(206) The waste from the combs, which varies from 15 to 17 per cent, is carried away by the brush, which in turn is stripped by a comb, and the strippings fall upon a lattice. By this they are carried to a calender roll and made into a lap which, as it contains fibres of good quality, but of insufficient length for the ordinary combed yarns, is used up in the manufacture of coarser qualities. The waste from the combing machine being considerable, its utilisation is important.
CHAPTER IX.
THE DRAWING MACHINE.
(207) The slivers produced on the carding engine, although, as previously noted, composed of approximately parallel fibres, are not perfectly laid in that way. If, however, they are subjected to a pull in a longitudinal direction they easily assume the parallel position. Even slivers produced on a combing machine, in which the fibres are, as has been observed, in much better order than when treated in a carding engine, are improved by being subjected to this drawing action. The net result of the process is an improvement in the strength of the resultant thread. Not only is it essential to improve the parallelisation of the fibres in the sliver, but it is equally desirable to produce a sliver of even weight and thickness. As it leaves the carding or combing machine the sliver is not so regular in weight as is requisite, and if this irregularity were allowed to go uncorrected a yarn of varying thickness would eventually be spun. It is true that the variations are not serious in amount, but they are of sufficient importance to render it desirable to correct them. Again, it is necessary to reduce these irregularities in order to facilitate future manipulation, and, generally speaking, the proper conduct of the drawing process is of prime importance to successful spinning.
(208) The essential feature in a drawing machine or frame is, of course, the mechanism by which the extension or drawing of the sliver is effected. As it is necessary to pass the material continuously through the machine while reducing it to parallel order, the use of rollers becomes imperative. These are arranged in pairs, one above the other, and there are four pairs arranged in parallel lines with each other, as shown in Fig. [124]. That illustration is a transverse section of the drawing frame as made by Mr. S. Brooks, Figs. [123] and [125] being respectively end and front views of the same machine. The lower rollers are borne, as shown, by brackets B fastened to a longitudinal beam C, known as the “roller beam.” They are made in sections and are coupled throughout the length of the frame, so as to form four continuous “lines,” which are driven from one end of the machine. Each set of four lower and four upper rollers constitutes a “head,” and there are usually from two to four heads in a machine. The lower rollers are made of a special class of wrought iron, very fine and clear in the grain, and are accurately turned throughout, being formed with two or three bosses to each head. They are also fluted with fine flutes in a longitudinal direction, great care being taken to ensure the flutes being smooth and quite free from anything likely to catch the cotton. The upper rollers are made of cast-iron, and are placed on the top of the lower lines, against which they are constantly pressed by means of the hooks D and weights E, the former passing over the arbors of the rollers. The arbors of the top rollers engage with grooves in the roller brackets, and the rollers are thus prevented from moving laterally, although they have freedom of vertical movement. Bars forming caps for the arbors of the top rollers are fitted, being known as “cap bars.” It is the practice to form the top rollers with as many bosses as there are on the bottom rollers in each head, and of a length corresponding to that of the latter. Thus if, in each head, the bottom rollers had three bosses the top rollers would be formed to correspond, and the slivers to be drawn would be passed between them. In this case the head would be said to be one of three “deliveries,” and a machine is usually described as being one of so many heads of a certain number of deliveries. It will be easily understood that the top rollers are not positively driven, but derive their motion by frictional surface contact with the lower set. The top rollers are accurately turned, and are usually covered with a specially-prepared soft leather, formed into a sheath, which can be drawn over the boss of the roller. Special care is taken in forming these coverings, so that they have no extra thickness at their joints, and, after they are drawn on to the rollers, the latter are subjected to a rolling and pressing action, which beds the leather firmly and ensures the roundness of the roller. The mode of preparing the rollers will be described in full in Chapter [XIV]. It is now almost the universal practice to use the loose boss top roller invented by the late Mr. Evan Leigh, and illustrated in Fig. [126] in longitudinal section and elevation. Its advantages are many, and arise from the lessened friction consequent upon the more perfect lubrication, which is also obtained with a smaller quantity of oil.
Fig. 126.J.N.
(209) The rollers are driven from the end of the machine in the way shown in Fig. [123] in end elevation. They may be arranged with all their driving wheels at one end of the frame, or may be—as is the case in Messrs. Howard and Bullough’s machine—driven at both ends. That is to say, the driving of the first and fourth rollers may be effected at the gearing end of the machine, while that of the intermediate lines is obtained at the other end. It will be, perhaps, as well to say that the first line here means the back rollers, and the fourth the front. Whatever be the system of driving adopted, the front roller is always the primarily driven one, and for this course there are good reasons. The thickness of the emerging sliver is determined by the relatively superior speed of the front roller, which runs at a faster rate than any of the others. Thus it becomes an easy matter to reduce the speed of the remaining rollers, and this course is preferable to using a slow running wheel as the driver from which higher velocities are to be obtained.