Rubber mould

Rubber product can be produced reliably and economiclly only if moulds are designed to suit the rubber moulding process. The three major moulding methods used in rubber product manufacture are compression rubber moulding, transfer rubber moulding and injection rubber moulding. rubber mould in general are made of metal such as steel, cast iron, aluminium and aluminium alloy. The moulds must be so designed that they can withstand large forces without deformation. Further there must be ready access for the introduction of blanks and the easy removal of finished rubber product. Apart from two-part rubber moulds, multi-plate rubber moulds with loose cores and split inserts, are also in use. Vertical face are given a small taper. Large undercuts are to be avoided. Ribs which protrude into the cavity should not be too thin as they may bend or be damaged during compression. Rubber mould must be provided with appropriate vents to avoid faults in rubber product because of incomplete filling of the cavity or voids in the rubber moulding caused by the entrapped air.

Rubber product are mostly produced by compression moulding. The numbers of cavities frequently amount to 1 to 12 or more. With transfer moulding up to 90 cavities may be served. This is possible because transfer moulding does not call for the insertion of prepared uncured blanks into cavities. Instead, the mixed blank is placed into transfer pot from where the mix flows through sprue and runner into single closed cavities under pressure of the transfer plunger. Rubber injection moulding of rubber product is as yet a comparatively new process. It draw on the processing of plastics and allow extensive automation with moulding times which are at the most up to a tenth of the time needed for compression or transfer moulding.