INDUSTRIAL HEATING AND WELDING
1. State the advantages of electric heating.
· Uniform heating
· Cheap furnace
2. What are the modes of heat transfer?
3. State Stephan’s law of radiation
In this process heat is transferred by means of heat waves governed by Stephan’s law
4. What are the properties of heating element material?
High specific resistance ---- free from oxidation
High melting point -----------small temp coefficient
5. Name the method of temp control in resistance oven.
· By varying the no. of elements
· Changing in connection
· External series resistance
· Changing transformer tappings
· Automatic control
6. How electric heating is classified?
· Resistance heating
· Induction heating
7. What are the applications of induction heating?
· Surface hardening
8. Mention few draw backs of core type furnace.
· Due to poor magnetic coupling, leakage reactance is high and power factor is low
· Low frequency supply is required
9. State the advantage of core less induction furnace
Time taken to reach the melting temp is less
There is no smoke and noise
10. What is induction heating?
Induction heating is a method of providing fast & consistent heating for manufacturing applications which involved bonding or changing properties of metlal for electrically conducting materials.
Todays advanced design concepts warrant most engineering components to be heated to either from different shapes or attain specific grain structures.
Microtech's range of induction heating systems are offered for custom built applications with suitable coils, materials handling solutions with complete automation
11. What are the classifications of power frequency method?
Direct resistance heating Indirect resistance heating Direct arc heating Indirect arc heating
12. What is meant by direct resistance heating?
In this method opf heating current is passed through the body to be heated.the resistance offered by the body to the flow of current produces ohmic loss which results in heating the body.
13. What is meant by indirect resistance heating?
In this method the current is produced through a high resistance wire known as heating element.the heat produced due to I^2*R loss in the element is transmitted by radiation or convection to the body to be heated.
14. What is the requirement of a good heating material?
· High specific resistance
· High melting point
· Free from oxidation
· Low temperature co efficient of resistance
15. What are the properties of steel?
1. Strength - the ability to withstand mechanical stress
2. Ductility - Ability to be formed without rupture
3. Hardness - Resistance to deformation, abrasion, cutting, crushing
4. Toughness - ability to absorb shock without breaking
16. What is annealing in heat treatment?
Annealing consists of heating the steel to or near the critical temperature (Temperature at which crystalline phase change occurs) to make it suitable for fabrication. Annealing is performed to soften steel after cold rolling, before surface coating and rolling, after drawing wired rod or cold drawing seamless tube. Stainless steels and high alloy steels generally require annealing because these steels are more resistant to rolling.
17. What is normalizing?
Normalizing consists of heating the steel above the critical temperature and cooling in air. This treatment refines the grain size and improves the uniformity of microstructure and properties of hot rolled steel. Normalizing is used in some plate mills, in the production of large forgings such as railroad wheels and axles, some bar products.
18. What is quenching?
Quenching consists of heating the steel above the critical point and holding at that temperature for enough time to change the crystalline structure. This heat is followed by quenching in a water or oil bath to bring the steel back through the critical temperature range without further changes to the microstructure. Quenching produces very hard, very brittle steel.
19. What is tempering?
Tempering is carried out by preheating previously quenched or normalized steel to a temperature below the critical range, holding, and then cooling to obtain the desired mechanical properties. Tempering is used to reduce the brittleness of quenched steel.Many products that require hardness and resistance to breakage are quenched and tempered.
20. What is dielectric heating?
The process of heating poor conductors of electricity (dielectrics) by- means of high-frequency electrical currents. The thermoplastic composite to be heated forms the dielectric of a condenser to which is applied a high-frequency (20-to-80 mc) voltage.The heat is developed within the material rather than being brought to it from the outside, and hence the material is heated more uniformly throughout.
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