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

  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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