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.