Heating and Welding

31. For intermittent work which of the following furnaces is suitable?

1. Indirect arc furnace
2. Core less furnace
3. Either of the above
4. None of the above

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32. Due to which of the following reasons it is desirable to have short arc length?

1. To achieve better heating
2. To increase the life of roof refractory
3. To have better stirring action
4. To reduce problem of oxidation
5. All of the above

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33. In the indirect resistance heating method, maximum heat-transfer takes place by

1. radiation
2. convection
3. conduction
4. any of the above

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34. Properly of low temperature co-eflficient of heating element is desired due to which of the following reasons?

1. To avoid initial rush of current
2. To avoid change in kW rating with temperature
3. Both (a) and (b)
4. Either (a) or (b)

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35. Which of the following methods is used to control temperature in resistance furnaces?

1. Variation of resistance
2. Variation of voltage
3. Periodical switching on and off of the supply
4. All of the above methods

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36. It is desirable to operate the arc furnaces at power factor of

1. zero
2. 0.707 lagging
3. unity
4. 0.707 leading

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37. Radiations from a black body are proportional to

1. T1
2. T2
3. T3
4. T*

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38. In arc furnace the function of choke is

1. to stabilize the arc
2. to imprpve, power factor
3. to reduce severity of the surge
4. none of the above

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39. Ajax Wyatt furnace is started when

1. it is filled below core level
2. it is filled above core level
3. it is fully empty
4. none of the above

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40. In electric press, mica is used because it is __________ conductor of heat but/and conductor of electricity.

1. bad, good
2. bad, bad
3. good, bad
4. good, good

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