Grinding element of an earthing contact and method for manufacturing the grinding element

Abstract

Grinding element (1) of an earthing contact (16) of a rail-bound vehicle, wherein the grinding element (1) has a contact surface (2) for a sliding contact with a brush body (17), wherein the contact surface (2) has a profile (3), characterized in that the profile (3) is embossed by a tool (9), wherein the profile (3) has several intersecting groove-shaped recesses (6-8), wherein an embossed bead projecting from the contact surface (2) is arranged adjacent to the at least one recess (6-8).

Description

[0001] The invention relates to a grinding element of an earthing contact of a rail-bound vehicle according to the features in the preamble of claim 1 and to a method for manufacturing the grinding element according to the features of claim 6.

[0002] Rail vehicles have grounding contacts for returning operating or signal current and for vehicle grounding. Grounding is achieved via a wheel and the rail. A movable friction element rotates with a wheelset axle and, with the aid of a spring, presses against a carbon brush that is stationary. This principle of fixed and rotating parts can also be used in reverse. In either case, a sliding contact occurs between a more wear-resistant friction element and a brush body. It is known to use carbon brushes with a circular contact surface as the brush body, which are soldered or clamped into a cover. The rotating movement of the friction element against a stationary round carbon brush can cause temporary squeaking noises. These noises do not affect the function of the grounding contact, but they do have a negative impact on the vehicle's noise characteristics.The squeaking noise is sometimes perceived as unpleasant by people both inside and outside the rail vehicle. This squeaking is caused by the so-called stick-slip effect on the sliding elements. Efforts to prevent this squeaking have been underway for years. The stick-slip effect can occur when static friction is significantly greater than kinetic friction. It is known that the squeaking noises are sometimes influenced by the season or humidity. Investigating the cause is complex. Numerous approaches exist to solving the problem, such as modifying the surfaces of the friction partners, for example, by milling grooves into the sliding element. However, the annoying squeaking noises often persist despite these measures.

[0003] Regarding the prior art, reference should be made to DE 10 2022 133 292 A1 concerning a current transmission device for a rotor of an electric machine, particularly for wet applications. Electrical contact elements, i.e., brushes, are pressed onto a radial outer surface of a conductor track, the conductor track having at least one recess in the outer surface in the circumferential direction, which is designed to receive a fluid. The recesses in the outer surface are intended to prevent rubbing in, i.e., a surface-level fit between the contact elements and the conductor track, in order to prevent the contact elements from floating. The recesses are particularly designed as swept-shaped grooves with isosceles V- or U-shaped depressions.

[0004] US RE 39,974 E describes the ideal surface properties for contact surfaces with electric brushes. It proposes creating a large number of contact points with predetermined shapes and distributions that exhibit low electrical contact resistance and promote a long service life. Preferably, the contact surface is provided with a hard, highly conductive coating that is resistant to wear and chemical influences. The objective is to reduce interfacial resistance and adhesion forces. The surface can incorporate a multitude of parallel depressions, produced, for example, by etching or mechanical ablation.

[0005] CN 216 649 484 U deals with slip ring arrangements in wind turbine generators, which are to be optimized with regard to vibration excitation. It is proposed to provide the sliding rings with a damping surface. Preferably, this surface consists of wave-shaped depressions that run in the sliding direction and extend over the entire circumference of the sliding ring.

[0006] DE 760 320 A discloses a method and a device for manufacturing embossing elements, in particular patterning rollers. These are used to produce finely and differently grooved surface pieces on webs of paper, metal foils, textiles, and the like. The production of embossing elements in the form of patterning rollers is to be facilitated by the fact that the grooves are formed by means of a grooving wheel.

[0007] CH 244 668 A relates to a method for embossing characters into round objects, using an embossing ring which has the embossing pattern raised on its inner surface, while the round object to be embossed, made of a softer material, rolls along the inner surface of the ring under pressure. The advantage of this type of embossing is that the angle at which the embossing dies enter and exit the material to be embossed is smaller than in a method with external embossing, so that the characters to be embossed can be placed much closer together.

[0008] The invention is based on the objective of providing an abrasive body with which squeaking can be largely and, in particular, completely avoided. Furthermore, a method for manufacturing a suitable abrasive body and a suitable tool for its manufacture are to be presented.

[0009] These problems are solved by an abrasive body having the features of claim 1 and a manufacturing method according to claim 6.

[0010] According to the invention, the grinding wheel has a contact surface with a profile. However, the profile is not milled, but rather embossed by a tool. The crucial difference is that milling involves material removal, whereas according to the invention, no material is removed, only displaced. Surprisingly, the embossed profile has completely different properties than a milled profile. Comparative tests have shown that no squeaking occurred with an embossed profile compared to grinding wheels with a milled groove. The tests were carried out with commercially available grinding wheels. The grinding wheels tested were made of bronze produced by continuous casting.

[0011] Bronze materials are particularly well-suited for manufacturing the grinding wheels according to the invention, as they can be more easily deformed by stamping using a tool than grinding wheels made of steel. According to the invention, the grinding wheels preferably consist of metal, in particular bronze, and most preferably CuSn6. The grinding wheels can be manufactured, in particular, from continuous casting GC-CuSn6 according to DIN 17662. GC-CuSn6 can have a nominal hardness of approximately 76 HB. Hot-rolled CuSn6 according to standard EN 1652 / 1997 is also suitable. It can have a hardness of approximately 114 HB. The hardness of continuous casting can also be higher, e.g., approximately 85 HB. However, when stamping, it must also be taken into account that the forming process becomes significantly more difficult with increasing hardness if the stamping is applied over a large area or to a deep depth. Therefore, the stamping may need to be carried out in several steps or at least in such a way that undesirable deformations of the workpiece do not occur.

[0012] Tests have shown that a groove-shaped depression yields particularly good results. Therefore, the tool for embossing the profile has at least one embossing ridge. With a circular contact surface, the groove-shaped depression should preferably extend substantially over the entire diameter of the contact surface, so that during the sliding movement of the contacting partners, the groove-shaped depression always lies in the path of motion of the sliding partners.

[0013] According to the invention, the abrasive bodies have several intersecting, groove-shaped depressions. Tests were conducted with such profiled abrasive bodies, and no squeaking occurred during these tests. One possible reason for this effect could be that the profiles do not have sharp edges at the transition from the groove-shaped depression to the contact surface. Another possible reason is that material displaced from the groove-shaped depressions forms an embossed ridge adjacent to the depressions. This embossed ridge is rounded by the material flow.

[0014] Preferably, the grooves should have a depth in the range of 0.1 to 0.6 mm. These depths have yielded very good results. Regarding the center-to-center spacing of the grooves, a range of 2 to 12 mm, preferably 2 to 8 mm, and particularly preferably 3 to 6 mm is considered advantageous. Tests were carried out with groove spacings of 4.5 to 5 mm, at which no stick-slip effect was observed.

[0015] The embossed, groove-shaped depressions had a width of 0.5 to 1.5 mm, preferably 0.8 to 1.2 mm, and in particular widths of approximately 1 mm. Including the rounded transition areas to the essentially flat contact surface, the width of the groove-shaped depressions increases by approximately 20%. With an initial width of 1 mm, the width of the depression relative to the contact surface is therefore approximately 1.2 mm. The groove-shaped depressions had a straight profile.

[0016] The grounding contact according to the invention can be produced, in particular, with a tool having at least one embossing ridge, wherein the embossing ridge tapers from its base to its tip. This allows the embossing ridge to penetrate the material of the grinding body more easily and to create sufficiently wide depressions with increasing penetration depth. Lateral material displacement is desirable. As explained above, the depth should be in the range of 0.1 to 0.5 mm, with aperture widths of approximately 0.5 to 1.5 mm. Due to the shape of the embossing ridge, the width and depth of the depressions are also not constant in cross-section.

[0017] Several groove-shaped indentations can be produced in successive embossing steps. Preferably, the tool has several parallel embossing guides to prevent deformation of the contact surface due to uneven loading. In particular, the tool for producing the profiled contact surface is large enough that the contact surface can be profiled in a single stroke of the embossing tool.

[0018] The embossing ridge is preferably triangular, with its sides arranged at an angle of 80 to 100°, particularly 90°, to each other. The embossing ridges can follow directly one another, so that the tool has a zigzag profile on its embossing side. Such an embossing profile is cost-effective to manufacture. It is by no means necessary for the individual embossing ridges to penetrate the material of the contact surface to their entire height. A depth of just 0.1 mm is sufficient to form effective groove-shaped indentations.

[0019] Tests have shown that the stick-slip effect is avoided when groove-shaped depressions intersect. Accordingly, a tool can be used in a manufacturing process for the grinding wheel that, in a first embossing step, produces depressions with a first orientation, and in a second embossing step, produces depressions with a second orientation, the orientations differing from each other and, in particular, intersecting at a 90° angle. It is expected that angles other than 90°, or a diamond pattern bounded by the depressions, will also effectively prevent squeaking. Depressions with other differing orientations can also be provided, e.g., for a triangular pattern.

[0020] Comparative tests of grinding wheels with exclusively non-intersecting parallel groove-shaped depressions and grinding wheels with multiple parallel groove-shaped depressions intersecting at 90° angles showed that after 100,000 revolutions, wear was significantly lower when the groove-shaped depressions intersected. No squeaking occurred in either case; however, the differences in wear of the friction partner were so pronounced that, for wear optimization, intersecting groove-shaped depressions are clearly preferable.

[0021] The method according to the invention is particularly suitable for embossing grinding media that possess high conductivity and are easily deformable. Therefore, cast or rolled copper materials are especially suitable.

[0022] The tool used to carry out the process preferably has a sharp point or edges that, due to their angular orientation, can penetrate sufficiently deeply into the surface without bending the entire grinding contact. The embossing is produced exclusively by material displacement. Sharp edges in the border region of the groove-shaped depressions should be avoided. Depending on the material selection and the geometry of the tool and the workpiece, sharp edges in the border region of the depressions can be avoided by carrying material along in the embossing direction, so that the flanks of the depression transition into a flow curve that represents a gently rounded transition to the contact surface. In particular, the depressions have walls that are at an angle to each other greater than 45°, for example, 90°. Smaller angles facilitate the embossing because the tool can penetrate more easily. Larger angles result in wider depressions.A 90° angle yielded good results. The tool is made primarily of steel, specifically a hardenable steel, with at least the tips of the tool penetrating the contact surface being hardened.

[0023] The term "embossing" as used in the invention refers to the displacement of material, not its removal. The direction of displacement is determined by the shape and movement of the tool during embossing. Embossing also includes the creation of multiple point-shaped indentations, as in dot peening or vibro-peening. These indentations can be created using very low force. If the point-shaped indentations are placed close together and / or overlap, linear profiles can be produced. The point-shaped indentations can be created using a carbide tip.

[0024] The term "marking" as used in the invention also includes scribing, in which a diamond or carbide tip is pressed into the workpiece surface and drawn through the material like a scribing needle. The force applied to the tool is minimal. The difference to, for example, needle marking, is that the tool is moved parallel to the contact surface and not essentially perpendicular to it.

[0025] The groove-shaped depressions typically have a straight, linear path. However, they can also have an arc-shaped or serpentine path. Grooves with differing paths, such as straight and odd paths, can be combined.

[0026] The subdivision of the contact surface into smaller contact area units by means of profiling effectively prevents the stick-slip effect on the more wear-resistant component of the friction pair by plastically deforming the contact surface. The advantages of the invention are demonstrably particularly evident in grounding contacts for rail vehicles. The brush bodies with embossed contact surfaces can also be used in other applications where squeaking noises need to be avoided.

[0027] The invention is explained in more detail below with reference to exemplary embodiments shown in the drawings. The drawings show: Fig. 1 a contact surface of a grinding body with a profile in a first embodiment; Fig. 2 a contact surface of an abrasive body with a second profile; Fig. 3 a perspective view of a tool for embossing a profile; Fig. 4 a detail of a profile in a contact surface in the top view; Fig. 5 a polished image through a grinding body with a profile according to the invention and Fig. 6 a grounding contact in longitudinal section.

[0028] The Fig. Figure 1 (not according to the invention) shows an abrasive body with a view towards its circular contact surface 2, which has a profile 3 in the form of parallel groove-shaped recesses 5, 6. Fig. Figure 2 shows groove-shaped depressions 5, 6, 7, 8 on a grinding body according to the invention, wherein the groove-shaped depressions 5, 6, 7, 8 intersect.

[0029] The profiling 3 in the contact surface 2 is produced by a tool 9 which is located in Fig. Figure 3 shows the tool 9 as an embossing tool with several parallel embossing dies 10, which can be seen on the upper side of the illustrated tool as a zigzag profile. Embossing, as defined in the invention, refers to the deformation of the grinding body by changing the material thickness in certain areas between an upper and lower die, wherein the engraving of the upper die is not the counterpart to the engraving of the lower die. Fig. Figure 3 shows the engraving of the upper die. The lower die (not shown) serves as a support. A relatively shallow relief is created in the contact surface of the grinding wheel by locally displacing the material.

[0030] The individual embossing bars 10 are triangular in cross-section and taper towards the apex 11, while the base 12 of each embossing bar 10 is wider. In this specific embodiment, the sides 13, 14 of all embossing bars 10 are at a 90° angle to each other.

[0031] With the in Fig. The tool 9 shown in Figure 3 can provide the entire contact surface 2 with groove-shaped depressions 5, 6 in a single embossing stroke, extending almost to an edge 4 ( Fig. 1) A grinding wheel profiled in this way already effectively prevents the stick-slip effect. The stick-slip effect does not occur, in particular, if further indentations 7, 8 are formed in a second embossing step at a 90° angle to the first indentations 5, 6, as shown in Fig. Figure 2 shows that the first depressions 5 and 6, and all parallel depressions, have a first orientation O1. The subsequent depressions 7 and 8, and all other parallel depressions, have an orientation O2 at a 90° angle to the first orientation O1.

[0032] The Fig. 4 and Fig. Figure 5 shows, in a highly delayed display, a practical embodiment that uses tool 9 of the Fig. 1 was produced. In Fig. Figure 4 shows a top view of a portion of the contact surface 2, with intersecting recesses 5, 6, 7 depicted. Fig. Figure 5 shows a cross-section through an embossed grinding body 1, which therefore has groove-shaped depressions 5, 6. Comparing the zigzag contour of the tool 9 with the profile produced in the contact surface 2, it can be seen that the tool 9 only penetrated the contact surface 2 with its tips 11. Between the adjacent groove-shaped depressions 6 to 8, contact surface areas with a width B1 remain, which are approximately 5 to 6 times larger than the width B2 of the groove-shaped depressions 5, 6. In the Fig. In part 5, the center-to-center distance A1 of the recesses is approximately 4.5 mm. The embossed, groove-shaped recesses have a width B2 of approximately 1 mm. Including the rounded flanks at the transition to contact surface 2, the width is 1.2 mm. The groove-shaped recesses 5 and 6 are not absolutely identical in this example, which is due to the manufacturing process.

[0033] The Fig. Figure 5 shows that the contour of the groove-shaped indentations 5, 6 has a smooth, rounded transition into the contact surface 2. Particularly pronounced embossing ridges are not visible in the chosen illustration; however, the embossing or pressing by the tool leads to material displacement and not material removal. The material is typically displaced laterally towards the undeformed contact surfaces 2. These can be particularly noticeable in the checkerboard design according to... Fig. 4. The stamp should be slightly curved after embossing.

[0034] It should be noted that the maximum depth T1 shown here will decrease in the range of 0.1 to 0.6 mm with increasing wear of the grinding wheel 1, whereby any embossed ridges or protrusions are initially removed. However, long-term tests have shown that the stick-slip effect is still avoided even after any embossed ridges have been removed.

[0035] The Fig.Figure 6 shows an example of an installation situation for an abrasive element 1 in a grounding contact 16. The abrasive element 1 is spring-loaded and pressed against a brush body 17 in a cover 18. The abrasive element 1 is arranged in a sleeve 19, against which a spring 20 presses. A cuff is arranged on the sleeve 19 to separate it from the interior of the cover 18. Reference symbol: 1 grinding wheel 2 contact area of ​​1 3 Profiling in 2 4 edge of 2 5 Grooved depressions 6 Grooved depressions 7 Grooved depression 8 Grooved depressions 9 tools 10 embossing bridge 11 Top out of 10 12 base of 10 Page 13 of 10 Page 14 of 10 15 Contact area 16 Grounding contact 17 brush bodies 18 lids out of 16 19 Sleeve 20 springs 21 cuff A1 Center distance between 5 and 6 B1 width of 15 B2 width of 5 T1 depth of 5 and 6

Claims

Grinding element (1) of an earthing contact (16) of a rail-bound vehicle, wherein the grinding element (1) has a contact surface (2) for a sliding contact with a brush body (17), wherein the contact surface (2) has a profile (3), characterized in that the profile (3) is embossed by a tool (9), wherein the profile (3) has several intersecting groove-shaped recesses (6-8), wherein an embossed bead projecting from the contact surface (2) is arranged adjacent to the at least one recess (6-8). Grinding body (1) according to claim 1, characterized in that the groove-shaped recesses (6-8) intersect at an angle of 90°. Grinding body (1) according to claim 1 or 2, characterized in that the profiling (3) has several point-shaped depressions produced by embossing. Grinding body (1) according to one of claims 1 to 3, characterized in that the recesses (6-8) are arranged at a center distance (A1) of 2 to 12 mm, in particular at a center distance (A1) of 3 to 6 mm. Grinding body (1) according to one of claims 1 to 4, characterized in that the recess (6-8) has a maximum depth (T1) of 0.1 to 0.6 mm. Method for producing an abrasive body (1) according to the features of one of claims 1 to 5, characterized in that a profile (3) is pressed into the contact surface (2) of the abrasive body (1) with a tool (9), wherein several intersecting groove-shaped depressions (6 - 8) and optionally additional point-shaped depressions are produced with the tool (9), wherein the material displaced from the depression (6-8) forms an embossed ridge adjacent to the depression (6-8). Method according to claim 6, characterized in that the embossing of the profiling (3) is carried out in several embossing steps, wherein in a first embossing step depressions (5, 6) with a first orientation (O1) are produced and in a second embossing step depressions (7, 8) with a second orientation (O2) are produced, wherein the two orientations (O1, O2) differ from each other.

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