For roll crushers, the typical value of the angle of nip (the angle between roll tangents at the points of contact with the particle being nipped) is approximately

Introduction / Context:
The angle of nip determines whether a particle will be successfully drawn into the rolls for crushing. It depends on friction and geometry and is central to sizing and performance predictions of roll crushers.

Given Data / Assumptions:

• Smooth or lightly corrugated rolls handling typical ores/rocks.
• Reasonable surface friction coefficient.
• Classical geometric nip criterion applies.

Concept / Approach:

The maximum practical angle of nip for most industrial roll crushers lies in the mid-teens to about 24 degrees. Values near 16 degrees are commonly cited for smooth rolls; higher angles risk slippage instead of nipping, especially for hard, smooth particles.

Step-by-Step Solution:

Verification / Alternative check:

Reference examples and solved problems typically use 16° as a representative nip angle for smooth rolls with ordinary friction levels.

Why Other Options Are Wrong:

32°, 52°, 64°: Too large for stable nipping; particles would slip rather than be drawn into the gap unless extreme roughness or special conditions exist.

Common Pitfalls:

Confusing half-angle versus full included angle; using unrealistic friction coefficients for smooth, hard particles.

Final Answer:

16°