Roll crushers: Pick the WRONG statement about operating characteristics and design.

Introduction / Context:
Roll crushers nip and compress particles between two counter-rotating rolls. Their design parameters include roll diameter, speed, surface pattern, and the possibility of differential speeds to improve nipping and throughput.

Given Data / Assumptions:

• Conventional two-roll crusher with adjustable gap.
• Hard/brittle feeds impose limits on reduction ratios.
• Feed size relative to roll diameter governs nipping feasibility.

Concept / Approach:

To draw particles into the nip, a sufficient angle of nip and friction are needed. Roll diameter scales with maximum feed size. Differential roll speeds are often used to improve nipping, minimize slippage, and tailor product size; equal speeds are not mandatory and not universal.

Step-by-Step Solution:

Verification / Alternative check:

Design texts and manufacturers describe differential speed rolls to reduce slippage and increase shearing action, especially for tough or moist feeds.

Why Other Options Are Wrong:

They are accurate statements concerning dependence on feed size, prudent reduction ratios for hard materials, and the influence of speed and ratio on performance.

Common Pitfalls:

Assuming symmetry implies identical speeds; overlooking the role of friction and nip angle in design.

Final Answer:

Both rolls must necessarily run at the same peripheral speed.