Hammer crusher product top size control\nIn a hammer crusher, which combination of operating variables primarily governs the final product size distribution?

Introduction / Context:
Hammer crushers (or hammer mills) are impactors widely used for intermediate to fine size reduction in minerals, cement rawmix, and biomass. Operators can shape the product size distribution (PSD) by adjusting several accessible variables. Recognising these variables and their coupled effects is central to stable operation and specification compliance.

Given Data / Assumptions:

• A conventional hammer crusher with breaker plates (liners) and a grate or classifying section.
• Material is moderately hard and friable; machine is not overfed.
• Steady-state operation is assumed.

Concept / Approach:
Product top size and fines generation in a hammer crusher are controlled by impact energy per collision and residence time. Impact energy scales with rotor tip speed (rotor speed and diameter). The clearance between hammers and breaker plates alters the severity of secondary breakage and the effective classification. Feed rate influences residence time and bed depth, which in turn affects the number of impacts a particle receives before exiting. Consequently, all three variables act together to define the PSD; changing any one often requires compensating changes in others to maintain the same product target.

Step-by-Step Solution:

Verification / Alternative check:
OEM manuals specify rotor speed ranges and breaker plate settings for target top sizes, with de-rating limits on feed rate to avoid oversize leakage or excessive fines.

Why Other Options Are Wrong:

• Single-variable answers ignore the coupled nature of impactors.
• Moisture content affects behavior but is not the primary knob for top size once within a normal operating window.

Common Pitfalls:
Increasing rotor speed alone to fix oversize, which often raises fines excessively; always balance speed with clearance and feed rate.

Final Answer:
All of the above together (feed rate, rotor speed, and clearance)