According to me Answer is ( D)
Because here shrinkage values
Brass is 15mm/m
Aluminum is 13mm/m
Cast iron is 10mm/m
Plain carbon steel is 20mm/m.
the highest value is plain carbon steel....
Shrinkage allowance
1.Bismith :Negligible
2.white metal:5mm/m
3.cast iron : 10mm/m
4: Aluminum:13mm/m
5: Brass: 15mm/m
6.copper: 17mm/m
7:steels: 20mm/m
8. Lead &zinc :23mm/m

Shrinkage Allowance in Casting Patterns

In the process of casting, a pattern is used to create a mold into which molten metal is poured. As the metal cools and solidifies, it undergoes shrinkage, resulting in a reduction in size. To compensate for this shrinkage, a pattern is made slightly larger than the desired final dimensions of the casting. This is known as the shrinkage allowance.

Explanation of the Answer

The correct answer is option 'A', which states that brass requires the largest shrinkage allowance while making a pattern for casting. This means that when casting with brass, the pattern must be made significantly larger than the final desired dimensions of the casting to account for the shrinkage that occurs during solidification.

Reasoning

The shrinkage allowance required for a specific material depends on its properties, particularly its coefficient of thermal expansion and solidification shrinkage. Brass has a relatively high coefficient of thermal expansion compared to other materials such as aluminum, cast iron, and plain carbon steel. This means that brass tends to expand and contract more significantly with changes in temperature.

When molten brass is poured into a mold, it undergoes solidification and cools down. During this process, the metal contracts and shrinks in volume, resulting in a reduction in size. Due to the higher coefficient of thermal expansion, brass experiences a greater amount of shrinkage compared to other materials.

To compensate for this significant shrinkage, a larger shrinkage allowance is required when making the pattern for casting with brass. This ensures that the final casting will have the desired dimensions after the shrinkage has occurred.

In contrast, materials like aluminum, cast iron, and plain carbon steel have lower coefficients of thermal expansion, which means they undergo less shrinkage during solidification. Therefore, the shrinkage allowance required for these materials is relatively smaller compared to brass.

Conclusion

In summary, brass requires the largest shrinkage allowance while making a pattern for casting. This is due to its higher coefficient of thermal expansion, which results in significant shrinkage during solidification. By providing a larger pattern, the shrinkage can be compensated for, resulting in a final casting with the desired dimensions.