Not a tumbling (revolving) mill: Which of the following is NOT classified as a tumbling/revolving mill for size reduction?
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ACompartment mill
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BPebble mill
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CCage mill
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DRod mill
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EBall mill
Answer
Correct Answer: Cage mill
Explanation
Introduction / Context:Tumbling (revolving) mills reduce size by cascading/cataracting media and particles inside a rotating cylindrical shell. Examples include ball, rod, pebble, and compartment mills. It is useful to distinguish these from impactor-style mills, which achieve reduction through high-speed particle impacts without a rotating, media-filled drum.
Given Data / Assumptions:
- Tumbling mills possess a rotating cylindrical shell.
- Charge motion (cascading/cataracting) is the dominant mechanism.
Concept / Approach:Cage mills are impact mills; they use one or more high-speed cages that fling material into counter-rotating impactors and breaker plates. There is no media-filled rotating cylindrical drum as in ball/rod/pebble/compartment mills. Therefore, the cage mill is not a tumbling mill, whereas the others listed are classic tumbling types.
Step-by-Step Solution:
Identify the common geometry of tumbling mills (rotating shell).Recognise that cage mills are impactors with spin cages.Select “Cage mill.”Verification / Alternative check:Equipment taxonomies in unit-ops texts list cage and hammer mills under “impact mills,” separate from tumbling mills.
Why Other Options Are Wrong:
- Compartment/pebble/rod/ball mills all have rotating cylindrical shells and are tumbling mills.
Common Pitfalls:Assuming any rotating device is a tumbling mill; internal mechanics matter.
Final Answer:Cage mill