Threshing and Shelling Questions and Answers

Answer: A

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

Both statements are true and the reason is why capacity must be defined this way. A thresher does not stall at a definite feed rate; it will accept more crop almost indefinitely, delivering steadily less of the grain.

Losses climb steeply once the mat is too thick for the cylinder and walkers to work, so there is no natural limit to point to - only a chosen one. Capacity is therefore quoted as the feed rate at which total loss reaches an agreed figure, and a capacity claim without its loss figure means nothing.

Answer: B

Correct answer: 1 and 2 only

Statement 1 is correct: a faster cylinder detaches more grain. Statement 2 is correct: it also cracks more, which is why the two are traded against one another.

Statement 3 is false. Impact energy rises with the square of the peripheral speed, not linearly, so raising the speed from 15 to 20 m/s increases it by 78 per cent rather than 33. That square law is precisely why damage climbs faster than threshing improves as the speed goes up.

Answer: C

Correct answer: 1 and 2 only

Statement 1 is correct: unthreshed loss is grain still attached to the head at discharge. Statement 2 is correct: separation loss is grain leaving with the straw.

Statement 3 is false. Breakage is grain damaged inside the machine, and it arrives in the grain tank - cracked, but present. It is a quality loss rather than a quantity one, which is why it is measured as a percentage of the sample rather than counted with the grain that never reached the tank at all.

Answer: D

Correct answer: 1 and 2 only

Statement 1 is correct: the crop follows a helical path along the rotor. Statement 2 is correct: that path gives it many passes over the concave rather than the single pass of a tangential machine.

Statement 3 is false and reverses the position. An axial-flow machine consumes more energy per tonne - around 8 kWh against 6.5 - because keeping the mat moving along the whole rotor costs power. What it buys is throughput and thoroughness, not efficiency.

Answer: A

Correct answer: 1 and 2 only

Statement 1 is correct: the shoe uses sieves to separate by size and an air blast to separate by weight, the two working together. Statement 2 is correct: a faster fan takes more grain out with the chaff.

Statement 3 is false. Separating grain from straw is the straw walkers' job, upstream of the shoe. By the time material reaches the cleaning stage the straw has gone, and what remains is grain mixed with chaff and short fragments.

Answer: B

Correct answer: A-2, B-1, C-4, D-3

Each component is matched to its function. The cylinder and concave (A) detach grain from the head (2). The straw walkers (B) shake grain out of the straw mat (1).

The cleaning shoe (C) separates grain from chaff with sieves and air (4), and the grain auger (D) conveys the clean grain to the tank (3). The sequence is a progression through ever cleaner mixtures - whole crop, then straw and grain, then grain and chaff, then grain alone.

Answer: C

Correct answer: A-2, B-1, C-4, D-3

Each cylinder is matched to its dominant action. The spike-tooth (A) works by impact of pegs on the crop (2); the rasp-bar (B) by rubbing against the concave (1).

The wire-loop (C) works by gentle rubbing with flexible loops (4), and the axial rotor (D) by repeated rubbing over a long helical path (3). The list runs from the most violent action to the gentlest and then to the most extended, which broadly tracks straw breakage and grain damage.

Answer: D

Correct answer: A-2, B-1, C-4, D-3

Each loss is matched to the setting that most directly reduces it. Unthreshed loss (A) is cured by a tighter concave clearance (2), which works the mat harder. Blown loss (B) is cured by a lower fan speed (1).

Separation loss (C) is cured by a lower feed rate (4), thinning the mat so grain can shake free of the straw. Breakage (D) is cured by a lower cylinder speed (3). Note that the first and last pull against each other, which is the central compromise in setting a thresher.

Answer: A

Correct answer: A-2, B-1, C-4, D-3

Each machine is matched to its separation. A thresher (A) separates grain from the head and straw (2); a maize sheller (B) separates kernels from the cob (1).

A decorticator (C) separates kernels from the shell (4), and a winnower (D) separates grain from chaff using air (3). The first three break a physical attachment; the winnower only sorts what is already loose, which is why it works on differences in terminal velocity rather than by any mechanical action.

Answer: B

Correct answer: Winnowing

Winnowing is a cleaning action, not a threshing one. It uses an air stream to carry away chaff after the grain has already been detached, and in a thresher it belongs to the cleaning shoe.

The four threshing actions are impact, rubbing, stripping and centrifugal throw - all of which act on the crop mat in the cylinder and concave to free the grain from the head. Every cylinder type uses some combination of them, differing mainly in which predominates.