MOTION IN WEAVING( let-off motion.).

Motion in weaving:-

As I am dealing with secondary motion in weaving, earlier I have explain about the let-off motion here is another type of let-off motion.

NEGATIVE LET-OFF MOTION:-

Let-off motion is to supply warp threads in the weaving zone at a pre determined rate. Negative let-off is mechanism for controlling the rotation of warp beam on weaving a warp knitting or other fabric forming machine, where the beam is pulled round by the warp against a breaking force applied to the beam.

Diagram of negative let-off motion.

Main parts,

A. Warp beam.

B. Beam ruffle.

C. Chain

D. Machine frame.

E. Weight lever.

F. Pivot.

G. Fulcrum.

H. Weight.

Working principle:-

The beam ruffle is wrapped around by chain . The one end of the chain is fixed at the machine frame whereas the other end is connected to fulcrumed device to the weight lever, which is pivoted and a weight is placed which can be moved along the length of the weight lever. In this system the tension of warp beam  is regulated by the friction between the chain and the beam ruffle. The friction is controlled by dead weight on the weight lever and the distance of dead weight from the pivot. Heavier the dead weight and longer the distance of it from the pivot lesser the let-off. The warp beam diameter softly decreases as weaving proceeds. So it necessary to increase the let-off rate. If the dead weight is kept on the same place , the let-off rate will stay unchanged. So an experienced worker is required to change the dead weight gradually with change of warp beam diameter. As a result irregular tension occurs and the rate of yarn breakage may increase.

Advantages:-

1. Cheap and simple in construction.

2. Suitable for light and medium weight of fabrics.

3.Easy to maintain.

Disadvantages:-

1. Difficulty in taking back the warp beam after picking.

2. Difficulty in regulating equal tension on the warp.

3. The varying tension on warp thread shows dark and light or shady places in the cloth.

4. Possibility of thread breakages due to tension variation. As a result, bad quality fabric produced.

5. Thick and thin places may occurs in fabric weft wise due to irregular tension of during weaving.

Diffrence between positive and negative let-off motion:-

In case of negative let-off warp is pulled from the warp beam against a slipping friction system. Warp beam is rotated a controlled rate in order to maintain constant warp tension. Positive let-off motion is a mechanism controlling the rotation of the beam on a weaving warp knitting or other fabric forming machine where the beam is driven mechanically.

Devlopment of let-off motion:-

ELECTRONIC LET-OFF MOTION:-

This is a modern type of let-off motion in which the weavers beam is driven with the help of servo motor, as the beam diameter changes rpm of the beam are controlled through load cell. Take-up which responsible to draw the fabric from the fell of the cloth at regular rate (picks/inch) and to wind the cloth on cloth roller. It is synchronised with the let-off motion. The speed of take up is less than the let-off motion due to crimp of warp.

Image of electronic c let-off motion.

CONCLUSION:-

The secondary motion facilitate the weaving of fabric in continuous way. The take-up motion withdraws the cloth from the weaving area at a constant rate so as to give required pick spacing and then winds it on a cloth roller. On the other hand let-off motion delivers the warp to weaving area at required rate and then at constant tension by unwinding.

 The secondary motions are carried out simultaneously. All this motion, it is very important that without this we can’t have more production from loom.

https://textilelearner.net