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/process_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