Threshing and Shelling Questions and Answers

Answer: A

Correct answer: Both Statement I and Statement II are correct

Both statements are correct and the second explains the practice. A rice kernel that is cracked at threshing does not merely look damaged - the crack is a plane of weakness along which the kernel breaks during hulling and whitening.

The loss therefore appears at the mill as a fall in head rice yield, and since whole grains fetch nearly twice the price of brokens, it is expensive. Threshing paddy more gently, at a lower cylinder speed, protects a value that is realised several steps later in the chain.

Answer: B

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

Statement I is incorrect. The straw-to-grain ratio has a direct bearing on loading, because it determines how much total material must pass through the machine for a given grain output.

Statement II is correct and is precisely why. A crop with a ratio of 1.5 requires 2.5 tonnes of material to be handled for every tonne of grain; one with a ratio of 2.5 requires 3.5. The cylinder, walkers and shoe are all sized on total throughput, so the ratio effectively sets the machine's grain capacity.

Answer: C

Correct answer: 2, 1, 3, 4

The crop passes through in this order. It is fed into the cylinder and concave (2), where the grain is detached and most of it falls through the grate.

The straw walkers then shake out the grain still caught in the straw (1). The cleaning shoe separates that grain from the chaff by sieving and air (3), and the clean grain is delivered to the outlet (4). Each stage handles a progressively cleaner mixture - crop, then straw and grain, then grain and chaff.

Answer: D

The cheapest and least damaging change comes first, then speed, then feed rate, and only as a last resort is the cylinder itself changed. Reaching for cylinder speed first is what produces the cracked grain so often seen.

Answer: A

Correct answer: 1, 2, 3, 4

The chain runs from the operator's decision to the measured loss. Feed rate is increased beyond the machine's capacity (1), and the mat passing through the cylinder and over the walkers thickens (2).

A thick mat is the problem: grain in the middle of it cannot reach the concave to fall through, and cannot shake free of the straw on the walkers (3). Unthreshed loss and separation loss therefore both rise (4) - which is why pushing a thresher for output so often reduces the grain actually recovered.

Answer: B

Correct answer: 2, 1, 3, 4

The sequence follows the crop. The cobs are harvested and dehusked (2), then shelled to remove the kernels (1).

Cleaning removes cob fragments, husk and dust (3), and drying to a safe storage moisture comes last (4). Drying is placed at the end because it is far cheaper to dry kernels than whole cobs - the cob is a third of the mass and holds a great deal of water - and because the material must be clean before it goes into store.

Answer: C

Correct answer: 1, 2, 3, 4

The actions follow the mat's passage round the cylinder. The teeth strike the incoming material first (1), which is the spike-tooth's dominant action and begins the detachment.

The mat is then rubbed between cylinder and concave (2) as it is carried round, remaining grain is stripped from the heads as it continues (3), and the freed grain is thrown centrifugally through the concave openings (4). All four contribute, which is why a spike-tooth cylinder threshes so thoroughly and damages so much.

Answer: D

Correct answer: Only three

Three pairs are right. A spike-tooth cylinder works by impact, a rasp-bar by rubbing, and a wire-loop by gentle rubbing suited to delicate crops.

The fourth is wrong. An axial-flow cylinder carries the crop in a helical path along the rotor, so the material passes over the concave repeatedly rather than once. That extended working is what gives axial-flow machines their thorough threshing and gentle action, since each pass need do only a little.

Answer: A

Correct answer: Only three

Three pairs are right. Unthreshed loss is grain still attached to the head at discharge, separation loss is grain leaving with the straw, and blown loss is grain carried out by the cleaning fan.

The fourth is wrong. Breakage is grain damaged by the machine - cracked or shattered kernels in the delivered sample. Grain left in the field before harvest is a harvesting or shattering loss, which occurs before the crop ever reaches the thresher.

Answer: B

Correct answer: Only three

Three pairs are right. A higher cylinder speed gives more threshing and more damage, a tighter concave does the same, and a higher fan speed gives a cleaner sample at the cost of more grain blown away.

The fourth is wrong on both counts. A higher feed rate thickens the mat, so grain cannot reach the concave or shake free of the straw: losses rise and cleaning gets worse. Pushing a thresher for throughput reduces the grain actually recovered.