2. Learning Outcomes;
Define what is plastic
Define the polymeric structure
Differentiate between thermoset and thermoplastic
List advantages and disadvantages of plastics application
Explain the making of plastic products processes
3. What is Plastic?
Organic polymer (synthetic / semi synthetic)
Moldable – easy to be shaped when heated
Categorized into two;
i)Thermoset plastic
ii)Thermoplastic
4. Terms in Polymeric Structure
Monomer – single / small molecule
Polymer – many monomer that held together by covalent bond in long chain.
Polymerization- chemical reaction process that produces a polymer from its monomer.
Amorphous – non-crystalline
5. Types of Polymer Chain
There are 4 types of polymer chains;
a. Linear chain polymers
- in the form of a long molecular chains
b. Branched chain polymers
- the linear chain with a series of branched
c. Cross-linked chain polymers
- with short links which connected the closer chains together
d. Network chain polymers
- molecular structure in 3 dimension networks
8. Thermoplastics
Can be softened every time they are heated
Can be reshaped / remolded
No chemical changes (curing) takes place during the molding operations
9. Thermoset
Can be heated and formed only once
Can never again be softened by heating
Undergo chemical changes (curing) during molding
11. Disadvantages of Plastic
1. Brittle at low temperature
2. Produce toxic fumes when its burnt
3. Low heat resistance
4. Softer and less elastic than metal
5. Not biodegradable
13. Injection Molding Process
Work Principles;
i)Resins inserted into hopper.
ii)Resins goes into injection channel while softened by heater.
iii)Softer resin injected into nozzle to the mould cavity by plunger / screw.
iv)Product will be solidify under water cooling system.
v)Lastly, ejector pins will ejected the product from the mould.
15. Injection Molding
ADVANTAGES
DISADVANTAGES
Good surface finish
Sink = caused by molding temperature or the pressure are higher
Lower cost (mold & labor)
Flashing = caused by unfitted mould
Various shape, intricate/thinner products can be produced
Bubble = caused by cold mould or the pressure are too low
Process can be highly automated
Weld line = caused by cold mould
16. Extrusion Molding Process
Work Principles;
i)Resins are inserted into hopper.
ii)Resins fed into the heated cylinder by rotating screw.
iii)When resin become softer, it will be forced continuously by the rotating screw ram.
iv)Product are formed into continuous shape.
v)Product cooled by air / water system.
18. Extrusion Molding
ADVANTAGES
DISADVANTAGES
Economical for mass production
Dies are easily wear out
Accurate measurement
Need to be closely controlled
Good surface finish
Thermoset plastic are not suitable
19. Blow Molding Process
Work Principles;
i)Resin inserted into hopper.
ii)Resins goes into injection / extrusion channel while softened by heater.
iii)Softer resin injected / extruded into nozzle to the mould cavity by plunger / screw.
iv)Air then blowed into the parison through a cavity at the top of the mould.
v)Product will be solidify under water cooling system.
vi)Lastly, ejector pins will ejected the product from the mould.
21. Blow Molding
ADVANTAGES
DISADVANTAGES
Various shape, intricate /thinner products can be produced
Not economical for small production
Doesn’t need the finishing / tidying
Certain mould only for certain product
22. Compression Molding Process
Work Principles;
i.Resin inserted into the mould as preformed powdered.
ii.The preheated resin is loaded into a hot mould containing the cavity.
iii.The upper part of the mould is forced down on the plastic resin.
iv.Pressure and heat are then applied, forces the softened resin to fill the cavity.
v.Lastly, product ejected from the mould.
24. Compression Molding
ADVANTAGES
DISADVANTAGES
Mould costs are low
Complicated shape difficult to make
Economical for mass production
Moderate dimension accuracy
More compact product are possible
Need further finishing (trim the flash)
