Farm Machinery and Power Engineering- ICAR JRF/SRF 2024

• Threshing Cylinders for Fine Straw (Bhusa) Production:
• In Indian agriculture, wheat straw (bhusa) is heavily valued as dairy cattle fodder and must be bruised and crushed into fine pieces.
• The Hammer mill type (or syndicated beater type with serrated concave) threshing cylinder uses high-speed swinging/fixed hammers that pulverize and bruise wheat straw into exceptionally fine fodder.
• Rasp-bar and spike-tooth cylinders thresh grain effectively but produce coarser straw pieces.
• Conclusion: Hammer mill type (Option 2).

Correct option: (2) Hammer mill type

• Forces on Gang of Disc Harrows:
• Assertion (A): Concave end of the disc harrow gang tends to penetrate more deeply than the convex end. $\implies$ True.
• The soil side forces acting on disc faces create a couple that tilts the gang, causing the outer concave end to dig in deeper while the convex end tends to ride out of the soil.
• Reason (R): The radial force, which includes the vertical support force on the disc blade, must pass slightly to the rear of the disc centerline. $\implies$ True.
• Due to soil resistance and forward travel velocity, the resultant radial reaction shifts slightly rearward of the vertical center axis.
• Relationship: Reason (R) describes longitudinal force line of action on an individual blade, but does not provide the causal explanation for gang-level moments across the width.
• Conclusion: Both (A) and (R) are true but (R) is NOT the correct explanation of (A) (Option 2).

Correct option: (2) Both (A) and (R) are true but (R) is NOT the correct explanation of (A).

• Rotary vs. Sickle Bar Mowers:
• Assertion (A): The power requirement of a rotary mower is much higher than that of a sickle bar mower of the same width. $\implies$ True.
• Rotary mowers cut by high-velocity impact without a ledger plate, operating at blade tip speeds of 70–80 m/s, incurring high aerodynamic windage and impact energy losses (3–5 times more power than sickle bar mowers).
• Reason (R): The knives of rotary mower are hinged to the disc or drum so that they can swing back if they hit a rock or other obstruction; centrifugal force keeps the knives in cutting position during normal operation. $\implies$ True.
• Rotary mower knives are freely pivoted for obstacle safety.
• Relationship: Reason (R) describes a safety mechanism for obstacle evasion, not the physical cause of high power consumption (which stems from aerodynamic drag and high-velocity impact).
• Conclusion: Both (A) and (R) are true but (R) is NOT the correct explanation of (A) (Option 2).

Correct option: (2) Both (A) and (R) are true but (R) is NOT the correct explanation of (A).