An ancient rule in drives for web handling is “we assume no slip occurs”. Of course, any roller can lose traction when conditions are not perfect. The web can slip past a roller. Layers of the web can slip past each other on a spindle winder. Slip may occur on a coater either before the coating is applied or once the coating is applied. The slip may get worse as roller coverings wear. The slip may increase if the running tension of the web or transporting fabrics changes. Drive belts may slip – timing belts anyone?
I recall one paper coater that regularly slipped by 8 FPM when running a particular product. I recall a similar paper coater that slipped by 50 FPM fast on the base sheet but came into control when the coating was applied.
My blog entry Detecting Roll Slip listed a couple of methods of detecting the grossest examples of slip.
When it occurs, slip should be reduced or eliminated. Slip introduces the following problems into a web handling line. Often one or more strange happenings on the line can indicate slip.
- Winding or unwinding roll diameters are incorrect
- The winder shuts down due to a false oversized roll
- Tension control is poor
- Drive torques are different than usual