Question

The grain size of moulding sand is expressed in terms of

• A. grain density
• B. sieve number
• C. average grain diameter
• D. grain fineness number

Hint:

When you see a question about quantifying sand grain size in a standardized way for foundries, the answer is the AFS Grain Fineness Number (GFN).

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
The size and distribution of sand grains are critical properties of moulding sand, as they affect permeability, strength, and the surface finish of the final casting. A standardized method is needed to quantify this property.

Step 2: Detailed Explanation:

• The fineness of moulding sand is a measure of the average size of the grains.

• The standard method for determining this, established by the American Foundrymen's Society (AFS), involves sieving a 50-gram sample of dried sand through a series of standard sieves with progressively smaller mesh sizes.

• The weight of sand retained on each sieve is measured.

• These weights are then used in a weighted average calculation to determine a single value known as the

Grain Fineness Number (GFN).

• The formula is: GFN = \( \Sigma (\text{Weight \% retained} \times \text{Multiplier}) / \Sigma (\text{Weight \% retained}) \).

• A high GFN indicates a fine-grained sand, while a low GFN indicates a coarse-grained sand. While related to sieve number and average grain diameter, the GFN is the specific, standardized index used in the foundry industry to express the overall grain size.

Step 3: Final Answer:
The standardized measure used in the foundry industry to express the grain size of moulding sand is the Grain Fineness Number (GFN).