After its introduction in 1946, the two guide bar British-built FNF tricot machine with its tubular compound needles (Section 3.16) became, for 10 years, the pacemaker of the industry, with its speed of 1000 courses per minute being more than twice that of contemporary bearded needle machines. It also incorporated many new features such as double eccentric element drive, positive warp let-off, light spring warp tension rails, and carefully-balanced machine parts. However, it required precise setting-up, its pattern scope was limited, and needles and other parts were expensive.
In 1965 the FNF Company ceased production, having failed to improve their machine in the face of increasing competition from high-speed bearded needle tricots with single eccentric drives built by the West German companies of Liba and Karl Mayer. The East German Kokett concern, however, continued its production of compound needle tricot machines.
In 1967 Liba, in a bid to increase production speeds, introduced a new design open-stem compound needle into both raschel and tricot machinery and by the mid 1970s Karl Mayer was pursuing a similar policy.
Now, the compound needle is employed in most high-speed warp knitting machines, excluding double needle bar raschels. Its short, simple action enables 3300 cpm to be achieved without the problems of metal fatigue and loop distortion associated with latch and bearded needles.
The open stem needle is simpler, cheaper and more adaptable than the FNF tube needle, having individually replaceable hook members and a wider open hook.
The designs of the other elements are similar to those in conventional machines except that the tricot sinkers have flat bellies because the compound needle does not require assistance in landing the old overlap.
The hook members are individually mounted in their bar whilst the tongues are set in leads that are mounted in the tongue bar.
Figure 24.7 illustrates the knitting action of a compound needle warp knitting machine:
1 Needle rise and guide bar swing. With the sinkers forward holding down the fabric, the hooks and tongues rise, with the hook rising faster, until the head of
the latter is level with the guide holes and is open. The guides then swing through to the back of the machine.
2 The overlap and return swing. The guides shog for the overlap and swing to the front of the machine; immediately, the hooks and the tongues start to descend with the tongues descending more slowly, thus closing the hooks.
3 Landing and knock-over. The sinkers start to withdraw as the needles descend so that the old loop is landed onto the closed hook and then knocked-over as it descends below the sinker belly. At this point the underlap occurs before the needles begin their upward rise and the sinkers move forward to hold down the fabric.
The Karl Mayer tricot model HKS 2-3 E is designed to knit elastic fabrics and has a maximum speed of 3300cpm with reduced noise levels and energy consumption. The vertical staggered arrangement of the guide bars enables the stroke to be reduced. The bars are hollow section which reduces their weight and expansion due to heat.
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