Jacquard Shedding Mechanism (Double Shed Jacquards):-

Jacquard Shedding Mechanism (Double Shed Jacquards):-

Jacquard have been built to weave fabrics that require two picks of weft , or one weft and one wire, to be superposed , both being simultaneously passed through separate sheds in the warp . In the case of swivelled fabrics, the lower shed receives ground weft , and upper one swivel weft.

Messrs. Howarth and Pearson, in 1868, constructed such a machine with the object of doubling the production of s loom. The device is shown at Fig. 105. This machine makes imperfect cloth , because the ground weft floats under the figure in precisely the same manner as swivel weft.

In the manufacture of pile fabrics, where wires are woven into the pieces in the same manner as weft threads , and subsequently withdrawn or cut out, a loom is furnished with a compound harness consisting of healds for controlling the ground warp and and a Jacquard for controlling the pile warp. Two sheds are opened simultaneously, one to receive a shuttle the other a wire. The healds from single shed, but the jacquard forms a double one. This is done by using hooks which are approximately 27" long, and by lifting them from two places . Thus the grid has a sufficient vertical movement imparted to it carry all the hooks to the top of the first shed , and the griffe moves far enough to carry a selected number of hooks to the top of the second shed. Both grid and griffe are moved by cams and levers in the usual manner.

Fig. 105 of double shed jacquard.

Instead of the foregoing , a cord machine may be employed in conjunction with healds. In that event a knot is tied upon every cord on a level with the upper face of the bottom board , and a vertical movement, equal to the depth of the bottom shed, is given to that board. Meanwhile the trap board carries up a number of cords to form the second shed.

COMPOUND JACQUARD:-

Certain compound fabrics whose figure effects depends solely upon colour are made by the aid of Jacquards having two sets of hooks to one set of needles and cards , ad in Fig. 106 . All hooks moved by the griffe Z are placed in succeeding rows to face the cylinder , and lift when vertical; while all hooks moved by Z' face the spring box,band are left down when vertical. 

Fig .106 Image of compound jacquard.

Each needle M governs two hooks that occupy corresponding positions in both sections of the machine . But succeeding needles in one vertical row do not govern succeeding hooks. It will be noticed that needles 1 to 8 respectively control hooks 1 and 9 , 5 and 13, 2 and 10, 6 and 14, 3 and 11, 7 and 15, 4 and 12 and 8 and 16. This is done to avoide crossing the harness at the comber boards, for the neck-cords from the first four hooks are connected to successive couplings in the comber board No. 1. Figs. 127, 128 and those from hooks 5 to 8 are attached to coupling in board No. 2. Hooks in the second section of the machine are similarly connected to couplings in boards 3 and 4 . The griffe governs one warp, Z ' another. The cylinder and griffes have separate action and only move once in two picks . Thus while S presses a card against the needles M griffe Z rises with the vertical hooks T. If one warp is blue , the other white , threads of blue will be lifted by Z , and a pick of white weft will be passed between white warp threads in plain or twill order. But the white threads are lifted independently of the Jacquard, Z then sinks, and Z' in ascending takes place with it the white warp threads that occupy position corresponding with those of the blue warp previously left down by Z, and blue weft is passed through a plain or twill blue shed, also formed independently of the Jacquard . During time card 1 had remained pressed against the needles, but the cylinder A now brings card 2 into contact with the needles, and the foregoing process is repeated.

Fig.127 double equal plain cloth tie (harness drawing) 

Fig.128. double equal plain cloth drawing in Comber boards.

This machine is excellent for the work it is capable of doing , but its application is necessarily limited.

SCALE JACQUARD:-

Scale harness preceded scale Jacquards by many years . But at present time there are several machines which do similar work to that formerly done by harness . The machine possess advantages over a harness whether the shafts are placed below the comber board, or slightly below the bottom board of a jacquard. In fig. 107 two vertical section A, B of a scale machine are shown. In section A each figuring needle M seen to govern two adjacent figuring hooks T, and the tail of each hook rests upon a twilling bar C , which is in turn supported by a grid D. The twilling bar C are laid at right angles to the needles, and each can be lifted at pleasure to cause to cause a line of hooks to rise .This is done by adding an extra hook T’, section B, to each end of every row of figuring hooks. a hook T' has coiled eye at G for the reception of one end of a twilling bar C. By lifting a corresponding hook T' at each end of the machine, a twilling ball will carry up all the figuring hooks Tin that line. Outside the space alloted for figuring needles M ,two small sets of cards are placed upon the cylinder H, and these are cut to lift single threads of warp to bind ground portion of the fabric, while the large cards weave the figure by lifting contiguous warp threads in pairs . Beneath the coil G, the twilling hooks T' are straight and are passed through guide holes in the grid D. In the drawing each needle M actuates two twilling hooks hence any ground weave made by this machine must repeatupon 8 threads . But by using two rows of needles at each end of the machine every twilling hook may be put under separate control , and patterns of 16 threads to a repeat may be woven. Also , each figuring needle M may control three or four hooks T, and by so doing a design will be made three or four times as large as it could be made with an ordinary Jacquard. The base of each hook T is bent to facilitate the attachment or detachment of harness.

fig 107 scale Jacquard.

Ref:-The Mechanism of Weaving Book by Thomas W.Fox.