Air Jet Spinning System- Modern Yarn Production
Dept. of Textile Technology
Sarvajanik College of Engineering & Technology, Surat, India
Cell: +91 9662020909
What is spinning?
- The term ‘spinning’ may be defined as the process or processes used to produce either fibres or filaments from natural or synthetic polymers, or convert natural or man-made fibres (mmf) and filaments into yarns by twisting or other means of binding together the fibers or filaments.
- This provides a relatively fine continuous length of thread that has properties suitable for conversion into a fabric form or for use directly for sewing or rope making. The spinning processes employed to make fibres or filaments may be generally classed as polymer extrusion methods.
- Air-jet spinning is the latest in a string of technological developments intended to increase production speed and flexibility. This technique is also known as fasciated yarn spinning. Air-jet spinning system which consists of a 3-over-3 high-speed roller drafting unit, The basic jet design is also shown. This has a central cylindrical channel (the spinning channel) through which the fibre ribbon from the drafting unit passes. Inclined to the channel axis but tangential to its circumference are four nozzles through which compressed air is injected into the channel, creating a vortex airflow.
- Each jet of compressed air entering and expanding into the channel has two velocity components of airflow: V1, a circular motion of the air around the channel circumference, and V2, the movement of the air to the channel outlet. The suction at the jet inlet created by V2 gives automatic threading-up of the spinning process. Provided the drafted ribbon is not tautly held between the front drafting rollers and take-up rollers, the V1 component of flow rotates it, inducing a false-twisting action via a rotating standing waveform (a spinning balloon) while V2 assists movement of the twisted ribbon through the channel.
|Flowchart of Air Jet Spinning|
- The nozzles of the first jet are set to give a counter-clockwise vortex producing a Z–S false-twist action; the second jet gives an S–Z false-twist action. The pressures applied to the jets are such that jet 2 has the higher twisting vortex. Although the jets impart a false twist, while doing so they do not have a positive hold on the ribbon being twisted. Because of this the Stwist from jet 2 propagates along the twisted ribbon and nullifies the Z-twist from jet 1, leaving some S-twist to travel towards the nip line of the front roller.
|Air Jet Spinning|
Operation Principle of Rieter Two- Nozzel Air-Jet Spinning:
- As shown in a draw frame sliver fed from a can is passed to a drafting arrangement , where it is attenuated by a draft in the range of 100 - 200. The fiber strand delivered then proceeds to two air jets arranged directly after the drafting arrangement. The second jet is the actual false-twist element.
- The air vortex generated in this jet, with an angular velocity of more than 2 million rpm, twists the strand as it passes through so that the strand rotates along a screw-thread path in the jet, achieving rotation speeds of about 250 000 rpm. The compressed air reaches the speed of sound when entering the central canal of the false-twist element. Since the axial forces are very low during this rotation, only low tensions arise in the yarn.
|Diagram of Air Jet Spinning|
|Twist direction of Air Jet Spinning|
- The ability of the vortex to impart torque is so high that the turns of twist in the yarn run back to the drafting arrangement. The fiber strand is therefore accelerated practically to full rotation speed as soon as it leaves the front roller.
- The edge fibers which ultimately bind the yarn together by becoming wrapping fibers are in a minority.
- For process reasons, they do not exceed about 5% of the total yarn mass. These edge fibers exhibit relatively few turns of twist in the same direction as the falsetwisted core fibers or can even be slightly twisted in the opposite direction. This is partly ensured by causing the strand to emerge from the nip line in a broadly spread form, but mainly by generating in the first jet a vortex with an opposite direction of rotation to the vortex in the second jet.
- This first vortex is in fact weaker in intensity than the second and cannot really affect the core fibers, but can grasp the edge fibers projecting from the strand at one end. Since the first vortex acts against the twist direction generated by the second jet, it prevents the edge fibers from being twisted into the core or even twists them in the opposite direction around the core fibers. As the strand runs through the second jet, the following occurs.
- The turns of twist generated by the jet are canceled in accordance with the falsetwist law. The core fibers, i.e. the vast majority, no longer exhibit any twist; these fibers are arranged in parallel. On the other hand, the edge fibers (which previously exhibited no twist, relatively little twist, or even twist in the opposite direction) receive twist in the direction imparted by the jet, as determined by the law of false twist; they are therefore wound around the parallel fiber strand. They bind the body of fibers together and ensure coherence. A twist diagram prepared by Dr. H. Stalder demonstrates this twisting procedure .
- The resulting bundled staple-fiber yarn passes from the take-off rollers through a yarn-suction device and an electronic yarn clearer before being wound onto a cross-wound package. The two nozzle air-jet spinning system represents a very interesting process, which has already been introduced into practical operation with some success.
SPECIFICATION OF THE MJS MACHINE:
- Spinning positions per machine .......up to 72 (SINGLE -sided machine)
- Delivery speed ..........150 - 300 m/min
- Raw material ............synthetic fibers and blends (combed cotton)
- Count range .............7.5 - 30 tex; Ne 20 - 80
- Feedstock type ........drawframe sliver
- Type of yarn ............bundled single yarns
- Yarn characteristics .......reasonable strength, low hairiness, rough outer surface
- Field of use ........ladies‘ outerwear, shirting, material, sheets
- Remarks ...........low production costs, low personnel demand, no rapidly rotating parts, three drawframe passages necessary
YARN CHARACTERISTICS OF AIR-JET SPIN YARNThe yarn character is slightly different from that of ring spun yarn. It is somewhat:
- stiffer, and
Additional points of comparison with ring-spun yarn are:
- Good evenness (like ring-spun yarn);
- Good abrasion resistance;
- Low tendency to pilling;
- Low snarling tendency;
- Shrinkage similar to that of ring-spun yarn;
- Higher resistance to bending;
- Slightly lower covering power;
- Wrapping fibers not uniformly distributed over the length; sometimes there are slightly more on the surface, sometimes slightly fewer.
- A large number of wrapping turns impart more strength but at the same time greater hardness. Synthetic fiber yarns and blends of synthetic fibers and cotton with a proportion of synthetic fibers of at least 50% achieve strength levels of about 80% or more relative to ring-spun yarn.