Electrical Heating 03-03

Electrical Heating -03-03

1. Mr. Vijay Balu Raskar -Electrical Engineer

2. CORE TYPE OF INDUCTION FURNACE
Mr. Vijay Balu Raskar -Electrical Engineer

3. DIRECT CORE TYPE INDUCTION FURNACE:-
Consists of a vertical furnace with a V shaped portion at the bottom.
Consists of a Transformer ±charge is magnetically coupled to the
primary windingandforms single-turnshort circuitedsecondary.
Secondary channel should not be emptied.
Magnetic coupling between primary & secondary is weakresulting in
large leakage reactance poor p.f
Leakage reactance is nullified using low frequency supply
Drawbacks.
1)Leakage reactance is high & p.fis low.
2)Low frequency requirement.
3) Suffersfrom PinchingEffect.
PinchingEffect= current, density above 500 A/cm2, flowing around the
melt interacts with the alternating field and produces force to squeeze
the melt ofa sectionandresults incomplete interruptionof current.
Use-preferablefor non-intermittent service, areobsolete these daysMr. Vijay Balu Raskar -Electrical Engineer

4. VERTICAL CORE TYPE INDUCTION FURNACE
Alsoknownas AJAX-WYATT FURNACE.
Verticalcrucible is usedfor the charge.
Bottom is usually V-shaped or U-shaped.
Molten metal is kept circulated round the V.
Pinch effect is counteracted by the weight of thecharge.
Capable of continuous operation.
Normal frequency can be used.
Use-melting & refining of non-ferrous metals .
Advantage-
Highlyefficient.
Lowoperatingcost.
Temperaturecontrolissimple.
Comparatively higher p.f
Mr. Vijay Balu Raskar -Electrical Engineer

5. INDIRECT CORE TYPE INDUCTION FURNACE
Charge is heated indirectly.
A metal container forms the secondary of the transformer.
Container is heated up by transformer action.
Temperature control isdone using different materials for the
detachable bar.
P.fiscomparatively poor(w.r.tdirect resistancefurnace,
approx-0.8)
Mr. Vijay Balu Raskar -Electrical Engineer

6. Vertical Core Type Ajax-Wyatt Furnace
Mr. Vijay Balu Raskar -Electrical Engineer

7. The limitation of core type induction furnace can be eliminated
by use of vertical type furnace called Ajax-wyattFurnace.
Construction :-
Mr. Vijay Balu Raskar -Electrical Engineer
The furnace is narrow V-shaped.
V –shaped tendency of the molten metal is to get itself accumulated at the bottom
and this helps at least a small amount of charge to be present for the secondary
circuit to be completed.
The probability of the discontinuity of the circuit is thus found to be less.
Pinch effects occurs in it.

8. OPERATION:-
The primary inductor coil is connected to the A.C.
Supply.
This causes an intense electromagnetic field to
fluctuate in the iron core.
The metal acts a short circuited secondary and carries
the induced currents.
Heat is mainly generated in the V shaped portion as it
has highest resistance due to small narrow section.
This heat is rapidly distributed to the metal with the
help of convection current and by electromagnetic
forces.
The heat ultimately results into melting of a charge.
Mr. Vijay BaluRaskar-Electrical Engineer

9. Verticalcrucible is usedfor the charge.
Bottom is usually V-shaped or U-shaped.
Molten metal is kept circulated round the V.
Pinch effect is counteracted by the weight of
thecharge.
Capable of continuous operation.
Normal frequency can be used.
Use-melting & refining of non-ferrous metals .
Advantage-
Highlyefficient.
Lowoperatingcost.
Temperaturecontrolissimple.
Comparatively higher p.fMr. Vijay Balu Raskar -Electrical Engineer

10. CORELESS TYPE INDUCTION FURNACE
Mr. Vijay Balu Raskar -Electrical Engineer

11. Coreless Type Consists of 3 parts
1) Primary coil 2) Ceramic crucible 3) Frame
*No iron core
*Primary coil is fed with ac supply
*Eddycurrent isinducedwithin thecharge
*Eddy current produces heating of the charge
*High frequency supply is to be used (flux density is
low)
*High frequency increases resistance due to skin effect
resulting
in high primary copper loss
*No magnetic core results in very lowp.f(between 0.1-
0.3)
*Static r is employed to improve p.f
Mr. Vijay Balu Raskar -Electrical Engineer

12. Use-
1)Steel production
2) Melting non-ferrous metals
3) Electronic industry
Advantages
Simple method to control
Semi skilled labor can handle
Fast operation
Required less space
Easy to maintain
Controllable by electrical clock or else
No oxidation
Can be used intermittently
Low cost / economical
Precise control of power
Low melting time
Mr. Vijay Balu Raskar -Electrical Engineer

13. Requirement of Good Electrode
Material
Mr. Vijay Balu Raskar -Electrical Engineer
Material Must have following properties:-
1)It should be good conductor of electricity.
2)It should have high resistance to thermal
shocks.
3)It should have sufficient mechanical
strength.
4)It should have low thermal conductivity.
5)It should be insoluble in the charge ,
chemically Inert and non-corrosive.

14. Low & Medium Temperature (up to1150°C)
Alloy of nickel & chromium
Ni= 80%, Cr= 20%
Alloy of nickel, chromium & iron Ni= 65%,
Cr=15%,Fe=20%
High Temperature (>1150 °C)
Silicon carbide
Molybdenum
Tungsten
Graphite
Mr. Vijay Balu Raskar -Electrical Engineer

15. ELECTRIC RESISTANCE FURNACE
These are insulated closed chambers with
a provision for ventilation
Heating elements may consists of circulars
wire or rectangular ribbons
Heating elements placed either on top or
sides of the oven
Charge is placed inside a heating chamber
Mr. Vijay Balu Raskar -Electrical Engineer

16. TEMPERATURECONTROL OF HEATING
FURNACE
TemperatureofFurnace depends upon–
Voltage (V)±can becontrolled by tapped
transformer.
Resistance (R)-can be controlled by switching in
various combinations of groups of resistance of
the furnace.
Time (t)-can be controlled by an on-off switch,
which determines the time for which the
furnace is connectedto supply or remain
isolated from the supply.
Mr. Vijay Balu Raskar -Electrical Engineer

17. LOSSES
Besidesraising thetemperature ofthe
Charge, heat energy is lost in following
operations:
-In raising the temperature of furnace
-In raising the temperature of the
container/carrier
-Heat conducted through wall
-Escapement of heat due to opening of
door
Mr. Vijay Balu Raskar -Electrical Engineer

18. Mr. Vijay Balu Raskar -Electrical Engineer