Raw Material Storage and Handling Questions and Answers

Answer: A

Correct answer: taking a representative sample for testing

Sampling comes first because once the load is tipped onto a stockpile it can no longer be rejected or segregated, and the material is no longer identifiable as that delivery. A sample taken from the vehicle, from several points and combined, is the only thing that lets the load be accepted or turned away on evidence rather than on hope.

Answer: B

Coarse particles roll to the base and fines stay near the point of discharge, so the top of a pile is systematically finer than its average. A representative sample requires increments from many points, or sampling from a moving stream.

Answer: C

Cutting the entire cross-section for a short time gives every particle the same chance of entering the sample, which is the definition of a correct increment. A heap has already segregated before any spoon is put into it.

Answer: D

Both are true and the reason gives the necessity: two loads of the same clay at eight and fourteen per cent moisture need different weighed masses to deliver the same dry solids, and nothing else in the batch reveals the difference.

Answer: A

Each fault has a distinct mechanism and therefore a distinct remedy: a steeper hopper for rat-holing, a larger outlet for arching, a distributor for segregation and a moisture barrier for caking. Treating them all as flow problems fixes none of them.

Answer: B

In mass flow the whole contents move, so the material discharges first in first out and no stagnant region forms. Funnel flow, its alternative, moves a central core and leaves the rest standing until the silo is run right down.

Answer: C

The first two are correct. The third is the wrong way round: funnel flow is last in first out for the core, which is exactly why time-sensitive materials are stored in mass flow silos. Wall friction and hopper angle together decide which regime you get.

Answer: D

An arch is stable only up to a critical span set by the strength of the consolidated material, so an outlet wider than that span cannot support one. Vibrators and air cannons treat the symptom of an outlet that is too small.

Answer: A

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

Both are true and the reason gives both mechanisms. Cohesive strength rises as particles get finer, because the van der Waals attraction between them grows relative to their weight, and moisture adds liquid bridges that pull the particles together directly. A fine damp powder can therefore support an arch over an opening that a coarse dry one would flow straight through.

Answer: B

Correct answer: increasing the depth of material held above it

More head does not help and often makes matters worse: the extra weight consolidates the material near the outlet and increases its cohesive strength, so the arch it can support becomes stronger. The genuine remedies all break the arch or reduce the friction - a mechanical agitator, aeration through porous pads, or an external vibrator - and the real fix is a hopper designed for mass flow in the first place.