Shaft-grounding ring

Abstract

The invention relates to a shaft-grounding ring (10), comprising a base ring (1) and a discharge element (2), connected to the base ring (1), for discharging voltages between a shaft (101) and a shaft housing (102), wherein the discharge element (2) has a first contact surface (2.2) for making conductive contact with the shaft (101) and a second contact surface (2.3) for making conductive contact with the shaft housing (102).

Description

[0001] Shaft grounding ring

[0002] The invention relates to a shaft grounding ring, comprising a base ring and a discharge element connected to the base ring for discharging electrical voltages between a shaft and a shaft housing.

[0003] Corresponding shaft grounding rings are used in various fields of technology to specifically dissipate electrical voltages between a shaft and a shaft housing that is stationary relative to the shaft. Without appropriate shaft grounding rings, voltage dissipation could occur, for example, in the area of ​​shaft bearings or gears, which could even lead to melt craters and thus damage, especially with large potential differences.

[0004] Corresponding shaft grounding rings typically comprise a base ring and a discharge element connected to the base ring. The discharge element typically contacts the rotating shaft on one side and the base ring or a housing of the shaft grounding ring on the other side, which in turn is in contact with the shaft housing. The shaft housing is typically grounded, allowing electrical charges to be conducted from the shaft to the shaft housing via the discharge element and the base ring or a housing of the shaft grounding ring. Potential equalization between the shaft and the shaft housing can thus be achieved via the shaft grounding ring. Such a shaft grounding ring is shown, for example, in DE 10 2022104417 A1.

[0005] However, a disadvantage of such known shaft grounding rings has been found to be the comparatively high overall electrical resistance of the shaft grounding ring. This is also due to the fact that the charges must flow from the discharge element via the base ring or a shaft grounding ring housing, and thus via multiple elements. The connection points between the discharge element and the base ring or the shaft grounding ring housing in particular can increase the overall electrical resistance of the shaft grounding ring due to the electrical contact resistance, which can have a detrimental effect on the discharge capacity. The multiple transitions can also contain sources of error.

[0006] Based on this, the invention sets itself the task of providing a shaft earthing ring which is characterized by more reliable charge dissipation.

[0007] This object is achieved in a shaft earthing ring of the type mentioned above in that the discharge element has a first contact surface for conductive contacting of the shaft and a second contact surface for conductive contacting of the shaft housing.

[0008] This design allows charges to be transferred directly between the shaft and the shaft housing via the discharge element, eliminating the need for charges to also flow via the base ring or a shaft grounding ring housing. Overall, the electrical resistance of the shaft grounding ring can therefore be comparatively low, ensuring reliable charge transfer. For potential equalization, charges can flow both from the shaft to the shaft housing and from the shaft housing to the shaft, depending on which of the two elements has the higher and which has the lower electrical potential. The shaft grounding ring thus allows bidirectional charge transfer. Furthermore, a corresponding shaft grounding ring is comparatively easy to manufacture, as will be explained in more detail below with regard to the manufacturing process.

[0009] In this respect, it has proven advantageous if the discharge element can be in direct, conductive contact with the shaft and the shaft housing via the contact surfaces. The discharge element can thus be in direct electrical contact with the shaft or with the surface of the shaft on the one hand and in direct electrical contact with the shaft housing, in particular with an inner side of the shaft housing, on the other. In order to achieve such direct conductive contact with the shaft and the shaft housing, the discharge element can physically contact both the shaft and the shaft housing via the respective contact surfaces. Since the charges do not have to be conducted via a shaft grounding ring housing, the shaft grounding ring can be designed without a housing. This means that there is no housing surrounding the discharge element on the circumference.This is because such a device could be arranged between the discharge element and the shaft housing when installed and thus prevent a direct and immediate electrical connection with the shaft housing.

[0010] With regard to the contact between the shaft and the shaft housing, it has proven advantageous if the diverting element can be in contact with the shaft via the first contact surface along a contact line. Furthermore, the diverting element can be in surface contact with the shaft housing via the second contact surface. The first contact surface is therefore preferably designed such that it enables line contact with the shaft and the second contact surface such that it enables surface contact with the shaft housing. The line contact with the shaft is particularly advantageous with regard to the frictional torque acting on the shaft from the diverting element. This is because the line contact allows the contact surface to be minimized, so that the friction counteracting rotation of the shaft is also kept to a minimum.Since there is advantageously no relative movement between the shaft housing and the discharge element, a larger-area contact can be used at this point. The charge flow per unit area can therefore be lower between the discharge element and the shaft housing than between the shaft and the discharge element. Furthermore, the discharge element can also have a third contact surface, e.g. to contact the shaft housing at two different points. The first and second contact surfaces can be arranged such that different sides of the shaft housing are contacted, in particular contacted over a large area. The two contact surfaces can be arranged at a right angle to one another so that, for example, a vertically oriented surface of the shaft housing and a horizontally oriented surface of the shaft housing can be contacted. In this respect, a certain degree of redundancy is created.The second contact surface can extend in the radial direction and contact the shaft housing in the axial direction, and the third contact surface can extend in the axial direction and contact the shaft housing in the radial direction. Advantageously, the outer diameter of the deflection element can be slightly larger than the outer diameter of the base ring, so that the deflection element can be placed on the outside of the shaft housing to create the third contact surface.

[0011] With regard to the connection between the discharge element and the base ring, it has proven advantageous if the discharge element is positively connected to the base ring at the microscopic level. Such a connection can ensure a reliable hold of the discharge element on the base ring. Even with larger forces, such as those that can occur during assembly of the shaft grounding ring or sometimes even at very high shaft speeds, a reliable hold can be ensured. To enable a corresponding positive connection at the microscopic level, the surface can have a certain roughness. The surface can have microscopic undercuts into which the material of the discharge element can engage to create a positive connection. Advantageous roughness values ​​are explained in more detail below.The discharge element can have a particularly annular connecting region via which it can be connected to the base ring. The second contact surface can be arranged at the connecting region, and the second contact surface and the base ring, or the radial section of the base ring explained in more detail below, can be opposite one another with respect to the connecting region. The connecting section can thus be arranged between the base ring and the shaft housing in the assembled state. The connection between the discharge element and the base ring can also be important with regard to the direct contact between the discharge element and the shaft housing. This is because known shaft grounding rings often use clamp connections in which the discharge element is clamped between two shaft grounding ring housing sections, or between the base ring and the shaft grounding housing.Due to the direct, positive connection to the base ring, a second element to create a clamping effect is not required. Further advantages of the positive connection at the microscopic level will be explained in more detail below with regard to the manufacturing process.

[0012] According to an advantageous development of the invention, the discharge element is made of filled PTFE. PTFE is characterized by a very low coefficient of friction. The use of PTFE can therefore reduce the friction between the discharge element and the shaft. In addition to PTFE, other materials, in particular plastics, can also be used. The coefficient of friction between the discharge element and the shaft should be kept low. Since PTFE and other possible materials are not conductive, these materials can be filled. In this context, filled means that the conductivity of the discharge element is improved by the introduction of conductive materials. Various conductive particles can be used. Graphite has proven successful in practice, especially since graphite generally has low coefficients of friction in addition to high conductivity.For example, FEP, especially filled FEP, can also be used for the discharge element. By using FEP, the use of an additional FEP film, which is discussed in more detail below, can be dispensed with. With regard to the direct contact with the shaft housing, it has also proven advantageous if the discharge element is made of plastic, especially PTFE. Because the shaft housing is usually made of metal and the discharge element is therefore significantly softer, the electrical contact resistance between the discharge element and the shaft housing can be comparatively low. This lower resistance becomes particularly clear when comparing a metal-plastic contact with a metal-metal contact.A corresponding metal-to-metal contact is generally used in known shaft earthing rings, in which the discharge element does not directly contact the shaft housing, but in which the charges must also flow through a generally metallic shaft earthing ring housing or a base ring.

[0013] The diverting element can have an overall annular geometry and extend circumferentially around the shaft. The shaft can, in particular, extend centrally through the diverting element, for which the diverting element has a particularly circular recess. The diverting element can be designed to be rotationally symmetrical, and the axis of rotation of the shaft can coincide with the axis of symmetry of the diverting element. In order to further reduce the friction between the diverting element and the shaft, it has also proven advantageous if the diverting element is designed as a segmented diverting ring. Due to the segmentation, the diverting element does not have to be in contact with the shaft around its entire circumference; rather, it can be sufficient if the diverting element only contacts the shaft in sections with regard to its circumference. Alternatively, however, the diverting element can also be designed as a non-segmented diverting ring.With this design, the diverter ring can rest on the shaft circumferentially. While this design ensures very reliable contact, the long contact line along the entire shaft circumference also results in comparatively large friction losses. Advantageously, the contact portion of the segmented diverter element is less than 80%, preferably less than 60%, and particularly preferably less than 40%, compared to a non-segmented diverter element. This means that the length of the contact line between the segmented diverter element and the shaft is shorter by this factor compared to the circumferentially closed contact line of a non-segmented diverter element.

[0014] In order to reduce friction losses, it has proven advantageous if the discharge element has at least three, preferably four, discharge tabs for contacting the shaft.

[0015] The discharge tabs can each have a first contact surface or surfaces and can be in electrical contact with the shaft via these surfaces. The contact surfaces can be arranged on the radial inner sides of the discharge tabs to make contact with the shaft. The discharge tabs can therefore be designed as projections that project radially inwards and that touch the shaft or shaft surface at each end. At the opposite end, the discharge tabs can be connected to one another via a connecting area, in particular an annular one, to form the discharge element. In practice, three discharge tabs have proven to be the minimum required to achieve reliable contact with the shaft. Due to manufacturing or assembly tolerances, the shaft may not run perfectly true but may oscillate to a certain extent in the radial direction.These vibrations can negatively impact the electrical contact between the shaft and the discharge element. Using three discharge tabs ensures that at least one of the discharge tabs is in contact with the shaft at all times, preventing charge accumulation. However, four or more discharge tabs can also be provided. This further reduces the risk of electrical contact between the shaft and the shaft housing being interrupted for a short time, particularly if the shaft is not precisely balanced and is therefore running unevenly. The discharge tabs can be evenly distributed around the circumference. The discharge tabs allow media to flow from one side of the shaft grounding ring to the other, i.e. in the axial direction along the surface of the shaft.However, even if the diverter ring is closed and the diverter lip thus rests closed against the circumference of the shaft, axial media flow can still occur. The shaft grounding ring cannot therefore function as a shaft sealing ring. To ensure reliable contact with the shaft, it has also proven advantageous if the diverter element is preloaded in the radial direction relative to the shaft or the shaft surface. The diverter element or the diverter tabs can therefore be pressed onto the shaft surface in the radial direction with a certain force. This increases friction but ensures reliable electrical contact. The corresponding area of ​​the diverter element, located radially inside, can be designed as a diverter lip.Due to the residual stress of the material, this deflection lip can be pressed onto the surface of the shaft in the radial direction with a certain elastic deformation.

[0016] With regard to the design of the base ring, it has proven advantageous if it has an axial section and a radial section. The axial section can extend essentially parallel to the shaft and the radial section perpendicular to it. The two sections can extend accordingly with regard to the axis of symmetry of the shaft grounding ring. The base ring can therefore have a substantially L-shaped cross-sectional geometry. The shaft grounding ring can rest against the shaft housing via the axial section. The shaft grounding ring can therefore be arranged so as to be immovable relative to the shaft housing and, for example, be clamped therein. The radial section can advantageously not be in contact with the shaft housing. Instead, the diverting element can be arranged on the surface of the radial section, so that the radial section primarily serves to fasten the diverting element.The deflection element can be arranged on the surface of the radial section opposite the axial section. Overall, the deflection element can thus extend substantially in the radial direction. This configuration allows the deflection element to contact the shaft housing, in particular a section of the shaft housing extending substantially in the radial direction. The corresponding surface to which the deflection element is connected can thus be the outer side of the base ring, with regard to the geometric configuration of the shaft grounding ring. This arrangement on the outer side allows the deflection element to come into direct contact with the shaft housing.

[0017] With regard to the material of the shaft grounding ring, it has proven advantageous if the base ring is made of metal, particularly steel or an aluminum alloy. The base ring can thus ensure sufficient stability of the shaft grounding ring. Due to the conductivity of the base ring material, its surface can be easily heated, which is important for the process for connecting the discharge element to the base ring, which is described in more detail below.

[0018] With regard to the object stated above, a machine element is further proposed with a rotatable shaft, a shaft housing stationary with respect to the shaft, and a shaft grounding ring for discharging voltages between the shaft and the shaft housing, wherein the shaft grounding ring is designed as described above. This results in the advantageous effects already described above. The machine housing can be grounded, and charges can be discharged from the shaft via the shaft housing via the shaft grounding ring or the discharge element. The discharge element is directly connected to both the shaft and the machine housing, so that the charges can flow from the shaft directly into the shaft housing or in the reverse direction without detours via the discharge element.The axial section of the base ring can be connected to the shaft housing, and the shaft grounding ring can be immovably mounted in the shaft housing. The machine element can be, for example, part of a motor, in particular an electric motor.

[0019] With regard to the object mentioned above, a method for producing a shaft grounding ring is also proposed. The shaft grounding ring can be designed as described above. To produce the shaft grounding ring, the base ring is first provided, the surface of which is roughened at least in sections before the discharge element is placed on the roughened surface. The base ring is then heated, and the discharge element is simultaneously pressed onto the roughened surface to connect the discharge element to the base ring.

[0020] By roughening the surface of the base ring, the effective surface area can be increased, resulting in better overall contact between the base ring and the discharge element. Compared to a smooth surface, the adhesion of the discharge element to the base ring can be improved. The additional heating of the base ring means that when the discharge element is pressed onto the base ring, the surface of the discharge element that is in contact with the base ring is liquefied or at least becomes more flowable. The improved flow properties and the resulting lower viscosity mean that the roughened surface of the base ring can be better wetted by the discharge element. In conjunction with the pressure force with which the discharge element is pressed onto the roughened surface, this ensures that the plastic wets the entire roughened surface.When the base ring with the pressed-on discharge element is cooled, the two components are firmly and inseparably connected.

[0021] With regard to the process, it has also proven advantageous if the surface is roughened by laser structuring. Roughening the surface by laser structuring, in particular by remote laser structuring, has advantages in terms of its suitability for automation. This is because surface roughening using a laser can be automated relatively easily and carried out in a single operation before the discharge element is placed and pressed, without the base ring having to be moved. However, it is also possible to carry out the process in different machines or stations and to roughen the base ring beforehand. To carry out the laser structuring, a laser robot can be provided that moves a laser beam over the surface to be roughened and removes material to create a specific roughness.Furthermore, roughening by laser structuring is characterized by a surface profile that can be defined relatively precisely in advance. This means that the roughness of the surface can be adjusted very precisely and adapted to the material of the discharge element as well as the temperature to which the base ring is heated and the pressure with which the discharge element is pressed onto the base ring. The parameters are preferably selected to ensure the best possible hold of the discharge element on the base ring. Furthermore, it is generally not necessary to clean a surface roughened by laser structuring before the next processing step. The wavelength of the laser can be adapted to the material of the base ring, ensuring good absorption of the applied laser radiation. As an alternative to laser structuring, however, it is also possible to roughen the surface using another method.Chemical processes such as etching or pickling, or abrasive processes such as sand or shot blasting, may be considered for this purpose.

[0022] It is advantageous if the surface has undercuts after roughening, resulting in interlocking of the discharge element or the bonding agent (explained in more detail below). These undercuts allow the discharge element to be positively connected to the base ring at a microscopic level. The geometric design of the undercuts can be achieved and adjusted, particularly through laser structuring of the surface.

[0023] To ensure reliable adhesion, it has proven advantageous if the surface is roughened to an average roughness of 70 to 220 μm, preferably 100 to 200 μm, in particular 120 to 180 μm. To ensure reliable adhesion of the two components to one another, the roughness of the surface must not be too low initially, as otherwise there will be insufficient bonding surface. Furthermore, the roughness must not be too great, as otherwise, despite heating and pressing on the discharge element, the surface cannot be sufficiently wetted and the material of the discharge element cannot penetrate deeply enough into the surface structure of the base ring due to an overly fine surface structure.In this respect, both too small and too large a surface roughness can result in poor adhesion of the discharge element, which could result in the element shearing off from the base ring during subsequent use. These roughnesses have proven particularly effective in practice for ensuring reliable adhesion.

[0024] To further improve adhesion, it has proven advantageous to apply a bonding agent to the roughened surface. The bonding agent can be applied to the roughened surface before the conductive element is placed and can thus essentially be arranged between the conductive element and the base ring. The bonding agent can be characterized by better wetting of the roughened surface of the base ring than direct wetting of the surface with the conductive element material. In addition, the melting point or glass transition temperature of the bonding agent can be lower than the melting point or glass transition temperature of the conductive element material. The bonding agent can also be chemically compatible with the conductive element material, so that the bonding agent or the polymer chains of the bonding agent can be inseparably bonded to the conductive element or the polymer chains of the conductive element.The adhesion promoter can be an FEP layer, especially an FEP film. Even very thin FEP films, for example, in the range of 100 μm, can be sufficient to achieve their positive adhesion. Furthermore, the adhesion promoter can also be sprayed onto the roughened surface. In both cases, it is not absolutely necessary to move the base ring, so the application of the adhesion promoter can be easily integrated into the manufacturing process.

[0025] To prevent the base ring from moving accidentally, particularly when pressing on the discharge element, it has proven advantageous to insert the base ring into a joining die. The base ring can be inserted into the joining die before roughening the surface and is thus secured against slipping. The discharge element can be pressed onto the base ring using a pressure stamp. The pressure stamp can be moved vertically and pressed from above onto the discharge element placed on the surface. In practice, good adhesion of the discharge element to the base ring has been achieved with pressures in the range of 200 N to 2000 N.

[0026] To heat the base ring, it has proven advantageous to inductively heat the roughened surface of the base ring. By inductively heating the surface, only the surface of the base ring, and thus the area in contact with the discharge element, can be heated in a very targeted manner. The remaining sections of the base ring cannot be actively heated, as heating these sections would not improve the adhesion. In fact, heating the entire base ring would not only require a significantly greater input of energy, but the amount of heat to be introduced and the surface temperature, which is crucial for the adhesion of the discharge element, could not be adjusted as precisely. Advantageously, only the roughened surface of the base ring is heated, while the rest of the base ring is not actively heated and therefore only heats up to a small extent.Inductive heating allows the amount of heat introduced to be precisely controlled and metered. This results in a very precisely defined heat input and thus a precisely defined heating of the dissipation element or the adhesion promoter via the heat exchanger.

[0027] Base ring. Thermal decomposition due to excessive heat input or an unintentional structural change in the discharge element can be reliably prevented. Since only the surface of the base ring is heated, it cools very quickly after heating, allowing the excess heat from the discharge element or the bonding agent to flow back into the base ring after the heating process. A heating tool, which can be integrated into the joining die, can be provided for heating. The heating tool can heat the surface of the base ring using eddy currents, so that the discharge element melts at the boundary layer and can wet the surface of the base ring. Other forms of heating the base ring or the base ring surface are also conceivable.

[0028] With regard to the heating process, it has been found to be advantageous if the roughened surface of the base ring is heated to 200 to 400 degrees Celsius, preferably to 250 to 350 degrees Celsius, in particular to 280 to 320 degrees Celsius for between 3 and 20 seconds, preferably between 5 and 16 seconds, more preferably between 8 and 14 seconds, and in particular between 10 and 12 seconds. As already indicated above, excessively long or excessive heating could lead to unwanted structural changes, which could ultimately have a negative impact on the electrical conductivity of the discharge element and also on the service life of the shaft grounding ring as a whole. The heating time and the surface temperature are advantageously set so that sufficient liquefaction or a reduction in viscosity of the discharge element orof the adhesion promoter, thus ensuring sufficient surface wetting, while avoiding any further energy input. In practice, these parameters have led to a reliable connection between the discharge element and the base ring.

[0029] According to an advantageous development of the invention, the discharge element continues to be pressed onto the base ring while it is cooling. The pressing process therefore advantageously takes longer than the heating process. The two processes can take place largely simultaneously. It can also be provided that the surface of the base ring is heated first and then the compressive force is applied to the discharge element only at a somewhat later point in time, e.g. when the boundary layer has already partially liquefied. By pressing on, the thermal contact resistance between the surface of the base ring and the discharge element can be reduced, which can be taken into account in the sequence of processes as well as in the heating duration and the surface temperature of the base ring. The longer pressing process allows the components to cool down in the pressed state.The compressive force can only be removed once the connection between the discharge element and the base ring has been reliably and securely established. Once the cooling process is complete and a desired final temperature has been reached, the finished shaft grounding ring can be ejected from the joining die. Advantageously, the entire manufacturing process can therefore only take approximately 40 seconds per shaft grounding ring. Furthermore, with regard to the aforementioned object, a device for producing a shaft grounding ring using a method of the type described above is proposed. Advantageously, the method can be used to produce a shaft grounding ring as described above. The device has a joining die into which the base ring can be inserted, a heating element for heating the surface of the base ring, and a pressure stamp over which the discharge element can be pressed onto the base ring.The heating element can be configured as an inductive heating element, which can be integrated into the joining die. The pressure stamp can be cup-shaped and have a circular pressure surface with which it can press the likewise annular discharge element onto the base ring. Furthermore, the device can also comprise a laser, in particular a laser movable in at least two axes, over which the surface of the base ring can be roughened, as described above. The laser thus allows the surface treatment to be performed directly in the joining die, which significantly simplifies the overall manufacturing process.

[0030] Further details and advantages of the invention will be explained in more detail below with reference to the accompanying drawings, in which:

[0031] Fig. 1 is a sectional view of a shaft grounding ring;

[0032] Fig. 2 is a sectional view of an installed shaft earthing ring according to Fig.

[0033] 1;

[0034] Fig. 3a shows a front and a rear view of a shaft grounding ring according to a first embodiment;

[0035] Fig. 3b shows a front and a rear view of a shaft grounding ring according to a second embodiment;

[0036] Fig. 4 is a schematic view of the steps for manufacturing a shaft grounding ring;

[0037] Fig. 5 is a schematic view of an apparatus for producing a shaft grounding ring;

[0038] Fig. 6 is a schematic view according to Fig. 5 with a pressed-on pressure stamp.

[0039] The illustration in Fig. 5 initially shows a device 6 with which shaft grounding rings 10 can be produced in a simple manner using a method as illustrated in the illustration in Fig. 4. The device 6 comprises a joining die 3, a pressure stamp 4, a heating element (not explicitly shown), and a laser (not shown).

[0040] According to method step S1, in a first step, a base ring 1 is provided and placed in the joining die 3. The base ring 1 has an L-shaped geometry, as can be seen, for example, from the illustration in Fig. 1, and essentially consists of two sections, namely a radial section 1.1, which extends parallel to the joining die 3, and an axial section 1.2 that circumferentially surrounds the radial section 1.1 and is arranged perpendicular to the radial section 1.1 and thus also to the surface of the joining die 3. After the base ring 1 has been placed in the joining die and fixed so that it can no longer move, the upward-facing surface 1.4 of the radial section 1.1 is roughened using a laser in step S2. The illustrations in Figs. 5 and 6 show how the axial section 1.2 of the base ring 1 is positioned upwards.However, as will be explained in more detail below with regard to the connection of the base ring 1 to the discharge element 2, also with reference to the illustrations in Figs. 1 and 2, it is advantageous if the axial section 1.2 points downwards and the base ring 1 is inserted into the joining die 3 rotated by 180 degrees. The joining die 3 can, for example, have a groove for this purpose, and the axial section 1.2 can be arranged in this groove. Thus, the side of the base ring 1 opposite the axial section 1.2, which essentially corresponds to the outer side of the base ring 1 or the shaft grounding ring 10, can then be roughened using the laser. The laser scans the surface 1.4 fully automatically, so that the surface 1.4 has a predefined roughness at the end of this roughening process. In step S3, a bonding agent is then first applied to the roughened surface 1.4 in the form of a thin FEP film, before, in step S4, a substantially annular conductive element 2 made of PTFE filled with electrically conductive particles is placed on the roughened surface 1.4 or on the adhesion promoter. The conductive element 2 can also be seen, for example, in the illustration in Fig. 1.

[0041] In the next step S5, the pressure stamp 4 is placed from above onto the discharge element 2 or onto the connecting area 2.1 of the discharge element 2 and pressed downwards onto the base ring 1 with a specific force. As can be seen, for example, from the illustration in Fig. 6, the pressure stamp 4 has a cup-shaped geometry and an annular contact surface at the lower end, via which it can be placed onto the discharge element 2 or the connecting area 2.1 over as full a surface as possible. At the same time, in step S6, the heating element is activated, which heats the roughened surface 1.4 of the base ring 1. Due to the contact of the base ring 1 with the discharge element 2, the surface boundary layer of the discharge element 2 facing the roughened surface 1.4 of the base ring 1 is also heated, which leads to a brief and locally limited liquefaction of the discharge element 2. At the same time, the adhesion promoter is also heated and liquefied.The bonding agent bonds with the discharge element 2 and flows into the previously created surface irregularities of the base ring 1. Through simultaneous heating and pressing, the roughened surface 1.4 can be wetted as completely as possible by the bonding agent or the connecting area 2.1 of the discharge element 2, so that the surface irregularities are filled by the material of the bonding agent and / or the discharge element 2. After roughening, the roughened surface 1.4 of the base ring has undercuts that enable a positive connection with the discharge element 2 at the macroscopic level.

[0042] The surface 1.4 of the base ring 1 only needs to be heated briefly to connect it to the discharge element 2, because the adhesion promoter and the discharge element 2 melt comparatively quickly due to their chemical composition, and to create a reliable connection it is sufficient if only the uppermost boundary layer of the discharge element 2 is briefly melted.

[0043] As soon as the heating element 5 no longer applies any heat, both the surface 1.4 of the base ring 1 and the surface of the discharge element 2 cool down quickly again. The material of the discharge element 2 or the bonding agent that has flowed into the unevenness of the roughened surface 1.4 of the base ring 2 hardens in the process, so that the discharge element 2 is then firmly connected to the base ring 2. Removing the discharge element 2 from the base ring 1 is then only possible with the application of very great force. In step S7, once the connection has cooled sufficiently and thus solidified sufficiently, the pressure stamp 4 is moved upwards again, and the finished shaft grounding ring 10 can be ejected from the joining die 3.

[0044] The illustration in Fig. 1 shows the shaft grounding ring 10 in a sectioned cross-sectional view. Only the upper part of the sectioned ring can be seen. The essentially L-shaped base ring 1 is firmly connected to the discharge element 2 on the outside of the radial section 1.1 in the manner described above. The positive connection, in which the material of the discharge element 2 flows in the outer boundary layer into the roughened surface 1.4 of the base ring 1, is illustrated by dashed lines. Below the connection area 2.1 connected to the base ring 1, the discharge element 2 has a discharge lip 2.5 which is slightly angled relative to the connection area 2.1. Due to this angulation, a contact force acting in the radial direction can be exerted on the surface shown in Fig. 1 due to the residual material stress of the discharge element 2.2, so that the deflection element 2 is in reliable contact with the shaft 101. The illustration in Fig. 2 thus illustrates a possible installation situation of the shaft earthing ring 10 in a machine element 100, which comprises a shaft housing 102 and a shaft 101 rotatably mounted in the shaft housing 101. At the end opposite the shaft 101, the deflection element 2 contacts the shaft housing 102, which is stationary relative to the shaft 101. The deflection element 2 points to the contacting of the shaft.

[0045] 101 has a first contact surface 2.2 and a second contact surface 2.3 for contacting the shaft housing 102. Since the discharge element 2 is electrically conductive and is connected not only directly physically but also electrically to the shaft 101 and the shaft housing 102 via the two contact surfaces 2.2, 2.3, charges can flow directly from the shaft 101 to the shaft housing 102 via the discharge element 2. A potential difference between the shaft housing

[0046] 102 and the shaft 101 can be equalized via the discharge element 2. Typically, the shaft housing 102 is grounded, so that the charges then flow from the shaft 101 via the discharge element 2 to the shaft housing 102. This charge flow L is also illustrated in the illustration in Fig. 2 by a dashed line. Electrical potential equalization is unidirectional and thus also possible in the other direction.

[0047] The second contact surface 2.3 of the discharge element 2, in the area of ​​the connection area 2.1, lies opposite the base ring 1 and ensures a surface contact with the shaft housing 102. The other contact surface 2.1, in contrast, is not as extensive, but rather contacts the shaft 101 or the surface of the shaft 101 in a much more targeted manner, as can be seen from the illustration in Fig. 2. Therefore, the first contact surface 2.2 only ensures a linear contact. While this leads to a greater charge flux density, the linear contact also results in very little friction between the stationary shaft grounding ring 10 and the rotating shaft 101.

[0048] Furthermore, the discharge element 2 can also have a third contact surface, which is not shown in the illustrations. According to the illustration in Fig. 2, the diameter of the discharge element 2 could be somewhat larger for this purpose, so that the discharge element 2 could contact the horizontally extending region of the shaft housing 102 via a radially outer section. The discharge element 2 would then be electrically coupled to the shaft housing 102 at two different locations via the second contact surface 2.3 and the third contact surface.

[0049] To secure the shaft grounding ring 10 in the shaft housing 100, the base ring 1, or the axial section 1.2 extending parallel to the shaft surface and thus in the axial direction, is in contact with the inside of the shaft housing 102 and ensures a firmly defined positioning of the shaft grounding ring 10. Although the base ring 1 can be made of a conductive metal such as steel, this is not absolutely necessary for the dissipation of charges due to the direct contact of the discharge element 2 of both the shaft 101 and the shaft housing 102. Rather, the majority of the charges are dissipated directly via the discharge element 2.

[0050] The illustrations in Fig. 3a and 3b now show two differently designed shaft earthing rings

[0051] 10 in a schematic plan view. The left-hand views each show the outer side, i.e., the side with the second contact surface 2.3, which can be seen from the left in the illustration in Fig. 1. The right-hand views show the inner side, which also reveals the base ring 1 and the radial section 1.1. The illustrations in Figs. 3a and 3b are somewhat simplified, and, for example, the geometric extension of the radial section 1.1 in the axial direction is not shown.

[0052] Overall, the annular geometry of the shaft grounding ring 10 can be seen. The free inner diameter serves to accommodate a shaft 101, so that the shaft grounding ring 10 is arranged concentrically to the shaft 101 and the axis of symmetry of the shaft grounding ring 10 corresponds to the axis of rotation of the shaft 101. As can be seen when comparing the illustrations in Figs. 3a and 3b, the shaft grounding ring 10 shown in Fig. 3b has a continuous first contact surface 2.2.

[0053] The first contact surface 2.2 thus lies circumferentially closed against the shaft 101. In contrast, the shaft grounding ring 10 or the discharge element 2 does not have a circumferentially continuous discharge lip 2.5, but rather the discharge lip 2.5 is segmented. Specifically, in the illustration in Fig. 3a, four discharge tabs 2.4 are provided which are evenly distributed around the circumference and project inwards in the radial direction, starting from the connecting region 2.1. Due to this segmented design, the shaft 101 is not contacted along its entire circumference, but only approximately 50% in the exemplary embodiment shown. The radial inner sides of the discharge tabs 2.4 are in contact with the shaft surface and thus each form a first contact surface 2.2, via which charges can be transferred between the discharge element 2 and the shaft 101. Due to the overall smaller contact surface orDue to the shorter contact line, the friction effects in this embodiment are lower compared to the embodiment shown in Fig. 3b. Nevertheless, it is ensured that at least one of the deflection tabs 2.4 is in contact with the shaft 101 at all times, even if the shaft 101 exhibits a certain imbalance.

[0054] LIST OF REFERENCE SYMBOLS

[0055] 1 base ring

[0056] 1.1 Radial section

[0057] 1.2 Axial section

[0058] 1.4 Surface

[0059] 2 discharge element

[0060] 2.1 Connection area

[0061] 2.2 First contact surface

[0062] 2.3 Second contact surface

[0063] 2.4 Discharge tab

[0064] 2.5 Discharge lip

[0065] 3 joining die

[0066] 4 printing stamps

[0067] 6 Device

[0068] 10 Shaft earthing ring

[0069] 100 machine elements

[0070] 101 Wave

[0071] 102 Shaft housing

[0072] L charge flow

Claims

PATENT CLAIMS 1. Shaft earthing ring, with a base ring (1) and a discharge element (2) connected to the base ring (1) for discharging electrical voltages between a shaft (101) and a shaft housing (102), characterized in that the discharge element (2) has a first contact surface (2.2) for conductively contacting the shaft (101) and a second contact surface (2.3) for conductively contacting the shaft housing (102).

2. Shaft earthing ring according to claim 1, characterized in that the discharge element (2) can be in direct conductive contact with the shaft (101) and with the shaft housing (102) via the contact surfaces (2.2, 2.3).

3. Shaft earthing ring according to one of claims 1 or 2, characterized in that the diverting element (2) is connected via the first contact surface (2.2) along a contact line with the shaft (101) in contact and via the second contact surface (2.3) flat with the shaft housing (102) may be in contact.

4. Shaft earthing ring according to one of the preceding claims, characterized in that the discharge element (2) is positively connected to the base ring (1) at the microscopic level.

5. Shaft earthing ring according to one of the preceding claims, characterized in that the discharge element (2) consists of filled PTFE.

6. Shaft earthing ring according to one of the preceding claims, characterized in that the discharge element (2) is designed as a segmented discharge ring.

7. Shaft earthing ring according to claim 6, characterized in that the discharge element (2) has at least three, preferably four, discharge tabs (2.4) for contacting the shaft (101).

8. Shaft earthing ring according to one of the preceding claims, characterized in that the base ring (2) has an axial section (1.2) and a radial section (1.1) and the discharge element (2) is arranged on the surface (1.4) of the radial section (1.1) which is opposite the axial section (1.2).

9. Machine element (100) with a rotatable shaft (101), a shaft housing (102) fixed relative to the shaft (101) and a shaft grounding ring (10) for dissipating voltages between the shaft (101) and the shaft housing (102), wherein the shaft grounding ring (10) is designed according to one of the preceding claims.

10. A method for producing a shaft grounding ring (10), in particular a shaft grounding ring (10) according to one of claims 1 to 9, comprising the following steps: Providing a base ring (1), roughening at least some sections of the surface (1.4) of the base ring (1); placing a discharge element (2) on the roughened surface (1.4); Heating the base ring (1.4) and simultaneously pressing the discharge element (2) onto the roughened surface (1.4) to connect the discharge element (2) to the base ring (1).

11. Method according to claim 10, characterized in that the surface (1.4) is roughened by means of laser structuring.

12. Method according to one of claims 10 or 11, characterized in that in order to improve the adhesion between the roughened surface (1.4) and the discharge element (2), an adhesion promoter is applied to the roughened surface (1.4).

13. Method according to one of claims 10 to 12, characterized in that the roughened surface (1.4) of the base ring (1) is heated inductively.

14. Method according to one of claims 10 to 13, characterized in that the discharge element (2) continues to be pressed onto the base ring (1) as the base ring (1) cools.

15. Device for producing a shaft earthing ring (10), in particular a shaft earthing ring (10) according to one of claims 1 to 9, with a method according to one of claims 10 to 14, comprising a joining die (3) into which a base ring (1) can be inserted, a heating element for heating the surface (1.4) of the base ring (1) and a pressure stamp (4) over which a discharge element (2) can be pressed onto the base ring (1).

Images