Fabrication of plastic:

• Fabrication of plastic is a process in which the prepared resins which are in the form of granules or powder are converted into desired shape by using different moulds or machines.
• The compounds are transformed into finished articles in many ways. The basic principle involved here is partially melting resinous mass by application of heat.
• These softened resins are compressed in moulds with the help of high pressure to get the desired shape.
• In case of thermosetting plastics moulded hot plastic is finally solidified further with polymerisation called curing stage while it is still in the mould.
• The moulded plastic material is cooled or chilled further for solidification of article in case of thermosoftening plastic.
• Various techniques are used for thermosoftening plastic material like injection moulding, extrusion, blow moulding and vacuum forming techniques.

Injection moulding method:

• Injection moulding method is the widely used for converting thermoplastic raw materials into finshed product. It is simple and easy to operate and capable of producing a wide range of industrial and domestic articles.
• In this process a predetermined quantity of the granular or powdered resin is fed into a heated cylinder from where it is injected at a controlled rate through a nozzle into the tightly locked mould by means of a screw arrangement or by a piston plunger.
• Pressure upto 1758 kg/cm2 is used for injections and the mould is kept cold to allow the hot plastic to cure and become rigid.
• When the material has been cured sufficiently, half of the mould is opened to allow the ejections of the finished article without any deformation. The entire cyclic operation can be made automatic.
• Injection moulding method is used for moulding of thermoplastic because of high speed production, low mould cost, very low loss of material and low finishing cost.
• There are limitations of design of articles to be moulded as a large number of caviities cannot be filled at the same time.