Plastic Manufacturing

Question 1

Explain Line Bending

Answer 1

A strip heater consists of a hot wire that is used to heat the acrylic to around 160 degrees.
At this temperature the acrylic becomes pliable and can be bent into shape.
Jigs and formers can be used to achieve consistent desired results for multiple products
You should be careful not to overheat the acrylic as it could blister or discolour

Question 2

Explain injection moulding and draw a diagram

Answer 2

Plastic granules are fed into the hopper.
2. The screw in the chamber below the hopper sends the granules forward.
3. Heated jackets around the screw melt the polymer.
4. The screw winds back and the hydraulic ram comes forward into position.
5. The mould is closed and sealed as the ram forces the melted plastic into the mould.
6. The plastic is allowed to cool and the halves of the mould release.

Question 3

Explain extrusion and draw a diagram of it

Answer 3

1. A motor turns a thread which feeds granules of plastic through a heater.
2. The granules melt into a liquid which is forced through a die, forming a long ‘tube like’ shape.
3. The extrusion is then cooled and forms a solid shape.
4. The shape of the die determines the shape of the tube.

Question 4

Explain vaccume forming

Answer 4

The mould is placed into the former.
2. A sheet of thermoplastic, such as HIPS is clamped over the mould.
3. The plastic is slowly heated to become soft.
4. The former is raised and the air is sucked out, drawing the plastic over the mould to take on its shape.
5. The plastic is allowed to cool and then removed from the mould.
6. The edges must then be trimmed and finished.

Question 5

Explain blow moulding

Answer 5

1. Mould is opened into it’s two halves.
   A hollow tube of polymer known as the parison is heated.
2. The parison is lowered into the mould.
3. Mould is clamped shut, leaving only a small hole for the air hose.
4. Air is forced into the mould at high pressure. The plastic is forced to the mould sides and cools.