Seal with friction-reducing etched structure; method for surface treatment of a seal

Abstract

The invention relates to a seal (1), for example for a wheel bearing, a gearbox, an e-bike, a wind turbine, an agricultural machine, made of an elastomer (2), such as rubber, for example NBR, with an outer surface (3) for contact with a sealing partner (4), wherein a friction-reducing geometric structure is introduced into the outer surface (3) by means of etching. The invention also relates to a method for surface treatment of an outer surface (3) of a seal (1).

Description

[0001] The invention relates to a seal, for example for a wheel bearing, a gearbox, an e-bike, a wind turbine, or an agricultural machine, made of an elastomer, such as rubber, for example NBR, with an outer surface for contact with a sealing partner, wherein a friction-reducing geometric structure is introduced into the outer surface by means of etching. The invention also relates to a method for surface treatment of an outer surface of a seal.

[0002] Prior art is disclosed in US patent document 4,667,968 A. This document discloses an improved double-lipped grease-retaining and dirt-exclusion shaft seal. The sealing element comprises a one-piece metal housing with a cylindrical bore sealing section and a radial flange, as well as a molded elastomeric element connected to the metal housing to provide a section connected to the radial flange, and an outer, substantially cylindrical section connected to the surface of the bore sealing section, providing a series of spaced, inwardly projecting retention sections.The elastomeric element also features two diverging lip sections with a cavity between them. One of these sections provides a grease-retaining lip with small, spaced-apart shallow depressions that allow small quantities of grease to pass into the cavity, while the other lip section is fitted with an attached polytetrafluoroethylene insert. A one-piece metal wear sleeve element has a cylindrical shaft engagement section into which the lips engage and a radially outward-extending flange with an axially inward-facing section. This flange has an outer section that is radially inwardly spaced from the outer, generally cylindrical, section of the elastomeric element but extends radially outward beyond the radially inner ends of the retaining sections.The publication also reveals that surface areas of the washer are pre-treated, for example by acid etching and subsequently with a binder, to improve the bonding of the elastomer to it.

[0003] German patent application DE 3 506 696 C1 discloses a lip seal with a metallic housing ring. In this lip seal with a metallic housing ring, the sealing element consists of a cylinder made of PTFE material, the cylinder having two cylindrical sections with different diameters. One section forms the dynamic sealing lip and bears against the machine part to be sealed with a circumferential surface, while the second section forms the connecting element and is joined to an axial leg of the housing ring by clamping, bonding, and / or vulcanization. The ring can be manufactured cost-effectively with low material consumption in simple steps and, due to the constant connection between the PTFE cylinder and the housing ring, offers improved sealing performance combined with high wear resistance.

[0004] Furthermore, it is generally known that bearing friction occurs in bearings, and especially in wheel bearings, which is often very high and depends on the dynamics of speed and load, tilting, and misalignment due to installation. The bearing's no-load friction depends on the amount of lubricant, the speed, the operating viscosity of the lubricant, the bearing's run-in condition, and the seals.

[0005] The ratio of frictional power in wheel bearings to heat dissipation from wheel bearings are key parameters that must be considered with regard to the thermally permissible operating number of the wheel bearings. In addition to rolling friction, sliding friction of the rolling elements, sliding friction of the cage, and fluid friction (flow resistance), the frictional power and frictional torques in the bearings are primarily due to sealing friction and, via the frictional heat, determine the thermal degradation of the bearings. This degradation is one of the factors influencing the service life / life of the bearings.

[0006] Seal friction is significantly influenced by the design and preload of the seal and occurs particularly at the seal of the bearings themselves and / or at the counter-running surfaces.

[0007] With regard to maintaining competitiveness, and considering the current state of the art, solutions are needed that contribute to a significant reduction in sealing friction in rolling bearings. The requirement for a significant reduction in sealing friction should be understood as reducing the sealing friction to a level relevant for maintaining the competitiveness of seal manufacturers and the industries dependent on them, particularly the automotive supply industry.

[0008] The present invention aims to achieve an improvement over the prior art. Known disadvantages are to be eliminated or at least reduced.

[0009] In the case of a seal presented at the outset, this is achieved according to the invention by introducing a friction-reducing geometric structure into the outer surface by means of etching.

[0010] In other words, the invention relates to a seal with a friction-reducing surface structure. The surface structure is preferably created by etching in the area of ​​the sealing lip contact with the counter-running surface through targeted surface treatment. That is, a friction-reducing structure is specifically created in the contact area of ​​the axial and radial lips with the counter-running surface. With regard to the generated surface structure, a distinction must be made between nano-, micro-, and macrostructures that have a friction-reducing effect.

[0011] Chemical etching is achieved by exposing the surface of the seal to an etching solution for a certain period of time. This means the etching solution contains chemicals that react with the elastomer surface and erode it accordingly. Typically, these are acids or alkaline solutions that chemically attack the surface of the elastomer.

[0012] In other words, modifying the surface structure of a wheel bearing seal, particularly in the contact area with the mating surface, influences its friction behavior. Etching and / or texturing reduces friction. Specifically, applying patterns or textures to the elastomer surface, preferably through chemical etching, reduces the effective contact area with other surfaces (e.g., the mating surface), thereby lowering friction.

[0013] Advantageous embodiments are claimed in the dependent claims and are explained in more detail below.

[0014] In the context of explaining the embodiments, a distinction must be made between a radial and an axial direction. The radial direction corresponds to a two-dimensional Cartesian coordinate system and is to be understood as the y-direction, while the axial direction corresponds to the x-direction.

[0015] Etching modification of the outer surface refers to the etching of the outer surface and the adjacent layers of the elastomer material. The depth of the etched area of ​​the elastomer / seal is preferably predetermined by the etching parameters.

[0016] It has proven advantageous if the structure is designed as a micro-, macro- and / or nanostructure.

[0017] By implementing the etched structure via nano-, micro-, and macrostructures, the surface of the sealing ring can be adapted across multiple scales and / or to different scales. In this way, the advantages of the surface structure can be advantageously utilized at the respective scale with regard to friction reduction, that is, preferably the reduction of external friction.

[0018] This means that friction, and therefore wear / tribological heat input in the wheel bearing, can preferably be influenced and reduced directly and / or indirectly by modifying the contact surfaces / surface structure between the friction partners. The friction partners are preferably the seal and the respective substrate (e.g., the mating surface).

[0019] The surface treatment is preferably designed such that targeted surface treatment can be achieved by directly influencing preferably physical and / or mechanical processes in order to affect preferably external friction. This includes influencing at least one interlocking of surface roughness and / or elastic instabilities and / or interlocking through physisorbed particles and / or plastic deformation and / or cold welding.

[0020] The indirect influence on friction behavior via the surface structure / surface treatment is preferably achievable by influencing the wettability of the sealing surface with cooling fluid and / or lubricating fluid.

[0021] With regard to the contact surfaces / surface structure, nanostructures in embodiments of, for example, functional groups by activating / increasing the surface energy / functionalizing the surface by influencing friction-reducing adhesion processes, microstructures in embodiments of, for example, grooves, microchannels or fine depressions, and / or macrostructures in embodiments of, for example, patterns on the sealing surface / rubber surface / elastomer surface can be adjusted.

[0022] Specifically, the nanostructure preferably comprises structural features on the order of one to several hundred nanometers, the microstructure preferably comprises structural features on the order of micrometers, and the macrostructure preferably comprises structural features on the order of at least millimeters.

[0023] Etching surface treatment preferably achieves at least a reduction or prevention of sliding friction and / or increases surface adhesion. This friction reduction results in a reduction of wear and friction-induced heat, which is advantageous with regard to seal service life.

[0024] Furthermore, it is advantageous if the etching process uses an acid or an alkaline solution.

[0025] The etching agents are preferably chemical in nature and in the form of chemical solutions. The chemical etching of the sealing lip surface attacks the surface of the elastomer and causes a removal of elastomer material.

[0026] The use of acids or alkalis advantageously enables the removal of material from the surface of the seal / elastomer material. According to the disclosure, the etching agents are preferably acids / oxidants. By chemically etching the sealing lip surface, it is advantageously possible to attack and remove material from the surface of the sealing material, preferably the elastomer material. The removal can preferably be carried out across the entire seal or selectively, i.e., locally.

[0027] Furthermore, advantageous material removal can be achieved using etching agents, preferably aqueous solutions (alkalis, such as sodium or potassium-based alkalis), solutions of bases, or, in the broadest sense, also non-aqueous solutions. These can be classified as alkaline if the concentration of hydroxide ions (OH) is low. - the oxonium ions / hydronium ions H3O +exceeds.

[0028] Furthermore, it is advantageous if the structure is designed as a texture.

[0029] By etching a texture onto the sealing surface / elastomer surface, it is advantageously possible to achieve a preferred orientation of the material and, consequently, the sealing properties. This preferred orientation preferably corresponds to direction-related, material-related mechanical and / or physical properties of the seal.

[0030] Due to the directional properties of the seal, i.e., the preferably elastomeric material of the seal, it is advantageously possible to adapt the seal to the given, preferably directional, stresses in the bearing and thereby reduce friction, wear, and heat generation. Thus, in the context of the disclosed seal, it is conceivable that the flow of lubricating fluid can be directed and / or that liquids such as dirt and / or condensation can be deflected from the seal to the outside.

[0031] Furthermore, it is advantageous if the elastomer is made of NBR.

[0032] The use of nitrile butadiene rubber (NBR) as the sealing material allows for the use of an oil- and fuel-resistant seal, which is advantageous in terms of media resistance. In addition to its resistance to mineral oil, its abrasion resistance is also advantageous.

[0033] It has proven advantageous if the elastomer contains fillers that are exposed by the etching process.

[0034] By combining the sealing material, preferably the elastomer material, with friction-reducing materials / fillers or particles / fibers or other fillers based on FKM, carbon, PTFE or molybdenum disulfide, a reduction in friction can be advantageously achieved, preferably by exposing the friction-reducing components of the mixture / elastomer material components via etching of the surface.

[0035] The fillers are preferably embedded in the elastomer material / the near-surface layers of the elastomer material and can be released or exposed by etching. The distance of the near-surface layers, which can be influenced by etching, from the elastomer surface is preferably dependent on the etching parameters, the etchant / etching solution, and in particular the etching time.

[0036] Furthermore, it is advantageous if the friction-reducing geometric structure is achieved by reducing the contact area and / or by activating the outer surface of the sealing lips.

[0037] By reducing the effective contact area and / or activating the outer surface, the friction behavior can be advantageously influenced via the geometric structure achievable through etching. While reducing the contact area preferably reduces the frictional contribution of the outer surface of the sealing lips, activating the outer surface advantageously influences the adhesion of the sealing lip surface. Targeted activation of the outer surface also advantageously enables functionalization of the outer surface.

[0038] Furthermore, the friction reduction preferably relates to the reduction of sliding friction, and more preferably to the reduction of static friction in an advantageous manner.

[0039] A method for surface treatment of the outer surface of a seal is also presented.

[0040] The method is based on the following, preferably three, process steps, carried out in the order listed below.

[0041] The first process step preferably involves cleaning, i.e., surface preparation for cleaning and / or pretreating the seal. This process step advantageously ensures that the seal surface is preferably clean / pretreated before the etching process. In this way, a uniform effect of the etching solution is advantageously guaranteed.

[0042] The second process step preferably involves etching, i.e., immersion and spraying with the etching solution. The etching solution is preferably applied to the elastomer surface, which is preferably suitable for etching. Advantageous methods for applying the etching solution are immersion or spraying. The etching time / duration can be varied depending on the preferred / technically required target surface structure.

[0043] The third process step preferably comprises neutralization and cleaning, i.e., rinsing the seal / seal surface with water and cleaning the seal / seal surface. Preferably, after reaching a predetermined etching time, the etching reaction can be stopped by neutralization. Stopping the etching reaction is preferably achieved by rinsing with water or a neutralizing solution. Following the stopping of the reaction, the surface can advantageously be thoroughly cleaned to remove all residues of the etching solution.

[0044] By carrying out the first process step, the cleaning of the surface from dirt particles, organic / inorganic layers can be achieved in a manner advantageous with regard to the etching result.

[0045] By carrying out the second process step, the actual etching surface treatment of the sealing material / elastomer material can be achieved advantageously with regard to the targeted adjustment of tribological properties under predetermined etching parameters, i.e., the etching duration / time and / or the etching agent / solution and other etching parameters. The exact structure that can be produced by chemical etching depends on various factors. These include the composition of the rubber / elastomer, the selected etching solution, and other process parameters.

[0046] By carrying out the third process step of neutralization / cleaning, it is advantageously possible to stop any chemical reactions that have begun with the etching and to produce a chemically stable state of the surface.

[0047] An advantage can be achieved by preferably carrying out the process steps in a direct sequence / in a directly successive manner. This advantage allows the effects intended by etching on the surface structure and the tribological behavior / friction reduction to be advantageously predetermined and realized.

[0048] For the process, it is still advantageous if a final cleaning is carried out in a fourth step following the third step.

[0049] By carrying out the fourth process step, it is advantageously possible to achieve a completely cleaned surface of the sealing material / elastomer material. The fourth process step is preferably carried out directly following the third process step.

[0050] Furthermore, it is advantageous in this process if the etching is carried out as plasma etching.

[0051] Plasma etching / instrumental plasma technology makes the etching process more environmentally friendly. Preferably, methods operating at atmospheric pressure are used, ideally without requiring complex and expensive vacuum technology. Furthermore, these methods are advantageously designed for simple process control and efficient surface modification. The use of etching solutions based on oxygen, nitrogen, or fluorine is also preferred.

[0052] The invention is explained in more detail below with the aid of a drawing. An embodiment of the seal according to the invention is shown. It shows: Fig. 1 a schematic representation of a seal according to the disclosure in a first embodiment in a cross-sectional view, Fig. 2 the elastomer of the seal according to the disclosure Fig. 1 as a chemical structural formula and Fig. 3 a flowchart of a disclosed method for surface treatment of an outer surface of the disclosed seal according to Fig. 1.

[0053] The figures are purely schematic and serve only to illustrate the invention. The same elements are identified by the same reference symbols.

[0054] The Fig. Figure 1 shows a schematic cross-sectional view of a seal 1 according to the disclosure. The seal 1 is suitable for use in a wheel bearing, a gearbox, an e-bike, a wind turbine, or an agricultural machine. An elastomer 2 is preferably used as the material for the seal 1. Materials preferably suitable for the seal 1 according to the disclosure are rubber, NBR, and / or blends with FKM, carbon, PTFE, or molybdenum disulfide as fillers. The seal 1 is designed with an outer surface 3 for contact with a sealing partner 4.

[0055] The outer surface 3 of the seal 1 is covered by a manifestation, in Fig. 1. Etching process 9 not shown, for example according to Fig. 2. The process 9 consists of a first process step 10, a second process step 11, a third process step 12, and an optional fourth process step 13 and is described in Fig. 2 explained in more detail.

[0056] Fig. Figure 1 shows a counter-running surface 5 as a sealing partner 4, against which a first, axial sealing lip 6 and a second, radial sealing lip 7 of the seal 1 according to the disclosure bear. The structuring of the outer surface 3 by the etching process / the etching method 9 preferably takes place selectively in the area of ​​contact between a counter-running surface 5 and sealing lips 6, 7.

[0057] The contact surfaces 8 of the first and second sealing lips 6, 7 of the seal 1 have an etched surface structure. The surface structure can exhibit structural features on the scale of the nanoscale, microscale or macroscale achieved by etching.

[0058] Examples of the influence of a modified nanostructure include the well-known lotus effect, or more precisely, the water repellency caused by the lotus effect. In the context of the seal 1, etching of the outer surface 3 of the elastomer 2 activates / increases the surface energy / functionalizes the outer surface 3, i.e., it leads to the formation of functional groups. This preferably influences the friction-reducing adhesion processes. The adhesive forces are preferably strengthened.

[0059] The Fig. Figure 3 shows the elastomer 2 of the seal 1 according to the disclosure. Fig. 1 as a chemical structural formula. The seal 1 in the first embodiment consists of the elastomer material NBR. This can be a blend with fillers such as FKM, carbon, PTFE, or molybdenum disulfide, which, when exposed by etching, have a friction-reducing effect. Another embodiment of fillers, such as fibers or particles, is conceivable.

[0060] The Fig. Figure 3 shows a flowchart of a disclosed method 9 for surface treatment of an outer surface 3 of a disclosed seal 1 according to Fig. 1.

[0061] Method 9 for surface treatment of an outer surface 3 of a seal 1 is divided into a first process step 10, a second process step 11, a third process step 12, and an optional fourth process step 13. Process steps 10, 11, 12, and 13 are preferably carried out consecutively. The etching process achievable via process steps 10, 11, 12, and 13 allows for the targeted application of various surface structures to the outer surface 3 of the seal, specifically to the first 6 and second 7 sealing lips.

[0062] The surface structures allow for targeted influence, preferably directly on the friction properties and / or indirectly on the functional properties of the elastomer 2 / the sealing material.

[0063] The first process step 10 of process 9 comprises cleaning and / or pretreating the seal 1. Included in this first process step is the surface preparation for cleaning and / or pretreating the seal 1, that is, for example, the removal of contaminants on the outer surface 3 of the elastomer 2.

[0064] The second process step 11 of process 9 comprises an etching and represents the crucial process step for adjusting the surface structure of an outer surface 3 of a seal 1 / elastomer 2 according to the disclosure. This second process step 11 includes the activation of the outer surface by the etching process. The etching enables the formation of functional groups and thus the modification of the surface structure / outer surface of the seal 1, more precisely of the sealing material / elastomer 2.

[0065] The third process step 12 of process 9 comprises stopping the chemical reaction initiated by etching through neutralization and cleaning. The parameters (exposure time) and agents for neutralization and cleaning must be determined depending on the seal 1 / the elastomer 2 and the treatment of the outer surface 3 carried out in the previous process step.

[0066] The fourth process step 13 of process 9 comprises the final cleaning of the outer surface 3 of the elastomer 2 of the disclosed seal 1. The third process step 12 and the fourth process step 13 of process 9 are optional. Reference symbol list 1 seal 2 Elastomer 3 Outer surface 4 sealing partners 5 Counter-running surface 6 First sealing lip / axial sealing lip 7 Second sealing lip / radial sealing lip 8 Contact area / Contact area of ​​elastomer and counter-running surface 9 procedures 10 First procedural step / first step 11 Second procedural step / second step 12 Third procedural step / third step 13 Fourth procedural step / fourth step QUOTES INCLUDED IN THE DESCRIPTION

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

[0000] US 4,667,968 A

[0002] DE 3 506 696 C1

[0003]

Claims

Seal (1) made of an elastomer (2) with an outer surface (3) for contact with a sealing partner (4), characterized in that a friction-reducing geometric structure is introduced into the outer surface (3) by means of an etching. Seal (1) according to claim 1, characterized in that the structure is designed as a micro-, macro- and / or nanostructure. Seal (1) according to one of claims 1 or 2, characterized in that the etching uses an acid or alkaline solution. Seal (1) according to one of claims 1 to 3, characterized in that the structure is designed as a texture. Seal (1) according to one of claims 1 to 4, characterized in that the elastomer (2) is designed as NBR. Seal (1) according to one of claims 1 to 5, characterized in that the elastomer (2) contains fillers which are exposed by etching. Seal (1) according to one of claims 1 to 6, characterized in that the friction-reducing geometric structure is caused by reducing the contact area (8) and / or by activating the outer surface (3) of the sealing lips (6, 7). Method (9) for surface treatment of an outer surface (3) of a seal (1), according to one of claims 1 to 3, wherein in an optional first step (10) a surface preparation is carried out to clean and / or pretreat the seal (1), in a second step (11) carried out thereafter an etching is used for an elastomer surface treatment and in an optional third step (12) following the second step a stopping of the chemical reaction started with the etching is achieved. Method according to claim 8, wherein a final cleaning is carried out in a fourth step (13) following the third step. Method according to claim 8 or 9, wherein the etching is carried out as plasma etching.

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