Shedding & Types of Shed

3.    Semi-open shed:

In this shed, the stationary bottom is retained but threads for the top line either passes to bottom at one movement and again carried to the top mid way and again carried to top. In this shed close and open shed occurred simultaneously. In it the stationary bottom line is retained, but threads for the top line either pass to the bottom at one movement, or are arrested midway and again carried to the top. Such a shed can be formed as expeditiously as an open shed, for the upward movement begins and ends with the downward through movement, and the arrested downward movement is converted into an upward movement immediately the falling threads are in the same plane as the rising ones. They all reach the top together but the strain upon them is not equally distributed. Upper and lower lines of a divided warp respectively

Semi-Open Shed

 

A   Stationary bottom line

B   Top point

C   The point where downward movement ceases in threads

D, E   Showing the movement of through healds

F   Arrow showing the threads which are to lift for the next pick

Advantages:

I)               Equal tension on the top and bottom warp line

II)         All the warp yarns are not required to move up and down in every pick

III)          Beat up takes places in the cross-shed condition

IV)          The loom can run at a faster speed

V)            Possible to produce compact fabric

VI)          Less complexity or disturbance in the shedding mechanism

VII)       Used in power, dobby and jacquard loom

VIII)     For fancy fabric

IX)          Less power consumption

X)             Less tear of threads

Disadvantages:

I)                   Unusable movement

4.    Open shed:

In open shed, the warp threads form two stationary lines, the top line and the bottom line and changes are made by carrying the threads from one fixed line to the other without any interval.

Open Shed

A, B   Stationary warp line

C, D Arrows which show the movement of rising and falling warp to equal the distance between A and B

Advantages:

I)           Beat up takes place in cross-shed condition

II)         Equal tension on the top and bottom warp line

III)      The loom can run at a fastest speed

IV)      Extensively used in tappet shedding mechanism

V)        Basic fabric (twill, sateen, plain) can be produced.

VI)      Less power consumption

VII)   Less wear of the weaving m/c

Disadvantages:

I)           High breakage rate

II)         If higher no of healds are used then the warp in back healds are more strained than the front ones

III)      Leveling apparatus should be added to open shed to place the headls in one plane.

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