Compound needles (Fig. 3.5) consist of two separately-controlled parts - the open hook and the sliding closing element (tongue, latch, piston, plunger). The two parts rise and fall as a single unit but, at the top of the rise, the hook moves faster to open the hook and at the start of the fall the hook descends faster to close the hook. It is easier to drive the hooks and tongues collectively from two separate bars in warp knitting than to move each hook and tongue individually, as in weft knitting.
A compound needle with a sliding latch was first patented by Jeacock of Leicester in 1856. It now dominates the warp knitting industry after suffering a set-back against high-speed bearded needle machines in the 1960s. However, in weft knitting, where versatility and needle selection are as important as knitting speed, it has only made limited inroads in certain specialist or prototype areas.
Two types of compound needle have been employed in warp knitting machines. The tubular pipe needle has its tongue sliding inside the tube of the open hook. It was successfully employed in Sir James Morton's high-speed FNF tricot warp knitting machine during the late 1940s and 50s. Development then ceased and bearded needle tricot machines recaptured their market with higher speeds, only to be later outpaced by a more efficient type of compound needle, the slide compound needle.
The open-stem 'pusher type' or slide needle (Fig. 3.6) has a closing wire or tongue that slides externally along a groove on the edge of the flat hook member. This needle is now preferred because it is simpler, cheaper, more compact and each of the two parts can be separately replaced.
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