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POLYMER PROCESSING - Coggle Diagram
POLYMER PROCESSING
Compression molding
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sufficient mould compound was placed in the mold and platen closes to minimize flash at mould part lines
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Advantage:
- low residue stress
- little erosion
- low capital and tooling cost
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Calendering
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The heated or cooled roller is placed above each other and plastic is forced through the gap between thecounter rotating roller
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Extrusion
Screw are used to progress the polymer in the molten or rubbery state along the barrel of the machine.
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3 zone:
- Feed zone-preheat the polymer
- Compression zone-Remove air bubbles
- Mentering zone-homogenize the melt
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Transfer molding
development of compression molding where reservoir of the moulding compound is located in the mold and upon closure is transferred via runner to the cavities
Advantage:
- Faster
- reduce risk of damage
- Give many small parts easily
Disadvantage:
- Increase wear and maintanence cost
- Complex tooling
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Injection molding
2 main section:
i)Injection unit:plasticizing
ii)Clamping unit:press closed by hydraulic or mechanical system
Method:
i)mould is closed and a short of melt is ready
ii)The melt flow around a moundel and exit the die as a tube
iii)Cooling ring is placed at the exit to give tube some dimensional stability
iv)Air flow upward inside the middle of the tube
v)The tube continues to expand,cool and crystallize until the strength of plastic equal to the pressure air inside
vi)Bubbles is forced into flat sheet and moved down over some rollers and sealed
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Blow molding
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Method:
i)Melt the resin in extruder
ii)Form the molten resin in parison inside a mold and inflated so the plastic pushed outward to cavity wall
iii)The part cooled and ejected and trimmed.
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Rotational molding
Method:
Polymer powder is loaded into cavity of a split mold
ii)Mold is heated and rotated simultaneously to gradually form a fused layer of uniform thickness
iii)Mold is cooled and plastic skin solidifies
iv)Mold is open and the part is unloaded
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Thermoforming
Use for :
- Utilize thermoplastic sheets or film
- Used on large scale
- Use for large parts(ex:swimming pool)
Method:
i)Soften thermoplastic sheets with heating
ii)Force the hot and pliable material against the contoursof mold by mechanical,air or vacuum pressure
iii)Held against mold and allow to cool and plastics retain it shapes
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Blown Film Extrusion
Method:
i)Extruded material flow through a tubular die
ii)The melt flow around a moundel and exit the die as a tube
iii)Cooling ring is placed at the exit to give tube some dimensional stability
iv)Air flow upward inside the middle of the tube
v)The tube continues to expand,cool and crystallize until the strength of plastic equal to the pressure air inside
vi)Bubbles is forced into flat sheet and moved down over some rollers and sealed
Continuous tube is extruded clamped between rolls at one end and blown with compressed air to form large hollow tube with thin wal
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Pultrusion
Methods:
i)Continuous rovings of the reinforcement are impregnated with resin
ii)Pulled through the heated die
iii)Curing
iv)Puller used to pull the whole system with certain speed
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