SHORT NOTE ON

SHED

SHED:

In weaving shed is the temporary separation between upper and

lower warp yarns through which the weft is woven

The shed is created to make it easy to interlace the weft into the warp and thus create the woven fabric

Shed is produced by means of healds or harness

CONDITION FOR GOOD SHED:

It should be as small as possible

Heald are to be placed at right angle to warp thread

Perfect leveling of healds are to be obtained

The velocity of the upward and downward movements of the healds

must be variable to correspond, as far as possible with the tension

upon the warp

Smooth movement of the heald frames

TYPES OF SHED:

SHED

CLOSED SHED

BOTTOM CLOSED

SHED

CENTRE CLOSED

SHED

OPEN SHED

SEMI OPEN SHED

OPEN SHED

CLOSE SHED:

BOTTOM CLOSED SHED:

This kind of shed 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 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

A bottom line of warp

B rising and falling line

C an arrow showing the space passed through

ADVANTAGES:

DISADVANTAGES:

Alternate tightening and slackening the warp threads produce a covered cloth

It is suitable for fine fabric particularly in silk fabric

Produce fine fabric

It takes long time to produce a shed

Not suitable for high speed loom

More chance of breakage of top warp line

It requires more power

Unequal warp tension

Low production

More tension on yarn

Not possible to produce compact fabric

USES:

Tappet loom

Single loom dobby

Jacquard loom

CENTRE 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

In the figure

A is the closed warp line,

B and C are respectively the upper and lower lines of a divided

warp

D and E are arrows which show the movement of each thread to

equal the depth of a shed, namely half the distance in an upward

and half in a downward direction.

MERITS:

DEMERITS:

Equal tension on the top and bottom warp line

Less time required so high production

Less wear and tear of the m/c

Less power consumption

Less tear of the threads

Beat up takes place in the closed shed condition

There is chance of weft being moved backward

Compact fabric can not be produced by this shed

Since every thread is moved to form each shed, strain on yarn is more

Possibility of yarn breakage due to rubbing

USES:

Tappet loom

Single lift jacquard loom

Dobby loom

Wood crafts tappers

Hand loom

OPEN SHED:

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.

They all reach the top together but the strain upon them is not

equally distributed.

Upper and lower lines of a divided warp respectively

In this shed close and open shed occurred simultaneously.

This shed is formed under both open and closed principal

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

MERITS:

Equal tension on the top and bottom warp line

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

Beat up takes places in the cross-shed condition

The loom can run at a faster speed

Possible to produce compact fabric

Less complexity or disturbance in the shedding mechanism

Used in power, dobby and jacquard loom

For fancy fabric,

Less power consumption

Less tear of threads

Required minimum time

Strain upon warp is low

DEMERITS:

uses:

Strain on yarn is not equally distributed

Difficult to find breakage yarn

Levelling the heald is difficult

Unusable movement

Double lift jacquard

Double lift dobbies

OPEN SHED:

In this types of shed, the warp threads form two stationary lines, one

at the top and another at the bottom .

After inserting a pick change are made by carrying threads from one fixed line to the other.

Some threads are lowered from the top line and some are raised

from the bottom line during the change raising and lowering of the

threads occurred simultaneously.

Here,

A & B two stationary lines of warp

C & D arrows which show the movement of rising and falling warp to

equal the distance between A & B

The fell of cloth E & lease F from two ends of the open shed

MERITS:

Beat up takes place in cross-shed condition

Equal tension on the top and bottom warp line

The loom can run at a fastest speed

Extensively used in tappet shedding mechanism

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

Less power consumption

Less wear and tear of the weaving m/c

More production

Strain upon the warp is less

DEMERITS:

USES:

High breakage rate

If higher no of healds are used then the warp in back healds are

more strained than the front ones

Problem in knotting, so some effective apparatus known as

“Leveling apparatus” should be added to open shed to place the

headls in one plane.

Ordinary tappet loom

Jacquard loom