EP0955644A2 - Method of manufacturing a metal oxide varistor and varistor made according to this method - Google Patents

Method of manufacturing a metal oxide varistor and varistor made according to this method Download PDF

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Publication number
EP0955644A2
EP0955644A2 EP99810304A EP99810304A EP0955644A2 EP 0955644 A2 EP0955644 A2 EP 0955644A2 EP 99810304 A EP99810304 A EP 99810304A EP 99810304 A EP99810304 A EP 99810304A EP 0955644 A2 EP0955644 A2 EP 0955644A2
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EP
European Patent Office
Prior art keywords
resistance body
varistor
face
electrodes
edge
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EP99810304A
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German (de)
French (fr)
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EP0955644B1 (en
EP0955644A3 (en
Inventor
Felix Dr. Greuter
Michael Hagemeister
Wolfgang Dr. Kluge
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ABB Research Ltd Switzerland
ABB Research Ltd Sweden
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ABB Research Ltd Switzerland
ABB Research Ltd Sweden
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01C—RESISTORS
    • H01C1/00—Details
    • H01C1/14—Terminals or tapping points or electrodes specially adapted for resistors; Arrangements of terminals or tapping points or electrodes on resistors
    • H01C1/142—Terminals or tapping points or electrodes specially adapted for resistors; Arrangements of terminals or tapping points or electrodes on resistors the terminals or tapping points being coated on the resistive element
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01C—RESISTORS
    • H01C17/00—Apparatus or processes specially adapted for manufacturing resistors
    • H01C17/28—Apparatus or processes specially adapted for manufacturing resistors adapted for applying terminals
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01C—RESISTORS
    • H01C7/00—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material
    • H01C7/10—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material voltage responsive, i.e. varistors
    • H01C7/105—Varistor cores
    • H01C7/108—Metal oxide
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T29/00—Metal working
    • Y10T29/49—Method of mechanical manufacture
    • Y10T29/49002—Electrical device making
    • Y10T29/49082—Resistor making
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T29/00—Metal working
    • Y10T29/49—Method of mechanical manufacture
    • Y10T29/49002—Electrical device making
    • Y10T29/49082—Resistor making
    • Y10T29/49101—Applying terminal

Definitions

  • the invention is based on a method for producing a varistor according to the preamble of patent claim 1.
  • the invention also relates to a varistor produced using this method.
  • a varistor manufactured according to the above-mentioned process is used in medium or high voltage systems for measurement, protection or control tasks. It has a cylindrical resistance body made of a sintered ceramic or a polymer highly filled with a ceramic sintered granulate with varistor behavior, which is arranged between two electrodes aligned in parallel.
  • the ceramic sinter granules generally consist of zinc oxide doped specifically with selected metals such as Bi, Sb, Co and Mn.
  • the varistor is preferably used in surge arresters and must be specified so that it can carry high-energy current pulses caused by lightning strikes or switching operations without damage. Such current pulses are applied to the electrodes of the varistor during the manufacturing process in order to check their high current resistance.
  • the electrodes are in each case attached to the edge of the end faces of the resistance body. Since in such a varistor each of the two electrodes extends over the entire end face of the resistance body, a homogeneous electric field is formed in the interior when a large current is briefly conducted. As a result, a uniform current density and thus also a uniform heating of the varistor are achieved. Since the unprotected resistance body has edges and tips in the area of the outer edges of the end faces, and since the electrode material guided to the outer edges can get into the outer surface of the resistance body, a ring made of a polymer with a high thickness becomes on the outer surface of the resistance body Dielectric constant and positioned with high temperature resistance. This ring ensures that the electric field in the outer surface is reduced and unwanted flashovers are avoided. Such a method for producing varistors is also very expensive and complex.
  • the invention is based on the object of specifying a method of the type mentioned at the outset for the rapid and economical production of a varistor.
  • a varistor manufactured according to this method should have both an excellent energy absorption capacity and a simple structure.
  • the method according to the invention is distinguished by the fact that it is suitable for series production and that varistors with high energy absorption capacity and high high current resistance can thus be manufactured quickly and economically.
  • a layer of electrode material that is guided to the outer edge thereof is applied, and either a circular ring of approximately 10 to approximately 500 ⁇ m wide, delimited from the outer edge and guided to the end face of the resistance body, is removed from the layer , or the resistance body and possibly also the layer of electrode material on the outer edge are chamfered.
  • the large energy absorption capacity and the high high-current strength of the varistors produced using the method according to the invention are due, on the one hand, to the fact that inhomogeneities in the electrical field and in the current density in the varistor largely occur due to electrodes guided as close to the outer edge of the end faces as possible when a high-energy current pulse occurs be avoided.
  • Such inhomogeneities can be caused by metallized edge defects or by metal splashes that protrude beyond the edge.
  • a narrow, electrode-free edge or a bevel slightly disturbs the ideal, homogeneous state with electrodes led to the edges, but the large inhomogeneities (metallized edge defects that lead to failure) are efficiently eliminated.
  • this surface can comprise its cylindrical outer surface and two adjoining, less than 500 ⁇ m wide circular sections of its end faces.
  • the surface contains bevels which extend directly to the edge of the electrodes and which merge into the cylindrical outer surface of the varistor.
  • the reference numeral 1 relates to a resistance body made of a ceramic which has varistor behavior and belongs to the prior art and which was produced as follows: Approx. 97 mol% Zn, approx.0.5 mol% Bi 2 O 3 , approx.1.0 mol% Sb 2 O 3 , approx.0.5 mol% Co 2 O 3 , approx.0.5 mol% MnO 2 0.5 mol% Cr 2 O 3 and other metal oxide additives were mixed in a ball mill and ground to a homogeneous powder mixture with particle diameters between approx. 1 and approx. 5 ⁇ m. The powder mixture was slurried in distilled water.
  • the slurry was converted into a free-flowing, dry granulate in a spray dryer.
  • the average size of the grains produced was approx. 100 ⁇ m.
  • Cylindrical compression bodies were formed from the granules, from which cylindrical disc-shaped resistance bodies of about 38 mm in diameter and about 20 mm in length were sintered at a temperature of about 1200 ° C. for about 2 hours.
  • the electrode material is advantageously used, for example, by flame spraying or sprayed on by arc application. This results in relatively porous layers, typically about 50-150 ⁇ m thick. Twenty varistors designed in this way were produced. Of these twenty, eight were kept unchanged and were used for comparison purposes in the experiments described below.
  • a circular ring 4 with a thickness d was delimited from the outer edge 9 and led to the end face of the resistance body.
  • Another six varistors were modified in accordance with the embodiment shown in FIG.
  • the resistance body 1 and the layer of electrode material were chamfered on the outer edge. This resulted in a conical bevel 5 of the lateral surface, which forms an obtuse angle of preferably 100 ° to 120 °, or up to 150 °, with the end surface.
  • the removal of the circular ring 4 or the chamfering is advantageously carried out by cutting with a gas or liquid jet 6, preferably loaded with an abrasive powder.
  • the gas or liquid jet 6 is guided obliquely from above onto the electrode 2.
  • a circular ring with a small thickness d in the region of the end face can thus be removed in a simple manner.
  • the circular ring is removed after the electrodes have been applied.
  • a porous electrode material can be attacked particularly effectively by the gas or liquid jet 6 and - without leaving dielectric undesirable holes or cracks - removed.
  • the circular ring should be at most 500 ⁇ m, preferably at most 300 ⁇ m, from the outer edge 9 of the end face carrying the electrode material. With a small distance of at least 10 ⁇ m, preferably at least 20 ⁇ m, it is ensured that inhomogeneities of the electrodes or removal of electrode material cannot reduce the dielectric strength of the varistor.
  • the gas or liquid jet 6 is guided obliquely from below to the resistance body 1 and the electrode 2. It is then ensured that the beveled electrode material does not touch the conical one Bevel 5 can reach the outer surface and impair the dielectric properties of the varistor. Instead of using a gas or liquid jet 6, the bevel can also be produced by grinding.
  • the twenty varistors were each loaded with several approximately rectangular current pulses of 2 ms duration and with an amplitude of several 100 A in a test device. The test resistors were then inspected by eye. It was found that half of the eight varistors according to FIG. 1 had suffered a defect, whereas the varistors designed according to FIGS. 2 and 3 had remained fully functional.
  • FIG. 4 shows a varistor during production, in which a combination of the methods according to FIGS. 2 and 3 is used, in which the circular ring 4 is first removed according to FIG. 2 and then the conical bevel 5 is made according to FIG .

Abstract

The varistor has a cylindrical body of resistive material that has a base of metal oxide. The end surfaces have electrodes (2,3) with an exposed section having a layer of electrode material (9). In a second stage the edge is formed with an angled surface.

Description

TECHNISCHES GEBIETTECHNICAL AREA

Bei der Erfindung wird ausgegangen von einem Verfahren zum Herstellen eines Varistor nach dem Oberbegriff von Patentanspruch 1. Die Erfindung betrifft auch einen nach diesem Verfahren hergestellten Varistor.The invention is based on a method for producing a varistor according to the preamble of patent claim 1. The invention also relates to a varistor produced using this method.

Ein nach dem obengenannten Verfahren hergestellter Varistor wird in Mittel- oder Hochspannungsanlagen für Mess-, Schutz- oder Steueraufgaben eingesetzt. Er weist einen zwischen zwei parallel ausgerichteten Elektroden angeordneten, zylinderförmigen Widerstandskörper aus einer Sinterkeramik oder einem mit einem keramischen Sintergranulat mit Varistorverhalten hochgefüllten Polymer auf. Die Sinterkeramik resp. das keramische Sintergranulat besteht im allgemeinen aus einem gezielt mit ausgewählten Metallen, wie Bi, Sb, Co und Mn, dotierten Zinkoxid.A varistor manufactured according to the above-mentioned process is used in medium or high voltage systems for measurement, protection or control tasks. It has a cylindrical resistance body made of a sintered ceramic or a polymer highly filled with a ceramic sintered granulate with varistor behavior, which is arranged between two electrodes aligned in parallel. The sintered ceramics. The ceramic sinter granules generally consist of zinc oxide doped specifically with selected metals such as Bi, Sb, Co and Mn.

Der Varistor wird bevorzugt in Überspannungsableitern verwendet und muss so spezifiziert sein, dass er durch Blitzeinschläge oder Schalthandlungen entstehende hochenergetische Stromimpulse schadlos führen kann. Solche Stromimpulse werden im Zuge des Fertigungsprozesses an die Elektroden des Varistors gelegt, um deren Hochstromfestigkeit zu überprüfen.The varistor is preferably used in surge arresters and must be specified so that it can carry high-energy current pulses caused by lightning strikes or switching operations without damage. Such current pulses are applied to the electrodes of the varistor during the manufacturing process in order to check their high current resistance.

STAND DER TECHNIKSTATE OF THE ART

Verfahren der eingangs genannten Art zum Herstellen von Varistoren sind in DE 34 05 834 C2 sowie EP 0 494 507 A1 angegeben. Dabei wird jeweils ein zylinderförmiger, keramischer Widerstandskörper auf der Basis von Zinkoxid hergestellt und auf den beiden zueinander parallelen, ebenen Stirnflächen des Widerstandkörpers je eine Elektrode aufgetragen.Methods of the type mentioned at the outset for producing varistors are specified in DE 34 05 834 C2 and EP 0 494 507 A1. In each case, a cylindrical, ceramic resistance body based on zinc oxide is produced and an electrode is applied to each of the two parallel, flat end faces of the resistance body.

Bei dem in DE 34 05 834 C2 beschrieben Verfahren, werden am Widerstandskörper in den Randbereichen beider Stirnflächen umlaufende Stufen abgeschliffen. Danach wird der Widerstandskörper die Umfangsfläche und die Stufen bedeckend mit einem Isolationsmaterial versehen. Anschliessend werden die Stirnflächen und ein Teil des auf den Stufen angebrachten lsolationsmaterials abgeschliffen. Schliesslich werden dann die Elektroden aus Metall die mit dem Isolationsmaterial gefüllten Stufen teilweise überlappend aber nicht ganz bis zum Rand der Stirnfläche reichend auf die Stirnflächen aufgetragen. Dieses Verfahren ist sehr aufwendig und zudem Fehleranfällig, da es beim Auftragen des Elektrodenmaterials zu Metallspritzer im Bereich des Randes kommen kann, die zu dielektrischen Ueberschlägen bei Hochfeldbeanspruchung führen können. Zudem entstehen wegen der unvollständigen Elektrodenüberdeckung im Widerstandskörper lokale Überhöhungen der Stromdichte resp. des elektrischen Feldes, welche die Spannungsfestigkeit eines derart ausgeführten Varistors herabsetzen.In the method described in DE 34 05 834 C2, circumferential steps are ground on the resistance body in the edge regions of both end faces. The resistance body is then provided with an insulating material covering the peripheral surface and the steps. The end faces and part of the insulation material applied to the steps are then ground off. Finally, the electrodes made of metal are applied to the end faces, partially overlapping the steps filled with the insulation material, but not reaching all the way to the edge of the end face. This method is very complex and moreover prone to errors, since when the electrode material is applied metal splashes can occur in the area of the edge, which can lead to dielectric arcing in the case of high field stress. In addition, due to the incomplete electrode coverage in the resistance body, local increases in current density or. of the electric field, which reduce the dielectric strength of a varistor designed in this way.

Bei dem in EP 0 494 507 A1 beschrieben Verfahren, werden die Elektroden jeweils bis an den Rand der Stirnflächen des Widerstandskörpers angebracht. Da sich bei einem solchen Varistor jede der beiden Elektroden über die gesamte Stirnfläche des Widerstandskörpers erstreckt, bildet sich beim kurzzeitigen Führen eines grossen Stromes in seinem Inneren ein homogenes elektrisches Feld aus. Hierdurch werden eine gleichmässige Stromdichte und somit auch eine gleichmässige Aufheizung des Varistors erreicht. Da der ungeschützte Widerstandskörper im Bereich der Aussenränder der Stirnflächen Kanten und Spitzen aufweist, und da das an die Aussenränder geführte Elektrodenmaterial in die Mantelfläche des Widerstandkörpers gelangen kann, wird auf der Mantelfläche des Widerstandskörpers ein Ring aus einem Polymer mit hoher Dielektrizitätskonstante und mit hoher Temperaturbeständigkeit positioniert. Dieser Ring sorgt dafür, dass das elektrische Feld in der Mantelfläche herabgesetzt wird und so unerwünschte Überschläge vermieden werden. Auch ein solches Verfahren zur Herstellen von Varistoren ist sehr kostspielig und aufwendig.In the method described in EP 0 494 507 A1, the electrodes are in each case attached to the edge of the end faces of the resistance body. Since in such a varistor each of the two electrodes extends over the entire end face of the resistance body, a homogeneous electric field is formed in the interior when a large current is briefly conducted. As a result, a uniform current density and thus also a uniform heating of the varistor are achieved. Since the unprotected resistance body has edges and tips in the area of the outer edges of the end faces, and since the electrode material guided to the outer edges can get into the outer surface of the resistance body, a ring made of a polymer with a high thickness becomes on the outer surface of the resistance body Dielectric constant and positioned with high temperature resistance. This ring ensures that the electric field in the outer surface is reduced and unwanted flashovers are avoided. Such a method for producing varistors is also very expensive and complex.

KURZE DARSTELLUNG DER ERFINDUNGSUMMARY OF THE INVENTION

Der Erfindung, wie sie in den Patentansprüchen definiert ist, liegt die Aufgabe zugrunde, ein Verfahren der eingangs genannten Art, zum raschen und wirtschaftlichen Herstellen eines Varistor anzugeben. Zugleich soll ein nach diesem Verfahren hergestellter Varistor sowohl eine hervorragendes Energieaufnahmevermögen, als auch einen einfachen Aufbau aufweisen.The invention, as defined in the claims, is based on the object of specifying a method of the type mentioned at the outset for the rapid and economical production of a varistor. At the same time, a varistor manufactured according to this method should have both an excellent energy absorption capacity and a simple structure.

Das erfindungsgemässe Verfahren zeichnet sich dadurch aus, dass es für eine Serienfertigung geeignet ist und dass damit Varistoren mit grossem Energieaufnahmevermögen und hoher Hochstromfestigkeit rasch und wirtschaftlich gefertigt werden können.The method according to the invention is distinguished by the fact that it is suitable for series production and that varistors with high energy absorption capacity and high high current resistance can thus be manufactured quickly and economically.

Das erfindungsgemässe Verfahren ist durch folgende Verfahrensschritte gekennzeichnet:The process according to the invention is characterized by the following process steps:

Auf jede der beiden Stirnflächen des Widerstandskörpers wird eine bis an deren Aussenrand geführte Schicht aus Elektrodenmaterial aufgebracht, und es wird entweder ein vom Aussenrand begrenzter und bis auf die Stirnfläche des Widerstandskörpers geführter Kreisring von ca. 10 bis ca. 500 µm Breite aus der Schicht enffernt, oder es werden der Widerstandskörper und gegebenenfalls auch die Schicht aus Elektrodenmaterial am Aussenrand abgeschrägt.On each of the two end faces of the resistance body, a layer of electrode material that is guided to the outer edge thereof is applied, and either a circular ring of approximately 10 to approximately 500 μm wide, delimited from the outer edge and guided to the end face of the resistance body, is removed from the layer , or the resistance body and possibly also the layer of electrode material on the outer edge are chamfered.

Gegenüber Verfahren zum Herstellen von Varistoren nach dem Stand der Technik, bei denen beim Aufbringen der Elektrodenschichten unvermeidlich auftretende Metallisierungsfehler mit sehr komplizierten und kostspieligen Prozessen zu vermeiden versucht werden, werden diese beim erfindungsgemässen Verfahren nachträglich entfernt.Compared to methods for producing varistors according to the prior art, in which attempts are made to avoid metallization errors which inevitably occur when the electrode layers are applied using very complicated and costly processes, these are subsequently removed in the method according to the invention.

Das grosse Energieaufnahmevermögen und die hohe Hochstromfestigkeit der mit dem erfindungsgemässen Verfahren hergestellten Varistoren sind zum einen dadurch bedingt, dass durch möglichst nahe an den als Kante ausgebildeten Aussenrand der Stirnflächen geführte Elektroden Inhomogenitäten im elektrischen Feld und in der Stromdichte im Varistor beim Auftreten eines hochenergetischen Stromimpulses weitgehend vermieden werden. Solche Inhomogenitäten können durch metallisierte Kantendefekte oder durch Metallspritzer hervorgerufen werden, welche über die Kante hinaustreten. Durch einen schmalen elektrodenfreien Rand bzw. durch eine Abschrägung wird zwar der ideale, homogene Zustand mit an die Kanten geführten Elektroden geringfügig gestört, aber die grossen Inhomogenitäten (metallisierte Randdefekte, welche zum Versagen führen) werden effizient eliminiert.
Zum anderen ist dies auch eine Folge einer geeigneten Ausbildung der hohen dielektrischen Belastungen ausgesetzten Oberfläche des Varistors zwischen den beiden Elektroden. Diese Oberfläche kann in einer ersten bevorzugten Ausführungsform des Varistors seine zylinderförmige Mantelfläche und zwei sich daran anschliessende, weniger als 500 µm breite kreisringförmige Abschnitte seiner Stirnflächen umfassen. In einer bevorzugten zweiten Ausführungsform enthält die Oberfläche unmittelbar bis zum Rand der Elektroden geführte Abschrägungen, die in die zylinderförmige Mantelfläche des Varistors übergehen.The large energy absorption capacity and the high high-current strength of the varistors produced using the method according to the invention are due, on the one hand, to the fact that inhomogeneities in the electrical field and in the current density in the varistor largely occur due to electrodes guided as close to the outer edge of the end faces as possible when a high-energy current pulse occurs be avoided. Such inhomogeneities can be caused by metallized edge defects or by metal splashes that protrude beyond the edge. A narrow, electrode-free edge or a bevel slightly disturbs the ideal, homogeneous state with electrodes led to the edges, but the large inhomogeneities (metallized edge defects that lead to failure) are efficiently eliminated.
On the other hand, this is also a result of a suitable design of the surface of the varistor which is exposed to high dielectric loads between the two electrodes. In a first preferred embodiment of the varistor, this surface can comprise its cylindrical outer surface and two adjoining, less than 500 μm wide circular sections of its end faces. In a preferred second embodiment, the surface contains bevels which extend directly to the edge of the electrodes and which merge into the cylindrical outer surface of the varistor.

KURZE BESCHREIBUNG DER ZEICHNUNGENBRIEF DESCRIPTION OF THE DRAWINGS

Bevorzugte Ausführungsbeispiele von mit dem erfindungsgemässen Verfahren hergestellten Varistoren und die damit erzielbaren weiteren Vorteile werden nachfolgend anhand von Zeichnungen näher erläutert. Hierbei zeigt:

Fig.1
eine Aufsicht auf einen axial geführten Schnitt durch einen Teil eines Varistors,
Fig.2
eine Aufsicht auf einen axial geführten Schnitt durch einen Teil einer ersten Ausführungsform des nach dem erfindungsgemässen Verfahren hergestellten Varistors während seiner Fertigung,
Fig.3
eine Aufsicht auf einen axial geführten Schnitt durch einen Teil einer zweiten Ausführungsform des nach dem erfindungsgemässen Verfahren hergestellten Varistors während seiner Fertigung,
Fig.4
eine Aufsicht auf einen axial geführten Schnitt durch einen Teil einer dritten Ausführungsform des nach dem erfindungsgemässen Verfahren hergestellten Varistors während seiner Fertigung, und
Fig.5
eine Aufsicht auf einen axial geführten Schnitt durch einen Teil einer vierten Ausführungsform des nach dem erfindungsgemässen Verfahren hergestellten Varistors.
Preferred exemplary embodiments of varistors produced using the method according to the invention and the further advantages which can be achieved thereby are explained in more detail below with reference to drawings. Here shows:
Fig. 1
a top view of an axially guided section through part of a varistor,
Fig. 2
2 shows a top view of an axially guided section through part of a first embodiment of the varistor produced by the method according to the invention during its manufacture,
Fig. 3
2 shows a top view of an axially guided section through part of a second embodiment of the varistor produced by the method according to the invention during its manufacture,
Fig. 4
a plan view of an axially guided section through part of a third embodiment of the varistor produced by the method according to the invention during its manufacture, and
Fig. 5
a plan view of an axially guided section through part of a fourth embodiment of the varistor produced by the inventive method.

WEGE ZUR AUSFÜHRUNG DER ERFINDUNGWAYS OF CARRYING OUT THE INVENTION

In allen Figuren bezeichnen gleiche Bezugszeichen auch gleichwirkende Teile. Das Bezugszeichen 1 bezieht sich auf einen Widerstandskörper aus einer Varistorverhalten aufweisenden, zum Stand der Technik zählenden Keramik, die wie folgt hergestellt wurde:
Ca. 97 Mol% Zn, ca. 0,5 Mol% Bi2O3, ca. 1,0 Mol% Sb2O3, ca. 0,5 Mol% Co2O3, ca. 0,5 Mol% MnO2, ca. 0,5 Mol% Cr2O3 und weitere Metalloxidzusätze wurden in einer Kugelmühle gemischt und zu einer homogenen Pulvermischung mit Partikeldurchmessern zwischen ca. 1 und ca. 5 µm gemahlen. Die Pulvermischung wurde in destilliertem Wasser aufgeschlämmt. Die Aufschlämmung wurde in einem Sprühtrockner in ein rieselfähiges, trockenes Granulat übergeführt. Die durchschnittliche Grösse der dabei erzeugten Körner lag bei ca. 100 µm. Aus dem Granulat wurden zylinderförmige Presskörper geformt, aus denen bei einer Temperatur von ca. 1200°C während ca. 2 h zylinderscheibenförmige Widerstandskörpern von ca. 38 mm Durchmesser und ca. 20 mm Länge gesintert wurden.In all figures, the same reference symbols also designate parts with the same effect. The reference numeral 1 relates to a resistance body made of a ceramic which has varistor behavior and belongs to the prior art and which was produced as follows:
Approx. 97 mol% Zn, approx.0.5 mol% Bi 2 O 3 , approx.1.0 mol% Sb 2 O 3 , approx.0.5 mol% Co 2 O 3 , approx.0.5 mol% MnO 2 0.5 mol% Cr 2 O 3 and other metal oxide additives were mixed in a ball mill and ground to a homogeneous powder mixture with particle diameters between approx. 1 and approx. 5 µm. The powder mixture was slurried in distilled water. The slurry was converted into a free-flowing, dry granulate in a spray dryer. The average size of the grains produced was approx. 100 µm. Cylindrical compression bodies were formed from the granules, from which cylindrical disc-shaped resistance bodies of about 38 mm in diameter and about 20 mm in length were sintered at a temperature of about 1200 ° C. for about 2 hours.

Auf den Stirnseiten des Widerstandskörpers 1 sind Elektroden 2 und 3 aus Elektrodenmaterial, wie insbesondere Aluminium, angeordnet. Zur Herstellung der Elektroden 2 und 3 wird auf jede der beiden Stirnflächen zunächst eine bis an den Aussenrand 9 der Stirnfläche geführte Schicht aus Elektrodenmaterial aufgebracht (Fig.1). Mit Vorteil wird das Elektrodenmaterial etwa durch Flammspritzen oder durch Lichtbogenauftrag aufgesprüht. Es entstehen so verhältnismässig poröse Schichten von typischerweise ca. 50 -150 µm Dicke. Es wurden zwanzig derart ausgebildete Varistoren hergestellt. Von diesen zwanzig wurden acht unverändert beibehalten und dienten in nachfolgend beschriebenen Versuchen zu Vergleichszwecken.Electrodes 2 and 3 made of electrode material, such as in particular aluminum, are arranged on the end faces of the resistance body 1. To produce the electrodes 2 and 3, a layer of electrode material which is guided to the outer edge 9 of the end face is first applied to each of the two end faces (FIG. 1). The electrode material is advantageously used, for example, by flame spraying or sprayed on by arc application. This results in relatively porous layers, typically about 50-150 µm thick. Twenty varistors designed in this way were produced. Of these twenty, eight were kept unchanged and were used for comparison purposes in the experiments described below.

Von den verbleibenden zwölf Varistoren wurden sechs entsprechend der Ausführungsform nach Fig.2 modifiziert. Zu diesem Zweck wurde ein vom Aussenrand 9 begrenzter und bis auf die Stirnfläche des Widerstandskörpers geführter Kreisring 4 mit einer Dicke d aus der Schicht entfernt. Weitere sechs Varistoren wurden entsprechend der Ausführungsform nach Fig.3 modifiziert. Bei dieser Ausführungsform wurden der Widerstandskörper 1 und die Schicht aus Elektrodenmaterial am Aussenrand abgeschrägt. Es entstand so eine konische Abschrägung 5 der Mantelfläche, welche mit der Stirnfläche einen stumpfen Winkel von vorzugsweise 100° bis 120°, gegegenenfalls bis zu 150° bildet. Das Entfernen des Kreisrings 4 oder das Abschrägen wird mit Vorteil durch Schneiden mit einem vorzugsweise mit einem abrasiven Pulver beladenen Gas - oder Flüssigkeitsstrahl 6 ausgeführt.Six of the remaining twelve varistors were modified in accordance with the embodiment according to FIG. For this purpose, a circular ring 4 with a thickness d was delimited from the outer edge 9 and led to the end face of the resistance body. Another six varistors were modified in accordance with the embodiment shown in FIG. In this embodiment, the resistance body 1 and the layer of electrode material were chamfered on the outer edge. This resulted in a conical bevel 5 of the lateral surface, which forms an obtuse angle of preferably 100 ° to 120 °, or up to 150 °, with the end surface. The removal of the circular ring 4 or the chamfering is advantageously carried out by cutting with a gas or liquid jet 6, preferably loaded with an abrasive powder.

Zum Entfernen des Kreisrings 4 nach Fig.2 wird der Gas - oder Flüssigkeitsstrahl 6 schräg von oben auf die Elektrode 2 geführt. Es kann so in einfacher Weise ein Kreisring mit geringer Dicke d im Bereich der Stirnfläche entfernt werden. Das Entfernen des Kreisringes wird nach dem Auftragen der Elektroden ausgeführt. Ein poröses Elektrodenmaterial kann besonders wirksam vom Gas- oder Flüssigkeitsstrahl 6 angegriffen und - ohne dielektrisch unerwünschte Löcher oder Risse zu hinterlassen - entfernt werden. Um dielektrisch gute Eigenschaften einhalten zu können, sollte der Kreisring höchstens 500 µm, vorzugsweise höchstens 300 µm, vom Aussenrand 9 der das Elektrodenmaterial tragenden Stirnfläche entfernt sein. Mit einem geringen Abstand von mindestens 10 µm, vorzugsweise mindestens 20 µm, ist sichergestellt, dass Inhomogenitäten der Elektroden bzw. Elektrodenmaterialabtrag die dielektrische Festigkeit des Varistors nicht herabsetzen können.To remove the circular ring 4 according to FIG. 2, the gas or liquid jet 6 is guided obliquely from above onto the electrode 2. A circular ring with a small thickness d in the region of the end face can thus be removed in a simple manner. The circular ring is removed after the electrodes have been applied. A porous electrode material can be attacked particularly effectively by the gas or liquid jet 6 and - without leaving dielectric undesirable holes or cracks - removed. In order to be able to maintain good dielectric properties, the circular ring should be at most 500 μm, preferably at most 300 μm, from the outer edge 9 of the end face carrying the electrode material. With a small distance of at least 10 μm, preferably at least 20 μm, it is ensured that inhomogeneities of the electrodes or removal of electrode material cannot reduce the dielectric strength of the varistor.

Beim Abschrägen nach Fig.3 wird der Gas - oder Flüssigkeitsstrahl 6 schräg von unten an den Widerstandskörper 1 und die Elektrode 2, geführt. Es ist dann sichergestellt, dass das abgeschrägte Elektrodenmaterial nicht an die konische Abschrägung 5 der Mantelfläche gelangen kann und die dielektrischen Eigenschaften des Varistors beeinträchtigt. Anstelle einen Gas - oder Flüssigkeitsstrahl 6 zu benutzen, kann die Abschrägung auch durch Abschleifen erzeugt werden.
In einer Prüfvorrichtung wurden die zwanzig Varistoren jeweils mit mehren annähernd rechteckigen Stromimpulsen von 2 ms Dauer und mit einer Amplitude von mehreren 100 A belastet. Danach wurden die Probewiderstände durch Augenschein begutachtet. Hierbei wurde festgestellt, dass von den acht Varistoren gemäss Fig.1 die Hälfte einen Defekt erlitten hatten, wohingegen die gemäss den Figuren 2 und 3 ausgeführten Varistoren vollauf funktionsfähig geblieben waren.3, the gas or liquid jet 6 is guided obliquely from below to the resistance body 1 and the electrode 2. It is then ensured that the beveled electrode material does not touch the conical one Bevel 5 can reach the outer surface and impair the dielectric properties of the varistor. Instead of using a gas or liquid jet 6, the bevel can also be produced by grinding.
The twenty varistors were each loaded with several approximately rectangular current pulses of 2 ms duration and with an amplitude of several 100 A in a test device. The test resistors were then inspected by eye. It was found that half of the eight varistors according to FIG. 1 had suffered a defect, whereas the varistors designed according to FIGS. 2 and 3 had remained fully functional.

Fig.4 zeigt einen Varistor während der Fertigung bei dem eine Kombination der Verfahren gemäss Fig.2 und Fig.3 angewendet wird, in dem zuerst gemäss Fig.2 der Kreisring 4 abgetragen wird und anschliessend gemäss Fig.3 die konische Abschrägung 5 vorgenommen wird.4 shows a varistor during production, in which a combination of the methods according to FIGS. 2 and 3 is used, in which the circular ring 4 is first removed according to FIG. 2 and then the conical bevel 5 is made according to FIG .

Für die zweite Seite des Varistors kann entweder das gleiche Verfahren wie für die erste Seite angewendet werden (Fig.2, Fig.3, und Fig.4), oder aber eines der anderen beiden Verfahren (Fig.5).For the second side of the varistor, either the same method can be used as for the first side (Fig. 2, Fig. 3, and Fig. 4), or one of the other two methods (Fig. 5).

BezugszeichenlisteReference list

11
WiderstandskörperResistance body
2, 32, 3
ElektrodenElectrodes
44th
KreisringCircular ring
5, 5'5, 5 '
konische Abschrägungen der Mantelflächeconical bevels of the lateral surface
66
Gas - oder FlüssigkeitsstrahlGas or liquid jet
88th
MantelflächeLateral surface
99
AussenrandOutside edge
dd
KreisringdickeCircular ring thickness

Claims (10)

Verfahren zum Herstellen eines Varistors, der in einem elektrischen Feld vorgegebener Grösse mit mindestens einem hochenergetischen Stromimpuls definierter Amplitude, Form und Dauer belastbar ist, und der einen zylinderförmigen Widerstandskörper (1) aus einem Werkstoff auf der Basis von Metalloxid sowie zwei jeweils auf einer von zwei parallel zueinander ausgerichteten Stirnflächen des zylinderförmigen Widerstandskörpers (1) angeordnete Elektroden (2, 3) aufweist, bei dem zuerst der Widerstandskörper hergestellt und danach mit den Elektroden (2, 3) versehen wird, dadurch gekennzeichnet,
dass auf die beiden Stirnflächen eine bis an deren als Kante ausgebildeten Aussenrand (9) geführte Schicht (2, 3) aus Elektrodenmaterial aufgebracht wird, und dass anschliessend je ein vom Aussenrand (9) begrenzter und bis auf die Stirnfläche des Widerstandskörpers (1) geführter Kreisring (4) mit einer Breite von ca. 10 bis ca. 500 µm aus der Schicht (2, 3) mit Elektrondenmaterial entfernt wird und/ oder der Widerstandskörper (1) am Aussenrand (9) abgeschrägt wird.Method for producing a varistor that can be loaded with at least one high-energy current pulse of defined amplitude, shape and duration in an electrical field of a specified size, and that has a cylindrical resistance body (1) made of a material based on metal oxide and two each on one of two End faces of the cylindrical resistance body (1) which are aligned parallel to one another and have electrodes (2, 3) arranged, in which the resistance body is first produced and then provided with the electrodes (2, 3), characterized in that
that a layer (2, 3) made of electrode material is applied to the two end faces up to the outer edge (9) formed as an edge, and that subsequently one layer which is delimited from the outer edge (9) and extends to the end face of the resistance body (1) Circular ring (4) with a width of approx. 10 to approx. 500 µm is removed from the layer (2, 3) with electrode material and / or the resistance body (1) is chamfered on the outer edge (9). Verfahren nach Anspruch 1, dadurch gekennzeichnet, dass das Entfernen des Kreisrings (4) oder das Abschrägen durch Schneiden mit einem gegebenenfalls mit einem abrasiven Pulver beladenen Gas- oder Flüssigkeitsstrahl (6) ausgeführt werden.A method according to claim 1, characterized in that the removal of the annulus (4) or the chamfering is carried out by cutting with a gas or liquid jet (6) optionally loaded with an abrasive powder. Verfahren nach Anspruch 1, dadurch gekennzeichnet, dass das Abschrägen durch Abschleifen ausgeführt wird.A method according to claim 1, characterized in that the chamfering is carried out by grinding. Verfahren nach einem der Ansprüche 1 bis 3, dadurch gekennzeichnet, dass das Elektrodenmaterial aufgesprüht wird.Method according to one of claims 1 to 3, characterized in that the electrode material is sprayed on. Varistor, hergestellt nach einem Verfahren der Ansprüche 1 bis 4, der in einem elektrischen Feld vorgegebener Grösse mit mindestens einem hochenergetischen Stromimpuls definierter Amplitude, Form und Dauer belastbar ist, und der einen zylinderförmigen Widerstandskörper (1) aus einem Werkstoff auf der Basis von Metalloxid aufweist sowie zwei jeweils auf einer von zwei parallel zueinander ausgerichteten ersten und zweiten Stirnflächen des zylinderförmigen Widerstandskörpers (1) angeordnete Elektroden (2, 3), dadurch gekennzeichnet, dass die Elektrode (2, 3) der ersten und/ oder zweiten Stirnfläche bis auf mindestens 500 µm und bis auf höchstens 10 µm an den als Kante ausgebildeten Aussenrand (9) dieser Stirnfläche geführt ist.Varistor, produced according to a method of claims 1 to 4, which can be loaded with at least one high-energy current pulse of defined amplitude, shape and duration in an electrical field of a given size, and which has a cylindrical resistance body (1) made of a material based on metal oxide and two each on one of two parallel first and second End faces of the cylindrical resistance body (1) arranged electrodes (2, 3), characterized in that the electrode (2, 3) of the first and / or second end face down to at least 500 µm and up to at most 10 µm on the outer edge formed as an edge (9) this end face is guided. Varistor, hergestellt nach einem Verfahren der Ansprüche 1 bis 4, der in einem elektrischen Feld vorgegebener Grösse mit mindestens einem hochenergetischen Stromimpuls definierter Amplitude, Form und Dauer belastbar ist, und der einen zylinderförmigen Widerstandskörper (1) aus einem Werkstoff auf der Basis von Metalloxid aufweist sowie zwei jeweils auf einer von zwei parallel zueinander ausgerichteten ersten und zweiten Stirnflächen des zylinderförmigen Widerstandskörpers (1) angeordnete Elektroden (2, 3), dadurch gekennzeichnet, dass der Widerstandskörper (1) eine von der Elektrode (2, 3) der ersten und/ oder zweiten Stirnfläche auf seine Mantelfläche (8) geführte konische Abschrägung (5, 5') aufweist.Varistor, produced according to a method of claims 1 to 4, which can be loaded with at least one high-energy current pulse of defined amplitude, shape and duration in an electrical field of a given size, and which has a cylindrical resistance body (1) made of a material based on metal oxide and two electrodes (2, 3) each arranged on one of two first and second end faces of the cylindrical resistance body (1) aligned parallel to one another, characterized in that the resistance body (1) is one of the electrodes (2, 3) of the first and / or second end face on its lateral surface (8) guided conical bevel (5, 5 '). Varistor, hergestellt nach einem Verfahren der Ansprüche 1 bis 4, der in einem elektrischen Feld vorgegebener Grösse mit mindestens einem hochenergetischen Stromimpuls definierter Amplitude, Form und Dauer belastbar ist, und der einen zylinderförmigen Widerstandskörper (1) aus einem Werkstoff auf der Basis von Metalloxid aufweist sowie zwei jeweils auf einer von zwei parallel zueinander ausgerichteten ersten und zweiten Stirnflächen des zylinderförmigen Widerstandskörpers (1) angeordnete Elektroden (2, 3), dadurch gekennzeichnet, dass die Elektrode (2, 3) der ersten und/ oder zweiten Stirnfläche bis auf mindestens 500 µm und bis auf höchstens 10 µm an den als Kante ausgebildeten Aussenrand (9) dieser Stirnfläche geführt ist, und dass der Widerstandskörper (1) eine von dieser Stirnfläche auf seine Mantelfläche (8) geführte konische Abschrägung (5, 5') aufweist.Varistor, produced according to a method of claims 1 to 4, which can be loaded with at least one high-energy current pulse of defined amplitude, shape and duration in an electrical field of a given size, and which has a cylindrical resistance body (1) made of a material based on metal oxide and two electrodes (2, 3) each arranged on one of two first and second end faces of the cylindrical resistance body (1) aligned in parallel to one another, characterized in that the electrode (2, 3) of the first and / or second end face except for at least 500 µm and up to a maximum of 10 µm is guided to the outer edge (9) of this end face, which is designed as an edge, and that the resistance body (1) has a conical bevel (5, 5 ') guided from this end face to its outer surface (8). Varistor, hergestellt nach einem Verfahren der Ansprüche 1 bis 4, der in einem elektrischen Feld vorgegebener Grösse mit mindestens einem hochenergetischen Stromimpuls definierter Amplitude, Form und Dauer belastbar ist, und der einen zylinderförmigen Widerstandskörper (1) aus einem Werkstoff auf der Basis von Metalloxid aufweist sowie zwei jeweils auf einer von zwei parallel zueinander ausgerichteten ersten und zweiten Stirnflächen des zylinderförmigen Widerstandskörpers (1) angeordnete Elektroden (2, 3), dadurch gekennzeichnet, dass die Elektrode (2) der ersten Stirnfläche bis auf mindestens 500 µm und bis auf höchstens 10 µm an den als Kante ausgebildeten Aussenrand (9) dieser Stirnfläche geführt ist und dass der Widerstandskörper (1) eine von der Elektrode (3) der zweiten Stirnfläche auf seine Mantelfläche (8) geführte konische Abschrägung (5') aufweist.Varistor, produced according to a method of claims 1 to 4, which can be loaded with at least one high-energy current pulse of defined amplitude, shape and duration in an electrical field of a predetermined size, and which has a cylindrical resistance body (1) made of a material based on metal oxide and two each electrodes (2, 3) arranged on one of two first and second end faces of the cylindrical resistance body (1) aligned parallel to one another, characterized in that the electrode (2) of the first end face to the at least 500 µm and up to at most 10 µm the outer edge (9) of this end face, which is designed as an edge, and that the resistance body (1) has a conical bevel (5 ') which is guided by the electrode (3) of the second end face onto its outer surface (8). Varistor nach den Ansprüchen 6 bis 8, dadurch gekennzeichnet, dass die konische Abschrägung (5, 5') mit der zugeordneten Stirnfläche einen stumpfen Winkel bildet.Varistor according to claims 6 to 8, characterized in that the conical bevel (5, 5 ') forms an obtuse angle with the associated end face. Varistor nach Anspruch 9, dadurch gekennzeichnet, dass der Winkel 100° bis 150°, vorzugsweise bis 100° bis 120° beträgt.Varistor according to claim 9, characterized in that the angle is 100 ° to 150 °, preferably up to 100 ° to 120 °.
EP99810304A 1998-05-06 1999-04-13 Method of manufacturing a metal oxide varistor and varistor made according to this method Expired - Lifetime EP0955644B1 (en)

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DE19820134A DE19820134A1 (en) 1998-05-06 1998-05-06 Varistor based on a metal oxide and method for producing such a varistor

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US20100189882A1 (en) * 2006-09-19 2010-07-29 Littelfuse Ireland Development Company Limited Manufacture of varistors with a passivation layer
CN113871118A (en) * 2017-05-16 2021-12-31 东莞令特电子有限公司 Base metal electrode for metal oxide piezoresistor

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ATE290251T1 (en) 2005-03-15
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US6199268B1 (en) 2001-03-13
US6346872B1 (en) 2002-02-12
DE19820134A1 (en) 1999-11-11
ES2239437T3 (en) 2005-09-16

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