Compression

Compression Moulding
MOULDING PROCEDURE:This is the least complex of the moulding processes but is ideal for large parts or short production runs. The pre-heated mould is removed from the press and opened. Pre-cut pieces of uncured rubber, at a set weight, are placed in the cavity on the lower plate, metal or fabric inserts are also placed in the cavity at this time if they are required. The top cover of the mould is replaced and the mould is placed in to the press. The closing press forces the plates together and the pressure and heat force the uncured rubber to flow into the cavities of the mould. The mould remains closed until the rubber has cured. The mould is removed from the press and opened. The moulding is removed by hand using unmoulding tools. Further processing may be required to remove the excess "flash" - the rubber that has formed a layer between and around the parts
Bank of small volume compression presses A compression mould is simply two pieces of steel with cavities cut into either one or both halves. If it is a grommet mould there will be an additional plate between the top and bottom plate with holes bored into it to form the groove in the grommet. It is far less complex than an injection mould.
Bridge bearings moulded using the compression moulding method
GENERAL COMMENTS: These moulds are relatively cheap to build and are ideal for low volume requirements, however the part price is generally higher because they take longer to cure, rubber for each cure has to be measured, cut and weighed by hand and the mould is packed with rubber and the cured parts are removed manually. While the moulded components are being removed and the next shot of rubber is being added the mould is cooling down. It again needs to be reheated in the press to obtain optimum cure temperature. For low volume requirements it is more economical to build a compression mould than an injection mould . Compression moulds are often used for proto-type mouldings, where samples are needed for testing fitment into assemblies. This allows for further design modification before building an injection mould for production volumes.