Since the last review of this subject (355), there have been many developments in mixing machinery and some departures of companies long established in the manufacture of rubber mixing equipment. There have also been significant reductions in the use of curable rubber, particularly in the motor industry, and also in domestic areas where the demands of recycling are favouring to an ever-greater degree the use of thermoplastic materials.

Developments that have taken place in mixing equipment over the last eight or nine years have been significant, with almost all major machinery makers having made innovations of one type or another. Some developments have been as small as re-profiling rotors of relatively conventional design. Others have been the introduction of completely new rotor designs, both intermeshing and tangential. Where possible, the potential advantages of various designs are discussed, particularly where these are developments of existing rotor shapes. In some cases these advantages are as indicated by the various manufacturing companies; in other cases comments are made from this writer's experience and should be regarded as his own personal opinion.

Material developments in the rubber industry are outside the scope of this report, other than where they may affect the mixing of rubbers. Where material developments impinge on mixer design, for instance where one particular design is favoured for technical reasons over another, then reference may be made to particular materials.

As indicated in the last report, significant reduction in cycle times with consequent increase in productivity has not been seen, nor...