Shed is the temporary separation between upper and lower warp yarns to facilitate the weft insertion.
Types of Shed:
Sheds are classified into four types, they are.
Semi Open Shed.
Center Closed Shed.
Bottom Closed Shed.
In Open Shed, warp yarns will form two stationary lines, one at the top and another at the bottom. Once the pick is inserted the two stationary lines of warp yarns will interchange. During this interchange, some threads are lowered, and some are raised up, but both are done at once.
Merits of Open Shed:
Low Power Consumption.
Strain on Warp Yarn is low.
Loom Can be runed at high speed.
By use of this type of shed there are less chances of warp rubbing.
It is suitable of base fabric.
Less chances of Wear and tear of Loom parts.
Equal amount of tension is applied on both top and bottom lines of warp yarns.
Demerits of Open Shed:
Broken ends cannot be easily inserted into the harness.
High Breakage rate of yarns.
The tensions of the yarn are not the same in different stages of shedding.
Open shed can be used for Ordinary tappet loom and for Jacquard Loom.
Semi Open Shed:
In semi open shed the bottom line is stationary and the top line is movable one after inserting a pick, the top lines move threads towards the bottom line. This type of shed is formed in power loom, Dobby and Jacquard.
Merits of Semi Open Shed:
Low Warp Strain
Required minimum time of shed.
Low Power Consumption.
This is mainly used for fancy and compact fabrics.
Loom can run at high speed.
Demerits of Semi Open Shed:
Difficult to find breakage yarn.
Heald leveling is difficult.
Strain on yarn is not equally distributed.
Uses of Semi Open Shed:
Double lift Dobby.
Double lift Jacquard.
Center Closed Shed:
Center close shed is produced by the upward movement of those threads which from the top line and downward movement to the threads form the bottom line, then after inserting a pick, both the lines meet the center. Here warp threads move in an upward & downward direction from a center line.
Merits of Center Closed Shed:
Low Power consumption.
Low wear and tear of Loom Parts.
Less time consumption.
Equal tension on both top and bottom warp lines.
Demerits of Center Closed Shed:
High Possibility of yarn breakage due to rubbing.
High Possibility of weft being moving backward.
Beat-up take place in the close shed condition.
Strain on yarn is more due to the movement for shed formation.
This method is not useful for compact fabric formation.
Uses of Center Closed Shed:
This type of shed is used in Tappet loom.
It can also be used in single lift jacquard loom.
Bottom Closed Shed:
Bottom Closed Shed is formed by the moment of warp yarns which forms the top/upper line. Under this condition the warp is level on the bottom line. Hence to form a top shed, it is necessary to move some threads through a space equal to twice the depth of shed, once up & once down, before a fresh section is made. A shed of this kind is known as a stationary bottom with a rising & falling top.
Merits of Bottom Closed Shed:
This is mainly suitable for fine fabrics especially in silk fabrics.
The altered tightening and slacking of threads produce a cloth with good cover.
Demerits of Bottom Closed Shed:
Unequal tension on warp yarns.
More Power Consumption.
High end breakages.
Not compactable for High-Speed Looms.
Consumes more time to produce shed.
Not suitable to produce Compact fabrics.
Uses of Bottom Closed Shed:
This type of shed can be used in Tappet Loom.
This type of shed can be used in Single Lift Dobby.
This type of shed can be used in Jacquard Loom.