Earthing ring, arrangement which comprises the earthing ring, and method for producing the earthing ring

Abstract

An earthing ring (1) composed of an electrically conductive nonwoven which has a first electrical conductivity, comprising a dynamically stressed earthing contact region (2), only the earthing contact region (2) having an electrically conductive coating (3) and / or electrically conductive particles (4), with a second electrical conductivity, and the second electrical conductivity being greater than the first electrical conductivity.

Description

[0001] 2024P00047WG

[0002] 1

[0003] September 1, 2025

[0004] Mat exchange / KL

[0005] Applicant: Carl Freudenberg KG, 69469 Weinheim

[0006] Grounding ring, arrangement comprising the grounding ring and method for its manufacture

[0007] Description

[0008] Technical field

[0009] The invention relates to an earthing ring, an arrangement comprising the earthing ring and a method for its manufacture.

[0010] State of the art

[0011] A grounding ring is known from EP 4 095298 B1. The grounding ring consists of an electrically conductive nonwoven fabric containing electrically conductive particles. The nonwoven fabric comprises a raw nonwoven with a first electrical conductivity, wherein the raw nonwoven fabric comprises electrically conductive particles, with a second electrical conductivity, and wherein the second electrical conductivity is greater than the first electrical conductivity.

[0012] The particles are preferably formed from silver particles and have a size of 3 pm to 8 pm, the raw nonwoven fabric comprising fibers with a fiber thickness of 4 pm to 10 pm. The particles have a weight fraction of 30% to 60%.

[0013] It is therefore advantageous that a sufficient number of particles are present in the nonwoven fabric to ensure good electrical conductivity. The particles are evenly distributed throughout the nonwoven fabric. Silver particles exhibit particularly high electrical conductivity and are therefore especially well-suited to significantly increasing the electrical conductivity of the raw nonwoven fabric.

[0014] From DE 10 2019 113 039 A1, an electrically conductive nonwoven fabric is known which is used in an arrangement comprising a shaft, a housing, and the electrically conductive nonwoven fabric for creating an electrically conductive connection between the shaft and the housing. The electrically conductive nonwoven fabric is fixed to a holding element and contacts the shaft and the housing.

[0015] The electrically conductive nonwoven fabric is impregnated with a PTFE dispersion, which stabilizes the fabric and reduces friction against the shaft. The electrically conductive nonwoven fabric comprises electrically conductive particles in the form of carbon fibers.

[0016] From DE 10 2018 105 376 A1, an earthing ring in an arrangement is known which is designed as a pre-seal for a seal and consists of an electrically conductive material.

[0017] From DE 10 2013 000 982 B4, a seal with a pre-seal is known, which is associated with a dynamically stressed sealing lip of the sealing ring at an axial distance. To create an electrically conductive connection and thus a potential equalization between machine elements to be sealed against each other, the pre-seal consists of an electrically conductive nonwoven fabric, wherein the machine elements to be sealed against each other are in contact with the pre-seal.

[0018] WO 2017 / 148586 A1 discloses a shaft grounding ring for dissipating induced voltages or electrical charges from a first machine element, preferably a shaft, to a second machine element. The shaft grounding ring has an annular housing made of electrically conductive material, which is electrically connected to one of the machine elements and is in electrically conductive contact with at least one discharge element. The discharge element is made of an electrically conductive material and is also in electrically conductive contact with the other machine element. Electrically conductive PTFE is mentioned as a material for the discharge element. Alternatively, a discharge element with an electrically conductive coating can be used, wherein the coating is applied to the discharge element or formed by a film.

[0019] If the conductive element is made of an electrically non-conductive material, this material can be coated with an electrically conductive layer of silver lacquer.

[0020] The silver lacquer is permanently bonded to a base body of the discharge element.

[0021] Another shaft grounding ring is known from DE 20 2016 009 162 U1. The shaft grounding ring is electrically conductively arranged between two machine elements by means of a grounding element, wherein the grounding element comprises a base body and is provided with open-edged recesses around its circumference in order to achieve resistance values ​​between the first and second machine elements of less than 1 Q during operation. The grounding element can be coated with an electrically conductive material, preferably with a silver lacquer.

[0022] The coating completely encases the base body of the discharge element.

[0023] All the grounding rings described above have in common that either the electrically conductive coating completely encases the grounding ring or the electrically conductive particles are evenly distributed throughout the entire grounding ring. If the coatings and / or the particles are made of an expensive material, such as silver, to achieve particularly good electrical conductivity, a comparatively large and therefore expensive quantity must be used. While this makes the previously known grounding rings effective, it also makes them expensive.

[0024] Description of the invention

[0025] The invention is based on the objective of further developing an earthing ring of the type mentioned above and an arrangement comprising such an earthing ring in such a way that they exhibit good effectiveness on the one hand and can be manufactured comparatively more cost-effectively on the other. Furthermore, a method for manufacturing such an earthing ring is to be described.

[0026] This problem is solved according to the invention by the features of claims 1, 5 and 8. Advantageous embodiments or further developments are addressed in the respective claims that refer back to them.

[0027] To solve the problem, an earthing ring made of an electrically conductive nonwoven fabric is provided, which has a first electrical conductivity, with a dynamically stressed earthing contact area, wherein only the earthing contact area has an electrically conductive coating and / or electrically conductive particles, with a second electrical conductivity and wherein the second electrical conductivity is greater than the first electrical conductivity.

[0028] For the purposes of the present invention, the term “grounding contact area” shall be understood to mean the area of ​​the grounding ring which, during its intended use and throughout its entire service life, is in contact with a surface of a machine element to be grounded.

[0029] The grounding ring's function is to prevent mechanical damage to machine elements, which it connects electrically, caused by electrical breakdown. Without electrical equipotential bonding, mechanical damage to the machine elements could occur when differing electrical potentials are equalized through electrical breakdown. Such breakdown is more likely the closer the machine elements with differing electrical potentials are located to each other. A breakdown can cause material loss on the machine element with a relatively low charge and alter the material structure in the area where the breakdown occurs.

[0030] In contrast to the grounding rings of the prior art mentioned above, the grounding ring according to the invention is designed so that only the grounding contact area has the electrically conductive coating and / or the electrically conductive particles. This prevents the expensive coating and / or the expensive particles from being used in other areas of the grounding ring that are irrelevant to the function of the grounding ring.

[0031] Surprisingly, it has been found that only a partial coating of the grounding ring, specifically a partial coating of only the grounding contact area, is sufficient for the grounding ring to be effective. Furthermore, it has been surprisingly found that the performance characteristics of the grounding ring are practically on par with those of grounding rings where the electrically conductive nonwoven fabric is completely coated with an electrically conductive layer or contains uniformly distributed electrically conductive particles.

[0032] An electrically conductive carbon fleece, for example, has an impedance of approximately 100 Ω or more. A fully coated / impregnated carbon fleece with a comparable construction exhibits an impedance of around 1 Ω. A partially silver-coated carbon fleece shows an impedance of approximately 1.2 to 2 Ω. Surprisingly, this resistance level is closer to that of fully coated / impregnated carbon fleeces than to that of uncoated carbon fleeces.

[0033] However, compared to fully coated / impregnated carbon fleeces, the manufacturing costs of a partially treated carbon fleece are significantly lower.

[0034] Furthermore, it is advantageous that, due to the electrically conductive coating and / or the electrically conductive particles, only the grounding contact area is free of coating and / or particles in the other areas of the grounding ring, thus avoiding adverse bending properties, in particular an increase in stiffness in the main bending zone of the grounding ring and adverse wear behavior due to an unnecessarily high contact pressure.

[0035] The stiffness component of the coating and / or the particles in the main bending zone of the axial protrusion of the grounding ring is eliminated due to the only partial coating and / or the only partial particles in the grounding contact area.

[0036] The nonwoven fabric can, for example, be a carbon nonwoven fabric that exhibits the first electrical conductivity.

[0037] In contrast, the coating or particles exhibit a second electrical conductivity. Due to the particularly high electrical conductivity of silver, a silver-based coating has proven advantageous for the good performance characteristics of the grounding ring.

[0038] The coating can, for example, be a silver-based lacquer.

[0039] When electrically conductive particles are used, it has proven advantageous if these particles are formed as silver particles due to their good electrical conductivity.

[0040] The grounding contact area can be designed as a lip-shaped free end, with only this lip-shaped free end enclosed by the coating and / or particles. It is advantageous that the grounding ring can be convex in both axial directions, depending on the application. In any case, it ensures equipotential bonding between the machine elements between which it is used.

[0041] The axial bulge of the grounding ring typically corresponds to the axial mounting direction of the machine element to be grounded. This simplifies the installation of the grounding ring and minimizes the risk of damage during installation.

[0042] Furthermore, the invention relates to an arrangement comprising an earthing ring as previously described, a first machine element, and a second machine element, wherein the earthing ring is in contact with a surface of the first machine element, the first machine element being arranged concentrically to the second machine element, the first machine element being arranged radially adjacent to the second machine element, the earthing ring being arranged in the gap formed by the distance, the second machine element being earthed to a defined ground potential, and the first and second machine elements being electrically connected by the earthing ring. The arrangement can be used, for example, in connection with e-mobility.

[0043] The first machine element can be formed by a shaft or by a housing enclosing the shaft, and the second machine element by a housing enclosing the shaft or by a shaft.

[0044] It is also possible that the grounding ring is associated with a sealing ring with at least one dynamically stressed sealing lip adjacent to it at an axial distance, and that the grounding ring is designed as a pre-seal for the sealing ring.

[0045] In such a case, the grounding ring not only ensures the previously described equipotential bonding between the machine elements. Additionally, it keeps contaminants away from the adjacent sealing ring and the space to be sealed within the assembly. This ensures that the sealing ring maintains consistently good performance characteristics over a long service life.

[0046] Depending on the application, in particular depending on the mounting direction of the machine element to be grounded in the axial direction, the grounding ring can be designed to be convex axially inwards or axially away from the sealing ring.

[0047] The grounding ring can be designed as an annular disc with a circumferential circumference that runs continuously around the circumference, or as an annular disc that is slotted radially around its circumference.

[0048] The aforementioned circumference can be the inner and / or outer circumference. Furthermore, the invention relates to a method for manufacturing a grounding ring, as previously described, wherein the coating is applied to the grounding contact area only by a pad printing process. Pad printing is an indirect gravure printing process in which the printing ink is transferred from the printing plate to the substrate by an elastic silicone rubber pad. In this case, the substrate is the electrically conductive nonwoven fabric from which the grounding ring is made. The coating is transferred to the nonwoven fabric of the grounding contact area by applying pressure of varying strengths.

[0049] The coating can be applied to the nonwoven fabric with exceptional precision and efficiency using the pad printing process. This is particularly advantageous when printing on expensive materials.

[0050] Alternatively, the coating can be applied using a brush.

[0051] The coating thickness can be varied by multiple overprints, thus adapting it to the specific requirements of the application. The coating thickness affects the service life of the grounding ring.

[0052] The coating can only be applied to the grounding contact area using multiple pad printing.

[0053] Preferably, the coating is printed at least four times onto the nonwoven fabric. With between four and eight prints, the grounding ring exhibits good performance characteristics over a long service life. A higher number of prints further improves performance characteristics but increases manufacturing costs. (Brief description of the drawing)

[0054] Different embodiments of arrangements with grounding rings are explained in more detail below with reference to Figures 1 to 8.

[0055] These show, in schematic representation:

[0056] Figure 1 shows a first embodiment of an arrangement with a grounding ring having a coating of a silver-based lacquer,

[0057] Figure 2 shows a second embodiment of an arrangement with a grounding ring in which silver particles are used.

[0058] Figure 3 shows a third embodiment of an arrangement with a grounding ring in which only the lip-shaped free end is enclosed by the coating and / or the electrically conductive particles,

[0059] Figure 4 shows a fourth embodiment of an arrangement in which the grounding ring is axially protruded in the direction of the space to be sealed in the arrangement and is designed as a pre-seal for the sealing ring.

[0060] Figure 5 shows a fifth embodiment of an arrangement, similar to the arrangement shown in Figure 4, wherein the grounding ring is axially convex towards the space to be sealed in the arrangement and is designed as a pre-seal for the sealing ring; Figure 6 shows a further embodiment of an arrangement, in which the direction of current / charge flow through the arrangement is shown.

[0061] Figure 7 shows an arrangement in one view, with an earthing ring designed as an annular disk, with an inner and an outer circumference which, viewed in the circumferential direction, are continuous.

[0062] Figure 8 shows an arrangement in a view with a grounding ring designed as an annular disk, wherein the inner and / or outer circumference is slotted in a radial direction.

[0063] Implementation of the invention

[0064] Figures 1 to 8 show schematic representations of arrangements according to the invention, including grounding rings 1. In all embodiments, the grounding ring 1 consists of an electrically conductive nonwoven fabric. The nonwoven fabric is an electrically conductive carbon nonwoven fabric.

[0065] The electrically conductive nonwoven fabric exhibits initial electrical conductivity. The grounding ring 1 comprises the dynamically stressed grounding contact area 2, wherein only the grounding contact area 2 has the electrically conductive coating 3 made of a silver-based lacquer 5 and / or electrically conductive particles 4, here silver particles 7.

[0066] Coating 3 is represented by solid lines, particles by thicker dots. If it could be either coating 3 or particles 4, it is shown with thicker dashed lines. Coating 3 and particles 4 each have a second electrical conductivity, which is greater than the first.

[0067] Figures 1 to 8 each show an arrangement comprising the grounding ring 1, as previously described, as well as a first machine element 8 and a second machine element 9, wherein the grounding ring 1 is in contact with a surface of the first machine element 8, wherein the first machine element 8 is arranged concentrically to the second machine element 9, wherein the first machine element 8 is arranged radially adjacent to the second machine element 9, wherein the grounding ring 1 is arranged in the gap formed by the distance, wherein the second machine element 9 is grounded to a defined ground potential, and wherein the first 8 and the second machine element 9 are electrically connected by the grounding ring 1.

[0068] The first machine element 8 is formed by a shaft, the second machine element 9 by a housing enclosing the shaft. In the arrangements shown, the shaft and the housing are each made of an electrically conductive metallic material.

[0069] In Figure 1, the grounding contact area 2 is designed as a lip-shaped free end 6, wherein only the lip-shaped free end 6 is provided with the coating 3 of silver-based lacquer 5 on the side facing the first machine element 8.

[0070] In Figure 2, the particles 4 are formed as silver particles 7 and, as in Figure 1, are arranged only on the side facing the first machine element 8. In Figure 3, only the lip-shaped free end 6 of the grounding contact area 2 is enclosed by the coating 3 and / or the particles 4.

[0071] It is advantageous that the lip-shaped free end 6, depending on the application, in particular the mounting direction 12 of the first machine element 8, can also be curved in the axial direction other than that shown here and still fulfill the task of potential equalization between the machine elements 8, 9.

[0072] In Figures 4 and 5, the sealing ring 10 is additionally arranged within the gap. With respect to the sealing ring 10, the grounding rings 1 are arranged on the side of the sealing ring 10 facing axially away from the space 11 to be sealed.

[0073] The free end 6 is always axially pre-curved in the assembly direction 12 of the first machine element 8.

[0074] Figure 6 shows the current / charge flow direction during potential equalization through the arrangement.

[0075] Potential equalization takes place from the first machine element 8 through the coating 3 and / or the particles 4 and then through the electrically conductive nonwoven fabric to the second machine element 9, whereby the second machine element 9 is grounded.

[0076] The grounding ring 1 can be circular, as shown in Figures 7 and 8. The grounding ring 1 can be unprotected (Figure 7) or slotted (Figure 8).

[0077] In Figures 3 to 8, the grounding ring 1 comprises a coating 3 and / or particles 4, depending on the application.

Claims

Patent claims 1. Earthing ring (1) made of an electrically conductive nonwoven fabric having a first electrical conductivity, with a dynamically stressed earthing contact area (2), wherein only the earthing contact area (2) has an electrically conductive coating (3) and / or electrically conductive particles (4), having a second electrical conductivity and wherein the second electrical conductivity is greater than the first electrical conductivity.

2. Grounding ring according to claim 1, characterized in that the coating (3) is silver-based.

3. Grounding ring according to claim 1, characterized in that the particles (4) are designed as silver particles (7).

4. Grounding ring according to one of claims 1 to 3, characterized in that the grounding contact area (2) is designed as a lip-shaped free end (6) and that only the free end (6) is enclosed by the coating (3) and / or the particles (4).

5. Arrangement comprising an earthing ring (1) according to any one of claims 1 to 4, and a first machine element (8) and a second machine element (9), wherein the earthing ring (1) is in contact with a surface of the first machine element (8), wherein the first machine element (8) is arranged concentrically to the second machine element (9), wherein the first machine element (8) is arranged radially adjacent to the second machine element (9), wherein the earthing ring (1) is arranged in the gap formed by the distance, wherein the second machine element (9) is earthed to a defined ground potential, and wherein the first (8) and the The second machine element (9) is electrically connected through the grounding ring (1).

6. Arrangement according to claim 5, characterized in that the first machine element (8) is formed by a shaft or by a housing enclosing the shaft and the second machine element (9) is formed by a housing enclosing the shaft or by a shaft.

7. Arrangement according to one of claims 5 or 6, characterized in that a seal (10) with at least one dynamically stressed sealing lip is associated adjacent to the grounding ring (1) at an axial distance and that the grounding ring (1) is designed as a pre-seal for the seal (10).

8. Method for manufacturing an earthing ring (1 ) according to one of claims 1 to 3, wherein the coating (3) is printed only onto the earthing contact area (2) by a pad printing process.

9. Method according to claim 8, characterized in that the coating (3) is printed only onto the grounding contact area (2) by means of multiple pad printing.

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