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Subjects · Leaving Cert Engineering

Leaving Cert Engineering: Plastics processing

How often Plastics processing comes up on the Engineering papers, every year it was asked, and questions to try.

HL Asked on 9 of the last 9 Higher Level papers, most recently in 2025. banker

OL Asked on 9 of the last 9 Ordinary Level papers, most recently in 2025. banker

June 2028 is the first exam on the new Engineering course. These come from the 2016–2025 papers, so read them as a guide.

Plastics processing, Higher Level(8 marks)

Quick ones on Plastics processing.

(a)In injection moulding, what does the reciprocating screw do?
  1. Cuts the extruded plastic to length at the die
  2. Melts the granules and forces the melt into the mould
  3. Blows air into a hot parison to inflate it
(b)In an injection mould, the sprue, runners and gates are?
  1. Heater bands wrapped around the barrel
  2. Pins that push the finished part out of the mould
  3. Channels that carry the melt into the cavity
(c)Sink marks on thick sections of an injection moulding are caused by?
  1. Greater shrinkage as the thick section cools
  2. Ejector pins that are set too long for the part
  3. Too much UV stabiliser in the plastic granules
Show the answers

(a) Melts the granules and forces the melt into the mould

(b) Channels that carry the melt into the cavity

(c) Greater shrinkage as the thick section cools

Your turn: Higher Level questions on Plastics processing.

Higher Level

Asked on 9 of the last 9 Higher Level papers, most recently in 2025. banker

Every paper, year by year

YearWhere it came up
2025Q7
2024Q7
2023Q7
2022Q7
2021Q1(d), Q7
2019Q6
2018Q6
2017Q6
2016Q6

Links open the State Examinations Commission’s paper for that year.

More Plastics processing questions

Plastics processing, 3 marks

Why does injection moulding suit high volumes but not one-offs?

  1. The machine makes only a few parts a day, however simple
  2. It cannot make complex shapes, only simple flat ones
  3. The mould costs a lot, but each cycle is fast and cheap
Show the answer

The mould costs a lot, but each cycle is fast and cheap

A steel mould can cost many thousands of euro, but cycle times are seconds. The cost only pays off when spread over many thousands of parts.

Ordinary Level

Asked on 9 of the last 9 Ordinary Level papers, most recently in 2025. banker

Every paper, year by year

YearWhere it came up
2025Q1(k), Q5
2024Q5
2023Q1(e), Q5
2022Q1(i), Q5
2021Q1(i), Q5
2019Q1(g), Q5
2018Q1(i), Q5
2017Q1(g), Q5
2016Q1(i), Q5

Links open the State Examinations Commission’s paper for that year.

More Plastics processing questions

Plastics processing, 2 marks

Which process makes a plastic toy car body in one shot?

  1. Line bending
  2. Dip coating
  3. Injection moulding
Show the answer

Injection moulding

Molten plastic is forced into a closed steel mould and cools to shape. The mould is costly, but each part takes seconds, so it suits mass-produced items like toys and chairs.

Plastics processing, 3 marks

In injection moulding, what does the rotating screw do?

  1. Trims the part and the sprue from the mould
  2. Carries granules forward to melt and inject them
  3. Cools the finished moulding before it is ejected
Show the answer

Carries granules forward to melt and inject them

Granules drop from the hopper onto the screw, which pushes them through heated zones of the barrel. The screw then rams forward, forcing the melt into the mould.

Plastics processing, 3 marks

What is the sprue on an injection moulding?

  1. Plastic left in the channel that fed the mould
  2. A crack caused by the plastic cooling too fast
  3. A metal insert moulded into the part
Show the answer

Plastic left in the channel that fed the mould

Molten plastic flows through the sprue and runners into the cavity. The sprue is cut off, and the waste thermoplastic can be ground up and reused.

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