Injection

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TYPICAL INJECTION MOULD
An injection mould can be a simple two plate mould with a runner system to allow the rubber compound to be injected into each cavity from the parting line or more complex mould with a number of plates, an ejector system and heating elements within the core, brush wiper system and a hydraulic parts removal system


MOULDING PROCEDURE
Injection moulding is the most complex of the moulding processes . The mould is loaded into the press by a qualified tool setter, machine parameters are set and the beginning of a continuous strip of compound is loaded into the injection system of the press. The tool is allowed to heat to operating temperature then initial cures are done and product is quality checked to specifications.

Injection moulding machines operate on a continuous process once the initial set-up is complete.The mould remains in the machine and the press closes, a large ram or screw forces preheated uncured rubber through the injection nozzle, through the runner system, down the sprues and into the cavities. The uncured rubber is then forced into the cavities in the mould. Sometimes a slight excess of material (flash) flows out of the cavities, along the grooves and vents.

The mould remains closed until the rubber is cured. The mould then opens, the parts are ejected and brushes wipe away the excess flash. When required the machine operator demoulds parts or rubber pieces and restarts the cycle.

A high level of automation in an injection mould adds significantly to the cost, however, for high volumes this can mean a significantly lower part price.
On less automated moulds the parts need to be removed manually each cycle. Some moulds are designed with core plates that need to be exchanged each cycle so the moulded parts can be removed manually.

Injection moulds are ideal for high volume production runs because once they are set up the cycle time is much faster than that of compression moulding . This is because the rubber is pre-heated in the injection cylinder, there is a rapid transfer of heat to the rubber while it is being forced through the runners and sprues and the mould opens, usually ejects the product and closes automatically.

Injection moulds are well suited to moulding delicately shaped or precision parts of high consistency. The time, temperature and pressure is computer controlled and an accurate shot of rubber compound is metered into the mould.

Although the design and manufacture of an injection mould is more complex this is often the most suitable alternative for production volumes.

Parts typically moulded using the injection moulding process:

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