Full definition
The critical process of incorporating all compound ingredients (polymer, fillers, plasticizers, curing agents, protective additives) into the raw rubber to produce a homogeneous, processable compound ready for shaping and vulcanization. Two primary equipment types: (1) Internal mixer (Banbury or intermeshing type) — enclosed chamber with two counter-rotating rotors; batch process; 3-8 minute cycles; handles large volumes (50-600 liters); dominant in industrial production. (2) Two-roll mill (open mill) — two counter-rotating rolls with adjustable nip gap; used for finish mixing, adding curatives (which require lower temperature), sheeting, and warming. Mixing is a carefully sequenced operation: polymer breakdown → carbon black and filler addition (with oils) → protectants and process aids → dump from mixer → curatives added on mill (below scorch temperature). Critical parameters: temperature (mixer dump temp typically 110-130°C for non-productive, below 110°C for curative addition), rotor speed, ram pressure, and batch time. Dispersion quality directly impacts finished product consistency. Per ASTM D3182 for standard rubber mixing procedure.