Subtopic: Functional requirements, principles of working, construction and operation of manual, animal, tractor and renewable energy operated equipment for tillage, sowing, planting, fertilizer application, inter-cultivation, spraying, mowing, chaff cutting, harvesting and threshing
Question Statement:
A power operated chaff cutter has an effective throat width of 450 mm and operating clearance of 150 mm. It is used for chopping straw at a moisture content of 20 % with bulk density of 60 kg·m⁻³ while passing through the feed rolls. The number of knives on the cutter head are 4, speed of the cutter head is 540 rpm and the theoretical length of cut is 10 mm. The theoretical capacity of the chaff cutter, in ton·h⁻¹, is _________. (Rounded off to 2 decimal places)
Options:
(A) 1.31
(B) 5.25
(C) 7.54
(D) 9.61
Official Answer Key:
B
Step-by-Step Solution & Explanation
Step 1 — cross-sectional area of the straw column passing through the feed rolls:
A = throat width × clearance = 0.450 × 0.150 = 0.0675 m²
Step 2 — number of cuts per hour:
= knives × rotational speed = 4 × 540 = 2160 cuts·min⁻¹ = 129,600 cuts·h⁻¹
Step 3 — length of material fed per hour. Each cut advances the straw by one theoretical length of cut (10 mm = 0.01 m):
L = 129,600 × 0.01 = 1296 m·h⁻¹
Step 4 — volume and mass throughput:
Volume = A × L = 0.0675 × 1296 = 87.48 m³·h⁻¹
Mass = 87.48 × 60 = 5248.8 kg·h⁻¹ = 5.25 ton·h⁻¹
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