Plastic Forming and Extrusion Questions and Answers

Answer: A

Eight hours is 28,800 seconds, and dividing by four gives 7,200 plates. Real output is lower once mould changes and stoppages are allowed for, but the figure shows the scale of the advantage. Continuous forming is what made mass-produced tableware possible.

Answer: B

Correct answer: flow like a thermoplastic into the mould

Injection moulding fills a closed mould under pressure, which requires the feedstock to behave as a molten polymer - and that takes 30 to 50 per cent binder by volume against a few per cent for pressing. Removing that binder afterwards is the process’s central difficulty.

Answer: C

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason gives the mechanism. Debinding proceeds from the surface inward, so the time rises steeply with thickness - roughly as its square - which confines the process to small sections. Add expensive tooling and the economics require a part complex enough that no cheaper route will make it.

Answer: D

The first two are correct. The third is precisely what extrusion cannot do, since the die imposes one cross section on the whole length of the product. A varying section requires pressing, casting or machining instead.

Answer: A

Correct answer: increasing the water content slightly

Water is what makes the body plastic, so a stiff body wants a little more of it. Raising the pressure instead forces a body that will not flow properly and produces laminations and die wear, and a smaller die makes the problem worse rather than better.

Answer: B

It increases wear, heats the body and makes laminations worse, without addressing the consistency. Adjusting the water content is the proper correction and is done in small steps against a measured target. Consistency is measured rather than judged by feel in a modern plant.

Answer: C

Going from 22 to 24 per cent of the wet mass means the dry solids of about 390 kilograms must carry more water, and the addition works out near 13 kilograms. Working from the dry basis avoids the circularity of the wet one.

Answer: D

Porous dies allow air to be drawn through to release the piece, and the method suits shapes with some relief. It occupies a middle ground between jiggering and pressing in both cost and capability. It suits shapes with relief that extrusion cannot produce.

Answer: A

Air blown back through the die lifts the piece away without distortion, and the same porosity removes some water during forming. Solid dies would make release difficult and the cycle much slower. The porosity is regenerated by cleaning between production runs.

Answer: B

Correct answer: slightly rough or dragged face

A wire pulled through the plastic column tears rather than cuts, leaving a slightly rough face and often a lip where the wire exits. It is a recognised characteristic rather than a fault, and where a better finish is wanted the face is smoothed afterwards or a different cutting method is used.