The Art of Calendering

The ease with which a compound can be calendered is largely governed by the carbon black loading in the rubber compound and the rubber content and scorch time. Examples of two typical topping compounds are given below. 

Reduction of up to 10% of the accelerator content may be permissible without seriously affecting the physical properties of the product. This will increase the mooney scorch time by as much as 4 units which is a safe condition. 

An increase of the mastication time for the uncompounded raw rubber will give an increased margin of safety. 

It is not possible to standardise operating temperatures for calender rolls. Although on each calender a set of conditions can be established for several runnings, this may vary approximately on calenders using different types of compounds. It is however a normal practice to operate with lower temperatures for those rolls around which the rubber bands rotate. 

It is desirable to operate with the lowest roll temperatures for 

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