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Weaving weft insertion rapier: Principles
Source :   Modern Textile Journal
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At present there is a great profusion of types of rapier looms on the market, both in terms of their markers and of their design. Furthermore, as regards loom design there is diversity at two levels; at the strategic level, of decisions about the general method to be used, such as whether or not to use rigid rapiers: at the tactical level , of decisions about, say, the type of rapier drive used to put a given design strategy in to effect. The present article is concerned only with the first of these types of diversity, giving an introductory account of the general methods employed in rapier looms and their implications. It is intended to discuss the mechanisms used for rapier actuation in a further article.


Weft Insertion


The main distinctions as regards weft-insertion methods are illustrated in Fig. 1. ln the simplest cases, in each loom cycle' the tip of a single rapier is inserted across the whole width of the shed and then withdrawn, weft being inserted during rapier motion in one direction only. Because the progress of shedding and beat-up is inhibited over the whole period for which the rapier is in the shed, the loom cycle is not utilized efficiently, and only a few looms use this method: is has the merit that problems of weft transfer do not arise. Furthermore, if double picks are inserted there is no need to cut the weft, no weft waste, and one selvedge is automatically secured. The loops of weft at the other selvedge can be secured either b knitting them together or with a catch thread. The rapier can simply have the weft permanently threaded through a hole near its tip, and it must then enter the shed from the weft supply side(Fig. la). This technique is widely used on narrow fabric looms and on carpet looms, but otherwise on a few special-purpose machines. If single picks are inserted then, of course, the normal range of weaves can be produced, but looms using this technique are slow running and it too is not often used (Fig. 1 b; for relative speeds see reference 1).


Normally, two rapiers enter the shed from opposite ends a(ld the weft is transferred from one to the other when they meet, and they are-then withdrawn. In this way, the intervals for rapier insertion and for rapier withdrawal are both used for weft insertion. Invariably, on full width looms, only a single pick of yarn from a given supply package is inserted, but it may be inserted as a loop up to the time of transfer,



and the transferred loop straightened out during rapier withdrawal from the shed (the loop-transfer or Gabbler system). Yarn withdrawal from the weft package is thus completed at the time of transfer. This has the disadvantage that prior to the transfer the rate of weft withdrawal from the up ply package is' high (it equals twice the rapier velocity), and subsequently it is zero; also after transfer the free end of the pick could untwist (Fig. 1 cO. Loop transfer was at one time widely used as it can facilitate the formation of semi-conventional selvedges, but it is now available as one of the options on only a few looms. With loop transfer the use of some form of weft accumulator is often standard.


Thus, almost invariably it is the cut end of the weft which is transferred (end or tip transfer, also known as the Dewas system, Fig. 1 d). This entails incorporating yarn clamps in the head of both the giver and taker rapiers, instead of just yarn

 

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