EP0586410B1 - Silver-based contact material for use in power-engineering switchgear, and a method of manufacturing contacts made of this material - Google Patents

Abstract

PCT No. PCT/DE92/00388 Sec. 371 Date Nov. 24, 1993 Sec. 102(e) Date Nov. 24, 1993 PCT Filed May 14, 1992 PCT Pub. No. WO92/22080 PCT Pub. Date Dec. 10, 1992.In particular for contacts in low-voltage switches, the contact material consists of silver and further active components. In accordance with the invention, there are present as active components, in combination, iron oxide (Fe2O3/Fe3O4) in a proportion of between 1 and 50% by weight and at least one oxide of a further chemical element in a proportion of between 0.01 and 5% by weight. In particular, contact materials of the constitution AgFe2O3ReO2 and AgFe2O3ZrO2 have proven suitable in practice. The manufacture of the material and fabricating of the contacts can be effected by methods of powder metallurgy with the inclusion of molding or extrusion technique.

Description

The invention relates to a silver-based contact material for use in switching devices in power engineering, in particular for contact pieces in low-voltage switches, wherein in addition to silver as active components, at least iron oxide as the main component and at least one further metal oxide as the secondary component are present.

For contact pieces in low-voltage switching devices in energy technology, for example in circuit breakers and in direct current, motor and auxiliary contactors, contact materials are known on the one hand of the silver-metal system (AgMe) and on the other hand of the silver-metal oxide (AgMeO) system. Representatives of the first system are, for example, silver-nickel (AgNi) or silver-iron (AgFe); Representatives of the second system are in particular silver-cadmium oxide (AgCdO) or silver-tin oxide (AgSnO2). In addition, there may be other metal oxides, such as, in particular, bismuth oxide (Bi ₂ O ₃ ), copper oxide (CuO) and / or tantalum oxide (Ta ₂ O ₅ ).

The practical usability of a contact material based on silver-metal or silver-metal oxide is determined by the so-called electrical contact property spectrum. Relevant parameters are the lifetime switching number on the one hand, which is determined by the erosion of the contact, and the so-called overtemperature, ie the contact heating at the contact bridge, which essentially results from the electrical resistance of the contact structure mentioned, on the other hand. A sufficiently low tendency to weld the contact pieces and corrosion resistance are also important, since long-term corrosion of the material in air switchgear can change the switching properties over time.

From DE-A-1 608 211 an electrical contact material of the silver-metal oxide system is already known, which in addition to cadmium or tin oxide can also contain iron oxide. Furthermore, DE-C-38 16 895 describes the use of a silver-iron material with 3 to 30% by weight of iron and one or more of the additives manganese, copper, zinc, antimony, bismuth oxide, molybdenum oxide, tungsten oxide, chromium nitride Quantities totaling 0.05 to 5% by weight, balance silver, proposed for electrical contacts. In addition, DE-A-39 11 904 discloses a powder metallurgical process for producing a semi-finished product for electrical contacts from a silver-based composite material with iron, in which 5 to 50% by weight of iron is the first secondary component and 0 to 5% by weight. % of a second secondary component from one or more substances from the group which contains the metals titanium, zirconium, niobium, tantalum, molybdenum, manganese, copper and zinc as well as their oxides and their carbides. The iron in elemental form is obtained in particular by chemical precipitation. Finally, JP-A-1/055345 discloses a material of the type mentioned at the outset, which consists of a silver matrix distributed in 0.5 to 20 percent by weight of iron oxide particles, in which part of the iron oxide is formed by at least one of the oxides of nickel, cobalt, Chromium, molybdenum, tungsten, cadmium, zinc, antimony, tin, bismuth, indium, lead, manganese, beryllium, calcium, magnesium or copper is replaced. The contact pieces produced from this are said to be distinguished by good mechanical properties and high arc resistance for use in switches.

In the case of the materials of the prior art, not all requirements of the switching property spectrum are usually met at the same time. Ultimately, the aim is to achieve an optimum of the most important parameters adapted to the respective application.

Based on the above requirements, it is an object of the invention to provide further contact materials based on silver-iron oxide to find. These materials should be characterized by low contact heating with stable heating behavior, low tendency to weld and a long service life in relation to the switching currents. Good corrosion resistance should also be provided.

The object is achieved according to the invention by the combination of iron oxide and rhenium oxide as the active component, the iron oxide as the main component being present in mass fractions between 1 and 50% and the secondary components in mass fractions between 0.01 and 5%. Alternatively, the object is achieved according to the invention by the combination of iron oxide with bismuth zirconate, by the combination of iron oxide with boron oxide or by the combination of iron oxide with zirconium oxide, the iron oxide as the main component likewise in mass fractions between 1 and 50% and the alternative secondary components in mass fractions between 0.01 and 5%. The iron oxide can have the constitution Fe ₂ O ₃ or Fe ₃ O ₄ , but optionally also a mixed form.

The use of bismuth zirconate on the one hand and zirconium oxide on the other hand is known from EP-A-0 369 282 and EP-A-0 369 283 for sintered contact materials of the constitution AgSnO ₂ Bi ₂ O ₃ CuO. However, these materials are not comparable to contact materials based on AgFe ₂ O ₃ / Fe ₃ O ₄ .

In the context of the present invention, however, it was recognized that especially iron oxide as the main active component in conjunction with one of the specified metal oxides as the secondary component improves the property spectrum as a contact material. The iron oxide is preferably present in mass fractions of less than 40%, in particular less than 30%. Of the other oxides mentioned, the rhenium oxide, bismuth zirconate, boron oxide or zirconium oxide can be present either individually or in combination with different weightings.

A contact material of the type mentioned at the outset, in which the iron oxide is present in mass fractions of 2 to 20%, with an addition of 0.5 to 2 m% rhenium oxide, the remainder being silver, is particularly advantageous. In the case of a contact material of the type mentioned at the beginning, in which the iron oxide is present in mass fractions of 2 to 20%, it is also advantageous to add 0.05 to 3 m% bismuth zirconate or to add 0.05 to 0.5 m% boron oxide or Add 0.05 to 2 m% zirconium oxide with silver as the respective residue. The boron oxide is preferably boric acid.

Further details and advantages of the invention result from the following description of exemplary embodiments. On the one hand, different methods for producing the claimed material and, on the other hand, on the attached table with individual examples for specific material compositions according to the invention are discussed.

The table shows measured values for the overtemperature of the stressed materials, which was measured at the contact bridge of the switching device. The first column of the measured temperature values contains the maximum overtemperature and the second column of the measured temperature values contains the average bridge temperature, which is the temperature difference from room temperature. The temperature measured values were determined in series of switching tests in a 15 kW contactor up to a switching number of n _s = 50,000 switching operations.

The table comprises three exemplary embodiments with meaningful compositions of the contact material claimed. The production of the actual material and the production of the relevant contact pieces can be carried out done according to different methods. The measured value of the materials according to the invention is compared with AgFe ₂ O ₃ 6.4. An AgFe9 contact material is also listed in the table. The results are discussed in more detail below.

First manufacturing process:

Appropriate proportions of silver powder, iron oxide powder and rhenium oxide powder are mixed to produce a contact material AgFe ₂ O ₃ 5.7 ReO ₂ 1.1. Commercial oxide powders of iron or rhenium are used for this.

A powder mixture is prepared by wet mixing the oxide powders. From the powder mixture, strips or wires of the material are first produced as semi-finished products for the contact pieces using the so-called extrusion technique. The process conditions with regard to temperature on the one hand and pressure on the other hand are chosen so that undesired evaporation of rhenium is taken into account. For secure connection technology, it is advantageous to use the two-layer extrusion process to produce tapes with a solderable silver layer. Contact pieces with a directional structure can then be separated from the semi-finished product thus produced.

The proportions of silver, iron oxide and rhenium oxide can be varied using the same procedure. A material with the composition AgFe ₂ O ₃ 5.7 ReO ₂ 2.2 was also investigated.

Second manufacturing process:

In another process, the contact pieces are produced by molding technology. This is particularly advantageous if the further oxide as a side effect component is not rhenium oxide but, for example, zirconium oxide. Appropriate proportions of silver powder, Iron oxide powder and the zirconium oxide powder mixed together. A material with the composition AgFe ₂ O ₃ 5.4ZrO ₂ 1.0 was examined in detail.

In addition to silver powder and iron oxide powder, it can also be advantageous to use a powder composed of a mixture of two or more components of rhenium oxide, bismuth zirconate, boron oxide and zirconium oxide as a further additive. With a suitable coordination of the proportions of such a mixture, the advantages of the individual additional oxides can be combined with one another.

After wet mixing for a suitable period of time, molded parts are pressed from the powder mixture into contact pieces at a pressure of approx. 200 MPa. For secure connection technology of the contact piece to the contact piece carrier by brazing, it is again advantageous in this pressing process to press a second layer of pure silver together with the actual contact layer into a two-layer contact piece.

The molded parts are then sintered at a temperature of approximately 850 ° C. for about an hour. To achieve the lowest possible porosity of the finished contact pieces, the sintered bodies are then pressed at a pressure of approx. 1000 MPa and sintered again at approx. 800 ° C for about an hour. The contact pieces thus produced are again calibrated at a pressure of approx. 1000 MPa.

It is also possible to produce long-term mixing of the silver and single oxide powders in the manner of what is known as mechanical to produce suitable silver-metal oxide powder mixtures Alloying. As a result, the structural properties of the finished material are advantageously influenced. The contact pieces can in each case alternatively be produced by extrusion technology or molding technology. Especially when using rhenium oxide as an additional active component, possible evaporation of rhenium must be taken into account. This danger does not exist with zirconium oxide.

The table shows that the first two examples of the material according to the invention each have an average bridge temperature which is above the value of AgFe9 and also AgFe ₂ O ₃ 6.4. In contrast, the corresponding value in the third example is below the comparative examples. It should be noted that AgFe and AgFe ₂ O ₃ materials show a similar temperature behavior in this context. Overall, all values for the average bridge temperature are in a range of 70 ± 5 K.

Apart from the average bridge temperature, however, it can now be seen that the maximum excess temperature for all materials according to the invention is significantly lower than the comparative examples. In particular, the statistically occurring maximum values of overtemperature, which can lead to damage in the switchgear, have so far hardly been mastered.

From the measured values it is therefore possible to derive the knowledge that the addition of either rhenium oxide or in particular zirconium oxide decisively stabilizes the temperature behavior of an AgFe ₂ O ₃ material. The latter is expressed in the significantly lower maximum overtemperature.

According to the table, AgFe ₂ O ₃ ReO ₂ and AgFe ₂ O ₃ ZrO ₂ materials were examined in detail. The same positive influence as that of rhenium oxide or zirconium oxide can also be expected from other suitable oxide additives. For example, bismuth zirconate (2Bi ₂ O ₃ × 3ZrO ₂ ) or boric acid (H ₃ BO ₄ ) can also be used as suitable secondary components to the iron oxide. Mixtures of the individual components are also possible.

In the materials according to the invention, the iron oxide can also be in the constitution Fe ₃ O ₄ or in a mixed form instead of the chemical constitution Fe ₂ O ₃ . In particular, it can be seen that the iron oxide, in particular in mass fractions of 2 to 20%, the addition of rhenium oxide between 0.5 and 3 m%, the addition of bismuth zirconate between 0.05 and 3 m%, the addition of boric acid between 0, 05 and 0.5 m% and the addition of zirconium oxide should be between 0.05 and 2 m%. table material T _{Ü (max)} in K middle Bridge temp. in K. AgFe ₂ O ₃ 6.4 162 71 AgFe ₂ O ₃ 5.7 ReO ₂ 1.1 109 75 AgFe ₂ O ₃ 5.7 ReO ₂ 2.2 120 73 AgFe ₂ O ₃ 5.4ZrO ₂ 1.0 89 66 AgFe9 145 67

Claims (11)

1. Silver-based contact material for use in power engineering switchgear, in particular for contacts in low-voltage switches, wherein, in addition to silver, there are present as active components at least iron oxide (Fe₂O₃/Fe₃O₄) as main component and at least one further metal oxide as secondary component, characterised by the combination of iron oxide (Fe₂O₃/Fe₃O₄) and rhenium oxide (ReO₂) as active components, wherein the iron oxide (Fe₂O₃/Fe₃O₄) is present in proportions of between 1 and 50% by weight and the rhenium oxide is present in proportions of between 0.01 and 5% by weight.
2. Silver-based contact material for use in power engineering switchgear, in particular for contacts in low-voltage switches, wherein, in addition to silver, there are present as active components at least iron oxide (Fe₂O₃/Fe₃O₄) as main component and at least one further metal oxide as secondary component, characterised by the combination of iron oxide (Fe₂O₃/Fe₃O₄) and bismuth zirconate (2Bi₂O₃x3ZrO₂) as active components, wherein the iron oxide (Fe₂O₃/Fe₃O₄) is also present in proportions of between 1 and 50% by weight and the bismuth zirconate (2Bi₂O₃x3ZrO₂) is present in proportions of between 0.01 and 5% by weight.
3. Silver-based contact material for use in power engineering switchgear, in particular for contacts in low-voltage switches, wherein, in addition to silver, there are present as active components at least iron oxide (Fe₂O₃/Fe₃O₄) as main component and at least one further metal oxide as secondary component, characterised by the combination of iron oxide (Fe₂O₃/Fe₃O₄) and boron oxide (H₂BO₄) as active components, wherein the iron oxide (Fe₂O₃/Fe₃O₄) is present at between 1 and 50% and the boron oxide (H₂BO₄) is present at between 0.01 and 5%.
4. Silver-based contact material for use in power engineering switchgear, in particular for contacts in low-voltage switches, wherein, in addition to silver, there are present as active components at least iron oxide (Fe₂O₃/Fe₃O₄) as main component and at least one further metal oxide as secondary component, characterised by the combination of iron oxide (Fe₂O₃/Fe₃O₄) and zirconium oxide (ZrO₂) as active components, wherein the iron oxide (Fe₂O₃/Fe₃O₄) is present in proportions of between 1 and 50% by weight and the zirconium oxide (ZrO₂) is present in proportions of between 0.01 and 5% by weight.
5. Contact material according to claims 1 to 5, characterised in that the iron oxide (Fe₂O₃/Fe₃O₄) is present in proportions of less than 40% by weight.
6. Contact material according to claim 5, characterised in that the iron oxide (Fe₂O₃/Fe₃O₄) is present in proportions of less than 30% by weight.
7. Contact material according to claims 1 to 4, characterised by iron oxide (Fe₂O₃/Fe₃0₄) in proportions of 2 to 20% by weight, with an addition of 0.5 to 3% rhenium oxide (ReO₂), balance silver.
8. Contact material according to claim 2, characterised by iron oxide (Fe₂O₃/Fe₃O₄) in proportions of 2 to 20% by weight, with an addition of 0.05 to 3% bismuth zirconate (2Bi₂O₃x3ZrO₂), balance silver.
9. Contact material according to claim 3, characterised by iron oxide (Fe₂O₃/Fe₃O₄) in proportions of 2 to 20% by weight, with an addition of 0.05 to 0.5% boron oxide (H₂BO₄), balance silver.
10. Contact material according to claim 9, characterised in that the boron oxide (H₂BO₄) is boric acid.
11. Contact material according to claim 4, characterised by iron oxide (Fe₂O₃/Fe₃O₄) in proportions of 2 to 20% by weight, with an addition of 0.05 to 2% zirconium oxide (ZrO₂), balance silver.