TABLE OF CONTENTS There is probably no industry more capable of using varying and variable raw materials than the rubber industry. The industry has grown up using a natural polymer which varies from plantation to plantation, mineral fillers which vary depending on the quarry and rock band in that quarry, and chemicals prepared from the detritus remaining when more valuable materials have been extracted in the oil refinery. In addition various chemical reactions are carried out to give a product, both in the mixer and in the manufacture of the finished article. For this reason the range of mixing methods used and adjustments made would take more space to discuss than is available here.
A summary of techniques used is included below, but for a more extensive discussion on achieving quality mixing, the reader is referred to articles by this author (185, 198).
This is popular for productivity reasons, but is only feasible for certain compounds, and where mixing time is not limited by temperature rise. Single stage mixing is very difficult to achieve with highly filled or highly viscous mixes. Conventional mixing techniques are usually used, where the polymer is added first to the mixer, possibly with small ingredients, but excluding the bulk of the fillers. After a period of mixing, the filler is added followed by any plasticisersor oils. Final addition would be the curatives and accelerators, although these are often added on the dump mill following the mixer. Upside down mixing, where the filler and oils...
