TOPICS OF DISCUSSION

Knitted loop shape and loop length,

Positive feeder and its classes and

advantages,

Different fabric relaxation states,

Tightness factor, Robbing back,

Needle bounce and its effect,

Positive needle control and Cadratex unit

Loop Length Control (I)  

The loop length is the basic element (cell) in the knitted fabric and is defined as the amount of yarn used to form one unit loop

Loop length = course length / no. of loopsLoop length will affect the following parameters– stitch density; tightness factors; fabric weight;– Fabric width; dimensional stability

Knitted fabric has also the ability of form fitting and elastic recovery, it is possible because of the ability of knitted loops to change shape when subjected to tension. HATRA( The Hosiery & Allied Trades Research Association) found that stitch length has influence on knitted fabric dimension.

HATRA was thus able to establish three basic laws governing the behavior of knitted structure:

1. Loop length is the fundamental unit of weft knitted structure.2. Loop shape determines the dimensions of the fabric, and this shape depends upon the yarn used and the treatment that the fabric has received.3. The relationship between loop shape and loop length may be expressed in the form of simple equations.

Loop Length and Fabric Properties

Yarn Speed MeterYarn speed meter is used to check the yarn consumption speed on the knitting feeders The results is good for circular machine without positive feeders. Yarn speed is affected by loop length, structure and machine speed

Yarn Length MeterThe yarn length meter

can be fixed onmachine to record yarnconsumption for anumber of courses ormachine revolutions.The results can be usedto calculate the loopLength.

Yarn FeedersYarn feeders can be divided into “positive” or “negative” types depending on the possibility of controlling the yarn feeding speed and uniformity.

(a) NEGATIVE YARN FEEDING SYSTEMA yarn feeder is the negative type when the needle takes theyarn directly from the package during the stitch formation step, and the feeding tension of the yarn cannot be controlled.This feeding technique can generate differences in the yarn length used for stitch formation. This is due to the variable tension of the yarn since a new spool has a certain diameter which gradually reduces as more yarn is unwound and fed into the machine. In addition, the spool can be too hard or too soft. 

Negative yarn feeding system

POSITIVE YARN FEEDING SYSTEM

It has two major parts:

A) Motorized yarn accumulator

The motorized yarn accumulator levels off the yarn tension since when rotating, it accumulates a certain/specific quantity of yarn on a constant-diameter pulley and then stops. The yarn wound on the accumulator is then conveyed to the thread guide always maintaining the same tension. The machine takes up the yarn, gradually emptying the accumulator, which is then restarted automatically to replenish (fulfill) its yarn reserve.

Yarn feeding accumulator with stop motionor Memminger Positive Feeder

B) POSITIVE BELT FEEDING

Positive feed systems control the tensions of the yarn fed by means of a drive wheel or a drive belt system.The drive wheel systems consist of two conical toothed wheels. The belt passes between the two wheels which further passes over yarn feeding accumulator namely Memminger Positive Feeder (MPF or IRO) arranged in series as shown in fig. This positive system grants a smooth (constant) feeding of the yarn on all the feed systems. For different type of yarn count, (if used in the same fabric) separate belt driven with different size of the pulley dia will be used.

Pulley groves toadjust the yarnfeeding, controlscourse (CM) / stitchlength.

MPF/ IRO

Toothed belt

Positive Belt Feeding

MPF P - Positive feederApplicationMain features1. Rapid threading thanks to open eyelets

2. Interchangeable yarn feed wheel

3.The colour-change LED stop light is an integral part of the feeder body and is clearly visible from any operator position

4. Number of windings ‘20’

5. Yarn tension range- 1 cN to 20 cN

Knot catcher

Magnetic type tensioner

Storage unit

Model name

Driving unit

Figure: Positive feeding system

Accessories:

Knot catcherAvailable in sizes 0.2; 0.4; 0.5; 0.6; 0.8; 1.0 and 1.2 mm

Barrel tensioner

Storage unit:

Trip-tape Positive Feeder

Trip-tape positive feeder

It is the simple measured yarn speed feeding system. The yarn speed is controlled by speed tape pulley which in turn, controlled by machine gearbox. Two or three speed tapes are equipped which machine can have two or three yarn feeding speeds for the fabric. When machine is properly adjusted, the yarn speed is equaled to tape speed, and the tape speed can control the suitable yarn tension and results in regular loop length

Storage Feeder

Storage Feeder

Positive feeder is designed for regular loop fabric. For fabric with different loop length in each course, a new concept of storage feed has employed To eliminate the yarn tension variation, all yarns are rewound onto a drum of equal diameter, under equal tension and speed. The amount of yarn on drum is automatically controlled so there will be no difference in package diameter. The yarn is consuming by the knitting needles at variable speeds, thus different loop length in each course is possible