139 (#193) ############################################ WOOLLEN YARN SPINNING 2. That drafting-twist is dependent upon the speed with which the carriage is drawn out (spindles usually running at a constant speed); and this is dependent upon a change-wheel which, without varying the speed of the spindles, varies the speed of the carriage and thus affects the turns per inch during the outward run of the carriage. There is usually a secondary change wheel which- coming after the slubbing peg wheel-may be used alone or in conjunction with the primary change wheel. Thus there are three means of control of drafting-twist, viz. primary change wheel, secondary change wheel primary and secondary change wheels. 3. The time that the double speed is in action decides the final twist given to the yarn. This again is dependent upon the twist-peg already referred to. In many cases twist may be calculated in mule spinning by spindle speed and time; but upon the whole this system is to be condemned-greater accuracy in mule spinning is much needed. 4. Calculation for Production : This is dependent upon three factors (a) Draws of carriage per minute ; (6) Length of draw; and (c) Count of yarn to be spun. Let a = draws of carriage per minute ; 6 length in yards of draw; = counts of yarn spun (yards per dram); then ахбо хъ = lb. per hour calculated (theoretical) pro- 6 X 256 duction per spindle. Example : с Let a = 3 b 70" C = 20 skeins, then 139
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