Plastic Forming and Extrusion Questions and Answers

Answer: C

The first two are correct. The third mistakes where the fault is created, since firing only reveals a weakness that the extruder had already built into the column. The kiln is where faults appear rather than where they are made.

Answer: D

Correct answer: False

Firing reveals faults far more often than it causes them. Laminations from the auger, voids from trapped air and stresses locked in during forming or drying all remain invisible until the shrinkage of firing opens them - so the investigation should begin at the forming stage, not at the kiln.

Answer: A

Correct answer: around 15 to 25 per cent by mass

That range gives a body stiff enough to hold its shape as it leaves the die and soft enough to flow through it. Dry pressing uses a few per cent, and slip casting 25 to 45, so the three forming routes occupy three distinct bands of water content.

Answer: B

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. Water gives flowability and takes away the ability to hold a shape, and each method needs a different point on that trade - a slip must pour, a plastic body must hold its form as it leaves the die, and a pressed powder must flow into a die and stay where the punch puts it.