Sliding element having coating and method for production thereof

Abstract

The invention relates to a sliding element having a base layer and a coating arranged on an outer surface of the base layer, a profile is defined such that the profile forms an outer surface of the coating, and a Radon transform g (theta, rho) of a square segment of the profile is defined, the value domain of which is standardized to a value between 0 and 1, theta describes the angle and Rho describes the distance from the origin of the coordinates, and the Radon transform g (Theta, Rho) is shortened in the Rho direction in factorial symmetry. For any angle [theta], the standard deviation [sigma] [rho] ([theta]) of the Radon transform and the value of the Radon transform are defined, where is the average value of all g ([theta], [rho]) for the respective angle [theta]. [sigma] max, [sigma] min, being a maximum standard deviation, a minimum standard deviation, and an average value of each standard deviation, being a maximum value of each value, a minimum value of each value, and an average value of each value, parameter A being defined and the profile having a parameter Alt; 1.0, preferably lt; 0.9, particularly preferably lt; and 0.7.

Description

Technical Field

[0001] This invention relates to a sliding element having a base layer and a coating disposed on the outer surface of the base layer. A profile is defined such that it forms the outer surface of the coating, and a Radon transform g(θ,ρ) of a square segment of the profile is defined. The Radon transform's range is normalized to values ​​between 0 and 1, where θ describes an angle and ρ describes the distance from the origin. The Radon transform g(θ,ρ) is factored in the ρ direction. Shorten, and for any angle θ, the standard deviation σ of the Radon transform. ρ (θ) and the value of the Radon transform Defined, where, It is the average value of all g(θ,ρ) for the corresponding angle θ, and σ max σ min , These are the maximum standard deviation, the minimum standard deviation, and the average of all standard deviations, and... These are the values The maximum value, each value Minimum and values The average value, and parameter A is defined as Background Technology

[0002] Applicable to sliding bearings in fluid dynamics, it is noted that the necessary lubricating film for low-wear operation is established only through the rotation of machine components, such as shafts. Here, the rotation of the shaft generates a fluid dynamic pressure distribution in the lubricant, which resists the supporting force acting from the outside. When this force is sufficiently large, reaching its minimum rotational speed, the shaft floats onto the lubricant and separates from the mating surfaces. In the case of sliding bearings in fluid dynamics, four operating ranges can be distinguished. These operating ranges are static friction, boundary friction, mixed friction, and / or fluid friction. In the absence of relative motion, it is in the range of static friction, or at low speeds, in the range of boundary friction, where the two contact surfaces are in direct mutual contact. As the rotational speed increases, the lubricating film becomes more load-bearing, and the sliding bearing transitions into the transition range. The range of mixed friction is discussed here. Above the minimum rotational speed, the sliding bearing is in the range where only fluid friction still occurs, and therefore there is practically no wear.

[0003] Especially in modern sliding bearing applications in industrial or energy harvesting sectors, extreme load conditions can occur, where the actual load often exceeds the bearing's nominal load, and the current sliding speed is very low. Due to the damaging characteristics caused by overload, these extreme load conditions lead to critical mixed friction, static friction, and boundary friction conditions with significantly increased wear and a higher probability of failure. An example of this is sliding bearings in wind power equipment, where the loads are typically high, and the rotational speed can vary drastically during operation depending on the prevailing wind conditions.

[0004] To reduce the failure probability of sliding bearings, additional coatings are typically used in such bearings. These additional coatings should optimize tribological properties in terms of friction values ​​and wear across the range of static friction, boundary friction, and mixed friction. An example of such a coating can be seen, for instance, in EP1764522B1, which illustrates a bearing element comprising a protective layer, a bearing metal layer disposed on the protective layer, and a sputtered sliding layer disposed on the bearing metal layer, on which a sliding varnish layer is disposed. Conversely, GB2363433A discloses a composite sliding material comprising polytetrafluoroethylene resin as a main component, and this composite sliding material should, in particular, result in improved wear resistance when used as a bearing material.

[0005] This solution is flawed in that it only improves the problem at the symptomatic level, namely, mitigating the negative impact of sliding bearing operation under unfavorable hydrodynamic conditions. Instead, a more attractive solution is to improve the pressure build-up of the hydrodynamics between the sliding bearing and the machine component, as this reduces the operating window and thus addresses the problem at the causal level, defined by the loads and rotational speeds of the machine component in which tribologically unfavorable operating conditions (static friction, boundary friction, and mixed friction) occur.

[0006] Here, an attractive approach is to structure the sliding surface of the sliding element so that the sliding surface inherently supports hydrodynamic pressure buildup. If we observe the microscopic surface morphology of such a sliding surface for this purpose, in this case, especially a machined sliding surface, is unfavorable for hydrodynamic pressure buildup because the number of microscopically usable hydrodynamic wedges is reduced. Summary of the Invention

[0007] Therefore, the object of the present invention is to provide a sliding element comprising a base layer and a coating disposed on the outer surface of the base layer, the outer surface of the coating being shaped such that hydrodynamic pressure construction is facilitated by the presence of numerous microscopic hydrodynamic wedges, particularly compared to machined sliding surfaces.

[0008] The task is solved by the sliding element according to claim 1.

[0009] An advantageous embodiment of the invention is a sliding element comprising a base layer and a coating disposed on the outer surface of the base layer. Here, a profile is defined that forms the shape of the outer surface of the coating. Furthermore, a Radon transform g(θ,ρ) of a square segment of this profile is defined, the range of which is normalized to values ​​between 0 and 1, where θ describes the angle and ρ describes the distance from the origin. Additionally, the Radon transform g(θ,ρ) is factored in the ρ direction. Symmetrically shortened. In this case, for any angle θ, the standard deviation σ of the Radon transform... ρ (θ) and the value of the Radon transform Defined. Here. It is the average of all g(θ,ρ) for the corresponding angle θ, and σ max It is the maximum standard deviation, σ min It is the minimum standard deviation, and It is the average of the standard deviations, and These are the values The maximum value, each value Minimum and values The average value. Additionally, parameter A is defined as... In this case, the profile has parameter A < 1.0, preferably < 0.9, and particularly preferably < 0.7.

[0010] The statement "Furthermore, the Radon transform g(θ,ρ) in the ρ direction by a factor" is also included. "Symmetrically shortened" here means that in the Radon transform, only the following points g(θ,ρ) are considered, which are at a distance of 0 from the origin. ρ max This is the maximum distance from the origin. This is necessary to prevent edge effects caused by square segments from the profile or by the square shape of the original surface topography map.

[0011] This approach offers the following advantages: such sliding elements significantly facilitate the hydrodynamic pressure buildup between the sliding element and the supported machine component, and simplify the exit from static friction, boundary friction, and mixed friction states, or reduce the duration of operation in these states. This is achieved by structuring such a profile so that it provides numerous hydrodynamic wedge-shaped surfaces at the microscopic level, especially in comparison to machined sliding surfaces.

[0012] In an advantageous embodiment of the invention, the profile is defined in an orthogonal xyz coordinate system, wherein the length dimension of the sliding element is described on the x-axis, the width dimension of the sliding element is described on the y-axis, and the thickness dimension of the sliding element is described on the z-axis. In this case, the dimension representing the thickness dimension of the sliding element can be, for example, the geometric thickness dimension of the surface topography, or it can be the grayscale value of the surface topography. Other representative dimensions or parameters may also be considered.

[0013] In an advantageous embodiment of the invention, the dimension representing the thickness of the sliding element is specified as the grayscale value of the surface topography of the coating of the sliding element of a specific size and positioning depth. Here, the determination of parameter A can be performed as follows: the surface topography is corrected around outliers and unmeasured points in a first step, and then a plane that can be described by a quadratic polynomial is subtracted to correct the background. The standard deviation σ is then determined... ρ(θ) Sum Previously, the Radon transform g was corrected as follows: BG(θ,ρ) A modified image with the same size and bit depth as the surface topography image is generated, wherein the grayscale value of each pixel is randomly distributed. Subsequently, a Radon transform of this modified image is formed, and the modified Radon transform g*... BG(θ,ρ) It is calculated on it, in the manner of transforming g from Radon. BG(θ,ρ) Subtract the Radon transform from the corrected graph. Finally, using the corrected Radon transform g* BG(θ,ρ) Achieve standard deviation σ ρ(θ) Sum The determination.

[0014] When determining parameter A on a surface topography map recorded using confocal imaging, the resolution in a plane (where the normal to the sliding surface is parallel to the normal) needs to be less than 1 / 5 of that of structures, especially fringes, produced by machining. Furthermore, the test points need to be large enough to contain at least 10 such machined structures, especially fringes. The resolution in the direction parallel to the direction orthogonal to the sliding surface needs to be less than 50 nm. These data still apply to structures beneath the coating, even if the machined structure is completely or partially obscured by a coating.

[0015] In an advantageous embodiment of the invention, the outer surface of the base layer has a parameter A > 1 and an arithmetic mean roughness Ra of at least 1 μm. Surfaces with parameter A > 1 are disadvantageous in terms of hydrodynamic pressure configuration because the profile is configured such that the number of microscopic hydrodynamic wedges is reduced compared to surfaces with parameter A < 1. Examples of surfaces with A > 1 include the surfaces of machined or drilled components. In a possible embodiment of the invention, the outer surface of the base layer with A > 1 is thus masked by covering it with a profile having a parameter A < 1.0, preferably < 0.9, particularly preferably < 0.7. This has the advantage that, in addition to other tribologically advantageous properties of the coating, the hydrodynamic pressure configuration of the sliding element is significantly improved.

[0016] In an advantageous embodiment of the invention, parameter A < 1.0, preferably < 0.9, particularly preferably < 0.7, is achieved solely through microscopic irregularities on the outer surface of the coating, and the coating has a macroscopically uniform thickness. Here, macroscopically uniform thickness means that the coating is of uniform thickness, taking into account microscopic irregularities or roughness on the outer surface of the coating or base layer, and taking into account possible process errors during coating application. Accordingly, the parameter is thus affected solely by microscopic irregularities on the outer surface of the coating, and not by intentional macroscopic variations in the coating thickness.

[0017] In an advantageous embodiment of the invention, the outer surface of the coating has an arithmetic mean roughness value Ra according to standard DIN EN ISO 4287, selected from a range having a lower limit of 0.1 μm and an upper limit of 15 μm. This has the advantage that such roughness characteristics, combined with a profile having a parameter A < 1.0, provide numerous microscopic hydrodynamic wedge surfaces and microscopic oil reservoirs of advantageous dimensions, and thus enable particularly rapid exit from tribologically unfavorable operating conditions.

[0018] In an advantageous embodiment of the invention, the coating is configured as a polymer-based layer, particularly as a layer based on polyimide, polyamide, polyamide-imide, polyetherketone, or polyhalogenated olefin, especially PTFE, or mixtures thereof. Here, the base layer is made of a material selected from the group consisting of: aluminum-based alloys, copper and copper-based alloys, bismuth-based alloys, tin and tin-based alloys, silver and silver-based alloys, and zinc-based alloys.

[0019] In particular, polymer coatings with imide groups exhibit improved wear resistance and reduced fracture tendency in this case. Layers based on polyetherketones or polyhalogenated olefins, such as PTFE, have the advantage of particularly good lubrication in low-speed applications.

[0020] To create a polymer-based layer, a dispersion is typically produced using a dispersant, particularly an organic solvent or solvent mixture, from individual components—the polymer precursor, possibly lubricant particles, possibly metal oxide particles, and perhaps possibly hard material particles. This dispersion is then applied to the surface to be coated using methods common in paint technology, such as splattering, brushing, or immersion.

[0021] To form a polymer-based layer with parameter A < 1.0, the solvent or solvent mixture used, as well as the temperature of the substrate or the surface to be coated, are particularly crucial. In the case of a PAI (polyamide-imide) based layer, advantageous solvent mixtures include NMP, NEP, NBP, GBL, DSMO, or DMF, mixed with one or more of the following highly volatile co-solvents: xylene, cyclohexane, n-hexane, solvent oil, naphtha, propanol, n-butanol, isobutanol, or butanediol. An advantageous mixing ratio between the solvent and co-solvent is, in this case, a solvent share between 70% and 90% by mass and a co-solvent share between 10% and 30% by mass. Besides parameter A, the mixing ratio can also affect, for example, the resulting surface roughness. Furthermore, a suitable substrate temperature for the PAI-based layer is between 70°C and 80°C. According to the invention, the substrate is, in this case, a base layer, upon which the coating is applied.

[0022] In another advantageous embodiment of the invention, the coating is applied by pulsed laser deposition or suspension plasma spraying. In this case, the base layer is made of a material selected from the group consisting of aluminum-based alloys, copper and copper-based alloys, bismuth-based alloys, tin and tin-based alloys, silver and silver-based alloys, and zinc-based alloys. These two manufacturing methods are particularly suitable for producing profiles with parameter A < 1.0. Suspension plasma spraying has the additional advantage of allowing for the segregation of finer microstructures by supplying powder as a suspension body, which improves the tribological properties of the coating. Both methods can also, in particular, produce coatings with fine columnar microstructures, which can influence the stress distribution in the tribological contact area and the deformation of the coating under heavy loads.

[0023] In an advantageous embodiment of the invention, the sliding element is, in this case, a sliding element in a wind turbine transmission configured as a planetary gear transmission. Improving the pressure build-up in such a sliding bearing is particularly important because the loads occurring in this type of bearing are typically high, and the rotational speed can vary drastically during operation depending on the prevailing wind conditions.

[0024] In an advantageous embodiment of the invention, the sliding element achieves good tribological properties under critical mixed friction conditions, static friction conditions, and boundary friction conditions. Here, the sliding element has a coefficient of kinetic friction of <0.04, preferably <0.03, and particularly preferably <0.02. Additionally, in the tribological test used to determine the wear height, the wear height is a maximum of 50 μm, preferably a maximum of 20 μm, and particularly preferably a maximum of 10 μm.

[0025] By definition, to determine the coefficient of dynamic friction, tests were conducted on the ring on the disk under key mixed friction, static friction, and boundary friction conditions, with low sliding speeds and high loads. The test procedure was structured as follows: an initial entry phase lasting 7200 seconds (2 hours) with a sliding speed of 0.2 m / s and a load of 20 MPa (expressed as pressure per unit area in MPa); subsequently, the sliding speed changed linearly at a rate of 0.025 m / s. 2 The speed was reduced to 0.02 m / s, and the load was continuously increased over 2800 seconds (at a rate of change of approximately 0.0179 MPa / s) until a load of 70 MPa was reached; then, the load was kept constant at this value. This test range (sliding speed of 0.02 m / s at a load of 70 MPa) was maintained for 7200 seconds, and the average value of the dynamic friction coefficient for the last 1800 seconds was determined accordingly. The test temperature was 60°C, and Amsoil Power Transmission EP Gear Lube ISO-320 was used as the lubricant. For the test, a WAZAU-Tribometer, model TRM 1000, was used. By definition, to determine the friction height, the ring-on-disk test was performed at low sliding speed and high load under key mixed friction conditions, static friction conditions, and boundary friction conditions. The test procedure was as follows: starting from an initial sliding speed of 0 m / s, the sliding speed was linearly increased at 1 / 20 m / s. 2 Increase the sliding speed until it reaches 1 m / s, maintain this speed for 20 seconds, and then immediately reduce the sliding speed to 1 / 20 m / s. 2The sliding speed was linearly decreased until it reached 0 m / s. This 0 m / s sliding speed was maintained for 20 seconds, and then the test cycle was repeated. Throughout the test cycle, the load was kept constant at 10 MPa. The test cycle was repeated a total of 2000 times, corresponding to a sliding stroke of 90,000 m. The test temperature was 60°C, and Amsoil Power Transmission EP Gear Lube ISO-320 was used as the lubricant. For the test, a WAZAU-Tribometer, model TRM 1000, was used. The friction height was determined optically using a Leica DCM8 optical 3D surface treatment system. The friction height was determined at four locations on the specimen, each staggered by 90°. Measurements were taken on two surfaces, with one measurement area located within the area of ​​maximum wear (“wear grave”) and the second measurement area outside the “wear grave”. The height difference between the surfaces was then determined. Such tribological testing is common for technicians, and characteristic values ​​are usually determined on different specimens.

[0026] According to one particular embodiment, a method for manufacturing a sliding element is specified, the method comprising the following steps:

[0027] - Provide sliding elements with a machined base layer;

[0028] - Apply a coating to the outer surface of the base layer to manufacture the sliding element according to claim 1. Attached Figure Description

[0029] The invention is explained below in a non-limiting manner with reference to preferred embodiments.

[0030] The attached image is as follows:

[0031] Figure 1 The sliding element, in the form of a half-shell, is shown in a perspective view.

[0032] Figure 2 A sliding element shown in the planetary gear transmission of a wind power device.

[0033] Figure 3 The evaluation of parameter A is shown when comparing a sliding element with a machined sliding surface to a sliding element having a coating according to the invention. Detailed Implementation

[0034] exist Figure 1 The image shows one embodiment of the sliding element 1 in a perspective view. The sliding element 1 here comprises a support 2, a base layer 3, and a coating layer 4. Figure 1The sliding element 1 has a semi-shell shape. This semi-shell can be combined with another semi-shell to form a sliding support device. The two semi-shells can be constructed identically or differently. However, it is also possible for the sliding element 1 to be constructed as a third shell, etc. In this case, the sliding element 1 is combined with a corresponding number of other sliding elements to form a sliding support device. The support body 2 is made of a metallic material, usually steel, but can also be made of a material capable of achieving the same or similar function (i.e., providing mechanical strength to the sliding element 1). For example, various different copper alloys such as brass and bronze can also be used. However, within the scope of the invention, direct coating of components (e.g., the eyelets of the connecting rod) is also possible. In this case, the support body 2 is constructed by the corresponding component itself. The base layer 3 is constructed of a bearing metal alloy. Such bearing metal alloys are known in the prior art. For example, the bearing metal alloy can be made of materials selected from the following set, which includes: aluminum-based alloys, copper and copper-based alloys, bismuth-based alloys, tin and tin-based alloys, silver and silver-based alloys, and zinc-based alloys. Although in Figure 1 The sliding element 1 is described as a three-layer bearing element, but it may also have fewer or more layers than three. For example, coating 4 can be applied directly to support 2, in which case support forms the base layer according to the invention. Similarly, a typical intermediate layer, such as at least one connecting layer or at least one diffusion barrier layer, may be provided as needed. The at least one connecting layer may be provided between support 2 and base layer 3 and / or between base layer 3 and coating 4. The at least one diffusion barrier layer may be provided between support 2 and base layer 3 and / or between base layer 3 and coating 4. Coating 4 may in this case be configured as a polymer-based layer having solid lubricant particles and / or metal oxide particles, but may also be configured as a metal coating, a ceramic coating, or a composite coating. Possible solid lubricants have long been known from the prior art for this application.

[0035] Figure 2The transmission device 5 of the wind power equipment is shown. This transmission device has a sun gear 6, which is torsionally connected to a shaft 7 leading to a generator rotor or other transmission stage (not shown). The sun gear 6 is surrounded by a plurality of planetary gears 8, for example two, preferably nine or fewer. Not only the sun gear 6 but also the planetary gears 8 have teeth 9 and 10 that are meshed together. Each planetary gear 8 is supported on a shaft 11 formed by planetary pins, which is called a planetary shaft. These shafts 11 can be either integrally formed with at least a portion of a planet carrier 12 or mounted as separate components into bores in the planet carrier 12. A gear ring 13 is provided on each planetary gear 8, which also has at least partially teeth 14 on its inner surface that are meshed with the teeth of each planetary gear 8. The gear ring 13 is torsionally connected to the rotor shaft 15 of the wind power equipment rotor. Each tooth 9, 10, and 14 is configured as a helical tooth.

[0036] One possible embodiment for arranging the sliding element 16 is as a bearing sleeve, which is torsionally connected to a planetary gear 8, for example by press fit or by other suitable methods. However, another possible embodiment is that the sliding element 16 is disposed directly on the shaft 11, in the region of the support of the planetary gear 8, and / or directly on the planetary gear 8 itself, in the region of the bore receiving the planetary pin. Other arrangements of the sliding element that are familiar to those skilled in the art are, of course, also conceivable.

[0037] Figure 3 The evaluation of parameter A is shown in box plot form. Figure 3.1 relates to a sliding element with a coating according to the invention, the parameter A of which is < 1.0; therefore, hydrodynamic pressure construction is facilitated due to the presence of numerous microscopic hydrodynamic wedges. Conversely, Figure 3.2 relates to a sequence of measurements consisting of metal-machined sliding surfaces without the coating according to the invention, having a parameter A > 1.0. Machining here includes, for example, grinding, turning, or precision drilling.

Claims

1. A sliding element having a base layer and a coating disposed on an outer surface of the base layer, the profile being defined such that the profile forms the outer surface of the coating, and a Radon transform g(θ,ρ) of a square segment of the profile being defined, the Radon transform being normalized to values ​​between 0 and 1, where θ describes an angle and ρ describes the distance from the origin, and the Radon transform g(θ,ρ) is factored in the ρ direction. Symmetrically shortened, and for any angle θ, the standard deviation σ of the Radon transform... ρ (θ) and the value of the Radon transform Defined, where, It is the average value of all g(θ,ρ) for the corresponding angle θ, and σ max σ min , These are the maximum standard deviation, the minimum standard deviation, and the average of all standard deviations, and... These are the values The maximum value, each value Minimum and values The average value, and the parameter A is defined as A = (σ max - Furthermore, the surface profile has parameter A < 1.0, preferably < 0.9, and particularly preferably < 0.

7.

2. The sliding element according to claim 1, characterized in that, The surface is defined in an orthogonal xyz coordinate system, wherein the length dimension of the sliding element is described on the x-axis, the width dimension of the sliding element is described on the y-axis, and the thickness dimension of the sliding element is described on the z-axis.

3. The sliding element according to claim 2, characterized in that, The dimension representing the thickness of a sliding element is the grayscale value of the surface topography of the coating of a sliding element of a specific size and positioning depth.

4. The sliding element according to any one of the preceding claims, characterized in that, The outer surface of the base layer has a parameter A>1, and the outer surface of the base layer has an arithmetic mean roughness value Ra of at least 1 μm.

5. The sliding element according to any one of the preceding claims, characterized in that, The parameter A of the surface is less than 1.0, preferably less than 0.9, and particularly preferably less than 0.7, achieved solely through microscopic unevenness on the outer surface of the coating, and the coating has a macroscopically uniform thickness.

6. The sliding element according to any one of the preceding claims, characterized in that, The outer surface of the coating has an arithmetic mean roughness value Ra according to standard DIN ENISO 4287, which is selected from a range having a lower limit of 0.1 μm and an upper limit of 15 μm.

7. The sliding element according to any one of the preceding claims, characterized in that, The coating is configured as a polymer-based layer, particularly as a layer based on polyimide, polyamide, polyamide-imide, polyetherketone, or polyhalogenated olefin, such as PTFE, or mixtures thereof; and the base layer is made of a material selected from the group consisting of: aluminum-based alloys, copper and copper-based alloys, bismuth-based alloys, tin and tin-based alloys, silver and silver-based alloys, and zinc-based alloys.

8. The sliding element according to any one of claims 1 to 6, characterized in that, The coating is applied by pulsed laser deposition or suspended plasma spraying, and the base layer is made of a material selected from the group consisting of: aluminum-based alloys, copper and copper-based alloys, bismuth-based alloys, tin and tin-based alloys, silver and silver-based alloys, and zinc-based alloys.

9. The sliding element according to any one of the preceding claims, characterized in that, The sliding element is a sliding element in the wind power equipment transmission device, which is configured as a planetary gear transmission device.

10. The sliding element according to any one of the preceding claims, characterized in that, The sliding element achieves good tribological properties under critical mixed friction conditions, static friction conditions, and boundary friction conditions. To this end, the sliding element has a dynamic friction coefficient of <0.04, preferably <0.03, and particularly preferably <0.02, and in tribological tests used to determine the wear height, the wear height is a maximum of 50 μm, preferably a maximum of 20 μm, and particularly preferably a maximum of 10 μm.

11. A method for manufacturing a sliding element according to claim 1, the method comprising the following steps: - Provide sliding elements with a machined base layer; - Apply a coating to the outer surface of the base layer to create a sliding element.

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