Behavior of a flexible web in contact with a roller

In the contact patch between a web and a roller, there may be regions of stick and microslip or full slip. Within the stick zone, the velocities of web and roller surface match, but in the microslip zone they differ by a small amount as the web deforms. Analysis of the stick zone indicates an upper limit to the shear stress in the web, determined by friction. As the web steering in the incoming span is increased, the shear stress increases to satisfy the condition of velocity matching. Eventually, friction in the stick zone cannot support the shear stress and a microslip zone forms on entry, resulting in a change in the behavior in the span. The influence of web bagginess and roller profile on the shear stress limit is analyzed.An exit microslip zone will normally be present, as the web changes tension or develops shear stress and bending moment as a result of steering in the outgoing span. Attempts to analyze this with a beam model, as used in a free span, will be described. However, the requirement to match conditions at the start of the span is impossible to meet, so partial width microslip zones are postulated.Work continues to understand these microslip zones