EP3579262B1 - Ferromagnetic part for an electromagnetic contactor, its manufacturing process and its use - Google Patents

Description

The present invention relates to a method of manufacturing a ferromagnetic part for an electromagnetic contactor, a method of manufacturing an electromagnetic contactor, a ferromagnetic part, an electromagnetic contactor, and a use of a ferromagnetic part.

The present invention relates to the field of electrotechnical devices, in particular for low voltage, and to ferromagnetic elements intended to equip such devices.

FR 2 746 541 A1 describes an example of a known electromagnetic contactor device, comprising an electromagnet provided with a coil with supply terminals, with a fixed part forming a fixed part of the magnetic circuit and with a movable part forming a movable part of the magnetic circuit. The moving part is mechanically connected to a contact holder of the device. The supply of the coil drives the displacement of the contact holder by displacement of the movable part relative to the fixed part under the effect of the electromagnetic field thus generated. This movement consists of moving the moving part closer to and apart from the fixed part.

For certain applications, it is known, in order to improve the electromagnetic behavior of the moving part and of the fixed part, to maintain a non-zero non-magnetic air gap between the fixed part and the moving part when these parts are in their closest position. . This makes it possible in particular to improve the drop-out time of the contactor, that is to say the time taken for the moving part to regain its position away from the fixed part, when the coil is no longer supplied. The drop-out time is an important parameter, since it corresponds to the time that the contactor will take to open or close the power circuit once it has received the command.

For this, it is known to introduce a fine non-magnetic wedge between the fixed and mobile parts in order to limit their proximity. However, it is difficult to design a wedge which has both a sufficiently small thickness for the non-magnetic air gap to be optimal and at the same time a sufficiently large thickness for the wedge to be mechanically durable.

It is also known practice to apply a surface treatment of the dry phosphating type, which makes it possible to apply to the surface of the fixed and mobile parts a thin layer of non-magnetic material. In this case, bringing the two parts together brings them into contact by means of their surface treatment layer. AT each contact, there is a shock between the two parts. After numerous maneuvers, the successive impacts undergone by these two parts lead to a deterioration of their surface treatment layer, as well as a matting, that is to say a deformation or a wear. Deterioration and matting cause electromagnetic properties to change over time, especially as the surface treatment layer shrinks and parts are deformed. Generally, during the use of the contactor, the drop-out time increases, or varies significantly.

JP 3 099945 B2 relates to an electromagnetic relay comprising a permanent magnet and a soft iron frame, covered with a nickel coating layer.

US 2017/040132 A1 describes a relay whose armature is coated with a layer which may be made of nickel.

FR 1 319 342 A describes an air gap filled with a body of copper, brass, chromium or nickel, arranged by an electrolytic or chemical process.

DE 75 20 386 U describes a relay for which magnetic parts are provided with a surface layer formed of an alloy composed of phosphorus, copper and nickel.

To remedy the aforementioned drawbacks, an aim of the invention is to provide a new method of manufacturing a ferromagnetic part exhibiting both particularly high mechanical endurance against shocks, good ferromagnetic properties and good corrosion resistance, while integrating a non-magnetic air gap.

• une étape a) de fourniture d'une pièce brute en métal ferromagnétique doux ; et
• une étape b) de nickelage chimique d'au moins une partie de la pièce brute pour obtenir la pièce ferromagnétique, dont la partie est revêtue en surface par une couche de nickel de surface, la pièce ferromagnétique obtenue comprenant le métal ferromagnétique doux, qui, pour ladite au moins une partie chimiquement nickelée, est disposé sous la couche de nickel de surface.

According to a first aspect, the subject of the invention is a method of manufacturing a ferromagnetic part for an electromagnetic contactor, the method comprising the following successive steps:

• a step a) of supplying a blank piece of soft ferromagnetic metal; and
• a step b) of chemical nickel plating of at least part of the blank to obtain the ferromagnetic part, the part of which is surface coated with a surface layer of nickel, the ferromagnetic part obtained comprising the soft ferromagnetic metal, which, for said at least one chemically nickel-plated part, is placed under the surface nickel layer.

• en surface externe, la couche de nickel de surface,
• le métal ferromagnétique doux recuit, sous la couche de nickel de surface pour ladite au moins une partie chimiquement nickelée au cours de l'étape b), et
• une couche de nickel diffusé dans le métal ferromagnétique doux en raison du recuit magnétique, la couche de nickel diffusé reliant la couche de nickel de surface et le métal ferromagnétique doux recuit.

According to the invention, the method comprises, after step b), a step c) of magnetic annealing of the ferromagnetic part coated during step b), so that the ferromagnetic part obtained at the end of the step c) includes:

• on the external surface, the surface nickel layer,
• the annealed soft ferromagnetic metal, under the surface nickel layer for said at least one chemically nickel-plated part during step b), and
• a layer of diffused nickel in the soft ferromagnetic metal due to magnetic annealing, the diffused nickel layer connecting the surface nickel layer and the annealed soft ferromagnetic metal.

Thanks to the invention, the surface layer of nickel confers impact resistance on the ferromagnetic part. When the ferromagnetic part is used in an electromagnetic contactor, its deterioration is slower than the means used in the prior art. In particular, the drift in the switch-off time of the contactor is much lower, and above all, less random. The surface nickel layer is non-magnetic, relative to the soft ferromagnetic metal, so that this layer can advantageously be used as an integrated non-magnetic air gap. The residual nickel layer also imparts corrosion resistance to the ferromagnetic part, since the ferromagnetic metal is likely to be sensitive to it. In a preferred embodiment where a magnetic annealing is applied to the ferromagnetic part, the chemical nickel plating is compatible with this magnetic annealing, which can therefore be carried out after the chemical nickel plating. Therefore, the magnetic properties of the ferromagnetic part can be made particularly good for application to an electromagnetic contactor.

Thanks to the invention, after the magnetic annealing step, the surface nickel layer has a very high hardness, for example between 750 and 900 HV. The diffused nickel layer has an intermediate hardness, for example about 220 to 260 HV. The soft ferromagnetic metal exhibiting a generally lower hardness, for example less than 150 HV. A hardness gradient is therefore obtained, suitable for improving the strength of the ferromagnetic part and for reducing the rate of wear of the surface nickel layer. Indeed, the presence of the diffused nickel layer prevents wear of the ferromagnetic parts, by improving the resistance of the surface nickel layer on the soft ferromagnetic metal core.

• l'étape b) comprend un trempage de la pièce brute dans un bain, le bain comprenant une solution aqueuse d'oxyde de nickel et un agent réducteur, de préférence de l'hydrophosphite de sodium, la pièce brute étant brassée dans le bain lors du trempage de sorte à être revêtue par la couche de nickel de surface sur au moins 95% de sa superficie, de préférence sur toute sa superficie.
• l'étape c) comprend une soumission de la pièce ferromagnétique, revêtue au cours de l'étape b), à une température comprise entre 800°C et 850°C, pendant une durée comprise entre 3 heures et 5 heures, de préférence 4 heures.
• le métal ferromagnétique doux est un alliage fer-carbone avec une teneur en carbone inférieure à 0,03 % en poids.

Other advantageous characteristics of the invention are defined in the following:

• step b) comprises soaking the blank in a bath, the bath comprising an aqueous solution of nickel oxide and a reducing agent, preferably sodium hydrophosphite, the blank being stirred in the bath during dipping so as to be coated with the surface nickel layer over at least 95% of its area, preferably over its entire area.
• step c) comprises subjecting the ferromagnetic part, coated during step b), to a temperature of between 800 ° C and 850 ° C, for a period of between 3 hours and 5 hours, preferably 4 hours.
• the soft ferromagnetic metal is an iron-carbon alloy with a carbon content of less than 0.03% by weight.

• un actionneur électromagnétique, comprenant au moins une bobine, une partie ferromagnétique mobile et une partie ferromagnétique fixe, les parties ferromagnétique mobile et fixe étant configurés pour basculer entre une position éloignée l'une de l'autre et une position de contact ; et
• au moins une paire de contacts de puissance, qui est actionnée par la partie ferromagnétique mobile lors du basculement entre la position éloignée et la position de contact, ladite au moins une paire de contacts de puissance étant alors basculée entre une configuration fermée et une configuration ouverte,

le procédé de fabrication du contacteur électromagnétique comprenant une étape dans laquelle on intègre au moins une pièce ferromagnétique, obtenue à l'aide du procédé de fabrication d'une pièce ferromagnétique conforme à ce qui précède, à au moins l'une des parties ferromagnétique mobile et fixe.The subject of the invention is also a method of manufacturing an electromagnetic contactor, the electromagnetic contactor comprising:

• an electromagnetic actuator, comprising at least a coil, a movable ferromagnetic part and a fixed ferromagnetic part, the movable and fixed ferromagnetic parts being configured to switch between a position remote from each other and a contact position; and
• at least one pair of power contacts, which is actuated by the movable ferromagnetic part upon switching between the remote position and the contact position, said at least one pair of power contacts then being switched between a closed configuration and an open configuration ,

the method of manufacturing the electromagnetic contactor comprising a step in which at least one ferromagnetic part, obtained using the method of manufacturing a ferromagnetic part according to the above, is integrated into at least one of the movable ferromagnetic parts and fixed.

• en surface externe, une couche de nickel de surface obtenue l'étape de nickelage chimique, et
• un métal ferromagnétique doux recuit, revêtu par la couche de nickel de surface en étant sous la couche de nickel de surface pour ladite au moins une partie chimiquement nickelée au cours de l'étape b), et
• une couche de nickel diffusé dans le métal ferromagnétique doux en raison du recuit magnétique, la couche de nickel diffusé reliant la couche de nickel de surface et le métal ferromagnétique doux recuit.

The subject of the invention is also a ferromagnetic part for an electromagnetic contactor, the ferromagnetic part being preferably obtained using a method in accordance with the above, the ferromagnetic part having undergone, for at least part of said ferromagnetic part. , a step b) of chemical nickel plating, and, after step b), a step c) of magnetic annealing of the ferromagnetic part coated during step b), said at least part of the ferromagnetic part comprising:

• on the external surface, a surface nickel layer obtained by the chemical nickel plating step, and
• an annealed soft ferromagnetic metal, coated with the surface nickel layer being under the surface nickel layer for said at least one chemically nickel-plated part during step b), and
• a layer of diffused nickel in the soft ferromagnetic metal due to magnetic annealing, the diffused nickel layer connecting the surface nickel layer and the annealed soft ferromagnetic metal.

Preferably, the surface nickel layer measures between 3 and 50 μm in thickness, preferably between 3 and 20 μm in thickness. Preferably, the layer of Diffused nickel is between 3 and 40 µm thick, preferably between 10 and 30 µm thick.

• un actionneur électromagnétique, comprenant au moins une bobine, une partie ferromagnétique mobile et une partie ferromagnétique fixe, les parties ferromagnétique mobile et fixe étant configurées pour basculer entre une position éloignée l'une de l'autre et une position de contact, au moins l'une des parties ferromagnétique mobile et fixe comprenant une pièce ferromagnétique conforme à ce qui précède ; et
• au moins une paire de contacts de puissance, qui est actionnée par la partie ferromagnétique mobile lors du basculement entre la position éloignée et la position de contact, ladite au moins une paire de contacts de puissance étant alors basculée entre une configuration fermée et une configuration ouverte.

The subject of the invention is also an electromagnetic contactor comprising:

• an electromagnetic actuator, comprising at least one coil, a movable ferromagnetic part and a fixed ferromagnetic part, the movable and fixed ferromagnetic parts being configured to switch between a position remote from each other and a contact position, at least l one of the movable and fixed ferromagnetic parts comprising a ferromagnetic part in accordance with the above; and
• at least one pair of power contacts, which is actuated by the movable ferromagnetic part upon switching between the remote position and the contact position, said at least one pair of power contacts then being switched between a closed configuration and an open configuration .

The invention also relates to the use of a ferromagnetic part in accordance with the above in an electromagnetic contactor in accordance with the above, the ferromagnetic part being used as part of the movable ferromagnetic part or of the fixed ferromagnetic part of the electromagnetic actuator.

• Les figures 1 et 2 sont deux coupes d'un même contacteur électromagnétique, selon deux configurations différentes, comportant des pièces ferromagnétiques conformes à l'invention ;
• la figure 3 est une vue en perspective de l'une des pièces ferromagnétiques des figures précédentes ;
• la figure 4 est un détail de la figure 2, représentant deux pièces ferromagnétiques du contacteur, de façon schématique et à plus grande échelle ; et
• la figure 5 est un graphe montrant les résultats d'un test comparatif.

The following description relates to embodiments of the invention, given by way of non-limiting examples, with reference to the appended drawings in which:

• The figures 1 and 2 are two sections of the same electromagnetic contactor, according to two different configurations, comprising ferromagnetic parts in accordance with the invention;
• the figure 3 is a perspective view of one of the ferromagnetic parts of the previous figures;
• the figure 4 is a detail of the figure 2 , showing two ferromagnetic parts of the contactor, schematically and on a larger scale; and
• the figure 5 is a graph showing the results of a comparative test.

On the figures 1 and 2 an electromagnetic contactor 2 is shown, making it possible to selectively interrupt the flow of current in a power circuit, for example between a power source and an electric load. To the figure 1 , the contactor 2 is shown in an open configuration, in which it blocks the flow of current. To the figure 2 , the contactor 2 is shown in a closed configuration, in which it allows current to flow.

This contactor 2 is preferably provided for a so-called "low voltage" power circuit, that is to say having a voltage of for example between 1V and 600V, preferably between 100V and 400V. For example, it can be a domestic network, that is to say a network supplying a dwelling, at a voltage of 110V or 230V in single phase. Alternatively, this may for example concern an industrial 380V three-phase network.

The contactor 2 comprises one or more pairs of power contacts, each pair comprising a movable contact 12 and a fixed contact 14. The contacts 12 and 14 are power contacts, because they are configured to block or be crossed by the current of the. aforementioned power circuit, depending on the open or closed configuration of the contactor 2. The number of pairs of contacts 12 and 14 is for example chosen as a function of the number of phases of the power circuit, each pair being associated with one phase. In the present example, two pairs of contacts 12 and 14 are provided, being a single-phase power circuit.

• la position dite « ouverte », représentée à la figure 1, dans laquelle les contacts mobiles 12 et les contacts fixes 14 sont séparés par une distance d'isolement électrique et
• la position dite « fermée » représentée à la figure 2, dans laquelle les contacts mobiles 12 et les contacts fixes 14 sont en contact et connectés.

The movable contacts 12 are carried by a contact carrier 10 which is movable along an axis X10 between:

• the so-called "open" position, shown in figure 1 , in which the movable contacts 12 and the fixed contacts 14 are separated by an electrical isolation distance and
• the so-called "closed" position shown in figure 2 , wherein the movable contacts 12 and the fixed contacts 14 are in contact and connected.

By moving the movable contact 12 integrally with the contact carrier 10, each pair of power contacts 12 and 14 therefore changes between a closed configuration, when the contact 12 is in the closed position, and an open configuration, when the contact 12 is in. open position.

The contactor 2 comprises an electromagnetic actuator 4 configured to actuate the contact carrier 10 between its two open and closed configurations, and therefore by extension, to simultaneously actuate each pair of contacts 12 and 14 between their open and closed position.

The electromagnetic actuator 4 comprises two coils 18, a fixed ferromagnetic part 6 and a movable ferromagnetic part 8. The part 8 is movable along the axis X10, between a position remote from the fixed part 6, shown in figure 1 and a position of contact with the fixed part 6, shown in figure 2 . The travel in translation of part 8 relative to part 6 is represented by the distance C at the figure 1 , measured parallel to the X10 axis. In the remote position, the parts 6 and 8 are spaced apart by the distance C. In the contact position, the parts 6 and 8 are in contact with each other and are therefore closer to each other.

The contact carrier 10, and therefore each contact 12 simultaneously, is moved, preferably in translation along the axis X10, by means of the movable part 8 of the electromagnetic actuator 4. When the part 8 is in the remote position, the pairs of contacts 12 and 14 are in the open configuration. When the part 8 is in the contact position, the pairs of contacts 12 and 14 are in the closed configuration. For this, provision is made for the position of the contact holder 10 to be linked to that of part 8. Here, the contact holder 10 and the movable part 8 of the actuator 4 are linked in translation along the axis X10. In the example, part 8 of the actuator is assembled on contact carrier 10 so as to make it integral with contact carrier 10.

As a variant, it could conversely be provided that the remote position of part 8 causes the pairs of contacts 12 and 14 to be placed in closed configuration, and that the contact position of part 8 causes the pairs to be placed in the open configuration. contacts 12 and 14.

The fixed part 6 comprises a ferromagnetic frame having a U-shaped architecture. The frame comprises a base 20 and two cores 21 which extend, from the base 20, parallel to the axis X10. The frame of the fixed part 6 also comprises two separate ferromagnetic parts 22. The parts 22 are mounted respectively at the free ends of the cores 21, opposite the base 20. The two parts 22 are each of flat shape in the same plane orthogonal to the axis X10.

Alternatively, the fixed part 6 could be formed by a single ferromagnetic part in one piece, rather than by assembling the various ferromagnetic parts 20, 21 and 22 mentioned above.

The movable part 8 comprises a ferromagnetic part 30, visible on the figures 1 and 2 , and represented alone on the figure 3 . The part 30 is preferably a flat part, which extends in a plane orthogonal to the axis X10. The mobile part also comprises a second ferromagnetic part 31, which also forms a flat part resting flat against the part 30.

As a variant, the mobile part 8 forms a single ferromagnetic part in one piece.

The fixed part 6 and the moving part 8 are qualified as “ferromagnetic”, that is to say that they are made of materials, and form structures, which makes them susceptible to magnetization under the effect of the field. magnetic generated by the coils 18 so as to form a magnetic circuit, conducting the magnetic flux produced by the coils 18. In the present example, the ferromagnetic parts 20, 21, 22, 30 and 31 form a closed magnetic circuit, in the form of a buckle, when part 8 is in contact with part 6.

Each coil 18 is wound around one of the cores 21. When supplied with electric current, the coils 18 generate a magnetic field which induces magnetization of the fixed part 6 and of the moving part 8. The parts 6 and 8 are thus mutually attracted to each other. When the coils 18 are supplied, the part 6 passes into the position of contact with the part 8. When the supply of the coils 18 is interrupted, the parts 6 and 8 become demagnetized, so that the parts 6 and 8 are no longer attracted. towards each other. Part 6 thus returns to a position remote from part 8, under the effect of return means described below.

The parts 22 are arranged opposite the part 30, parallel to the axis X10. The parts 22 extend in the same plane which is parallel to the plane of the part 30, these planes being orthogonal to the axis X10. Each part 22 comprises a respective contact face 41 and the part 30 comprises a contact face 42. In the remote position, the part 30 is away from the parts 22, the contact face 42 being separated by the distance C of the faces. 41. In the contact position, the part 30 rests flat against the parts 22, the face 42 resting flat against the faces 41.

The electromagnetic actuator 4 comprises means for returning the movable part 8 to the remote position, which extend for example between the fixed part 6 and the movable part 8. In the example illustrated, these return means are formed by two helical compression springs 24 interposed parallel to the axis X10 between the part 31 and the cores 21. For the clarity of the drawings, the springs 24 are not shown in figure 2 .

The springs 24 are held in position vis-à-vis parts 6 and 8. For this, each spring 24 is introduced into a respective orifice 33 passing through part 30 and into a respective orifice 25 passing through one of the parts. 22. Each pair of through-holes 25 and 33 associated with one of the springs 24 is respectively coaxial with an axis parallel to the axis X10. The orifices 25 extend respectively from the faces 41 to the core 21. The orifices 33 extend from the face 42 to the part 31.

The contactor 2 comprises a housing 16 at least partially enclosing the contacts 12 and 14, and completely enclosing the actuator 4.

Preferably, as explained below, the faces 41 and 42 are in a non-magnetic material which constitutes an air gap integrated into the parts 22 and 30. Thus, the air gap material is integral with the parts 22 and 30, respectively. “Air gap” denotes a part of the magnetic circuit in which the induction flux does not circulate in a ferromagnetic material. In other words, the air gap is a cut in the magnetic circuit formed by parts 6 and 8, which is kept in the contact position of part 8 of contactor 2. In the remote position, an air gap is therefore formed at that time by the air separating the faces 41 and 42, and by the layer of non-magnetic material forming the faces 41 and 42.

As a variant, provision can be made to insert a wedge of non-magnetic material, in addition to the air gap already provided by the faces 41 and 42. Consequently, the faces 41 and 42 are not in mutual contact. In the contact position, the wedge of non-magnetic material receives the faces 41 and 42 in contact, being interposed between them. This makes it possible to obtain a thicker air gap in the contact position. This wedge of non-magnetic material is for example made of bronze or of polymer-based plastic, which are non-magnetic materials, compared to the ferromagnetic material of parts 6 and 8.

The term “drop-out time” is used to mean the time that elapses between the moment when the electrical supply to the coils 21 of the contactor 2 is stopped and the moment when the part 8 reaches the remote position. In other words, the drop-out time indicates how quickly contactor 2 can change state, i.e. for example open and cut off the current flowing in the power circuit, from the moment where the contactor 2 has received the order, that is to say the moment when the coils 21 of the actuator 4 are no longer supplied with electrical energy. It is generally desirable to obtain the lowest possible fallout time. Without wishing to link the dropout time to any theory, it seems that the thinner the air gap, obtained in the contact position, is, the smaller the dropout time itself.

Depending on the application, other shapes can be provided for the fixed and mobile ferromagnetic parts of the contactor and for the coils. For example, FR 2 746 541 A1 describes a movable magnetic circuit part, called the yoke, and a fixed magnetic circuit part, which are each in the shape of an “E”, that is to say each have three parallel branches, in particular a central branch. In this document, a single coil is provided around the respective central branch of these two magnetic parts, and surrounds this branch. The movable and fixed ferromagnetic parts, as well as the single coil described in FR 2 746 541 A1 are suitable for the invention.

In the following description, the expression “ferromagnetic part” relates to at least one part of the ferromagnetic parts of the contactors described above, in particular parts 6 and 8 of the contactor 2. More precisely, the expression “ferromagnetic part” can apply to at least one ferromagnetic part among the ferromagnetic parts 22 and 30. Preferably, in the contactor 2, at least the ferromagnetic parts 22 and 30 are concerned by the following.

Schematically with an enlarged scale, and exaggerated to facilitate understanding, figure 4 shows one of the ferromagnetic parts 22 and the ferromagnetic part 30 in the contact position, that is to say in contact with one another via their respective faces 41 and 42.

The ferromagnetic part essentially comprises a soft ferromagnetic material, that is to say in particular for the main part of its volume. This soft ferromagnetic metal is at least present at the heart of the ferromagnetic part, that is to say in a central internal part of its volume. For example, as shown on figure 4 , parts 22 and 30 include the soft ferromagnetic metal 100 at the core. In certain embodiments of the invention, the soft ferromagnetic metal is also present on the surface of the ferromagnetic part, for surfaces not occupied by the layer of nickel described below.

By "soft" is meant that the chosen metal easily magnetizes under the action of a magnetic field and easily loses its magnetization when it is no longer subjected to the magnetic field.

The chosen soft ferromagnetic metal is, for example, a soft iron alloy, or a low carbon steel. For example, provision is made for the soft ferromagnetic metal to be an iron-carbon alloy having a carbon content, that is to say a carbon content by mass, of less than 0.03% by weight. We can provide a pure iron.

The ferromagnetic part may have a laminated structure, i.e. be the result of a laminated stack of sheets made of the aforementioned ferromagnetic metal.

Alternatively, the structure each of the ferromagnetic part can be massive, that is to say without lamination. In this case, the ferromagnetic part is formed integrally by the soft ferromagnetic metal.

The ferromagnetic part comprises, for the entire surface of at least one of its faces, a surface layer of nickel, obtained by a chemical nickel plating step. This surface nickel layer is present in the skin of the ferromagnetic part, on the face or faces concerned. The surface nickel layer coats the soft ferromagnetic metal for that face (s). At this point, the soft ferromagnetic metal is therefore located under the surface nickel layer.

For parts 22 and 30 visible on the figure 4 , the contact faces 41 and 42 comprise a surface layer of nickel 102, in accordance with the above.

In order to obtain that the ferromagnetic part comprises a skin surface layer of nickel and a core-soft ferromagnetic metal, a blank is first provided in the desired soft ferromagnetic metal, with the structure desired, for example laminated or massive, and the desired geometry, for example that described above for the parts 22 and 30. Then, one proceeds to the chemical nickel plating of at least a part of the raw part, to obtain the ferromagnetic part desired. At the end of the chemical nickel plating, the chemically nickel plated part is coated, on the surface, with a surface layer of nickel.

Any suitable chemical nickel plating process can be used, preferably, provided that medium or high phosphorus chemical nickel is used, i.e. greater than 5% phosphorus by weight.

Preferably, in order to carry out the chemical nickel plating, the raw part is dipped in a bath. Preferably, the bath comprises an aqueous solution of nickel oxide and a reducing agent, preferably sodium hydrophosphite. A reduction reaction of the nickel oxide occurs by itself, under the action of the reducing agent, so that it is not necessary to use an electric current. The raw part is preferably stirred in the bath during soaking, so that the entire desired surface is coated, and is coated uniformly. For example, this brewing can be carried out in a barrel, an enclosure or a tank. The thickness of the surface nickel layer is determined in particular by the immersion time in the bath and the concentration of reagents in the bath.

The nickel layer advantageously forms a non-magnetic layer on the surface of the ferromagnetic part. For the actuator 4, the layer of nickel being provided on the faces 41 and 42, it advantageously serves as an air gap for the magnetic circuit formed by the parts 6 and 8.

As a variant, the layer of nickel could be provided on only one of the two faces 41 and 42, the other face being advantageously treated by a different process.

Thanks to this air gap integrated into parts 6 and 8, or at least one of them, it is not compulsory to provide the separate air gap wedge, which makes it possible to obtain an air gap whose thickness , measured parallel to the X10 axis, is particularly weak and regular, perpendicular to the X10 axis. Contactor 2 is therefore particularly efficient and has a particularly low drop-out time that is stable over time. Contactor 2 is more durable. This does not exclude the possibility of providing all the same a separate air gap part as explained above, without departing from the scope of the invention.

At the end of the chemical nickel plating step, the surface nickel layer directly coats the soft ferromagnetic metal without an intermediate layer. The ferromagnetic part can be used in this form.

The surface nickel layer being provided on at least one of the faces 41 and 42, it effectively protects the parts 22 and / or 30 from any impact liable to occur each time these ferromagnetic parts are brought into contact with each other, during of the passage in the contact position of the actuator 4 of the contactor 2. In fact, the surface nickel layer has a high hardness compared to the soft ferromagnetic metal, for example between 400 and 500 HV (Vickers hardness measurement). Therefore, more generally, it is advantageously provided that the surface nickel layer covers at least one surface of a ferromagnetic part of the contactor, which surface comes into contact with another ferromagnetic part when the actuator is tilted from the remote position to the contact position.

For the outer surfaces of parts 22 and 30 which are not coated with the surface nickel layer, the soft ferromagnetic metal is preferably bare.

It is possible to provide for coating a single face with nickel, as explained above. Preferably, however, provision is made for at least 95% of the surface area of the outer surface of the ferromagnetic part to be coated with the surface nickel layer. Even more preferably, provision can be made to coat the entire external surface of the ferromagnetic part, that is to say, the entire external surface of the part concerned. In this case, the ferromagnetic metal is present only at the heart of the ferromagnetic part, being entirely covered, in skin, by the surface layer of nickel. Thus, the ferromagnetic metal of the core is fully protected from impact and corrosion.

For the use of the ferromagnetic part within the contactor 2, the surface nickel layer is advantageously external, that is to say it extends from the surface of the part 22 or 30 concerned.

The chemical nickel plating step is preferably carried out until the surface nickel layer has a thickness of between 3 and 50 μm, preferably between 5 and 25 μm.

The air gap obtained is therefore thinner than that which could be obtained using a non-magnetic shim, the thickness of which can hardly be less than 100 μm. The thickness of the desired air gap is adjusted as a function of the application, in particular as a function of the type of contactor that is desired to be obtained, and of the type of power circuit into which it is desired to be integrated. This adjustment is easy to obtain, since it depends essentially on the time during which the ferromagnetic part is immersed in the chemical nickel plating bath and on the concentration of the reagents in this bath. The thickness of the air gap being so small, the electrical energy to keep the movable and fixed ferromagnetic parts in the contact position is particularly low, even when the contactor is used. in a severe environment, that is to say including subjecting the contactor to shocks and vibrations.

The ferromagnetic part comprising the surface nickel layer has preferably undergone a magnetic annealing step, at least as regards the ferromagnetic metal. The term “magnetic annealing” is understood to mean a heat treatment of the part concerned. This treatment is preferably aimed at restoring to the treated part its magnetic properties which may have been lost after deformations that the ferromagnetic metal of the part concerned may have undergone for the manufacture of the part. Magnetic annealing is preferably aimed at enlarging the iron grains of the ferromagnetic metal by stabilizing the carbides in the grain boundaries, thus promoting magnetic fluxes in the material. Magnetic annealing comprises for example a step in which the ferromagnetic part is subjected to a rise in temperature, from ambient, to a temperature Tmax of between 800 and 850 ° C, with a maximum speed of 200 ° C per hour. The ferromagnetic part is then maintained at the temperature Tmax of between 800 and 850 ° C., this first step lasting between 3 and 5 hours. A duration of 4 hours is preferred. In a subsequent magnetic annealing step, following the step of maintaining the temperature Tmax, the temperature is slowly lowered to 500 ° C., before returning to ambient temperature. The total duration of the magnetic annealing operation comprising the first and the second stage is preferably about 20 hours.

In an embodiment which is not illustrated and which does not relate to the invention, the magnetic annealing can be carried out before application of the surface nickel layer by chemical nickel plating, in order then to apply the surface nickel layer on the surface. ferromagnetic metal which has undergone magnetic annealing. In this case, the nickel layer advantageously coats the annealed ferromagnetic metal without an intermediate layer, in particular with the thickness ranges mentioned above.

In an embodiment described below and an example of which can be seen on the figure 4 , a diffused nickel layer is provided, intermediate between the surface nickel layer and the core soft ferromagnetic metal. For this, the magnetic annealing is implemented while the ferromagnetic part concerned is already coated with the surface nickel layer. Indeed, the presence of nickel on the surface is not incompatible with magnetic annealing. In this case, the nickel layer diffuses in the direction of the core, that is to say that a new layer is created, called a “diffused nickel layer” between the surface nickel layer and the soft ferromagnetic metal, this diffused nickel layer comprising a mixture of nickel and soft ferromagnetic metal, the nickel of the surface nickel layer having propagated towards the core. In the case of an iron-carbon alloy or a pure iron, the diffused nickel layer is therefore of the type NiFe. The diffused nickel layer extends from the surface nickel layer towards the core of the ferromagnetic part.

On the figure 4 , the ferromagnetic pieces 22 and 30 thus each comprise a layer of diffused nickel 104.

According to a variant not relating to the invention, it is advantageously possible to provide that the part 22 does not include a diffused nickel layer 104 if it has not undergone the annealing step. It is even possible to provide that the part 22 comprises, instead of the nickel layer 102 applied by chemical nickel plating, a layer of electrolytic nickel, or has undergone another suitable treatment.

After the magnetic annealing step, the surface nickel layer has a very high hardness, for example between 750 and 900 HV. The diffused nickel layer has an intermediate hardness, for example about 220 to 260 HV. The soft ferromagnetic metal exhibiting a generally lower hardness, for example less than 150 HV. A hardness gradient is therefore obtained, suitable for improving the strength of the ferromagnetic part and for reducing the rate of wear of the surface nickel layer. Indeed, the presence of the diffused nickel layer prevents wear of the ferromagnetic parts, by improving the resistance of the surface nickel layer on the soft ferromagnetic metal core.

Preferably, the diffused nickel layer has a thickness of between 3 and 40 μm, preferably between 10 and 30 μm. The formation of the diffused nickel layer occurs to the detriment of the thickness of the surface nickel layer, which, while it was initially between 5 and 25 μm, is reduced, for example to a thickness between 3 and 20 µm.

In a first test, a raw piece of soft iron was supplied, which was subjected to chemical nickel plating to obtain a surface layer of nickel 10 μm thick. This blank was then subjected to magnetic annealing, including subjecting the ferromagnetic part to a temperature of 820 ° C for a cycle of 4 hours. After magnetic annealing, the surface nickel layer has a thickness of about 6.6 µm and the diffused nickel layer has a thickness of 10.3 µm. In a second test, a soft iron blank was provided, which was subjected to chemical nickel plating to obtain a 25 µm thick surface nickel layer. This blank was then subjected to magnetic annealing, including subjecting the ferromagnetic part to a temperature of 820 ° C for a cycle of 4 hours. After annealing, the surface nickel layer has a thickness of about 14.8 µm and the diffused nickel layer has a thickness of 23.9 µm.

In the case where the layers 102 and 104 are provided, one obtains, when the parts 30 and 32 are in the contact position as shown in the figure figure 4 , an air gap whose thickness is designated by the arrow 106. The thickness of the air gap then includes the surface nickel layer and the diffused nickel layer.

Any ferromagnetic part manufactured using the manufacturing process steps can be integrated, that is to say mounted or assembled, in an electromagnetic contactor such as contactor 2, in order to form all or part of the ferromagnetic part. mobile or the fixed ferromagnetic part.

The following comparative test was carried out. An endurance test was carried out on two three-pole contactors, one belonging to the prior art, the other being in accordance with the invention. For each of these contactors, approximately two million cycles were performed at regular time intervals. Each cycle consists of tilting the movable part of the actuator from the remote position to the contact position, then from the contact position to the remote position. Each cycle has a number, from one to two million, carried on the x-axis X of the figure 5 . For about thirty cycles among the two million, the fall-out time was measured and plotted on the y-axis of the figure 5 . The dropout time is expressed in milliseconds.

The actuator of the contactor of the prior art comprises, for the fixed part and for the movable part, two respective ferromagnetic parts, which come into contact with one another each time they pass into the contact position. The mobile part is coated with a layer of phosphate, applied by dry phosphating, for its contact face, and the fixed part is coated with a layer of electrolytic nickel. Before the implementation of the aforementioned cycles, the thickness of the phosphate layer applied to each of the parts is approximately 3.5 µm. No air gap part is interposed between the two ferromagnetic parts. These ferromagnetic parts have undergone magnetic annealing carried out before dry phosphating.

The drop-out time values for this prior art actuator is illustrated by curve 90 of the figure 5 .

The contactor according to the invention is identical to the contactor of the prior art, except that the movable part has been coated, on its contact face, with a layer of nickel applied by chemical nickel plating, then has undergone an applied magnetic annealing. after nickel plating. Before the implementation of the above-mentioned cycles, the thickness of the surface nickel layer applied to the movable part is approximately 25 μm, and that of the diffused nickel layer is approximately 30 μm.

The drop-out time values for this actuator according to the invention is illustrated by curve 92 of the figure 5 .

For the first 5000 cycles, it is observed that the drop-out time of the actuator according to the invention, comprised between 35 and 40 ms, is less than that of the actuator of the prior art, comprised between 40 and 50 ms .

After two million cycles, it is observed that the drop-out time of the actuator according to the invention, comprised between 45 and 50 ms, is less than that of the actuator of the prior art, comprised between 160 and 170 ms.

For the contactor of the prior art, the drop-out time increases irregularly as the cycles are carried out. Peaks are observed, particularly at 720,000 cycles, where the drop-out time is 142 ms, and at 1,779,300 cycles, where the drop-out time is 211 ms. Troughs are observed consecutively to the two aforementioned peaks, at 805987 cycles where the drop-out time is 111 ms and at 1944121 cycles where the drop-out time is 163 ms. It seems that these irregular variations are caused by the deformation of the ferromagnetic parts under the effect of impact, in combination with the detachment of parts of the phosphate layer.

For the contactor according to the invention, the drop-out time increases more slightly, and more regularly. No significant peak or trough is observed for this growth.

The contactor according to the invention has the advantage of offering a very regular drop-out time, with a small deviation over time and particularly good repeatability. After two million cycles, the ferromagnetic parts of the contactor according to the invention exhibit a surface condition of acceptable and regular wear, while the surface condition of the ferromagnetic parts of the contactor of the prior art is much more deteriorated. : the parts have lost part of the phosphate coating, so that the ferromagnetic metal present in the core is visible on the surface. The ferromagnetic parts of the contactor of the prior art are deformed on the surface, as if dented, and exhibit significant matting marks, whereas, in comparison, the ferromagnetic parts of the contactor of the invention have better retained their original geometry.

Claims (10)

1. Method for manufacture of a ferromagnetic part (22, 30) for an electromagnetic contactor (2), the method comprising the following successive steps:

   - a step a) of supplying an unfinished part made of soft ferromagnetic metal (100); and

   - a step b) of chemical nickel-plating of at least one part of the unfinished part in order to obtain the ferromagnetic part (22, 30), the part of which is coated on the surface by a surface nickel layer (102), the obtained ferromagnetic part comprising the soft ferromagnetic metal (100) which, for said at least one chemically nickel-plated part, is disposed under the surface nickel layer (102),

   characterised in that the method comprises, after step b), a step c) of magnetic annealing of the ferromagnetic part coated during step b), so that the ferromagnetic part (22, 30) obtained at the end of step c) comprises:

   - on the external surface, the surface nickel layer (102),

   - the annealed soft ferromagnetic metal (100), under the surface nickel layer (102) for said at least one part which is chemically nickel-plated during step b), and

   - a nickel layer (104) diffused into the soft ferromagnetic metal (100) due to the magnetic annealing, the diffused nickel layer (104) connecting the surface nickel layer (102) and the annealed soft ferromagnetic metal (100).
2. Method for manufacture of a ferromagnetic part (22, 30) according to claim 1, characterised in that step b) comprises immersion of the unfinished part in a bath, the bath comprising an aqueous solution of nickel oxide and a reducing agent, preferably sodium hydrophosphite, the unfinished part being swirled in the bath during immersion so as to be coated by the surface nickel layer (102) over at least 95% of its surface, preferably over all its surface.
3. Method for manufacture of a ferromagnetic part (22, 30) according to any of the preceding claims, characterised in that step c) comprises subjection of the ferromagnetic part (22; 30), coated during step b), to a temperature between 800°C and 850°C for a duration of between 3 hours and 5 hours, preferably 4 hours.
4. Method for manufacture of a ferromagnetic part (22, 30) according to any of the preceding claims, characterised in that the soft ferromagnetic metal (100) is an iron-carbon alloy with a carbon content less than 0.03% by weight.
5. Method for manufacture of an electromagnetic contactor (2), the electromagnetic contactor (2) comprising:

   - an electromagnetic actuator (4) comprising at least one coil (18), a movable ferromagnetic part (8) and a fixed ferromagnetic part (6), the movable (8) and fixed (6) ferromagnetic parts being configured to rock between a position removed one from the other and a position of contact; and

   - at least one pair of power contacts (12, 14) which is actuated by the movable ferromagnetic part (8) during rocking between the removed position and the contact position, said at least one pair of power contacts (12, 14) being then rocked between a closed configuration and an open configuration,

   the method for manufacture of the electromagnetic contactor (2) comprising a step in which there is integrated at least one ferromagnetic part (22; 30) obtained by means of the method for manufacture of a ferromagnetic part according to one of claims 1 to 4, with at least one of the movable (8) and fixed (6) ferromagnetic parts.
6. Ferromagnetic part (22, 30) for an electromagnetic contactor (2), the ferromagnetic part (22, 30) being preferably obtained by means of a method according to any of claims 1 to 4, the ferromagnetic part (22, 30) having undergone, for at least one part of said ferromagnetic part, a step b) of chemical nickel-plating and, after step b), a step c) of magnetic annealing of the ferromagnetic part coated in step b), said at least one part of the ferromagnetic part comprising:

   - as outer surface, a surface nickel layer (102) obtained by the step of chemical nickel-plating,

   - an annealed soft ferromagnetic metal (100), coated by the surface nickel layer (102) by being under the surface nickel layer for said at least one part chemically nickel-plated during step b), and

   - a nickel layer (104) diffused into the soft ferromagnetic metal (100) due to the magnetic annealing, the layer of diffused nickel (104) connecting the surface nickel layer (102) and the annealed soft ferromagnetic metal (100).
7. Ferromagnetic part (22, 30) according to claim 6, characterised in that the surface nickel layer (102) measures between 3 and 50 µm in thickness, preferably between 3 and 20 µm in thickness.
8. Ferromagnetic part (22, 30) according to any of claims 6 or 7, characterised in that the diffused nickel layer (104) measures between 3 and 40 µm in thickness, preferably between 10 and 30 µm in thickness.
9. Electromagnetic contactor (2) comprising:

   - an electromagnetic actuator (4) comprising at least one coil (18), a movable ferromagnetic part (8) and a fixed ferromagnetic part (6), the movable (8) and fixed (6) ferromagnetic parts being configured to rock between a position removed one from the other and a position of contact, at least one of the movable (8) and fixed (6) ferromagnetic parts comprising a ferromagnetic part (22, 30) according to any of claims 6 to 8; and

   - at least one pair of power contacts (12, 14) which is actuated by the movable ferromagnetic part (8) during rocking between the removed position and the contact position, said at least one pair of power contacts (12, 14) being then rocked between a closed configuration and an open configuration.
10. Use of a ferromagnetic part (22, 30) according to any of claims 6 to 8, in an electromagnetic contactor (2) according to claim 9, the ferromagnetic part (22, 30) being used as part of the movable ferromagnetic part (8) or of the fixed ferromagnetic part (6) of the electromagnetic actuator (4).

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