Question

The resin mainly used in shell moulding is

• A. Phenol formaldehyde
• B. Ethanol formaldehyde
• C. Phenol
• D. Ethanol

Hint:

Shell moulding always uses a {thermosetting resin}, most commonly phenol formaldehyde.

Answer 1

The Correct Option is A

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.

Answer 2

Shell moulding needs a binder that can hold sand grains together as a rigid shell after brief contact with a hot metal pattern. Checking what each option chemically is settles which one can actually do that job.

1. Phenol formaldehyde: This is a true thermosetting resin, formed by the condensation of phenol and formaldehyde. When coated sand contacts the heated pattern (typically around \( 230\text{-}260^\circ\text{C} \)), the resin cures and cross-links within seconds, permanently binding the sand grains into a rigid shell. Its fast cure and high bond strength are exactly what shell moulding requires.
2. Ethanol formaldehyde: Ethanol does not undergo the same type of condensation polymerization with formaldehyde that produces a cross-linked thermosetting network, so this combination is not used as a foundry sand binder.
3. Phenol: Phenol by itself is just one of the two starting reactants. Without formaldehyde to react with, it cannot cross-link or cure into a rigid binder around sand grains.
4. Ethanol: Ethanol is a simple alcohol, commonly used only as a solvent or fuel. It has no ability to cross-link and bind sand grains together at all.

Only phenol formaldehyde is a genuine thermosetting resin capable of curing quickly under the pattern's heat to bind the sand into a strong shell.

Therefore, the correct answer is Phenol formaldehyde.