Comminution mechanism – cage mills In a cage mill, one or more concentric rows of alloy steel bars rotate in opposite directions to crush mineral particles. This type of mill primarily operates on which grinding mechanism?

Introduction / Context:
Choosing a size-reduction device depends on matching material characteristics with the dominant breakage mechanism: impact, compression, shear, or attrition. Cage mills are common in fertilizer, chemical, and mineral processing for medium-fine reduction.

Given Data / Assumptions:

• Cage mill has rotating cages with bars; feed is accelerated and struck repeatedly.
• Target is brittle to moderately tough solids (e.g., limestone, gypsum, salts).
• Product size typically in the coarse to medium-fine range.

Concept / Approach:
In cage mills, particles are flung by centrifugal force and collide at high relative velocities with bars and other particles. The dominant energy transfer is through impact, causing crack initiation and propagation in brittle solids.

Step-by-Step Solution:

Verification / Alternative check:
Operating curves show throughput increasing with tip speed (impact intensity), and wear patterns on bars indicate repeated striking, confirming impact dominance.

Why Other Options Are Wrong:

• Roll: Requires opposing cylindrical rolls; not the geometry of a cage mill.
• Vibratory: Uses oscillation and attrition; different mechanism and equipment class.
• None of these: Incorrect because impact clearly applies.

Common Pitfalls:
Feeding excessively damp or gummy materials can lead to build-up and reduced impact effectiveness; pre-drying or conditioning may be necessary.

Final Answer:
impact