Cleaning and Grading Equipment Questions and Answers

Answer: A

Correct answer: Size and terminal velocity together

An air screen cleaner combines two separations in one machine. The screens sort by size - a scalping deck removing what is larger than the grain and a grading deck removing what is smaller - while the aspiration section sorts by terminal velocity, lifting away chaff, dust and light immature grain.

Using both properties catches material that either alone would miss: a light seed of grain size passes every screen but is removed by the air, and a dense stone of grain size passes the air but not always the screen. Neither colour nor density alone is exploited here.

Answer: B

Correct answer: Removes material larger than the grain

The scalping screen has apertures larger than the grain, so the grain and everything smaller pass through while straw, stalks, pods, string and clods are carried over the deck and out.

It comes first in the line precisely so that this coarse trash never reaches the finer decks, where it would bridge the apertures and blind them. Removing material smaller than the grain is the grading screen's job, and removing light chaff is the aspirator's.

Answer: C

Correct answer: Length

An indented cylinder separates on length. The indents in the cylinder wall are sized to hold a short seed but not a long one, so as the cylinder rotates the short seeds are lifted clear of the bed and drop into a trough set at the appropriate height, while the long seeds fall back before reaching it.

This is the only common separation that works on length, which makes the machine valuable for removing broken kernels, or weed seeds that match the grain in width and thickness but differ in length.

Answer: D

Correct answer: An indented cylinder

A disc separator makes the same separation as an indented cylinder - on length - but with a different geometry. Discs carrying indents on their faces rotate through the seed bed, lifting the short seeds out while the long ones fall back.

The advantage over the cylinder is capacity: many discs can be mounted on one shaft in the space a single cylinder would occupy, so throughput per unit floor area is higher. The separating principle, and the type of impurity each removes, are identical.

Answer: A

Round seeds gain speed rolling down the helix and are thrown outward, while flat or irregular ones slide and stay inside. It has no moving parts and no power requirement at all, which makes it among the cheapest separators to run.

Answer: B

Correct answer: Round seeds that roll and flat ones carried up

An inclined belt separator exploits shape and surface behaviour. The belt runs upward while the material is fed onto it: round, smooth seeds roll back down against the belt's motion, while flat, rough or irregular seeds grip the surface and are carried up and over.

It is used where the fractions differ in shape rather than in size or density - separating round weed seeds from flat crop seed, for instance, or removing broken and chipped material that has lost its rolling character.

Answer: C

Air blown up through a porous deck fluidises the bed so that heavy particles sink and contact the deck while light ones float, and the oscillation then walks the two fractions apart. It is the standard way to remove insect-damaged and immature grain.

Answer: D

Correct answer: Stones and dense foreign matter

A destoner is a specific gravity separator arranged to lift the grain and leave the heavy fraction behind. Air is blown up through a perforated oscillating deck, fluidising the bed so the lighter grain floats and the denser stones, mud balls and metal fragments settle to the deck surface and are walked uphill to a separate outlet.

The separation is essential before milling: a stone entering a huller or a roller mill damages the machine and can strike sparks in a dust-laden atmosphere.

Answer: A

Correct answer: Remove ferrous tramp metal

A magnetic separator removes ferrous tramp metal - nails, bolts, wire, harvester and handling debris - picked up between field and mill.

Its purpose is protective rather than qualitative. A piece of steel entering a roller mill, huller or hammer mill can damage the machine severely, and in a dust-laden atmosphere it can strike a spark and cause an explosion. Magnets are therefore fitted immediately ahead of every such machine, and are inspected and cleaned on a fixed schedule.

Answer: B

Correct answer: Surface electrical conductivity

Electrostatic separation exploits differences in how readily a particle's surface accepts and holds a charge. The material is charged, usually by contact or by an ionising field, and passes over a rotating earthed drum: conductive particles lose their charge to the drum and leave immediately, while non-conductive particles retain it, cling to the drum and are carried further before release.

It is used where the fractions match closely in size, shape and density but differ in surface character - some weed seeds from crop seed, for instance.