What is the compression moulding and injection moulding of plastics

Injection moulding

Finely powdered plastic is put into the feed hopper at the top and heated so that it becomes soft and can be moulded. The hot softened plastic is forced through or injected into the mould. The cooling process is very quick and after a few seconds the mould is opened and the finished object removed.

• Injection moulding moulds plastic through heat and pressure.
• Injection moulded plastics are invariably thermoplastics gives a good surface finish and can be used for very complex mouldings.
• ( because thermosetting plastics assume their final shape through heat and so can not be moulded with this process.)
• very rapid & low production cost
• most commonly used process.
• Injection moulding products: computer enclosures, milk crates, CD cases and mobile phones.
• The plastics used are :
  • polythene,
  • low density polyethylene (LDPE),
  • high density polyethylene (HDPE),
  • polystyrene (PS),
  • polypropylene (PP)

Compression moulding

Compression moulding is the process that moulds molten plastic, through compression, into the desired shape of the moulding.

• The upper moulding dye is placed over the lower moulding dye with the help of gliding pins and pressure is applied, temperature is increased.

• The moulded article is taken out with the help of extraction pin.

• Compression moulding is the only plastic moulding processes that can mould thermosetting plastics.

• It Is a method applied for both thermoplastics & thermosetting plastics.

• The plastics used are:

  • Urea formaldehyde,
  • Phenol formaldehyde resin
• Products : toilet seats, handles of pressure pans, switch boards etc.