Air entrainment on two sides of a web passing through the nip of two rigid rolls

Abstract

When web materials (paper, plastic films, or metal foils) are wound into rolls, excessive amounts of air can be entrapped between layers of the web, resulting in defective rolls. Entrapped air layer between a coated film and a heating/cooling drum can significantly reduce the heat transfer rate. The most widely adopted method for reducing the amount of entrapped air in winding rolls and at heating/cooling drums is to use a nip roller, which pushes down on the incoming web. A computational method was used to determine the amounts of air passing through the nip on the two sides of the web. The study model included the effects of air compressibility, but it was assumed that the two rolls are rigid. Main variables included the wrap angle of the incoming web, web speed, nip force, and diameters of the rolls. It was found that, when the nip force is not very small and the two rolls are rigid, the amounts of air on the two sides of the web are nearly the same and can be determined using a simple model which includes only a rigid roller and a flat surface.