Although the American Scott and Williams Patent of 1908 for interlock was extended for 20 years, underwear manufacturers found the needles expensive, especially on the larger 20 inch (51 cm) diameter model. Suitable hosiery twist cotton yarn only became available in 1925, and the first stationary cam-box machine appeared in 1930.
Originally, interlock was knitted almost solely in cotton on 20 gauge (needles per inch) machines for underwear, a typical weight being 5 oz per square yard (170g per square metre) using 1/40's s cotton, but from the 1950s onwards, 18 gauge machines were developed for knitting double-jersey for semi-tailored suiting because the open-width fabric could be finished on existing equipment. As the machines became more versatile in their capabilities, the range of structures became greater.
Interlock has the technical face of plain fabric on both sides, but its smooth surface cannot be stretched out to reveal the reverse meshed loop wales because the wales on each side are exactly opposite to each other and are locked together (Fig. 7.14). Each interlock pattern row (often termed an 'interlock course') requires two feeder courses, each with a separate yarn that knits on separate alternate needles, producing two half-gauge 1 x 1 rib courses whose sinker loops cross over each other. Thus, odd feeders will produce alternate wales of loops on each side and even feeders will produce the other wales.
Interlock relaxes by about 30-40 per cent or more, compared with its knitted width, so that a 30-inch (76 cm) diameter machine will produce a tube of 94-inch (2.4m) open width which finishes at 60-66 inches (1.5-1.7m) wide. It is a balanced, smooth, stable structure that lies flat without curl. Like 1 x 1 rib, it will not unrove from the end knitted first, but it is thicker, heavier and narrower than rib of equivalent gauge, and requires a finer, better, more expensive yarn.
As only alternate needles knit at a feeder, interlock machines can be produced in finer gauges than rib, with less danger of press-offs. Interlock knitting is, however, more of a problem than rib knitting, Because productivity is half, less feeders can be accommodated, and there are finer tolerances. When two different-coloured
Fig. 7.14 Interlock fabric structure.
yarns are used, horizontal stripes are produced if the same colour is knitted at two consecutive feeders, and vertical stripes if odd feeders knit one colour and even feeders knit the other colour. The number of interlock pattern rows per inch is often double the machine gauge in needles per inch.
The interlock structure is the only weft knitted base not normally used for individual needle selection designs, because of the problems of cylinder and dial needle collision. However, selection has, in the past, been achieved by using four feeder courses for each pattern row of interlock, long and short cylinder needles not selected at the first two feeder courses for colour A being selected at the second two feeders for colour B. This knitting sequence is not cost effective.
Eightlock is a 2 x 2 version of interlock that may be produced using an arrangement of two long and two short needles, provided all the tricks are fully cut through to accommodate them and knock-over bits are fitted to the verges to assist with loop formation on adjacent needles in the same bed.
It was first produced on double-system V-bed flat machines having needles with two butt positions, each having its own cam system. This involved a total of eight locks, four for each needle bed, making one complete row per traverse. Set-outs for 4 x 4 and 3 x 3 can also be produced.
It is a well-balanced, uniform structure with a softer, fuller handle, greater width-wise relaxation, and more elasticity than interlock. Simple geometric designs with a four wale wide repeat composed of every two loops of identical colour, can be achieved with careful arrangement of yarns.
Interlock is produced mainly on special cylinder and dial circular machines and on some double-system V-bed flat machines (Fig. 7.15). An interlock machine must have the following:
1 Interlock gating, the needles in two beds being exactly opposite each other so that only one of the two can knit at any feeder.
2 Two separate cam systems in each bed, each controlling half the needles in an alternate sequence, one cam system controlling knitting at one feeder, and the other at the next feeder.
3 Needles set out alternately, one controlled from one cam system, the next from the other; diagonal and not opposite needles in each bed knit together.
Originally, the interlock machine had needles of two different lengths, long needles knitting in one cam-track and short needles knitting in a track nearer to the needle heads. Long needle cams were arranged for knitting at the first feeder and short needle cams at the second feeder. The needles were set out alternately in each bed, with long needles opposite to short needles. At the first feeder, long needles in cylinder and dial knit, and at the second feeder short needles knit together; needles not knitting at a feeder follow a run-through track. On modern machines the needles are of the same length.
Typical cotton counts for particular gauges would be:
E 16 Nm 1/28-1/50, E 22 Nm 1/50-1/80, E 18 Nm 1/34-1/60, E 24 Nm 1/56-1/90, E 20 Nm 1/40-1/70, E 28 Nm 1/60-1/100.
Fig. 7.15 Knitting interlock.
A 30-inch (76 cm) diameter E 28 machine running at 28rpm and 85% efficiency, knitting 38 courses/in (15 courses/cm) from Nm 1/70 yarn would produce 34.4lb/hr (15.6kg/hr) of 4.45oz/yd2 (151g/m2) interlock fabric.
Figure 7.16 shows the cylinder and dial needle camming to produce one course of ordinary interlock fabric, which is actually the work of two knitting feeders. In this example, the dial has a swing tuck cam that will produce tucking if swung out of the cam-track and knitting if in action.
A Clearing cam which lifts the needle to clear the old loop. B, C Stitch and guard cams respectively, both vertically adjustable for varying stitch length.
D Upthrow cam, to raise the cylinder needle whilst dial needle knocks-over.
E, F Guard cams, to complete the track.
G, H Guide cams that provide the track for the idling needles.
The dial cam system 1 Raising cam to tuck position only. 2, 3 Dial knock-over cams (adjustable).
4 Guard cam to complete the track.
5 Auxiliary knock-over cam to prevent the dial needle re-entering the old loop.
Odd feeder Even feeder
Fig. 7.16 Interlock cam system.
Odd feeder Even feeder
6,7 Guide cams that provide the track for the idling needles. 8 Swing type clearing cam, which may occupy the knitting position as shown at feeder 1 or the tuck position as shown at feeder 2.
Interlock thus requires eight cam systems or locks in order to produce one complete course, two cam systems for each feeder in each needle bed. Basic cylinder and dial machines and flat-machines having this arrangement are often referred to as eightlock machines.
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