Indian Journal of Fibre & Textile Research Vol. 36, June 2011, pp. 152-157 Influence of process parameters on packing density of open-end and core-sheath friction spun yarns S M Ishtiaque, A Das a & Prashant Vishnoi Department of Textile Technology, Indian Institute of Technology, New Delhi 110 016, India Received 29 January 2010; revised received and accepted 31 March 2010 The effect of opening roller speed, difference in drum speed and suction air pressure on packing density parameters of open-end and core-sheath friction spun yarns has been analyzed using the Box-Behnken method and response surface equations. The trends of change in packing density with process variables are found to be opposite to those of yarn diameter. Yarn diameter decreases, and helix angle and packing density increase with the increase in suction air pressure for open-end and core-sheath friction spun yarns. Core-sheath friction yarns have lower yarn diameter and helix angle, but higher packing density than open-end friction yarns. Keywords: Core-sheath yarn, Friction spun yarn, Helix angle, Helix twist, Open-end yarn, Packing density, Yarn diameter 1 Introduction The study of idealized packing of circular fibres in the yarn cross-section was started long ago by Schwarz 1 . Morton 2 showed that for staple fibre yarns of various counts and twists, the fibre packing density over the yarn cross-section was not uniform. Later on, Hearle et al. 3 gave few formulas to calculate specific volume of yarn based on yarn twist, twist angle and yarn linear density. The twist angle in fibre at the yarn surface is found to be different than that in the fibres towards the centre of the yarn. The formula given by Hearle et al. 3 is valid for idealized ring structure only and is not applicable for various other structures of the yarns manufactured by other technologies, like rotor, air jet, and friction. In this regard, Ishtiaque 4 derived a formula to calculate the packing density of the yarn. This formula is applicable for the yarns manufactured by different technologies. It is based on the actual values of yarn diameter, helix twist and number of fibres in the cross-section, as obtained by the study of fibre migration behaviour in the yarn structure. Tyagi et al. 5 showed that packing density of core- sheath friction spun yarn increases with the increase in yarn linear density and friction ratio. Packing density in the inner zone is significantly higher and it gradually decreases towards the outer surface. Gowda 6 observed that for core-sheath friction spun yarn the packing density increases with the increase in fibre to fibre frictional force. Ishtiaque 7 studied the influence of spinning drum speed, delivery speed and throttle diameter on packing density of core-sheath friction spun cotton yarn. He observed that packing coefficient increases with the increases in friction drum speed, decrease in delivery rate and increase in throttle diameter up to 52 mm. However, not much work has been carried out on the comparison of packing densities between open- end and core-sheath friction spun yarns. In the present work, the effect of opening roller speed, drum speed and suction air pressure on yarn diameter and packing density of open-end and core- sheath friction spun yarns has been studied. 2 Materials and Methods Yarn samples were prepared for both open-end and core-sheath friction yarns according to sample preparation plan as discussed in earlier paper by Ishtiaque et al. 8,9 using three variables three level Box and Behnken 10 factorial deigns (Table 1). The actual values of these three variables along with the coded levels are given in Table 2. The parameters needed for the calculation of packing density, like fibre twist, fibre helix angle, helix diameter, and yarn diameters were studied by using the classical tracer fibre technique proposed by Hearle et al. 3 . The packing density in the yarn was calculated by using the following formula, derived by Ishtiaque 4 : 2 2 Packing density 2 /[ 1 ( ) 1] nFZ DZ π π = + - of yarn ( ) μ ____________ a To whom all the correspondence should be addressed. E-mail: apurba65@gmail.com