Increase the temperature by 20 to 40 degrees F when the rolls are stopped to maintain a more uniform roll surface temperature.
The TCU (Temperature Control Unit) controls the temperature of the water exiting the calender not the roll surface temperature. This is an important distinction. When the calender is not actively processing rubber, i.e. during warm-up and when the calender is stopped, the roll surface is losing heat to the ambient and thus the TCU is actively heating the water loop. In this condition the roll surface temperature is between 10 degrees to 20 degrees F below the water temperature.
When the calender is running and actively processing rubber, heat is being generated so the TCU is actively cooling the water loop. In this condition the roll surface temperature is between 10 to 30 degrees F above the water temperature.
From this description it becomes apparent that for a constant water loop temperature, the roll surface temperature changes as much as 50 degrees F between the calender normal running condition and when the calender is stopped. This difference in roll surface temperature means that the rubber processed is being processed under substantially different conditions. Shrinkage and other properties will therefore be different.
To minimize the difference in processing conditions, the roll temperatures should be increased 30 degrees F whenever the calender stops. The temperature increase should be gradual and the specific amount should be experimentally determined by comparing roll surface temperatures in normal operation and after the calender has been stopped for 20 minutes. This function is available as a standard option as part of FACTS TCC 1600 calender control systems.
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