"Weaving on the loom"

                                                        

LOOM: A machine for weaving fabric by interlacing a series of vertical, parallel threads (the warp) with a series of horizontal, parallel threads (the weft/filling). The warp yarns from a beam pass through the heddles and reed, and the filling is shot through the “shed” of warp threads by means of a shuttle or other device and is settled in place by the reed and lay. The woven fabric is then wound on a cloth beam.
The major components of the loom are the warp beam, heddles, harnesses, shuttle, reed and takeup roll. In the loom, yarn processing includes shedding, picking, battening and taking-up operations.

The principal elements of any type of loom are the shedding, picking, and beating-up devices.

• Shedding. Shedding is the raising of the warp yarns to form a hed through which the filling yarn, can be inserted. The shed is the vertical space between the raised and unraised warp yarns. On the modern loom, simple and intricate shedding operations are performed automatically by the heddle or heald frame, also known as a harness. This is a rectangular frame to which a series of wires, called heddles or healds, are attached. The yarns are passed through the eye holes of the heddles, which hang vertically from the harnesses. The weave pattern determines which harness controls which warp yarns, and the number of harnesses used depends on the complexity of the weave. Two common methods of controlling the heddles are dobbies and a Jacquard Head.

Dobby Shedding System:
The dobby shedding motion of the warp ends is created by the movement of the heald frames. The maximum practical number of harness frames in terry weaving machines with dobby is 20. Dobby looms can produce weaves in limited numbers and limited designs. The difference of this system from the other traditional dobby looms is that the motion of the pile and ground warps is transferred separately. There are also systems in which the pile warps are given shedding motion by dobby and the ground warp ends by cam

Jacquard Shedding System:

Each warp end is controlled through a separate motion. Very different and very complex structures can be woven. In terry fabric it is the pile warp which shows the design. The ground warp ends are woven 2/1 ribs (most commonly), 2/2 ribs, 1/1 plain weave and 3/3 ribs (the rarest) As these weaves do not require a jacquard shedding system, in some weaving machines, the pile warp ends take the shedding motion from the jacquard system whereas the ground warp ends take from the cam. Jacquard machines may either work in a traditional mechanical system with the help of needles and design cards or a contemporary electronic system which works through electronic transmitting elements with design files and electronic. The pile warp ends are looser than input. The pile warp ends are looser than ground pile ends, thus the shedding of the pile weft ends must be wider than that of ground warps. Otherwise, contact may occur between the pile warp ends and the pick carrying device, which may cause high numbers of end breakages. A wider shed also improves the loop formation. Pile tension rod should guide the pile warp ends from the position which has the same level with the center of the shed. With this, the pile warp ends in the upper and in the lower shed will maintain the same tension. Thus, the pile loops on both sides of the fabric will have the same length.

• Picking. As the harnesses raise the heddles or healds, which raise the warp yarns, the shed is created. The filling yarn in inserted through the shed by a small carrier device called a shuttle or by other methods described below.

Types of Picking Mechanism

Picking mechanisms are classified into two main types. These are :

1. Conventional picking mechanism or negative picking mechanism
2. Unconventional picking mechanism or positive picking mechanism

 Conventional Picking Mechanism or Negative Picking Mechanism

In this mechanism, a carrier known as shuttle carries the weft yarn in a package called the “pirn”.

Picking through the open shed

Figure indicates the insertion of weft yarn by passing the shuttle through the warp shed.

Unconventional Picking Mechanism or Positive Picking Mechanism

In this mechanism, the weft yarn is inserted through the warp shed directly or positively by air, water, a projectile, a rapier or a needle. These mechanisms are therefore known as “positive picking mechanisms”. Looms which do not use shuttles for weft insertion are known as “shuttleless looms”.

• Beating. As the shuttle moves across the loom laying down the fill yarn, it also passes through openings in another frame called a reed (which resembles a comb). With each picking operation, the reed presses or battens each filling yarn against the portion of the fabric that has already been formed. The point where the fabric is formed is called the fell.

Classification Of Loom

Loom may be classified into two basic types with respect to picking medium,

1. Shuttle loom
2. Shuttleless loom

Shuttle Loom
The term Shuttle loom refers to any loom that uses a shuttle. 

Shuttle is a boat-shaped device, usually made of wood with a metal tip that carries filling yarns through the shed in the weaving process. It is the most common weft-insertion device. The shuttle holds a quill, or pirn, on which the filling yarn is wound. It is equipped with an eyelet at one end to control rate. The filling yarn is furnished during the weaving operation.

Shuttle

Shuttleless Loom
A loom in which some device other then a shuttle is used for weft insertion, Shuttleless loom is further classified into follows:

1. Projectile loom
2. Rapier loom
3. Air jet loom
4. Water jet loom

Projectile Loom
A shuttleless loom that uses small metal devices i-e a bullet-like projectiles to carry the filling yarn through the shed. Fill is inserted from the same side of the loom for each pick. A tucked selvage is formed.

The mechanism of weft insertion is as follow:

          A - Warp shed
B - Weft
        C - Projectile

Rapier Loom
Looms in which either a double or single rapier (thin metallic shaft with a yarn gripping device) carries the filament through the shed. In a single rapier machine, the yarn is carried completely across the fabric by the rapier. In the double machine, the yarn is passed from 

one rapier to the other in the middle of the shed.

Structure of rapier loom 

Weft insertion mechanism of rapier loom

          A - Warp shed
B - Weft
     C - Rapier

Air jet Loom
A loom that employs a jet of air to carry the filling yarn through the shed.

Air-Jet Loom mechanism

Air-Jet weft insertion

Water jet Loom
A loom that employs a jet of water to carry the filling yarn through the shed