Mechanics: The Science of Machinery

by A. Russell Bond

FIG. 69.—THE HEDDLES OF A LOOM

Every industry has a vocabulary of its own to furnish names for its machine parts and products peculiar unto itself, and in this respect the textile industry is by no means an exception. The threads that run lengthwise in a piece of woven cloth are known as the “weft,” “woof” or “filling.” In the loom the warp threads are threaded through loops on what are known as “heddles”; in fact, there are two “heddles,” A and B, Figure 69. Alternate warp threads (C) pass through the loops of one heddle, and the other threads through the loops on the other heddle. When one heddle is raised and the other lowered, the threads form a wedge-shaped space (D) which is known as a “shed.” The filling thread is sent through the shed and is then pressed closely into the wedge-shaped space against the cloth already woven by means of a “reed” (E) which is a comblike member with teeth or flat pieces of metal that pass between the warp threads. This done, the position of the heddles is reversed, so that A is now lowered and B raised, thus binding the warp thread in place and forming another shed for the next warp thread; and thus the process continues.

The filling thread is placed in a shuttle (F) which carries a bobbin on which the thread is wound. As the shuttle is thrown back and forth through the shed, the thread is unwound and trails behind it. Formerly the shuttle was thrown back and forth by hand, but years ago, long before the invention of the steam engine, the flying shuttle was invented. In other words, a mechanism was provided for striking the shuttle a blow and throwing it across the warp from side to side. By this means the speed of operations was greatly increased.

About the middle of the eighteenth century the drop box was invented. This consists of a receptacle for shuttles carrying different colors of thread which may be selected in a definite order and thrown back and forth so as to vary the pattern of the cloth.

In present looms a special machine is provided for taking the threads from the bobbins or cops and laying them in an even sheet to form the warp of the loom. These are wound on a beam and the machine is known as a beam warper. As the threads are apt to be somewhat fuzzy it is necessary to size them, and a machine known as a slasher is employed for this purpose. This machine coats each thread of warp yarn with a sizing compound or an adhesive and dries the sheet of warp preparatory to its use in the loom.

In common weaving the weft or filling threads run alternately under and over the warp threads with perfect regularity. A pattern can be formed by passing the weft threads under and over alternate groups of warp threads, and this is effected in the ordinary loom by threading the weft in groups through the heddles, i. e., instead of having every second thread pass through one heddle and the intervening threads through the other heddle; the threads are arranged in alternate groups of two or more. This gives a regular pattern, but it may be varied to form ornamental designs if the groups are varied. Such designs used to be worked out by hand very slowly and laboriously, with the result that figured weaving was very expensive.

THE JACQUARD LOOM

At the French Exposition of 1801 a loom was exhibited that made a sensation. With seemingly human intelligence it selected individual warp threads or groups of threads and raised them or lowered them so as to work out elaborate ornamental designs. The inventor, Joseph Marie Jacquard, of Lyons, received a medal for his marvelous invention and was decorated with the Cross of the Legion of Honor.

The “brains” of the Jacquard loom is a set of pasteboard cards that are perforated in accordance with a prearranged design. The warp threads, instead of being passed through the loops of two heddles, are passed through what might be termed individual heddles, one for each thread, or for a small group of threads. These consist of cords in each of which is an eyelet through which the warp thread passes. The cord is weighted at its lower end and its upper end is fastened to a hook in a box at the top of the machine. The hooks engage transverse bars known as “griffes” or “knives,” and when the griffes are raised, the hooks engaging them are also raised. In this way the warp threads that pass through the eyelets that are connected to the hooks are raised. But running horizontally across the hooks there are “needles” or rods with eyelets or bends in them through which the hooks pass. These needles may be moved lengthwise to make the hoops engage or disengage the knives. The mechanism is illustrated in Figure 70, where the knives are shown in section at A, the hooks at B and the needles at C. For the sake of simplicity only eight hooks and needles are shown; in actual practice there are hundreds in a single machine. At the right-hand end of each needle there is a spring which pushes the needle toward the left, thereby bringing the hook through which it passes into position to be lifted by its griffe. At the left-hand side of the machine there is a card (D) which presses back the needles and thereby bends the hooks out of position to engage the griffes. However, there are perforations in the card through which certain of the needles can pass, letting the hooks they control engage the needles. The cards thus select the particular weft threads that are to be raised. In our illustration most of the needles have entered holes in the card, but the second, fourth and sixth from the top have been pushed back by the blank wall of the card and their hooks have been bent back clear of the griffes. Only four cards are shown in the drawing arranged in a four-sided box or “cylinder,” and the cards are successively presented to the needles. For more elaborate designs a large number of cards are used, arranged in a slatted belt, and these come successively into position. As many as thirty thousand cards have been employed to carry out a single pattern.