I recently had a call about a winder shutting down due to oversized rolls. This happened only when orders for large rolls were run. The rolls were not actually oversized. The diameter calculator was calculating incorrectly.
Before discussing the cause and cure for the incorrect diameter, I want to mention some of the other problems associated with incorrect diameter calculation.
- Accurate diameter calculation is required to determine the correct spindle RPM.
- Accurate diameter calculation is required to set the motor torque which establishes tension.
- Accurate diameter calculation is required to provide the correct inertia compensation for speed changes.
- Accurate diameter calculation is required if rolls are sold by diameter.
These other problems had been observed but were given a lower priority than the winder shutting down due to oversized rolls.
Most diameter calculators in web handling divide line speed (measured with a tacho) by spindle RPM. On this turret winder, both spindles were showing incorrect diameter. It is unlikely that both spindles would read incorrect RPM. The problem was that the web was slipping past the traction point used by the diameter calculator. In fact, the problem turned out to be a stripped gear.
I cannot stress enough the need for accurate roll diameter calculation in web handling.