Quality control and the mixing process

Abstract

Some of the factors that repeatedly enter into the mixing of rubber compounds are relatively straightforward: the raw materials used must be consistent; the same mix procedure must be followed, with the same heat and shear history throughout the process; contamination must be avoided. Other factors are less obvious, but nevertheless important: the compound should be formulated so as to minimize the effect of small variations in processing, and to minimize the chances for errors in composition. The type of mixing procedure (the order in which the ingredients are added) should be appropriate to the formulation of the ingredients and to the design of the internal mixer, so as to minimize the dependency of compound properties on small process variations. Finally, the mixer itself must be well maintained (clearances within specifications, proper circulation of coolant, etc.) for a consistent product to be obtained. This chapter will be concerned with measurement of the consistency of raw materials and finished compound.