Threshing and Shelling Questions and Answers

Answer: C

Correct answer: 0.80 t/h

Divide the output by the time taken:

\[ \frac{5.2}{6.5} = 0.80\ \mathrm{t/h} \]

This is the effective capacity over the whole period, which includes any time lost to blockages, refuelling and waiting for crop. It is the figure that matters for planning a day's work, and it is always lower than the machine's rated throughput measured while it is actually running.

Answer: D

Correct answer: 3.0

Divide the new figure by the old:

\[ \frac{3.6}{1.2} = 3.0 \]

Damage has tripled. The distractor 2.4 is the arithmetic difference in percentage points, which understates what has happened - a rise from 1.2 to 3.6 per cent is a threefold increase, and expressing it as a factor rather than as a difference is what makes the severity apparent. Broken grain is unsaleable at full price, so this is a direct loss of revenue.

Answer: A

Correct answer: 98.2 per cent

Grain recovery is the proportion of the grain entering the shoe that leaves in the clean stream:

\[ \frac{340 - 6}{340} \times 100 = \frac{334}{340} \times 100 = 98.2\ \mathrm{per\ cent} \]

The 400 kg/h total feed is not the denominator; the measure concerns grain. Recovery and cleaning efficiency pull against each other - raising the fan speed gives a cleaner sample but blows more grain away - so the shoe is set at the compromise between them.

Answer: B

Correct answer: 700 rev/min

Peripheral speed is circumference times rotational speed, so rearranging:

\[ N = \frac{v}{\pi D} = \frac{22}{\pi \times 0.60} = \frac{22}{1.885} = 11.7\ \mathrm{rev/s} \]

\[ 11.7 \times 60 = 700\ \mathrm{rev/min} \]

It is the peripheral speed that governs threshing, not the rotational speed, so cylinders of different diameter must run at different revolutions to achieve the same effect - which is why settings cannot be carried between machines without converting.

Answer: C

Correct answer: Both Statement I and Statement II are correct

Both statements are correct and the second explains the first. The energy delivered to a grain in an impact rises with the square of the peripheral speed, so a modest increase in speed produces a much larger increase in the work done on the crop.

Raising the speed from 15 to 20 m/s - a third faster - increases the impact energy by 78 per cent. Threshing improves, but damage improves faster, which is why cylinder speed is set as low as will thresh the crop rather than as high as the machine allows.

Answer: D

Correct answer: Both Statement I and Statement II are correct

Both statements are correct and the second explains the first. A rasp-bar drags the crop mat against the concave, working it by friction and shear, whereas a spike-tooth cylinder strikes the material with rigid teeth.

Impact shatters straw; rubbing does not. The consequence matters downstream as well as in the machine: broken straw passes through the concave and over the walkers with the grain, loading the cleaning shoe heavily and making a clean sample harder to obtain.

Answer: A

The helical path is correctly described, and it is exactly what gives the crop many passes rather than one. The long residence time is why the design handles damp and tough material so well and why it consumes more power.

Answer: B

Correct answer: Both Statement I and Statement II are correct

Both statements are correct and the second is the mechanism. A wider gap between cylinder and concave means the mat is compressed less and rubbed less severely, so less energy is put into each grain and fewer are cracked.

The cost is threshing thoroughness: some grain will leave still attached to the head. That trade is made deliberately on seed crops, where a cracked grain will not germinate and the unthreshed remainder can be recovered by a second pass.

Answer: C

The reason is right, but past a point the blast carries sound grain out as well and blown loss climbs. The sample looks cleaner while the yield quietly falls, which is why the loss must be measured rather than judged by eye.

Answer: D

Correct answer: Both Statement I and Statement II are correct

Both statements are correct, and the distinction they draw is worth holding firmly. Threshing efficiency asks how much grain was detached from the head; cleaning efficiency asks how pure the delivered stream is.

A machine can score well on one and badly on the other. It might detach every grain and still deliver a sample full of chaff, or produce a beautifully clean sample while leaving grain on the heads. They are set by different adjustments - cylinder and concave for one, fan and sieves for the other.