225 (#297) ############################################ TYPES OF DRAWING MACHINES diameter of the barrel +4 (diameter of the sliver) ; for 3rd layer of the barrel + 6 (diameter of the sliver) ; for 4th layer of the barrel + 8 (diameter of the sliver); and so on. From these diameters the increase in circumference may readily be calculated. Now if the sliver could be fed to the bobbin at an increased rate exactly coinciding with the increase in the circumference of the bobbin, the flyer continuing to revolve at the same rate, the bobbin would also continue to revolve at the same rate. But the actual turns would be the same, therefore fewer turns per inch per unit length. Further, the varied delivery of the sliver would necessitate such complexities that it is apparently not to be thought of—a uniform delivery of the sliver is invariably adopted. Now this means that as the bobbin—layer by layer—increases in circumference it must more and more nearly approach the flyer in speed. The difference between open and cone" drawing may now be readily understood. In "open" drawing the bobbin is so tensioned that while it will not over-run” it will not strain the sliver in its “ lagging behind.” But to ensure this, as already noted, considerable twist must be put into the sliver. Careful consideration of the conditions prevailing at the start and at the finish of the finer drawing or spinning frames will reveal an added difficulty. In "cone ” drawing the bobbin may be positively driven at the calculated rate of increase, or decreased as required. By this means- (a) strain is taken off the sliver and levelness so far as possible ensured ; b) much or little twist may be inserted ; (c) bobbins of any desired size may be employed. P 225
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