Measuring inter-layer slippage in unwinding rolls

Scope and Method of Study. Web materials undergo number of defects during winding and unwinding processes some of which are inter-layer slip related. The primary goal of this study was to find an appropriate method of measuring inter-layer slip that can be effectively used during unwinding of a roll with unknown winding history. These measurements could then be used to control unwind tension and eliminate slippage in the unwinding roll. Analyzing the behavior of web materials during slip, experiments were conducted using various sensors on Dupont 377 and Mitsubishi white polyester whose material properties were very different from one another.Findings and Conclusions. On number of trials using various methods, an effective method was established to eliminate inter-layer slip for any type of web material. Methods implemented include acoustic emission transducers, ultrasonic sound transducers and encoders. Encoders are devices that accurately measure the distance travelled by the material that it is in contact with. Implementing two encoders to measure differential velocity at two different points on the unwinding roll, one at the point of exit of web and another at a point of less/no slip, produced a consistent slip measurement.