A system of “counts” is used to indicate the size of yarn and it is based on the number of hanks it takes to make a pound. A hank is always 840 yards and 50’s would mean that the yarn is of such fineness that it would take 50 × 840 yards (=4,200 yards) of it to weigh a pound. Yarn below 30’s is graded as coarse; between 30’s and 60’s as medium and above 60’s as fine. To prepare cotton as it comes from the bale for a fine yarn of, say, 100’s, it must go through no less than sixteen machines before it reaches the mule.
We have not the space to describe all of these machines, but in general it will suffice to say that the cotton is graded by passing it through a series of pickers. These machines throw out the fibers and beat them so as to knock out the impurities and, at the same time, a blast of air blows out the dust. The cotton is treated by a number of such machines in succession and is finally delivered in a broad sheet known as a “lap,” after which it passes through the carding machine which combs out the tangled bunches and removes further impurities from the lap. The lap is then gathered into a compact rope known as a “sliver.” The sliver goes through the drawing rolls which serve to parallelize the fibers and make the sliver of even thickness, and at the same time to give a moderate amount of twist so that it will hold together, and it issues from the machine as “roving.” In the case of fine yarn the sliver issuing from the carding machine goes through a combing machine so as to remove the finer fibers. The bobbins of the roving are then placed in the spinning machine, which may be either the spinning mule or the ring spinning machine. The principal difference between the two is that the spinning mule is intermittent in its operation, while the ring spinner not only spins the roving into yarn but at the same time winds it up on a bobbin.
FIG. 66.—ARKWRIGHT’S DRAWING ROLLS
ARKWRIGHT’S DRAWING ROLLS
The first advance over the old-fashioned spinning wheel, which dates back to the fifteenth century, was in 1770, when the first spinning jenny was invented by Hargreaves. This consisted practically of a multiple spinning wheel by which one man could spin a large numbers of bobbins of yarn at the same time. It was at about the same time that Arkwright invented the drawing rolls which have played a most important part in the preparation of yarn, and this invention is worthy of our attention because it contains an interesting mechanical principle. As shown in Figure 66, a number of pairs of rolls are provided through which the roving passes, but successive pairs operate at higher velocities. Thus, the second pair of rollers through which the roving passes run at a little higher speed than the first pair, the third a little higher than the second pair, and so on. As a result, the roving is drawn out by the operation and issues from the last pair of rollers at a higher speed than it entered the first pair of rollers. The only way in which it can accommodate itself to this accelerated motion is to be attenuated or drawn out. Weights are used, as shown in the drawing, to press the upper rollers against the lower ones.
THE SPINNING MULE
Shortly after Arkwright’s invention came the mule spinner, invented by Crompton between 1774 and 1779. Machines operated on the same general principle as this are in general use to-day. In the old-fashioned method of spinning by hand the worker took a small quantity of cotton, pulled it out into a long sliver, attached one end to a bobbin and gave the bobbin a twirl between his hands in order to spin the fiber into yarn; then the yarn was wound up on the bobbin and the process was repeated. The spinning mule does practically the same thing, but infinitely faster and on a much larger scale. As shown in Figure 67, the bobbins of roving (A) are mounted on a stand and passed through a set of drawing rolls (B) which are regulated to pull the rovings out to the desired thickness of yarn. The roving then passes to the nose of a “cop,” or spindle (C), which is revolved at very high speed. The cop is carried by a carriage (D) which moves away from the bobbins of roving to the position indicated by dotted lines, while the cop is revolving. The cop has a travel of about five feet during the time the yarn is drawn out and spun. Then the carriage moves back toward the stand upon which the bobbins of roving are mounted and the spun yarn is wound up on the cop. The reason the yarn does not wind up on the cop while it is spinning is because it runs to the nose of the cop and, at each turn of the cop, the coil twists on the nose and slips off. On the return of the carriage, however, a set of wires (E), called “fallers,” press the yarn down so that the revolving cop will wind up the slack.
