Fabrication processes

Fabrication processes:

Compression moulding:

Mould having two parts upper part & lower part, both the parts are connected with guiding pins.
There is cavity in the lower part of the machine, in this cavity maximum amount of mixture (polymer & additives) is placed.
Volume of this mix. Taken is greater than the volume of cavity to avoid the flows in design of article.
Moulding temperature in the range of = 90–150⁰C & pressure = 1000–3000 psi.
During Curing pressure is not released, curing is done by heating.
After the curing pressure released & article taken out by separating the parts of mould.

Advantages::

This method is used for both types of plastics-thermosoftning & thermoplastics.
Machinery is very simple. Simple designs can be fabricated. Thus initial cost of fabrication is comparatively less.

Disadvantages.

Injection moulding:

Injection moulding method is used only for the fabrication of thermoplastic material.
Mixture of polymer & additives is taken in the injection & mould is kept at room temp & high pressure is applied hydrolytically.
Mixture is heated in the injection (cylinder) till softening temp, and then forced through healer & there is device called torpedo which spread the material uniformly in the injection.
Thereby avoiding the heating & cooling of the mould increases the rate of production.
Temp. Depends on material, range 90⁰C – 150⁰C & pressure 1500 kg/cm².
After plastic is injected in the mould & acquires the shape, mould is cooled by cold water, keeping pressure on. Thus articles are cured & the mould is opened to eject the articles.
Rate of production is high, less limitations on the design of articles.
Finishing of article is better. Machine is durable thereby decreases the fabrication cost.

Transfer moulding:

It is mainly used for continuous moulding of thermosoftening plastics into articles of uniform cross section like tubes, rods, strips, insulation of metal wire
Cross-section of filaments, rods, lubes can be varied by changing the shape of die.
Material of thermoplastics are fed into the hopper then screw conveyer pushes the material into a heater, where material softens & it is forced through the die to gel require shape.
Extrudes product cooled by atmospheric exposure.
Garden hose, insulated wire, water pipes etc are the good example of extrusion type of moulding.

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