INJECTION MOULDING
WORKING PRINCIPLE
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.
OPERATION
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.
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