EP0440620B2 - Semifinished product for electrical contacts, made of a composite material based on silver and tin oxide, and powder metallurgical process for producing it - Google Patents

Abstract

A semifinished product for electrical contacts, made of a composite material based on silver and tin oxide, has a microstructure in which regions containing little or no metallic oxide alternate with regions in which all or most of the metallic oxide component is finely distributed. Also described is a powder metallurgical process for producing the product.

Description

Technical field:

The invention relates to a semi-finished product for electrical Contacts made of a composite material based on silver-tin oxide and a powder metallurgical Process for its manufacture.

State of the art:

The invention is based on an entanglement with those specified in the preamble of claim 1 Characteristics or of a semi-finished product with the specified in the preamble of claim 12 Characteristics.

Contact materials based on silver-tin oxide currently have the best views, the proven ones but because of the toxicity of the cadmium in Contact materials based on bad reputation of silver-cadmium oxide to replace. The size Meaning, the contact pieces made of silver-cadmium oxide in low-voltage switchgear, in particular in motor contactors is due to that they have long life, low Welding tendency, consistently low contact resistance (and thus a small one Contact heating), good arc quenching and Optimally combine good workability. Today known contact pieces on the base The contact pieces are exposed from silver-tin oxide Silver-cadmium oxide in the combination of their properties closest, but still reach not such favorable properties in all of the above mentioned points at the same time.

It is known (DE-26 59 012 B2) that a distribution of the metal oxides as fine as possible in the Silver matrix with favorable contact properties leads. Silver cadmium oxide materials are therefore often by internal oxidation of a silver-cadmium alloy produced. Semi-finished products made of silver-tin oxide however, in general not by internal oxidation of a corresponding one Manufacture the workpiece from a silver-tin alloy, because a complete oxidation of the inside of the workpiece located by the Formation of passive layers is hindered, so that the oxidation is practically on a surface layer is limited. By adding more oxidizable Metals, namely indium or bismuth, can form a passivating layer are largely suppressed (DE-A 29 08 923). Contact pieces formed from such materials can contact pieces made of silver-cadmium oxide in service life under AC3 and AC4 test conditions (specified in IEC standard 158-1) be, however, show a stronger contact warming in the switchgear. what the lifespan of the Switchgear can impair. Moreover can the internally oxidized contact pieces subsequently no longer be deformed.

It is also known to make contact materials made from silver-tin oxide to manufacture by powder metallurgy, namely by mixing a silver powder with a tin oxide powder, forming silver tin oxide blanks by pressing and sintering the Powder mixture, and forming of the blanks by extrusion or by extrusion and rollers. Compared to a silver-cadmium oxide contact material can be such a powder metallurgy manufactured material if it is additional small amounts of tungsten oxide or molybdenum oxide contains, in contact heating approximately equally good and in the AC4 durability test perform better in the AC3 endurance test however, it does worse. Forming the blanks by rolling or extrusion is difficult because the tin oxide particles in the Silver-tin oxide composite whose plastic Extremely hinder deformation. Aggravating In addition, the processability of the Silver-tin oxide becomes more difficult the finer the tin oxide is dispersed in the material, because the more effectively the tin oxide particles interfere during mechanical forming of the composite material its plastic deformation. To the Countering poor processability is therefore proposed in DE-A 29 52 128 that Tin oxide powder before mixing with the silver powder to glow at 900 ° C to 1600 ° C, whereby the tin oxide powder particles are coarsened and so the later mechanical transformation of the Hinder composite less. The better one However, workability is bought with a partial deterioration of the switching properties of the contact pieces because the tin oxide is not is distributed as finely as possible in the composite material formerly.

Semi-finished products for electrical contacts made from a powder metallurgically manufactured composite based on silver-tin oxide an addition of at least one further metal oxide (Molybdenum oxide, tungsten oxide, bismuth titanate) and a carbide component (tungsten carbide and / or molybdenum carbide) consist of known from DE-32 32 627 C2.

It is known from EP 0 170 812 A2 Silver, tin, bismuth and copper an AgSnBiCu alloy to melt, by pressure atomization to produce an alloy powder from the melt, to oxidize this internally and from it Pressing and sintering to form contact pieces. Compared with contacts made of silver-cadmium oxide these contact pieces show approximately one equally strong warming and have a longer one Service life in the AC3 test, but a shorter one Service life in the AC4 test.

From DE-29 29 630 A1 it is known a Silver-tin oxide composite powder after a pyrolytic Process to manufacture and from this composite powder by pressing and sintering contact pieces to shape. Compared to contact pieces Silver-cadmium oxide contact pieces show this Contacts have a longer lifespan, but more contact warming and one poorer processability. The same applies for powder metallurgy known from DE 32 12 005 A1 from a silver tin oxide composite powder manufactured contact piece with an oxide-free Back made of copper or a copper alloy. From the same DE 29 29 630 A1 it is also known, additionally tungsten oxide in the composite powder or store molybdenum oxide. This can contact heating is reduced, at the same time, however, the lifespan decreases AC3 exam.

DE-B-26 59 012 is a powder metallurgy Process for the production of a contact material made of silver with two different ones Metal oxides known in which two silver-metal oxide composite powders mixed, pressed and sintered, one of which is Compound powder just one metal oxide and that other composite powder only the other metal oxide contains.

Presentation of the invention:

The object of the present invention is to achieve this based on a semi-finished product for electrical contacts to provide the base silver-tin oxide which is despite a very small content Tin oxide particles work well by extrusion and rolling can be processed and at the same time regarding Lifetime, tendency to weld and contact heating is as good or better than semi-finished products are based on silver-cadmium oxide.

This problem is solved by a method with the features specified in claim 1 and by a semi-finished product with the in claim 12 specified features. Advantageous further training the invention are the subject of the dependent claims.

The semifinished product produced according to the invention consists of a composite material, which is through a special rough structure in combination with a special fine structure. The Coarse structure is given by the fact that in the composite material oxide rich areas where everything Metal oxide or the vast majority of Metal oxide component is concentrated, alternate with low-oxide areas. the only a small one Contain or even share of the metal oxide component are oxide free. Contain the low-oxide areas at most a small amount of metal oxide finely distributed in one from the material of the first component formed matrix. The oxide rich areas contain the lion's share of the metal oxide component (in a concentration that is far greater is higher than the usual average metal oxide concentration in a contact material based on silver-tin oxide) and the rest of the material of the first component like a penetration or a storage composite finely divided into one another. These areas have emerged from low-oxide and high-oxide powders, which were mixed, pressed and, if necessary, sintered. The size of the low and high oxide areas, which is the rough structure of the composite determine therefore depends on the size of the powder particles from. The fine structure of the composite is given by a finely dispersed oxide distribution in the oxide-rich forming the rough structure Areas of the composite, if necessary also in low-oxide areas, so far are present in these metal oxides. It is best total metal oxide component used in the Composite powder concentrated, so the other Powder, which is the major part of the silver or mainly containing silver Alloy (first component) contains, completely oxide-free is. In this case, change in the composite material Areas where the metal oxide component is focused, with areas that are completely devoid of of the metal oxide component. That has the advantage, that the areas that the metal oxide component, in particular the tin oxide, from one another largely through an oxide-free matrix are separated (they "swim" as it were in one oxide-free matrix) so that they undergo plastic deformation when rolling or extruding the Semi-finished goods much less than in the case of more or less evenly over the whole Distributed metal oxides material. In contrast stands out the semi-finished product according to the invention through improved ductility. However, this is not bought by an increased one Tendency to sweat or due to a reduced service life or by an increased electrical Contact resistance.

This surprisingly favorable behavior of the Contact material produced according to the invention is probably due to the fact that the Contact material from known contact materials on silver-tin oxide basis not by an altered Overall oxide content, but by that this total oxide content is due to novel Distributed in the material, namely, that areas with honer metal oxide concentration in Alternate material of the first component with Areas of low or vanishing metal oxide concentration in the material of the first component, being because of the powder metallurgical manufacture the size of these areas by the size depends on the powder particles that make up the composite will be produced. In the fields of of the composite in which the metal oxide component is present, it should according to the invention in very fine distribution. The total salary the metal oxide component in the semifinished product can and should be in the usual range between 5 and 25% by weight lie.

Whilst it is preferred, the entire metal oxide component in which a composite powder concentrate with the result that you are in the semi-finished product Has areas that are completely free of metal oxides and therefore the deformability of the semi-finished product becomes particularly good, it is possible a small amount of metal oxide in the second powder to accommodate most of the Contains silver or the silver alloy; in this second powder, which is a composite powder or can be a powder mixture, the content of the tin oxide and, if applicable, the further oxides taken together 3 % By weight (based on the weight of this second Powder). This share could can be added individually or as a composite powder.

Surprisingly, it has been shown that produced from the semi-finished product according to the invention Contact pieces opposite in a conventional way manufactured contact pieces of the same composition a lower electrical contact resistance have and thus a lower Contact heating show what another essential advantage of the invention is. Probably this is related to the fact that the invention The tin oxide contacts less accumulates strongly on the contact surface, whereby the only partially high, finely dispersed distributed, tin oxide content for switching behavior is cheap, e.g. only a slight tendency to weld has the consequence.

It has also been shown that from the inventive Semi-finished contacts one suffer less burnout than conventional ones Wise manufactured contact pieces of the same composition. The lifespan based the AC3 and AC4 tests is higher than at comparable AgCdO contacts.

This is also an advantage of the invention.

To the working material structure according to the invention with the low-oxide and high-oxide areas the majority of the metal oxide component must come concentrated in the composite powder and be involved. Only the relatively small one Metal oxide content, which may still be in the contain low-oxide areas of the composite material can be e.g. in the form of a pure Oxide powder with the powder from the first component of the material are mixed. Doing so it prefers that in the low-oxide areas the same oxides are present as in the oxide-rich ones Areas. The part of the second component any metal carbides still present (especially tungsten carbide and / or molybdenum carbide) and those not solved in the first component Metals (especially tungsten and / or molybdenum) can separate the powder mixture in the form Powders are added; they are suitable in switching operation the wetting of the tin oxide with To promote silver and thereby the contact resistance to humiliate.

The composite powder is produced by that you have an aqueous solution of salts of the metals of the first component and tin in a hot, oxidizing atmosphere sprayed and so the salts pyrolytic decomposes. This is also known as spray pyrolysis The procedure is e.g. in US-A 3,510,291, in EP-0 012 202 A1 and in DE-29 29 630C2 described. Doing so for the composite powder intended metals dissolved in a liquid and the solution in a hot reactor or in a Flame atomized into it, leaving the solvent evaporated suddenly. The resulting Solid particles react with the oxygen in the oxidizing atmosphere in the flame or in the reactor at a temperature below that Melting temperature of the dissolved metals, whereby Powder particles arise in which the metals of the first component, i.e. the silver or the silver alloy, and the metal oxide component, so essentially tin oxide, in a very fine distribution tied together. In the through the spray pyrolysis produced composite powder the metal oxide particles mostly in sizes between 0.1 µm and 1 µm (diameter) before what for the inventive method is advantageous. The Presence of such fine metal oxide particles favors the formation of the desired properties the contact pieces (low erosion, low Welding tendency, consistently lower Contact resistance) especially if this oxide component in combination with an electrical highly conductive material (first component) is present, which is the case according to the invention.

The use of spray pyrolysis Compound powder is also advantageous because by spray pyrolysis, in particular powder particles arise that are spherical or potato-shaped Have shape, the emergence of a deformable Semi-finished products favored because the spherical or potato-shaped particles of a plastic Deformation of the contact material less oppose as irregularly jagged powder particles.

The possibly in addition to the tin oxide provided oxidic and carbidic components sometimes lower the contact point temperature in switching operation and partly an extension of the life of the contact pieces not only with small and medium current loads, but also in the heavy load area. Molybdenum carbide and tungsten carbide already work in small amounts. The additional carbides and Oxides should make up 6% by weight of the contact material not exceed so this does not gets too hard.

The addition of nickel can also be advantageous to the composite material, which is not in silver is soluble and either as a very fine powder that formed from silver or a silver alloy Powder is mixed or also as spray-pyrolysized silver-nickel powder is introduced.

WAYS OF CARRYING OUT THE INVENTION: 1st example

A silver-tin oxide composite powder with 32% by weight of tin oxide is produced by spraying an aqueous solution of silver nitrate and tin-II-chloride in a reactor heated to approx. 950 ° C. with an oxygen-containing atmosphere, whereby a silver-tin oxide composite powder fails , in the powder particles of which the tin oxide is present in a very fine distribution. Then 75 parts by weight of a silver powder with a particle size smaller than 40 microns with 25 parts by weight of the silver-tin oxide, composite powder are dry mixed for one hour, then isostatically pressed to blocks of about 50 kg in weight and then at a temperature sintered at 830 ° C for 1.5 hours. The block thus formed is placed in the recipient of an extrusion press and hot-extruded, reducing the cross-section to a strand with a cross-section of 10 x 75 mm ² , at a temperature of approx. 850 ° C., and then hot-rolled plated with a 1.5 mm thick fine silver sheet , hot rolled down to its final thickness of 2mm and processed into contact wafers according to the usual methods. The silver-tin oxide composite in the contact wafers has a tin oxide content of 8% by weight.

2nd example

The second example is modified that the powder mixture still contains 0.5% by weight Tungsten oxide (particle size smaller than 10 µm) and 0.3 wt% tungsten carbide (particle size smaller than 2.5 µm) are added. Furthermore is operated as in the first example. The addition of tungsten oxide and tungsten carbide leads to one Lowering the contact point temperature and to an extended lifespan from the Semi-finished electrical contact pieces.

3rd example

A silver-tin oxide-tungsten oxide composite powder with 20% by weight of tin oxide and 0.5% by weight of tungsten oxide is made by spraying an aqueous Solution of silver nitrate, tin-II-chloride and Tungsten ll chloride in a heated to approx. 950 ° C Reactor with an oxygen-containing atmosphere, being a silver-tin oxide-tungsten oxide composite powder precipitates, in the powder particles of the tin oxide and the tungsten oxide is in a very fine distribution. Then 50 parts by weight of a Silver powder with a particle size smaller than 40 µm with 50 parts by weight of the silver-tin oxide-tungsten oxide composite powder dry for an hour mixed and as in the 1st example for contact plates processed further.

4th example

A silver-tin oxide composite powder with 30 % By weight of tin oxide is produced as in the second example. A silver-nickel composite powder with 2 wt .-% Nickel is made by spraying one aqueous solution of silver nitrate and nickel-II-chloride in a reactor heated to approx. 950 ° C with a protective gas atmosphere (e.g. argon), whereby a silver-nickel composite powder fails, in the Powder particles the nickel in a very fine distribution is present.

Then 50 parts by weight of the silver-tin oxide composite powder and 50 parts by weight of the Silver-nickel composite powder for one hour mixed dry and as in the first example too Contact plates processed further.

5th example

The fourth example can be modified accordingly be that instead of a silver-nickel composite powder a silver powder and a carbonyl nickel powder mixed with the silver-tin oxide composite powder will. Otherwise the same as in the 4th example method.

Description of the drawing:

The attached figure shows schematically the Structure of one according to the second example manufactured composite, in which silver-tin oxide areas 1, mostly less than 50 µm, are in a silver matrix that consists of the oxide-free silver powder particles has emerged.

Industrial applicability:

Semi-finished products produced according to the invention are suitable are particularly suitable for contact pieces in low-voltage switching devices, e.g. in motor contactors.

Claims (28)

1. A powder-metallurgical process of producing a semi-finished product made of silver and tin oxide for use in electric contacts, consisting of a composite material which consists of 60 to 95 % by weight of a first component having a high electric conductivity, namely, silver or an alloy mainly consisting of silver,

   whereas the remainder consists of a second component, which is insoluble in the first component and decreases the tendency to exhibit contact welding and the contact burn-off and consists based on the weight of the composite material of 3 to 25 % by weight tin oxide, 0 to 10 % by weight of one or more further metal oxides which together with the tin oxide will be described hereinafter as the metal oxide component, 0 to 10 % by weight of one or more metal carbides and 0 to 10 % by weight of one or more further metals, which are insoluble in the first component,

   wherein the tin oxide predominates in the second component and the average content of the metal oxide component is not in excess of 25 % by weight of the composite material, wherein

   a composite powder which is produced in that a solution of salts of metals of the first component and of a salt of tin is sprayed into a hot oxidizing atmosphere, in which the salts are pyrolytically decomposed, and which contains less than one-half of the first component and 60 to 100 % based on the metal oxide component of the metal oxide component

   is mixed with one or more powders which contain the remainder of the first component and of the second component and

   the powder mixture is compacted to form shaped pieces consisting of the composite material.
2. A process according to claim 1, characterized in that the shaped bodies are subsequently sintered.
3. A process according to claim 1 or 2, characterized in that the shaped bodies are subsequently deformed by coining extruding or by extruding followed by rolling.
4. A process according to claim 1, characterized in that the entire metal oxide component is incorporated in the composite powder.
5. A process according to claim 4, characterized in that the entire second component is incorporated in the composite powder.
6. A process according to claim 1 or 4, characterized in that the further metal oxides in pulverulent form are mixed with the powder of the first component and with the composite powder of the second component.
7. A process according to claim 1 or 4, characterized in that the metal carbides in pulverulent form are mixed with the powder of the first component and with the composite powder of the second component.
8. A process according to claim 1 or 4, characterized in that the further metals of the second component in pulverulent form are mixed with the powder of the first component and with the composite powder of the second component.
9. A process according to claim 1, characterized in that the solution contains also salts of the further oxidizable metals.
10. A process according to claim 9, characterized in that the solution contains salts of all oxidizable metals which are intended for the second component.
11. A process according to any of the preceding claims, characterized in that the composite powder is not in excess of 45 % by volume of the powder mixture.
12. A semi-finished product produced by a process according to claim 1,which is made of silver and tin oxide and intended for use in the manufacture of electric contacts, consisting of a composite material that consists of 60 to 95 % by weight of a first component having a high electrical conductivity, namely of silver or an alloy which mainly contains silver, and 40 to 5 % by weight of a second component, which is distributed but insoluble in the first component and reduces the tendency to exhibit contact welding and burn-off and which based on the weight of the composite material contains 3 to 25 % by weight of tin oxide, 0 to 10 % by weight of one or more further metal oxides which together with the tin oxide will be described hereinafter as the metal oxide component, 0 to 10 by weight of one or more metal carbides and 0 to 10 % by weight of one or more further metals, which are insoluble in the first component,
       wherein the tin oxide predominates in the second component and the average content of the metal oxide component is not in excess of 25 % by weight of the composite material,
       characterized in that the structure of the composite material comprises low-oxide regions, in which the content of the metal oxide component is 0 to 20 % of its average content and is present in a fine distribution in a matrix consisting of the material of the first component, in alternation with high-oxide regions comprising the metal oxide component in an amount of 1.5 to 6 times its average content as averaged over the semi-finished product and the remainder of the first component finely distributed one into another,
       wherein the low-oxide regions and the high-oxide regions are present in the composite material in a statistically uniform distribution and a substantial part of the high-oxide regions is surrounded by the low-oxide regions.
13. A semi-finished product according to claim 12, characterized in that the low-oxide regions occupy at least 40 % by volume of the composite material and the high-oxide regions occupy the remainder of the volume of the composite material.
14. A semi-finished product according to claim 13, characterized in that the low-oxide regions occupy at least 55 % by volume of the composite material.
15. A semi-finished product according to any of claims 12 to 14, characterized in that the metal oxide component has the same composition in the low-oxide regions and in the high-oxide regions.
16. A semi-finished product according to any of claims 12 to 14, characterized in that the entire metal oxide component is concentrated in the high-oxide regions.
17. A semi-finished product according to claim 16, characterized in that the entire second component is concentrated in the high-oxide regions.
18. A semi-finished product according to any of claims 12 to 17, characterized in that the high-oxide regions are smaller than 500 x 10^-6 mm³.
19. A semi-finished product according to claim 18, characterized in that the high-oxide regions are smaller than 35 x 10^-6 mm³.
20. A semi-finished product according to any of claims 12 to 19, characterized in that the first component consists of fine silve
21. A semi-finished product according to any of claims 12 to 19, characterized in that the first component is an alloy of silver and 0.1 to 10 % by weight of copper.
22. A semi-finished product according to any of claims 12 to 19, characterized in that the first component is an alloy of silver and 0.1 to 10 % by weight of palladium.
23. A semi-finished product according to any of claims 12 to 21, charcterized in that the second component contains a refractory metal in an amount of 0.1 to 10 % by weight of the entire composite material.
24. A semi-finished product according to claim 23, characterized in that the refractory metal is tungsten or molybdenum.
25. A semi-finished product according to any of claims 12 to 24, characterized in that the further metal oxides contained in the second component are selected from the group consisting of tungsten oxide, molybdenum oxide, vanadium oxide, bismuth oxide, bismuth titanate, and copper oxide.
26. A semi-finished product according to any of claims 12 to 25, characterized in that the metal carbide contained in the second component is selected from the group comprising tungsten carbide and molybdenum carbide.
27. A semi-finished product according to any of claims 12 to 26, characterized in that the composite material contains up to 10 % by weight of nickel.
28. A semi-finished product according to claim 27, characterized in that the composite material contains less than 1 % by weight of nickel.

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