EP0468203A1 - Device for protection of electrical heated vacuum furnace - Google Patents

Device for protection of electrical heated vacuum furnace Download PDF

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Publication number
EP0468203A1
EP0468203A1 EP91110222A EP91110222A EP0468203A1 EP 0468203 A1 EP0468203 A1 EP 0468203A1 EP 91110222 A EP91110222 A EP 91110222A EP 91110222 A EP91110222 A EP 91110222A EP 0468203 A1 EP0468203 A1 EP 0468203A1
Authority
EP
European Patent Office
Prior art keywords
auxiliary electrode
surrounded
thermocouple
insulation
bushings
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.)
Withdrawn
Application number
EP91110222A
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German (de)
French (fr)
Inventor
Robert Dr. Hack
Wilhelm Polhede
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.)
Pfeiffer Vacuum GmbH
Original Assignee
Arthur Pfeiffer Vakuumtechnik Wetzlar GmbH
Balzers Pfeiffer GmbH
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 Arthur Pfeiffer Vakuumtechnik Wetzlar GmbH, Balzers Pfeiffer GmbH filed Critical Arthur Pfeiffer Vakuumtechnik Wetzlar GmbH
Publication of EP0468203A1 publication Critical patent/EP0468203A1/en
Withdrawn legal-status Critical Current

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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
    • H05B3/00—Ohmic-resistance heating
    • H05B3/62—Heating elements specially adapted for furnaces
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS, OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
    • F27D11/00—Arrangement of elements for electric heating in or on furnaces
    • F27D11/02—Ohmic resistance heating
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS, OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
    • F27D21/00—Arrangements of monitoring devices; Arrangements of safety devices
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS, OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
    • F27D21/00—Arrangements of monitoring devices; Arrangements of safety devices
    • F27D2021/0057—Security or safety devices, e.g. for protection against heat, noise, pollution or too much duress; Ergonomic aspects
    • F27D2021/0071—Security or safety devices, e.g. for protection against heat, noise, pollution or too much duress; Ergonomic aspects against explosions

Definitions

  • the invention relates to a device for protecting electrically heated vacuum furnaces according to the preamble of the first claim.
  • Heat treatment furnaces in which the heater is located within the vacuum chamber, are provided with special electrical feedthroughs which serve to transmit current to the heating elements in the vacuum chamber.
  • These bushings must meet high requirements, which are caused by extreme operating conditions, e.g. high currents, high temperatures, tightness, vacuum suitability and resistance to high pressure (e.g. with pressure sintering furnaces).
  • the invention has for its object to develop a device with which it is possible to detect a gas discharge within an electrically heated vacuum furnace in order to use it to take the appropriate measures, such as Switching off the heating power to derive to protect the system.
  • an auxiliary electrode is attached to the insulation of the current leadthrough.
  • This must be electrically insulated and can, for example, take the form of a spiral, a wire mesh or a sheet metal tube.
  • a gas discharge between the current feedthrough and the boiler wall thus leads to an easily detectable short circuit between the auxiliary electrode and the boiler wall, which can be detected with commercially available intrinsically safe resistance measuring devices and processed into a switching signal, as a result of which the arc is also switched off by switching off the heating power.
  • thermocouple is wound around the ceramic insulation of the current feedthrough. If the thermocouple is blown by the arc, either the measuring circuit is opened at this point, or a new connection is created between the two thermocouple legs, which emits a large amount of EMF at the new welding bead at the moment it occurs.
  • thermocouples Both events, open measuring circuit or high temperature, can be reliably detected by commercially available, intrinsically safe threshold switchgear for thermocouples, so that when the alarm is triggered by the measuring device, the heating power can be switched off immediately, which also extinguishes the arc.
  • the use of a metal-clad thermocouple is recommended.
  • a flange 2 On the boiler wall 1 of a vacuum furnace, a flange 2 is attached, which is provided with the electrical feedthrough 3, hereinafter also referred to as the electrode.
  • This can consist of copper or graphite, for example. A construction from a combination of several materials is also possible.
  • the electrode conducts the electrical current to heating elements 4 within the vacuum chamber 5. It is surrounded by an insulation 6, which consists for example of ceramic.
  • An auxiliary electrode 7 is attached around this isolaton, which in the example shown has the shape of a spiral.
  • thermocouple 7 the insulation 6 can also be surrounded by a thermocouple 7.
  • the representation is the same in the illustration.
  • the auxiliary electrode or the thermocouple is electrically isolated led out of the boiler room and connected to the shutdown electronics 9.

Landscapes

  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Waste-Gas Treatment And Other Accessory Devices For Furnaces (AREA)
  • Furnace Details (AREA)
  • Control Of Resistance Heating (AREA)
  • Muffle Furnaces And Rotary Kilns (AREA)

Abstract

Ein elektrisch beheizter Vakuumofen ist mit speziellen Durchführungen (3) zur Übertragung von Strom zu Heizelementen (4) versehen. Um Gasentladungen, welche zwischen einer Durchführung und der Kesselwand (1) stattfinden können, zu erkennen, ist die Isolation (6) der Durchführung von einer Hilfselektrode (7) umgeben. Anstelle einer Hilfselektrode kann auch ein Thermoelement verwendet werden. <IMAGE>An electrically heated vacuum furnace is provided with special bushings (3) for the transmission of electricity to heating elements (4). In order to detect gas discharges that can take place between a bushing and the boiler wall (1), the insulation (6) of the bushing is surrounded by an auxiliary electrode (7). A thermocouple can also be used instead of an auxiliary electrode. <IMAGE>

Description

Die Erfindung betrifft eine Einrichtung zum Schutz elektrisch beheizter Vakuumöfen nach dem Oberbegriff des ersten Patentanspruches.The invention relates to a device for protecting electrically heated vacuum furnaces according to the preamble of the first claim.

Wärmebehandlungsöfen, bei welchen sich die Heizung innerhalb der Vakuumkammer befindet, sind mit speziellen elektrischen Durchführungen versehen, die der Übertragung von Strom zu den Heizelementen in der Vakuumkammer dienen. Diese Durchführungen müssen hohen Anforderungen genügen, welche durch extreme Betriebsbedingungen, wie z.B. hohe Ströme, hohe Temperaturen, Dichtheit, Vakuumtauglichkeit und Beständigkeit gegen hohen Druck (z.B. bei Drucksinteröfen), bedingt sind.Heat treatment furnaces, in which the heater is located within the vacuum chamber, are provided with special electrical feedthroughs which serve to transmit current to the heating elements in the vacuum chamber. These bushings must meet high requirements, which are caused by extreme operating conditions, e.g. high currents, high temperatures, tightness, vacuum suitability and resistance to high pressure (e.g. with pressure sintering furnaces).

Durch mechanische Unregelmäßigkeiten, wie z.B. Schäden in der Isolationskeramik und Verschmutzung im Stutzendurchgang oder durch Überspannung, kann es in oder in der Nähe einer solchen Durchführung zum elektrischen Durchbruch der isolierenden Gasstrecke kommen. Es handelt sich dann um eine Gasentladung, welche durch einen Hochfrequenzfunken, der jedoch nur während eines Zeitraumes von einigen Millisekunden ansteht, eingeleitet wird und dann in einem Lichtbogen weiterbesteht.Due to mechanical irregularities, e.g. Damage in the insulation ceramics and contamination in the nozzle passage or due to overvoltage, electrical breakdown of the insulating gas line can occur in or near such a bushing. It is then a gas discharge, which is initiated by a high-frequency spark, which, however, is only present for a period of a few milliseconds, and then persists in an arc.

Während der Gasentladung in Form eines Lichtbogens findet ein Materialtransport statt. Dadurch werden einerseits Bauteile, zwischen denen die Gasentladung abläuft, durch Materialabtrag geschwächt, so daß es zum Bruch kommen kann, was einer teilweisen Zerstörung der Durchführung gleich kommt. Andererseits stellen das abgetragene Material und eventuelle Bruchstücke von Teilen der Durchführung oder ihre Umgebung eine Gefahr für die gesamte Anlage sowie ein Störfaktor für das durchzuführende Verfahren dar.Material transport takes place during the gas discharge in the form of an arc. Components on the one hand, between which the gas discharge occurs, are thereby weakened by material removal, so that breakage can occur, which is equivalent to partial destruction of the bushing. On the other hand, the removed material and any fragments of parts of the bushing or their surroundings pose a danger to the entire system and a disruptive factor for the process to be carried out.

Da eine solche Gasentladung trotz aller Gegenmaßnahmen nicht grundsätzlich verhindert werden kann, wäre es von großem Vorteil, sie wenigstens nachweisen zu können. Ein Nachweis bei geschlossenem Ofen während eines Verfahrens ist jedoch sehr schwierig. Die Hochfrequenzüberwachung ist insofern problematisch, als der hochfrequente Funke nur während eines Zeitraumes von einigen Millisekunden oder weniger ansteht. Danach geht die Entladung in einen Lichtbogen über, welcher mit Hochfrequenz nicht mehr zu erkennen ist. Ein Nachweis über den Isolationswiderstand während dieser Phase ist nur sehr schwer durchführbar, da der Isolationswiderstand zwischen Heizung und anderen Einbauten, welche zum Teil aus Graphitfilz bestehen, niederohmig ist und außerdem der Messung stets die Heizspannung überlagert ist.Since such a gas discharge cannot be prevented in principle despite all countermeasures, it would be a great advantage to be able to at least prove it. However, detection with the furnace closed during a process is very difficult. High frequency monitoring is problematic in that the high frequency spark is only present for a period of a few milliseconds or less. Then the discharge turns into an arc, which can no longer be recognized at high frequency. It is very difficult to prove the insulation resistance during this phase, since the insulation resistance between the heater and other internals, which partly consist of graphite felt, has a low resistance and, in addition, the heating voltage is always superimposed on the measurement.

Der Erfindung liegt die Aufgabe zugrunde, eine Einrichtung zu entwickeln, mit welcher es möglich ist, eine Gasentladung innerhalb eines elektrisch beheizten Vakuumofens nachzuweisen, um daraus die entsprechenden Maßnahmen, wie z.B. Abschalten der Heizleistung, zum Schutze der Anlage abzuleiten.The invention has for its object to develop a device with which it is possible to detect a gas discharge within an electrically heated vacuum furnace in order to use it to take the appropriate measures, such as Switching off the heating power to derive to protect the system.

Die Aufgabe wird entsprechend den kennzeichnenden Merkmalen des ersten Patentanspruches dadurch gelöst, daß um die Isolation der Stromdurchführung eine Hilfselektrode angebracht ist. Diese muß elektrisch isoliert sein und kann zum Beispiel die Form einer Spirale, eines Drahtgewebes oder eines Blechrohres haben. Damit führt eine Gasentladung zwischen Stromdurchführung und Kesselwand zu einem einfach nachweisbaren Kurzschluß zwischen Hilfselektrode und Kesselwand, der mit handelsüblichebn eigensicheren Widerstandsmeßgeräten nachgewiesen und zu einem Schaltsignal verarbeitet werden kann, infolgedessen durch Abschalten der Heizleistung auch der Lichtbogen abgeschaltet wird.The object is achieved according to the characterizing features of the first claim in that an auxiliary electrode is attached to the insulation of the current leadthrough. This must be electrically insulated and can, for example, take the form of a spiral, a wire mesh or a sheet metal tube. A gas discharge between the current feedthrough and the boiler wall thus leads to an easily detectable short circuit between the auxiliary electrode and the boiler wall, which can be detected with commercially available intrinsically safe resistance measuring devices and processed into a switching signal, as a result of which the arc is also switched off by switching off the heating power.

Eine weitere Möglichkeit zum Nachweis einer Gasentladung besteht darin, daß um die Keramikisolation der Stromdurchführung ein Thermoelement gewickelt ist. Wird das Thermoelement durch den Lichtbogen durchgebrannt so wird an dieser Stelle entweder der Meßkreis geöffnet, oder es entsteht eine neue Verbindung beider Thermoelementschenkel, die im Moment des Entstehens eine große EMK, entsprechend der hohen Temperatur an der neuen Schweißperle abgibt.Another possibility for the detection of a gas discharge is that a thermocouple is wound around the ceramic insulation of the current feedthrough. If the thermocouple is blown by the arc, either the measuring circuit is opened at this point, or a new connection is created between the two thermocouple legs, which emits a large amount of EMF at the new welding bead at the moment it occurs.

Beide Ereignisse, offener Meßkreis oder hohe Temperatur, sind durch handelsübliche, eigensichere Schwellwertschaltgeräte für Thermoelemente sicher nachweisbar, so daß bei der Alarmauslösung durch das Meßgerät sofort die Heizleistung abgeschaltet werden kann, wodurch auch der Lichtbogen erlischt. Aus mechanischen Gründen ist der Einsatz eines metallgemantelten Thermoelementes empfehlenswert.Both events, open measuring circuit or high temperature, can be reliably detected by commercially available, intrinsically safe threshold switchgear for thermocouples, so that when the alarm is triggered by the measuring device, the heating power can be switched off immediately, which also extinguishes the arc. For mechanical reasons, the use of a metal-clad thermocouple is recommended.

In der einzigen Abbildung ist die Erfindung näher dargestellt.In the single figure, the invention is shown in more detail.

An der Kesselwand 1 eines Vakuumofens ist ein Flansch 2 angebracht, welcher mit der elektrischen Durchführung 3, im folgenden auch Elektrode genannt, versehen ist. Diese kann zum Beispiel aus Kupfer oder Graphit bestehen. Es ist auch ein Aufbau aus einer Kombination mehrerer Werkstoffe möglich. Die Elektrode leitet den elektrischen Strom zu Heizelementen 4 innerhalb der Vakuumkammer 5. Sie ist von einer Isolation 6 umgeben, welche zum Beispiel aus Keramik besteht. Um diese Isolaton herum ist eine Hilfselektrode 7 angebracht, welche im dargestellten Beispiel die Form einer Spirale hat.On the boiler wall 1 of a vacuum furnace, a flange 2 is attached, which is provided with the electrical feedthrough 3, hereinafter also referred to as the electrode. This can consist of copper or graphite, for example. A construction from a combination of several materials is also possible. The electrode conducts the electrical current to heating elements 4 within the vacuum chamber 5. It is surrounded by an insulation 6, which consists for example of ceramic. An auxiliary electrode 7 is attached around this isolaton, which in the example shown has the shape of a spiral.

Anstelle der Hilfselektrode 7 kann die Isolation 6 auch von einem Thermoelement 7 umgeben sein. Die Darstellungsweise ist in der Abbildung die gleiche.Instead of the auxiliary electrode 7, the insulation 6 can also be surrounded by a thermocouple 7. The representation is the same in the illustration.

Mit Hilfe der Durchführung 8 wird die Hilfselektrode oder das Thermoelement elektrisch isoliert aus dem Kesselraum herausgeführt und mit der Abschaltelektronik 9 verbunden.With the help of the bushing 8, the auxiliary electrode or the thermocouple is electrically isolated led out of the boiler room and connected to the shutdown electronics 9.

Claims (5)

1. Einrichtung zum Schutz elektrisch beheizter Vakuumöfen, welche mit Durchführungen (3) versehen sind, die zur Übertragung von elektrischem Strom zu Heizelementen (4) in der Vakuumkammer (5) dienen, wobei die Durchführungen (3) jeweils von einer Isolation (6) umgeben sind, welche vorzugsweise aus keramischem Material besteht, dadurch gekennzeichnet, daß die Isolation (6) von einer elektrisch isoliert eingebauten Hilfselektrode (7) umgeben ist und eine Abschaltelektronik (9) für die Heizleistung vorhanden ist, welche durch ein Signal betätigt wird, das bei Entstehen eines Lichtbogens zwischen der Durchführung (3) und der Kesselwand (1) durch den dadurch absinkenden Widerstand zwischen Hilfselektrode (7) und Kesselwand (1) hervorgerufen wird.1. Device for protecting electrically heated vacuum ovens, which are provided with bushings (3) which are used to transmit electrical current to heating elements (4) in the vacuum chamber (5), the bushings (3) each being insulated (6) are surrounded, which preferably consists of ceramic material, characterized in that the insulation (6) is surrounded by an electrically insulated built-in auxiliary electrode (7) and there is a switch-off electronics (9) for the heating power which is actuated by a signal which If an arc arises between the bushing (3) and the boiler wall (1), the resistance between auxiliary electrode (7) and boiler wall (1), which thereby decreases, is caused. 2. Einrichtung nach Anspruch 1, dadurch gekennzeichnet, daß die Hilfselektrode in Form einer Spirale um die Isolation gewickelt ist.2. Device according to claim 1, characterized in that the auxiliary electrode is wound in the form of a spiral around the insulation. 3. Einrichtung nach Anspruch 1, dadurch gekennzeichnet, daß die Hilfselektrode die Form eines Drahtgewebes aufweist.3. Device according to claim 1, characterized in that the auxiliary electrode has the shape of a wire mesh. 4. Einrichtung nach Anspruch 1, dadurch gekennzeichnet, daß die Hilfselektrode die Form eines Metallrohres aufweist.4. Device according to claim 1, characterized in that the auxiliary electrode has the shape of a metal tube. 5. Einrichtung zum Schutz elektrisch beheizter Vakuumöfen, welche mit Durchführungen (3) versehen sind, die zur Übertragung von elektrischem Strom zu Heizelementen (4) in der Vakuumkammer (5) dienen, wobei die Durchführungen (3) jeweils von einer Isolation (6) umgeben sind, welche vorzugsweise aus keramischem Material besteht, dadurch gekennzeichnet, daß die Isolation (6) von einem Thermoelement umgeben ist und eine Abschaltelektronik (9) vorhanden ist, welche bei Übertemperaturanzeige des Thermoelementes oder nach Durchbrennen des Thermoelementes betätigt wird.5. Device for protecting electrically heated vacuum ovens, which are provided with bushings (3) which are used to transmit electrical current to heating elements (4) in the vacuum chamber (5), the bushings (3) each being insulated (6) are surrounded, which preferably consists of ceramic material, characterized in that the insulation (6) is surrounded by a thermocouple and there is an electronic switch-off (9) which is actuated when the thermocouple is overheated or after the thermocouple has burnt through.
EP91110222A 1990-06-29 1991-06-21 Device for protection of electrical heated vacuum furnace Withdrawn EP0468203A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE4020818 1990-06-29
DE4020818 1990-06-29

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EP0468203A1 true EP0468203A1 (en) 1992-01-29

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EP91110222A Withdrawn EP0468203A1 (en) 1990-06-29 1991-06-21 Device for protection of electrical heated vacuum furnace

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US (1) US5193100A (en)
EP (1) EP0468203A1 (en)
JP (1) JPH04227472A (en)
DE (2) DE9116930U1 (en)

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2223244A4 (en) * 2007-11-05 2011-10-12 Chacha Search Inc Method and system of accessing information
DE102011008304B4 (en) * 2011-01-11 2013-04-11 Von Ardenne Anlagentechnik Gmbh Arrangement for detecting a Heizmittelbruches
DE102011077967A1 (en) 2011-06-22 2012-12-27 Wacker Chemie Ag Electrode and method for powering a reactor
CN115232952B (en) * 2022-06-17 2023-11-21 中国科学院空天信息创新研究院 Preparation method of spiral line in high-frequency component

Citations (3)

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DE1565534A1 (en) * 1965-06-09 1972-03-02 Finkl Charles W Method and device for additional heating of a metal melt under vacuum
DD120275A1 (en) * 1975-04-16 1976-06-05
DE3228471A1 (en) * 1982-07-30 1984-02-09 Dehn + Söhne GmbH + Co KG, 8500 Nürnberg Overvoltage protection apparatus

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US3637438A (en) * 1965-05-13 1972-01-25 Redwood L Springfield Thermocouple guide
DE1533253C3 (en) * 1966-12-01 1975-02-13 Bayer Ag, 5090 Leverkusen Electrodes for heating oxygen and a process carried out by means of these electrodes
US3715441A (en) * 1971-07-26 1973-02-06 H Collins Induction furnace with thermocouple assembly
US3763704A (en) * 1972-04-28 1973-10-09 P Blau Apparatus for continuously measuring the temperature of molten metal
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US4268708A (en) * 1979-04-19 1981-05-19 Autoclave Engineers, Inc. Apparatus for vacuum sintering and hot isostatic pressing
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Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1565534A1 (en) * 1965-06-09 1972-03-02 Finkl Charles W Method and device for additional heating of a metal melt under vacuum
DD120275A1 (en) * 1975-04-16 1976-06-05
DE3228471A1 (en) * 1982-07-30 1984-02-09 Dehn + Söhne GmbH + Co KG, 8500 Nürnberg Overvoltage protection apparatus

Also Published As

Publication number Publication date
DE4107096A1 (en) 1992-01-02
US5193100A (en) 1993-03-09
JPH04227472A (en) 1992-08-17
DE9116930U1 (en) 1995-02-02

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