Comminution principle: for the coarse reduction of hard, strong solids (e.g., run-of-mine ore or clinker), which primary breakage mechanism is preferred for efficient size reduction and control of product shape?

Introduction / Context:
In particle technology and mineral processing, different breakage mechanisms are favored at different size scales and material strengths. For very hard, strong, and abrasive solids that must be reduced from large lumps to manageable sizes, the dominant and most reliable mechanism is typically compression. This question tests your understanding of how material properties and duty (coarse vs. fine) guide the choice of crusher type and the underlying breakage physics.

Given Data / Assumptions:

• Material: hard/strong solids (e.g., hard ore, clinker, rock aggregates).
• Duty: coarse reduction (primary or secondary crushing).
• Goal: robust operation, control of top size, acceptable product shape, manageable wear.

Concept / Approach:
Compression applies a relatively slow, high force over a contact area; it is effective for large, hard particles and results in predictable fracture along planes of weakness. Primary crushers (jaw, gyratory) and some secondary units (cone, smooth rolls) are compression based. Impact is better for brittle materials at smaller sizes or where cubicity is prioritized; attrition suits intermediate to fine grinding; cutting is for fibrous or soft, ductile materials.

Step-by-Step Solution:
Identify duty: coarse reduction of hard solids.Map duty to mechanism: compression is favored for primary/secondary crushing of hard rocks.Eliminate alternatives: impact (better for brittle shattering and fines control), attrition (fine grinding), cutting (fibrous/soft).

Verification / Alternative check:
Flowsheets show jaw or gyratory crushers as standard primaries in mines and cement plants because compression handles large feed with lower catastrophic wear compared to pure impact on hard lumps.

Why Other Options Are Wrong:
Impact: efficient for brittle materials and shaping at smaller sizes, but high wear on very hard, coarse feed.Attrition: dominant in mills for fine size reduction, not coarse crushing.Cutting: used for fibrous materials (plastics, rubber, biomass), not hard rock.

Common Pitfalls:
Assuming impact is always “more powerful.” Power and effectiveness depend on material properties and scale; for hard, coarse duty, compression is more controllable and economical.

Final Answer:
compression