24—Short-Wave Variation in Cotton Rovings Caused by Machinery Defects in the Speed Frames

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Abstract
Uneven rotation of the bottom middle roller is identified as the primary mechanical cause of irregular drafting in cotton speed frames. The defect Produced has an abnormally short wavelength, between one-third and two-thirds of an inch, and is not apparent as a thickness variation in the roving, being hidden by the overlap of the fibres. The fault is only developed as a thickness variation at the next stage of drafting, when the period length becomes long compared with the length of the fibres. The main cause of uneven rotation of the roller arises from lack of rigid support of the back roller shaft; secondary causes are rubbing of the draft gear teeth against obstructions and deep setting of the carrier pinion. Defective drafting due to these causes may occur in any of the speed frames, but is most objectionable at the intermediate frame since the equivalent length of the period in weft yarn is then such as to give rise to diamond pattern barring in cloth. The remedies in the majority of cases are fairly obvious and include alignment of rollers and frequent removal of waste trapped in the roller necks to ensure easy turning. The initial production of periodic short-wave defects in the roving is not Particularly dependent upon draft, hank of roving, or cotton, although the drafting quality of the cotton may influence the thickness variation developed in the yarn upon subsequent drafting. The amplitude of the defect developed depends upon the direction in which the defective roving is presented at the next stage of drafting, being reduced, fortunately, when the roving is reversed as occurs in unwinding from the bobbin; even so, the thickness variation in yarn is frequently of large amplitude. The presentation of defective roving in the same direction as that in which it was originally drafted develops the Periodicity almost to its full extent as a thickness variation, and this feature may have important practical consequences in “through-drafting” systems Where there is no reversal to mitigate the effect. Moreover, the abnormally slow motion of the back rollers in such systems is likely to enhance uneven rotation.

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