- 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.
- 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.
Rate of production is low.
Hard, strong filler cannot be used.
- 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.
- 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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