FACTS Tech Blog

Severe thermal run-out can be introduced during warm-up of the calender if it is not kept running. Remember that the calender gap will be reduced as the rolls grow (get larger) as their temperature increases. Good practice is to open the calender at least 100 mils (0.10”) before starting to increase the roll temperature above ambient. Keeping the calender rolls turning during warm-up and cool down also eliminates the possibility of warping the rolls.

Most modern calender rolls are the drilled type. This means that water passages are drilled across the roll face under the surface. This effectively forms a radiator-like heat exchanger around the periphery of the roll.

If these passages become plugged, then non-uniform heat transfer will occur and this results in a thermal ‘out-of-round’ condition for the roll or rolls. This has the same effect as if the rolls were machined ‘out-of-round’.

To avoid this condition only treated water should be used and the rolls should be periodically flushed.

How do you check for plugs? Compare the roll run-out at ambient temperature and at operating temperatures.

Calender roll bearings may have excessive run-out. The result is the same as, and will appear as calender roll surface run-out. Excessive bearing clearance will result in the roll shifting during operation as roll separating forces vary.

These conditions will adversely affect the ability to control the calendered gauge.

When investigating run-out issues, check the calnder roll surface AS WELL AS the bearings!

Calender rolls must be round and free of run-out at ambient temperature. Any run-out of the individual calender rolls will be amplified as the high spots and low spots periodically match up between the roll pairs.

Differences between high and low spots is relatively easy to check with dial indicators.

How to:

• Run the calender without rubber (or your product)
• Make Sure there is a slight gap between the rolls.
• Check the differences between high and low spots with simple dial indicators.

Give us a call - we’re happy to walk you through it and help diagnose your problem. Call FACTS, Inc.- 330.928.2332