Yarn Feeding Mechanism:
Basic principle of yarn feeding mechanism is yarn fed to the needles in order to form the fabric must be conveyed along a predetermined path from the spool/cone to the knitting zone. The various motions along this path guide the yarn (thread guides), adjust the yarn tension (yarn pensioners’), and check for eventual yarn breaks.
The yarn is taken down from the spool arranged on a special holder called creel if placed beside the machine, or rack if placed above it. The yarn is then guided into the knitting zone through the thread guide, which is typically a small plate with a steel eyelet for the yarn. In order to obtain particular designs such as intarsia and vanisé effects, the machines are equipped with special thread guides.
A uniform feeding tension is fundamental for obtaining regular loops. On flat-bed machines, this parameter is controlled through the yarn tensioner, which consists essentially of a metal arm adjusted by means of springs in order to contrast and level off the spool unwinding tension peaks. On circular knitting machines, the yarn feeding control on the various systems is performed with various methods.
Yarn Path Sequence from Creel to Needle:
Ceramic Eye Pot
Yarn Wheel (Positive/negative feeder)
Previous Sensor Guide
After Sensor Guide
Ceramic Eye Pot (feeder Ring)
There are two types of feed device.
- Positive feed device
- Negative feed device
Positive feed device:
Positive feed device is a knitted loop-shape and loop-length control device which employs small pulleys moved by belts, or gears etc., to exactly control the yarn feeding speed and keep it constant.
Positive feed device are designed to overcome loop-shape and loop-length variation by positively supplying yarn at the correct rate under low yarn tension to the knitting point instead of allowing the latch needles or loop forming sinkers to draw loops whose length could be affected by varying yarn input tension.
A continuous tape driven from the machine drive by a single pulley encircles the machine above the feeders and provides identical and constant feed for any yarn threaded through the nip it forms with a free running feed wheel at each feed position.
The faster the tape speed relative to the machine speeds, the faster the rate of yarn feed and the longer the resultant course length. The tape speed is altered by adjusting the scrolled segments of the drive pulley (V.D.Q pulley) to produce a larger or smaller driving circumference.
Negative Feed Device:
Negative feed device is a knitted loop-shape and loop-length control device as a yarn guide which employs direct drive by yarn tension. In negative feed device, yarn is not wrapped.
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