This set of Casting, Forming and Welding Multiple Choice Questions & Answers (MCQs) focuses on “Gas Welding”.
1. Which of the following types of fuel gas is commonly used in gas welding?
a) Biogas
b) Coal gas
c) Acetylene
d) Methane
View Answer
Explanation: Gas welding is usually referred as oxy welding or oxy-fuel welding which is a process of joining metallic materials by application of heat produced by the gas flame. In gas welding, acetylene is commonly used as fuel gas which mixed with proper proportion of oxygen in a mixing chamber of welding torch. Gas welding can produce a hot flame of temperature about 3000-3500 ⁰C.
2. In gas welding, the joint can be made even much stronger than the original.
a) True
b) False
View Answer
Explanation: In gas welding, various metals like cast iron, steel, aluminium, copper etc. can be used for joining operation. First they brought into a molten state and then a fusion is taking place between two pieces of metal in such a way that the point of fusion closely approaches the strength of the metal fused. In this process, the union or joint can be made even much stronger than the original.
3. Acetylene is a hydrocarbon which molecule is made up of two carbon atoms and four hydrogen atoms.
a) True
b) False
View Answer
Explanation: In gas welding, acetylene is used as a fuel gas which is a hydrocarbon like other as propane, methane etc. However, it generally differs from those hydrocarbons in a manner that its molecule is made up of two carbon atoms and two hydrogen atoms. And the carbon atoms are joined with hydrogen atoms by making a triple bond.
4. Acetylene is a blue color gas which mixed with oxygen to produce a hot flame.
a) True
b) False
View Answer
Explanation: In gas welding, acetylene is basically a colorless gas with a very distinctive odour and highly combustible when it is mixed with oxygen. Acetylene gas is formed by mixing the calcium carbide with water and then it is composed, which forms a compound of carbon and hydrogen having the chemical formula C2H2.
5. Gas welding is mainly suited for welding of thin sheets, small diameter pipes and tubes.
a) True
b) False
View Answer
Explanation: Gas welding process is mainly suited for the welding of a thin sheet, tubes, and small diameter pipe because it cannot provide very high temperature as compared to that provided by the electric arc welding. This method of joining is also used for repairing work, maintenance and in body shops.
6. Acetylene is a non-toxic gas which can be kept or stored in a cylinder at any pressure.
a) True
b) False
View Answer
Explanation: In gas welding, acetylene is used as a fuel gas which produces hot flame when it is mixed with oxygen. Acetylene may be non-toxic gas, but if it is stored in a cylinder at more than the pressure of 2 bar, then the acetylene becomes self explosive, that’s why the pressure of stored acetylene should be maintained with great care.
7. Single stage gas regulator cannot be used in cold weather for regulating the acetylene or oxygen gas.
a) True
b) False
View Answer
Explanation: Single stage converter is used to reduce the pressure from the cylinder pressure to the welding pressure, which can take place in a single stage. However, it tends to freeze in cold weather. This is because an abrupt expansion and resulting drop in initial pressure makes rapid cooling of the gas and may cause ice formation in the presence of moisture.
8. In gas welding, the hoses are mainly used for making the connection between gas torch and regulators.
a) True
b) False
View Answer
Explanation: In gas welding, the hoses are mainly used for making connections between the gas torch and the regulators, which should be made strong, light and flexible enough to make torch movements smooth. In general, welding hose can be of two types that are twin welding hose and double welding hose.
9. A flashback is a condition in gas welding, when the pure methane gas is used as fuel gas instead of acetylene.
a) True
b) False
View Answer
Explanation: In gas welding, a flashback is a condition in which the flame burns inside the gas torch. Flashback is generally caused by improper mixing of gases, which further increases the rate of flame propagation to high extent that the flame goes back to the mixing chamber. If it is not stopped, the flame may burn the mixture and may travel back into the cylinder.
10. A welding torch is mainly used for mixing and burning the gases in the desired proportions.
a) True
b) False
View Answer
Explanation: In gas welding, a welding torch is mainly used for mixing oxygen and acetylene in the desired proportions. It is also used for burning the mixture at the end of the tip, and also provides a mean for moving and directing the flame front. Welding torch can be of high pressure type or low pressure type.
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