Looming Process PDF

Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) The Looming Process Once warp and weft yarns are properly prepared, they become ready for actual weaving into a fabric on the loom. The actual weaving of woven fabric on the loom is...

Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) The Looming Process Once warp and weft yarns are properly prepared, they become ready for actual weaving into a fabric on the loom. The actual weaving of woven fabric on the loom is called as the looming process. There are several different types of looms but most commonly looms are classified based on the picking medium they use. Types of Looms Basic Loom Components Prepared By: Shakeel Ahmad Paracha Page 1 of 24  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) Drive to The Loom Loom Specifications Method of picking, i.e., whether shuttle or Shuttle-less (air-jet, rapier, water-jet, projectile, etc.) The speed of the loom in terms of: o Picks per minute (PPM) o Picking rate in metres per minute Metres per minute = PPM x Reed space (metres/mm) Type of shedding mechanism installed on the loom, i.e., crank, tappet, dobby or jacquard. Design capabilities, i.e., a maximum number of frames that can be handled by the loom. Working width of the loom. Type of raw material handled by the loom, e.g., cotton, silk, polyester, etc. The weight of the fabric weavable on the loom, e.g., light-weight, medium-weight, heavy- weight fabrics. A specific type of fabric that can be produced on the loom, e.g., terry, velvet, leno, carpet, etc. Motions of The Loom The necessary mechanisms or motions required to weave fabric are categorized as: o Primary motions o Secondary motions o Tertiary/Auxiliary/Stop-motions On a handloom, all these motions are performed manually by the weaver whereas in power looms these motions are carried out through an external source of power. Looms have a main motor which is driven by electricity which in turn transmits the drive to its various parts. The Primary Motions The primary motions are the essential motions of the loom without which weaving cannot take place. The three primary motions of the loom are: o Shedding motion o Picking motion o Beating-up motion Also, these motions must be performed in the sequence as given above. Prepared By: Shakeel Ahmad Paracha Page 2 of 24  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) The Shedding Motion The process of lifting and lowering of the warp yarns is called shedding, and the mechanism that does shedding is called as the shedding motion or mechanism. The warp yarns are lifted to make a shed so that weft yarns can be inserted through the shed and interlacement can be done. Types of Shedding Mechanisms There are four different methods of creating a shed: o Crank shedding o Tappet/Cam shedding o Dobby shedding o Jacquard shedding The first three shedding mechanisms make use of frames to lift and lower the warp yarns whereas the jacquard shedding mechanism uses an individual harness to lift an individual warp yarn. The Jacquard Shedding Jacquard shedding mechanism was invented by a French silk weaver Joseph Marie Jacquard in 1801. In jacquard shedding motion instead of heald frames, several harnesses are used. Each end is passed through an individual harness eye whose lifting and lowering is individually controlled by the jacquard shedding mechanism. Prepared By: Shakeel Ahmad Paracha Page 3 of 24  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) So, by eliminating the frames and using individual harnesses, the capacity of jacquard shedding motion is increased considerably. The capacity of the latest electronic jacquard shedding motion has reached up to 25000 hooks or ends per repeat. The jacquard shedding mechanism is suspended from the ceiling and is placed above the loom. The jacquard shedding mechanism is connected to the loom through the jacquard harness system. The jacquard harness is the system of cords, harness eyes and lingoes that transmit the movement of the jacquard hooks to the individual warp yarn. At about one metre below the jacquard mechanism, a comber board is placed. The harnesses after passing through the comber board come straight and parallel on the loom. Prepared By: Shakeel Ahmad Paracha Page 4 of 24  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) The Scope of Various Shedding Mechanisms Different shedding mechanisms have different design capabilities, i.e., the number of frames that it can handle. The scopes of different shedding mechanisms are as follows: o Crank shedding → 2 frames only o Tappet/Cam shedding → 8 - 12 frames o Dobby shedding → 28 - 32 frames o Jacquard shedding → up to 25,000 hooks The Picking Motion The insertion of weft yarns into the shed of the warp yarns is called as the process of picking. Picking is done to complete the interlacement process so that a woven fabric can be formed. Different types of picking techniques are classified as: o Shuttle picking o Shuttle-less picking Shuttle V/S Shuttle-less Looms Shuttle looms use shuttle as picking medium whereas in all shuttle-less looms medium other than shuttle is used. In shuttle looms the picking medium also carries the weft supply package, but in all shuttle- less looms large weft supply package is placed outside the loom generally at the left-hand side. In shuttle looms the picking medium reciprocates from one side of the loom to the other. In shuttle-less looms, the weft is only inserted from one side only. Shuttle Checking Mechanism The average speed of the shuttle is 40 feet/sec and is achieved through an acceleration of 2500 inches/sec2. As the shuttle is thrown from one side of the loom to the other, it reaches the opposite shuttle box with this great velocity. To avoid damage to loom parts, the shuttle should be completely stopped as it is collected in the opposite shuttle box before it is thrown back by the picker stick. To stop the shuttle, a shuttle checking mechanism is used as shown below: Prepared By: Shakeel Ahmad Paracha Page 5 of 24  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) Shuttle-less Methods of Picking Loom Width Comparison Prepared By: Shakeel Ahmad Paracha Page 6 of 24  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) Loom Picking Rates Use of Weft Accumulators in Shuttle-less Looms To supply weft yarn at a constant and uniform tension, weft accumulators are used. A specific amount of yarn is unwound from the supply package and is wound on the drum of the accumulator from where it is taken by the weft supply medium. This ensures a constant and uniform tension on the weft during picking. The weft accumulators generally store 2 - 3 pick length of weft yarn on its drum. Working of Weft Accumulators Weft Accumulator or Yarn Feeder Prepared By: Shakeel Ahmad Paracha Page 7 of 24  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) The Projectile Picking Introduced commercially in 1952 by Sulzer. It uses a projectile with a gripper to insert the weft yarn. This picking technique is suitable for any yarn, i.e., cotton, wool, synthetic & blended. Wide variety of fabrics ranging from light to medium-weight dress fabrics to heavy-weight industrial fabrics. Advantages of Projectile Picking Low power consumption at high speeds as compared to shuttle picking. Wider widths are possible to weave easily up to 212" allowing higher picking rates of up to 2000 metres per minute. Wider widths allow more savings in energy and space. Up to six multi-colour pick insertion. The Projectile V/S The Shuttle The Projectile Projectiles are either made up of steel or carbon composite materials. D1, D12 & D2 are different types of steel projectiles. Carbon composite projectiles are classified as K3 type. These types of projectiles are used for weaving different types of fabrics. K3 type is preferred for weaving delicate fabrics. Prepared By: Shakeel Ahmad Paracha Page 8 of 24  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) Types of Projectiles Characteristics of Projectiles Projectile Picking Mechanism Prepared By: Shakeel Ahmad Paracha Page 9 of 24  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) The projectile is grabbing the weft yarns presented to it. The projectile after being struck by the picking stick moves over the guides. Passing of weft yarn through projectile guides. Prepared By: Shakeel Ahmad Paracha Page 10 of 24  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) The projectile is arriving in the receiving unit. The projectile after being stopped at the receiving unit is ejected onto a conveyer belt that takes back to the picking unit. Four colour weft presenting mechanism. Prepared By: Shakeel Ahmad Paracha Page 11 of 24  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) The Air-jet Picking Introduced commercially by Swedish engineer Max Paabo in 1951. Weft yarn is propelled using compressed air. Gives the highest rate of picking going as high as up to 2400 metres per minute. Simple operation with reduced mechanical parts and hence the maintenance cost is very low. Significant reduction in noise and vibration. Air-jet weaving is the most popular form of weaving. The basic principle of air-jet picking Air-jet Picking – Principle of Operation The tandem and main nozzles are turned on. The yarn is released from the clamp or stopper. Compressed air then propels the weft yarn across the shed. The speed of weft yarn is maintained by using sub-nozzles that supply additional air pressure to the weft yarn. To avoid the scattering of air pressure, a profiled reed is used that acts as a channel for the air and the weft yarn. When all the length of the pick is pulled off the feeder, the stopper again closes. The timing diagram of main & sub-nozzles Prepared By: Shakeel Ahmad Paracha Page 12 of 24  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) The timing diagram of a typical air-jet loom Historical Development – Air-jet Weaving The Maxbo air-jet loom introduced in 1951 only made use of the main nozzles, and its width was restricted to about 30 to 36 inches with a speed of 350 ppm. In early 1960s confusors (guides) were introduced to stop the air from spreading, and the width of air-jet looms was extended up to 60 inches. The idea of using multiple sub-nozzles along with the main nozzles and the use of profiled reed was given in 1969. Based on this, in 1975 air-jet looms running at 600 ppm on 130 inches width were introduced. In early 1980s Picanol and Bonas introduced multiple colour weft selection on air-jet looms. Nissan and Toyoda of Japan introduced plastic nozzle covers to prevent air leakage that helped to increase the width of looms up to 156 inches. In the last 25 years, intensive research on nozzle and reed design has made air-jet looms wider, faster and economical than ever before. Air jet looms with a width of 172 and picking rates of up to 2400 metres per minute are available in the market today. It is also now possible to make heavier fabrics like terry, denim, etc. with air-jet weaving which was not possible earlier. Prepared By: Shakeel Ahmad Paracha Page 13 of 24  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) Yarn Feeders in Air-jet Weaving Air jet Picking – Use of profiled Reed & Relay Nozzles Types of relay nozzles based on the number of holes in the head Prepared By: Shakeel Ahmad Paracha Page 14 of 24  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) Types of relay nozzles w.r.t. Nozzle tops The Rapier Picking In rapier looms, either one or two arms are used to transfer the weft yarn from one side of the loom to the other. The term rapier is named after a two-edged sword. Since, the rapier arms resemble such a sword, so they are called as rapier. Rapier weaving was introduced in the late 1960s. Since, then it is proven to be a versatile method as it can form fabrics ranging from 20 - 850 gsm. Rapier looms in addition to traditional yarns like wool, cotton & man-made fibres can also handle difficult filament yarns such as glass fibres. Classification of Rapier Looms Single Arm Rigid Rapier Looms Prepared By: Shakeel Ahmad Paracha Page 15 of 24  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) Double Arm Rigid Rapier Looms Dewas system of weft transfer or tip to tip transfer Gabler system of weft transfer or loop transfer Double Arm Flexible Rapier Looms Double arm rapier heads Yarn transfer in double arm rapier Prepared By: Shakeel Ahmad Paracha Page 16 of 24  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) Rapier grippers Prepared By: Shakeel Ahmad Paracha Page 17 of 24  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) The Beating-up Motion Beating-up is the third and the final primary motion of the loom. The process of pushing the newly inserted weft yarn into the fell of the cloth is called as beating-up or beating-in. The fell of the cloth is the line that divides the warp yarns and the cloth. The beating-up motion is performed by a loom accessory called as the reed. Reed is a wooden, plastic or metallic frame having vertically held metallic wires placed at a fixed pre-determined distance. Reeds are specified by their reed number or count indicating number of dents present in the reed per unit length. The Reed Beating-up on Shuttle Looms Prepared By: Shakeel Ahmad Paracha Page 18 of 24  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) Prepared By: Shakeel Ahmad Paracha Page 19 of 24  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) The beating-up mechanism is connected to the crank shaft. Here, the crank shaft is connected to the machine pulley. The crank shaft contains the crank. Each crank is connected to the crank arm by the crank pin, and it contains bearing for the smooth operation. The Crank arm and the sley sword are attached with the sword pin. The position of the reed is at top of the sley at the race board. The Reed cap is placed on the top of the reed. The whole parts of the beating-up mechanism are mounted on the rocking shaft. The crank shaft achieves motion from the machine pulley. When the crank shaft rotates due to the structure of the crank it moves forward and backward. Each crank is connected to the crank arm which is connected to the reed. So, when the crank shaft rotates, the reed moves forward and backward for the beat-up. (1) (2) (3) (4) Prepared By: Shakeel Ahmad Paracha Page 20 of 24  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) (5) Eccentricity The motion of the sley and the reed deviates from the simple harmonic motion (SHM) because of the cranks. The deviation from the SHM is called as eccentricity which is found out as: Eccentricity = e = Crank radius/Crank arm length Because of eccentricity, the sley moves faster when it approaches the front position to beat-up and moves slower as it reaches the back position where picking is done. The value of eccentricity ranges from 0.25 to 0.40. Greater the value of (e) greater will be the eccentricity and so as the force of beat-up. Beating-up on Shuttle-less Looms Prepared By: Shakeel Ahmad Paracha Page 21 of 24  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) (1) (2) (3) (4) Forces Acting on Yarns in Beat-up Prepared By: Shakeel Ahmad Paracha Page 22 of 24  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) The Secondary Motions In addition to the necessary primary motions of the loom to weave fabric, following two secondary motions are also necessary for continuous weaving at high speeds: o Warp Let-off motion/Force o Warp Take-up motion/Force These motions are called as secondary motions of the loom and are always present in all commercial looms except the handloom. Warp Let-off Motion/Force It is that type of secondary motion which allows the warp to move forward by unwinding it from the weaver’s beam maintaining a pre-determined warp tension to keep uniform pick spacing. Warp Take-up Motion/Force The take-up motion is responsible for dragging the woven fabric forward from fell of cloth and to wind it on to the cloth roller. The take-up motion also controls the weft thread density of woven fabric on the loom. This is done by controlling the rate of take-up. It is synchronized with let-off motion. The speed of take-up is less than that of let-off motion due to crimp of yarn. The Tertiary/Auxiliary/Stop-motions The tertiary/auxiliary/stop-motions are the additional motions. Auxiliary/tertiary motions have the following objectives: o To deliberately stop the loom in case there is a yarn breakage so that the final fabric produced is free from faults, i.e., to improve the quality of the fabric. o To automate various mechanism of the loom so that unnecessary stoppages can be avoided. Following four motions are an example of auxiliary/tertiary motions and these motions are also necessary for continuous weaving at high speeds: o Warp stop-motion o Weft stop-motion Stop-motions Tertiary/Auxiliary Motions o Warp protector motion o Weft Replenishing motion Weft Stop-motion The purpose of weft stop-motion is to stop the loom whenever the weft yarn breaks or when the weft yarn on the weft supply package finishes. Warp Stop-motion Warp stop-motion is responsible for stopping the loom whenever any warp yarn breaks during the process of weaving. Warp Protector Motion The purpose of warp protector motion is to stop the loom whenever the shuttle gets entrapped in the shed and fails to reach in opposite or receiving side during picking. Prepared By: Shakeel Ahmad Paracha Page 23 of 24  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) Weft Replenishing Motion The weft replenishing motion is used to automatically change the pirn just before it is about to exhaust with a new one without stopping the loom. Prepared By: Shakeel Ahmad Paracha Page 24 of 24