Coated Sliding Element Surface for Hydrodynamic Wedge Formation
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Solution Overview
Problem
Existing plain bearings in industrial and energy sectors, particularly in wind turbines, face extreme load cases leading to critical mixed, static, and boundary friction conditions, resulting in increased wear and failure probability due to overload-related damage, as conventional coatings only mitigate symptoms rather than addressing the root cause of unfavorable hydrodynamic conditions.
Innovation Solution
A sliding element with a base layer and a coating on its outer surface is designed to enhance hydrodynamic pressure build-up by structuring the surface to create numerous microscopic hydrodynamic wedge surfaces, utilizing a Radon transform to define a parameter A that ensures optimal surface roughness and symmetry, promoting efficient transition from static to fluid friction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional coatings are applied to sliding elements, then wear resistance is improved, but the root cause of unfavorable hydrodynamic conditions is not addressed
Solution Approach 1:
The coating surface is segmented into numerous microscopic wedge-shaped structures instead of being smooth or uniformly textured. These micro-wedges are created by controlling the solidification process of a molten coating layer, which naturally forms a segmented pattern of ridges and valleys. This segmentation provides multiple hydrodynamic wedge surfaces that actively generate pressure to separate bearing surfaces, addressing the root hydrodynamic problem while maintaining wear resistance.
Solution Approach 2:
The invention changes the surface geometry parameters by creating micro-wedges with specific dimensional ratios (width to height between 2:1 and 10:1). This parameter change transforms the coating from a passive wear-resistant layer into an active hydrodynamic pressure-generating structure. The controlled solidification process parameters (cooling rate, substrate temperature, coating thickness) are also changed to achieve the desired wedge morphology.
2Ease of manufacture
If mechanically machined sliding surfaces are used, then manufacturing is simplified, but hydrodynamic pressure build-up is reduced due to fewer microscopic wedge surfaces
Solution Approach 1:
The invention replaces mechanical machining processes with a thermal processing approach. Instead of using cutting tools or abrasives to create surface textures, a coating material is applied in molten or semi-molten state and then controlled to solidify into the desired wedge pattern. This substitution eliminates complex machining operations while naturally forming the hydrodynamic micro-wedge structures through thermal gradients and solidification physics.
Solution Approach 2:
The coating material undergoes a phase transition from liquid or semi-liquid state to solid state during the surface treatment process. As the molten coating solidifies on the substrate, it naturally forms wedge-shaped structures due to heat dissipation patterns and surface tension effects. This phase transition approach creates the hydrodynamic micro-wedges without requiring mechanical intervention, simplifying manufacturing while ensuring reliable hydrodynamic pressure build-up.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The designed surface significantly improves hydrodynamic pressure build-up, reducing wear and failure probability by quickly exiting tribologically unfavorable conditions, achieving a dynamic coefficient of friction < 0.04 and wear height < 10 µm under critical mixing and boundary friction conditions.
Implementation Method 1
a Radon transform g(θ,ρ) of a square segment of this shaped surface is defined, the range of values of which is normalized to values between 0 and 1
Implementation Method 2
the rotation of the shaft creates a hydrodynamic pressure distribution in the lubricant, which counteracts the external bearing force
Implementation Method 3
Above the minimum rotational speed lies the range of the plain bearing in which only fluid friction occurs, and therefore there is practically no wear
Data Source
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AI summary
The invention relates to a sliding element with a base layer and a coating provided on an outer surface of the base layer, wherein a shaped surface is defined such that it represents an outer surface of the coating, and wherein a Radon transform g(θ,ρ) of a square section of this shaped surface is defined, the range of values of which is normalized to values between 0 and 1, and wherein θ represents the angle and ρ the distance to the origin of the coordinate system, and wherein the Radon transform g(θ,ρ) is reduced in the ρ-direction by a factor of 1/√2, and wherein for each angle θ a standard deviation of the Radon transform σρ(θ) and a value (θ) = Σρ |g(θ,p )- g| the Radon transform is defined, where g is the mean of all g(θ,ρ) of the respective angle θ, and where σmax, σmin, σ , is the maximum standard deviation, the minimum standard deviation and the mean of the standard deviations, and , , is the maximum of the values ,the minimum of the values and the mean of the values is , and where a parameter A is defined as A = (σmax-σmin)/σ * ()/().,