Mixing of tire compounds

Abstract

Tire compounds are generally based on unsaturated diene polymers reinforced with carbon black, and vulcanized by an accelerated (usually a sulfenamide) sulfur system. The ingredients are normally mixed in a minimum of two steps. Polymers, carbon black, zinc oxide, stearic acid and any antiozonant or antioxidant system are put in the first step; curatives go in the second. The second step uses a lower temperature than the first step; this allows the stock (compound) to retain a window of processing safety. A typical first step starts with the polymers added at time zero, carbon black goes in at 30 s, and oil is added at 90 s; the dump temperature is 160 °C. A typical second step, or final step, has all the first pass and curatives put in at time zero, with a dump temperature of 110 °C.