Abrasive selection: Which abrasive is generally recommended for grinding materials of low tensile strength (e.g., nonferrous alloys, cast iron with free graphite)?

Introduction / Context:
Grinding wheel selection balances work material properties, required finish, and economics. Abrasive type is a first-order choice: aluminium oxide (corundum) is usually preferred for ferrous, higher tensile strength materials, while silicon carbide is preferred for lower tensile strength or hard/brittle nonferrous materials and cast irons.

Given Data / Assumptions:

• Conventional vitrified or resinoid-bond grinding wheels.
• Work examples: aluminium alloys, brass, bronze, grey cast iron with free graphite.
• General-purpose surface or cylindrical grinding.

Concept / Approach:
Silicon carbide is harder and more brittle than aluminium oxide, providing sharp cutting edges suitable for softer, gummy nonferrous metals and certain cast irons where chip loading is a risk. It fractures more readily, self-sharpening to reduce wheel loading. Aluminium oxide is tougher and better for high tensile steels where durability against heavy forces is needed.

Step-by-Step Solution:

Verification / Alternative check:
Standard grinding references specify silicon carbide (green/black) for aluminium, brass, copper, and for grey cast iron to mitigate loading and provide efficient chip removal.

Why Other Options Are Wrong:

• Aluminium oxide is better for steels and high tensile materials.
• Sand stone is obsolete and inconsistent for precision grinding.
• Diamond is reserved for carbides/ceramics; it reacts with iron at high temperature.
• CBN excels on ferrous hard steels, not low tensile nonferrous materials.

Common Pitfalls:
Using aluminium oxide on soft aluminium causes wheel loading and burnishing; ignoring wheel grade and structure, which also affect performance and loading tendency.

Final Answer:
silicon carbide