn hairiness is concerned an increase of 20-30% for combed counts and 25-45% for carded counts is generally observed.

Pulling tension on the yarn

Winding tension has a profound effect on yarn imperfections, higher tension leading to an accelerating increase in imperfections. 

In some of the modern winding machines tension control attachments are provided with a view to maintain uniform yarn tension throughout the winding process and thereby achieve higher speed.  With the tension controller the increase in imperfections after winding may be expected to be low.  On the other hand, the yarn hairiness may go up due to additional surface contact.  Studies in a few counts have shown that for the same level of yarn imperfections use of tension controller helps to increase winding speed by about 35%.  If hairiness is also taken into account, the achievable speed increase is lower at about 10%.

Abrasion of the yarn with rough surface

Due to abrasion of the yarn with metallic the parts of the winding  machine, the imperfections in ring yarn increase and the surface hairs in the ring yarn get rolled up together and   tend  to form fibre clustures and nep like defects.  In addition to abrasion, there is also directional effect during winding.  i.e. during spinning, the yarn fibrous mass is twisted and wound in one direction.  But during winding the yarn unwinds from the bobbin opposite to the direction in which it is wound on the bobbins.  Due to this directional effects some redistribution of the fibres on the yarn surface may takes place which can be expected to influence  yarn quality.

Yarn quality on imperfections rise

The extent of increase in yarn imperfections due to winding is also found to be influenced by the level of imperfections and yarn hairiness at the bobbin stage.  Ring yarns with the higher level of imperfections and hairiness cause higher percentage increase in imperfections in cone yarn.  Studies conducted by SITRA have shown that the increase in yarn imperfections during winding was greater both in absolute quantity and on a relative ring for yarns having higher imperfections.   For every unit increase in basic yarn imperfections there is an increase of 1.5 to 2 imperfection in the wound yarn.  This could be probably due to redistribution of fibres in the imperfection zone.  Hairiness is another parameter which is a significant influence of increase in imperfections during winding.  For every 1% increase in ring yarn hairiness the imperfections in winding may increase to 1.5%. 

Yarn quality during winding

In Autowinders as compared to ring yarn there is a fairly large level of yarn quality deterioration particularly in the case of imperfections and hairiness.  The various yarn imperfections increased by 15-20% in medium counts and by 40-50% in fine counts.  The higher rate of increase in finer counts may be largely due to greater stretch during winding in finer yarns which have lower single yarn strength.  The level of hairiness generally increases by about 25-50% in the count range 20s to 80s.

Thus ring yarns having fewer imperfections, less number of protruding hairs, optimum choice of winding speed and the tension and less number of mechanical parts and proper humidity condition in the winding department are some of the essential pre-requisites to control the imperfections in  yarns.

Reference: 1) Quality Control in Spinning Published by SITRA 1999

                  2) Yarn Quality Improvement with ‘SITRA CON-HAIR’ system

                       in manual cone winder, Volume 46, July 2001