Foundry Metallurgy

Step 1: Understanding shell moulding process.
Shell moulding is an advanced sand casting process in which a thin shell is formed around a heated metal pattern using sand mixed with a thermosetting resin. The resin binds the sand grains together to form a strong shell.
Step 2: Role of resin in shell moulding.
The resin used must have good bonding strength, thermal stability, and should harden quickly when heated. Phenol formaldehyde resin fulfills all these requirements and is therefore widely used.
Step 3: Analysis of other options.
(B) Ethanol formaldehyde: Not used as a binding resin in shell moulding.
(C) Phenol: Phenol alone is not a resin and cannot act as a binder.
(D) Ethanol: Ethanol is a solvent, not a resin.
Step 4: Conclusion.
Hence, phenol formaldehyde resin is mainly used in shell moulding.

Step 1: Understanding precision investment casting.
Precision investment casting, also known as lost wax casting, involves coating a wax pattern with a refractory slurry to form a ceramic shell. This slurry must provide strength and thermal resistance.
Step 2: Composition of slurry.
The slurry typically consists of fine refractory materials mixed with binders. Ethyl silicate and sodium silicate are commonly used binders because they provide good bonding and strength to the ceramic shell.
Step 3: Eliminating other options.
(A) Zinc stearate: Used as a lubricant or release agent, not as slurry material.
(B) Stearic acid: Used in wax patterns, not in ceramic slurry.
(D) Neither Ethyl nor Sodium silicate: Incorrect, as silicates are essential binders.
Step 4: Conclusion.
Therefore, the slurry used in precision investment casting is made up of both ethyl silicate and sodium silicate.