Shedding & Types of Shed

Shedding:

Deviation of warp threads into two parts for insertion of weft threads is called shed and the mechanism of shed is called shedding, it is the first primary motion of weaving.

Types of shed:

1.      Bottom close shed

2.      Center close shed

3.      semi-open shed

4.      Open shed

1.    Bottom close shed:

This type of shedding is produced by giving motion only to threads that are to form the upper line. Under this condition, the warp is level on the bottom line. Hence in order to form a top shed, it is necessary to move some threads through a space equal to twice the depth of a shed, once up and down, before a fresh selection is made. A shed of this kind is known as stationary bottom with a rising and falling top.

Bottom Close Shed

 

A   Bottom line of warp

 B   Rising and falling line

C   An arrow showing the space passed through

Advantages:

I)              Alternate tightening and slackening the warp threads produce a covered cloth

II)                 Produce fire fabric (silk)

III)              Used in hand loom

Disadvantages:

I)                   More stress or tension on the top warp line and less tension on the bottom warp line.

II)                 More chance of breakage on top warp line

III)              Unequal warp tension produces poor quality fabric

IV)              Loom speed/ waving speed is slower

V)                Not possible to produce compact fabric

VI)              More power consumption

VII)           More time required

2.    Center close shed:

This type of shed is produced by imparting an upward movement to those threads which are to form the top line and the downward movement to the threads which are to form the bottom line. Then after inserting a pick, both the lines meet at the center between the highest and lowest lines of a divided warp.Upper and lower lines of a divided warp respectively

Center close shed

  

A   Closed warp line

B, C   Upper and lower lines of a divided warp respectively

D   Arrow showing the half distance of a shed in an upward direction

E   Arrow showing the half distance of a shed in a downward direction

                      

Advantages:

I)            Equal tension on the top and bottom warp line

II)          Less time required so high production

III)       Less wear of the m/c

IV)       Less power consumption

V)         Less tear of the threads

Disadvantages:

I)                   Beat up takes place in the closed shed condition

II)                 There is chance of weft being moved backward

III)              Compact fabric can not be produced by this shed