JACQUARD SHEDDING MECHANISM (DAMASK OR TWILLING JACQUARD):-

DAMASK OR TWILLING JACQUARD:-

(1) Damask napkins, dress goods, etc. belongs to the class, technically denominated 'warp and weft figures’. The damask or twilling jacquard is extensively used for weaving warp figures on these fabrics, whereas, multiple boxes produce weft figures.

(2) The twilling mechanism to bind automatically, in steen or twill order, each group of warp threads selected by the Jacquard machine to form the upper and the lower lines of the figuring shed.

(3) The mechanism which produces the binding is combined with the jacquard and requires no external apparatus. The binder weaves is usually on 8 or 5-end sateen or both.

(4) The figuring capacity of a single lift twilling jacquard is always equal to the product of the number of needles and the average number of hooks per needle. The number of picks in the complete repeat of the woven pattern is equivalent to the product of one repeat of the pattern cards and the average number of picks per card. 

The principle of pressure harness is entirely different to the principle of twilling Jacquard, but on the handlooms to produce large figure effects for the finer silk fabrics the pressure harness is universally uused.

Features of Twilling Jacquard:-

(a) One end is drawn through each ‘mail eye’.

(b) A seperate hook is required for every end ;

(c) Each needle serves two or more hooks: and 

(d) One card serves for several picks.

Bressbrook Damask Jacquard:-

The principle of the 'Bressbrook' damask or twilling Jacquard is illustrated in figs. 136A and 136B.

Fig.136 A and 136 B of bressbrook Damask Jacquard.

This is a single lift Jacquard. There may be any numbers of hooks to each needle. In the illustration, there are three. The machine is necessarily a single-lift , the griffe goes up and down every pick. Only two needle are shown operating six hooks. When the top needle is pressed back , it will press back the hooks 1,2 and 3 : and when the bottom needle is pressed back, it will press back the hooks 4, 5 and 6. These hooks are bent at the bottom.

A bar or rod A is passed through each row of hooks, the full length of the machine. These bars A are lifted by the twilling hooks, shown in the digram in dotted lines .These hooks are placed at the sides of the machine; two hooks for each long row of the ordinary hooks , if one for each end of every bar A. The blades and griffe are moveable about the center EE. At each end of the blades and immediately behind each twilling hook (dotted) there is a projecting piece P, also shown in a dotted line in the digram. 

Now , when the griffe is at the bottom, the blades are operated by a pegged barrel. By turning the blades one at a time out of way of the hooks as the blade misturned, a whole row of hooks can be left down which would otherwise be lifted .

 Turning the blades has also effect, on the front of the blade at each end , ad previously pointed out, is a projecting piece P . When the blade in turned , this projection pushes the twilling hook in front of it (dotted) on to the next blade of the griffe, and the twilling hook is lifted. The bottom of the twilling hook is fastened to the end of a bar A and the bar is lifted. Thus it lifts a whole row of hooks which would otherwise be left down . In this manner by operating the blades of the griffe in regular order, the figure can be woven warp twill and the ground weft twill or vice versa.

Working principle:-

At fig.136B , the position of the six hooks is shown after the griffe is lifted . It will be seen that the blank opposite the top needle pressed the first, second and third hook back. These three hooks have been left down but for the bar A being lifted . The hole opposite the bottom needle leaves the fourth , fifth and sixth hook over the griffe. These three hooks have been lifted but for blade M being turned , which also cause the bar A to be lifted. The twill must repeat on the number of bars A or on the number of rows of hooks on the machine. Like a split harness the ground weave must repeat on the number of shafts or rods used undre the comber board. 

In these machines as in the pressure harness, the same card is pressed against the needles two, three, or more times in succession , so as to give a great extent of pattern of patterns with a small number of cards. The number of times a card is pressed against the needles , depends on the number of hooks there are to each needle , and on the relative amount of warp and weft in the fabric. If there are three hooks to a needle and the same number of picks as ends per inch or 2.54 cm. the card should be used three times in succession. Sometimes there are more picks per inch or 2.54 cm. than ends in which case each card should be used more frequently. Again , as in silk damasks there are 400 or more warp threads per inch or 2.54 cm. and 100 picks. Supposing there were eight threads in a mail eye, it would make a step of eight ends in the warp. It is therefore, to make the steps in the weft balance , it would be necessary to bring the same card against the needles only twice in succession. 

Ref:- Weavning Mechanism Book Vol.1 by Prof. N. N. Banerjee.