Question

Limitations of thermit welding is

• A. applicable only to ferrous metal parts of heavy sections
• B. heat necessary for welding is obtained from a chemical reaction
• C. No flux or separate shielding gas is used
• D. as the energy input is in a narrow concentrated beam, distortion is almost eliminated

Hint:

Remember Thermit welding for its niche application: welding huge steel parts like railway tracks. This specific, narrow application is its key limitation.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Thermit welding is a chemical welding process that uses an exothermic reaction to produce molten metal for the weld. The question asks to identify a limitation of this process, not a feature.

Step 2: Detailed Explanation:
Let's analyze the options:

• (A) applicable only to ferrous metal parts of heavy sections: This is a significant limitation. The standard thermit reaction (\( \text{Fe}_2\text{O}_3 + 2\text{Al} \rightarrow 2\text{Fe} + \text{Al}_2\text{O}_3 \)) is designed to produce molten steel. The process generates a massive amount of superheated metal and heat, making it suitable only for joining very large and thick sections (like railroad tracks, large shafts). It cannot be controlled easily for thin sections and is not typically used for non-ferrous metals. Therefore, its narrow range of application is a limitation.

• (B) heat necessary for welding is obtained from a chemical reaction: This is a description of how the process works, a feature, not a limitation.

• (C) No flux or separate shielding gas is used: The molten aluminum oxide (slag) produced in the reaction is lighter and floats to the top, forming a protective layer over the weld. This is an advantage of the process, not a limitation.

• (D) as the energy input is in a narrow concentrated beam, distortion is almost eliminated: This statement is false. The energy input in thermit welding is massive and widespread, not a narrow beam (that would describe electron beam or laser welding). Consequently, distortion can be a significant issue.
Thus, the primary limitation among the choices is its restricted applicability.

Step 3: Final Answer:
The main limitation of thermit welding is that it is primarily applicable only to the joining of heavy sections of ferrous metals.