Moulding of Plastics

1
Moulding of Plastics

• Thermoplastic Materials and Processing

2
Classification of Plastics

• Thermoplastic Materials
• Fluidic when subject to heat, harden when cooled
• Usually rigid
• Thermostatic Materials
• Fluidic or powder form before processing, cure
  permanently when subject to heat or mixed with
  catalyst
• Rigid or elastic

3
General Purpose Thermoplastic Materials

• Polyethylene (PE)
• Buckets
• Polypropylene (PP)
• Microwavable food containers, electric kettles
• Polystyrene (PS)
• CD cases
• PolyVinylChloride (PVC)
• Sewage pipes, flexible hoists

4
Engineering Thermoplastic Materials

• Polyamides (PA, Nylon)
• Rope
• Polymethylmethacrylate (PMMA, Acrylic)
• Cups
• AcrylonitrileButadieneStyrene (ABS)
• Product casing
• Polycarbonate (PC)
• Outdoor screenings, Bullet-proof windows,
  Electric kettles
• PolyethyleneTerephthalate (PET)
• Soft-drink bottles

5
Thermostatic Materials

• Melamine Formaldehyde, Urea Formaldehyde (MF, UF)
• Dishes, lamination
• Phenolics (PF)
• Ashtrays, Pot handles, plugs and switches
• Polyurethane
• Shoe heels
• Unsaturated Polyester (UP)
• Fibre-glass installations
• Epoxy (EP)
• Glue, filler

6
Injection Moulding

• The injection moulding machine consists of a
  heated barrel equipped with a reciprocating screw
  (usually driven by a hydraulic motor), which
  feeds the molten polymer into a temperature
  controlled split mould via a channel system of
  gates and runners. The screw melts (plasticises)
  the polymer, and also acts as a ram during the
  injection phase. The screw action also provides
  additional heating by virtue of the shearing
  action on the polymer. The pressure of injection
  is high, dependant on the material being
  processed it can be up to one thousand
  atmospheres.
• Animation Injection Moulding

7
Typical Injection Mould Job-shop
8
Typical Injection Moulding Plant
9
Rotational Moulding

• The Rotational Moulding process is essentially
  split into four operations
• A pre-determined amount of polymer powder is
  placed in the mould. With the powder loaded, the
  mould is closed, locked and loaded into the oven.
  
• Once inside the oven, the mould is rotated around
  two axis. The ovens are heated by convection,
  conduction and, in some cases, radiation. As the
  mould becomes hotter the powder begins to melt
  and stick to the inner walls of the mould.
• When the melt has been consolidated to the
  desired level, the mould is cooled either by air,
  water or a combination of both.
• When the polymer has cooled sufficiently to
  retain its shape and be easily handled, the mould
  is opened and the product removed.
• Animation Rotational Moulding

Adapted from http//www.bpf.co.uk/bpfindustry/pro
cess_plastics_rotational_moulding.cfm
10
Rotational Moulding
MT3 by Ron Arad
11
Blow Moulding

• The process is divided in to three.
• The injection blow moulding machine is based on
  an extruder barrel and screw assembly which melts
  the polymer. The molten polymer is fed into a
  manifold where it is injected through nozzles
  into a hollow, heated preform mould. The preform
  mould forms the external shape and is clamped
  around a mandrel (the core rod) which forms the
  internal shape of the preform.
• The preform mould opens and the core rod is
  rotated and clamped into the hollow, chilled blow
  mould. The core rod opens and allows compressed
  air into the preform, which inflates it to the
  finished article shape.
• After a cooling period the blow mould opens and
  the core rod is rotated to the ejection position.
  The finished article is stripped off the core rod
  and leak-tested prior to packing.
• Animation Extrusion Blow Moulding
• Animation Injection Stretch Blow Moulding
• Animation Injection Blow Moulding

12
Compression Moulding

• Compound or blend is placed in mould and heated
  under pressure. When reaction is complete,
  product is cooled and ejected.
• Animation Compression Moulding

13
Plastic Resources
http//www.matweb.com
http//www.materialconnexion.com
14
Plastic Resources
http//plastics.bayer.com