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Friday, 02 June 2023
Injection Molding Machines PDF Print E-mail
Along with extrusion, injection moulding ranks as one of the prime processes for producing plastics articles. It is a fast process and is used to produce large numbers of identical items from high precision engineering components to disposable consumer goods.

The Process
The injection moulding machine consists of a heated barrel equipped with a reciprocating screw (usually driven by a hydraulic motor), which feeds the molten polymer into a temperature controlled split mould via a channel system of gates and runners. The screw melts (plasticises) the polymer, and also acts as a ram during the injection phase. The screw action also provides additional heating by virtue of the shearing action on the polymer. The pressure of injection is high, dependant on the material being processed; it can be up to one thousand atmospheres.

Size of Machine
On most machines the mould is held closed by a combination of toggle clamping and hydraulic pressure. This is known as the locking force. In a large machine this can be up to thousands of tons and is spread over the area of the mould. To counteract the injection pressure, a moulding with a large surface area will therefore need a machine with a higher locking force than a moulding with smaller surface area.

Computer controlled
Modern day injection moulding machines are controlled by a built-in computer. Acting on sensor fed information, it controls all the actions of the machine and ensures consistent output and shot to shot quality.

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