On an industrial scale rubber is compounded in an internal mixer. The art of compounding is to determine the precise mix required for a given application, and then to add exactly the right quantity of each ingredient in the correct predetermined sequence.
The mixing process initiates shear. As the temperature builds up, this helps disperse many of the ingredients. When all the materials have been thoroughly blended together the shear forces start to reduce again, and the compound is formed.
The compound then exits the mixer as a spherical mass, and is transferred on to a two-roll mill. This process has three key purposes:
To finally complete the blending process.
To cool the compound
To simultaneously convert it into a usable form, thinning it to approximately 9mm.
The compound is then treated in an antitak bath to prevent it sticking together when stacked, and continues to automated finishing lines where it can be finished and packed in a variety of forms, to suit customer requirements.