Under Pick Mechanism

Experiment Name: -Study on the under 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 under picking mechanism.
2. To identify the different parts of this mechanism.

3. To learn the construction of under 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.

Features of under picking mechanism:

1. Picker arm is placed under the race board.
2. Suitable for wider loom.
3. Under picking work less smoothly.
4. More direct action.
5. Rough in action.
6. More clean mechanism.
7. Consumes more power.
8. Used for heavy weight fabrics in silk and rayon looms.

Under picking mechanism:

Main parts:

A =Treadle lever

B =Bowl

C =Fulcrum

D =Arm

E =Curve metal plate

H =Picking arm

I =Shuttle box

J =Coiled spring

S = Bottom shaft wheel

T =Leather band

P =Loom framing

 Fig: Under picking mechanism.

In under picking mechanism a race board is situated over picking arm. Under picking is controlled by picking cam which is fixed on the bottom shaft. At first the motion comes from motor and m/c pulley.

Then the motion comes in to the bottom shaft and thus picking cam. When picking cam rotates and its nose portion comes in contact with treadle lever and pushes it then the treadle lever pushes the angular lever. The picking arm gets motion from angular lever which is connected with picking arm. A picker is placed in the picking arm which pushes the shuttle. When shuttle gets motion by picking arm then shuttle begins to move to and fro on the race board. Thus picking is done.

A spring is situated which causes the picking arm and picker to move back after the delivery of the pick. At the two end of bottom shaft, two picking tappets are fixed. By increasing nose length picking speed may be increased.


How to increase PPM:

1. By increasing motor seed.
2. By increasing the nose shape of picking tappet.
3. By decreasing the length of picking arm.

Uses:

This mechanism is used in all non-automatic cotton looms. It is also used in jute looms.

Conclusion:

This picking mechanism is very important for loom. In the loom under picking is directly done by picker and picking arm. Again under picking is necessary for weft yarn insertion. So we should learn about this mechanism very carefully, this experience will help us in our future practical life.