Over Pick Mechanism

Experiment Name: -Study on the over pick mechanism.

Introduction:

Picking is the second primary motion in weaving. It consists in passing a pick of weft between the upper and lower lines of a divided warp. It builds up half of the cloth. The shuttle is the vehicle of weft for picking in the conventional and automatic looms.

Objectives:

1. To know the over picking mechanism.
2. To identify the different parts of this mechanism.

3. To learn the construction of over picking mechanism.

Types of picking mechanism:

1.     Conventional or negative picking mechanism.

2.     Unconventional or positive picking mechanism.

Conventional or negative picking mechanism:

In this mechanism, a carrier known as shuttle carries the weft yarn in a package called pirn. The main function is:

a)     To deliver the shuttle along the correct flight path.

b)    To project the shuttle at a predetermined velocity.

Conventional or negative picking mechanisms are two types

1.     Over picking

2.     Under picking

Unconventional or positive picking mechanism:

In this mechanism, the weft yarn is inserted through the warp shed directly or positively by air, water, projectile, needle or rapier. This mechanism is known as positive picking mechanism.

Main Parts:

1.     Picking arm

2.     Picking strap

3.     Picker

4.     Bottom shaft

5.     Picking spindle

6.     Shuttle

7.     Picking cam

8.     Vertical shaft

9.     Cone

10.  Bowl

11.  Angular

12.  Crank shaft

Here,

A - Loom bottom shaft
B - Picking cam
C - Picking cone
D - Picking shaft
E - Picking stick
F - Picking band
G - Picker

Fig: Over Picking Mechanism

  

Features of Over Picking Mechanism:

1. Picking arm is over shuttle.
2. Suitable for narrow loom.
3. Higher picks per minute.
4. Less power required.
5. Works more smoothly.
6. Shortening the picking strap and changing the shape of the cam can increase picking force.

Mechanism of Over Picking:

Over picking mechanism is used on cotton and jute loom. It is robust and easy to adjust and maintain. The spindle is situated over the shuttle box and is essential to guide the shuttle along the correct path. It is normally set slightly up and slightly towards the front of the loom and its inner end.

The back end of the shuttle will thus receive a similar lift at the end of the stroke, so that its leading end will receive correct delivery down and into the shed. A flexible leather-picking strap is used to control the picker, which has tendency to stretched slowly in use, and vary with regard to its elastic property.

The cone over pick motion consist a vertical shaft placed either inside or outside the loom framing. The shaft serves as fulcrum of the picking arm, it is held against the loom frame. There is a spiral spring at the picking shaft, which causes the picking arm and picker to move back after the delivery of the pick.

At the two end of the bottom shaft, two picking cams are fixed. In revolving its nose the tappet strikes the cone shaped ant frictional roller strut, positively rotates the shaft and causes the pick to move inward with sufficient velocity to drive the shuttle across the loom. The timing of the picker begins to move can be attend by turning the picking tappet on its boss.

How to Increase PPM:

1. By increasing motor speed.
2. By setting the cone stud nearer to the picking tappet.
3. By decreasing the picking strap.
4. By altering the position of picking arm towards the centre of the loom.
5. By decreasing the length of the stroke of picking tappet.

Uses:

This is used for narrow and fast running looms, weaving light and medium weight fabrics and for many narrow and wide looms for weaving heavy fabrics.

Conclusion:

The over picking motion is negative one; the exact amount of power is required to drive a shuttle. By this experiment we learned about the over picking mechanism and how it works. This experience will help us in our future practical life.