EP0586411B1 - 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/DE92/00384 Sec. 371 Date Nov. 23, 1993 Sec. 102(e) Date Nov. 23, 1993 PCT Filed May 13, 1992 PCT Pub. No. WO92/22079 PCT Pub. Date Dec. 10, 1992.The contact material in particular for contacts in low-voltage switches consists of silver and further active components. In accordance with the invention, iron (Fe) in proportions of between 1 and 50% by weight and rhenium (Re) in proportions of between 0.01 and 5% by weight are present in combination as active components. The manufacture of the material and the fabricating of the contacts can be effected by methods of powder metallurgy with inclusion of molding or extrusion techniques, the active components being used in the form of separate powders, as fusible alloy or as mechanically alloyed powder.

Description

The invention relates to an improvement in a silver-based contact material for use in switchgear in power engineering, in particular for contact pieces in low-voltage switches, which, in addition to silver, contains at least one higher-melting metal, a metal alloy or a metal compound as further active components. In addition, the invention also relates to a method for producing contact pieces from such a material.

For contact pieces in low-voltage switching devices in energy technology, e.g. In circuit breakers as well as in direct current, motor and auxiliary contactors, contact materials of the silver-metal system (AgMe) have proven themselves for a long time. Examples of this system are silver-nickel (AgNi) and silver-iron (AgFe).

Silver-nickel has advantageous contact properties which, together with the test methods for contact materials, for example in INT.J. Powder Metallurgy and Powder Technology, Vol. 12 (1976), P 215-228. However, it is disadvantageous that nickel dust in particular has harmful effects on the human organism.

The use of iron in silver-based contact materials has been proposed in various ways. It has However, it has been shown that silver-iron does not yet meet the requirements, since excessive heating occurs when such contact pieces are supplied with current, which can be explained by the formation of a contact layer in this system which increases the contact resistance. Furthermore, DE-OS 3 813 311 (WO-A-89/10417) discloses a sintered contact material of the type mentioned at the outset which, in addition to silver, contains at least iron and / or titanium as the active component. Particularly when the iron and the titanium are in an alloyed form and form an intermetallic compound, good results have been observed in switching tests. Optionally, nitrides, carbides and / or borides of metals, in particular titanium, may be present as further active components.

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, the remainder silver proposed for electrical contacts. Finally, 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 wt .-% iron as a first minor component and 0 to 5 wt .-% of a second minor component from one or more substances from the group comprising the metals titanium, zirconium, niobium, tantalum, molybdenum, manganese, copper and contains zinc as well as their oxides and their carbides.

DE-C-888 178 specifies a contact material which can contain silver, rhenium and iron.

Starting from the above prior art, it is an object of the invention to provide a further contact material based on silver-iron and find the associated manufacturing process. The new material should be characterized by low contact heating with stable heating behavior, acceptable tendency to weld and a long service life in relation to specified switching currents.

The object is achieved according to the invention in a material of the type mentioned at the outset that the active components in combination are iron in mass fractions between 1 and 50% and rhenium in mass fractions between 0.01 and 5%. To produce contact pieces from the material according to the invention, the iron and the rhenium can be added to the silver in the form of pure metals and / or as an alloy, the material being produced by powder metallurgy. The ratio of the mass fractions of iron to rhenium can be between approximately 4: 1 and approximately 20: 1.

In the context of the present invention, it was recognized that especially rhenium in combination with iron and silver improves the property spectrum as a contact material. The use of rhenium in combination with silver has already been proposed in the specialist literature. There, however, the rhenium was provided as the only component with a comparatively high proportion, for example around 20 percent by mass. Due to the high price, such a material could not prevail. It has now been recognized in the context of the invention that rhenium, as a minor component, improves a silver-iron material to the desired extent.

In a preferred development of the invention, the iron content will be considerably less than 50%. Especially With such a material, the iron will be in a mass fraction of 2 to 25% and the rhenium in a mass fraction of 0.1 to 3%. Switching tests with contact materials in which the iron is in a mass fraction of 2 to 10% and the rhenium in a mass fraction of 0.1 to 1% have shown particularly advantageous results. The total volume fraction of the two active components can fluctuate within comparatively wide limits. For example, it is 6, 12 or 18%.

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

The table shows measured values for the overtemperature of the stressed materials, which were measured on the contact bridge of the switching device. The first column of the temperature measurements contains the maximum overtemperature (T _{Ü max} ) and the second column the mean bridge temperature (T _Ü ), which are the temperature difference to the room temperature. The temperature measured values were determined in tests with a 15 KW contactor up to a switching number of n _s = 50,000 switching operations.

The table comprises six exemplary embodiments with meaningful compositions of the claimed silver-iron-rhenium contact material. Here is the manufacture the actual material and the manufacture of the relevant contact pieces is carried out according to partly different methods. The measured values of the individual AgFeRe materials are compared with AgFe9 and AgRe20 and with pure silver. The results are discussed in more detail below.

First manufacturing process:

To produce a contact material Ag (FeRe20) 5,7, an iron-rhenium alloy is first melted from 80 parts of iron and 20 parts of rhenium. This alloy melt is atomized in the molten state by known methods, so that a FeRe composite powder is present in each case. A particle size of about 25 »m is sieved from the powder.

A corresponding amount of commercially available silver powder is then weighed into the alloy powder, so that a material with a mass fraction of 5.7 iron-rhenium and the rest silver is formed. 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 a secure connection technique of the contact piece to the contact piece carrier by brazing, it can be 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 sintered at a temperature of approx. 850 ° C. for about an hour in a vacuum or under protective gas. To achieve the lowest possible porosity of the finished contact pieces are then the sintered bodies are pressed at a pressure of approx. 1000 MPa and sintered again at approx. 650 ° C for about an hour in a vacuum or under protective gas. The contact pieces thus produced are again calibrated at a pressure of approx. 1000 MPa.

The proportions of silver and FeRe alloy can be varied using the same procedure. A material with 9.9 parts by mass of FeRe20 was examined, the rest silver.

Second manufacturing process:

Another process uses separate powders of iron, rhenium and silver as the starting material. A powder mixture is prepared by wet mixing the individual powders. From the powder mixture, strips or wires of the material are first produced as semi-finished products using the so-called extrusion technique. The process conditions with regard to temperature on the one hand and pressure on the other hand are in the known order of magnitude. Contact pieces with a directional structure can then be separated from the semi-finished product thus produced.

The powder metallurgical method for producing the additional components was used to produce three materials in which the ratio of iron to rhenium was approximately 4: 1 or 9: 1. The total proportion of the additional components was selected as an alternative to 5.3 m%, 5.7 m% and 9.4 m%. Another material was manufactured with a ratio of iron to rhenium of 19: 1 and a total share of the additional components of 8.8 m%.

It is also possible to combine the different methods given by way of example in the production of the additional components on the one hand and the production of the contacts on the other in a different way. In particular, the alloys or the powder mixtures can be produced by so-called mechanical alloying of single-component individual powders. As a result, the structural properties of the finished material are advantageously influenced.

The table shows that in all five examples of the material according to the invention according to different methods or the contact pieces made therefrom, there are sufficient switching numbers, which in any case are more than 50,000. Such switching numbers cannot be achieved with silver-rhenium or pure silver.

In addition to the number of switching operations, the overtemperature in the switching device is decisive for the use of the switching material. The latter can be measured at different points on the switchgear and is recorded directly on the bridge in the case of available examinations. In this respect, the comparative examples must be observed.

As can be expected, pure silver or silver-rhenium 20 have a favorable overtemperature behavior with low switching numbers. In contrast, AgFe9 shows such a high excess temperature that is no longer accepted in practice. The high excess temperature can be explained by the formation of the cover layer, which increases the contact resistance and thus leads to increased heating at the contact.

In contrast, all examples of the material according to the invention show that the excess temperature is reduced. Although the values of pure silver or silver-rhenium are not reached, the order of magnitude permits the use of the material in switchgear. It must be taken into account that the maximum overtemperature values of the contact bridge are given in the first column. If you also take into account the average bridge temperatures according to the last column, you get extremely favorable values there.

The comparison of the material with the prior art shows that the combination of silver with iron and rhenium realizes a material with low contact heating and stable heating behavior and a long service life in relation to the switching current values. This represents a considerable advance over the state of the art.

Claims (19)

1. Contact material based on silver for use in switchgear and control gear in power engineering, in particular for contact makers in low-tension switches, which material contains, in addition to silver, at least one metal of higher melting point, one metal alloy or one metal compound as further active components, characterised in that iron (Fe), in proportions by mass of between 1 and 50%, and rhenium (Re), in proportions by mass of between 0.01 and 5%, are present in combination as active components.
2. Contact material according to Claim 1, characterised in that iron (Fe) is present in proportions by mass of less than 40%.
3. Contact material according to Claim 2, characterised in that iron (Fe) is present in proportions by mass of less than 30%.
4. Contact material according to Claim 1, characterised in that rhenium (Re) is present in proportions by mass of less than 4%.
5. Contact material according to Claim 4, characterised in that rhenium (Re) is present in proportions by mass of less than 3.5%.
6. Contact material according to Claim 1 or one of Claims 2 to 5, characterised in that iron (Fe) is present in proportions by mass of 2 to 25% and rhenium (Re4) is present in proportions by mass of 0.1 to 3%.
7. Contact material according to Claim 6, characterised in that iron (Fe) is present in proportions by mass of 2 to 20% and rhenium (Re) is present in proportions by mass of 0.1 to 2%.
8. Contact material according to Claim 7, characterised in that iron (Fe) is present in proportions by mass of 2 to 10% and rhenium (Re) is present in proportions by mass of 0.1 to 1.0%.
9. Contact material according to one of the preceding claims, characterised in that the ratio of the proportions by mass of iron (Fe) to rhenium (Re) is between 4:1 and 20:1.
10. Contact material according to one of the preceding claims, characterised in that the proportion by volume of the active components together is about 6%.
11. Contact material according to one of the preceding claims, characterised in that the proportion by volume of both active components together is about 12%.
12. Contact material according to one of the preceding claims, characterised in that the proportion by volume of the active components together is about 18%.
13. Process for the production of contact makers from material according to Claim 1 or one of Claims 2 to 12, characterised in that the production is carried out by powder metallurgy, an alloy first being produced from iron and rhenium and said alloy being atomised to form an alloy powder and the contact makers being produced from silver powder and the alloy powder, optionally via a semi-finished product.
14. Process according to Claim 13, characterised in that the production of the FeRe alloy is carried out by melting under vacuum or under a blanketing gas.
15. Process according to Claim 13, characterised in that the production of the FeRe alloy is carried out by mechanical alloying under vacuum or under a blanketing gas.
16. Process for the production of contact makers from a material according to Claim 1 or one of Claims 2 to 12, characterised in that the production is carried out by powder metallurgy, separate silver, iron and rhenium powders being used, from which the contact makers are produced, optionally via a semi-finished product.
17. Process for the production of contact makers from a material according to Claim 1 or one of Claims 2 to 12, characterised in that the production is carried out by powder metallurgy, separate silver, iron and rhenium powders being mechanically alloyed, from which alloy the contact makers are produced, optionally via a semi-finished product.
18. Process according to one of Claims 13, 16 or 17, characterised in that the production of the contact makers is carried out by means of a moulding technique.
19. Process according to one of Claims 13, 16 or 17, characterised in that the production of the contact makers is carried out by means of extrusion moulding, to which end an extrusion-moulded semi-finished product, from which contact makers can be separated off, is first produced from the powders.