SHUTTLE LOOMS
Loom: An apparatus for making fabric by weaving yarn or thread. The basic purpose of any loom is to hold the warp threads under tension to facilitate the interweaving of the weft threads. The precise shape of the loom and its mechanics may vary, but the basic function is the same.
Shuttle Loom:
The shuttle loom is the oldest type of weaving loom which uses a shuttle which contains a bobbin of filling yarn that appears through a hole situated in the side. The shuttle is batted across the loom and during this process, it leaves a trail of the filling at the rate of about 110 to 225 picks per minute (ppm). Although very effective and versatile, the shuttle looms are slow and noisy. Also the shuttle sometimes leads to abrasion on the warp yarns and at other times causes thread breaks. As a result the machine has to be stopped for tying the broken yarns.
The basic mechanisms in any type of loom can be classified as follows:
1. Primary motions 2. Secondary motions 3. Auxiliary motions Primary motions Shedding Picking or filling or weft insertion Beating up
Secondary motions Warp let-off Take-up
Primary motions of weaving
. Shedding: Separating the warp yarns into two layers by lifting and lowering the shafts, to form a tunnel known as the ‘shed’
Shedding
. Picking or Filling: Passing the weft yarn (pick) across the warp threads through the shed.
Picking elements: Picking-stick, Picker, Shuttle, Buffer, Binder
Picking . Beating-up: Pushing the newly inserted weft yarn back into the fell using the reed.
Beat-up elements: Reed
Beating-up
Secondary motions of weaving: 4. Warp let-off 5. Take-up
. Let off: The warp yarns are unwound from the warp beam during the above three processes.
Let-off elements: Warp beam, Drop wire
. Take up: The woven fabric is wound on the cloth beam during the above three processes.
Take-up elements: Cloth roll.
Auxiliary Mechanism
To get high productivity & good quality of fabric, additional mechanisms, called “Auxiliary mechanisms” are added to a plain power loom. The auxiliary mechanisms are useful but not absolutely essential. 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. These are listed below:
1. Warp protector mechanism 2. Weft stop motion 3. Temples 4. Brake 5. Warp stop motion
The above operations must be synchronized to occur in the correct sequence and not interfere with one another. The full sequence is repeated for the insertion and interlacing of each weft yarn length with the warp yarns, and is therefore called ‘The Weaving Cycle’.
Shedding mechanism A process of raising and lowering of warp yarns by harnesses to make an opening for the filling (weft) yarn to pass through. The raised and lowered form of warp yarns is called shed
Three types of shedding motions (opening) are available for different type of fabrics. They are: . Tappet shedding . Dobby shedding . Jacquard shedding
1. Tappet Shedding A tappet is given a rotary motion so that it depresses a follower and a lever, known respectively as the anti-friction bowl and the treadle arrangement, by means of which the heald shaft is operated. Scope of Tappet Shedding: . Tappet shedding uses tappets and cams to control the up/down movement of shafts.
. The bulkiness of its mechanical movement limits the loom to control up to 8 shafts (repeat not more than 8)
. Therefore, tappet shedding is the simplest and least versatile shedding motion.
. The design is restricted to plain weave, simple twill and simple sateen or satin weave.
. Any design more than 8 shafts requires dobby loom
2. Dobby Shedding This is a compact, electronically guided shedding motion and capable of having up to 28 shafts. More complex and versatile shedding motion. A dobby loom, therefore, can have up to 28 shafts, and much greater weave repeat is possible. Design may be woven with two or more basic weaves and their variation. Such fabrics may be referred as dobby cloths or dobby weave, towels usually show geometric designs when pattern is provided by dobby. Scope of Dobby:
. It can produce more complex design.
. Theoretically it can control maximum 48 heald frame but practically 36.
. For cotton yarn it can control maximum 48 heald frame.
. Production is less than tappet.
3. Jacquard Shedding
To provide with unlimited design width, jacquard shedding is needed. This shedding motion has no shafts, instead, a hardness consisting of as many cords as there are ends in the warp sheet connects each end individually to the jacquard machine. Each warp could weave independently of all others. Complex and most versatile shedding motion. Biggest weave is possible with jacquard shedding as each warp yarn may be individually controlled.
Scope of Jacquard Shedding:
. No heald frame is used
. Harness is used to lift & lower the warp thread
. One warp thread for each harness
. Most complex design is produced
. Maximum no. of warp yarn it can control.
Under picking mechanism
Picking is the second primary motion in weaving. The action of inserting weft yarn through the warp yarns is called picking.
The functions of picking mechanism are:
1. To deliver the shuttle along the correct flight length. 2. To throw the shuttle at a predetermined speed.
Main parts:
Under picking mechanism
1. Picking arm 2. Picker 3. Picking cam 4. Picking bowl 5. Race board 6. Shuttle 7. Bottom shaft 8. Treadle lever 9. Angular lever 10. Crank shaft
Features of under picking mechanism: 1. Picker arm is placed under the race board. 2. Suitable for wider loom. 3. Under picking works less smoothly. 4. More direct action. 5. Rough in action. 6. More clean mechanism. 7. Consumes more power. 8. Used for heavy weight fabrics in silk and rayon looms.
Under picking mechanism:
In under picking mechanism a race board is situated over picking arm. Under picking is controlled by picking cam which is fixed on the bottom shaft. At first the motion comes from motor and m/c pulley.
Then the motion comes in to the bottom shaft and thus picking cam. When picking cam rotates and its nose portion comes in contact with treadle lever and pushes it then the treadle lever pushes the angular lever. The picking arm gets motion from angular lever which is connected with picking arm.
A picker is placed in the picking arm which pushes the shuttle. When shuttle gets motion by picking arm then shuttle begins to move to and fro on the race board. Thus picking is done.
A spring is situated which causes the picking arm and picker to move back after the delivery of the pick. At the two end of bottom shaft, two picking tappets are fixed. By increasing nose length picking speed may be increased.
Beat up mechanism
The beating-up is the third primary motion of weaving. It consists in driving the last pick of weft to the fell of the cloth. This is accomplished with the help of a reed fixed in the sley. The sley is given a sudden and quick movement towards the fell of the cloth by the cranks in the crankshaft. The sleywood runs from one shuttle box to another, and when at its backward movement, the shuttle travels over its race. Main parts: 1. Crankshaft 2. Crank 3. Crank arm 4. Reed cap 5. Reed 6. Sley race 7. Sley 8. Sleysword
Description:
The crankshaft gets drive from motor via motor pulley and m/c pulley. The crankshaft has two cranks. These cranks transform the rotary motion into swinging motion. The reed cap is connected by crank arm to crank of the crankshaft. Again the reed is connected between reed cap and sley. There is sleysword under the sley that is bolted to the rocking shaft. There is also shuttle box on the sley. Now the crank gives the swinging motion to the sley by crank arm. When the sley is moving towards the heald shaft at certain position the shuttle passes through warp shed. Again when the sley is coming towards the front rest at last position the reed pushes the last pick to the previous pick of cloth. This is the beating-up motion and the cloth increases in lengthwise in this way.
Secondary Motions: These mechanisms are next in importance to the primary mechanisms. If weaving is to be continuous, these mechanisms are essential. So they are called the ‘secondary’ mechanisms. They are:
Take-up motion
Let-off motion
Take-up motion The take-up motion withdraws the cloth from the weaving area at a constant rate so as to give the required pick-spacing (in picks/inch or picks/cm) and then winds it on to a cloth roller. The main part of the mechanism is the take up rollers, which draws the cloth at the regular rate, and the number of picks per inch decides this rate. The take up roller is covered with emery cloth or hard rubber depending upon the type of cloth woven. The drive to the take up roller is by a train of gear wheels put into motion directly from the main shaft.
Let-off motion
The let-off motion delivers the warp to the weaving area at the required rate and at constant tension by unwinding it from the weaver’s beam. The secondary motions are carried out simultaneously. The speed of the servo motor is transmitted to warp beam gear via reduction gear, thus driving beam.
Yarn path of the shuttle loom
Advantages of shuttle looms:
. Shuttle loom is more economical . It is suitable for low scale production types industry . Easy to operate . Separate parts are available in the market
Disadvantages of shuttle looms:
. Causes more noise in working field . Shuttle cause abrasion on warp yarn which increase the wastage percentage . Production rate is slower than shuttle-less loom . Higher labour cost . Value of fabric lost because of shuttle movement . Efficiency is lower than shuttle-less loom
References: . textilefashionstudy.com . textilehelpguide.blogspot.in . textilelearner.blogspot.com