EP0005838A1 - Four à induction à creuset - Google Patents

Four à induction à creuset Download PDF

Info

Publication number
EP0005838A1
EP0005838A1 EP79101680A EP79101680A EP0005838A1 EP 0005838 A1 EP0005838 A1 EP 0005838A1 EP 79101680 A EP79101680 A EP 79101680A EP 79101680 A EP79101680 A EP 79101680A EP 0005838 A1 EP0005838 A1 EP 0005838A1
Authority
EP
European Patent Office
Prior art keywords
electrode
coil
crucible
melt
inductor coil
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP79101680A
Other languages
German (de)
English (en)
Other versions
EP0005838B1 (fr
Inventor
Fritz Dipl.-Ing. Hegewaldt
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
BBC Brown Boveri AG Germany
Original Assignee
BBC Brown Boveri AG Germany
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by BBC Brown Boveri AG Germany filed Critical BBC Brown Boveri AG Germany
Priority to AT79101680T priority Critical patent/ATE120T1/de
Publication of EP0005838A1 publication Critical patent/EP0005838A1/fr
Application granted granted Critical
Publication of EP0005838B1 publication Critical patent/EP0005838B1/fr
Expired legal-status Critical Current

Links

Images

Classifications

    • 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
    • H05B6/22—Furnaces without an endless core
    • H05B6/24—Crucible furnaces
    • H05B6/28—Protective systems
    • 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
    • H05B6/22—Furnaces without an endless core
    • H05B6/24—Crucible furnaces

Definitions

  • the invention relates to an induction crucible furnace with a crucible made of refractory material, an inductor coil attached to the outside of the crucible and a spiral wound electrode inserted into the crucible wall for monitoring the crucible for melt penetrating through cracks.
  • the melt and the inductor coil which generates the alternating field that heats the melt, are separated only by a relatively thin-walled crucible made of oxidic refractory material.
  • the crucible wall thickness is made as thin as possible, since with increasing crucible wall thickness the electrical reactive power of the furnace increases significantly, which then has to be compensated for by larger capacitor banks.
  • the melt escaping through the crack can bridge the insulating space between two coil turns, which creates a short circuit. Larger currents then flow from one turn to the other, resulting in arcing, melting on the conductors, local destruction of the conductors and leakage of the cooling water flowing in the inductor coil. Apart from the danger that liquid metal and water then mix, the coil also becomes inoperable.
  • a known measure is that electrodes are used in the bottom of the refractory crucible, which produce an electrically conductive connection from the melt to the earth.
  • the power supply to the inductor coil is carried out potential-free by a transformer.
  • a measuring device which essentially contains a direct current source, a direct current measuring device and a choke, which acts as a barrier for the alternating voltage of the energy supply circuit of the inductor coil, the insulation resistance of the coil against earth and thus simultaneously against the melt is monitored. If melt penetrates to the coil through a crack in the crucible, the electrical resistance between the melt and the coil is greatly reduced, which is in the ammeter is recognized and triggers an alarm message and possibly also an automatic shutdown of the system to avoid the dangers mentioned above.
  • a disadvantage of this known system is the fact that the melt must have reached the coil before an indication is given.
  • a measurement of the reduction in the electrical resistance between the coil and the melt approaching in a crack, which seems to be possible per se, is practically not feasible because this elec.
  • trical resistance is still large compared to the leakage resistance between coil and earth caused by the water cooling of the coil.
  • the connection from the melt to the earth which is a prerequisite for this type of monitoring, can also become insecure under certain conditions.
  • a monitoring device which indicates that melt is escaping before an electrically conductive connection to the coil is established.
  • shield electrodes are used in the crucible wall, which cover the entire height of the inductor coil and are made of electrically conductive material. These electrodes are slotted in the axial direction to avoid short-circuit currents that would be induced by the electromagnetic field generated by the inductor coil. Now you monitor in the previously be. wrote the electrical resistance between the melt and this shield electrode, it is ready; an indication when the melt has reached this Elektror. This leaves more time to take countermeasures or to finish a melting process before the furnace has to be switched off. Because of the temperature conditions in the crucible wall, these electrodes must be installed close to the cold inductor.
  • an induction crucible furnace is known, in the crucible wall of which a bifilar, spiral winding made of resistance wire is wrapped.
  • the bifilar arrangement is intended to achieve an induction-free structure.
  • the penetrating melt destroys the insulation between the two wires or interrupts one of the two wires, this is recognized and displayed as a change in resistance in an evaluation circuit designed as a resistance bridge.
  • this version too, there is a risk of: electrical short circuit due to the high voltages between the monitoring electrode and the induction coil.
  • the present invention has for its object to provide an electrode for monitoring an induction crucible furnace, which covers the entire height of the inductor coil, but at no point assumes a potential difference compared to the inductor coil, which is more than about 20% of the coil voltage, so that the risk of Short circuit is reduced or eliminated.
  • This object is achieved in that the electrode is designed with the same pitch as the turns of the inductor coil.
  • the electrode according to the invention represents a precise image of the inductor coil, with only its diameter deviating slightly from the diameter of the coil. Because of this design, the electrode is linked with practically the same alternating magnetic fields as the inductor coil itself. In this way, practically the same voltage is induced at every point as in the coil. Since the magnetic field strength is essentially constant in the space between the coil and the melt, the ratio of the voltage induced in the electrode designed according to the invention to the voltage in the inductor coil depends on the distance between the electrode and the inductor coil and the melt and can therefore be determined by a suitable position can be controlled as desired.
  • the electrode is preferably arranged as close as possible to the inductor coil. The closer the electrode is to the inductor coil, the lower the voltage between the electrode and the coil and the thermal load on the electrode, and the less the insulation between the electrode and the coil is loaded. The distance between the electrode and the coil is practically only determined by how early a crack in the crucible wall should be detected.
  • the turns of the electrode are advantageously arranged at the same height as the turns of the inductor coil (15 in FIG. 2). This provides optimal protection against an unnoticed metallic connection between the melt and the inductor coil, which could lead to a dangerously high voltage potential.
  • the turns of the electrode are arranged at the level of the insulation spaces between two adjacent turns of the inductor coil (16 in FIG. 2). This results in an optimal protection against interturn turns due to escaping melt.
  • the electrode can consist of one or two individual wires spaced next to one another. If two adjacent individual wires are used, they are not connected to one another at their end facing away from the electronic monitoring device; they therefore do not form a current loop. In this case, the occurrence of an electrical short circuit between the two individual wires can be used to signal the passage of melt, so that an electrically conductive connection to the melt, e.g. via a bottom electrode, is not necessary.
  • the electrode must be arranged at a certain distance from the coil. Since the temperature rises rapidly with the distance from the coil to values which are above approximately 250 ° C., the electrode is preferably surrounded with inorganic insulation material, which in turn is surrounded by a closed tubular metal jacket. Such electrodes can be used up to temperatures of about 1000 ° C with appropriate material selection.
  • Fig. L shows schematically a cross section through an induction crucible furnace with a device for monitoring the penetration of melt through a crack according to the prior art.
  • the crucible 1 is made up of an inner layer 1.1, an outer layer 1.3 and an intermediate thin thermal insulation layer 1.2 made of asbestos.
  • an electrode 4 is inserted, which produces an electrically conductive connection from the melt 3 to the earth.
  • An inductor coil 2 is placed around the outside of the crucible 1. At the two ends of the inductor coil 2, the supply voltage is applied, which: by a rule baren three-phase transformer 8 is supplied.
  • the reactive power requirement of the furnace is compensated by a capacitor battery.
  • the LC combination 6, 7 serves to symmetrize the single-phase load of the coil compared to the three-phase Ne
  • a monitoring device 10 is used, consisting of a blocking choke 11, a DC voltage source 12 and a DC indicator 13. As soon as melt 3 hits the inductor coil 2 through a crack 9 in the crucible wall , the electrical resistance decreases, as a result of which the direct current measuring device 13 indicates a noticeable deflection.
  • the inductor coil 2 Due to the fact that the inductor coil 2 has to be constantly cooled by flowing water inside it, there is a constant current path from the inductor coil 2 to earth, which is represented by a resistor 14. For this reason, a small current constantly flows through the resistance measuring device 10. Resistance changes that are not significantly greater than the constant resistance 14 can therefore not be reliably detected by the resistance monitoring device 10.
  • FIG. 2 shows a section of a crucible wall, electrodes according to the invention being provided.
  • the inner crucible layer 1.1, the heat insulating layer 1.2 and the outer crucible layer 1.3 which, as usual, is designed as a ceramic spreading layer covering the inside of the coil.
  • the inductor coil 2 On the outer side of the crucible is the inductor coil 2, the conductors of which have an inner cavity 2.1 through which cooling water flows.
  • spirally wound electrodes 15 and 16 are arranged. Either only the electrode 15 or the electrode 16 or both can be used. The slope of these electrodes 15, 16 corresponds to the slope of the In Ductor coil 2.
  • One electrode 15 lies exactly in the middle between two neighboring windings of the inductor coil 2; Therefore, it is particularly suitable for the early Signalisier ist of advancing through a crack 9 melt, which could result in their further advance to a W-making domestic circuit.
  • the turns of the electrode 16 lie exactly at the level of the turns of the inductor coil 2; It is therefore particularly suitable for early warning of a connection between the molten pool and the coil, which can lead to a dangerous voltage between the melt and earth if the bottom electrode is not fully functional.
  • the distance between the melt and the electrode is denoted by d E
  • the distance between the melt and the inductor is denoted by d s . Since the field strength between the coil and the melt is essentially constant, the ratio of the voltage U E induced in the electrode 15, 16 to the voltage U s induced in the coil 2 is the same
  • the voltage at the electrode is also only about 10% less than the voltage of the coil. If there is a voltage of 3000 V on the coil, for example, then there is a maximum potential difference of 300 V between the coil and the electrode. It is easy to see that the risk of an electrical flashover between the coil and the electrode is thus considerably less than in the case of the Known electrodes, in which a potential difference of about 3000 V would occur between the coil and the electrode in the present example.
  • Fig. 3 shows a cross section through a high temperature resistant electrode.
  • the electrode is formed with two wires 17 running in parallel.
  • the two wires 17 are surrounded by inorganic insulating material 18, which in turn is surrounded by a closed tubular metal jacket 19.
  • inorganic insulating material 18 With a corresponding design of the outer jacket, such electrodes can be used up to temperature ranges of approximately 1000 ° C., for example also on the side of the insulation layer facing the weld pool. Since the potential differences between the electrode and the inductor coil remain small, the continuous metal jacket of the electrode does not have to be insulated separately from the spit. With this configuration of the electrode, the change in resistance can be monitored either between the melt and the electrode, or between the two electrode wires and the electrode jacket.
  • the electrode according to the invention can also be used to measure the moisture released when starting up a new crucible.
  • This moisture comes to the surface in the form of water vapor between the coil turns.
  • the steam condenses to water on the water-cooled coil conductors.
  • This water reduces the electrical creep resistance of the coil insulation, so that considerable creeping currents can occur between the turns when the nominal coil voltage is applied, to mica phenomena and to flashovers with subsequent turns.
  • the oven must therefore be operated with reduced voltage until the moisture is sufficiently reduced. In the absence of an objective measurement method, one has so far only relied on empirical values. Using the spiral electrode according to the invention, however, it can be concluded from the measured insulation resistance between the electrode and the coil or between two electrodes that the water content of the crucible wall.

Landscapes

  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Crucibles And Fluidized-Bed Furnaces (AREA)
  • General Induction Heating (AREA)
  • Furnace Details (AREA)
EP79101680A 1978-06-05 1979-05-31 Four à induction à creuset Expired EP0005838B1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AT79101680T ATE120T1 (de) 1978-06-05 1979-05-31 Induktionstiegelofen.

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE2824590 1978-06-05
DE19782824590 DE2824590A1 (de) 1978-06-05 1978-06-05 Induktionstiegelofen

Publications (2)

Publication Number Publication Date
EP0005838A1 true EP0005838A1 (fr) 1979-12-12
EP0005838B1 EP0005838B1 (fr) 1981-07-22

Family

ID=6041065

Family Applications (1)

Application Number Title Priority Date Filing Date
EP79101680A Expired EP0005838B1 (fr) 1978-06-05 1979-05-31 Four à induction à creuset

Country Status (4)

Country Link
EP (1) EP0005838B1 (fr)
JP (1) JPS5528488A (fr)
AT (1) ATE120T1 (fr)
DE (1) DE2824590A1 (fr)

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH0781785B2 (ja) * 1989-03-13 1995-09-06 富士電機株式会社 誘導加熱による金属溶湯炉
JP2722794B2 (ja) * 1990-08-01 1998-03-09 富士電機株式会社 低融点金属対策を施したるつぼ形誘導炉
JP3407749B2 (ja) * 1992-09-03 2003-05-19 富士電機株式会社 誘導炉の棚吊り保護装置
EP2715262B1 (fr) 2011-05-23 2015-11-25 Inductotherm Corp. Four à induction électrique doté d'un système de détection de l'usure du revêtement
US10598439B2 (en) 2011-05-23 2020-03-24 Inductotherm Corp. Electric induction furnace lining wear detection system

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR675969A (fr) * 1928-06-05 1930-02-17 Perfectionnements aux fours électriques à induction
FR741578A (fr) * 1933-02-14
FR836760A (fr) * 1937-10-06 1939-01-25 Swift Levick & Sons Ltd Four électrique à induction
DE742270C (de) * 1940-01-20 1943-11-26 Siemens Ag Verfahren zur Herstellung eines elektrischen kabelaehnlichen Heizkoerpers
DE1127034B (de) * 1959-05-29 1962-04-05 Bbc Brown Boveri & Cie Vorrichtung zur Signalisierung einsetzender und Verhuetung vollstaendiger Schmelztiegeldurchbrueche
FR1298096A (fr) * 1961-08-17 1962-07-06 Asea Ab Améliorations aux procédés pour indiquer les défauts dans les creusets des fours de fusion à induction
DE2005240B2 (de) * 1970-02-05 1971-08-05 Norddeutsche Affinerie, 2000 Hamburg Induktionstiegelofen mit ueberwachungseinrichtung fuer den tiegel

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR741578A (fr) * 1933-02-14
FR675969A (fr) * 1928-06-05 1930-02-17 Perfectionnements aux fours électriques à induction
FR836760A (fr) * 1937-10-06 1939-01-25 Swift Levick & Sons Ltd Four électrique à induction
DE742270C (de) * 1940-01-20 1943-11-26 Siemens Ag Verfahren zur Herstellung eines elektrischen kabelaehnlichen Heizkoerpers
DE1127034B (de) * 1959-05-29 1962-04-05 Bbc Brown Boveri & Cie Vorrichtung zur Signalisierung einsetzender und Verhuetung vollstaendiger Schmelztiegeldurchbrueche
FR1298096A (fr) * 1961-08-17 1962-07-06 Asea Ab Améliorations aux procédés pour indiquer les défauts dans les creusets des fours de fusion à induction
DE2005240B2 (de) * 1970-02-05 1971-08-05 Norddeutsche Affinerie, 2000 Hamburg Induktionstiegelofen mit ueberwachungseinrichtung fuer den tiegel

Also Published As

Publication number Publication date
ATE120T1 (de) 1981-08-15
EP0005838B1 (fr) 1981-07-22
DE2824590A1 (de) 1979-12-13
JPS5528488A (en) 1980-02-29

Similar Documents

Publication Publication Date Title
EP0519231A2 (fr) Installation d'avertissement pour un four de fusion à induction
DE2722475C2 (fr)
EP0005838B1 (fr) Four à induction à creuset
DE4329509A1 (de) Brückenbildungsschutzvorrichtung für Induktionsöfen
DE2333956B2 (de) Ofen zum Schmelzen oder Warmhalten von Metallen
DE102018217239B4 (de) Heizvorrichtung und Verfahren zur Temperaturerfassung an einer Heizvorrichtung
DE102018203609B4 (de) Verfahren und Vorrichtung zur Erfassung einer Temperatur an einem Heizelement
DE496462C (de) Elektrischer Induktionsofen zum Schmelzen oder zur Behandlung von Stoffen in Waerme
DE4322463A1 (de) Vorwarneinrichtung für Induktionsschmelzöfen
DE3811864C2 (fr)
EP0660644A2 (fr) Elément chauffant tubulaire avec protection de surcharge et détecteur de température
WO2017137193A1 (fr) Dispositif haute tension
DE19602249A1 (de) Vorwarneinrichtung für Induktionsschmelzöfen
DE828894C (de) Rinnenloser Induktionsschmelzofen mit gestampftem Tiegel
DE1220086B (de) Vorrichtung zur Anzeige beginnender und zur Verhuetung vollstaendiger Schmelztiegeldurchbrueche
EP0465688B1 (fr) Four de fusion de verre adapté en particulier à la vitrification de déchets
DE1208451B (de) Vorrichtung zur Signalisierung entstehender Schmelztiegeldurchbrueche bei Induktionschmelzoefen
DE1127034B (de) Vorrichtung zur Signalisierung einsetzender und Verhuetung vollstaendiger Schmelztiegeldurchbrueche
EP0103075B1 (fr) Manchon en matière plastique pour l'assemblage des éléments de conduit
DE1996595U (de) Schutzvorrichtung fuer elektrische spulen
DE19746872C2 (de) Heizelement und unter seiner Verwendung hergestellter Ofen
DE1092575B (de) Induktionsofen
DE338682C (de) Elektrischer Induktionsofen und Verfahren zu seinem Betriebe
DE1265444B (de) Elektrischer Niveauwaechter
DE60209462T2 (de) Düse für Druckgiessmaschine

Legal Events

Date Code Title Description
PUAI Public reference made under article 153(3) epc to a published international application that has entered the european phase

Free format text: ORIGINAL CODE: 0009012

AK Designated contracting states

Designated state(s): AT BE CH FR GB IT NL SE

17P Request for examination filed
ITF It: translation for a ep patent filed

Owner name: DE DOMINICIS & MAYER S.R.L.

GRAA (expected) grant

Free format text: ORIGINAL CODE: 0009210

AK Designated contracting states

Designated state(s): AT BE CH FR GB IT NL SE

REF Corresponds to:

Ref document number: 120

Country of ref document: AT

Date of ref document: 19810815

Kind code of ref document: T

PG25 Lapsed in a contracting state [announced via postgrant information from national office to epo]

Ref country code: CH

Effective date: 19820531

Ref country code: BE

Effective date: 19820531

Ref country code: AT

Effective date: 19820531

PG25 Lapsed in a contracting state [announced via postgrant information from national office to epo]

Ref country code: SE

Effective date: 19820601

PG25 Lapsed in a contracting state [announced via postgrant information from national office to epo]

Ref country code: NL

Effective date: 19821201

NLV4 Nl: lapsed or anulled due to non-payment of the annual fee

Free format text: CORRECTION TO A PAMPHLET

REG Reference to a national code

Ref country code: CH

Ref legal event code: PL

PG25 Lapsed in a contracting state [announced via postgrant information from national office to epo]

Ref country code: FR

Free format text: LAPSE BECAUSE OF NON-PAYMENT OF DUE FEES

Effective date: 19830331

REG Reference to a national code

Ref country code: FR

Ref legal event code: ST

GBPC Gb: european patent ceased through non-payment of renewal fee
PG25 Lapsed in a contracting state [announced via postgrant information from national office to epo]

Ref country code: GB

Effective date: 19881118

EUG Se: european patent has lapsed

Ref document number: 79101680.1

Effective date: 19850612

PLBE No opposition filed within time limit

Free format text: ORIGINAL CODE: 0009261

STAA Information on the status of an ep patent application or granted ep patent

Free format text: STATUS: NO OPPOSITION FILED WITHIN TIME LIMIT