Suppose the sizes and velocities to be as represented in the preceding table, that the engine is a double card 36 inches broad, and that it is furnished with a lap from the lap-machine of which 30 feet in length weigh 5 lbs. In one minute the surface of the feed-rollers, e, passes 2·55 inches of that lap onwards; in the same time the main drum f will work it off. To card the whole 30 feet, therefore, 141 minutes, or 2 hours and 21 minutes will be required. In this time the circumference of the rollers, u v, moves through a space of 141 × 42,908 in. = 5042 ft., and delivers a card-end of that length, weighing 5 lbs., minus 6 per cent. for waste, that is 4 lbs. 111⁄2 oz. One pound will form a riband 1072 feet long, being, according to the English mode of counting, about number 1⁄3, or 0·357. The extension of the cotton-fleece to this degree proceeds as follows:—In the 141 minutes which the feed-rollers take to introduce the 30 feet of lap, the doffer, h, makes 617·58 revolutions, and the comb, or doffer knife, i, detaches from the doffer teeth, a thin fleecy web of 2262 feet in length. The first drawing pair of fluted rollers, by its quick motion, with the aid of the funnel, m, converts this fleece into a riband 2535 feet long. The second pair of the fluted rollers extends this riband to 4390 feet, since their surface velocity is greater than the first pair in that proportion. The slight elongation (of only 112 feet, or about 1⁄44) which takes place between the delivery fluted rollers and the smooth cylinders, v, u, serves merely to keep the card-end steadily upon the stretch without folding. [Fig. 325.] is a plan of the card and the fleece, where h is the cylinder, n is the funnel, u the pressing rollers, and h′ the card-ends in the can.
[Figs. 326], [327.] represent skeletons of the old cards to facilitate the comprehension of these complex machines. [Fig. 326.] is a plan; F is the main drum; M M is the doffer knife or comb; G, the carded fleece hemmed in by the funnel a, pressed between the rollers b, and then falling in narrow fillets into its can. [Fig. 327.] K L are the feed rollers; A B, the card drum; C D, the tops; E F, the doffer card; M N, the doffer knife; d, b, c, the card-end passing between compressing rollers into the can a.
The drawing and doubling are the next operation. The ends, as they come from the cards, are exceedingly tender and loose, but the filaments of the cotton are not as yet laid so parallel with each other as they need to be for machine spinning. Before any degree of torsion therefore be communicated, a previous process is required to give the filaments a level arrangement in the ribands. The drawing out and doubling accomplish this purpose, and in a manner equally simple and certain. The means employed are drawing-rollers, whose construction must here be fully explained, as it is employed in all the following machines; one example of their use occurred, indeed, in treating of the cards.
Let a and b, [fig. 328.], represent the section of two rollers lying over each other, which touch with a regulated pressure, and turn in contact upon their axes, in the direction shown by the arrows. These rollers will lay hold of the fleecy riband presented to them at a, draw it through between them, and deliver it quite unchanged. The length of the piece passed through in a given time will be equal to the space which a point upon the circumference of the roller would have percured in the same time; that is, equal to the periphery of one of the rollers multiplied by the number of its entire revolutions. The same thing holds with regard to the transmission of the riband through between a second pair of rollers, c, d, and a third, e, f. Thus the said riband issues from the third pair exactly the same as it entered at a, provided the surface speed of all the rollers be the same. But if the surface speed of c and d be greater than that of a and b, then the first-named pair will deliver a greater length of riband than the last receives and transmits to it. The consequence can be nothing else in these circumstances than a regulated drawing or elongation of the riband in the interval betwixt a, b, and c, d, and a condensation of the filaments as they glide over each other, to assume a straight parallel direction. In like manner the drawing may be repeated by giving the rollers, e, f, a greater surface speed than that of the rollers, c and d. This increase of velocity may be produced, either by enlarging the diameter, or by increasing the number of turns in the same time, or finally by both methods conjoined. In general the drawing-machine is so adjusted, that the chief elongation takes place between the second and third pairs of rollers, while that between the first and second is but slight and preparatory. It is obvious, besides, that the speed of the middle pair of rollers can have no influence upon the amount of the extension, provided the speed of the first and third pair remains unchanged. The rollers, a, b, and c, d, maintain towards each other continually the same position, but they may be removed with their frame-work, more or less, from the third pair, e, f, according as the length of the cotton staple may require. The distance of the middle point from b and d, or its line of contact with the upper roller, is, once for all, so calculated, that it shall exceed the length of the cotton filaments, and thereby that these filaments are never in danger of being torn asunder by the second pair pulling them while the first holds them fast. Between d and f, where the greatest extension takes place, the distance must be as small as it can be without risk of tearing them in that way; for thus will the uniformity of the drawing be promoted. If the distance between d and f be very great, a riband passing through will become thinner, or perhaps break in the middle; whence we see that the drawing is more equable, the shorter is the portion submitted to extension at a time, and the nearer the rollers are to each other, supposing them always distant enough not to tear the staple.