Polyester Fibre manufacturing process - 4
Crimp take up is % difference between relaxed length and straightened length of fibre in fibre stage. Normally this difference is around 18 to 20%. If the difference is much smaller, then it means the crimps are shallow and would have lower cohesion.
After the tow is crimped , the crimps are set by passing tow through a hot air chamber.
If crimp per inch is low, then that could be due to lower stuffer box pressure, but if crimp stability and/or crimp take up is low, it means the steam supply to crimper steam box is low.
Undrawn fibre: As the draw line, 1.6 to 3.0 million filaments are drawn or pulled, if a filament had a break at spinning and this is fed as a trailing end to the drawing, then that end cannot be drawn fully, and causes plasticises and fused fibres.
Undrawn fibres are generated if the draw point is not uniform i.e not in a straight line.
Plasticised fibre: When drawline is running and if some filaments breaks then these broken filaments wrap themselves around a rotating cylinder, since most of these cylinders are steam heated, the wrapped portion solidifes. The operator then cuts out the solid sheet and throws it away as waste but then usually picks up the plastic end and uses it to thread the material and so a small piece of plastic material goes into the cutter and falls into the baler.
Tenacity / Dye ability: Both these properties are controlled by acutal draw ratio and annealer temperature. Draw ratio does not change in running, but annealer temperature can fall due to problem of condensate water removal. Most drawlines have temperature indicators - but then some buttons have to be pressed to see the temperatures so if the annealer temperature falls, tenaciy will fall and dye ability will increase which could lead to a change in merge.
PROBLEMS FACED IN CUTTING / BALING:
Nail Head / Tip Fusion: In the cutting process, a highly tensioned tow is first laid over sharp blades and the pressed down by a Pressure Roll, resulting in filaments being cut. However if some blades become blunt, then the pressing of tow on to those blades creates high temperature and so tips of neighbouring fibres stick to each other and so separating this cluster becomes impossible. If it is not getting removed in Lickerin it will go into the yarn and cause a yarn fault. The tip fusion occurs when the blade is fully blunt. If the blade is not very sharp, it does not give a straight edge, there could be some rounding at the cut edge. Such fibres are called nail heads.
Tungsten carbide blades gives sharp cut
Opening of fibre cluster after opening: When fibres are cut, they fall down by gravity into the baler. Because of crimping clusters get formed; and so those need to be opened out; otherwise these can cause choking either in blowrrom pipes or in chute feed. This opening is obtained by having a ring of nozzles below the cutter through which high pressure air jets are pointed up; and these jets open up fibre clusters.
Over length / Multilength: Over length fibres are those whose length is greater than the cut length plus 10mm and are casued by broken filaments which being broken cannot be straightened by tensioning at the cutter. Multilength are fibre whose length is exactly 2 or 3 times the cut length and are caused by nicks in neighbouring blades.
SPECIALITY FIBRES IN POLYESTER:
- HIGH/LOW SHRINK FIBRES: The high shrink fibre shrinks upto 50% at 100 degree C while that of low shrinkage is 1%. The high shrink fibre enable fabrics with high density to be produced and is particularly used in artificaial leather and high density felt. Low shrinkage fibre is recommended for air filters used in hot air, furniture, shoes etc.
- MICRO DENIER: Available in 0.5/0.7/0.8 deniers in cutlengths 32/38 mm. Ideal for high class shirts, suitings, ladies dress material because of its exceptional soft feel. It is also available in siliconised finish for pillows. To get the best results, it is suggested that the blend be polyester rich and the reed/pick of the fabric be heavy.
- FLAME RETARDANT: Has to be used by law in furnishings / curtains, etc where a large number of people gather - like in cinema theatres, buses, cars etc in Europe and USA. It is recommended for curtains, seat covers, car mats, automotive interior, aircraft interiors etc.
- CATIONIC DYEABLE: Gives very brilliant shades with acid colours in dyeing / printing. Ideal for ladies wear
- EASY DYEABLE: Can be dyed with disperse Dyes @98 degrees C without the need for HTHP equipment. Ideal for village handicrafts etc.
- LOW PILL: In 2 and 3 deniers, for suiting end use and knitwear fibre with low tenacity of 3 to 3.5 gm/denier, so that pills which forms during use fall away easily.
- ANTIBACTERIAL:It is antibacterial throughout the wear life of the garment inspite repeated washing. Suggested uses are underwears, socks, sports, blankets and air conditioning filters
- SUPER HIGH TENACITY: It is above 7 g/denier and it is mainly used for sewing threads. Low dry heat shrinkage is also recommended for this purpose. Standard denier recommended is 1.2 and today 0.8 is also available.
- MODIFIED CROSS SECTION: In this there are TRILOBAL, TRIANGULAR, FLAT, DOG BONE and HOLLOW FIBRES with single and multiple hollows. Trilobal fibre gives good feel. Triangular fibre gives excellent lustre. Flat and dog bone fibres are recommended for furnishings, while hollow fibres are used as filling fibres in pillows, quilts, beddings and padding. For pillows silicoised fibres is required. Some fibre producers offer hollow fibre with built in perfumes.
- CONDUCTING FIBRE: This fibre has fine powder of stainless steel in it to make fibre conductive. Recommended as carpets for computer rooms.
- LOW MELT FIBRE: It is a bi-component fibre with a modified polyester on the surface which softens at low temperature like 110 degree C while the core is standard polyester polymer. This fibre is used for binding non woven webs.
REFERENCE: POLYESTER STAPLE FIBRE AND BLEND SPINNING SEMINAR BY MR.S.Y.NANAL M.TEXT, F.T.I
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