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Electric Heating & Welding
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Page 1
Utilisation of Electrical Energy
UNIT 2
Electric Heating
INTRODUCTION
Heat plays a major role in everyday life. All heating requirements in domestic purposes
such as cooking, room heater, immersion water heaters, and electric toasters and also
in industrial purposes such as welding, melting of metals, tempering, hardening, and
drying can be met easily by electric heating, over the other forms of conventional
heating. Heat and electricity are interchangeable. Heat also can be produced by
passing the current through material to be heated. This is called electric heating; there
are various methods of heating a material but electric heating
is considered far superior compared to the heat produced by coal, oil, and natural gas.
ADVANTAGES OF ELECTRIC HEATING
The various advantages of electric heating over other the types of heating are:
(i) Economical
Electric heating equipment is cheaper; they do not require much skilled persons;
therefore, maintenance cost is less.
(ii) Cleanliness
Since dust and ash are completely eliminated in the electric heating, it keeps
surroundings cleanly.
(iii) Pollution free
As there are no flue gases in the electric heating, atmosphere around is pollution free;
no need of providing space for their exit.
(iv) Ease of control
Page 2
Utilisation of Electrical Energy
UNIT 2
Electric Heating
INTRODUCTION
Heat plays a major role in everyday life. All heating requirements in domestic purposes
such as cooking, room heater, immersion water heaters, and electric toasters and also
in industrial purposes such as welding, melting of metals, tempering, hardening, and
drying can be met easily by electric heating, over the other forms of conventional
heating. Heat and electricity are interchangeable. Heat also can be produced by
passing the current through material to be heated. This is called electric heating; there
are various methods of heating a material but electric heating
is considered far superior compared to the heat produced by coal, oil, and natural gas.
ADVANTAGES OF ELECTRIC HEATING
The various advantages of electric heating over other the types of heating are:
(i) Economical
Electric heating equipment is cheaper; they do not require much skilled persons;
therefore, maintenance cost is less.
(ii) Cleanliness
Since dust and ash are completely eliminated in the electric heating, it keeps
surroundings cleanly.
(iii) Pollution free
As there are no flue gases in the electric heating, atmosphere around is pollution free;
no need of providing space for their exit.
(iv) Ease of control
Utilisation of Electrical Energy
In this heating, temperature can be controlled and regulated accurately either manually
or automatically.
(v) Uniform heating
With electric heating, the substance can be heated uniformly, throughout whether it
may be conducting or non-conducting material.
(vi) High efficiency
In non-electric heating, only 40–60% of heat is utilized but in electric heating 75–100% of
heat can be successfully utilized. So, overall efficiency of electric heating is very high.
(vii) Automatic protection
Protection against over current and over heating can be provided by using fast
control devices. (viii) Heating of non-conducting materials
The heat developed in the non-conducting materials such as wood and porcelain is
possible only through the electric heating.
(ix) Better working conditions
No irritating noise is produced with electric heating and also radiating losses are low.
(x) Less floor area
Due to the compactness of electric furnace, floor area required is less.
(xi) High temperature
High temperature can be obtained by the electric heating except the ability of the
material to withstand the heat.
(xii) Safety
The electric heating is quite safe.
MODES OF TRANSFER OF HEAT
The transmission of the heat energy from one body to another because of the
temperature gradient takes place by any of the following methods:
1. conduction,
2. convection, or
3. radiation.
Conduction
In this mode, the heat transfers from one part of substance to another part without the movement in
the molecules of substance. The rate of the conduction of heat along the substance
Page 3
Utilisation of Electrical Energy
UNIT 2
Electric Heating
INTRODUCTION
Heat plays a major role in everyday life. All heating requirements in domestic purposes
such as cooking, room heater, immersion water heaters, and electric toasters and also
in industrial purposes such as welding, melting of metals, tempering, hardening, and
drying can be met easily by electric heating, over the other forms of conventional
heating. Heat and electricity are interchangeable. Heat also can be produced by
passing the current through material to be heated. This is called electric heating; there
are various methods of heating a material but electric heating
is considered far superior compared to the heat produced by coal, oil, and natural gas.
ADVANTAGES OF ELECTRIC HEATING
The various advantages of electric heating over other the types of heating are:
(i) Economical
Electric heating equipment is cheaper; they do not require much skilled persons;
therefore, maintenance cost is less.
(ii) Cleanliness
Since dust and ash are completely eliminated in the electric heating, it keeps
surroundings cleanly.
(iii) Pollution free
As there are no flue gases in the electric heating, atmosphere around is pollution free;
no need of providing space for their exit.
(iv) Ease of control
Utilisation of Electrical Energy
In this heating, temperature can be controlled and regulated accurately either manually
or automatically.
(v) Uniform heating
With electric heating, the substance can be heated uniformly, throughout whether it
may be conducting or non-conducting material.
(vi) High efficiency
In non-electric heating, only 40–60% of heat is utilized but in electric heating 75–100% of
heat can be successfully utilized. So, overall efficiency of electric heating is very high.
(vii) Automatic protection
Protection against over current and over heating can be provided by using fast
control devices. (viii) Heating of non-conducting materials
The heat developed in the non-conducting materials such as wood and porcelain is
possible only through the electric heating.
(ix) Better working conditions
No irritating noise is produced with electric heating and also radiating losses are low.
(x) Less floor area
Due to the compactness of electric furnace, floor area required is less.
(xi) High temperature
High temperature can be obtained by the electric heating except the ability of the
material to withstand the heat.
(xii) Safety
The electric heating is quite safe.
MODES OF TRANSFER OF HEAT
The transmission of the heat energy from one body to another because of the
temperature gradient takes place by any of the following methods:
1. conduction,
2. convection, or
3. radiation.
Conduction
In this mode, the heat transfers from one part of substance to another part without the movement in
the molecules of substance. The rate of the conduction of heat along the substance
Utilisation of Electrical Energy
depends upon the temperature gradient. The amount of heat passed through a cubic body with
two parallel faces with thickness ‘t’ meters, having the cross-sectional area of ‘A’ square
meters and the temperature of its two faces T1°C and T2°C, during ‘T’ hours is given by:
where k is the coefficient of the thermal conductivity for the material and it is measured
in MJ/m3/°C/hr.
Ex: Refractory heating, the heating of insulating materials, etc.
Convection
In this mode, the heat transfer takes place from one part to another part of substance
or fluid due to the actual motion of the molecules. The rate of conduction of heat
depends mainly on the difference in the fluid density at different temperatures. Ex:
Immersion water heater.
The mount of heat absorbed by the water from heater through convection depends
mainly upon the temperature of heating element and also depends partly on the
position of the heater. Heat dissipation is given by the following expression.
H = a (T1 – T2)b W/m2,
where ‘a’ and ‘b’ are the constants whose values are depend upon the heating surface and
T1and T2 are the temperatures of heating element and fluid in °C, respectively. Radiation In
this mode, the heat transfers from source to the substance to be heated without heating the
medium in between. It is dependent on surface.
Ex: Solar heaters.
The rate of heat dissipation through radiation is given by Stefan's Law.
where T1 is the temperature of the source in kelvin, T2 is the temperature of the
substance to be heated in kelvin, and k is the radiant efficiency:
= 1, for single element
= 0.5–0.8, for several elements
e = emissivity = 1, for black body
Page 4
Utilisation of Electrical Energy
UNIT 2
Electric Heating
INTRODUCTION
Heat plays a major role in everyday life. All heating requirements in domestic purposes
such as cooking, room heater, immersion water heaters, and electric toasters and also
in industrial purposes such as welding, melting of metals, tempering, hardening, and
drying can be met easily by electric heating, over the other forms of conventional
heating. Heat and electricity are interchangeable. Heat also can be produced by
passing the current through material to be heated. This is called electric heating; there
are various methods of heating a material but electric heating
is considered far superior compared to the heat produced by coal, oil, and natural gas.
ADVANTAGES OF ELECTRIC HEATING
The various advantages of electric heating over other the types of heating are:
(i) Economical
Electric heating equipment is cheaper; they do not require much skilled persons;
therefore, maintenance cost is less.
(ii) Cleanliness
Since dust and ash are completely eliminated in the electric heating, it keeps
surroundings cleanly.
(iii) Pollution free
As there are no flue gases in the electric heating, atmosphere around is pollution free;
no need of providing space for their exit.
(iv) Ease of control
Utilisation of Electrical Energy
In this heating, temperature can be controlled and regulated accurately either manually
or automatically.
(v) Uniform heating
With electric heating, the substance can be heated uniformly, throughout whether it
may be conducting or non-conducting material.
(vi) High efficiency
In non-electric heating, only 40–60% of heat is utilized but in electric heating 75–100% of
heat can be successfully utilized. So, overall efficiency of electric heating is very high.
(vii) Automatic protection
Protection against over current and over heating can be provided by using fast
control devices. (viii) Heating of non-conducting materials
The heat developed in the non-conducting materials such as wood and porcelain is
possible only through the electric heating.
(ix) Better working conditions
No irritating noise is produced with electric heating and also radiating losses are low.
(x) Less floor area
Due to the compactness of electric furnace, floor area required is less.
(xi) High temperature
High temperature can be obtained by the electric heating except the ability of the
material to withstand the heat.
(xii) Safety
The electric heating is quite safe.
MODES OF TRANSFER OF HEAT
The transmission of the heat energy from one body to another because of the
temperature gradient takes place by any of the following methods:
1. conduction,
2. convection, or
3. radiation.
Conduction
In this mode, the heat transfers from one part of substance to another part without the movement in
the molecules of substance. The rate of the conduction of heat along the substance
Utilisation of Electrical Energy
depends upon the temperature gradient. The amount of heat passed through a cubic body with
two parallel faces with thickness ‘t’ meters, having the cross-sectional area of ‘A’ square
meters and the temperature of its two faces T1°C and T2°C, during ‘T’ hours is given by:
where k is the coefficient of the thermal conductivity for the material and it is measured
in MJ/m3/°C/hr.
Ex: Refractory heating, the heating of insulating materials, etc.
Convection
In this mode, the heat transfer takes place from one part to another part of substance
or fluid due to the actual motion of the molecules. The rate of conduction of heat
depends mainly on the difference in the fluid density at different temperatures. Ex:
Immersion water heater.
The mount of heat absorbed by the water from heater through convection depends
mainly upon the temperature of heating element and also depends partly on the
position of the heater. Heat dissipation is given by the following expression.
H = a (T1 – T2)b W/m2,
where ‘a’ and ‘b’ are the constants whose values are depend upon the heating surface and
T1and T2 are the temperatures of heating element and fluid in °C, respectively. Radiation In
this mode, the heat transfers from source to the substance to be heated without heating the
medium in between. It is dependent on surface.
Ex: Solar heaters.
The rate of heat dissipation through radiation is given by Stefan's Law.
where T1 is the temperature of the source in kelvin, T2 is the temperature of the
substance to be heated in kelvin, and k is the radiant efficiency:
= 1, for single element
= 0.5–0.8, for several elements
e = emissivity = 1, for black body
Utilisation of Electrical Energy
= 0.9, for resistance heating element.
From Equation (4.1), the radiant heat is proportional to the difference of fourth power
of the temperature, so it is very efficient heating at high temperature.
ESSENTIAL REQUIREMENTS OF GOOD HEATING ELEMENT The
materials used for heating element should have the following properties:
o High-specific resistance
Material should have high-specific resistance so that small length of wire may be
required to provide given amount of heat.
o High-melting point
It should have high-melting point so that it can withstand for high temperature, a small increase
in temperature will not destroy the element.
o Low temperature coefficient of resistance
From Equation (4.1), the radiant heat is proportional to fourth powers of the
temperatures, it is very efficient heating at high temperature. For accurate temperature
control, the variation of resistance with the operating temperature should be very low.
This can be obtained only if the material has low temperature coefficient of resistance
o Free from oxidation
The element material should not be oxidized when it is subjected to high temperatures;
otherwise the formation of oxidized layers will shorten its life.
o High-mechanical strength
The material should have high-mechanical strength and should withstand for
mechanical vibrations.
o Non-corrosive
The element should not corrode when exposed to atmosphere or any other chemical fumes.
o Economical
The cost of material should not be so high.
MATERIAL FOR HEATING ELEMENTS
The selection of a material for heating element is depending upon the service conditions such
as maximum operating temperature and the amount of charge to be heated, but no single
element will not satisfy all the requirements of the heating elements. The materials normally
used as heating elements are either alloys of nickel–chromium, nickel–chromium–iron, nickel–
Page 5
Utilisation of Electrical Energy
UNIT 2
Electric Heating
INTRODUCTION
Heat plays a major role in everyday life. All heating requirements in domestic purposes
such as cooking, room heater, immersion water heaters, and electric toasters and also
in industrial purposes such as welding, melting of metals, tempering, hardening, and
drying can be met easily by electric heating, over the other forms of conventional
heating. Heat and electricity are interchangeable. Heat also can be produced by
passing the current through material to be heated. This is called electric heating; there
are various methods of heating a material but electric heating
is considered far superior compared to the heat produced by coal, oil, and natural gas.
ADVANTAGES OF ELECTRIC HEATING
The various advantages of electric heating over other the types of heating are:
(i) Economical
Electric heating equipment is cheaper; they do not require much skilled persons;
therefore, maintenance cost is less.
(ii) Cleanliness
Since dust and ash are completely eliminated in the electric heating, it keeps
surroundings cleanly.
(iii) Pollution free
As there are no flue gases in the electric heating, atmosphere around is pollution free;
no need of providing space for their exit.
(iv) Ease of control
Utilisation of Electrical Energy
In this heating, temperature can be controlled and regulated accurately either manually
or automatically.
(v) Uniform heating
With electric heating, the substance can be heated uniformly, throughout whether it
may be conducting or non-conducting material.
(vi) High efficiency
In non-electric heating, only 40–60% of heat is utilized but in electric heating 75–100% of
heat can be successfully utilized. So, overall efficiency of electric heating is very high.
(vii) Automatic protection
Protection against over current and over heating can be provided by using fast
control devices. (viii) Heating of non-conducting materials
The heat developed in the non-conducting materials such as wood and porcelain is
possible only through the electric heating.
(ix) Better working conditions
No irritating noise is produced with electric heating and also radiating losses are low.
(x) Less floor area
Due to the compactness of electric furnace, floor area required is less.
(xi) High temperature
High temperature can be obtained by the electric heating except the ability of the
material to withstand the heat.
(xii) Safety
The electric heating is quite safe.
MODES OF TRANSFER OF HEAT
The transmission of the heat energy from one body to another because of the
temperature gradient takes place by any of the following methods:
1. conduction,
2. convection, or
3. radiation.
Conduction
In this mode, the heat transfers from one part of substance to another part without the movement in
the molecules of substance. The rate of the conduction of heat along the substance
Utilisation of Electrical Energy
depends upon the temperature gradient. The amount of heat passed through a cubic body with
two parallel faces with thickness ‘t’ meters, having the cross-sectional area of ‘A’ square
meters and the temperature of its two faces T1°C and T2°C, during ‘T’ hours is given by:
where k is the coefficient of the thermal conductivity for the material and it is measured
in MJ/m3/°C/hr.
Ex: Refractory heating, the heating of insulating materials, etc.
Convection
In this mode, the heat transfer takes place from one part to another part of substance
or fluid due to the actual motion of the molecules. The rate of conduction of heat
depends mainly on the difference in the fluid density at different temperatures. Ex:
Immersion water heater.
The mount of heat absorbed by the water from heater through convection depends
mainly upon the temperature of heating element and also depends partly on the
position of the heater. Heat dissipation is given by the following expression.
H = a (T1 – T2)b W/m2,
where ‘a’ and ‘b’ are the constants whose values are depend upon the heating surface and
T1and T2 are the temperatures of heating element and fluid in °C, respectively. Radiation In
this mode, the heat transfers from source to the substance to be heated without heating the
medium in between. It is dependent on surface.
Ex: Solar heaters.
The rate of heat dissipation through radiation is given by Stefan's Law.
where T1 is the temperature of the source in kelvin, T2 is the temperature of the
substance to be heated in kelvin, and k is the radiant efficiency:
= 1, for single element
= 0.5–0.8, for several elements
e = emissivity = 1, for black body
Utilisation of Electrical Energy
= 0.9, for resistance heating element.
From Equation (4.1), the radiant heat is proportional to the difference of fourth power
of the temperature, so it is very efficient heating at high temperature.
ESSENTIAL REQUIREMENTS OF GOOD HEATING ELEMENT The
materials used for heating element should have the following properties:
o High-specific resistance
Material should have high-specific resistance so that small length of wire may be
required to provide given amount of heat.
o High-melting point
It should have high-melting point so that it can withstand for high temperature, a small increase
in temperature will not destroy the element.
o Low temperature coefficient of resistance
From Equation (4.1), the radiant heat is proportional to fourth powers of the
temperatures, it is very efficient heating at high temperature. For accurate temperature
control, the variation of resistance with the operating temperature should be very low.
This can be obtained only if the material has low temperature coefficient of resistance
o Free from oxidation
The element material should not be oxidized when it is subjected to high temperatures;
otherwise the formation of oxidized layers will shorten its life.
o High-mechanical strength
The material should have high-mechanical strength and should withstand for
mechanical vibrations.
o Non-corrosive
The element should not corrode when exposed to atmosphere or any other chemical fumes.
o Economical
The cost of material should not be so high.
MATERIAL FOR HEATING ELEMENTS
The selection of a material for heating element is depending upon the service conditions such
as maximum operating temperature and the amount of charge to be heated, but no single
element will not satisfy all the requirements of the heating elements. The materials normally
used as heating elements are either alloys of nickel–chromium, nickel–chromium–iron, nickel–
Utilisation of Electrical Energy
chromium–aluminum, or nickel–copper. Nickel–chromium–iron alloy is cheaper when
compared to simple nickel–chromium alloy. The use of iron in the alloy reduces the
cost of final product but, reduces the life of the alloy, as it gets oxidized soon. We have
different types of alloys for heating elements. Table 4.1 gives the relevant properties of
some of the commercial heating elements.
Table : Properties of some heating elements
The properties of some commercial heating element materials commonly employed for low
and medium temperatures up to 1,200°C are Ni–Cr and an alloy of Ni–Cr–Fe composition
of these alloys are given in Table 4.1. For operating temperatures above 1,200°C, the
heating elements are made up of silicon carbide, molebdenum, tungsten, and graphite.
(Ni–Cu alloy is frequently used for heating elements operating at low temperatures. Its
most important property is that it has virtually zero resistance and temperature coefficient.)
CAUSES OF FAILURE OF HEATING ELEMENTS
Heating element may fail due to any one of the following reasons.
1. Formation of hot spots.
2. Oxidation of the element and intermittency of operation.
3. Embrittlement caused by gain growth.
4. Contamination and corrosion.
Formation of hotspots
Read MoreFAQs on Electric Heating & Welding
| 1. What's the difference between electric heating and resistance heating in welding applications? |  |
Ans. Electric heating and resistance heating are closely related but distinct. Resistance heating uses electrical current flowing through a conductor to generate heat via Joule's law (H = I²Rt), while electric heating is a broader term encompassing all methods using electricity to produce thermal energy. In welding, resistance heating is the primary electric heating method, where high current passes through the workpiece and electrode contact to create concentrated heat for fusion.
| 2. How does Joule heating work in electric arc welding? | |
Ans. Joule heating in arc welding occurs when high-intensity electric current flows across the gap between electrode and workpiece, generating extreme temperatures exceeding 3000°C. The formula H = I²Rt shows that heat depends on current squared, resistance, and duration. This intense heat melts both the electrode material and base metal, allowing them to fuse together when cooled, creating a strong joint.
| 3. Why is current the most important factor in electric heating and welding efficiency? | |
Ans. Current is crucial because heat generation follows the relationship H = I²Rt, meaning heat increases with the square of current. Doubling the current quadruples the heat output. This makes current the primary control variable in welding and industrial heating processes. Higher current allows faster heating and deeper penetration, directly affecting weld quality and efficiency.
| 4. What are the main types of electric welding processes used in SSC JE exams? | |
Ans. Key electric welding processes include arc welding, resistance spot welding, seam welding, and butt welding. Arc welding uses an electrical arc between electrode and workpiece; resistance welding relies on Joule heat at contact points; seam welding creates continuous joints; butt welding joins end-to-end surfaces. Each process varies in application, heat distribution, and equipment requirements for different industrial purposes.
| 5. How do you calculate heat generated in resistance welding applications? | |
Ans. Heat generated (H) in resistance welding is calculated using H = I²Rt, where I is current in amperes, R is resistance in ohms, and t is time in seconds. This Joule's law formula determines energy converted to heat. For effective welding, practitioners adjust current and contact time to achieve optimal heat without damaging surrounding material or creating weak joints.
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