Cellular rubber (Foams)

There are two processes for the manufacture of foams from natural and synthetic latices. The introduction of air or gas into the latex to create foam is common to both processes. This foam is then gelled, cast into moulds, vulcanised and dried. With latex beating the latex mix is suspended in soap or gelatine and beaten from a 7- to 14-fold vulcanisable volume. For this machine wire beater with a selected steplessly variable beater speed is used. Gelling with sodium silicate fluoride keeps the foam for an extended time in a castable condition. The foam is cast into a mould and vulcanised at approximately 373 K . The cured foam rubber is removed from the mould washed free of clinging chemicals and dried.

With blown latex, hydrogen peroxide is added together with blowing agents to a vulcanisable latex mix which is decomposed. The created oxygen foams up the volume of the latex from 8 to 14 fold, the foam consisting of small regularly spaced cells. It is frozen at 258 to 263 K and carbon dioxide is passed through the rigid foam. After thawing out, the foam becomes liquid. It is then vulcanised, washed and dried in the usual way.

The manufacture of plastic foams is basically different from natural and synthetic latex foams. Polystyrene foam contains a blowing agent which expands by heating the mass to over 350 K and produces a cell structure. With polyether or polyester respectively the foam structure is built by a chemical reaction which releases carbon dioxide; the mass rises and sets simultaneously.