CHAPTER IX
TWINES, CORDS AND LINES
There are many instances in which yarns made by the foregoing operations are incorporated in twines, cords and ropes, while, on the other hand, special types of machinery are utilized to manufacture certain grades of such goods with an entirely different system of machinery. It is in connection with the latter branch that this chapter will for the most part treat, but, before dealing with these machines for specific purposes, we might just say that there are huge quantities of yarn spun by the methods already described, and the single yarn so spun is then twisted so that the resulting compound may contain two single threads twisted together, or any other greater number twisted either in one operation, or two or more separate operations, to obtain the desired type of cordage. In many cases the yarns have to be bleached before they are twisted, and Fig. 28 illustrates the drying of bleached yarns.
[Illustration: FIG. 28 DRYING BLEACHED YARNS]
The terms twine, cord and rope all indicate to the textile technologist a multiple structure, that is, an article in which two or more single threads are united by the process known as doubling, folding or twisting.
Thus, in the manufacture of twines, of which there is a great variety, the process is a comparatively simple one. A number of bobbins are arranged on pins in a creel somewhat similarly to those illustrated in the spinning frame in Fig. 24. The requisite yarns, from 2, 3, 4 ... n bobbins, for the type of twine in process are led from the bobbins through an eye or guide or through a “register plate,” then between a pair of drawing rollers, and thence to the flyer and spindle as in the spinning operation. As the spindle and flyer rotate, the group of single yarns are drawn through the guide or eye, or through the register plate by the drawing rollers, and the necessary amount of twist applied before the finished product is wound on to the bobbin. The amount of twist, or the technical term “twist per inch,” is fixed by the speed of the spindle and the delivery of the yarn by the drawing rollers. In other words we have--
revs. per min. of spindle ───────────────────────────────── = the number of turns per delivery of twine in in. per min. in. or the twist per in.
There is this difference between spinning and doubling or twisting; when a thread breaks in spinning, the supply of yarn to the bobbin ceases, and the production from that spindle stops until the broken thread is repaired; on the other hand, when two or more threads are being twisted together and wound on to a bobbin, it is evident that if one thread breaks the supply is not stopped entirely, but the product is defective because it is short of that yarn. In order to prevent the production of faulty goods and to minimize waste, it is a common practice to introduce delicate mechanical parts to such frames, the function of which parts is to stop the delivery of yarn to any spindle in connection with which any of the constituent threads are broken. A frame so fitted is said to have an “Automatic Thread Stop Motion.”
In many cases the twines made by the above process are taken to another machine in which a number of bobbins are again arranged on pins, the twines passed under rollers and immersed in polishing mixtures of starch or size contained in troughs or boxes. A quantity of the size adheres to the twines as they pass through it, and revolving brushes are used to remove the excess of size and to clean the twines. These operations are repeated a few times and ultimately the twines so starched, cleaned and polished are led over drying cylinders in front of which are placed rollers covered with suitable material, usually coir yarns. These rollers rotate at a high speed, and sometimes wax is applied to the coir yarn-covered rollers, so that the twines are dried, polished and finished simultaneously before they leave the hot cylinders to be wound on to a second set of empty bobbins. This machine is usually termed a “bobbin to bobbin polishing machine,” and the bobbins upon which the twine is finally wound are frictionally driven because the delivery of twine is constant. In this way the requisite finish or polish is applied to the surface of the twine, and this gives the twine the smart appearance which makes it quite attractive.
In the operation of twisting single yarns, that is, in the roving frame and in the spinning frame, it is usual to impart what is known as a “right twist.” Thus, if one looks down on a spinning or roving spindle and the direction of rotation is clockwise, then the twist imparted is right hand. On the other hand, if, when viewed from the same position, the spindle rotates counter-clockwise, the definition is “reverse” or left-hand twist. When two single threads of right-hand twist are combined in twisting as in the formation of the above-mentioned twines, it is usual for the doubling or twisting spindles to rotate counter-clockwise. This is done for practical reasons which need not be discussed here, but, although this is the usual way, there are cases in the twisting of textile threads where two right-hand twists are combined with the same direction of twist. Some such definition as the above will help considerably to elucidate the structure of more complicated multiple-twist cords.
CORDS.--In the manufacture of cords, three or more twines are combined. Thus, if three twines, each of reverse or left-hand twist and made from two single yarns of right-hand twist, are combined together by a further process of twisting, it is usual to apply a right-hand twist to these three two-ply twines. When treated in this way, the finished article is termed a cord which is “cable laid.” And, in general, in the twisting of such cords, each successive twisting operation is in the opposite direction to that which immediately preceded it.
Whip-cords, fishing lines and window-blind cords are typical of this structure which, in general, involves the use of complicated machinery or else a long rope walk. The single yarns are first made into twines and finished as already described; afterwards the necessary number of twines to form the cable-laid cord are united.
The operation is a costly one when compared with the simpler process of twine making, but the cable-laid cord is a much more handsome product than the twine, and is admirably adapted for purposes where a smart compact and ornamental structure is desired or necessary.
BOX CORD.--Box cord is a very simple form of cordage, the method of manufacture being quite different from that of the foregoing laid cords. In the box-cord process there are two distinct groups of twisting operations conducted simultaneously. The single threads, of which there may be from two to eight, receive the necessary additional twist by a corresponding number of flyers which differ in shape, however, from the ones in roving and ordinary spinning in that they are known as enclosed flyers. While these individual threads are being twisted, the several yarns converge towards, and pass direct to, the eye of another enclosed flyer which completes the process by twisting the component threads in the opposite direction to that imparted to the single threads by the two to eight different flyers. It should be mentioned that the building of the completed box-cord on the bobbin is accomplished by suitable mechanism attached to the flyer.
The machine is comparatively simple, and the attendants need little experience beyond that of detecting broken threads and repairing them. It need hardly be pointed out that the omission of a thread from the requisite number in the group for the finished cord is a fault the prevention of which constitutes one of the chief duties of the attendant. The finished product is termed two-ply, three-ply, ... eight-ply box-cord according to the number of single yarns which are utilized. Practically all classes of fibre are used in the manufacture of these goods, and this method of twisting is largely adopted for the making up of comparatively light cords from fairly heavy sizes of yarn. The product is used extensively for tying boxes and large packages and thus serves the purpose of a light rope which is a more expensive article.
PLAITING OR BRAIDING.--Special classes of lines and cords are now made on a machine of an ingenious design. One of the advantages of this machine is the fact that great lengths of line can be made; indeed, there is practically no limit to the length which may be made beyond that of the difficulty of handling the huge size of the finished product.
The machine, which is complicated and costly in its upkeep, is used extensively for the production of log lines, sash cords, and a large variety of blind cords. The requisite number of threads for the cord are wound on a suitable number of bobbins, and the latter are placed in carriers in the machine. The yarns or twines are passed over or across each other in such a way that they are locked in position and in the well-known plaited form which is characteristic of this class of goods. This scheme of interlocking is formed by an even number of groups of threads, usually eight or more, and the movements of these groups, or rather the bobbins which contain them, are practically identical with the familiar “grand-chain” in circle dances practised by children and also by grown-up persons. Alternate bobbins move sinuously round a circle in one direction, while the remaining alternate bobbins move similarly in the opposite direction. Each bobbin passes those in the other group first on the left and then on the right of a circle whose path is the centre of the two sinuous paths described by the two sets of bobbins.
The continuous movements of the two sets of bobbins in each machine form the elegant cord which, when plaited, passes through a guide eye in the centre of the circle but in a higher plane. From this eye the cord rises to a pair of hauling-winch pulleys around which it passes a few times forming the figure 8. Finally, the cord passes between a pair of delivery rollers into a large box at the back of the machine. The hauling-winch pulleys and the drawing rollers, which combined give the necessary firmness, are driven positively and accurately so that their surface speeds may coincide with the amount of cord which is formed at the guide eye.