Pig iron grades for casting: which type is the most unsuitable for light and ornamental castings? (Consider fluidity, shrinkage, and machinability requirements.)

Introduction / Context:
Selection of pig iron for castings depends on graphite form, fluidity, and contraction behavior. Light and ornamental castings demand good fluidity to fill thin sections and intricate details, along with easy machining. This question targets the pig iron type that fails to meet these needs.

Given Data / Assumptions:

• Grey pig forms graphite flakes in cast iron → good fluidity and machinability.
• White pig solidifies as cementite-rich → hard, brittle, poor machinability.
• Mottled pig is intermediate between grey and white.

Concept / Approach:
For thin, ornate castings, graphite-bearing irons (from grey pig) are ideal. White pig iron leads to white cast iron with low fluidity and very poor machinability, making it the least suitable choice for delicate, detailed work.

Step-by-Step Solution:

Verification / Alternative check:
Foundry practice recommends grey irons for intricate castings and cautions against white irons except where abrasion resistance is the primary goal.

Why Other Options Are Wrong:

• Grey or foundry pig: preferred for light, ornate casting.
• Bessemer pig: process label; suitability depends on composition, but not inherently the worst.
• Mottled pig: intermediate behavior; still better than white pig for fluidity and machining.

Common Pitfalls:
Assuming harder always means better; for ornamentals, fluidity and machinability outrank hardness.

Final Answer:
White or forge pig