Web sag and the effect of camber on steering

A web in a horizontal span will deflect downwards due to gravity. This sag is more pronounced for heavy materials in long spans under low tension. It is possible for a web whose unstretched length is greater than the span to be under positive tension.A cambered web will sag more on the baggy side, especially under low web tension. This side therefore has a longer path length between rollers in good alignment, which provides a mechanism for lateral steering. The boundary conditions of normal entry and velocity matching on the downstream roller (which successfully predict the steering of straight webs by misaligned and tapered rollers) can still be applied without modification.A horizontal span of cambered web under tension has been simulated using Finite Element Analysis, showing that the web steers to the tight side. The amount of movement varies with span length, tension, density, amount of camber and width. For low tensions, the displacement can be quite large, but it falls rapidly as tension is increased