Tricot machines (Figures 24.1 and 24.2) have a gauge expressed in needles per inch (E) and chain link numbering 0,1,2,3,4, etc., generally with three links per course. Their sinkers, which are joined to each other at the front and back, never move clear of the needles as they combine the functions of holding-down, knocking-over, and supporting the fabric loops.
The fabric is drawn-away towards the batching roller almost at right angles to the needle bar. The warp beams are accommodated in an inclined arc towards the back of the machine, with the top beam supplying the front guide bar and the bottom beam supplying the back guide bar. The warp sheets pass over the top of the guide rocker-shaft to their tension rails situated at the front of the machine. The machines have a simple construction and a short yarn path from the beams.
Mechanical attention to the knitting elements is carried out at the front of the machine as the warp beams prevent access to the back. As all the warp sheets are drawn over the rocker-shaft to the front of the machine it is easier to thread up the guide bars commencing with the back bar; otherwise the front warp will obscure this operation. The guide bars are therefore numbered from the back towards the front of the machine because of this threading sequence.
The conventional tricot beam arrangement generally restricts the maximum
number of beams and guide bars to four, but this is not of major importance as the majority of tricot machines employ only two guide bars.
The small angle of fabric take-away and the type of knitting action produce a gentle and low tension on the structure being knitted. This is ideal for the high-speed production of simple, fine-gauge (28-44npi), close-knitted, plain-and-patterned structures, particularly for lingerie and apparel, especially using two guide bar structures with both bars overlapping and underlapping.
In the past, the two guide bar tricot or locknit machine proved most popular in E 28 and E 32 gauge, with knitting widths of 84 and 168 inches (213 and 426 cm) using 40-denier nylon. It is possible to knit from 10-denier nylon up to 1/20's cotton count. Machine gauges can range from E 10 for coarse staple fibre yarns to E 20E 24 for textured yarn fabrics and E 36-E 44 gauge for fine fabrics, in knitting widths up to 260 inches (660 cm).
The needles, like the sinkers and guides, may be cast in leads or they may be individually cranked to fit into the needle bar.
24.2.1 The knitting cycle of the bearded needle tricot machine
Figure 24.3 illustrates the knitting cycle of the bearded needle tricot machine:
1 The rest position (a). The needles have risen to 2/3 of their full height from knock-over and have their beards towards the back of the machine. The presser
is withdrawn and the guides are at the front of the machine with the sinkers forward, holding the old overlaps in their throats so that they are maintained at the correct height on the needle stems.
2 Backward swing and overlap shog (b, c). After swinging through the needles to the beard side, the guides are overlapped across the beards, usually by one needle space in opposite directions.
3 The return swing and second rise (c, d). As the guides swing to the front, the needles rise to their full height so that the newly-formed overlaps slip off the beards onto the stems above the old overlaps. This arrangement reduces the amount of guide-bar swing necessary and therefore the time required.
4 Pressing (e). The needle bar descends so that the open beards cover the new overlaps. There is a slight pause whilst the presser advances and closes the beards.
5 Landing (f). As the sinkers withdraw, the upward curve of their bellies lands the old overlaps onto the closed beards.
6 Knock-over and underlap shog (g). The presser is withdrawn and the continued descent of the needle bar causes the old overlaps to be knocked-over as the heads of the needles descend below the upper surface of the sinker bellies. The underlap shog which can occur at any time between pressing and knock-over usually occurs in opposite directions on the two guide bars.
7 The sinkers now move forward to hold down the fabric loops and push them away from the ascending needles, which are rising to the rest position.
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