SHAPE OF LASHING-END CURVE AND AIR-DRAG

A portion of yarn is unwound from the rotating bobbin when yarn breaks in the spinning, the doubling and the covering process. This portion is called the lashing-end and the distance from the center to the free extremity is called the lashing-end radius, which is related to the bobbin radius, air-drag and centrifugal force. These relations are investigated by Mack and Smart on the assumption that air-drag per unit length is K times the square of the normal component of air velocity and acts in the same direction. For discussing fully the effect of air-drag on the shape of the lashing-end curve, the theoretical and the experimental investigation of the curve should be carried out. The theoretical lashing-end curve is compared with those of cotton 30s, 60s, twisted polyester yarn 250 den and thick nylon yarn 1420 den on the tangential coordinate and the following results are obtained.(1) By plotting the length of the perpendicular from the center to the tangent at the radius against the radius, the influence of air-drag on the shape of the lashing-end curve can be found easily. The actual curve on the polar coordinate can be obtained by using an approximate equation.(2) K for cotton yarn decreased with increasing radius. K for twisted polyester yarn and thick nylon yarn increased in the vicinity of the free extremity.(3) The relations between the lashing-end curve and air-drag coefficient are investigated for the point which locates at 0.7 times the lashing-end radius. The effective diameter for air-drag of cotton 30s is 1.8 times as large as the yarn diameter measured by a profile projector.