Indian Journal of Fibre & Textile Research Vol. 29, June 2004, pp. 179-183 Study on drafting force of roving: Part II - Effect of material variables A Das a , S M Ishtiaque & Rajesh Kumar Department of Textile Technology, Indian Institute of Technology, New Delhi 110 016, India Received 4 April 2003; revised received and accepted 4 July 2003 The effect of some material variables, namely fibre-to-fibre friction, roving hank and roving twist, on drafting force of roving has been studied. A very good correlation (R 2 = 0.903) between material var.iables .and force has obtained. The drafting force increases sharply with the increase in fibre friction and roVIng tWist ?ue to the rapl? increase in mutual coherence among the fibres. The drafting force is less influenced by the change In roVIng hank, but It decreases initially and then increases as the roving hank becomes finer. Keywords: Cotton, Drafting force, Fibre friction, Roving hank, Twist multiplier IPC Code: Int. Ct.? D02G 3/00; DOIH 5/00 1 Introduction The effect of process variables, namely draft, drafting speed and roller setting, on drafting force, keeping the material variables constant, has been studied earlier I . Apart from process variables, the material variables, namely fibre and roving parameters, also affect the drafting force of roving significantly. The frictional force acting on fibre assembly during drafting can be determined experimentally by measuring the total resistance of fibre assembly. The frictional force depends on relative fibre velocities and density distribution 2 • It is very difficult to predict the relative velocities of short fibres as their velocities are highly variable. In addition, the material density distribution is also not constant along the drafting line. Due to these, the fibre movement during drafting becomes irregular and causes generation of drafting waves. Therefore, drafting force becomes highly variable and results in variability in the output material. In roller drafting, the significance of drafting force is necessary to overcome inter-fibre frictional forces, which generate due to inter-fibre contacts and also to counteract fibre bending 3 . Thus, fibre bending or flexural rigidity of a fibre is also an important factor which affects the drafting force. Deluca and Thibodeaux4 found that in cotton card sliver the fibre torsional and bending rigidities are more important to sliver cohesive forces than fibre-to-fibre frictional forces. On the other hand, in roving the twist and "To whom all the corres pondence should be addressed. Phone: 26591413; Fax: +91-11 -26851103 ; E-mail: apurba_das@hotmait.com/apurba@textile.iitd.ernet.in improved fibre orientation cause fibre-to-fibre frictional forces to be more important to roving cohesive forces than fibre torsional and bending rigidities. Fibre crimp and fibre-to-fibre friction determine the surface properties of a fibre. Fibre crimp 3. 5 plays a dominant role in drafting by affecting the motion of fibre in drafting zone, bulk properties of roving and drafting force. The more highly crimped fibres exhibit a larger drafting force because the fibre has more opportunity to interlock spatially, entangle and mesh with neighboring fibres. The role of friction in textile processing, though not quantified, is well recognized. In traditional textile processing, fibres are converted into yarn through a series of opening and drafting processes involving between different groups of fibres and other materials. These interactions determine relative fibre position and fibre movement during processing. The main mechanism governing these interactions is friction 6 . The knowledge of the frictional values of individual fibres is very important to predict whether the processing will be satisfactory or not, when other physical properties are satisfactory. Audivert and DeCastellar 7 found that the fibre length is significantly more correlated with the drafting force as compared to the fibre fineness. Graham and Bragg 8 experimentally found that 1 % change in fibre length changes the drafting force by about 5%. It has also been studied 8 • 9 that the increase in roving twist causes increase in drafting force. In the present study, attempts have been made to correlate the material variables, namely fibre-to-fibre