Cleaning and Grading Equipment Questions and Answers

Answer: C

Correct answer: 12.0 m/s

Velocity is volumetric flow divided by area:

\[ v = \frac{1.8}{0.15} = 12.0\ \mathrm{m/s} \]

Inlet velocity governs cyclone performance directly, since the centrifugal force separating the dust from the air rises with its square. Too low and fine material escapes with the exhaust; too high and pressure drop and erosion rise steeply. Design velocities for grain dust cyclones typically fall in the range of 12 to 20 m/s, so this machine sits at the gentle end.

Answer: D

Correct answer: 0.8 tonnes

The smallest class is 10 per cent of the total:

\[ 8 \times 0.10 = 0.8\ \mathrm{tonnes} \]

The four percentages sum to 100, which is the check that the grading has been fully accounted for. Distribution across classes is itself commercially significant: the size profile determines how much of a crop reaches the premium grades, and it depends on variety, growing conditions and harvest timing as much as on the grader.

Answer: A

Correct answer: 1000 kg/h

Multiply the per-flight capacity by the number of flights:

\[ 250 \times 4 = 1000\ \mathrm{kg/h} \]

A spiral separator has no moving parts and no power requirement - round seeds gain speed descending the helical flight and are thrown to the outer wall, while flat or irregular seeds stay on the inner track. Capacity per flight is therefore modest and fixed, and throughput is increased simply by running more flights in parallel around the same column.

Answer: B

Correct answer: 0.6 per cent

Express the stones removed as a percentage of the feed:

\[ \frac{18}{3000} \times 100 = 0.6\ \mathrm{per\ cent} \]

A stone content well below one per cent still matters a great deal, because a single stone reaching a huller or a roller mill can damage it and, in a dust-laden atmosphere, strike a spark. The destoner's value is not in the mass it removes but in what that mass would have done downstream.

Answer: C

Correct answer: Both Statement I and Statement II are correct

Both statements are correct and the second explains the first. The scalping screen has apertures larger than the grain, so it removes straw, stalks, pods and clods while the grain passes through.

Placing it first protects everything downstream: large trash reaching a fine grading deck would bridge and blind the apertures, cutting the effective open area and degrading both capacity and separation. The general principle in a cleaning line is to remove the coarsest contaminant first and work progressively towards the finest.

Answer: D

Both statements are correct and the second describes the mechanism. It is the standard way of removing broken kernels and short weed seeds that a size screen cannot catch, because they are no narrower than sound grain.

Answer: A

Correct answer: Statement I is incorrect but Statement II is correct

Statement I is incorrect. A specific gravity separator depends absolutely on air flow: air is blown upward through the perforated deck to fluidise the bed, so that dense particles sink to the deck surface and light ones float above.

Statement II is correct and describes the other half of the mechanism. The deck oscillates to walk the settled heavy fraction uphill to its outlet while the fluidised light fraction flows downhill to another. Both actions are needed - air alone would stratify the bed without conveying it anywhere.

Answer: B

The second is correct, and beyond a point it defeats the first: a bed too deep for particles to reach the deck can reduce the absolute recovery, not merely the percentage. Capacity and effectiveness trade against one another.

Answer: C

Correct answer: Both Statement I and Statement II are correct

Both statements are correct and the second explains the first. Nails, bolts, wire and harvester debris are picked up between field and mill, and a piece of steel entering a huller, roller mill or hammer mill can wreck it.

Worse, in the dust-laden atmosphere of a mill a steel fragment striking a rotating part can strike a spark, and grain dust is explosive. Magnets are therefore fitted immediately upstream of every such machine and cleaned on a fixed schedule, since a magnet allowed to load up stops catching anything.

Answer: D

Correct answer: Both Statement I and Statement II are correct

Both statements are correct and the second explains the first. A slot is long in one direction, so a particle can present itself edge-on and pass provided its thickness fits - its width and length are then irrelevant.

This is why aperture shape determines which dimension a screen sorts on. Round holes, which a particle cannot turn to advantage, sort on width; slots sort on thickness; and an indented cylinder is needed for length. A full cleaner uses several in combination for that reason.