A screw injection system delivers a metered quantity of rubber into the closed mould. The injection unit is fed from a continuous strip or a reservoir of uncured rubber and is cooled to avoid premature curing.
This process is generally used for multi-cavity moulds and can produce hundreds of components per press cycle. Because of the amount of rubber in the system, it is inadvisable to change materials frequently
Large moulds require complex feed systems to balance the pressures in each cavity. Generally these are in the heated top half of the mould and cure at the same time as the components. Unlike thermoplastics, cured thermoset rubber cannot be reground or reused and the additional waste has to be included in the material usage per piece. Where very large volumes of mouldings are required, cold runner systems should be considered. These are justified by material savings over £10,000 pa.
This process lends itself to relatively large quantities, a large number of cavities and infrequent changes of materials or moulds. Parts are repeatable and can be made to a high level of precision.