Manufacturing Practices (BT-106) - Important Questions

Describe the complete sequence of operations in the sand casting process. Explain the different types of patterns used in sand casting and state the advantages and limitations of each type.

List the essential properties of molding sand required for good castings. Explain the purpose and procedure of two standard laboratory tests on molding sand such as permeability and compressive strength.

State and derive Chvorinov's rule for solidification time of a casting. Using Chvorinov's rule, calculate the solidification time for a cubic casting of side $L$ and a riser of spherical shape with the same volume. Use the relation $$t = C_{m} \left( \frac{V}{A} \right)^{2}$$ and clearly state any assumptions made.

Explain the modulus method of riser design. For a given cylindrical riser of diameter $D$ and height $H$, derive the expression for its modulus and explain how it is compared with the casting modulus to decide riser dimensions.

Explain the principles of gating system design in sand casting. Derive the relation between volumetric flow rate $Q$, the gating cross-sectional area $A$ and pouring velocity $v$, and discuss typical gating ratios used to ensure proper fill and minimize turbulence.

List and describe common casting defects such as sand blow, porosity, cold shuts, misruns, shrinkage cavities, and hot tears. For each defect give typical causes and practical remedies adopted in foundry practice.

Compare investment (lost-wax) casting and die casting in terms of process steps, materials, dimensional accuracy, surface finish, production rate and typical applications. State advantages and limitations of each process.

Explain centrifugal casting and continuous casting processes. Describe their working principles, applications, and advantages compared to conventional sand casting.

Describe core making in sand casting. Explain the purposes of core prints and the common materials and binders used for cores. List typical core defects and suggest remedies.

Explain different types of pattern allowances used in pattern making such as shrinkage allowance, machining allowance, draft allowance and shake allowance. Illustrate with numerical examples how total pattern dimensions are derived from final casting dimensions.

Define chills and feeders in casting practice. Explain internal and external chills, their purpose, and the effect of chills and feeders on the solidification pattern and prevention of shrinkage defects.

Explain the concept of directional solidification and how it is achieved in casting design. Discuss how solidification rate and cooling conditions influence dendrite formation and final microstructure in metal castings.