Threshing and Shelling Questions and Answers

Answer: C

It measures only detachment, and grain still attached to the head at discharge counts as unthreshed loss. Cleaning efficiency and breakage are separate measures, and a machine can score well on one and badly on another.

Answer: D

It looks at the quality of the delivered stream rather than at whether the grain came free of the head. A machine with excellent threshing efficiency may still deliver a thoroughly dirty sample if its shoe is misadjusted.

Answer: A

Setting the fan too fast carries sound grain out of the back with the light material, and the loss is invisible unless it is measured deliberately. It trades directly against sample cleanliness, which is why fan speed needs care.

Answer: B

The cob is worked between the rotor and the cage until the kernels shear from the rachis, and the empty cob is then discharged separately. Shelling is easiest at moderate moisture, since very dry kernels crack and very wet ones cling.

Answer: C

The pods are cracked between a beater and a screen sized so that the freed kernels pass through while the shell fragments are carried on. Detaching the pods from the plant is a separate operation, done by a stripper or picker.

Answer: D

Correct answer: Paddy grain cracks more readily

Rice kernels are brittle, and a crack put into the grain at threshing does not stay a crack - the kernel breaks along it during hulling and whitening, so the damage appears later as a fall in head rice yield, where the money is.

Paddy straw is not especially tough and the heads are not hard to detach, so nothing about the crop requires a high speed. The lower setting is a deliberate concession to the fragility of the grain, and the same reasoning governs drying and handling throughout the chain.

Answer: A

Correct answer: Energy per tonne of grain threshed

Specific energy consumption is the energy used divided by the mass of grain produced, in kilowatt-hours per tonne. A machine drawing 9 kW while threshing 1.2 t/h consumes 7.5 kWh per tonne.

Expressing it this way makes machines of different size and throughput comparable, which a raw power figure cannot do. Energy per hour ignores output entirely, and dividing power by cylinder speed or concave area produces quantities with no useful physical meaning.

Answer: B

The cylinder and the separating section have to handle everything that enters, not just the grain, so the whole mat is the meaningful load. A crop with a high straw-to-grain ratio loads a machine far more heavily at the same grain output.

Answer: C

Too thick a mat prevents grain from reaching the concave and from shaking free on the walkers, so both loss terms climb at once. Capacity is normally defined as the feed rate at which total loss reaches an accepted figure.

Answer: D

Correct answer: Crop moisture content

Moisture governs how readily the grain detaches and how easily it cracks, and it changes through the day as the dew dries and again as the evening comes on. A crop that threshed cleanly at midday may need a tighter concave by late afternoon, or a slower cylinder once the grain has dried and become brittle.

That is why an operator adjusts settings during a day's work rather than setting the machine once. Colour, slope and row spacing affect harvesting or field operations but not the threshing action itself.