Combing being thus completed, the riband of cotton passes to the rollers i i', and is drawn by them through a trumpet tube, which presses it together to form a round sliver. The slivers from the six heads are then united, passed through the drawing head at the end of the machine, and coiled into a can.
As the combing process has for its object not only the removal of dirt and neppy cotton, but also the separation of the short fibres contained therein, the disposal of these may be briefly described. When the roller gl and the fluted segment have got hold of the front ends of the half-combed fibres, the top comb falls a little in front of the part upon which the cylinder combs had previously operated. The roller gl and the fluted segment of the oylinder then draw the fibres forward, the top comb preventing anything coming forward, except the long fibres protruding through the teeth of the comb. The short fibres are thus left in the portion of the fleece from which the long ones have been drawn, and on the rollers dd' delivering a fresh length through the nipper e e' , the combs on the cylinder fl pass through the projecting part of the fleece, and separate from it the naps, dirt, and all the fibres not long enough to be firmly held. They thus take the waste from the front ends of the fibre, and that whioh was left by the top comb. As the cylinder revolves, the waste is cleaned out by the action of the revolving brush 4, which has a more rapid motion than the cylinder ; the brush then throws the fibres upon a doffing cylinder, covered with card clothing, which is stripped by an oscillating comb, when it drops into a receptacle at the back of the maohine. This short fibre and waste is subsequently used in spinning low and coarse qualities of yarn, in which cleanli ness is not an important requisite.
Drawing.—One of the main purposes of each successive process in cotton spinning is to eliminate the defects and irregularities left by preceding operations. An intermittent or irregular supply of cotton to the lap machine produces variations in the weight of the laps, occasionally to the extent of 3-6 per cent. These, in the carding process, give correspondingly irregular slivers, and, if passed through the subsequent stages, would yield the most unsatisfactory results.
In order to obviate this, in the drawing process, 6-8 slivers from as many different cards are combined, and attenuated to the dimensions of one ; six of these are again put up, and the operation is repeated ; this takes place usually a third time, when the sliver is regarded as having been sufficiently drawn. The series of doublings stands thus-8 x 6 x 6 = 288, so that the irregularities existing at the commencement are reduced to an imperceptible amount.
The machine by which this is accomplished is the drawing-frame, a front view of which is shown in Fig. 539. It is one of the simplest machines employed in oott,on spinning. It is the first, however, in which is introduced the important principle of drawing or attenuating the material by means of rollers. Of these rollers, there are four pairs in this machine, arranged in parallel order behind each other. The front pair are visible at a. The two pairs at the rear are fluted ; whilst in the two front pairs, it is only the bottom ones that are so constructed, the upper ones being covered with dal: or leather. These pairs of rollers revolve at differ ent velocities, the speed inoreasing from the back to the front. By this action, the fibres are drawn into parallel order, the sliver is attenuated, and the unevenness of eaoh, and the irregu larities of the whole, are eliminated. The speed is graduated between the different pairs, in such a manner that the front or delivery rollers have a surface speed equal to about six times that of the taking-in rollers. Where eight slivers are drawn into one, it becomes correspondingly increased. The usual speeds of the rollers are in the fol lowing ratio :—Taking-in, 1-00 ; 2nd, 1.50 ; 3rd, 5-75 ; 4th, 6-00. These will differ as the draught 113 mole or less, but the proportions will be maintained.
In the drawing-frame, the cans containing the slivers are arranged behind ; the slivers are passed through holes in a horizontal plate, for the purpose of preventing their passing up in the form of loops, knots, or kinks. From here they go over a semicircular plate to a guide plate, in front of which the ordinary lever-stop motion is placed. This is a compound lever balanced in the middle. One end of this is spoon-shaped, and rises in front of the guide plate. The opposite projects beneath the semicircular plate, and has a loose bar, attached by a joint, pendant from its extremity. Beneath this bar is a notched shaft. The sliver, after passing the semicircular plate, is carried upon the spoon-shaped end of the lever ; its weight and the draught upon it depresses it, so as to lift the pendant bar out of the way of the revolving notched shaft ; thence, by means of the coiler, ft is neatly deposited in the cans. When the sliver is finished, or breaks, the spoon end of the lever rises, the pendant bar at the opposite extremity is depressed, and stops the notched shaft, which, being driven by a catch box, its sliding portion is pushed aside, and stops the frame.