Secondary crushing of hard, tough stone:\nWhich machine is most commonly selected as a secondary crusher for hard and tough rock?

Introduction / Context:
Crushing circuits are staged: primary crushers accept run-of-mine rock, while secondary units reduce product to sizes suitable for tertiary crushing or milling. Matching crusher type to material hardness and abrasiveness is crucial for capacity, product shape, and liner wear economics.

Given Data / Assumptions:

• Material: hard and tough stone (e.g., granite, basalt).
• Duty: secondary stage after primary reduction.

Concept / Approach:
Jaw crushers serve as robust primaries for hard rock. For secondary duty on hard, abrasive material, cone crushers (gyratory derivatives) provide high reduction with good cubicity and handle abrasive wear better than many impactors. Impact crushers excel on softer, less abrasive rock where shattering dominates. Toothed rolls are suited to friable materials and sized coal, not hard stone.

Step-by-Step Solution:

Verification / Alternative check:
Typical quarry flowsheets: primary jaw → secondary cone → tertiary cone/VSIs for shape, confirming the widespread use of cones for tough stone.

Why Other Options Are Wrong:

• Jaw crusher: primarily a primary crusher in hard-rock service.
• Impact crusher: wear-heavy on hard, abrasive feeds.
• Toothed roll/hammer: not preferred for very hard, tough rock.

Common Pitfalls:
Selecting impactors for abrasive rock leads to excessive blow-bar wear and downtime.

Final Answer:
Cone crusher