Quiz: Mechanical Engineering 18th May

Quiz: Mechanical Engineering
Exam: DFCCIL
Topic: Welding Process

Each question carries 2 mark
Negative marking: 1/3 mark
Time: 10 Minutes

Q1. How are the metals to be welded connected to each other in spot welding?
(a) Electric contact
(b) Magnetic field
(c) Mechanical pressure
(d) Direct contact

Q2. Consider the following welding processes:
1. TIG welding
2. Submerged arc welding
3. Electro-slag welding
4. Thermit welding
Which of these welding processes are used for welding thick pieces of metal?
(a) 1,2 and 3
(b) 1,2 and 4
(c) 1,3 and 4
(d) 2,3 and 4

Q3. Which one of the following processes consists of smaller Heat Affected Zone(HAZ)?
(a) Arc welding
(b) Electron beam welding
(c) MIG welding
(d) Thermit welding

Q4. Welding of aluminium is normally difficult due to which one of the following reasons?
(a) Low melting temperature of aluminium
(b) Formation of oxide film
(c) Chances of cracking
(d) formation of carbide film

Q5. Which effect is not seen in alloys on weldability?
(a) Control of ductile-malleable transformation temperature
(b) Provision for oxidation to molten metal
(c) Reduction in segregation
(d) Grain refinement

Q6. Oxy-acetylene process is most suited for which of the following process of joining?
(a) Metal wires
(b) Metal sheets
(c) Metal tubes
(d) Metal bars

Q7. In arc welding process, the high-quality alternator functions at what frequency?
(a) 250 Hz
(b) 300 Hz
(c) 350 Hz
(d) 400 Hz

Q8. Which type of electrode is designed for melting quickly?
(a) Fast fill
(b) Fast freeze
(c) Quick fill
(d) Fill freeze

Q9. In an iron thermit, how many moles of aluminium reacts with three moles of iron oxide to give nine moles of iron?
(a) 6
(b) 7
(c) 8
(d) 9

Q10. What is the magnitude of temperature produced in a thermit reaction?
(a) 2500°C
(b) 3000°C
(c) 3500°C
(d) 4000°C

Solutions

S1. Ans.(c)
Sol. In spot welding process, the metal or the alloy parts which are to be welded, are heated in their in their zones. To bring these parts in contact with one another, mechanical pressure is applied, causing them to connect.

S2. Ans.(d)
Sol. TIG welding is most commonly used to weld thin sections of stainless steel and non-ferrous metals such as aluminium, magnesium and copper alloys.

S3. Ans.(b)
Sol. Electron beam welding has the smallest Heat Affected zone (HAZ).

S4. Ans.(b)
Sol. Welding of aluminium is considered to be slightly difficult than the steel due to high thermal and electrical conductivity, high thermal expansion coefficient, refractory aluminium oxide formation tendency and low stiffness

S5. Ans.(b)
Sol. On weldability, there are some effects seen in the alloying elements. Some of them are Control of ductile-malleable transformation temperature, Reduction in segregation, Grain refinement and provision for deoxidation to the molten metal

S6. Ans.(b)
Sol. Oxy-acetylene process is most suited for the joining of metal sheets or for joining metal plates which are having a thickness of 2mm to 50mm. While joining, the molten metal flows together to form a continuous joint.

S7. Ans.(d)
Sol. In an arc welding process, there are alternators used for producing high current and function at lower frequency, and there are alternators which are of high quality and work at high frequency. The functioning frequency of these alternators is 400 Hz.

S8. Ans.(a)
Sol. Electrodes which are classified into three types, fast fill, fast freeze and fill freeze. Among these, the fast fill electrodes are considered to be able to operate at extremely high welding speeds, and hence fast fill electrodes are designed for quick melting.

S9. Ans.(c)
Sol. The thermit process, which is used for welding depends on the chemical reaction between oxide of iron and aluminium metal. According to this reaction, when 8 moles of aluminium reacts with 3 moles of iron oxide, then, 4 moles of aluminium oxide and 9 moles of iron is formed.

S10. Ans.(b)
Sol. Thermit welding is called as fusion welding. A superheated melt operates in this type of melt. The heat that is produced has the temperature approximately twice than that of the melting point of steel, which is about 3000°C.

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