Topic: Manufacturing Processes
Addition of coal dust to the green moulding sand is to improve
- A. Permeability
- B. Surface finish
- C. Mouldability
- D. Green strength
Answer: B. Surface finish
Explanation: Adding coal dust (sea coal) to green moulding sand creates a reducing atmosphere when heated by the molten metal. This prevents the metal from wetting and penetrating the sand grains, thereby substantially improving the surface finish of the final casting.