Feeding Requirements — Which Alloy Needs the Largest Riser? For the same casting size and similar conditions, which metal typically requires the largest riser to compensate for solidification shrinkage and avoid feeding-related defects?

Introduction / Context:
Risers (feeders) supply liquid metal to compensate for volumetric shrinkage during solidification. The required riser size depends on the alloy’s freezing characteristics and shrinkage behavior.

Given Data / Assumptions:

• Same casting geometry and mold conditions.
• Comparison among common foundry metals.
• Goal is to prevent shrinkage cavities and porosity.

Concept / Approach:
Steel exhibits relatively high solidification shrinkage and a pasty (mushy) freezing range that demands sustained feeding. Grey cast iron often shows graphitization expansion that partially offsets shrinkage, reducing feeder demand. Aluminum and copper-base alloys have lower feeding difficulty than steel for equal geometry, though still require appropriate risers and chills.

Step-by-Step Solution:
Compare shrinkage behavior: steel has higher volumetric shrinkage without compensating expansion.Assess freezing range: steel’s feeding distance is limited, necessitating larger or multiple risers.Conclude that, for equal size castings, steel typically requires the largest riser.

Verification / Alternative check:
Foundry design rules and modulus calculations (Chvorinov-based) often result in larger riser volumes for steel than for grey iron.

Why Other Options Are Wrong:
Cast iron: graphite expansion reduces feeder demand.Aluminium/copper: still shrink, but generally easier to feed than steel for the same shape.

Common Pitfalls:
Assuming the lightest metal needs the largest riser; density is not the deciding factor.

Final Answer:
Steel