In hand crocheting, a hook is used to draw a new loop through the old loop with the chains of loops being joined together at intervals.
On crochet machines, the warp chains are separate from the weft inlay and it is the latter threads that join the chaining wales to each other. The crochet galloon machine, as developed by Sander and Graff and popularised by Kholer, is essentially a highly versatile raschel with the following unique features (Figures 24.8 and 24.9):
• A single horizontal needle bar whose simple reciprocating action can be used to operate individually-tricked latch, carbine or embroidery needles.
The patent or carbine bearded needle is used for fine structures and has a sideways crimped beard placed in a permanently-pressed position. Although warp threads can only be fed into the beard from the left (necessitating a unidirec-
tional closed overlap), the old overlaps are automatically cleared and landed by the movement of the needle. It is still the most frequently used needle, achieving speeds up to 2500 rpm. Reduced machine speed and high needle wear make its use uneconomical for knitting single end cotton yarns.
Embroidery or lace needles are carbine needles with pointed heads that can penetrate pre-woven structures to produce embroidery effects. The needles can be arranged for coarser gauges or for fancy set-outs, when the floating inlay threads may be cut to produce separated fringed edgings.
The compound needle patented by Müller produces less stress on the yarn during loop formation so a wider range of yarns can be used, and compound needles last up to six times longer than bearded needles.
Latch needles operate at uneconomic speeds and have a short life due to latch breakage.
Inlay t Trick p
Inlay t Trick p
Crochet machines, with their simple construction, ease of pattern and width changing, and use of individual yarn packages or beams provide the opportunity for short runs on coarse- or fine-gauge fancy and open-work structures and edgings, as well as the specialist production of wide fancy fabrics or narrow elastic laces.
The weft inlay bars may either be electronically-driven or mechanically-controlled in the traditional manner by chain links or levers. The choice is governed by the requirements either of long complex pattern repeats and quick pattern changes as in sampling, or for simple structures and long production runs .
Very approximately, the knitting widths of crochet machines may vary between 16 and 122 inches (400 and 3100mm). Gauges, often expressed in needles per centimetre, are between 2 and 10 (E 5 to E 24).
Müller quote gauges in needle pitch; this means that the lower the number, the finer the gauge. For example, '10' means that the distance between one needle centre and the next is 10 mm; therefore in one inch (25.4 mm) there will be 2.5 needles (E 2.5).
Machines run at speeds between 200 and 350 courses per minute (or much more on simple structures). Crochet machines can process a range of filament yarns from 20dtex to 1000dtex.
24.5.1 The knitting action of the crochet machine
Figure 24.10 illustrates the knitting action of a crochet machine:
1 The inlay. Whilst the needle is withdrawn into its trick during knock-over of the previous warp overlap, the weft inlay tube is lowered. As it traverses in an under-lap shog, the weft is laid below the level of the needle and on top of the warp thread that extends from its head to the warp guide.
2 Clearing the warp overlap. The weft tube rises slightly on completion of its traverse movement to allow the needle to move out of its trick to clear its old warp overlap.
3 The warp overlap wrap. The warp guide rises between the needles and
automatically overlaps from the left, lowering itself again on the right side of its needle.
4 Warp knock-over and underlap. The needle now retires into its trick to knockover the old overlap, whilst the warp guide is cammed under its needle to the start position for its next overlap, thus completing the closed lap pillar. NB: The closed lap is used for the carbine needle but the alternating overlap of the open lap pillar stitch used with the conventional latch and bearded needles gives a more balanced loop structure. Tricot lapping with two guide bars produces a secure fabric which does not unrove.
A range of crochet fabrics is illustrated in Fig. 24.11.
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