Space Rolling Bearing Coating for Rust and Radial Gap Stability
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Solution Overview
Problem
Rolling bearings used in extremely low-temperature and vacuum environments face issues with radial gap reduction due to differing linear expansion coefficients between steel and ceramic components, leading to impaired rolling motion and rust susceptibility of bearing steel.
Innovation Solution
A space rolling bearing comprising a bearing steel inner ring, martensitic stainless steel outer ring, and ceramic rolling elements, with a ceramic rust-preventive coating applied via aerosol deposition to prevent rust and maintain radial gap stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a coating of solid lubricant is formed on parts to be lubricated, then lubrication is achieved in vacuum environment, but rust prevention is insufficient
Solution Approach 1:
The invention uses a composite coating structure with two distinct layers: a solid lubricant layer (such as MoS2, WS2, or PTFE) for lubrication and a rust-preventive coating layer (such as phosphate, chromate, or organic phosphate conversion coating) for corrosion protection. This composite coating approach allows both lubrication and rust prevention functions to be achieved simultaneously on the bearing steel inner ring surface.
2Object-affected harmful factors
If a typical rust-preventive coating is applied to bearing steel, then rust is prevented, but the heat from coating process anneals the steel and decreases strength
Solution Approach 1:
The invention specifies that the rust-preventive coating process must be conducted at temperatures below the annealing temperature of bearing steel (typically keeping the coating temperature under 150-200°C). This parameter control ensures that the coating provides rust protection without causing thermal annealing that would reduce the steel's strength and hardness properties.
3Stability of the object's composition
If ceramic rolling elements are used with steel rings, then radial gap stability is improved, but rust susceptibility increases
Solution Approach 1:
The invention applies rust-preventive treatment specifically and locally to the bearing steel inner ring surface, while the outer ring can be made of rust-resistant martensitic stainless steel. This localized treatment approach protects the steel components from rust without affecting the ceramic rolling elements, thereby maintaining radial gap stability while preventing corrosion.
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 solution effectively suppresses radial gap fluctuations and prevents rust, ensuring proper rolling motion and lubrication in extreme low-temperature vacuum environments, suitable for space strain wave gearing devices.
Implementation Method 1
a rust-preventive coating formed by aerosol deposition (AD)
Implementation Method 2
bearing steel is susceptible to rust, and it is difficult to prevent bearing steel from rusting, especially when used in space rolling bearings where solid lubrication (powder lubrication) is performed in a vacuum
Implementation Method 3
a gap inside the bearing decreases as the temperature decreases due to the difference in linear expansion coefficient between the steel and ceramic
Data Source
AI summary
A wave bearing of a space strain wave gearing device comprises an inner ring formed from a bearing steel, an outer ring formed from a martensitic stainless steel, and balls formed from ceramics. On the inner ring formed from a bearing steel, a ceramic coating formed by an AD method is formed as a rust-preventive coating. In the space strain wave gearing device that adopts solid lubrication (powder lubrication), it is possible to reliably prevent rust from developing on the inner ring formed from a bearing steel of the wave bearing. In a space environment where the temperature greatly changes, appropriate setting of the linear expansion coefficients of the inner ring, the outer ring, and the balls enables a change in the radial gap of the wave bearing to be suppressed to a range that does not interfere with practical use.