Stress intensity In a thermoroll

Abstract

During the manufacture of coated paper products, a paper-making stock consisting of water and 1% or less wood fibers is prepared by chemically or mechanically separating the fibers from wood. A screening process removes most of the water; the remainder is removed through pressing against felts and contact drying. The web is further densified by passing it through high pressure calender rolls, resulting in about a two-fold decrease in caliper of the pressed and dried paper. The web may then pass through a number of calender nips. This last stage of densification involves high temperatures and pressures that lead to high stresses in the roll material.

A stack consists of two rolls: one has a polymeric elastomer covering, the other is a solid iron alloy (the thermoroll). It is our task to estimate the stresses in the thermoroll under standard operating conditions, and determine whether it is possible, under certain conditions, for cracking or roll failure to occur.

The main focus of our group was to calculate the temperature gradient in the thermoroll and to determine whether this gradient can lead to an intensification of stress in the nip region.