HEATING AND WELDING
1. State the advantages of electric heating.
2. What are the modes of heat transfer?
3. State Stephan’s law of radiation
this process heat is transferred by means of heat waves governed by Stephan’s
4. What are the properties of heating element
specific resistance ---- free from oxidation
melting point -----------small temp coefficient
5. Name the method of temp control in resistance
varying the no. of elements
External series resistance
Changing transformer tappings
6. How electric heating is classified?
7. What are the applications of
· Surface hardening
8. Mention few draw backs of core
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
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.
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
What are the classifications of power frequency
Direct resistance heating Indirect resistance
heating Direct arc heating Indirect arc heating
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.
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
What is the requirement of a good heating
temperature co efficient of resistance
What are the properties of steel?
- the ability to withstand mechanical stress
- Ability to be formed without rupture
- Resistance to deformation, abrasion, cutting, crushing
Toughness - ability to absorb shock without breaking
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.
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.
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
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.