The dynamic behaviour of latch-needles during weft-knitting

The research described was initially concerned with the development, design, and, manufacture of measuring instruments to facilitate a better understanding of the knitting process. Subsequently these instruments were used to measure the following physical properties, (i) the forces between a single needle and the cams during knitting; (ii) the force exerted upon the verge and needle by the yarn during loop formation; (iii) the impact forces, when the needle first contacts the stitch and guard cams; (iv) the frictional tension build-up as the yarn passes over the verges and needles and (v) the bounce of the needles on the cams. The steadier components of the cam-forces, impact forces, and yarntensions, were all theoretically analysed, and the subsequent predictions were compared with the experimental results. The mechanism of needle fracture was examined. The wave propagation process in the needle shank, subsequent to impacts with the cams, was investigated using micro-miniature straingauges. A technique was developed which used dynamic photoelasticity to examine the wave passage through a needle model but the experimental work using the technique is uncomplete and will be continued as further works non-linear stitch-cams and: guard-cams were designed, within cam dimensions, specified by the sponsoring company, so as to enable good quality fabric to be knitted at high speed: whilst minimising the needle damage. Some recommendations were made for the redesign of the needle elements, although it is expected that more comprehensive designs will evolve after the results of the dynamic photoelastic technique are available. Finally, recommendations are made for extending the work to measurements on commercial cylinder and dial machines, using similar instrumentation to that developed in this investigation, with the intention of increasing knitting machine productivity.