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PLASTICS

Course: B.E (EEE) – Part Time Subject: APPLIED SCIENCE Unit: V. PLASTICS. Dr. K. SIVAKUMAR Dept. of Chemistry, SCSVMV University. Syllabus: Plastics Thermoplastics Thermosetting plastics Processing of plastics Injection moulding Blow moulding Extrusion processes.

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PLASTICS

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  1. Course: B.E (EEE) – Part Time Subject: APPLIED SCIENCE Unit: V PLASTICS Dr. K. SIVAKUMAR Dept. of Chemistry, SCSVMV University • Syllabus: Plastics • Thermoplastics • Thermosetting plastics • Processing of plastics • Injection moulding • Blow moulding • Extrusion processes

  2. THERMOPLASTICS & THERMOSETTING PLASTICS

  3. Thermoplastics (resins): Thermoplastics soften when heated and subsequently melt. When cooled they become hard and rigid once again. Example: Polyethylene, PVC, Nylon Uses: Bags, Mugs, Toys Thermosetting plastics (resins): Thermosetting resins do not become softy on heating & they never melt once set. Example: Bakelite Uses: Electric switches, Telephone parts, Cooker handles

  4. Moulding constituents of plastic: Higher polymer material is mixed with 4 to 10 ingredients each of which imparts some useful property to the moulded products. Some are, Resins: Holds the different constituents together Example: Linear polymers with low molecular weights. Resins form 40-50% of moulding mixture Plasticisers: To increase the plasticity and flexibility Example: Castor oil, Dibutylphthalate, Alkyl & Aryl Phosphate etc.,

  5. Fillers: To impart valuable service properties such as strength, resistance, finish and workability. Reducing cost, shrinkage on setting and brittleness. Example: Wood flour, asbestos, china clay, talc, gypsum, saw dust. Fillers form 60% of plastics Lubricants: To facilitate the moulding operations. Gives glossy finish Example: Waxes, soaps, Oleates, stearates Catalyst/accelerators: To accelerate the polymerisation (added only in thermosetting resins) Example: Hydrogen peroxide, Benzoyl peroxide, Metals (Ag, Cu & Pb)

  6. Difference between Thermoplastics & Thermosetting plastics

  7. INJECTION MOULDING (for Thermoplastics): • Materials of definite quantity at Hi Temp. is injected into a cold mould under P • In cold mould, the polymer solidifies • Polymer is fed as granules, pellets / powder through hopper • Polymer get softened in horizontal cylinder • Hydraulic piston pushes the molten material into mould • Uniform spreading inside the hot cylinder is ensured by torpedo • Molten plastic is injected through a nozzle into moulded cavity • Mould: • Consists of movable & stationary parts • Molten plastic is injected at a P of 15000kg/cm2 • Proper flow of material is ensured by preheating the mould to appropriate T • Mould is cooled by circulating water and then opened to eject the moulded article

  8. BLOW MOULDING (for thermoplastics); [for hollow plastic articles] • To produce soft drink bottles, containers using Polyethylene, PVC, Polystyrene • PARISON – hot softened thermoplastic made by injection / extrusion moulding • Parison is placed inside a two piece hollow mould (as 2 halves) • Parison kept between two halves encloses a blowing pin at one end • Other end pinches and closes • Parison is blown using pressurized air through the blow pin

  9. BLOW MOULDING: Continued…… • Parison kept under hot condition is inflated and expands until it comes in contact with inner area of the cold hollow mould • Under pressure • Parison acquires the shape of hallow cavity of mould • Mould is cooled and the thermoplastic article is removed from the mould by opening the mould

  10. EXTRUSION MOULDING: • For producing common plastic materials • eg: films, filaments, hoses, sheets & coating wires and cables with PVC • Plastic material as powder / granules is fed into a cylinder thru hopper • Cylinder is with the provision for heating • Hot plastic is pushed thru cylinder by helically revolving screw • Due to friction the Temperature increases

  11. EXTRUSION MOULDING: (Continues….) • Plastic material passes through three zones • Feed zone • Compression zone • Metering zone

  12. EXTRUSION MOULDING: (Continues….) • In compression zone, powder charge is melted by heating element • It is compressed by revolving screw • Polymer flows at a constant rate due to helical movement of screw • Pressure in this zone enables plastic to be in melted stage & enters the die

  13. EXTRUSION MOULDING: (Continues….) • From die moulded plastic is coming out in desired profile • Extrudated material from die is hot and hence it is cooled rapidly to avoid any deshaping • Cooling by passing extrudate over a conveyor belt through which tubes of cold water/cold air are passed

  14. The End Dr. K. SIVAKUMAR Department of Chemistry SCSVMV University chemshiva@gmail.com +91 98423 61378 Good Luck!

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