The conventional method of spinning core yarns using a ring spinning frame is reported to produce uneven looping of the core yarn which influences detrimentally the yarn quality. This method is also claimed to be inefficient since in wrapping the core filament with the loosened fibrous material an additional twist is imparted to the core yarn. These problems are not apparent when the OE spinning procedure is applied to core yarn spinning1. Three various methods of core yarn production in rotor spinning are there. There will be slight modifications in the rotor spinning unit for the core yarn production.
Key Words: Core yarn, Rotor modifications, Production Methods, Advantages, Features.
The rotor spinning is proving the economic source of producing the coarser number yarns, which satisfies the manufacturers profit need. It is the ever growing sector and the investment requirement will be lower than the other spinning systems. Though it is in the second place of yarn production technique, it has the domination over, all the spinning systems due to its remarkable advantages like higher production, low hairiness, more even yarn with good bulkiness. The strength of the rotor yarn is less when compared with ring spun yarn but the coefficient of variation in strength is very less2. Three methods are followed in this regard to produce the core yarn in rotor spinning machine.
3.1 Method 1
Fig.1 shows an arrangement for core yarn spinning. The illustration shows a rotor having apertures for generating an air flow, but suction devices external to the rotor may be used. In the base of the rotor is fitted a feed channel for feeding a filament in to the rotor. The feed channel is situated within the axis of rotation of the rotor and extends into the rotor chamber by a predetermined length. The diameter of the bore of the feed channel must be equal to the diameter of the core yarn or slightly larger than the feed filament; this is intended to prevent the intake of useless air through the feeding channel. Opposite the feed channel from the open side of the rotor chamber a stationary doffing tube is mounted co- axially with the axis of rotation. Above the doffing tube, a pair of delivery rollers and the yarn package drive are arranged to constitute the yarn winding-up mechanism. The wrapping yarn is spun in the known OE manner. Once spinning of the wrapping yarn is in progress, core filament is unwound from the supply bobbin and is sucked into the rotor chamber by the effect of the under pressure. The core filament is then caught up by the wrapping yarn and passes with it through the doffing tube. In the steady state condition, the wrapping of the filament yarn by the rotor spun yarn occurs within the doffing tube as shown in fig. every rotation of the peeling-off point produces one coil of the wrapping1.
3.2 Method 2
A simple method for the production of core spun yarn by the rotor spinning system is described by Nield and Ali. In this method, a feed tube positioned in the base of the rotor but in line with the axis of the doffing tube is used to feed the continuous filament core. The filament component must be fed with a suitable tension, in the absence of which it will fly to the collecting surface of the rotor instead of remaining taut along the axis of the rotor. To start spinning, the staple fiber yarn is pieced up in the usual manner. The doffing tube is then made to rotate in the direction opposite to that of the rotor, and the continuous filament core is next passed through the feed tube in to the rotor. It attaches itself to the staple fiber yarn being spun and is then pulled through the doffing tube by the staple fiber yarn. The rotating doffing tube acts as a false twister and pushes extra twist along the spun yarn to the peel-off point, while the rotation of the rotor wraps the spun yarn around the continuous filament core. Any type of material, including metallic wires of high torsional rigidities, can be used as cores to produce a core spun yarn. Thus the technique could be used for producing high insulation covered electrical flex2. Tests carried out at the Shirley Institute, using a continuous filament polyester core and short American cotton for the wrapping yarn; reveal severe limitations in the counts that could be spun. These limitations are the result of several technical problems, which would require a sizeable effort to solve. However, if these problems can be solved it is believed that the technique will produce a better core yarn using such materials as wire, rubber, and similar filament cores, as well as extruded synthetic filaments.
3.3 Method 3
A core thread is combined with staple fiber in a spinning rotor by feeding the core thread to form a loop in the fiber collection surface while feeding and withdrawing the core thread in a manner to maintain it substantially linear, and the staple fiber is spun into an outer yarn shroud twisted about the axis of the core thread. The core thread feed tube is located at one side of and spaced from a diametral plane through the fiber collection surface, and the fiber feed tube is located at the opposite side of and spaced from such plane through the fiber collection surface. A loop is formed in the core thread by delaying start up of draw off rollers for a predetermined interval after startup of core thread supply rollers, and the loop is laid on the circumference of the fiber collection surface by rotating of the spinning rotor. The rate of core yarn draw off is determined by the rate of core thread feed less an allowance for a slight shortening of the core thread during twisting of staple fiber onto the core thread. It is the principal object of the present invention to provide a method and apparatus by which a core yarn is produced in an open end spinning device having a central substantially linear core thread and an outer covering of spun fibers twisted onto the core thread. The foregoing object can be accomplished by supplying a core thread concentrically through the
spinning rotor, diverting a stretch of the concentric thread to the fiber collection surface to lie along a circumferential portion of the collection surface and twisting the fibers located on the collection surface about the axis of the core thread. In accordance with a further characteristic of the present invention, the core thread is supplied to the spinning rotor at one speed and the core yarn formed in the rotor is drawn off at a lower speed, the difference in the supply and draw off speeds corresponding to the extent to which the core thread is shortened by twisting of the fibers onto it. Apparatus for performing this process includes a supply tube for the core thread having its out feed end located within the spinning rotor; a fiber feed tube emptying into the spinning rotor and a yarn draw off tube having its feed end in the spinning rotor. Each of these tube having ends terminates on a rotor diametral plane spaced from the diametral plane through the fiber collection surface. In accordance with a further feature of the present invention, the fiber feed tube and the core thread supply tube are located at opposite sides of the fiber collection surface diametral plane, and the core thread supply tube may be carried in the hollow rotor shaft or the shaft itself may serve as the supply tube. With the method and apparatus of the present invention, a high density core yarn can be produced in which relative slippage or shifting of the core thread and the fiber covering is eliminated because the core thread is completely and concentrically wrapped by spun fibers. In addition, the quantity or rate of delivery of the core thread can be changed relative to constant rate of fiber supply to produce yarn of various characteristics. The drawing is a section through an open end spinning device taken axially of the spinning rotor and showing the apparatus of the present invention3.
The possible advantages listed for producing core spun yarns on a rotor spinning system are a) the core spun yarn is more likely to retain all the strength contributed by the core component and the full length of the core component, since the continuous filaments are not twisted during spinning and will therefore not suffer twist contraction. b) Since the evenness of rotor spun yarns is better than that of equivalent ring spun structures, the evenness of rotor core spun yarns is expectedly better than that of equivalent ring core spun yarns. c) The bulkiness of rotor core spun yarn should be greater than that of the equivalent ring spun structures, since the staple fiber yarns spun on the rotor spinning machine are more bulky than the equivalent yarns spun on the conventional system; thus a reduction in cloth set will be required to obtain the same cover from rotor core spun yarns. d) The production rate of the rotor spinning machine in terms of the yarn delivery rate is higher than that of the ring spinning machine; hence the production rates for rotor core spun yarns should also be greater than those for conventional systems. e) The direct winding of the core spun yarn from the rotor onto cheeses or cones eliminates the rewinding process necessary for the conventional system and thus results in a significant cost reduction2.
The higher twist requirement of rotor yarns and the difference in structure compared with ring spun yarns mean that a straight substitution of one for the other cannot be made when considering end use requirements. The rotor spinning system is particularly advantageous in the coarse and medium count range, which will have limitation in the only property, strength. This can be rectified by the core spinning. And also to produce the hollow yarns by dissolving the core from the rotor spun core yarns while using the dissolve material as core and the undisclosed material as sheath. Thus the core yarn production in rotor spinning gains importance in new spinning techniques.
- Vaclar Rohlena et al, Open-end spinning, Textile Science and Technology, Elsevier Scientific Publication Company, Amsterdam Oxford, New York, 1975.
- CA Lawrence and K Z Chen. Rotor Spinning-The Textile Institute, Textile Progress, Vol:13, No:4,
- Peter Artzt, Reutlingen; Albert Bausch, Melchingen; Gerhard Eigbers, Eningen, all of Germany, - Method and apparatus for the manufacture of core yarn in an open end spinning Device. United States Patent, May 3, 1976.
- Dr. K.R.Salhotra, Dr.S.M.Ishtiaque, Rotor spinning: its advantages, limitations and prospects in India, 1995.
The Authors are students of P.S.G College of Technology, Coimbatore.