Injection moulding process is generally used to achieve high speed moulding of thermo plastic. It works on the principle that the molten thermo plastic is injected into a mould and a high pressure is applied the desired shape is obtained. Plunger system is used for achieving high pressure.
The material that is to be used for moulding is loaded into hopper from where it is transferred to the heating section. It is transferred using a feeding device where the temperature is about 150°C – 370°C.The material is melted and it is forced by an injection ram or by a plunger through a nozzle in a closed mould. There are two types of injection moulding. They are,
RAM OR PLUNGER TYPE INJECTION MOULDING
This type of injection moulding system has two units. They are the injection unit and clamping unit. In some cases these units may be split inorder to eject the finished component. First the selected thermosetting plastic is filled in a hopper. Then it goes to the heating section where the thermo setting plastic is melted and the pressure is increased. With the help of ram the heated material is injected under pressure. This makes the material to get filled in the mould cavity through the nozzle to get the required shape of the plastic. In this type of moulding system water is generally is used for cooling purpose.
SCREW TYPE INJECTION MOULDING
This type of moulding also has two units to split and eject the finished components. The two units are injection unit and clamping unit.
The injection unit consists of hopper, screw and the heating section. Mould cavity is present in the clamping unit. In this type of moulding machine the pellets are first fed into the hopper. The resins are pushed along with the reciprocating screw which is in the heated condition. The screw is moved forward to push the plastic material into the mould. The screw itself moves backward and allows the accumulation of enough material to fill the mould. The rotation of the screw provides the plasticizing action by frictional and shearing effects. The axial motion of the screw provides the filling action. The jet moulding process is used for finding the problems occurring in the injection moulding process. The reaction moulding is the recent development in injection moulding. In reaction moulding, the low viscosity monomers are used in the mould. There is a chemical reaction taking place between the resins at low temperatures and a polymer is created.
In the jet moulding process the thermo setting plastic is preheated about 93°C in the cylinder surrounding nozzle. The reaction moulding is suitable for the production of polyurethane moulding.
It used in the manufacturing of parts of complex threads. Production of intricate shapes like thin walled parts is made easier using this process. Mainly used for the Production of electrical and communication components like telephone cables.