Plastic Moulding Processes

Question 1

What are all the moulding processes for thermoplastics?

Answer 1

• injection moulding
• blow moulding
• rotational moulding
• extrusion
• calendaring

Question 2

What are all the moulding processes for Thermosetting plastics?

Answer 2

-Compression moulding

Question 3

What is Injection moulding (thermoplastics)?

Answer 3

This is the process used to produce complex 3D shapes.

• plastic granules in the hopper
• screw rotated towards heaters
• ram forces heated polymer into mould
• cools

Question 4

What are some advantages and disadvantages of injection moulding?

Answer 4

Advantages:
-complex 3D shapes
-high volume can be produced consistently 
-Metals inserts can be included
Disadvantages:
-set up cost is high
-expensive moulds

Question 5

What is blow moulding (thermoplastic)?

Answer 5

Process in manufacture of hollow products i.e.bottles.

• a heated tube is extruded vertically
• mould closed
• hot air is then blow into mould shape
• cools

Question 6

What are some advantages and disadvantages of blow moulding?

Answer 6

Advantages:
-rapid method of producing hollow products
- non-circular shapes can be produced
Disadvantages:
- expensive moulds
- triangular shape bottles are difficult to produce.

Question 7

What is rotational moulding (thermoplastic)?

Answer 7

Used in manufacture of 3D hollow products.
- a number of mechanical arms rotate about a fixed central point. The moulds ,filled with thermoplastic powder, attached to the end of each arm are rotated continuously to form a hollow 3D thermoplastic.

Question 8

What are the advantages and disadvantages of rotational moulding?

Answer 8

Advantages:
-ideal for both rigid, tough and flexible shapes
- big sizing range
-surface textures can be applied in mould
-cheaper moulds
-low production runs
Disadvantages:
- only hollow shapes

Question 9

What is extrusion (thermoplastic)?

Answer 9

• The process used where products with a continuous cross-section are required.
• The process forces molten plastic through a die that has the reared cross-sectional shape.

Question 10

What are the advantages and disadvantages of extrusion?

Answer 10

Advantage:
-low cost process for simple dies
Disadvantage:
-can only produce continuos cross-sectional shapes

Question 11

What is calendaring (thermoplastic)?

Answer 11

• Used for manufacturing thermoplastic, generally PVC is used.
• involves rolling out a mass of pre-mixed plastic material between large rollers to form a continuous, accurate film/sheet.

Question 12

What are some advantages and disadvantages of calendaring?

Answer 12

Advantages:
-control over thickness 
- increases the strength of material 
-any pattern or texture can be applied
Disadvantages:
-high operating cost
-low tolerance

Question 13

What is compression moulding (thermosetting)?

Answer 13

Compression moulding is a combination of heat, pressure and time is needed to ensure all of the material’s form and structure changes.

• compressed powder is placed between two halves of a mould
• the mould is heated to a temperature that will allow cross-links to form within a material
• moulds are held closed together
• ejected while it is still hot

Question 14

What are the advantages and disadvantages of compression moulding?

Answer 14

Advantages:
-moderately complex parts can be produced over production runs
-start up costs are relatively low
-moulds are cheaper
-little waste material
Disadvantages:
-necessary to manufacture preform
-less complex shapes