Effects of air entrainment on vacuum drive roller traction

Abstract

Vacuum assisted drive rollers are commonly used to provide additional traction in web tension control schemes. Single-sided web contact makes them a natural choice between a coating station and an oven where lower tensions are often desired. Many vacuum rollers are designed by the manufacturer according to customer provided specifications, and very little is published on their effective traction capacity where air entrainment is significant. In this paper, an empirical study is carried out to measure the traction on a vacuum drive roller as a function of vacuum level, web tension and speed. Loss of traction is determined by measuring the differential velocity between the web and vacuum roller surface in conjunction with the inability to maintain a programmed tension differential across the roller. Comparison is made between experimental measurements and the traction that would be expected for a simply wrapped roller.