219 (#291) ############################################ TYPES OF DRAWING MACHINES All these frictions give rise to electrification, but if the roller * fibre friction gives rise, say, to negative electrification of the sliver and the fibre x fibre gives rise to positive electrification, then the one may neu- tralize the other. The interesting researches conducted by Dr. Shorter at the University of Leeds on behalf of the University and the British Research Association for the Woollen and Worsted Industries have shown that even the nature of the guide or roller round which the wool passes has an electrical effect, and may add to or take from the tendency of slivers so passed to electrification. The electrical natures of chrome leather and tan leather are so different that it will not do to use either indiscriminately. It is also well to note that certain firms place on the market neutralizing (con- ducting) roller-coverings. These, however, usually con- tain a good conductor (glycerine), and as this becomes sticky in a moist atmosphere their use is very limited. Examination of worsted drawing machines will reveal the fact that rollers for controlling long fibres are soft covered as against rollers controlling short fibres being hard covered. That is to say, that the covering for long wool drafting rollers is first a layer of felt cloth and then the leather outer covering. The reason for this would seem to be that length of grip (roller contact) should bear some relationship to the length of fibre being treated—long fibre, long grip; short fibre, short grip. But again almost rule-of- thumb methods are being employed—there is here also again much room for research. The relative sizes of back and front rollers and their weighting is again a matter of much interest. With the thick, inert slivers entering the back rollers it will be evident that dead weighting will be the best, this resulting in fibre weighting fibre. But if the natural 219
174 176 Textile Machine
192 192 Textile Machine Part
298 299 Textile Machine Part
84 84 Textile Machine Part
86 86 Textile Machine Part
148 148 Textile Machine Part
182 182 Textile Machine Part
208 210 Textile Machine Part
279 280 Textile Machine Part