EP2297757A1

EP2297757A1 - Use of an electrical contact material for blowing an electric arc

Info

Publication number: EP2297757A1
Application number: EP09749760A
Authority: EP
Inventors: Laurent Doublet; Christine Bourda; Didier Jeannot; Pierre Ramoni; Dominique Givord; Sophie Rivoirard
Original assignee: Metalor Technologies International SA
Current assignee: Metalor Technologies International SA
Priority date: 2008-05-22
Filing date: 2009-05-14
Publication date: 2011-03-23
Anticipated expiration: 2029-05-14
Also published as: PT2297757E; PL2297757T3; CA2723770A1; HK1152146A1; MX2010012523A; ES2380310T3; US20110068088A1; JP2011521418A; BRPI0913030A2; CN102037530A; SI2297757T1; WO2009141270A1; ATE545144T1; EP2124236A1; EP2297757B1; IL209303A0

Abstract

The material has an array of conductor metal and non-magnetized magnetic entities, where the entities are magnetized with an average orientation defined by a direction of a magnetic field applied on the material for blowing an electrical arc between electrical contact studs. Each electrical contact stud has an upper layer that comprises material such as silver or copper, or stable refractory compound. The magnetic entities are rare earth based hard magnetic compounds such as nanostructured alloy of neodymium/praseodymium, iron and boron. An independent claim is also included for a method for fabricating an electrical contact stud.

Description

Description USE OF AN ELECTRIC CONTACT MATERIAL FOR BLOWING

TECHNICAL FIELD [0001] The present invention relates to the field of electrical contacts. It relates, more particularly, to the use of an electrical contact material with arc extinguishing effect.

State of the art

Such a type of material finds its application mainly for the realization of so-called "low voltage" contacts, that is to say whose operating range is approximately between 10 and 1000V and between 1 and

10000A. These contacts are generally used in the domestic, industrial and automotive fields, both in direct current and AC, for switches, relays, contactors and circuit breakers, etc.

When opening a pair of electrical contact pads under voltage, the current continues to pass from one pad to the other by ionizing the gas it passes through. This column of ionized gas, commonly called "electric arc", has a maximum length that depends on various parameters such as the nature and pressure of the gas, the terminal voltage, the contact material, the geometry of the device, the impedance of the circuit, etc.

The energy released by the electric arc is sufficient to melt the material constituting the pads, resulting not only in the degradation of the metal parts but also sometimes their solder, resulting in the blockage of the metal. 'apparatus.

In AC applications, the passage of the voltage by zero facilitates the cutting of the arc. Nevertheless, some protective devices have to cut very high currents, which cause arcs sufficiently energetic to damage the contacts. In contrast, for DC applications, the arcs are very stable, especially when the voltage is well above 10V. A solution to cut the arc is to increase its length so that it becomes unstable and disappears on its own. For a voltage of 14V, a distance of the order of a millimeter is sufficient whereas for a voltage of 42V, particularly when in the presence of an inductive load, this distance can be several centimeters. This seriously complicates the construction of the cut-off devices and the duration of the arcs created greatly reduces their service life. The problem arises particularly in the automotive industry which envisages the use of circuits to 42V continuous or more to adapt to the ever increasing number of electrical devices present in cars (up to one hundred engines in a high-end vehicle). At such tensions, the interest of limiting the problems related to arcs becomes paramount. Thus, the materials of the electrical contacts must meet the following three requirements: a low and stable contact resistance to prevent excessive heating during the passage of the current;

- good resistance to welding in the presence of an electric arc; and - weak erosion under the effect of the arc.

To meet these partially contradictory requirements, one solution is to use pseudo-alloys comprising a matrix of silver or copper and, inserted in this matrix, a fraction consisting of about 10 to 50% by volume of refractory particles. (For example, Ni, C, W, WC, CdO, SnO 2) of a size generally between 1 and 5 microns. The material thus obtained is more resistant to the energy released by the electric arc. Although an interesting solution, this method does not allow to limit the mergers and, because of their repetition, problems of erosion and welding of the studs can occur in the short or medium term. Another solution, described in US Pat. No. 3,626,124, is to use a material comprising single-domain magnetic particles. Such particles are spontaneously magnetized in a random orientation in the absence of an applied external field. These particles are therefore initially magnetized and do not need an external source of magnetization. The field generated by each magnetized particle acts on the arc of cutoff, facilitating its blowing. The particles described remain monodomains even after a heating beyond their Curie temperature so that the blowing efficiency is not affected by heating due to the arc of cut, during previous openings of contact. However, each particle acts individually on the breaking arc so that the magnetic blow effect is very small. This solution is therefore not satisfactory.

Furthermore, when it comes, in alternating current, to provide protection devices (circuit breakers) capable of cutting very high currents, it has been proposed to use auxiliary means to facilitate the extinction of the arc or avoid reignition: electromagnetic or pneumatic blow.

For example, such an electromagnetic extinction solution by devices external to the contact itself is described in EP 1 482 525. The latter discloses a magnetic device placed at a distance from the contact and which generates an elongating magnetic field. an electric arc that would occur between the studs, in order to extinguish it. However, the extra cost, size and overweight caused by this solution make it problematic, especially for automotive applications.

Among other things, it was proposed to replace the gas present in the space between the two contacts with a very stable gas and therefore difficult to ionize, such as SFΘ. However, this solution is complex to implement.

An object of the present invention is therefore to overcome these disadvantages, by proposing to use an electrical contact material to make contact pads whose operation is not altered in the short term or in the long term, by the energy of an electric arc. Disclosure of the invention More specifically, the invention relates to the use of a material comprising a conductive metal matrix and magnetic entities representing between 8 and 80% by weight of the material and comprising hard magnetic phases, said magnetic entities being non-magnetized and being capable of being made magnetized with a mean orientation, defined by the direction of a magnetic field applied to said material, for blowing an electric arc between two pads of electrical contacts, at least one of which comprises said material, and thus reduce the duration of the arc.

The invention also relates to the use of a material comprising a matrix of conductive metal and magnetic entities representing between 8 and 80% by weight of the material and comprising hard magnetic phases, said magnetic entities initially not magnetized having been rendered magnetized with an average orientation, defined by the direction of a magnetic field applied to said material, for blowing an electric arc between two pads of electrical contacts, at least one of which comprises said material, and thus reducing the duration of the bow.

Alternatively, the material may further comprise a refractory fraction stable at a temperature above 900 ° C.

Advantageously, at least one of the phases of the magnetic entities is a hard magnetic compound based on rare earths.

To enable use according to the invention, said material is capable of generating a magnetic induction field, measured at its surface, greater than 20 mT, preferably greater than 60 mT, and more preferably greater than 100 mT. Particularly remarkable effects on the extinction of an electric arc have been observed for use according to the invention, according to which said pads define between them an axis, at least one of said pads being made in said material and having a magnetization generating a magnetic field perpendicular to said axis. Advantageously, at least one of said pads which comprises said material with the magnetic entities, has an overlayer comprising a material selected from silver and copper.

In another aspect, the present invention relates to a constituent material of an electrical contact pad comprising a conductive metal matrix and magnetic entities representing between 8 and 80% by weight of the material and comprising hard magnetic phases, said magnetic entities being non-magnetized and capable of being made magnetized with a mean orientation, defined by the direction of a magnetic field applied to said material, at least one of the magnetic phases being a rare earth-based compound; except the samarium.

The present invention also relates to a constituent material of an electrical contact pad comprising a conductive metal matrix and magnetic entities representing between 8 and 80% by weight of the material and comprising hard magnetic phases, said magnetic entities initially not magnetized having been made magnetized with a mean orientation, defined by the direction of a magnetic field applied to said material, at least one of the magnetic phases being a compound based on rare earths, with the exception of samarium. In another aspect, the present invention relates to a method of manufacturing an electrical contact pad comprising the following steps:

- developing a material from silver or copper to form the matrix of said material and magnetic entities comprising hard magnetic phases, said magnetic entities being non-magnetized, at least one of the magnetic phases being a compound rare earth base,

- shaping of the stud,

- assembly on a support, and

magnetization of the stud. In another aspect, the invention relates to a pair of pads of electrical contacts, said pads defining between them an axis, in which that at least one of said pads is made of a material as defined above and has a magnetization generating a magnetic field perpendicular to said axis.

In the case of direct current, very good results have also been observed for a pair of electrical contact pads comprising, at the cathode, a contact pad made of a material defined above.

Brief description of the drawings

The invention will be better understood on reading the description which follows, with reference to the accompanying figure, illustrating different orientations of the magnetic field presented by the pads of an electrical contact.

Mode (s) of realization of the invention

The contact material used in the present invention essentially consists of:

a conductive metal matrix, generally made of silver or copper; and

magnetic entities representing between 8 and 80% by weight of the material and comprising hard magnetic phases, said magnetic entities being initially non-magnetized and capable of being magnetized, with a mean orientation, defined by the direction of an applied magnetic field on said material.

Therefore, the material used according to the invention initially contains multidomain magnetic entities forming a set initially largely unmagnetized, and then to be magnetized by the application of a field. Preferably, the material used according to the invention does not initially contain spontaneously magnetized monodomain entities.

Preferably, the magnetic entities represent between 10 and 50% by weight of the material, preferably between 12 and 30% by weight, and more preferably between 18 and 22% by weight of said material.

The magnetic entities comprise magnetic phases that can be obtained from one or more ferromagnetic or ferrimagnetic hard compounds. Advantageously, they are chosen from compounds based on rare earths, among which mention may be made of the so-called RE-Fe-B type compounds (RE being the abbreviation of Rare Earth, Rare Earth). Preferably, RE is neodymium or praseodymium. Other compounds of the RE-M type can be used, RE being preferably La, Gd, Y or Lu, of the 1/5, 1/7 or 2/17 type, and M being predominantly Co or Fe and possibly containing Cu, Zr, Al and other minority elements. The compounds of the RE-Fe-N type can also be used.

Other compounds such as those of the family Pt (Fe ₁ Co) may also be suitable, or compounds of the ferrite type of barium or strontium. Other materials can still be envisaged, the essential being that the magnetic entities have a sufficient coercive field and remanent induction to allow their use in the targeted applications, these two parameters can be evaluated by simple experimental tests. Indeed, as will be explained below, it is necessary that the contact generates a certain magnetic field so as to destabilize a possible electric arc occurring between the pads. In particular, it must be that after having been exposed to a magnetic field, the material has a sufficient and stable long-term residual induction for long-term use. This induction, obtained by magnetization of the pads under an external magnetic field, can be characterized by the magnetic field generated on the surface of the pads, and persistent after removal of the applied magnetic field. As an indication, the field generated on the surface must be greater than 20 mT, preferably 60 mT, and more preferably greater than 100 mT, measured using a Hall effect probe distributed by Lakeshore.

Optionally, the matrix comprises a refractory fraction, stable at a temperature above 900 ° C. The refractory fraction may comprise one or more of the elements selected from the following group: CdO, 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 refractory fraction is added in amount so that the percentage of the magnetic entities is at least 8% and the amount of conductive metal is at least 20%. Advantageously, the magnetic entities are dispersed in the matrix, either regularly, or in a concentration gradient, or again in localized blocks.

In addition, the material may also contain dopants or minor additives, facilitating the implementation of the material, which may be, for example, Ni, Co, Fe, Bi, Re, Zr and their oxides.

The material described above is used to make pads of electrical contacts. The first steps of the process of developing the material and forming the contact pads are common and are known to those skilled in the art who can choose between several techniques. In addition, the method comprises an additional step of magnetizing the material on the already developed pads.

In particular, and without it being necessary to detail it further for the person skilled in the art who will be able, by means of a few tests of current practice, to implement the following techniques, the elaboration of the material used according to the invention. invention can be achieved by:

- powder metallurgy,

- chemical way of precipitation of salts in solution,

- atomization, - thin or thick layer deposition, or

extrusion from a billet or a mixture of powders.

Advantageously, the material development step can be performed by metallurgy powders, one of the magnetic entities being nanostructured RE-Fe-B, where RE is a rare earth element. A preferred direction of the magnetic entities may be obtained by applying a suitable method during the development of the pads (pressure, magnetic field, heat treatment). This operation is not essential but it makes it possible to increase the magnetization of the studs induced by the field, applied after elaboration of the pads. It should be noted that, without limitation, the use as a starting material for constituting the magnetic entities of the contact, a ribbon The nanostructured RE-Fe-B obtained by a rapid solidification technique, particularly by the technique known as melt spinning gives excellent results. It is not necessary to further describe this technique known to those skilled in the art. In summary, it consists in flowing, through a nozzle, molten metal contained in a reservoir, and in bringing a net of liquid metal in contact with a cylinder, for example copper, rotating great speed. Thanks to this technique, the RE-Fe-B cools by taking a microstructure, which allows it to present remarkable hard magnetic characteristics for the intended use.

The RE-Fe-B may be associated with other magnetic materials to optimize the magnetic properties of the assembly, the RE-Fe-B advantageously representing at least 50% by weight of the magnetic entities.

Contact pads are then shaped by cutting strips, stamping son, unitary compression. They are then arranged on a suitable support, by any traditional method of assembling electrical contacts, in particular: resistance welding, resistance brazing, induction brazing, flame or oven brazing, crimping, incrustation ... view of their use as electrical contacts. Alternatively, the material used according to the invention can be formed into a washer or a layer, forming a magnetic system, made integral with a traditional electrical contact pad by inlaying, welding, brazing or riveting, or even layer deposition (s). In the latter case, the magnetic material, the contact material or both may be in the form of one or more layers. The magnetic system can also serve as a mechanical support and supply current to the electrical contact. It is advantageously possible to adapt the magnetic system according to the variant in existing installations, while retaining the initial contact material, since it occupies only a small space in addition to the contact, unlike the electromagnetic members of the prior art. In the shaped pads, the magnetic entities are not magnetized. The pads must then undergo the magnetization step by applying a magnetizing magnetic field to provide the magnetic non-magnetized entities global magnetization in a mean orientation defined by the applied field. The studs can then fully play their role of blower or arc extinguisher. This operation can take place in the factory, after development of the stud. It can also take place at the user, before or after the final assembly of the contact. It is carried out by exposing the pads to a magnetic field of intensity between 0.5 and 30 T, preferably between 1 and 30 T, and still more preferably between 1 and 10 T. Thus, according to the invention, the material used in the form of pads comprises magnetic entities initially not magnetized which are either capable of being made magnetized by the application of a magnetic field to the user, or already made magnetized by the application of a magnetic field in factory.

By this application of a magnetic field of appropriate direction and intensity, the pads already developed, an overall magnetization of the pads is created, whose orientation is defined by the applied field. As a result, a magnetic field is generated in the environment of the pad. This field acts on the arc of cutoff and contributes to its blowing.

The field may in particular be applied in parallel or preferably perpendicular to the longitudinal axis of a stud, so that the latter has field lines as illustrated, respectively, in Figures 1a and 1b. . The conditions of the magnetization step (duration and intensity of the field) are adapted to the magnetic material so that, after having undergone the magnetization step, the studs are source of a magnetic induction field, which, measured on their surface, is greater than 20 mT, preferably 60 mT, and more preferably greater than 10O mT. The pads thus obtained are then implemented in electrical contacts formed of two pads defining between them a first axis. The contact may comprise a single pad obtained according to the above method, arranged in the case of a DC circuit, the anode or the cathode. It is also possible that the two studs forming the contact are made of a magnetic material used according to the invention. Various magnetic field orientations are possible and conceivable, for example, when a single magnetic pad is used, the field it generates can be oriented parallel or perpendicular to the first axis.

Alternatively, the stud may comprise an overlay deposited on the magnetic material. Such an overcoat comprises a conductive material selected from silver and copper and optionally a refractory compound selected from the group consisting of compounds CdO, SnO 2, ZnO, Bi 2 O 3, C, WC,

MgO, In2O3, as well as Ni, Fe, Mo, Zr, W or their oxides.

This overlay advantageously allows to isolate the magnetic entities of the pad of the contact surface and thus reduce the risk of soldering on closing. Indeed, the blowing effect can be attenuated by the ionization of the constituent elements of the magnetic compound, the latter can increase the contact resistance and promote welding. In any case, the extreme surface of the contact is strongly heated under the effect of the arc so that the magnetic properties of the surface entities are generally destroyed in operation. The overlayer must be thin enough so that the field created by the underlying magnetic entities in the arc area remains sufficiently intense, and possibly thick enough not to be completely melted under the effect of the arc. However, it turns out that the reduction in the duration of the arc obtained according to the invention leads to very low erosion. Thus, the overlay may have a thickness of between 0.05 mm and 3 mm, preferably between 0.1 mm and 2 mm, and more preferably between 0.2 mm and 1 mm. The following examples illustrate the present invention without however limiting the scope thereof. Example 1

The elaboration of the material is done by metallurgy of the powders. Thus, a ribbon of Nd-Fe-B produced by the technique known as "melt spinning" is reduced to powder, under argon, by ball milling, until a particle size of between 1 and 50 μm is obtained. . The duration of this operation is about 5h.

The powder thus obtained is mixed with powdered silver, the particles have a mean diameter of between 15 and 50 microns. The mixture is produced in a mass proportion of 80% of silver and 20% of EM magnetic entity powder. A magnetic material is obtained constituting an electrical contact pad.

An electrical contact pad is then shaped by unit compression and compacted under a pressure of 700MPa.

Then the pad is sintered under vacuum at 400 ° C for about 30 minutes. The pad is then assembled on a support according to one of the techniques mentioned above, to be used in an electrical contact.

Finally, the pad is magnetized by exposing it to a magnetic field of 8 T. The pad is oriented perpendicularly to the magnetic field, as illustrated in FIG. 1a so that it has a perpendicular magnetization to its longitudinal axis. With the magnetization conditions above, the pad is a source of a remanent induction field of about 60 mT at the surface.

The pad obtained above is then used in a contact of a resistive type electrical circuit, operating under a continuous voltage of 42 V, with an intensity of 37.5 A. For example, only one magnetic pad is disposed at the cathode, the other being silver.

With this configuration (perpendicular magnetization, a single magnetic pad at the cathode), we measure the opening arc duration. Closure tests are also performed to simulate the risks of welding, under the same conditions as for opening, but with a current of 90 A. measures the percentage of welding obtained, whose breaking force is greater than 0.1 N.

The results obtained are reported in Table 1 below. Example 2 [0064] Example 1 is reproduced by replacing 6% by weight of silver of the matrix with 6% by weight of a refractory compound (SnO 2).

The same tests as for Example 1 are carried out. The results obtained are reported in Table 1 below.

Example 3 An overlayer of 0.6 mm thick is applied to the magnetic material of the pad obtained in Example 1. Said overlayer comprises 100% silver.

The same tests as for Example 1 are carried out. The results obtained are reported in Table 1 below. Examples 4-6

For comparison, Example 1 is reproduced by not subjecting the pad to a magnetization (Example 4) or by using other materials to make the pads of the contact (Examples 5 and 6).

The same tests as for Example 1 are carried out. The composition of these materials as well as the results obtained with the elaborate pads are reported in Table 1 below:

Table I

The results of Table 1 show that the use according to the invention of the magnetic material described above for making pads of electrical contacts can reduce the arc duration at the opening of 9 ms or 24 ms at 3 ms. Example 4 also shows the importance of the magnetization step of the stud since a contact comprising a non-magnetized stud has an arc duration at the opening of 9 ms while the contact comprising the magnetic pin has a arc duration at opening of 3 ms.

In addition, the addition of a refractory compound (Example 2) or the use of an overlayer (Example 3) makes it possible to greatly reduce the welding tendency of the studs consisting of the magnetic material defined above without affecting significantly the arc duration on opening. The use of an overlay makes it possible to obtain particularly interesting results.

Claims

claims

1. Use of a material comprising a matrix of conductive metal and magnetic entities representing between 8 and 80% by weight of the material and comprising hard magnetic phases, said magnetic entities being non-magnetized and being capable of being made magnetized with a medium orientation, defined by the direction of a magnetic field applied to said material, for blowing an electric arc between two pads of electrical contacts, at least one of which comprises said material.

2. Use of a material comprising a matrix of conductive metal and magnetic entities representing between 8 and 80% by weight of the material and comprising hard magnetic phases, said initially non magnetized magnetic entities having been made magnetized with a mean orientation, defined by the direction of a magnetic field applied to said material, for blowing an electric arc between two pads of electrical contacts, at least one of which comprises said material.

3. Use according to claim 1 or 2, characterized in that the magnetic entities represent between 10 and 50% by weight of said material, preferably between 12 and 30% by weight, and more preferably between 18 and 22% by weight of said material.

4. Use according to any one of the preceding claims, characterized in that said material further comprises a refractory fraction stable at a temperature above 900 ° C.

5. Use according to claim 4, characterized in that said refractory fraction comprises one or more of the elements selected from the following group: CdO, 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.

6. Use according to any one of claims 1 to 5, characterized in that at least one of the phases of the magnetic entities is a hard magnetic compound based on rare earths.

7. Use according to claim 6, characterized in that the magnetic entities are nanostructured RE-Fe-B alloys, where RE is a rare earth element.

8. Use according to claim 7, characterized in that RE is neodymium or praseodymium.

9. Use according to any one of claims 1 to 8, characterized in that the material is capable of generating a magnetic induction field, measured at its surface, greater than 20 mT, preferably greater than 60 mT, and more preferably greater than 100 mT.

10. Use according to any one of the preceding claims, characterized in that said pads define between them an axis, at least one of said pads being formed in said material and having a magnetization generating a magnetic field perpendicular to said axis.

11. Use according to any one of the preceding claims, characterized in that at least one of said pads comprising the magnetic entities has an overlayer comprising a material selected from silver and copper.

12. Use according to claim 11, characterized in that said overlayer further comprises a refractory compound selected from the group consisting of compounds CdO, SnO 2, ZnO, Bi ₂ O 3, C, WC, MgO, In ₂ O 3, and also Ni , Fe,

Mo, Zr, W or their oxides.

13. Use according to claim 11 or 12, characterized in that said overlayer has a thickness of between 0.05 mm and 3 mm, preferably between 0.1 mm and 2 mm, and more preferably between 0.2 mm and 1 mm.

14. Material of an electrical contact pad comprising a conductive metal matrix and magnetic entities representing between 8 and 80% by weight of the material and comprising hard magnetic phases, said magnetic entities being non-magnetized and capable of being magnetized with a mean orientation, defined by the direction of a magnetic field applied to said material, at least one of the magnetic phases being a compound based on rare earths, with the exception of samarium.

15. Material of an electrical contact pad comprising a conductive metal matrix and magnetic entities representing between 8 and 80% by weight of the material and comprising hard magnetic phases, said initially non magnetized magnetic entities having been made magnetized with an orientation mean, defined by the direction of a magnetic field applied to said material, at least one of the magnetic phases being a compound based on rare earths, with the exception of samarium.

16. A method of manufacturing an electrical contact pad comprising the following steps:

- shaping of the stud,

- assembly on a support, and

magnetization of the stud.

17. The manufacturing method according to claim 16, wherein the step of producing the material is carried out by powder metallurgy, one of the magnetic entities being nanostructured RE-Fe-B, where RE is a rare earth element. .

18. Method according to one of claims 16 and 17, characterized in that the magnetization step is performed so that said pad generates a magnetic induction field measured at its surface, greater than 20 mT, of preferably greater than 60 mT, and more preferably greater than 100 mT.

19. Pair of pads of electrical contacts, said pads defining between them an axis, characterized in that at least one of said pads is made of a material according to one of claims 14 and 15 and has a magnetization generating a magnetic field. perpendicular to said axis.

20. Pair of pads of electrical contacts comprising, at the cathode, a contact pad made of a material according to one of claims 14 and 15.

21. Electrical contact pad made of a material according to one of claims 14 and 15, having an overlayer comprising a material selected from silver and copper and optionally a refractory compound selected from the group consisting of compounds CdO, SnO2, ZnO, Bi 2 O 3, C, WC, MgO, In 2 O 3, as well as Ni, Fe, Mo, Zr, W or their oxides.