Long thin places which have lengths of approximately 8 cm and longer and cross-section if about 30 to 75% of average yarn diameter is relatively seldom occurring in short-staple yarn. The long thin places could result in short-serious cloth defects like streaks, variation in dye pick up etc. Thus control of long thin places needs no further emphasis. This type of fault is produced mainly by separation of sliver or roving in the process prior to spinning. This paper deals with various control measures that are required in different departments of the mill and raw material management to minimize long thin places.
Carding is the heart of the spinning & rightly so as all the quality related settings are primarily controlled in carding only.
Web falling in cards is a source of long thin places. The major cause for this is loading of cylinder under casing. Frequent air cleaning of under casing and petrol washing during full setting for cotton and tinted synthetic material would help to avoid loading. The causes of loading would be the condition of wire points, too high or too low tension draft, static generation in PV and PC counts, etc.
Missing slivers in drawing process can also be the reason for very long thin places in the yarn. The effectiveness of sliver stop motions should be checked regularly. The piecing practice of tenters also needs attention.
Rubbing of slivers in drawing can also be a source .The mills can increase the gap between cans and slivers rubbing against the inner surface of cans by suitable changing coiler speed change wheel/can bottom change wheel.
Reducing creel tension draft and web tension draft in draw frames, maintaining and smooth rotation of creel rollers would also help in the control.
The condition of trumpets should be good.
Sliver guides at feed should be adjusted in such a way that the slivers run into the drafting system side by side but not crossing over each other.
Too low top roller pressure would also cause long thin and thick faults.
However, with the advent of very sensitive auto levelers the faults from Carding & Drawing frames may be nullified.
Excessive roving stretch due to improper function of builder mechanism and use of empty roving bobbins with wide variation in diameter are cause for long thin places. Sliver stretch in the creel in speed frames due to too higher creel draft has to be avoided. Creel tension draft should be as minimum as possible; at the same time ensuring no sagging of drawing sliver. To high break draft in speed frames and inappropriate selection of condensers are other vital causes for long thin places.
The method of feeding slivers in fly frames and condition of cans are important. Slivers crossing each other, damaged edges of drawing sliver cans etc. would disturb the free withdrawal of slivers from cans.
Roller lapping in fly frames could be a reason for long thin places. Excessive top arm pressure would lead to roller lapping and would result in to long thin places.
Creel stretch in ring frames due to the obstruction of bobbin holders, vibration of bobbins in creel, jerky movement of ring rails, broken roving guides etc. are a few points to be looked into in ring frames for the control of long thin places.
Optimum back-zone settings with a reduced break drafts helps to produce yarns with less number of thick/thin places and slubs. Studies have shown that there is a tendency for the long thick and thin places to increase when the setting is made wider. Hence, it is suggested to conduct controlled trials to arrive at optimum settings.
The author is AVP & Head Textile Research & Application Development Centre (TRADC)