Pick the wrong statement — size-reduction mechanisms and jaw crushers: Identify the incorrect statement about crushing mechanisms and jaw-crusher types.

Introduction / Context:Most size-reduction devices can be mapped to a few dominant mechanisms: compression, impact, attrition, and cutting (shear). Knowing which mechanism a machine uses informs material suitability and expected product shape. This question also checks recognition of common jaw-crusher variants and their usage prevalence.

Given Data / Assumptions:

• Standard definitions of mechanisms and jaw types are assumed.
• “Cutting machines” refers to guillotines, rotary cutters, knife mills, etc.

Concept / Approach:Cutting machines remove material by shear along a narrow zone using sharp edges; they do not rely mainly on attrition (surface rubbing). Attrition mills (e.g., colloid mills) reduce size primarily by rubbing and abrasion between surfaces. Blake jaw crushers are indeed more common than Dodge type for primary service, and universal jaws share motion characteristics of both classic types (top pivot and complex motion). Therefore, the lone incorrect statement is that cutting employs attrition.

Step-by-Step Solution:

Verification / Alternative check:Equipment catalogs: knife cutters list shear angles, blade speeds; attrition mills specify gap and abrasive surfaces.

Why Other Options Are Wrong:

• (a), (b), (d) are standard facts in unit operations.

Common Pitfalls:Assuming any rubbing in a cutter equates to attrition; the dominant energy mode is shearing across a cutting edge.

Final Answer:Cutting machines mainly employ attrition for size reduction.