Proccesing of Rubber

Raw elastomers as received from the manufacturer or from plantation in the case of natural rubber have few uses as such, because they all have poor physical properties and chemical properties. The levels of properties such as resilience, abrasion resistance, hardness, and tensile strength that raw elastomers possess are completely inadequate for such typical end applications such as tyre tread, fuel hose, radiator hose, or an oil seal. To develop the required level of such elastomers have to be mixed with various compounding ingredients, shaped and cured. These three components, mixing, shaping, and curing together constitute rubber processing.

Mixing

Mixing is the first and most critical process. If each of the various components rubbers, fillers, oils and chemicals is not thoroughly distributed and dispersed through the mass of the compound, then problems cascade down through the subsequent process of shaping and curing and result in less than optimum physical properties in the end product.

A compound is formulated first to meet the requirements of the end application. Before mixing, there is a mastication step. In this step, the reduction of viscosity and increase of plasticity is brought about by mechanical milling and working.

Mixing process is carried out in any of the two basic machines: two roll mill and the internal mixer. Among these, internal mixer is widely used, particularly for large scale production. The compounding ingredients are mixed and uniformly distributed though intensive shearing action of rolls. After mixing, the compound is either stored for maturation or taken to shaping operations.

Shaping

Shaping operation is carried out after mixing. There are three general shaping processes: extrusion, calendaring and moulding. The first two are followed by a curing stage, often an inline continuous system, whereas in moulding, whether compression, transfer or injection, curing takes place in the mould. In shaping operation, the rubber compound is formed into the shape required by the end product. After shaping, the product is either transferred to dispatch or to curing stage.

Curing (Vulcanising)

                The final step in processing is the vulcanization or curing of the shaped product. Basically, the process is that of applying heat at a certain temperature for a certain time. In curing stage, the curing or vulcanizing agents incorporated in the rubber compound reacts with rubber and forms crosslinks, which will convert the compound into the final product with required properties.