Plastics

Question 1

How do you mark out plastic?

Answer 1

Marking out plastic should be done on the protective polyethylene layer that usually covers plastic. If the protective layer has been removed then masking tape can be placed over the area to be marked out. Marking out should always be done in the corner of the plastic.

Question 2

Where do you mark out plastic?

Answer 2

Marking out should always be done in the corner of the plastic to reduce the amount of plastic waste and to make it easier to cut out.

Question 3

How do you saw plastic?

Answer 3

Thin plastic sheets are sawn with a coping saw while thicker plastic should be sawn using a hack saw. When sawing, the plastic must be supported securely in a vice with pieces of waste wood on either side of the plastic or held against a bench hook.

Question 4

How do you file plastic?

Answer 4

Thin sheets of plastic should always be filed at an angle. If you file at right angles the plastic may crack. The plastic should always be firmly held in a vice and be sandwiched between two pieces of waste wood.

Question 5

How do you drill holes in plastic?

Answer 5

A regular hand drill or a milling machine can be used to cut holes in plastic. The plastic must always be held securely so it does not move when being drilled. For thinner pieces, cracking can be prevented, by placing a scrap piece of wood underneath the plastic to help an absorb pressure. You should also be gentle with the amount of force you place on the plastic. Larger holes should be pilot holed first so the hole is not misaligned.

Question 6

Why is plastic finished?

Answer 6

Plastics do not rot and corrode, however, they are susceptible to UV damage from the sun, which can make them brittle and shatter easily.

Question 7

How do you smooth rough flat edges on plastic?

Answer 7

Rough flat edges on plastic can be removed by rubbing them over a board in a linear motion that has wet and dry paper attached.

Question 8

How do you smooth rough concave or convex edges on plastic?

Answer 8

Rough concave or convex edges are removed by rubbing them with a half round file that was wet and dry paper wrapped around.

Question 9

How do you polish plastic?

Answer 9

Plastic can be polished by using a buffing wheel coated with a light abrasive wax. The plastic should be moved towards you and then let to cool for a few seconds before making a second pass through the wheel. After this process is repeated a few times, a polish should be gained.

Question 10

What are the precautions one should take when using a buffing wheel?

Answer 10

When using a buffing wheel, never hold the plastic with gloves or a rag since they and your hands can be dragged into the wheel. Also, if the plastic feels hot in your hands then it is near to burning and should be given time to cool down.

Question 11

How can plastic be joined?

Answer 11

Plastic can be drilled and then joined by mechanical fixings such as screws, rivets, nuts & bolts and hinges. Plastic may also be joined by adhesives called plastic cements.

Question 12

How do you join plastic with plastic cements?

Answer 12

Before applying the cement, the joining surfaces must be cleaned with wet & dry abrasive paper. To stop cement spillage from permanently marking the plastic, masking tape should then be applied to the surfaces surrounding the joining area. After applying the adhesive to the joining surfaces, the joint should be clamped together until the adhesive has set.

Question 13

What type of process is vacuum forming?

Answer 13

Vacuum forming is used to make products like bowls and car frames.
It can be used for batch or mass production.

Question 14

What are the conditions for a vacuum forming mould?

Answer 14

1. The mould must be made from MDF as it is very smooth.
2. The sides should be tapered to allow the polymer to release from the mould more easily.
3. The edges should also be rounded.
4. The overall shape of the mould can not be too complicated.

Question 15

What is the vacuum forming process?

Answer 15

1. The MDF mould is placed on the bed of the machine.
2. The polymer sheet is placed in the machine above the mould and a heater is pulled over to soften the sheet.
3. When the polymer has softened, the bed is raised into the softened polymer.
4. The vacuum pump is switched on, sucking the polymer onto the mould.
5. When the polymer has cooled the bed is lowered and the vacuum pump is switched off.
6. The plastic product is removed from the machine and any excess polymer is trimmed off with a profile router.

Question 16

What is press forming used for?

Answer 16

Press forming produces shapes with depressions such as baths or trays.
It is a mass production process.

Question 17

What is the process of press forming?

Answer 17

Press forming is a similar process to vacuum forming except there is an additional MDF mould that is pressed onto the polymer at the same time as it is being sucked down onto the mould. The two moulds trap the softened polymer between them.

Question 18

How do you line bend plastic?

Answer 18

The line to be bent is placed over a heater, which softens the line. Once soft enough, the line can be bent around a former.

Question 19

What is injection moulding used for?

Answer 19

Injection moulding allows complex shapes to be produced.
It is a mass production process due to the high cost of the equipment and moulds.

Question 20

What is an injection moulding mould made from?

Answer 20

The mould can be made from aluminium or steel with both allowing detailed shapes to be produced.

Question 21

What is the injection moulding process?

Answer 21

1. Polymer granules are poured into a hopper.
2. A screw thread pushes the granules through a chamber and past heaters.
   The heaters melt the granules.
3. A hydraulic ram pushes the screw, injecting the polymer into an aluminium or steel mould.
4. The mould is water cooled, enabling the polymer to harden quickly.
5. The mould is opened, the product is ejected and any excess polymer is trimmed off with a profile router.

Question 22

What is blow moulding used for?

Answer 22

Blow moulding is the process used to produce hollow products like plastic bottles.
It is a mass production process and the equipment and moulds are very costly.

Question 23

What is the process of blow moulding?

Answer 23

1. Polymer granules are fed into a hopper.
2. A screw thread pushes the granules through heaters.
3. The polymer is pushed through a die and into a hollow mould.
4. Air in injected into the mould which forces the polymer to the sides.
5. The polymer is left to cool for a few seconds before the mould is opened and the product is ejected.

Question 24

What is extrusion moulding used for?

Answer 24

Extrusion moulding is the process of producing plastic rods, hollow tubes or channels.
It is a mass production process.

Question 25

What is the extrusion moulding process?

Answer 25

1. Polymer granules are loaded into a hopper.
2. A screw thread pushes the granules through heaters which turn the granules into softened polymer.
3. A hydraulic ram pushes the screw, forcing the polymer through a steel die.
4. The polymer is forced through the die into an extrusion of the shape of the die and is left to cool. It can then be cut to the desired length.

Question 26

What is compression moulding?

Answer 26

Compression moulding is used to shape thermosetting plastic.