Modern Weaving – Shuttleless Weaving
Modern weaving machines stand out as an expensive class compared to conventional machines in terms of capital investment. This basic difference requires certain prerequisites to be considered while planning to venture into modern weaving machines.
The quality of yarn used on shuttleless looms is the prime criteria considered for quality weaving. The machine parameters to be controlled for an optimised preparatory operation have been dealt with respect to winding, war ping and sizing operations. Guidelines for machine stoppages corresponding to warp and weft breakages in weaving are considered as important in deciding the efficiency of a shuttless weaving shed.
For the successful installation of shuttleless looms, it becomes inevitable to go for quality yarn and optimization of the preparatory operations prior to weaving. A better quality yarn leads to a quality war p and sized beam which consequentially gives and efficient weaving operation both qualitatively and quantitatively. The parameters to be checked as regards yarn quality, winding of warp and weft yarns, warping and sizing are dealt with in some detail in the following sections.
Yarn Quality Requirements
Tension on the warp on a high speed shuttleless weaving machine is higher than that on conventional loom. On some Repier looms, interference by rapiers, at the initial points of entry and terminal point of shed exit, can cause bending of the top yarn sheet around the rapier head producing excessive warp strain on the selvedge region of war p. Weft tension on Sulzer Ruti projectile weaving machine, is equally high, where tucked-in selvedge is for med. Consistency of single end strength, C.V. of count and elongation is essential. Quality of yarn should be at least within 25% Uster which means the quality is among the best 25% of the mills in the world. Normally shuttleless weaving machine works three to four times faster and if the quality of war p remains the same, warp breaks will increase three to four times resulting in low production. Yarn should be more even and the following parameters of yarn are to be critically reviewed; C. V. of count, single thread strength, C. V. of single thread strength, imperfections per 1,000 meters such as thick places, thin places, and neps. Hairy yarn will not be suitable in air jet weaving as it will misdirect the weft insertion.
Warp and Weft Preparation
It is absolutely necessary that machine stoppage rate per 10,000 war p ends and 1,00,000 picks should be considerably reduced for successful installation of shuttleless looms. Because of much smaller shed size,reed sweep and abrasion time, the war preparation standards acceptable for automatic looms will lead to less warp breakages if the same yarn is used on high speed looms. Yarn imperfections which would pass into the cloth on an automatic loom fail to do so on a machine like projectile loom because of the following reasons:
The reed is less flexible.
The characteristics of beat-up are considered to be more detrimental than those with conventional sley.
When the movement of adjacent shed is impeded due to some projection hanging in the form of wild yarn, fluff, scissoring action of the knots, etc, hindrance in the path of the yar n will be chopped off to cause a multiple break.
Number of abrasion cycles is more because of high speed.
All medium and fine counts and all blended yarns with polyester components should be wound on automatic winding machines like Autoconer, Murata, etc. In choosing optimum clearing settings, indiscrimate removal of thick places is not desirable since removal of each fault is replaced by another fault namely a knot. Knots act as sharp instruments on the adjacent threads, besides being responsible for peak tensions generated during weaving. Tail ends of knots come in the way of clear shed formation and can be a cause of multiple breaks. Hence, each thick place is to be assessed with respect to its length, and only objectionable faults may be removed. This is possible only with electronic yarn clearer in conjuction with Uster Classimat which classifies yar n faults into twenty one categories (reference length & C.S.) The size of the tail ends of knots should be small. The knotter is to be selected based upon the yarn number. A spliced yarn gives good results. It would be desirable that a splicer is provided instead of a knotter on the winding machine to give good results and to get rid of all the disadvantages of knots. A large no. of automatic winding machines are equipped with knot / splice tester which ensures 90-95% prefect joints.
At warping, the goal should be to avoid missing ends. Number of thread breakages should not exceed seven per 10 million meters. This can be achieved by ensuring a top quality yarn package and by following the warping process parameters mentioned below :
Precise creel alignment
Reliable stop motion on creel and on warping drum, so that broken ends are traceable for knotting.
Minimum wobbling of warping beams.
Uniform selvedge with good flanges.
Yarns should by preferably warped on spindle driven machines to avoid thermal damage due to abrasion. Warping machines such as Benninger or Hacoba are preferable. With drum driven warpers such as the BC Warper, the following precautionary measures are to be taken :
A) Frictional drum should be kept in a polished state.
B) Brake should be very efficient.
C) Aluminium cast flanges should be used to get faulteless selvedges.
D) Breakages rate should not exceed 0.3~0.5 breaks per 1000 m / 500 ends.
E) For wider width looms, wider war ping machines are preferred.
The process of sizing greatly influences the performance of the shuttleless weaving machine. The concept of single end sizing is more ideal for yarn prepared for all shuttleless weaving machines particularly wider width machines with a large number of ends. Single end sizing facilitates proper encapsulation of size on the yarn and reduces hairiness particularly of blended yarns resulting in a ver y clear shed formation which is a must for shuttleless weaving. Double size beams are recommended to avoid over crowding. An optimum number of ends in the size box is given by optimum ends = 0.5 x (width of nip of size box) / dia. of yarn.
Weft insertion rate is high and unwinding is intermittent on shuttleless weaving machines. Hence it is necessary to have a hard wound package. It is essential to have anti patterning device to prevent slough-off on the fabrics. For spun yar ns, parallel wound package with core diameter of package of 95 mm and a traverse of 90 mm give a good performance. Smaller core diameter of package increases the unwinding tension and enhances the possibility of high weft breakage. Weft accumulators are to be used on high speed weaving machines when the weft insertion rate is above 1000 m/min.
The parameters and machinery in preparatory for the conventional shuttle looms should be thoroughly assessed and suitably modified or replaced for their performance for the efficient functioning of a shuttleless weaving shed. The above factors play a deciding role in giving quality weaving and better returns thereof.