Bypass device with improved contact surface and rolling bearing device with a bypass device with improved contact surface

Abstract

The invention relates to a bypass device (1), an electrically conductive bypass conductor (3), and a first machine element (12), wherein the bypass conductor (3) is in contact with the first machine element (12), the first machine element being contacted by the bypass conductor (3) at a contact surface (K), and the contact surface (K) comprising a layer system (3) electroplated onto the first machine element (11), wherein the layer system (3) optionally comprises a first layer (3a) arranged on the first machine element (11) and at least one second layer (3b) arranged on the first machine element (11) or, if present, on the first layer (3a), wherein the optional first layer (3a) is formed of copper or nickel, and the at least one second layer (3b) is formed of an alloy comprising at least two of the elements tin, copper, nickel, silver, zinc, bismuth, antimony, cobalt, manganese, and tungsten.where the alloy contains non-metallic particles, including a comprehensive number of electrically conductive particles.

Description

Field of invention

[0001] The invention relates to a bypass device with a contact surface and a rolling bearing device with a bypass device having a contact surface. Background of the invention

[0002] In many applications, for example between the rotor shafts and housings of electric motors and generators, unwanted voltage potentials frequently arise. Without countermeasures, these voltage potentials can discharge through the rolling bearings. The current flowing through the affected rolling bearing can generate sparks in the rolling contact between the rolling elements and the raceways. The rolling raceways are damaged by melt pitting or erosion pitting.

[0003] Measures are already known in the field to prevent the build-up or decay of voltage potentials in machine elements that rotate relative to each other. For example, bypass devices are used, which divert discharges around the rolling bearings of the electric motor via so-called shaft grounding rings. Such a bypass device, consisting of a shaft grounding ring, is disclosed in DE 10 2016 010 926 A1. This shaft grounding ring has a disc-shaped, electrically conductive bypass conductor, which is clamped between two conductive angle brackets on the housing side and bears against a shaft with elastic preload. The angle brackets forming the holder for the bypass conductor are inserted into a housing at any suitable location. The bypass conductor is made of a conductive material that has low resistance to current flow.The advantage of such a bypass device is that the shaft grounding ring is easy and inexpensive to manufacture.

[0004] Bypass conductors are also frequently integrated into sealing devices by experts. An example of a pre-seam seal designed as a bypass conductor is disclosed in DE 10 2014 010 269 B4. The pre-seam seal is connected in series upstream of a main seal and simultaneously establishes an electrically conductive connection between two machine elements as a bypass conductor. The disc-shaped bypass conductor is intended to protect the sealing lip of the main seal from environmental contamination and is attached to the main seal. The main seal is mounted in the housing with a holder formed from an angle bracket.

[0005] In general, rolling bearing manufacturers are interested in using such bypass conductors in the direct and immediate vicinity of the rolling bearings, which can be exposed to the damage described above due to the reduction of stress potentials. Furthermore, the bypass conductors should be installed in the most space-saving way possible. Therefore, such bypass conductors are integrated, for example, into the main seals of rolling bearings. Such a device is disclosed in DE 10 2015 224 044 A1. The main seal used in this device is impregnated with a conductive filler.

[0006] It is known that contact with lubricants limits the performance of discharge devices. Therefore, mating surfaces of discharge devices can be fitted with sleeves made of precious metals to compensate for this and to achieve improved conductivity. Description of the invention

[0007] The object of the invention is to create an improved bypass device and an improved rolling bearing device.

[0008] The problem is solved according to the subject matter of claim 1.

[0009] The bypass device is designed for transmitting electrical currents to a rotating component, comprising at least one electrically conductive bypass conductor and a first machine element, wherein the bypass conductor is in contact with the first machine element, and the first machine element is contacted by the bypass conductor at a contact surface. The contact surface comprises a layer system electroplated onto the first machine element, wherein the layer system optionally comprises a first layer arranged on the first machine element and at least one second layer arranged on the first machine element or, if present, on the first layer.The optional first layer is formed from copper or nickel, and the at least one second layer is formed from an alloy comprising at least two of the elements tin, copper, nickel, silver, zinc, bismuth, antimony, cobalt, manganese, tungsten, wherein non-metallic particles comprising electrically conductive particles are incorporated in the alloy.

[0010] Generally, bypass devices do not have a coating on the counter-running surface, i.e., the contact surface, because this is usually integrated into the existing system, for example, as the shaft of an electric motor or as the bearing ring of a rolling bearing, and is therefore difficult to coat. Surprisingly, however, it has been found that an electroplated coating system, as described above, exhibits ideal properties as a contact surface for a bypass conductor. Firstly, ideal and improved current transmission can be observed, even with the presence of lubricant layers. Secondly, such a coating system exhibits ideal properties with regard to friction and wear. The invention takes this as an opportunity to equip the contact surface with the aforementioned coating system, despite the aforementioned constraints.

[0011] The electrically conductive particles exhibit an electrical conductivity ranging from 0.25 mΩ*cm*cm to 10 mΩ*cm*cm within a temperature range of 20 to 25°C. The presence of non-metallic particles, embedded in the alloy in the second layer, improves the mechanical stability of the layer system and, depending on the particle material, further reduces the interfacial resistance, thereby increasing the current transfer capacity at the contact surface.

[0012] In a preferred embodiment, the bypass device comprises a bypass conductor, a first machine element, and a holder. The holder and bypass conductor are electrically connected, and the holder serves to attach the bypass conductor to a second machine element and to hold the bypass conductor in place. This ensures a secure fit of the bypass device and allows for maximum flexibility in the choice of bypass conductor. This enables the ideal selection of the bypass conductor for the specific application. Thus, it is conceivable that a highly elastic bypass conductor, for example, to achieve low friction or wear, could be used, ideally held to the second machine element by the holder.

[0013] With regard to the electroplated layer system of the contact surface of the first machine element, an alloy is particularly preferably formed from a tin-nickel alloy with a nickel content in the range of 20 to 40 wt.%. Such a low nickel content is of great advantage, since second layers of such a tin-nickel alloy with electrically conductive particles dispersed therein, in particular carbon and / or graphite and / or carbon nanotubes and / or carbon fibers and / or carbon black and / or graphene and / or graphene oxide, have proven to be more stable in the long term than comparable layers of gold.

[0014] The alloy is alternatively formed from a copper-tin alloy, or a tin-silver alloy, or a tin-zinc alloy, or a tin-bismuth alloy, or a tin-antimony alloy, or a tin-cobalt alloy, or a nickel-tungsten alloy, or a tin-manganese alloy.

[0015] SnCu, in particular, has proven to be a high-performance material composition for a contact surface of a bypass device.

[0016] The first layer is made of copper or nickel. This ensures good adhesion of the layer system to the base material of the first machine element, i.e., the metal substrate.

[0017] The non-metallic particles preferably comprise a proportion of electrically conductive particles which cause a significant reduction in the interfacial resistance of the component and are in particular formed from at least one material of the group comprising carbon, graphite, carbon nanotubes, carbon fibers, carbon black, graphene, graphene oxide, metal nitride, metal carbide.

[0018] The proportion of electrically conductive particles is, in particular, more than 50% of the non-metallic particles. It has been shown that the electrically conductive particles protruding from the second layer maintain the electrical contact between the contact surface of the first machine element and the bypass conductor with exceptional reliability.

[0019] Particularly preferred is a combination of a tin-nickel alloy with a nickel content in the range of 20 to 40 wt.% with non-metallic particles dispersed therein, consisting of at least one material from the group comprising carbon, graphite, carbon nanotubes, carbon fibers, carbon black, graphene, and graphene oxide. Although this alloy forms an oxide layer on its surface as passivation, this layer is itself conductive and improves the start-up behavior of rotating machine elements.

[0020] The non-metallic particles may also include a proportion of particles formed from a non-electrically conductive material, such as at least one material from the group comprising metal sulfide, metal oxide, diamond, mica, PTFE.

[0021] Preferably used metal oxides include Al₂O₃, BeO₂, CdO, MgO, SiO₂, TiO₂, ZrO₂, Fe oxides, and the like. Preferably used metal carbides include SiC, WC, VC, TiC, Cr₂C₃, Cr₃C₂, and the like. Preferably used metal nitrides include BN or SiN and the like. Carbon is particularly preferred in the form of graphite, carbon nanotubes, carbon fibers, carbon black, graphene, or graphene oxide. Preferably used metal sulfides include MoS₂, MoS₂, Ni-FeS₂, and the like.

[0022] A preferred particle size for the non-metallic particles is in the range of 100 nm to 8 µm, particularly in the range of 500 nm to 6 µm. Particles that are particularly stable when dispersed in an electrolyte for the electroplating of the second layer are especially preferred. In particular, the particle size is selected such that it protrudes from the surface of the at least one second layer to ensure contact with the counterbody.

[0023] A preferred volume fraction of non-metallic particles in the second layer is in the range of 1 to 50 vol.%. This ensures reliable binding of the particles in the metallic matrix.

[0024] The optional first layer and at least one second layer are formed by electroplating. Electroplating processes readily allow the deposition of electrolyte-dense layers with a thickness of up to 30 µm. This enables the creation of electroplated, conductive, and durable layers on metallic substrates such as bearing steels or similar materials. The non-metallic particles are dispersed in an electrolyte to form the second layer and are incorporated into the alloy deposited on the first layer, forming at least one second layer.

[0025] A single second layer or several second layers can be applied on top of each other.

[0026] Furthermore, electroplating can be carried out using a so-called "pulse plating" process, in which the voltage applied to the electrolyte is periodically switched off or reversed. The brief current pulses received during switching on increase the number of nuclei for metal deposition, thus creating a basis for fine-grained deposits and a glossy finish.

[0027] The first layer preferably has a thickness of up to 5 µm, particularly up to 3 µm. The at least one second layer preferably has a thickness of up to 30 µm, particularly between 5 and 20 µm. The preferred total thickness of the layer system is < 10 µm, particularly between 4 and 8 µm.

[0028] The aforementioned bypass device is suitable for any application where the transmission of electrical currents to a rotating component is intended or required, for example, to mitigate damage to components caused by high voltage potentials. The bypass device is particularly well-suited for use in a rolling bearing assembly consisting of at least one rolling bearing and a bypass device, as well as a third and a fourth machine element. The rolling bearing is already part of the bypass device, since the first machine element is in the form of a first bearing ring and the second machine element is in the form of a second bearing ring, with the bearing rings arranged concentrically on an axially aligned axis of rotation of the rolling bearing. In one embodiment, it is also conceivable that the first machine element is in the form of a sleeve mounted on the bearing ring.The rolling bearing is provided with rolling elements arranged radially between the bearing rings, with at least one electrical connection between the third and fourth machine elements being formed via the aforementioned bypass device. The holder of the bypass device is radially attached to one of the bearing rings between one of the bearing rings and the third or fourth machine element, and holds the bypass conductor, with one of the bearing rings being attached to the third or fourth machine element. One of the bearing rings has a contact surface that comprises a layer system, at least partially applied electroplated, as described above.

[0029] The holder is mounted, for example, radially on an outer ring between the outer ring and a housing, or alternatively radially on an inner ring between the inner ring and a shaft. The holder can have one or more retaining rings and one or more retaining washers.

[0030] One or more bypass devices are integrated into the rolling bearing assembly. The advantage of the invention lies in the fact that the bypass conductor is integrated into the rolling bearing, thereby forming an ideal contact surface for all operating conditions. The bypass device can be attached to the rolling bearing in such a way that it is radially space-saving, not inside the rolling bearing but in the bearing seat – i.e., on the outside of the rolling bearing between a housing, shaft, or other machine element and one of the bearing races of the rolling bearing. In this case, no separate axial installation space is required for attaching the bypass conductor. The radial installation space is already available due to the dimensions of the rolling bearing.This has a particularly positive effect on applications in rolling bearing systems with small-diameter bearing series, where there is little radial and axial space between the bearing rings for accommodating seals and bypasses. The limited space can be fully utilized for housing the bypass device. Therefore, the components for attaching the bypass conductor do not need to be as delicate and can often be manufactured more cost-effectively.

[0031] The rolling bearing device comprises one or more rolling bearings. It is conceivable that the rolling bearing is sealed against the environment or surrounding structure by one or more seals. The bypass device is arranged axially on one side of the rolling elements. At least one electrical connection is formed via the bypass device between the first and second machine elements. It is therefore also conceivable that further electrically conductive connections between other machine elements are formed via the bypass device, either permanently or preferably switchable.

[0032] Two machine elements are rotatably mounted relative to each other using at least one rolling bearing. Either one or the other machine element is mounted so that it can rotate about the bearing's axis of rotation, or one or the other machine element is fixed to the housing. Alternatively, both machine elements can be arranged to rotate relative to each other about the bearing's axis of rotation. Machine elements include shafts, such as rotor shafts of an electric machine; housings, such as bearing shields or housing sections or bearing shields of an electric machine; gears or shafts or housings of a gearbox; or any other machine elements suitable for being mounted relative to each other by means of rolling bearings.

[0033] In the cases considered, the axis of rotation of the rolling bearing is always axially oriented, but can run horizontally, vertically, or obliquely in space. Radial orientation is perpendicular to the axis of rotation.

[0034] The rolling bearing serves for the rotatable mounting of machine parts, components, and assemblies. To reduce friction, it incorporates rolling elements that glide between the inner and outer rings, thus minimizing friction in the rotating bearing. As previously mentioned, the rolling bearing has an inner ring and an outer ring. Alternatively, the rolling bearing may have more than one inner and / or outer ring. Furthermore, the bearing rings can also be split, each featuring a raceway or a portion thereof. The inner ring typically has one or more outer raceways, and the outer ring correspondingly has one or more inner raceways. The rolling elements that glide on the raceways are either balls or rollers. The balls or rollers are often guided and held in cages.The rolling elements of a rolling bearing are either arranged in a row in the circumferential direction, or alternatively, the rolling bearing has several rows of rolling elements arranged side by side. Rolling bearings can also be thrust bearings. In this case, both the inner ring and the outer ring are thrust washers, which have thrust raceways.

[0035] In the context of the invention, a bypass is understood to mean the diversion of a current or voltage around one or more rolling bearings and / or machine components. The rolling elements and bearing rings are usually made of bearing steel and contact each other at the raceways. The contact zones formed are potential pathways for currents, at which the dreaded discharges lead to the damage to the raceways already described in the chapter "Background of the Invention".

[0036] The bypass, or bypass device, is intended to divert the currents. This can be achieved, firstly, by ensuring that the bypass device, or at least the bypass conductor, has comparatively lower electrical or specific electrical resistances than the rolling bearing.

[0037] The bypass device can include a holder, which may have one or more retaining rings and one or more retaining discs. It is conceivable that the holder or the retaining ring is provided with at least one, preferably several, recesses distributed around the circumference of the rolling bearing's axis of rotation, extending axially through a substantially radially extending, annular base body. The retaining disc engages in the recess with at least one retaining clip and is held against the base body. The bypass conductor is held axially between the electrically conductive retaining ring and the retaining disc. The retaining clip(s) can be positively and / or frictionally locked or hooked into the recess. Such an arrangement is advantageously easy to assemble. The individual parts of the holder can be manufactured cost-effectively from sheet metal.

[0038] It is conceivable to design the retaining element or retaining ring of the rolling bearing device such that it has several clamps distributed around the circumference of one of the bearing rings, or that the retaining elements themselves are such clamps. These clamps are arranged radially between the bearing ring and the machine element, for example, between the outer ring and a housing or between the inner ring and a shaft, and overlap the bearing ring axially and engage it radially behind it. The clamps are elastically resilient and are preloaded radially between one of the machine elements and one of the bearing rings against the bearing ring.

[0039] The advantage of this design is that the areas on the bearing ring to which the retaining ring is attached, or against which the retaining elements are preloaded, do not require precision machining, as the retaining elements are at least radially elastically preloaded against these areas. The elasticity of the individual retaining elements is ensured by the fact that they are separated from each other circumferentially around the axis of rotation of the rolling bearing by axially continuous recesses. This extends the retaining elements from a base on the retaining ring by a radially extending elastic lever. In conjunction with a snap-fit ​​geometry, the retaining element can bridge large tolerances during press-fitting and is securely fixed both axially and radially. The retaining rings are easy and cost-effective to manufacture from sheet metal or spring steel.

[0040] It is conceivable that one or more clamping elements or retaining clips, either attached to the retaining disc or separately formed, engage in one of the recesses, or even more than one, and hold the retaining disc and the retaining ring together in a form-fitting manner. The bypass conductor is then axially clamped between the clamping element and the holder, or between the retaining disc and the retaining ring. The clamping element can, for example, be a simple clip inserted into the recess, or the clamping element or retaining clip can be formed on the retaining ring of the holder. Clamping elements are either detachably or permanently clamped to the retaining ring, and retaining clips are, for example, positively clipped or snapped into the recesses and may also be detachable.

[0041] It is conceivable that the holder, in contact with one of the bearing rings, is electrically conductive against it. The holder is made of electrically conductive material, has a conductive coating, or is equipped with conductive elements. Crucially, an electrically conductive connection between the machine element and the holder must be established, either via the electrically conductive bearing ring or through direct contact with the holder. The bearing ring must be made of a conductive material or have an electrically conductive coating. In general, it can be assumed in this case that the electrical resistance of the bypass device is lower than the electrical resistance in the passage through the rolling contacts of the rolling bearing.

[0042] The rolling contacts are the contacts where the rolling elements bear against the raceways during operation or when the respective rolling bearing is at rest. The rolling contact zones are therefore the zones in which the rolling elements roll on the raceways of the bearing rings during operation. The electrically conductive connection for discharging the potential differences between the first and second machine elements is established by means of the bypass device. As mentioned earlier, the machine elements can be housings or shafts, or alternatively, other machine parts. It is conceivable, for example, that the fourth machine element is formed integrally with the inner ring of the rolling bearing. Thus, it is not impossible that, for instance, in the case of a cylindrical roller bearing, the raceway of the rolling elements is directly the shaft, which, in this understanding, forms the bearing ring and the fourth machine element as a single unit.

[0043] The rolling elements of the rolling bearings covered by the invention can be guided between the bearing rings with or without a cage. A cage has one or two side edges. Cages with only one side edge are crown- or comb-shaped, meaning that cage webs project axially from the side edge like the teeth of a crown or the tines of a comb. The circumferentially adjacent gaps between the teeth or tines are the pockets in which the rolling elements are received. The cages are developed in imaginary flat planes in the manner of a perforated strip for balls and in a ladder-like shape for rollers. In both cases, the cage webs connect two parallel side edges. The gaps, which appear as holes or windows in the flat planes, are three-dimensionally formed circumferential pockets between the cage webs in which the rolling elements are received. Description of the drawings

[0044] The invention is explained in more detail below using exemplary embodiments. The figures show: - Fig. 1 - a representation of the basic structure of the bypass device 1 comprising a bypass conductor as well as a first machine element and a layer system; - Fig. 2 - the first machine element according to Fig. 1 in section II-II; - Fig. 3 - a rolling bearing arrangement 9 in a partial section along the axis of rotation 16;

[0045] Fig. 1 - Fig. Figure 1 shows the basic structure of the bypass device 1 for transmitting electrical currents to a rotating component that rotates about the axis of rotation 16. The bypass device 1 comprises an electrically conductive bypass conductor 2 and a first machine element 5, wherein the bypass conductor 2 is in contact with the first machine element 5. The first machine element 5 is contacted by the bypass conductor 2 at a contact surface K. The contact surface K comprises a layer system 3 that is at least partially electroplated onto the first machine element 5.

[0046] The bypass device 1 can also have a holder 6, wherein the holder 6 and bypass conductor 2 are electrically connected to each other and the holder 6 is used to attach the bypass conductor 2 to a second machine element 7, in Fig. 1 not shown in detail, serves as well as holding the bypass conductor 2.

[0047] Fig. 2 - shows component 1 according to Fig. 1 in section II-II. Same reference symbols as in Fig. 1 denotes identical elements. The first machine element is now identifiable with its base material 8, here for example made of bearing steel.

[0048] The contact area K represents the area in contact with the bypass conductor 2. The first machine element 5 can be electroplated with a first layer 3a of nickel, with a layer thickness of up to 5 µm, particularly in the range of up to 3 µm. On the first layer 3a is an electroplated second layer 3b of a tin-nickel alloy containing non-metallic graphite particles with a layer thickness of up to 30 µm, particularly in the range of 5–20 µm.

[0049] Fig. 3 - The rolling bearing device 9 is formed from the rolling bearing 10 shown, the bypass device 1, and also a third machine element 14 and a fourth machine element 18. The rolling bearing 10 has a first machine element 5 in the form of a first bearing ring 11 and a second machine element 7 in the form of a second bearing ring 13, wherein the bearing rings 11, 13 are arranged concentrically on an axially aligned axis of rotation 16 of the rolling bearing 10. The rolling bearing 10 is provided with rolling elements 17 arranged radially between the bearing rings 11, 13. At least one electrical connection is formed between the third machine element 14 and the fourth machine element 18 via the bypass device 1. The holder 6 of the bypass device 1 is radially attached between one of the bearing rings 11, 13 and the third or fourth machine element 14, 18 to one of the bearing rings 11, 13 and holds the bypass conductor 2.The holder 6 can be formed in one piece, for example by means of bent retaining elements 15 that hold the bypass conductor 2, or it can have a further component 12 that holds the bypass conductor 2. One of the bearing rings 11, 13 can be attached to the third or fourth machine element 14, 18, wherein in . Fig. 3. The bearing ring 13 is attached to the fourth machine element 18. It is conceivable that the third machine element 14 is formed integrally with the first bearing ring 11 of the rolling bearing 10. Thus, it is not excluded that, for example, in the case of a cylindrical roller bearing or a set of cylindrical rollers, the raceway of the rolling elements 17 is directly the shaft 19, which in this understanding then integrally represents the bearing ring 11 and the third machine element 14. It is further conceivable that the first machine element is designed as a sleeve 4 that is mounted on the first bearing ring 11. Fig.3 merely represents the possible position of the sleeve 4. Reference sign 1 Bypass device 2 bypass conductors 3 electroplated coating system 3a First shift 3b Second shift 4 Sleeve 5 First machine element 6 holders 7 Second machine element 8 Basic materials 9 rolling bearing device 10 rolling bearings 11 First bearing ring 12. Another component 13 Second bearing ring 14 Third machine element 15 retaining elements 16 Rotation axis 17 rolling elements 18 Fourth machine element 19th wave K Contact surface QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2016 010 926 A1

[0003] DE 10 2014 010 269 B4

[0004] DE 10 2015 224 044 A1

[0005]

Claims

[1] Bypass device (1) for transmitting electrical currents to a rotating component, wherein the bypass device (1) comprises at least one electrically conductive bypass conductor (2) and a first machine element (5), wherein the bypass conductor (2) is in contact with the first machine element (5), wherein the first machine element is contacted by the bypass conductor (2) at a contact surface (K), characterized by , that the contact surface (K) comprises a layer system (3) applied galvanically to the first machine element (5), wherein the layer system (3) optionally comprises a first layer (3a) arranged on the first machine element (5) and at least one second layer (3b) arranged on the first machine element (5) or, if present, on the first layer (3a), wherein the optional first layer (3a) is formed from copper or nickel and the at least one second layer (3b) is formed from an alloy comprising at least two of the elements tin, copper, nickel, silver, zinc, bismuth, antimony, cobalt, manganese, tungsten, wherein non-metallic particles comprising electrically conductive particles are incorporated in the alloy. [2] Bypass device (1) according to claim 1, characterized by that the bypass device (1) has a holder (6) and an electrically conductive bypass conductor (2) and the holder (6) and bypass conductor (2) are electrically connected to each other and the holder (6) serves to fasten the bypass conductor (2) to a second machine element (7) and holds the bypass conductor (2). [3] Bypass device (1) according to claim 1 or 2, wherein the alloy is formed from a tin-nickel alloy having a nickel content in the range of 20 to 40 wt%. [4] Bypass device (1) according to claim 1 or 2, wherein the alloy is formed from a copper-tin alloy or a tin-silver alloy or a tin-zinc alloy or a tin-bismuth alloy or a tin-antimony alloy or a tin-cobalt alloy or a nickel-tungsten alloy or a tin-manganese alloy. [5] Bypass device (1) according to one of claims 1 to 4, wherein the non-metallic particles comprise a proportion of electrically conductive particles formed from at least one material selected from the group comprising carbon, graphite, carbon nanotubes, carbon fibers, soot, graphene, graphene oxide, metal nitride, metal carbide. [6] Bypass device (1) according to one of claims 1 to 5, wherein the non-metallic particles further comprise a proportion of particles formed from at least one material selected from the group comprising metal sulfide, diamond, metal oxide, mica, PTFE. [7] Bypass device (1) according to one of claims 1 to 6, wherein the first machine element (5) is formed from a material selected from the group consisting of copper, a copper alloy, nickel, a nickel alloy, low-alloy carbon steel, and no first layer (3a) is present. [8] Bypass device (1) according to one of claims 1 to 7, wherein the first layer (3a) has a layer thickness of up to 5 µm. [9] Bypass device (1) according to one of claims 1 to 8, wherein the at least one second layer (3b) has a layer thickness of up to 30 µm. [10] Rolling bearing device (9) which is formed from at least one rolling bearing (10) and a bypass device (1) and also comprises a third machine element (14) and a fourth machine element (18), wherein: the rolling bearing (10) has a first machine element (5) in the form of a first bearing ring (11) and a second machine element (7) in the form of a second bearing ring (13), and wherein the bearing rings (11, 13) are arranged concentrically on an axially aligned rotation axis (16) of the rolling bearing (10), the rolling bearing (10) is provided with rolling elements (17) arranged radially between the bearing rings (11, 13), wherein at least one electrical connection is formed between the third machine element (14) and the fourth machine element (18) via the bypass device (1), wherein the holder (6) is fixed radially between one of the bearing rings (11, 13) and the third or fourth machine element (14, 18) to one of the bearing rings (11, 13) and holds the bypass conductor (2), wherein one of the bearing rings (11, 13) is fixed to the third or fourth machine element (14, 18), and one of the bearing rings (11, 13) has a contact surface comprising a galvanically applied layer system (3) according to claims 1-9. [11] Rolling bearing device (9) which is formed from at least one rolling bearing (10) and a bypass device (1) and also comprises a third machine element (14) and a fourth machine element (18), wherein: the rolling bearing (10) has a first machine element (5) in the form of a sleeve (4) applied to the first bearing ring (11) and a second machine element (7) in the form of a second bearing ring (13), and wherein the bearing rings (11, 13) are arranged concentrically on an axially aligned axis of rotation (16) of the rolling bearing (10), the rolling bearing (10) is provided with rolling elements (17) arranged radially between the bearing rings (11, 13), wherein at least one electrical connection is formed between the third machine element (14) and the fourth machine element (18) via the bypass device (1), wherein the holder (6) is fixed radially between one of the bearing rings (11, 13) and the third or fourth machine element (14, 18) to one of the bearing rings (11, 13) and holds the bypass conductor (2), wherein one of the bearing rings (11, 13) is fixed to the third or fourth machine element (14, 18), and the sleeve (4) has a contact surface comprising a galvanically applied layer system (3) according to claims 1-9. [12] Rolling bearing device (1) according to claim 10 or 11, characterized by that the holder (6) is fixed radially between the second bearing ring (13) and the fourth machine element (18) and the third machine element (14) is formed integrally with the second bearing ring (13).

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