yarn joining methods have received considerable attention by researchers.
Methods for Producing Knot-Free Yarns
The development of methods for producing knotless yarns began during the early 1970s. Various methods have been used for producing knot-free yarn piecing, including.
Welding or fusing
Fig1;-Different methods for producing knot-free yarn.
In the wrapping method, two yarn ends are overlapped, and an auxiliary yarn is wrapped around them to produce a joint of high strength, as shown in Fig. 1a. This method produces a thick and rigid joint, and the mechanism involved is very complicated. The auxiliary thread often causes problems during subsequent processing. In the gluing method, two overlapped ends of yarns are glued by a special adhesive, as shown in Fig.1 b. This technique produces a thick joint and rigid structure because of the rigidity of the glue (adhesive) used. Also, drying of the adhesive takes a long time, resulting in lower productivity of the process. In the welding technique two yarn ends are welded together by a melting process, as shown in Fig. 1c. Although this technique produces a short but high strength joint, it can be applied only for thermoplastic fibers (e.g., nylon), and the welded portion has a different structure due to the melting process. The first three methods listed above are no longer used in practice because the pieced portion (joint) is thicker and more rigid and also in one case contains an extraneous material, namely, the adhesive.
In splicing, the joint is more or less like the yarn itself and produces sufficiently strong piecing without adversely affecting the appearance of the final fabric, and consequently it is more widely used in modern winders. The concept of splicing is similar to the method of joining rope (or cable) ends together. For the purpose of joining, the two ends of a rope are untwisted and then intermingled by some mechanical means. The methods of yarn splicing involve mechanical, electrostatic, and pneumatic systems.
In mechanical splicing the yarn ends are untwisted to open the fibers. Two ends are overlapped and then twisted together again to essentially the same twist level as in the basic yarn, as shown in Fig. 1d. The fibers at the end of the yarn are used to bind the splice joint resulting in a corkscrew-like appearance. The disadvantages of this system are
(1) it is difficult to open up the yarn ends consistently due to irregular twist distribution;
(2) it is possible to achieve proper separation of fibers at yarn ends only for short staple fibers—for long staple yarn it is somewhat difficult to separate fibers at the yarn ends, which has a negative effect on binding of fibers;
(3) different twisting wheels are required for opening and twisting of yarns of different twist levels and made from different staple length fibers, involving costly adjustments;
(4) in this splicing technique it is not possible to splice plied yarns as opening by untwisting is not possible; and
(5) mechanical splicers require more frequent maintenance and servicing due to the entry of dust and fly.
Fig1;-Different methods for producing knot-free yarn.
The yarn ends are separated and untwisted in the opening zone. The opened-up yarn ends are then spread out evenly in an electrostatic field, after which they are intermingled and bound again by a pole change, while simultaneously twist is inserted corresponding to the twist in the basic yarn, as shown in Fig. 1e. Theoretically, this method of splicing
is very suitable as it provides ideal blending of fibers in the splice zone, but it suffers from some practical drawbacks; these include
1. Required opening and separation of fiber ends for effective spread-out in the electronic field is not always achieved satisfactorily. This is due to irregular twist distribution in the base yarn.
2. For a yarn containing a large number of fibers in the cross section the intermingling of prepared fibers at the yarn ends is a problem as fibers obstruct one another.
3. Plied yarns cannot be spliced due to difficulty in opening fibers at the yarn ends by mechanically untwisting.
4. The time taken to splice the yarn is quite long, thus decreasing the efficiency of the winding process. Also, high voltage is required to achieve the desired charge. The climatic condition of the winding room has an obvious effect on the electrostatic field.
In this method, the yarn ends are inserted into a splicing chamber and then overlapped to join them together by means of a strong current of compressed air, as shown in Fig. 1f. The splicing time and air pressure are determined according to fiber type and yarn characteristics. The splicing operation consists of the vertical application of air to the fibers and a simultaneous rotational movement of the air to twist/untwist the yarn. This type of air movement is achieved by the position of the blower apertures and the design of the shape of the splicing chamber. Pneumatically spliced yarn produces a joint that can meet all the requirements in subsequent processing, both in terms of strength and appearance. The time taken to carry out efficient pneumatic splicing is relatively short, thus winding efficiency is not severely limited. Moreover, pneumatic splicing can be applied to a wide range of fiber and yarn types without requiring precise adjustments or settings,
thus facilitating efficient winding.
This splicing technique has attained considerable importance in the synthetic fiber manufacturing industry because knots have a detrimental effect on quality. Anew splicing technique called ‘‘double splice’’, based on the principle of pneumatic splicing, is normally used in joining continuous filament yarns and tire cords. In this technique, yarn filaments are intermingled by using an air splicer, leaving virtually no protruding ends.