Heating And Welding MCQ [Free PDF] – Objective Question Answer for Heating And Welding MCQ Quiz

Ques.71. If the temperature coefficient of silver is 0.0038, the temperature coefficient for Manganin may be expected to be

  1. 0.001
  2. 0.00002
  3. 0.0038
  4. 0.0001

Answer.2. 0.00002

Explanation:-

The temperature coefficient of silver is 0.0038 at 20°C so the temperature coefficient for manganin for 20°C  is .000002

 

Ques.72. Nichrome wire can be safely used for heating upto

  1. 2000 °C
  2. 1600 °C
  3. 1450 °C
  4. 1150 °C

Answer.4. 1150 °C

Explanation:-

Nichrome (NiCr, nickel-chrome, chrome-nickel, etc.) is any of various alloys of nickel, chromium, and often iron (and possibly other elements).

The Ni-Cr-based heating elements are typical metallic heating elements and are the most popular because they are inexpensive and easy to manufacture. Two types, one is composed of Ni 80% and Cr 20%, whereas the other is composed of Ni 60% and Cr 17% (plus Fe), are most widely used. The oxide film (Cr2O3) formed on the surface of the heating element functions as a protective film.

Heating elements made of Nichrome can be used for continuous operation at a temperature up to 1200oC.

 

Ques.73. If a furnace is to be heating to temperatures around 1500°C which of the following material for heating elements should be selected?

  1. Eureka
  2. Kanthal
  3. Platinium molybdenum carbon compound
  4. Nichrome

Answer.3. Platinium molybdenum carbon compound

Explanation:-

  • The melting point of Eureka is 1221 to 1300 °C
  • The melting point of Kanthal is 1,425 °C
  • The melting point of Nichrome is 1400 °C
  • Molybdenum compounds (about 14% of world production of the element) are used in high-pressure and high-temperature applications as pigments and catalysts. The melting point of platinum-molybdenum carbon compound is around 3000°C

 

Ques.74. Which of the following elements will have the least range of temperature?

  1. Eureka
  2. Nichrome
  3. Silicon carbide
  4. Kanthal

Answer.1. Eureka

Explanation:-

  • The melting point of Eureka is 1221 to 1300 °C
  • The melting point of Kanthal is 1,425 °C
  • The melting point of Nichrome is 1400 °C
  • The melting point of Silicon Carbide is 2,730 °C

Hence Eureka has the least range of temperature.

 

Ques.75. Which of the following device is necessarily required for automatic temperature control in a furnace?

  1. Thermocouple
  2. Thermostat
  3. Autotransformer
  4. Heating elements of variable resistance material

Answer.2. Thermostat

Explanation:-

For the heat treatment process to be in control it is essential that the furnace is in control. If a furnace is out of control the heat treatment process is bound to be out of control. It’s like driving a car that is out of control; you don’t know whether or not you will reach your destination safely. An example of the need for critical temperature control is the solution heat treatment of titanium alloys which is performed at a temperature only slightly below (50 -150 °F). If the temperature is exceeded, tensile properties, especially ductility, are reduced and cannot be fully restored by subsequent heat treatment.

The automatic controls used in an electric heating system are designed to ensure its safe and efficient operation. In a central heating system, the wall-mounted room thermostat is the control that governs the normal operation of the furnace. The operating principle is simple. The temperature selector on the thermostat is set for the desired temperature. When the temperature in the room falls below this setting, the thermostat will call for heat and cause the first heating circuit in the furnace to be turned on. There is generally a delay of about 15 seconds before the furnace blower starts. This prevents the blower from circulating cool air in the winter. After about 30 seconds, the second heating circuit is turned on. The other circuits are turned on one by one in the timed sequence.

Note:- A thermocouple is a device used to measure the temperature, a thermostat is a control device that measures the temperature (could be using a thermocouple to do that) and comparing the measured temperature with the required temperature (setpoint) and based on these data control a heating and/or cooling device.

 

Ques.76. Furnaces used for cremation use

  1. Resistance heating
  2. Induction heating
  3. Dielectric heating
  4. Arc heating

Answer.1. Resistance heating

Explanation:-

Cremation is the combustion, vaporization, and oxidation of human bodies to basic chemical compounds, such as gases, ashes, and minerals. Cremation reduces the body to its basic elements through a process that exposes it to open flames, intense heat, and evaporation. This is done in a specially designed furnace called a cremation chamber or retort.

Temperature up to 3000°C can be obtained in the furnace chamber hence direct resistance heating are preferred for cremation.

 

Ques.77. Induction heating is possible On

  1. On ferrous material only
  2. On magnetic material only
  3. On dc supply only
  4. On AC supply only

Answer.4. On AC supply only

Explanation:-

Induction heating is defined as the process of heating an electrically conducting object (usually a metal) by electromagnetic induction, through heat generated in the object by eddy currents.

Frequency is one of the most critical parameters in these applications. If the frequency is too low, an eddy current cancellation within the heated body will take place, resulting in poor coil efficiency.

However, when the frequency is too high, the skin effect will be highly pronounced, resulting in a current concentration in a very thin surface layer compared to the diameter/thickness of the heated component.

Since in DC current the frequency is Zero hence the induction heating is applicable for AC power supply only.

 

Ques.78. A piece of steel is to be heated to a predetermined temperature. In which of the following furnace it will attend the desired temperature in the shortest possible time?

  1. Oil fired furnace with the heat exchanger
  2. Electric resistance furnace
  3. Induction heating furnace
  4. Electric arc furnace

Answer.3. Induction heating furnace

Explanation:-

Induction heating is an extremely versatile heating method that can perform uniform surface hardening, localized surface hardening, through hardening and tempering of hardened pieces. Heating is accomplished by placing a steel part in the magnetic field generated by high-frequency alternating current passing through an inductor, usually a water-cooled copper coil. The depth of heating produced by induction is related to the frequency of the alternating current: the higher the frequency is, the thinner or more shallow the heating. Therefore, deeper case depths and even through hardening are produced by using lower frequencies. 

Induction hardening offers a number of advantages over other heat treatment methods. The most important advantages are short heat treatment times, good repeatability concerning the hardened-layer quality, small or negligible subsequent distortion, and a minimum subsequent product surface oxidation. 

 

Ques.79. In a domestic cake baking oven, the temperature is controlled by

  1. Series-parallel operation
  2. Autotransformer
  3. Thermostat
  4. Voltage variation

Answer.3. Thermostat

Explanation:-

Practically all ovens are now temperature-controlled; failing a built-in thermostat, use a small portable oven thermometer.

The thermostat used ovens where it controls the flow of electricity or gas to the oven’s burner. If the oven temperature rises above the desired value, the thermostat’s switch turns the burner off. When the oven temperature falls back below the desired value, the switch turns the burner back on. In this manner, the thermostat keeps the oven temperature within a narrow range.

Note:- A thermocouple is a device used to measure the temperature, a thermostat is a control device that measures the temperature (could be using a thermocouple to do that) and comparing the measured temperature with the required temperature (setpoint) and based on these data control a heating and/or cooling device.

 

Ques.80. If the supply frequency is reduced from 50 Hz to 1 Hz, which of the following method of heating will be least affected

  1. Resistance heating
  2. Dielectric heating
  3. Induction heating
  4. None of above

Answer.1. Resistance heating

Explanation:-

When the electric current is made to pass through a high-resistive body (or) substance, a power loss takes place in it, which results in the form of heat energy, i.e., resistance heating is passed upon the I2R effect. Since this heating process is purely resistive in nature i.e it does not have any capacitor or inductor part hence resistance heating method is free from frequency variation

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