Definition check: the term "angle of nip" is specifically associated with which type of crusher operation?

Introduction / Context:
The angle of nip is a fundamental concept in roll crushing. It determines whether a particle will be drawn into the gap between rolls and nipped for crushing, or whether it will simply ride along the surface and not be reduced. Understanding this definition helps in selecting roll diameters and setting gaps for desired size reduction.

Given Data / Assumptions:

• Two-roll crusher with parallel, counter-rotating rolls.
• Angle between roll faces at the point where a particle is just captured.
• Friction and particle shape influence the effective nip.

Concept / Approach:
The angle of nip (commonly denoted 2α) is defined for roll crushers as the included angle between the roll faces at the location where a particle just enters the crushing zone. For successful nipping, the frictional forces must be sufficient to draw the particle in; excessive smoothness or too large a particle relative to the gap reduces nipping probability.

Step-by-Step Solution:
Identify the concept: "nip" refers to capture between opposing surfaces.Associate with equipment: classical with roll crushers, not with jaw or gyratory mechanisms.Choose "roll" as the correct answer.

Verification / Alternative check:
Design equations for roll crushers explicitly include the angle of nip when relating feed size, product size, and roll diameter.

Why Other Options Are Wrong:
Jaw/gyratory: while they grip material, the term "angle of nip" is not the standard design parameter used; jaw crushers focus on "set" and "throw," gyratories on "gape" and "mantle angle."

Common Pitfalls:
Using nip-angle formulae for non-roll machines; each crusher family has its own governing geometry.

Final Answer:
roll