FACTS Tech Blog

Keep the calender running – stops cause the rolls to become egg shaped and introduce significant gauge thickness variation.

When the calender is stopped, roll heat loss is not uniform around the roll. Heat loss along the circumference near adjacent rolls is minimal while heat loss in other areas is much higher. This leads to different temperatures and therefore different degrees of roll expansion. A few degrees on a 24” to 30” diameter will result in measurable “out-of-roundness” of each roll. This is true when the calender is empty but even more so when there is a hot bank of rubber between the rolls. The longer the calender is stopped the worse the condition.

Since the rolls run at different speeds, periodically the high spots match up resulting in thin gauge spots. When the low spots match up a thick spot results. This results in an effective doubling of any roll “out-of-round” or run-out error.

Typical short-term thermal out-of-round gauge variations are plus or minus .5 mils (.0005”) to 2 mils (.002”). Thermal run-out is gradually reduced as the calender runs, but takes 15 to 25 minutes to be eliminated. To minimize “thermal run-out” the following procedures are recommended:

• Keep the calender running during warm up/start up
• Minimize calender stops
• When the calender is being stopped for more than a very brief time, remove the rubber from the banks. This is considered good practice anyway for the rubber compound.
• On gum calendars always keep the calender running when there is no rubber on it
• On textile calendars or on any calender when leader is going thru the calender, dropping off tension and allowing the uncoated fabric (advance the calender 18” if necessary) or leader to go slack will permit running the calender during delays and personnel breaks. This will dramatically reduce thermal run-out.