Engineering Forming processes for polymers

• Forming Processes for Thermoplastics


  Injection moulding, Extrusion, Blow moulding, thermoforming, rotational moulding, calendering.
• Forming Processes for Thermosets


  Compression moulding, transfer moulding, injection moulding.
• How are thermoplastics / softens, supplied

  Supplied as granules or powders
• How are Thermosets supplied 


  Partially polymerised powder or dough.
• How does polymers set in the mould

  Polymerisation also known as Crosslinking or curing takes place and the polymer hardens.
• Compression Moulding 


  Thermoset is compressed between two parts of the mould. Heating under pressure initiates polymerisation (cross linking).
• Transfer Moulding


  Differs from compression in that the polymer is heated in a chamber and then forced into the mould by the punch.
• Benefits of Transfer moulding

  Faster and can produce more complex shapes than compression moulding
• Injection Moulding


  Polymer is fed by a hopper into the chamber, where the hydraulic ram pushes it past heaters, into a split mould, let cool.
• Uses of Injection Moulding

  Rubbish bins to electric drill casings, nearly everything
• Extrusion


  Continuous process for converting plastic materials into tube and other long lengths of a wide range of shape.
• How does Extrusion Work

  Hopper fed thermoplastic is fed into a screw which feeds it past multiple heating coils, liquifying the polymer, and then into an extrusion die, shaping into final cross section.
• Other types of Extrusion

  Blown film and Flat sheet extrusion, used to make bags and other types of films.
• Extrusion Blow moulding Uses


  Milk bottles, dishwashing liquid bottles etc. Due to the split die it forms a line which separates the product in half. Produces even wall thickness
• Extrusion blow moulding process

  Extruded thermosoften polymer is fed into a die and pressurised air is blown in to form walls of equal thickness and to fill any gaps in the mould, whilst retaining a hollow inside.
• Process of Thermoforming - Vacuum forming + pressure forming

  Thermoplastic sheet is heated to its softening temp and then drawn or forced onto an open mould, allowed to cool then removed.
• Vacuum Forming uses


  Used for large objects - baths, Fridge lining
• Pressure forming uses


  Fast food containers, dairy tubs, smaller applications
• Rotational Moulding


  Simultaneous heating and spinning to evenly distribute thermosoften polymers in a closed mould. 170 - 270 degrees C
• Rotational moulding uses


  toys, canoes, fuel tanks etc
• Calendering


  Extruded polymer is put through multiple hot rollers of decreasing size that is then cooled, to make large rolls of film or sheet.
• Calendering uses


  Vinyl (PVC) for shoe linings, shower curtains, floor covering etc