Loom- The weaving Machine

The Loom

The machine used for weaving fabric is a loom. The ancient Egyptians and Chinese used looms as early as 4000 BC. The basic purpose of any loom is to hold the warp threads under tension to facilitate the interweaving of the weft threads.

Photo: A Loom of wooden frame.

The working process of a loom:

1.      The warp beam, located in the back of the loom, is a large roller on which all the warp yarns to be used for the cloth is wound parallel to each other. If the fabric is to have warp stripes, the various yarns are wound onto the beam in color groupings to obtain the desired colored-stripe effect.

2.      The warp yarns pass through the harnesses, which look like picture frames (pic-2) holding many thin vertical wires called heddles, each with a hole (eye) in the middle. Each warp yarn is threaded through the eye of one heddle and is thereby controlled by that harness.

3.      The purpose of the harnesses is to raise and lower groups of warp yarns. The number of harnesses varies from 2 to about 30, depending on the complexity of the weave. The warp yarns are separated into an upper group and a lower group, thus creating an opening, or shed. For example, to make a plain weave. Every other warp yarn is raised by half of the harnesses, as the harnesses controlling the other warp yarns remain lowered.

4.      The shade is made when a harness or groups of harnesses are raised. It allows the filling yarn to travel across the loom over some warp yarns but under other warp yarns. A shuttle of other insertion device carries the filling yarn. As the insertion device moves through the shed, it leaves a trail of filling yarn behind it when it passes over the lower set of warp yarns and under the upper set.

5.      The warp yarns, after passing through the harnesses, pass through a reed, which is a frame with thin, vertical, no movable wires. Narrow openings, of dents, exist between the wires; their purpose is to keep the warp yarns separated. In the process of weaving, the insertion device passes in front of the reed, placing a filling yarn (pick). Then the reed, which resembles a comb, bushes the loose pick in the shed up to the edge of the already made cloth and returns to a position near the harnesses. This is called beating-up.

6.      Before the insertion device returns across the loom, some of the harnesses may change position, by either being raised or lowered. The sequence in which the harnesses are raised or lowered determines the weave that is made in the fabric.

7.      This completes one cycle of a filling yarn insertion. These steps are continually repeated so that many thousands of filling yarns are inserted to produce the woven fabric. The completed cloth is slowly wound onto the cloth roll located in the front of the loom.

Types of looms:

a.      Shuttle loom or conventional loom: Looms that use a shuttle to insert the filling yarn in the shed are known as shuttle, fly shuttle, or conventional looms. A shuttle is a wooden, boat-like device with a bobbin or quill placed inside with filling yarn wound around it. As the shuttle is projected (forced with great pressure) across the loom, the filling yarn unwinds from the bobbins, leaving a trail of yarn behind. Example- 1. Plain loom 2. Box loom

1.      Plain loom: the loom which consist of only one shuttle.

2.      Box Loom: The loom which consists of two or more shuttle.

b.      Shuttleless Loom: Shuttleless looms use other devices to bring the filling yarn through the shed. The yarn comes from cones placed at the side of the loom; one the filling yarn is bought across the loom, the yarn is cut, often leaving a little fringe at the edges of the fabric. (Something the fringe is tucked into the fabric, making a tucked selvage). Except for the means of transporting the yarn across the shed, the steps in the weaving process are the same. The main devices used to insert the filling yarn in the shed are a missile of projectile, a rapier, of a jet nozzle.

Shuttleless looms are designed to produce a higher production rate (more yards per hour) than shuttle looms. The speed of a loom is usually expressed as the number of picks per minute (PPM) that a loom can insert for a specified width.

It is generally assumed that it takes more than three shuttle looms to equal the production of one shuttleless loom.

a.      Missile of Projectile Loom: The missile of projectile is a small, light gripper device (about the size of a pocket knife) that is propelled across the loom, pulling filling yarn behind it. The dragging of the filling yarn across a loom created strain on this yarn, so projectile looms are not suited for weaving with fragile of very weak filling yarns, they are, however, excellent for use with heavy and bulky yarns, as well as regular size yarns. This loom is the most versatile of the suttleless looms In regard to the range of fabrics it can produce. Also, it can produce the widest material, up to 18 foot carpet widths.

b.      Rapier Loom: A rapier loom uses a rapier to pull the filling yarn across the loom. The rapier is a metal rod, either rigid of flexible, that has a gripper on one end. One rapier pulls the filling yarn across the entire loom width, and a second rapier is ready to follow with the next filling insertion of pick.

Because the rapier is not in free flight as is a projectile, less strain is placed on the filling yarn and so rapier looms are capable of weaving with delicate filling yarns. A wide range of fabrics can be produced with them.

c.       Jet Loom: Jet looms take the filling yarn across the loom by using a high speed jet of either air of water. The force of the air or water carries the yarn from one side to the other. Jet looms are faster than missile of rapier looms (higher picks per minute). They cannot, however, produce as great a variety of fabrics (no heavy and bulky yarns), nor can they produce as wide a fabric (jet have less yarn-carrying power than projectiles and rapiers). Jet looms also do less damage to the warp because there is no abrasion of this yarn by the jets of air of water. This is in contrast to the missile of rapier, which rides across the warp yarns left in the down position of the shed.

With Air-Jet looms, the initial propulsion force is provided by a main nozzle. Relay nozzles along the shed produce additional booster jets to help carry the yarns across the loom.

With the Water-Jet looms, there is only a main nozzle to provide the propulsion of the filling yarn. This loom is very efficient, with only a small amount of water required, and it is the fastest type of shuttleless loom.

Comparative study on different types of looms:

Loom type		Method of inserting weft yarn	Characteristics
looms with shuttles		The weft yarn is inserted through the back-and-forth motion of the shuttle.	Great all purpose loom. Vibration and noise are severe problems and high speed operation is difficult.
Looms without shuttles	Gripper loom	A small metal gripper shuttle grasps the weft yarn and inserts it.	A very versatile loom, but it is noisy and there is a limit to its operation at high speed.
	Rapier loom	Two bands at the center of the fabric receive and pass on the weft yarn. The catch method is the most popular method, and is further broken down into two types, the band method and the pole method.	A very versatile loom, but it is noisy and there is a limit to its operation at high speed.
	Water jet loom	A jet of water is used to insert the weft yarn.	High speed operation is possible. Since water is used only filament yarns (synthetic fabrics) can be woven.
	Air jet loom	A jet of air is used to insert the weft yarn.	High speed operation is possible. At present this is the most popular type of loom and its functions are excellent overall.

Devices of a Loom:               1.    Warp Beam

2.      Harnesses

3.      Heedles

4.      Shuttle

5.      Reed

6.      Cloth Beam

Below is the short description of the above mentioned parts of a loom;

1. Warp Beam: The warp threads are wound on a roller called the warp beam, and attached to the cloth beam which will hold the finished material. Because of the tension the warp threads are under, they need to be strong.
2. Harnesses: Harness is the device of the loom composed with a number of fine heedles. Harness of the loom actually holds the heddle. On the modern loom, simple shedding operations are performed automatically by the harness. This is a rectangular frame to which a series of wires, called heddles 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.
3. Heedle: A heddle is an integral part of a loom. Each thread in the warp passes through a heddle, which is used to separate the warp threads for the passage of the weft. The typical heddle is made of cord or wire. Each heddle has an eye in the center where the warp is threaded through. As there is one heddle for each thread of the warp, there can be near a thousand heddles used for fine or wide warps.

Photo: heddle

4. 
   
   Shuttle: A shuttle is a tool designed to neatly and compactly store weft yarn while weaving. Shuttles are thrown or passed back and forth through the shed, between the yarn threads of the warp in order to weave in the weft. The simplest shuttles, known as "stick shuttles", are made from a flat, narrow piece of wood with notches on the ends to hold the weft yarn.

Photo: Large stick shuttle & Shuttle with Bobbins.

5. Reed: A reed is part of a loom, and resembles a comb. It is used to push the weft yarn securely into place as it is woven, separates the threads and keeps them in their positions, keeping them untangled, and guides the shuttle as it moves across the loom. It consists of a frame with lots of vertical slits.

                                                            Photo: Reed and its structure.

6. Cloth Beam: It’s a roller like device in a loom, which is connected with the warp beam by warp yarns of the loom. When a fabric is weaved in a loom then cloth beam or takeup roll is used to fold the finished fabrics. It also helps in creating tension of warp yarns to produce a fine fabric.

Motion of a Shuttle loom

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.

1. Shedding:  Shedding is the raising of the warp yarns to form a shed through which the filling yarn, carried by the shuttle, can be inserted. The shed is the vertical space between the raised and unraised warp yarns.
2. Picking:  As the harnesses raise the heddles, 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. The shuttle is normally pointed at each end to allow passage through the shed.  A single crossing of the shuttle from one side of the loom to the other is known as a pick. As the shuttle moves back and forth across the shed, it weaves an edge, or selvage, on each side of the fabric to prevent the fabric from raveling.
3. Battening:  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. Conventional shuttle looms can operate at speeds of about 150 to 160 picks per minute.

4.      Take Up: With each weaving operation, the newly constructed fabric must be wound on a cloth beam. This process is called taking up. At the same time, the warp yarns must be let off or released from the warp beams. To become fully automatic, a loom needs a filling stop motion which will brake the loom, if the weft thread breaks.

The motions that are described above are the primary and secondary motions of a loom, beside these there are also some motions known as Auxiliary motion of the loom.

Auxiliary motions of the loom are:

1. Weft-stop motion.
2. Warp-stop motion.
3. Warp –Protection motion
4. Weft-accommodation motion.
5. Weft measuring device.
6. Shuttle changing machine.
7. Automatic weft removing.
8. Automatic weft package supply.
9. Automatic cloth rolls dofting.