EP2513932B1 - Methods for manufacturing a stud of an electric contact and an electric contact - Google Patents

Description

Technical area

The present invention relates to the field of electrical contacts. It relates, more particularly, to a method of manufacturing an electrical contact pad and a method of manufacturing an electrical contact, as well as an electrical contact pad and an electrical contact that can be obtained by their manufacturing method. respective.

State of the art

The so-called "low voltage" electrical contacts, that is to say whose operating range is approximately between 10 and 1000V and between 1 and 10000A, are generally used in the domestic, industrial and automotive fields, as well as in electricity. AC current, for switches, relays, contactors and circuit breakers, etc.

• une résistance de contact faible et stable pour éviter un échauffement excessif lors du passage du courant ;
• bonne résistance au soudage en présence d'un arc électrique ; et
• faible érosion sous l'effet de l'arc.

The electrical contacts are made from materials that must meet the following three requirements:

• a low and stable contact resistance to prevent overheating during current flow;
• good resistance to welding in the presence of an electric arc; and
• weak erosion under the effect of the arc.

In order to satisfy these partially contradictory requirements, one solution consists in using pseudoalloys comprising a matrix of silver or copper in order to make the stud, and, inserted in this matrix, a fraction consisting of approximately 10 to 50% by volume. refractory particles (for example, Ni, C, W, WC, CdO, SnO ₂ ) generally between 1 and 5 microns in size. The material thus obtained is more resistant to the energy released by the electric arc.

In a conventional manner known to those skilled in the art, the pad can be obtained from powders, by compacting-sintering or compacting-sintering-extrusion-rolling-cutting. Then, the stud is assembled on a suitable contact support, very good conductor of electricity and heat, to get electrical contact. The assembly of the stud on the contact support can be done by welding, brazing or riveting, for example.

More particularly, the contact support is traditionally copper. The pad being made to be resistant to welding, the assembly of the pad on the copper by welding is difficult. It is therefore necessary to add on the pad a silver bonding layer for example.

These conventional processes involve many operations that result in a high manufacturing cost.

Moreover, it is very difficult to assemble the stud by welding or brazing on an aluminum contact support, because it requires heating the support to a temperature close to its melting point.
The document FR 2 931 303 A1 describes a method according to the preambles of claims 1 and 3.

An object of the present invention is therefore to overcome these disadvantages by providing a method of manufacturing an electrical contact pad and methods of manufacturing an electrical contact to simplify the known methods by reducing the number of operations.

Another object of the present invention is to provide a method of manufacturing an electrical contact making it easier to use aluminum as an electrical contact support material.

Disclosure of the invention

For this purpose, and according to a first aspect of the present invention, there is provided a method of manufacturing at least one electrical contact pad comprising a pad support and at least one contact layer, said method comprising a step of deposition, by dynamic spraying by cold gas, of a first powder on said pad support to form said contact layer, said first powder containing at least particles comprising grains of at least one refractory material incorporated in a matrix based on conductive metal selected from silver or copper.

• une étape de fabrication dudit plot par le procédé de fabrication d'un plot défini ci-dessus, et
• une étape d'assemblage dudit plot sur ledit support de contact.

According to another aspect, the invention relates to a method of manufacturing an electrical contact comprising a contact support and at least one pad, said method comprising:

• a step of manufacturing said pad by the method of manufacturing a pad defined above, and
• a step of assembling said stud on said contact support.

According to another aspect, the invention relates to a method for manufacturing an electrical contact comprising a contact support and at least one contact layer, said method comprising a deposition step, by dynamic cold gas projection, of a first powder on said contact support for forming said contact layer, said first powder containing at least particles comprising grains of at least one refractory material incorporated into a conductive metal matrix selected from silver or copper.

The present invention also relates to an electrical contact pad that can be obtained by the method of manufacturing an electrical contact pad defined above.

The present invention also relates to an electrical contact that can be obtained by one or other of the methods of manufacturing an electrical contact defined above.

Brief description of the drawings

The invention will be better understood on reading the description which follows, made with reference to the figure 1 attached, schematically representing a spray gun by cold spray.

Embodiments of the invention

The present invention relates to a method of manufacturing at least one electrical contact pad comprising a pad support and at least one contact layer and a similar method applied to the manufacture of at least one electrical contact comprising a support of contact and at least one contact layer. The methods according to the invention are distinguished first of all in that they use the cold gas dynamic projection technique to deposit a first powder on said pad support or said contact support in order to form said contact layer.

This technique of depositing a powder by dynamic projection by cold gas, also called "cold spray" is characterized, contrary to other thermal spraying processes, by a low projection temperature and a high speed of spraying powder particles up to Mach 5. Unlike plasma or HVOF processes where the powder particles are melted before impacting the substrate, the cold spray, from a projection gas temperature generally not exceeding 600 ° C, does not cause melting of the particles which remain in the solid state throughout the duration of projection. During the impact on the substrate, the particles deform plastically and agglomerate to form a deposit. The advantage of the cold spray process compared to plasma spraying for example is not to overheat the particles comprising the deposit and the support, resulting in favorable low oxidation to obtain better electrical conductivity and good cohesion. The cold spray process is for example described in the patent EP 0 484 533 .

In practice, the principle of the cold spray process can be described in the following manner with reference to the figure 1 . The powder 1, with a particle size ideally comprised between 5 and 50 μm, is conveyed under pressure at the level of the spray nozzle 2 via a carrier gas, generally of the same nature as the propellant gas 3. The kinetic energy input The particles are effected by means of a carrier gas which can be heated between 200 ° C and 650 ° C in order to increase the expansion and therefore its speed. The powder + carrier gas mixture is brought to a supersonic speed at the outlet of the nozzle 4 by virtue of its particular shape (Laval nozzle 5) which carries the mixture at its outlet at a speed that is largely supersonic. Although the temperature of the gases may seem high at first, the divergent nozzle 5 causes a relaxation of the gases and therefore a significant lowering of temperature (650 ° C to 250 ° C). The powder particles, which moreover have an extremely limited residence time in the flow of hot gases, remain in all cases in a solid or slightly viscous state (surface heating).

• décapage de la surface du substrat : sert de sablage pour nettoyer le support (par exemple élimination des oxydes de surface), afin de permettre ensuite une bonne adhésion de la première couche
• formation de la première couche sur le substrat
• construction du dépôt et densification des couches.

Cold spray deposits can be considered to be formed as follows:

• stripping of the surface of the substrate: serves as sandblasting to clean the support (for example removal of surface oxides), in order to then allow a good adhesion of the first layer
• formation of the first layer on the substrate
• construction of the deposit and densification of the layers.

• la nature du gaz propulseur (air, azote, hélium et leurs mélanges)
• la température du gaz propulseur
• la géométrie de la tuyère
• la pression d'introduction des gaz dans la buse de projection (détente ensuite dans la buse)
• les caractéristiques intrinsèques à la poudre (nature, forme, granulométrie, état d'oxydation)
• la distance de projection (qui influence la vitesse d'impact sur le substrat)
• l'angle de projection.

In the cold spray process, it is possible to control seven parameters, namely:

• the nature of the propellant (air, nitrogen, helium and their mixtures)
• the temperature of the propellant
• the geometry of the nozzle
• the pressure of introduction of the gases in the projection nozzle (relaxation then in the nozzle)
• the characteristics intrinsic to the powder (nature, shape, particle size, oxidation state)
• the projection distance (which influences the impact velocity on the substrate)
• the projection angle.

The main influence parameter on the quality of the deposits obtained is the projection speed of the particles. Indeed, too slow a speed causes poor cohesion between the powder particles.

Another important parameter to consider is the nature of the powder used.

The processes according to the invention are also distinguished in that the powder deposited to form the contact layer of the pad or electrical contact, hereinafter referred to as the first powder, contains at least particles comprising grains of at least one refractory material. embedded in a conductive metal matrix selected from silver or copper.

The first powder is prepared prior to the deposit. More particularly, the particles comprising the grains of at least one refractory material incorporated in the conductive metal matrix are obtained from a process selected from the group consisting of physical vapor deposition (PVD) processes, chemical vapor deposition (CVD) processes, electroless processes, chemical precipitation on suspended particles.

The particles obtained by chemical precipitation on particles in suspension, described for example in the US Patents 5,846,288 and US 5,963,772 are particularly preferred. Indeed, these particles have a spongy structure, with "percolating" porosity, that is to say communicating with each other, resulting in a great ability to deform so as not to bounce during deposition by cold spray.

Advantageously, the refractory material may be chosen from the group comprising CdO, CuO, SnO ₂ , ZnO, Bi ₂ O ₃ , C, WC, MgO, In ₂ O ₃ , as well as Ni, Fe, Mo, Zr , W or their oxides.

The first powder may contain between 2% and 50%, preferably between 5% and 40%, and more preferably between 10% and 40% by volume of grains of refractory material relative to the total volume of the first powder.

The conductive metal present in the contact layer of the pad or electrical contact may constitute 100% of the matrix comprising the grains of refractory material or a smaller amount. In the latter case, the first powder further contains pure metal particles corresponding to the conductive metal of the matrix containing the grains of refractory material, representing the conductive metal residue present in the contact layer.

In addition, the first powder may also contain at least one doping agent.

According to a first possibility, particles comprising grains of at least one doping agent are incorporated in a metal matrix whose metal corresponds to the conductive metal of the matrix containing the grains of refractory material. These particles are prepared in the same manner as the particles comprising the grains of refractory material incorporated in the conductive metal matrix, and are then mixed with said particles comprising the grains of refractory material incorporated in the conductive metal matrix and optionally to pure metal particles to form the first powder.

According to a second possibility, at least one doping agent is incorporated with grains of refractory material to combine them in their conductive metal matrix.

According to a third possibility, at least one doping agent is introduced into the matrix containing the grains of refractory material.

Preferably, the doping agent is a metal or an oxide of this metal, said metal being chosen from the group comprising Bi, Mo, W, Re, In and Cu.

Preferably, the particle size of the first powder is between 10 μm and 300 μm.

At the end of the processes according to the invention, it may further be provided a step of shaping the stud or the contact, at its surface. This shaping can be done for example by plastic deformation (stamping, pegging, rolling), by removal of material (milling, planing, grinding) or both.

According to a first variant of the invention, the method of manufacturing an electrical contact makes it possible to directly obtain an electrical contact comprising a contact support and at least one contact layer as defined above.

The contact support is a conductive support, preferably consisting of a very good metal conductor of electricity and heat. Typically, the contact support may be made of a material selected from the group consisting of copper, aluminum, copper alloys, aluminum alloys, or a composite consisting of a conductive metal and a metal with high elastic limit, for example copper on steel.

The contact support may be coated with a galvanic deposit of silver or copper.

The contact support may be in the form of individual pre-cut pieces. The contact support may also be in the form of a continuous strip. In this case, the process may further comprise a step of cutting said strip to form the electrical contacts. If the contact support is in the form of a strip, the contact layer can be deposited on the contact support by cold spray deposition, in accordance with the invention, so as to form discrete contact points or at least one continuous track.

In this variant, the electrical contact manufacturing method according to the invention makes it possible to directly obtain an electrical contact, in a few operations, contrary to conventional methods of manufacturing electrical contacts.

The cold spray deposition method also has the advantage of cleaning the support of any traces of oxide, the particles of powder sprayed at the beginning of the process acting as a sanding of the surface of the support. The adhesion of the powder particles then projected is improved.

Such a method notably makes it possible to eliminate the oxides present on the aluminum supports, and thus to deposit the first powder on an aluminum support to form an electrical contact comprising an aluminum contact support.

According to a second variant of the invention, the method of manufacturing an electrical contact is such that the electrical contact is manufactured in two stages: a step of manufacturing the pad on a pad support, in accordance with the manufacturing method of a plot described above, and a step of assembling the pad on a suitable electrical contact support for use as an electrical contact.

In this variant, the stud support may consist of a thin continuous band of silver or copper (0.1-1 mm) which serves as an underlayer for soldering or welding. The deposition of the first powder by cold spray to form the contact layer can take place directly on this band. As described above, this band will be able to undergo a final shaping operation, either by plastic deformation (rolling), or by removal of material (milling, planing, grinding), or possibly both. It is also possible to start from a solder band, then to add the different layers described above. A multi-metallic strip is then obtained. The method may further comprise a step of cutting said strip to form pads to be assembled by a conventional method (welding or soldering) for use as an electrical contact.

Moreover, the method of manufacturing an electrical contact according to the invention may comprise, in addition, prior to the step of depositing the contact layer, at least one step of applying at least one underlayer connecting between the contact support and the contact layer.

Advantageously, said step of applying the bonding sub-layer is carried out by dynamic projection by cold gas, of a second powder on said contact support to form the bonding sub-layer, said second powder containing at least particles of a conductive metal compound.

The presence of such a link sublayer is optional.

The bonding sub-layer may consist of a metal or a metal alloy having a hardness of the same order of magnitude as that of the support and a relatively high electrical conductivity, for example silver, a silver alloy with 5% copper or silver solder.

In a similar manner, the method for manufacturing an electrical pad according to the invention may comprise, in addition, prior to the step of depositing the contact layer, at least one application step, by dynamic projection by cold gas, at least one second powder on said pad support to form at least one bonding sub-layer between the pad support and the contact layer. In this case, the melting range of the bonding sub-layer must be significantly higher than the solder subsequently used for the assembly of the stud on the contact support.

As for the first powder, the particle size of the second powder is between 10 microns and 300 microns.

Furthermore, the manufacturing process of the stud or the manufacturing of the electrical contact may furthermore comprise, after the deposition step of the contact layer, at least one deposition step, by dynamic projection by cold gas, of at least one third powder for forming at least one overlayer, said third powder having a composition different from the first powder.

As for the first and second powders, the particle size of the third powder is between 10 microns and 300 microns.

More particularly, another advantage of the cold spray deposition method is to be able to modify the spray nozzle, the composition of the powders used and the flow rates to obtain above the contact layer, different layers, which can correspond to different contact layers having different compositions. For example, a layer adapted to weak currents may be provided on the surface, and another layer adapted to stronger currents below. It is also possible to provide the deposition of a protective overcoat to protect the pad or the contact during storage, this overcoating being made of a material chosen to be eliminated rapidly when using the electrical contact.

The following examples illustrate the present invention without, however, limiting its scope.

Examples

In Examples 1 to 3 described below, the "Kinetic 3000M" model manufactured by Cold Gas Technology (CGT) is used as a cold gas dynamic projection system. It includes a control cabinet, a LINDSPRAY® Cold Spray Heater HT 800/30, a CGT-PF4000 Comfort powder dispenser, and a POWER-JET 3000 spray gun.

Example 1 (comparative)

A mixture of silver powders ranging in size from 30 to 80 microns and a tin oxide whose grains were less than 20 microns, the composition being 8% by mass oxide (about 12% volume).

1. a. la porosité du dépôt ne dépassait pas 3%
2. b. la structure était macroscopiquement homogène, mais microscopiquement hétérogène
3. c. mais la composition de la couche obtenue ne correspondait pas à la composition initiale : il y avait une perte d'oxyde d'environ 50%.

Said mixture of powders was sprayed with cold spray at 30 bar and 300 ° C. on a copper plate 50 mm long, 27 mm wide and 1.5 mm thick. A 2 mm layer was deposited.

1. at. the porosity of the deposit did not exceed 3%
2. b. the structure was macroscopically homogeneous, but microscopically heterogeneous
3. vs. but the composition of the layer obtained did not correspond to the initial composition: there was an oxide loss of about 50%.

Example 2 (Invention)

1. a. la porosité du dépôt était faible (< 0,5%)
2. b. la structure était homogène
3. c. la composition de la couche obtenue était celle de la poudre projetée
4. d. toutefois, un recuit de détente a mis en évidence une fissuration du dépôt, et
5. e. un test électrique dans les conditions AC3 sur un appareil du commerce (3x400 VAC, 37A) a montré une érosion anormalement élevée comparée au matériau standard obtenu par métallurgie des poudres traditionnelle.

A powder of tin oxide was coated with silver by CVD, so as to achieve the desired volume composition (20%). The grain size was between 10 and 40 microns. A 1.5 mm layer was sprayed on cold pre-cut substrates made of copper and UZ15 brass (thickness 1.5 mm) in the conditions optimized for this particle size distribution. The conditions were 30 bar and 400 ° C.

1. at. the porosity of the deposit was low (<0.5%)
2. b. the structure was homogeneous
3. vs. the composition of the layer obtained was that of the projected powder
4. d. however, a stress relief annealing revealed a cracking of the deposit, and
5. e. an electrical test under AC3 conditions on a commercial device (3x400 VAC, 37A) showed abnormally high erosion compared to standard material obtained by traditional powder metallurgy.

Example 3 (Invention)

1. a. la porosité du dépôt était inférieure à 0,1 %
2. b. la structure était homogène
3. c. la composition de la couche obtenue était celle de la poudre projetée
4. d. un test électrique dans les conditions AC3 (460Ampères, 3x400V) sur un appareil du commerce a montré que la durée de vie était de l'ordre de grandeur de celle des contacts habituels à ce type d'appareil. Une fissuration en fin de vie a été constatée, similaire à celle du matériau standard mais moins profonde.

A spongy powder of silver and tin oxide obtained chemically (14% weight of oxide, ~20% volume) according to the method described in US Patent 5,846,288 a was projected by cold spray at 30 bars and 600 ° C, on preformed copper supports (thickness deposited: 3 mm, support: 4 mm). Its particle size was between 40 and 300 microns.

1. at. the porosity of the deposit was less than 0.1%
2. b. the structure was homogeneous
3. vs. the composition of the layer obtained was that of the projected powder
4. d. an electrical test under conditions AC3 (460Ampers, 3x400V) on a commercial apparatus showed that the service life was of the order of magnitude of that of the usual contacts with this type of apparatus. End-of-life cracking was observed, similar to that of the standard but shallower material.

Example 4 (Invention)

Silver contacts - refractory metal (nickel) have been developed by spraying with cold spray, according to the invention, on pre-cut copper and brass UZ15 supports (thickness 1.5 mm). The conditions were 30 bar and 400 ° C.

1. a. la perte de nickel était entre 25% et 50%
2. b. la structure est homogène macroscopiquement, mais des amas de nickel de l'ordre de 50 µm ont été observés
3. c. la porosité du dépôt était limitée à moins de 1 %
4. d. un test électrique dans les conditions AC3 sur un appareil du commerce a montré une érosion inférieure de moitié à celle observée avec le matériau standard équipant habituellement cet appareil. Les amas de nickel observés ne sont pas gênants dans la mesure où aucun collage ou aucune résistance de contact prématurés n'ont été observés.

The initial composition was 30% by weight (33.5% volume) of nickel. The size of the nickel grains was between 5 and 10 microns.

1. at. the nickel loss was between 25% and 50%
2. b. the structure is macroscopically homogeneous, but nickel clusters of the order of 50 μm have been observed
3. vs. the porosity of the deposit was limited to less than 1%
4. d. an electrical test under AC3 conditions on a commercial device showed an erosion less than half that observed with the standard material usually equipping this device. The observed nickel clusters are not troublesome as no premature bonding or contact resistance was observed.

Example 5 (Comparative)

1. a. la porosité était très inférieure au 1 % (extrusion)
2. b. la structure était homogène
3. c. le même test électrique AC3 sur les appareils du même type que ceux de l'exemple 3 a mis en évidence une fissuration importante dès le premier tiers de leur « vie ».

Refractory silver-oxide contacts, of the same composition as those of Example 3, but produced by traditional powder metallurgy (billet compaction, extrusion, rolling, cutting) were brazed on copper substrates by induced current (soldering). HF).

1. at. the porosity was much lower than 1% (extrusion)
2. b. the structure was homogeneous
3. vs. the same AC3 electrical test on the devices of the same type as those of Example 3 showed significant cracking in the first third of their "life".

Claims (23)

1. A method for manufacturing at least one electric contact pad comprising a pad support and at least one contact layer, comprising a step for depositing, by cold gas dynamic spraying, a first powder onto said pad support in order to form said contact layer, characterized in that said first powder contains at least particles comprising grains of at least one refractory material incorporated into a matrix based on a conducting metal selected from silver or copper.
2. A method for manufacturing at least one electric contact comprising a contact support and at least one pad, characterized in that it comprises:

   - a step for manufacturing said pad with the method according to claim 1, and

   - a step for assembling said pad onto said contact support.
3. A method for manufacturing at least one electric contact comprising a contact support and at least one contact layer, comprising a step for depositing, by cold gas dynamic spraying, a first powder onto said contact support in order to form said contact layer, characterized in that said first powder contains at least particles comprising grains of at least one refractory material incorporated into a matrix based on a conducting metal selected from silver or copper.
4. The method for manufacturing an electric contact pad according to claim 1 or an electric contact according to any of claims 2 and 3, characterized in that the first powder further contains pure metal particles, corresponding to the conducting metal of the matrix containing the grains of refractory material.
5. The method according to any of the preceding claims, characterized in that the first powder further contains particles comprising grains of at least one doping agent incorporated into a metal matrix, the metal of which corresponds to the conducting metal of the matrix containing the grains of refractory material.
6. The method according to any of the preceding claims, characterized in that at least one doping agent is incorporated with grains of refractory material into their conducting metal matrix.
7. The method according to any of the preceding claims, characterized in that at least one doping agent is introduced into the matrix containing the grains of refractory material.
8. The method according to any of claims 5 to 7, characterized in that the doping agent is a metal or an oxide of this metal, said metal being selected from the group comprising Bi, Mo, W, Re, In and Cu.
9. The method according to any of the preceding claims, characterized in that the refractory material is selected from the group comprising CdO, CuO, SnO₂, ZnO, Bi₂O₃, C, WC, MgO, In₂O₃, as well as Ni, Fe, Mo, Zr, W or oxides thereof.
10. The method according to any of the preceding claims, characterized in that the first powder contains between 2% and 50% and preferably between 5% and 40% and more preferentially between 10% and 40% by volume of grains of refractory material based on the total volume of the first powder.
11. The method according to any of the preceding claims, characterized in that the particles comprising the grains of at least one refractory material incorporated into the conducting metal matrix are obtained from a method selected from the group comprising physical vapor deposition methods (PVD), chemical vapor deposition methods (CVD), electroless methods, chemical precipitation on suspended particles.
12. The method according to claim 3, characterized in that the contact support appears as precut individual parts.
13. the method according to claim 3, characterized in that the contact support appears as a continuous strip, and in that said method further comprises a step for cutting out said strip in order to form electric contacts.
14. The method according to claim 13, characterized in that the contact layer forms on the strip, discrete contact points.
15. The method according to claim 13, characterized in that the contact layer forms on the strip, at least one continuos track.
16. The method according to any of claims 12 to 15, characterized in that the contact support is made in a material selected from the group comprising copper, aluminium, copper alloys, aluminium alloys and a steel-copper composite.
17. The method according to any of claims 3 and 12 to 16, characterized in that it further comprises prior to the step for depositing the contact layer, at least one step for applying by cold gas dynamic spraying, at least one second powder on said contact support in order to form at least one binding sublayer, said second powder containing at least particles of a conducting metal compound.
18. The method according to any of the preceding claims, characterized in that it further comprises, after the step for depositing the contact layer, at least one step for depositing, by cold gas dynamic spraying, at least one third powder in order to form at least one overlayer, said third powder having a composition different from the first powder.
19. The method according to claim 1, characterized in that it further comprises, prior to the step for depositing the contact layer, at least one step for applying, by cold gas dynamic spraying, at least one second powder on said pad support in order to form at least one binding sublayer.
20. The method according to any of claims 17 to 19, characterized in that the size of the particles of the first, second and third powders is comprised between 10 µm and 300 µm.
21. The method according to claim 1, characterized in that the pad support appears as a continuos strip, and in that said method further comprises a step for cutting out said strip in order to form electric contact pads.
22. An electric contact which may be obtained according to any of claims 2 and 3 and 12 to 17.
23. An electric contact pad which may be obtained by the method according to any of claim 1, 19 and 21.

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