Injection moulding is the process of manufacturing finished products from thermoplastic material by heating it at the required temperature and then injecting the molten material into the mould cavity.
All injection moulding machines have several heating zones depending on the length of the screw which are used to regulate the temperature of the molten material in the barrel of the injection moulding machine. These heaters are controlled by a set of temperature controllers, thermocouples and contactors which periodically switch the heaters on or off depending on the temperature set by the operator. As different thermoplastics have different melting points, it is very important to set the temperature accurately according to the resin you wish to mould.
The heaters are fixed on the barrel of the machine which encloses the "screw" which is instrumental in homogenizing the molten resin and pushing it forward when it is injected into the mould. The way the mould is fitted on the platten of the machine depends on the design of the mould. It can be fitted either with clamps or direct bolting on the platten itself. One platten is fixed to the body of the machine whereas the other platten is moving and attached to the ram / toggle of the machine depending on its make.
On starting the machine motor, the "oil pump" kicks into action by generating pressure which directs the oil through a series of valves into the ram / toggle cylinder of the machine. On activating the mould close mechanism via the control panel, oil is released into the ram chamber and the ram in turn pushes the mould ahead and the mould closes. After the mould closes the machine depending on the parameters set by the operator begins to develop tonnage by applying pressure via the ram unit. Machines are commonly described on the basis of the tonnage developed by them.(80 ton, 180, ton, 300 ton,etc).
After the mould is closed and the locking is developed the injection cycle starts. The machine injects the molten raw material into the mould with the use of the plunger mechanism at the head of the screw. After the material is injected into the mould the machine cycles cold water through the mould, cooled using a cooling tower / chiller to a set temperature. Due to this the molten material in the mould solidifies and the moulds is then opened. Depending on the moulds design the finished product is ejected either by using "Air Purge" , "Ejector Rods" or manually.
If the mahcine has "a nozzle shut off valve" the refilling cycle will begin without waiting for the moulds to close again. If however the machine does not have the nozzle shut off valve the refilling cycle will only begin after the article has been removed from the mould and the mould has closed again and the tonnage has developed which increases the cycle time.
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