(213) A reference to Figs. [123] and [125] will show that extending along the frame is a shaft having a hand-wheel at the end, and a number of worms keyed on it. The latter gear into worm wheels, on the axes of which cams are fixed by which a bar—through which the weight-rods pass—is lifted. As the rods have a loop at their upper end which cannot pass through the holes in the bar, it is clear that the elevation of the latter will also raise the weights. In this way the pressure on the rollers is relieved. This is of value when the frame is stopped for any prolonged period, as the maintenance of the pressure during that time results in the formation of flat places on the rollers, which are detrimental to good work. It is undesirable to put on or take off the weight suddenly, and some makers prefer to use a simple lifting appliance by which each weight can be released singly.
(214) The important features in connection with the roller portion of the mechanism are—first, their perfect finish; second, the adoption of such diameters and distances as are suitable for different lengths of staples; third, their effectual cleansing; and, fourth, the regulation of their velocity so as to suit the material being dealt with.
(215) It was pointed out in paragraph 207 that there are certain irregularities in the size of the slivers, as obtained from the carding engine. Up to the present the machine has been considered as though each sliver was treated separately, a course which would result in the delivery of a sliver longer than, but possessing the same defects as, the original one. That this must be so is apparent, unless some provision is made for the acceleration of the speed of delivery when a thin place was passing, or its retardation when a thick place occurred. It therefore becomes necessary to find a method of rectifying these defects, and it is obtained by passing several slivers through the machine simultaneously. Reference is now more particularly made to Fig. [123], which shows the mode pursued clearly. A number of full cans from the carding engine—up to eight—are placed behind each delivery, and the slivers they contain are combined and passed through the rollers together. Before passing on to consider the exact effect of this arrangement, a few words may be said as to the method of feeding the cans to the machine. As each can contains approximately the same length, it follows that, the rate of passage being the same throughout the machine, they would all become empty at practically the same time. This implies the necessity for the attendant to remove the cans and piece up the new slivers all along the frame almost simultaneously. This is practically impossible, and it is therefore highly desirable that there should be an arrangement adopted which would enable the cans to be substituted at different times along the frame. In a little but valuable work, “Progress in Cotton Carding,” the late Mr. F. A. Leigh, of Boston, U.S.A., makes the following remarks: “If there are 10 pounds (or 1,000 yards), say, in a full can, instead of putting them all up full at first, it is better to put them up at back of drawing in four sections, say:—
| 4 or 6 cans | 4 or 6 cans | 4 or 6 cans | 4 or 6 cans | |||
| 21⁄2lbs. | 5lbs. | 71⁄2lbs. | 10lbs. |
After that replace with the full 10 pounds (or the 1,000 yard) cans, and they will continue to empty in rotation, all full cans having the same length. The tender [minder] will know exactly where to find them.”
(216) The diminution of the irregularities in the slivers is most important. The plan pursued is to pass several slivers through the same set of rollers, and deliver the combined sliver at the front of the machine. The number of slivers which are combined varies considerably according to the practice of different spinners, but is not more than eight. Now, if it be assumed that an irregularity of 40 per cent existed in one sliver, and that it was drawn simultaneously with five others in which that irregularity did not exist, the latter would be reduced to one-sixth, or 162⁄3 per cent. It is, however, the custom to “put up,” or feed, the slivers so obtained to another head of the machine, and subject several of them to a second or even a third drawing. Assume, therefore, that four of the partially drawn slivers were fed and again drawn. The irregularity would be reduced to 12⁄3 per cent, and a further drawing would again reduce it. The figures given are hypothetical, and it is not likely, of course, that only one sliver would be irregular in thickness, but the example serves to show the principle. The number of “doublings” given to the sliver is arrived at by multiplying the number of ends passed through at each drawing. Thus, in the case stated, the doublings are 6 × 4 × 4 = 96, and it can be easily seen that any difference in substance which existed at first would be very speedily rectified, and would not be of much moment by the time the finished sliver was produced.
(217) The number of times the material is passed through the machine and the draught to which it is subjected varies, as was shown, with the class of cotton treated. Thus, the harsh, wiry varieties of cotton stand more drawing, but if well drawn will spin fairly well into weft, which does not receive so much twist as warp, and should be full bodied. How much any class of cotton should be doubled and drawn is a matter to be determined by practice only, and even then great variations in the course pursued will occur. The one thing which must be remembered is that as soon as an even sliver is produced further drawing is unnecessary, and only results in a diminution of the strength of the spun yarn.
(218) A necessary corollary to the process of doubling slivers is the provision of means whereby the passage of all the combined slivers is ensured throughout their entire length. Assuming, for instance, that eight ends were being passed through the machine, and one of them from some cause failed, it is clear that the delivered sliver would be diminished in thickness one-eighth. Of course the attendant would rectify this at the earliest moment, but, in the interim, a large amount of the thin sliver might have been produced. In order to avoid this serious evil, it is the practice to fit all machines of this class with a detector motion, which operates on the failure of any of the ends. Referring now to Fig. [123], it will be seen that, after passing through the guide-plate F, the sliver is conducted over the end of the short lever G, which oscillates on a knife-edge bearing. The end over which the sliver passes is hollowed out, and is highly polished, while the other end—which is slightly heavier—is beneath a curved guide-plate, shown in section. The lever G is balanced so that the pressure of the sliver during its passage is sufficient to keep the spoon-shaped end down, while, on the breakage or failure of the sliver, the lever oscillates on its bearing. A reference to Fig. [124] will show that a shaft H, driven from the main shaft, as shown, has on it an eccentric, to which the rod I is attached. This rod is attached to a bell crank lever J, on the shaft K, which is oscillated, and thus gives a reciprocal movement to the levers L, carrying a square bar. A bell crank lever M is also placed upon the shaft H, and ordinarily engages with a snug on the stop rod N. The latter has a helical spring attached, which always tends to pull it longitudinally, and when it is released, to throw over the strap from the fast to the loose pulley.
(219) Assuming now that one of the slivers has failed, its spoon lever will oscillate and its weighted end will fall. It thus comes in the path of the reciprocating bar in the lever L, which is prevented from completing its traverse. The result is that the lever M is oscillated and the stop rod N released, so that the spring named at once throws the strap on to the loose pulley and stops the machine. As the reciprocations of L are very rapid, no considerable length of the sliver can pass without causing the stoppage of the machine. The attendant is compelled to piece up the broken end, and “single” is thus prevented.