US3021413A - High-frequency furnace for inductive heating - Google Patents

High-frequency furnace for inductive heating Download PDF

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Publication number
US3021413A
US3021413A US860424A US86042459A US3021413A US 3021413 A US3021413 A US 3021413A US 860424 A US860424 A US 860424A US 86042459 A US86042459 A US 86042459A US 3021413 A US3021413 A US 3021413A
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US
United States
Prior art keywords
coil
circuit
heating
coupling
frequency furnace
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Expired - Lifetime
Application number
US860424A
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English (en)
Inventor
Blok Lourens
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US Philips Corp
North American Philips Co Inc
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US Philips Corp
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    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B6/00—Heating by electric, magnetic or electromagnetic fields
    • H05B6/02—Induction heating
    • H05B6/04—Sources of current

Definitions

  • load matching the coil of this tuned circuit is variably coupled with a coupling coil which is connected in the load circuit and is provided with terminals for connection to a heating coil.
  • variable coupling between the circuit coil and the coupling coil can be designed in various ways, for example by arranging the circuit coil and the coupling coil so as be-dis'placeable relatively to one another, by the use of a movable ferromagnetic or copper coil, and the like.
  • the oscillator valve is matchedto the load circuit by adjustment of the variable coupling between the circuitcoil and the coupling coil, the load circuit usually having a low resistance and being pro* vided with a heating coil having a small number of turns, so that the inductance of this heating coil lies between,
  • Such high-frequency furnaces can be used with advantage for various applications, in particular for high-frequency heating with very is also provided with terminals for connection of a second 1 heating coil, which terminals are includedin the tuned anode circuit of the oscillator valve in series with the circuit coil, and with-an interconnection device associated with the connecting terminals of the two heating coils so that in one positionof the interconnection device the first heating coil is connected to the'coupling coil and the terminals for connecting the second heating coil to the tuned anode circuit are short-circuited, while in asecond position of the interconnection device the second heating coil is connected in series with the circuit coil of the tuned anode circuit of the oscillator valve, the terminals for connecting the first heating coil to the coupling coil being short-circuited.
  • the interconnection device can be designed in various manners, for example as interconnecting strips, switches I and the like.
  • the inductance of the heating coil can be'inc'reased, for example, from 1 .h. to 40 h.
  • FIG. 1 shows a high-frequency furnace in accordance with the invention
  • FIG. 2 shows another embodiment of a high-frequency I furnace in accordance with the invention.
  • FIG. 3 is a furtherdevelopment of the high-frequency furnace of FIGS. 1 and 2.
  • FIG. 1 shows a high-frequency furnace for inductive heating in accordance with the invention, which has a rated power of, say, 25 kw.
  • the high-frequency energy required for heating is taken from a thermionic valve oscillator comprising a triode 1.
  • the anode circuit of the valve oscillator which is designedas a Colpitts circuit, contains a resonant circuit 2 which determines the oscillator frequency and comprises a circuit coil 3, 3' shunted by two series-connected circuit capacitors 4 and 4'.
  • One end of the circuit 2 is connected, through a blocking capacitor 5, to the anode and the otherend, through a grid capacitor 6, to the control grid of the triode 1, a leakage resistor 7 being connected, in series witha choke coil 8, to the earthed cathode of the triode 1.
  • the junction point of the capacitors 4, 4 is connected to earth by a connecting lead, while the supply voltage for the anode of the triode 1 is taken through a choke 9 from a direct-voltage source 10.
  • the current produced in the resonant circuit 2 by oscillating of the circuit arrangement is used for heating a workpiece 14 arranged in a heating coil 13, and for this purpose the circuit 2 is inductively coupled to a coupling coil 11 having terminals 12 for connection to the heating coil 13.
  • the load circuit is a low-resistance circuit in i which a heating coil 13 is used comprising a single turn and having an inductance of approximately 0.6,uh.
  • the circuit coil 3, 3' and the coupling coil 11 are coupled to one another variably with the use of a copper coil core 15, which can be displaced in the axialdirection of the circuit coil 3, 3 so that the transformation ratio can be varied, for example, from 11:1 to 6:1, Due to transformation of the circuit current a very large heating current of, for example, approximately 1200 amps flows in the load circuit of thehigh-frequency furnace with a resulting very high energy density in the heating coil 13, which may be used to advantage for the progressive hardening of steel shafts.
  • the high-frequency furnace described is provided with terminals 17 for connection of a second heating coil 16, which is connected in the resonant circuit 2 in series with the circuit coil 3, 3,'and also with an interconnection device associated with the connecting terminals 12 andl7 of the coupling coil 11 and circuit coil 3, 3, respectively, the first heating coil 13 being connected to a coupling coil 11, and the connecting terminals for the second heating coil 16 being short-circuited in the first position of the connection device, whereas in a'second position of the interconnection device the second heating coil 16 is connected in series with the circuit coil 3, 3' of the circuit 2 of triode 1 and the connecting terminals 12 of coupling coil 11 are short-circuited.
  • the second heating coil 16 has,,for example, 12 turns, its inductance being about 151.011. I
  • the interconnection device comprises two switches 18 and 19 and in the first position of the interconnection device the switch 18 connectsthe second position of the interconnection device the switch 19 connects the heating coil 16 in series with the circuit coil 3, 3 and the switch 13 short-circuits the connecting terminals 12 of the coupling coil 11 through an interconnection '21.
  • the two switches 13 and 19 may be mechanically coupled together.
  • the high-frequency furnace shown has an extended field of application in that it is also suit able for high-frequency heating through a high-resistance load circuit.
  • the high-resistance load circuit of the highfrequency furnace consists of the second heating coil 16, which for this purpose is connected in series with the circuit coil 3, 3' by means of the switch 19, the coupling coil 11 being short-circuited through the interconnection 21.
  • variable coupling of the circuit coil 3, 3' to the coupling coil 11 is set to a suitable value by means of a copper coil core which is displaceable in the axial direction of the circuit coil, for, when the coupling of the circuit coil 3, 3 to the coupling coil 11, which is short circuited through the interconnection 21, is varied, the inductance of the resonant circuit 2 varies so that the power delivered to the high-resistance load circuit can be adjusted to a maximum value, while in particular the circuit inductance together with the second heating coil 16 forms an auto-transformer, the transformation ratio of which can be varied between 10:6 and 1012.5.
  • the high-frequency furnace shown can also be used for high-frequency heating by means of a high-resistance load circuit and this is of advantage, for example, for high frequency heating through a long connecting lead to the heating coil 16, for in this manner a decrease in efiiciency owing to the long connecting lead is materially reduced, since the heating current flowing through heating coil 16 of the high-resistance load circuit is a fraction of the heating current in heating coil 13 of the low-resistance load circuit, for example, approximately 200 amps.
  • the high-frequency furnace described can be adapted at will to high-frequency heating through a lowresistance load circuit and to high-frequency heating through a high-resistance load circuit, the load matching being controlled in the same manner in both cases by variation of the coupling of the circuit coil to the coupling coil 11.
  • the high-frequency furnace combines simplicity in construction and operation with a considerable expansion of the field of application so that it is highly suitable for use in practice.
  • the circuit coil is divided in two parts 3, 3 and the terminals 17 of this coil are arranged between the two coil parts 3 and 3', while these coil parts 3 and 3' are in the same ratio to one another as the reactances of the circuit capacitors 4- and 4', so that always some point of the second heating coil 16 is at earth potential.
  • circuit capacitors 4 and 4 and hence the coil parts 3 and 3' also are equal to one another, while furthermore, in order to adjust the grid excitation to its optimum value, there is connected in parallel with the series combination of the grid resistance 7 and the choke 8 a capacitor 22, which together with the grid capacitor 6 forms a capacitive voltage divider,
  • circuit coil 3, 3' and of the coupling coil 11 hold for the drawn out condition of the coil core 15.
  • FIG. 2 shows an alternative embodiment of a device according to the invention, which can be used to advantage in a high-frequency furnace with a rated power of 6 kw. Similar elements are designed by like reference numerals.
  • the circuit coil 3, 3' and the associated circuit capacitors 4, 4' are arranged in fixed relationship to one another and united to form an integral structure 23 which, to vary the coupling between the circuit coil 3, 3 and the coupling coil 11, is adapted to be displaced relatively to the stationary coupling coil 11 of the load circuit.
  • supply leads 24, 25, 26 connecting this integral structure 23 to the valve oscillator are designed flexible.
  • the circuit coil 3,3 is designed as a cylindrical winding and axially displaceable by displacement of the integral structure 23 relative to the insulated coupling coil 11, which encloses the circuit coil 3, 3' and consists of a cylindrically bent broad copper band.
  • the structure 23 is displaceable through a distance equal to the length of the circuit coil 3, 3, and the length of the coupling coil 11 is adapted to this length.
  • the high-frequency furnace can be used for high-frequency heating through a low-resistance load circuit and for high-frequency heating through a highresistance load circuit, and in the first case the coupling coil 11 is connected to the first heating coil 13 and the terminals 17 of the circuit coil 3, 3 are short-circuited through the interconnection 26, while in the second case the second heating coil 16 is connected in series with the circuit coil 3, 3' and the terminals 12 of the coupling coil 11 are short-circuited through the interconnection 21.
  • the operation is entirely similar to that of the high-frequency furnace described with reference to FIG. 1
  • FIG. 3 shows a further development of the high-frequency furnace in accordance with the invention.
  • each of the circuit coil parts 3 and 3 which are included in the anode circuit of the oscillator valve, is provided with second coupling coils 27 and 28, respectively, the output terminals of the coupling coils 27, 28 being designated by 29, 30 and 31, 32, respectively.
  • Each of the circuit coil parts 3 and 3 together with the associated coupling coils 27, 28, respectively, can be designed as a separate coil set, and this if of particular advantage from the point of view of manufacturing technology.
  • this construction enables the coupling coils 27 and 28 to be connected, atwill, either in series or in parallel by means of interconnecting strips; thus, for parallel connection the output terminals 29, 31 and 30, 32 are connected together through interconnecting strips 33 and 34 and the output terminals 29, 30 are connected to the first heating coil 13, while for series connection the output terminals 30, 31 are connected together through an interconnecting strip 35 shown as a broken line and the output terminals 29, 32 are connected to the first heating coil 13.
  • This step provides the important advantage that the matching control range for the low-resistance load circuit can be appreciably extended and, in particular, the transformation ratio can be increased by a factor of two by with the circuit coil means and thefirst switch shortcircuits the first heating coil to the coupling coil means.
  • the interconnection device of FIGS. 1, 2, and 3 enables not only the first heating coil 13 to be connected to the coupling coil but also the second heating coil 16 to be connected to the tuned anode circuit 2.
  • a high frequency furnace for induction workpieces comprising an electron discharge device having an output electrode, oscillatory circuit means coupled to said output electrode, said oscillatory circuit means comprising a circuit coil means and capacitance means, coupling coil means in inductive coupling relationship with said circuit coil means, means to vary said inductive coupling relationship, first load circuit means having a low resistance load impedance, said first load circuit means comprising a first heating coil, second load circuit means heating of having a high-resistance load impedance, said second load a circuit means having a second heating coil, and an interconnection device having first switchingmeans to couple said first heating coil to said coupling coil means toprovide said induction heating for work-pieces associated with said first load circuit, and second switching means to short circuit said coupling coil means and couple said second heating coil to said circuit coil means for said inductive 3.
  • a high-frequency furnace as claimed in claim 1 wherein the inductance of the. first heating coil lies between 0.02nh. and Lab. and the inductance of the'second heating coil lies between
  • a high frequency furnace as claimed in claim 6 comprising further means to connect said first coupling coil in parallel with said second coupling coil.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • General Induction Heating (AREA)
US860424A 1958-12-22 1959-12-18 High-frequency furnace for inductive heating Expired - Lifetime US3021413A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
NL234527 1958-12-22

Publications (1)

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US3021413A true US3021413A (en) 1962-02-13

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US860424A Expired - Lifetime US3021413A (en) 1958-12-22 1959-12-18 High-frequency furnace for inductive heating

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US (1) US3021413A (it)
DE (1) DE1136033B (it)
FR (1) FR1245149A (it)
GB (1) GB930376A (it)
NL (2) NL102015C (it)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3637970A (en) * 1970-07-06 1972-01-25 Ronald J Cunningham Induction heating apparatus
US3740516A (en) * 1972-01-10 1973-06-19 Park Ohio Industries Inc Radio frequency transformer for induction heating installation
US5824998A (en) * 1995-12-20 1998-10-20 Pulsar Welding Ltd. Joining or welding of metal objects by a pulsed magnetic force
US20130259181A1 (en) * 2012-04-02 2013-10-03 Commissariat A L'energie Atomique Et Aux Energies Alternatives Device for Generating a High Temperature Gradient in a Nuclear Fuel Sample
CN104517657A (zh) * 2013-10-03 2015-04-15 原子能和能源替代品委员会 用于在样品中产生高温度梯度的包含光学监测装置的设备

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3651301A (en) * 1968-05-12 1972-03-21 Ncr Co Installation for casting microwire in glass insulation
AT348017B (de) * 1974-03-20 1979-01-25 Siemens Ag Selbsterregter hochfrequenzgenerator
DE29819251U1 (de) * 1998-10-29 2000-02-24 KUKA Schweissanlagen GmbH, 86165 Augsburg Wechselstromgenerator mit einer Röhrenanordnung

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2321189A (en) * 1942-12-26 1943-06-08 Induction Heating Corp Induction heating apparatus
US2452365A (en) * 1944-03-01 1948-10-26 Gen Electric Control system
US2593959A (en) * 1949-03-01 1952-04-22 Westinghouse Electric Corp Dielectric heating unit
US2662162A (en) * 1951-01-12 1953-12-08 Hartford Nat Bank & Trust Co High-frequency furnace

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE898503C (de) * 1942-12-04 1953-11-30 Deutsche Edelstahlwerke Ag Schaltung fuer elektroinduktive Heizeinrichtungen
US2551756A (en) * 1944-07-21 1951-05-08 Mittelmann Eugene High-frequency heating method and apparatus

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2321189A (en) * 1942-12-26 1943-06-08 Induction Heating Corp Induction heating apparatus
US2452365A (en) * 1944-03-01 1948-10-26 Gen Electric Control system
US2593959A (en) * 1949-03-01 1952-04-22 Westinghouse Electric Corp Dielectric heating unit
US2662162A (en) * 1951-01-12 1953-12-08 Hartford Nat Bank & Trust Co High-frequency furnace

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3637970A (en) * 1970-07-06 1972-01-25 Ronald J Cunningham Induction heating apparatus
US3740516A (en) * 1972-01-10 1973-06-19 Park Ohio Industries Inc Radio frequency transformer for induction heating installation
US5824998A (en) * 1995-12-20 1998-10-20 Pulsar Welding Ltd. Joining or welding of metal objects by a pulsed magnetic force
US20130259181A1 (en) * 2012-04-02 2013-10-03 Commissariat A L'energie Atomique Et Aux Energies Alternatives Device for Generating a High Temperature Gradient in a Nuclear Fuel Sample
CN104517657A (zh) * 2013-10-03 2015-04-15 原子能和能源替代品委员会 用于在样品中产生高温度梯度的包含光学监测装置的设备

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Publication number Publication date
GB930376A (en) 1963-07-03
DE1136033B (de) 1962-09-06
NL102015C (it)
FR1245149A (fr) 1960-11-04
NL234527A (it)

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