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Electrical Heating 03-03
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Electrical Heating 03-03

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Electrical Heating 03-03

Electrical Heating 03-03

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  • 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 theprimary winding and forms single-turn short circuited secondary.Secondary channel should not be emptied.Magnetic coupling between primary & secondary is weak resulting inlarge leakage reactance poor p.fLeakage reactance is nullified using low frequency supplyDrawbacks.1)Leakage reactance is high & p.f is low.2)Low frequency requirement.3) Suffers from Pinching Effect.Pinching Effect = current, density above 500 A/cm2, flowing around themelt interacts with the alternating field and produces force to squeezethe melt of a section and results in complete interruption of current.Use-preferable for non-intermittent service, are obsolete these days Mr. Vijay Balu Raskar - Electrical Engineer
  • 4. VERTICAL CORE TYPE INDUCTION FURNACEAlso known as AJAX-WYATT FURNACE.Vertical crucible is used for 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 the charge.Capable of continuous operation.Normal frequency can be used.Use-melting & refining of non-ferrous metals .Advantage-Highly efficient.Low operating cost.Temperature control is simple.Comparatively higher p.f Balu Raskar - Electrical Engineer Mr. Vijay
  • 5. INDIRECT CORE TYPE INDUCTION FURNACECharge is heated indirectly. A metal container forms the secondary of the transformer.Container is heated up by transformer action.Temperature control is done using different materials for thedetachable bar.P.f is comparatively poor (w.r.t direct resistance furnace,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 eliminatedby use of vertical type furnace called Ajax-wyatt Furnace.Construction :-The furnace is narrow V-shaped.V – shaped tendency of the molten metal is to get itself accumulated at the bottomand this helps at least a small amount of charge to be present for the secondarycircuit to be completed.The probability of the discontinuity of the circuit is thus found to be less.Pinch effects occurs in it. Mr. Vijay Balu Raskar - Electrical Engineer
  • 8. OPERATION:-The primary inductor coil is connected to the A.C.Supply.This causes an intense electromagnetic field tofluctuate in the iron core.The metal acts a short circuited secondary and carriesthe induced currents.Heat is mainly generated in the V shaped portion as ithas highest resistance due to small narrow section.This heat is rapidly distributed to the metal with thehelp of convection current and by electromagneticforces.The heat ultimately results into melting of a charge. Mr. Vijay Balu Raskar - Electrical Engineer
  • 9. Vertical crucible is used for 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 ofthe charge.Capable of continuous operation.Normal frequency can be used.Use-melting & refining of non-ferrous metals .Advantage-Highly efficient.Low operating cost.Temperature control is simple.Comparatively higher p.f Mr. Vijay Balu Raskar - Electrical Engineer
  • 10. CORELESS TYPE INDUCTION FURNACE Mr. Vijay Balu Raskar - Electrical Engineer
  • 11. Coreless Type Consists of 3 parts1) Primary coil 2) Ceramic crucible 3) Frame*No iron core*Primary coil is fed with ac supply*Eddy current is induced within the charge*Eddy current produces heating of the charge*High frequency supply is to be used (flux density islow)*High frequency increases resistance due to skin effectresulting in high primary copper loss*No magnetic core results in very low p.f (between 0.1-0.3)*Static r is employed to improve p.f Mr. Vijay Balu Raskar - Electrical Engineer
  • 12. Use-1) Steel production2) Melting non-ferrous metals3) Electronic industry AdvantagesSimple method to controlSemi skilled labor can handleFast operationRequired less spaceEasy to maintainControllable by electrical clock or elseNo oxidationCan be used intermittentlyLow cost / economicalPrecise control of powerLow melting time Mr. Vijay Balu Raskar - Electrical Engineer
  • 13. Requirement of Good Electrode MaterialMaterial 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. Mr. Vijay Balu Raskar - Electrical Engineer
  • 14. Low & Medium Temperature (up to1150°C) Alloy of nickel & chromiumNi= 80%, Cr= 20%Alloy of nickel, chromium & iron Ni= 65%,Cr=15%,Fe=20%High Temperature (>1150 °C)Silicon carbideMolybdenumTungstenGraphite Mr. Vijay Balu Raskar - Electrical Engineer
  • 15. ELECTRIC RESISTANCE FURNACEThese are insulated closed chambers with a provision for ventilationHeating elements may consists of circulars wire or rectangular ribbonsHeating elements placed either on top or sides of the ovenCharge is placed inside a heating chamber Mr. Vijay Balu Raskar - Electrical Engineer
  • 16. TEMPERATURE CONTROL OF HEATINGFURNACETemperature of Furnace depends upon–Voltage (V) ±can be controlled by tappedtransformer.Resistance (R)-can be controlled by switching invarious combinations of groups of resistance ofthe furnace.Time (t)-can be controlled by an on-off switch,which determines the time for which thefurnace is connected to supply or remainisolated from the supply. Mr. Vijay Balu Raskar - Electrical Engineer
  • 17. LOSSESBesides raising the temperature of theCharge, heat energy is lost in followingoperations:- 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