Making Cotton Yarn
Almost all cotton comes to the mill in standard compress bales of five hundred pounds gross. The cotton is condensed to about 22 pounds per cubic foot at the compress, wrapped in coarse jute bagging, and circled with iron hoops. For some time there has been a movement to improve the so-called square bale, or to replace it with a different form of packing. Sea Island cotton is frequently packed in a smaller round bale, and there is much to be said for this practice. What we are concerned with here, however, is that the mill receives the cotton in a compressed form which must be loosened before anything can be done with it. Accordingly, the first thing that happens is that the hoops are cut, the bagging removed, and the cotton thrown by hand into the feed-apron of the bale-breaker. This machine does nothing more than to pick the compressed cotton apart and deliver it in tufts about the size of a hand-full on a belt conveyor.
The travelling belt or feeder delivers these bunches of cotton into machines called Openers, which simply repeat the operation of the bale-breaker on a more thorough scale, reducing the large tufts into many smaller ones. These small pieces are dropped into an air chute and drawn along parallel rods up to the picker room. During transit in the trunk much of the heavier dirt falls between the rods and is removed.
In the most recent installations larger bale-breaker s are used which reduce the cotton to small tufts and deliver through an air pipe to a condenser in the picker-room. The condenser either empties into bins or else on to the automatic feed of the breaker-pickers.
As the tufts come out of the chute they fall into the first of three machines known as Pickers , whose function is to beat out the coarser impurities and deliver the cotton in rolls of batting called laps. In the first, or breaker-picker the tufts are thoroughly whirled and pounded over grid-bars by rollers armed with short flail-like projections, and then compressed into a continuous sheet or lap of a given weight per yard, which is wound on a large spool and delivered to the second, or intermediate picker. This machine practically repeats the operation only that it combines four laps from the first picker into one which it hands over to the last, or finisher picker. The latter again takes four intermediate laps and forms them into one sheet of fairly clean cotton, containing very little dirt or seed, but still fairly filled with small particles of leaf. In these preliminary operations the cotton has lost about five per cent, of its weight.
Before anything else can be done it is now necessary to remove the leaf particles, and to separate the individual fibres from their matted position. Both these functions are performed by the machine known as the Card, the principle of which is that of two surfaces armed with fine wire teeth revolving not quite tangent to each other. Originally carding was performed by hand with two instruments similar to butter- pats, but the Wellman carding machine was one of the earliest textile inventions. This was considerably improved by the revolving flat card in 1857.
The lap from the finisher picker is fed over a plate on to a revolving cylinder bearing wire teeth, which combs it over a set of knives, thereby removing coarse dirt, and passes it on to a large cylinder armed with millions of fine wire teeth. The latter carries the cotton past a slowly revolving endless chain of flats which remove the neps and fine dirt. The clean, separated fibres are then picked off the cylinder by a smaller rapidly revolving roller called the doffer, which carries them in a filmy sheet to be in turn removed by the doffing comb.
The latter, working so rapidly that the eye fails to see lifts the sheet of fibres clear so that may be passed through funnel and condensed into a single untwisted rope little under an inch in diameter. This rope is called sliver, and automatically coiled into can like an umbrella- stand.
We have now for the first time reduced the raw material to a continuous strand, comparatively free from impurities. Up to this point,no matter what kind of yarn is to be spun, the operations are practically identical, but from here on the processes vary according to the product desired. A hank of yarn is 840 yards (not to be confused with the worsted hank of 560 yards) and the number of hanks it takes to make a pound is the basis upon which yarn is classified. Thus a coarse yarn which weighs only twenty hanks to the pound, would be called 20s, while 80s would be a very fine yarn. Various fabrics require different grades of yarn, just as different finenesses of yarn must be spun from varying grades of cotton. The processes preparatory to spinning vary, not only with the counts to be spun, but with the use to which the yarn is to be put. Ordinary coarse and medium yarns for weaving usually follow one process, while fine counts for weaving, or knitting yarn, or coarse yarn made from long-staple cotton such as that used for tire- duck, go through a different preparation. The former are simply drawn and reduced, while the latter are in addition combed.
In the ordinary process, which is by far the most commonly used, the sliver from the card is put through successive similar operations, known as drawing, the object of which is to draw out the fibres and cause them to lie parallel to each other. Six card slivers are fed together between two pairs of rollers, the second of which is revolving faster than the first. The obvious result of this is the stretching of that portion of the slivers which is between the two sets of rollers. The operation is usually performed two or three times, in each case combining six strands into one. The sliver delivered by the third drawing machine will be of the same diameter as the original card sliver, but will contain more or less parallel fibres.
There remains now only one series of operations before the yarn is ready to be spun. The sliver must be reduced in size and given a certain amount of twist; these objects are accomplished by the roving frames, of which there are either three or four. The first, or slubber, passes the drawn sliver through rollers without combining, and winds it up on bobbins set in spindles. The sliver is twisted by being fed onto the bobbin by an arm, or flyer, which revolves a little more slowly than the spindle, being drawn around after it.
The result is a slightly twisted sliver, now called a roving, about the diameter of a clothes-line. The intermediate, fine frame, and jack frame, — or, if there are only three roving boxes, the intermediate and fine frames, — combine two rovings into one of smaller size and more twist. The mechanism is much the same, except that in each successive frame the spindles are smaller and revolve faster, until finally the thread is small enough to spin.
Where it is desired to spin special kinds or very fine yarns twenty card slivers are usually combined in a machine similar to a drawing frame and known as a sliver-lapper. The twenty ends are drawn between rollers and delivered not as we should expect in one strand, but in a narrow band or lap, which is wound on spools. Four of these laps are again combined and drawn over a spiral surface in the rib- bon lapper which delivers its product to the comb. The cotton is now in a band less than a foot wide, with fibres more or less parallel and practically clean. Since it is desired to spin a yarn which demands not only parallel but uniform fibres, the short fibres must be eliminated. There are a considerable number of combing machines in use at the present time, but their differences are mechanical rather than in the function they perform. The Heilmann principle is the most commonly used in this country. Eight rolls from the ribbon-lapper are placed in separate rests, or heads, end to end, and each lap is fed through rollers between teeth of a very fine and rapidly oscillating steel comb. Every back and forth motion, known as a nip, delivers about half an inch of filmy sheet from which the short fibres have been combed out. The eight combed sheets are then once more condensed into a single sliver and coiled into a cylindrical can.
Following the comb there are usually two drawing frames, each combining six slivers into one, and these are followed by the three or four roving frames as in the other process. In the ordinary process the last roving as it leaves the jack frame has been doubled 27,648 times; in the combed yarn there are 2,959,120 doublings before spinning begins. Spinning proper is done either on the mule or the ring spindle. Very little cotton is spun on mules in this country, although mules are extensively used in Europe. We shall concern ourselves here only with the ring spindle, and that in bare outline. The principle of the ring frame is very similar to that of the roving operations which immediately precede it. The thread is again drawn through two or three sets of rollers running at successively higher rates of speed, and then passes as shown on the accompanying sketch through a guide to a small metal loop, called the traveller, which runs around on a metal track or ring within which the spindle with its bobbin is revolving. Since the spindle pulls the traveller around after the yarn is twisted or spun as wound on the bobbin. Sometimes two spools of roving are spun into single thread, but more frequently there no combination. All the rings on one frame, usually about 256, are moved up and down together on their spindles, so that yarn will be wound evenly on the bobbin.
Not only is a different bobbin used for spinning warp and filling yarns. hut they are also wound differently on the bobbin. Warp yarn is wound evenly up and down the whole length of the bobbin, while the filling bobbins, which go straight from the spindle into the shuttle of the loom, are wound on in sections to facilitate rapid unwinding.
We have now proceeded as far as the finished yarn. Sometimes, however, when a particularly strong thread is desired, or in cases of fancy designs, it is desirable to twist two or more threads of yarn together, this being known as two-ply, three-ply, etc. Various effects are obtained by twisting different yarns together, and sometimes worsted and cotton strands are twisted together. The operation is done on a frame similar to the spinning frame.
In these and subsequent operations the Barber Knotter, a little device worn on the hand of the operative, has enormously increased efficiency. By a single motion an entirely unskilled girl can knot and cut off evenly the ends of two threads.
Weaving Gray Goods
The principle of weaving cloth from yarn is of course a familiar one. The warp threads are stretched out parallel to each other, and the filling, or weft, passed back and forth over and under alternate warp threads. Inasmuch as the weft bobbins are simply placed in the shuttle as they come from the spindle, the preparatory processes of weaving are entirely concerned with arranging the warp. The modern loom is the culmination of years of technical endeavor, and the actual weaving is now done entirely automatically, even to the replacing of empty shuttles with new ones without stopping the loom.
The only time when the human operative has to step in is when through the breaking of a single thread the entire mechanism comes to a standstill, or when the beam contains no more warp threads, or the filling magazine is empty. The work of preparing the warp however, still an arduous process in which highly skilled labor must be employed.
The first operation consists of winding the yarn from the bobbins on to spools, each containing the same length of yarn. This must be done with care or considerable waste will result.
The next step to place these spools in rack or creel where they fit on glass bearings so that they may be arranged in the proper orderand run through the warper on to the section beam. The latter is a large roller several of which are combined to form a beam. The beam is the name given to the roller which is placed in the loom to deliver the warp threads.
In order both to strengthen the warp threads and to make them smoother for weaving it is usual to apply some starchy or glutinous substance to them. This operation, which is performed in a machine called the Slasher, is termed yarn sizing, and consists of running the threads through a bath of preparation and then drying them quickly on a large steam-filled drum or can. One slasher will do enough work for 200 to 500 looms.
Since it is necessary that the warp threads may be lowered or raised in various combinations to allow the passage of the shuttle, each warp thread must be passed through an eye in the centre of a harness wire. Where, for instance, the warp is to be raised and depressed in three even sections there will be three harness frames, each fitted with enough heald-wires to accomodate one-third of the number of threads in the entire warp. In the Jacquard loom, used for intricate patterns, each warp-thread is separately controlled. The passing of the ends of the warp through their proper harness wires is a delicate and skilfull operation known as healding, or drawing-in. At the same time that this is done the threads are passed through individual stop-motion wires, relaxed tension on any one of which will bring the loom to a stop.
Closely connected with drawing-in, is the final step in the preparation of the warp, and this is called reeding or sleying. In order to keep the warp threads in proper position during weaving they are passed through the wires of what looks like a comb with a strip across the open ends.
This, the sley or reed, is attached to the batten on the loom and serves in addition to drive home each weft thread after the shuttle has passed.
When the loom has devoured all the warp threads contained on one beam, all that is necessary, if the pattern is to be continued, is to tie the ends of the old warp to the ends of the new, and this is accomplished with marvelous accuracy by a little machine built on the same principle as the Barber Knotter. This avoids drawing-in a second time. When the preparatory processes have been completed the actual weaving is done, as we have seen, practically without human agency. The shuttle flies back and forth at the rate of from one to two hundred picks per minute, and when its thread is exhausted it drops out and, in the automatic loom, is immediately supplanted by a fresh one. The harness frames jerk up and down, forming and reforming the V shaped shed through which the shuttle passes; and after each pick the batten drives home the new thread into the ever-growing stretch of cloth. Like the film in a kodak, where a roller at one end gives out plain paper which is rolled up at the other end as a magic sheet of pictures, so in the loom the homely warp threads are rolled out at one end, while the roller at the other extreme winds up smooth gray cloth.
We have now made yarn out of cotton, and unbleached cotton cloth, or gray goods, out of our yarn. All that remains before the fabric goes to the finisher is an inspection for imperfections and their removal where possible, usually by hand.
COTTON AND COTTON MANUFACTURE (1921)