Sliver or high-pile knitting is single-jersey made on a circular machine having sliver feeds where the stock- or dope-dyed slivers are drawn from cans at ground level. They are then prepared by mini three-roller drafting card units followed by two wire-covered rollers that draw and transfer the thin film of fibres to the needles (Fig. 14.6). At each sliver feed, the needles are lifted to an extra high level where they rise through the wires of the doffer roller to collect a tuft of staple fibres in their hooks.
Air-jet nozzles over the knitting points ensure that the tufts are retained in the needle hooks and that the free fibre ends are orientated through to the inside of the fabric tube (the technical back), which is the pile side.
As the needles start to descend, the ground yarn is fed to them, so that each has a ground loop and a tuft of fibres that are drawn through the previous loop. A range of facilities are available from different machines including up to 16 roller speed settings, the use of two different fibre lengths, and mechanical or electronic needle selection and sliver selection. Electronic selection can select needles to take fibres from one of four different coloured slivers.
Borg Textiles pioneered specialised sliver knitting in the 1950s in co-operation with Wildman Jacquard although J. C. Tauber obtained US patents as early as 1914. A typical machine now has a diameter of 24 inches in a gauge of 10npi and runs at 45rpm with 12-18 sliver feeds.
The fabric finishes 54-58 inches wide (137-147cm) in a weight of about 450g/m when knitting 360 denier fibrillated polypropylene ground yarn and a modacrylic sliver having a 3 denier 1- inch staple.
Fibre staple lengths can range from 20 to 120 mm, in sliver weights from 8 to 25 g/m2, giving greige (unfinished) weights of 200-2000 g/m2, for end-uses such as fun furs, linings, gloves, cushions, industrial polishers and paint rollers.
A typical high-pile finishing route is: rough shearing, heat setting and back-coating, pile cropping, electrifying or polishing (to develop the lustre and remove
crimp from the fibre ends), tiger framing (to distribute the pile effect), and controlled torque winding (to further develop the pile uniformity).
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