The 1st Step is breaking down of natural rubber, often in presence of a peptizer to shorten the long molecule chains……..The 2nd step are one or more different non-productive mixing stages at temperatures of 150 - 180, where a large variety of ingredients, such as filler material ( e.g. carbon black, silica ), oils and other chemicals are added to the (broken down) rubber or polymer to give it the properties it needs for the many applications of a tire.The 3rd step is the remill stage no additional ingredients are added but the stock is mixed up to temperatures between 135 - 175 .The purpose of remilling is primarily to reduce the compound plasticity, especially for NR based stocks, and to some extentto further improve the dispersion and homogeneity.HD-silica compounds are mainly remilled to obtain a further reaction of silica/silane.The 4th step is the productive mixing stage up to temperatures of 110 - 125 maximum.Because with the addition of curing agents and sulfur at higher temperatures, scorchingcould occur.