188 (#250) ############################################ WOOLLEN AND WORSTED SPINNING T = TT I 2 д the slipping of the fibres upon one another without breakage should be attained if by any means possible: the addition of oil may be one means-drawing in water, if mechanically possible, another means. The formula given to hold a rope tight round a post is— T, TI = e 2nTM, in which tension on slack side ; T the tension on the tight side when rope or sliver is about to slip; = number of turns of belt on the pulley or roller in no. of rollers worsted spinning, -1 -) ; the co-efficient of friction between belt and the pulley. With knowledge of the strength of the sliver being dealt with and of the type of holding rollers, no doubt on these lines the turns per yard, per foot or per inch might well be worked out. But the working would be somewhat complex. The factors involved in deciding the desirable twist for drafting worsted slivers are certainly many, and their bearings upon one another are somewhat difficult to define and to group into a useful formula. It might be taken, for example, that fibre length should be made the basis. If it were then discovered by experiment that the longest fibres should make, say, three turns round the sliver (see Fig. 38), then for thin slivers (for the finisher and roving boxes) the formula would roughly stand- 3 fibre length turns per I". But in deciding the twist for a sliver it may be deemed necessary to maintain the same relative twist * in the drafted sliver, and as diameters decrease as v draft, Angle of exterior fibres. 13 188
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