Grinding practice: choosing grain size for brittle materials For grinding brittle materials (e.g., hardened tool steels, ceramics), is a coarse-grained grinding wheel preferred?

Introduction / Context:Wheel selection involves four key parameters: grain size (grit), grade (hard/soft), structure (open/dense), and bond. For brittle materials, preventing micro-chipping and achieving a fine finish are paramount.

Given Data / Assumptions:

• Work materials are brittle, tending to fracture at edges.
• Goal is to balance stock removal, surface integrity, and wheel life.
• Coolant is available but not relied upon to solve edge damage alone.

Concept / Approach:Fine grit produces small chips and lower cutting point penetration, reducing crack initiation at the surface. Coarse grit creates larger, deeper scratches, which can nucleate edge fractures and cause micro-chipping on brittle substrates.

Step-by-Step Solution:Relate brittleness to chip formation: brittle → crack-sensitive → require small chip thickness.Select finer grit to reduce indentation depth and scratch size.Complement with an open structure and appropriate (often softer) grade to avoid loading while maintaining edge integrity.

Verification / Alternative check:Process handbooks recommend finer grits for hardened steels/carbides/ceramics where finish and edge integrity dominate.

Why Other Options Are Wrong:

• (A) reverses best practice for brittle materials; coarse grits suit soft, ductile, loading-prone materials.
• (C) references soft/gummy materials, not brittle ones.
• (D) Grade and grain are independent; soft grade does not justify coarse grit on brittle parts.

Common Pitfalls:Using coarse grit to chase removal rate and then seeing chipped edges; confusing grade with grit size.

Final Answer:Disagree — finer grain is preferred to limit edge chipping