BASIC LOOM MECHANISM | GENERAL PASSAGE OF THROUGH A LOOM | DESCRIPTION OF IMPORTANT PARTS OF A LOOM

BASIC LOOM MECHANISM:

The basic mechanisms in any type of loom can be classified as follows:

1. Primary motions
2. Secondary motions, and
3. Auxiliary motions.   

Primary motions: 

The primary motions can further be divided as shedding, picking and beat up motions. The shedding opens the warp sheet into layers to facilitate passage of shuttle. The picking motion causes the shuttle carrying weft to be propelled from one end of loom to another. The beat up motion lays the previously laid weft to the fell of the cloth.

Secondary motions:

The secondary motions comprise of take up and let off motions. The take up motion helps to wind the cloth on to the cloth roller and also influences the pick density in the cloth. The let off motion helps to let the warp from the weaver’s beam at an uniform rate thus maintaining the warp tension constant throughout the weaving process.

Auxiliary motions:

The auxiliary motions consist of the warp stop motion, weft stop motion and warp protector motion. The warp stop motion is used to stop the loom in the event of warp breakages. This is necessary to prevent fabric defects such as missing ends and floats. The weft stop motion is used to stop the loom in the event of weft exhaustion or weft breakages. This is necessary to prevent missing weft threads called cracks, in the fabric. The warp protector is used to prevent multiple warp thread breakages in the event of shuttle getting trapped in the middle of the warp sheet.

GENERAL PASSAGE OF THROUGH A LOOM:

The passage of warp through a loom is shown in Fig. 1.1. The warp after leaving the weaver’s beam 1 passes over two bars 2 and 3 connected by a bracket at each end. One half of the warp end now passes under the back lease rod 4, and the other half passes over this rod. Those warp ends which pass under the back lease rod pass over the front lease rod 5, and ends from over the back lease rod pass under the front lease rod. Therefore, the warp is completely divided as it passes through the lease rods, and facilitates the straightening of any warp ends which may break and become entangled before they reach the healds 6 and 7. The lease rods also assist in forming an even shed. Leaving the lease rods, the warp ends next pass through the healds. Odd numbered pass through the front heald 7, and the even numbered ends pass through the back heald 6. The healds consists of heald wires with eyes at the centre through which the warp ends are passed, the warp ends being thus controlled in their upward and downward movement. The warp ends next pass through the reed 8, this being comprised of a flat wire comb with the teeth secured at both ends. Usually two ends pass between one tooth and the next—this space being termed “dent”. In the figure, two warp ends are represented as being in the same dent.

Passage of warp in a loom

At the point 9 is what is known as the ‘Cloth fell’. It may be considered as the point where the warp and weft become cloth, because it is at this point where the last pick of weft, which was left by the shuttle, becomes beaten up. Passing forward, the cloth is held at each side by a temple 10 which holds the cloth fell out to the width of the warp yarn, in the reed. From the temples the cloth passes over the breast beam/front rest 11, partly round the sand or emery roller K, over the steel roller, or tension rod L, and then on to the cloth roller M.

DESCRIPTION OF IMPORTANT PARTS OF A LOOM:

Heald shaft:

This part is related to the shedding mechanism. The heald shaft is made of wood or metal such as aluminium. It carries a number of heald wires through which the ends of the warp sheet pass. The heald shafts are also known as ‘heald frames’ or ‘heald staves’. The number of heald shafts depends on the warp repeat of the weave. It is decided by the drafting plan of a weave. The main function of the heald shaft is as follows:

•  It helps in shed formation
•  It is useful in identifying broken warp threads
•  It maintains the order or sequence of the warp threads.
•  It determines the order of lifting or lowering the required number of healds for a pick. In other words it helps in forming the design or pattern in a fabric.
•  It determines the warp thread density in a fabric, i.e. the numbers of heald wires per inch determine the warp thread density per inch.

Sley or. lay:

It is made of wood and consists of the sley race or race board, reed cap and metal swords carried at either ends. The sley mechanism swings to and fro. It is responsible for pushing the last pick of weft to the fell of the cloth by means of the beat up motion. The sley moves faster when moving towards the fell of the cloth and moves slower when moving backwards. This unequal movement is known as ‘eccentricity of the sley’. It is needed in order to perform the beat up and also to give sufficient time for passage of shuttle to pass through the warp shed. The beat up of the lastly laid pick of weft is accomplished through a metal reed attached to the sley.

Shuttle:

It is basically a weft carrier and helps in interlacement of the weft with the warp threads to form cloth. The shuttle which is made of wood passes from one end of the loom to the other. It travels along the wooden sley race and passes between the top and bottom layers of the warp sheet. The shuttle enters a shuttle box fitted at either ends of the loom, after passing through the warp shed. A shuttle normally weighs about 0.45 kgs.

Shuttle Box:

It is the housing for the shuttle and is made of wood. It has a spindle and a picker. It may also

accommodate the picker without spindle. The top and side of the box towards the sley race are open. The shuttle dwells inside the box for the intermediate period between two successive picks.

Picker:

The picker is a piece made either of leather or synthetic material. It may be placed on a spindle or grooves in the shuttle box. It is used to drive the shuttle from one box to another. It also sustains the force of the shuttle while entering the box.

Reed:

It is a metallic comb that is fixed to the sley with a reed cap. The reed is made of a number of wires and the gap between wires is known as dents. Each dent can accommodate one, two or more warp ends. The count of the reed is decided by the number of dents in two inches. The reed performs a number of functions which are enumerated as follows:

•  It pushes the lastly laid pick of weft to the cloth fell.
•  It helps to maintain the position of the warp threads.
•  It acts as a guide to the shuttle which passes from one end of the loom to the other.
•  It determines the fineness of the cloth in conjunction with the healds.
•  It determines the openness or closeness of the fabric.There are various types of reed such as ordinary reed, gauze reed, expanding reed, V reed etc.

Warp Beam:

This is also known as the weaver’s beam. It is fixed at the back of the loom. The warp sheet is wound on to this beam. The length of warp in the beam may be more than a thousand metres.

Back Beam:

This is also known as the back rest. It is placed above the weaver’s beam. It may be of the fixed or floating type. In the first case the back rest merely acts as a guide to the warp sheet coming from the weaver’s beam. In the second case it acts both as a guide and as a sensor for sensing the warp tension.

Breast Beam:

It is also known as the front rest. It is placed above the cloth roller at the front of the loom and acts as a guide for the cloth being wound on to the cloth roller. The front rest together with the back rest helps to keep the warp yarn and cloth in horizontal position and also maintain proper tension to facilitate weaving.

Cloth Beam:

It is also known as the cloth roller. The woven cloth is wound on to this roller. This roller is placed below

the front rest.