Needle bounce and high-speed knitting
On circular knitting machines, higher productivity involves faster needle movements as a result of an increase in the number of knitting feeds and of machine rotational speeds. On fabric Knitting machines, the machine revolutions per minute have almost doubled and the number of feeders have increased twelve-fold over the past 25 years, so that as many as 4000 courses per minute can be knitted on some plain machines, whilst on some high-speed seamless hose machines the tangential speed of the needles can be more than 5 meters per second.To achieve this productivity, research and development has been necessary into machine, cam and needle design. The horizontal cam track sections have been reduced to a minimum whilst needle hooks and latches have been reduced in size wherever possible in order to reduce the extent of the needle movement between the clearing and knock-over points.‘Needle bounce’ is a major problem in high speed tubular machine knitting. This is caused by the needle butt being suddenly checked by the impact of hitting the upper surface of the up-throw cam after it has accelerated away from the lowest point of the stitch cam. At this moment, inertia at the needle head may cause it to vibrate so violently that it may fracture; also the up-throw cam becomes pitted in this section. Needles passing though in the miss section are particularly affected as their butts contact the lowest part of the cam only and at a sharp angle that accelerates them downwards very rapidly. To reduce this effect, a separate cam is often used to guide these butts at a more gradual angle. The smoother profiles of non-linear cam help to reduce needle bounce and a braking effect is achieved on the butts by keeping the gap between the stitch and up throw cams to a minimum. For this reason, on some hose machines the up-throw cam is horizontally-adjustable in conjunction with the vertically-adjustable stitch cam.The Reutlingen Institute of Technology has carried out a considerable amount of research into this problem and, as a result, a new design of latch needle with a meander-shape stem, a low smooth profile, and a shorter hook is now manufactured by Groz-Beckert for high-speed circular knitting machines. The meander shape assists in the dissipation of the impact shock before it reaches the needle head, whose shape improves resistance to stress, as does the low profile, whilst the gently-shaped latch is designed to open more slowly and fully onto a cushioned position produced by a double saw cut.
Intimate apparel with special functions
Machinery/technology innovation
Pantyhose were traditionally made using circular knitting machines . The RDPJ 6/2 warp knitting machines from Karl Mayer were debuted in 2002 and are used to create seamless, jacquard-patterned tights and fish-net pantyhose. The MRPJ43/1 SU and MRPJ25/1 SU jacquard tronic raschel knitting machines from Karl Mayer are capable of producing pantyhose with lace and relief-like patterns . Other improvements in machines were made to boost effectiveness, productivity, and pantyhose quality. The regulation of sheerness in pantyhose materials has also been the subject of some research by Matsumoto et al. [18,19,30,31]. They created a hybrid experimental knitting system made up of two experimental circular knitting machines. Two single covered yarn sections were present on each covering machine. The single covered yarns were created by managing the covering levels of 1500 twists per meter (tpm) and 3000 tpm in nylon yarn with a draw ratio of 2 = 3000 tpm/1500 tpm for the core polyurethane yarn. The pantyhose samples were knit under a constant state. A higher sheer in the pantyhose was achieved by the lower covering level. Different tpm coverage levels in various leg regions were used to create four different pantyhose samples.The findings demonstrated that altering the single covered yarn covering level in the leg portions had a significant impact on the aesthetics and sheerness of pantyhose fabric, and that the mechanical hybrid system could enhance these features.
Post time: Feb-04-2023