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Wound-in-tension in a non-woven web

Balaji, K. K.
Good, J. K.
Literature on wound roll structure of non-homogeneous webs is scarce. Experimental and analytical research on wound roll structure of homogeneous materials such as plastic films and paper has been reported extensively, although at some scale the homogeneity of paper can be questioned. This paper will focus on a non-woven polyethylene. Results from the literature for film and paper webs show proportionality between wound-in-tension and nip load at lower nip loads and at higher nip loads the wound-in-tension becomes independent of nip load in both surface winding and center winding with an undriven rider roller. The proportionality between wound-in-tension and nip load at lower nip loads has been shown to approach the kinetic coefficient of friction between web layers for those materials. In the non-woven polyethylene web studied the proportionality was much less than the kinetic coefficient of friction. Tests conditions, including slip velocity, are known to affect measured friction coefficients. Wound-in-tension is the result of micro-slippage and elongation of the web in the contact zone beneath the rolling nip which involves the field of contact mechanics. Theorists in this field have presented arguments that friction coefficients used in contact analyses must be appropriate for the conditions of micro-slip which occur in the contact zone. Results of winding tests and finite element contact analysis will be presented which focus on this problem.