Grinding wheel grade and grain retention A grinding wheel is said to be of which grade if its abrasive grains are relatively easy to dislodge from the bond during operation?

Introduction / Context:
Grinding wheel performance depends on grit size, bond type, structure, and grade. Among these, grade expresses how strongly the bond holds the abrasive grains (i.e., wheel hardness in the grinding sense, not the grain’s mineral hardness).

Given Data / Assumptions:

• Conventional vitrified or resinoid bonded wheels.
• Steady grinding with proper dressing and coolant.
• Focus on the definition of grade (holding power), not grit size or structure.

Concept / Approach:
A “soft grade” wheel releases dull grains readily, exposing fresh sharp edges and avoiding glazing. This is helpful when grinding hard materials or when self-sharpening is desirable. A “hard grade” wheel retains grains longer, which can be useful on softer materials to avoid rapid wear but risks glazing.

Step-by-Step Solution:

Verification / Alternative check:
Manufacturer catalogs and standards list grade letters (softer to harder). Recommendations match material hardness and wheel loading tendencies.

Why Other Options Are Wrong:
Medium/Hard/Super-hard: imply stronger grain retention, contrary to the statement.Open structure: spacing between grains; not a measure of bond holding strength.

Common Pitfalls:
Confusing grit size (coarse/fine) and structure (open/dense) with grade; each affects performance differently and must be selected together.

Final Answer:

Soft grade