Moulding Plastics Flashcards
What is the process of Line Bending?
Plastic sheet is heated along the line of the intended fold
Softened area is then bent shape using a bending jig for accuracy
What is used for Line Bending?
Line Bender or Strip Heater
How are acrylic sheets often bent?
Line Bending
What is the process of Vacuum Forming?
Plastic heated and mould moves close to it
Air is ‘sucked out’ to form a vacuum
Causes the hot plastic to be sucked onto mould
As temperature falls, a rigid impression of mould is formed
Vacuum Pump is turned off allowing air to enter
Former is lowered separating from final product
What is a former?
A wooden mould around which the softened plastic will be held by the vacuum until it has cooled
What is Vacuum Forming?
When a heated plastic is ‘sucked’ onto the former which forms the required shape
What is the most popular material used Vacuum Forming? Why is it used?
High-Impact Polystyrene (HIPS)
Cheap and easy to form
What size sheets can be formed in vacuum forming?
1.5-1.8m
What is the process of Yoke Moulding?
Use an oven set to 110 degrees to soften the material
The pressure from a close fitting yoke will hold the plastic until it has hardened
What is Yoke Moulding used for?
Making half shells which can be solvent welded together
Why is foamed PVC a good material to use?
Because it has a long working time once hot
What is Yoke Moulding?
Requires only one former to go inside soft plastic
What are typical materials used in Injection Moulding?
Polythene
Polystyrene
Polypropylene
Nylon
What is step 1 of injection moulding?
Plastic powder or granules are fed from the hopper into a hollow steel barrel
What is step 2 of injection moulding?
The heaters melt the plastic as the screw moves it along towards the mould
What is step 3 of injection moulding?
Once enough melted plastic has collected the screw forces the plastic into the mould
What is step 4 of injection moulding?
Pressure is maintained on the mould until it has cooled enough to be opened
How can injection moulding be done in school?
Hot glue gun
Simple mould made from 2 pieces of steel with a cavity between them
What are typical materials used in extrusion?
Polythene
PVC
Nylon
What are the steps of extrusion?
Plastic granules are fed into the hopper by rotating screw
Plastic granules heated as they’re fed through
Softened plastic is forced through die in continuous stream to create long tube
Extrusions are passed through a cooling chamber and cut to required length
What are common materials used for blow moulding?
PVC
Polythene
Polypropylene
How is Blow Moulding different to Extrusion?
An air supply and split mould is used instead of cooling chamber
What is the process of Blow Moulding?
Air is blown into an extruded section of tube
Air forces plastic to the sides of the mould
Moulding is cooled and then opened to remove the product
What is Rotational Moulding?
A rotational moulding machine is rotated continuously with heated thermoplastic power inside
