Foil Bearing Trailing Edge Key Design
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Solution Overview
Problem
Thin foil, hydrostatic journal bearings in rotating machinery experience fatigue failure due to non-synchronous, high-cycle loading, particularly at the tight radius of the formed key, leading to cracking and material degradation.
Innovation Solution
A trailing edge key design is implemented in the foil bearing, featuring a large radius anti-rotation tab that sits within a key way, replacing the 180° bend with a dogleg bend to reduce stress risers and prevent excessive foil elongation, thereby enhancing fatigue strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a 180° bend is used to form the anti-rotation key, then the key can be formed in the foil, but the tight radius creates high stress risers and exceeds ultimate elongation, leading to cracking and fatigue failure
Solution Approach 1:
The patent replaces the sharp 180° bend with a dogleg bend configuration that uses larger radii of curvature. This reduces stress concentration at the key formation location by eliminating tight radius bends, thereby preventing cracking while still forming the anti-rotation key in the foil.
2Ease of operation
If the foil is folded into a 180° bend to create the key, then the anti-rotation function is achieved, but the forming operation exceeds ultimate elongation and causes orange peel condition and material degradation
Solution Approach 1:
The dogleg bend configuration uses gradual curves instead of sharp 180° folds, reducing the strain imposed on the foil material during forming. This prevents exceeding ultimate elongation and avoids orange peel condition, maintaining material integrity and fatigue strength while achieving anti-rotation functionality.
3Ease of operation
If a formed key is used for anti-rotation, then the key provides restraint, but the tight radius geometry creates inherent high stress risers that lead to cracking under high-cycle loading
Solution Approach 1:
The dogleg bend configuration eliminates tight radius geometry by using larger, gradual curves in the key formation. This removes the inherent stress risers that would otherwise concentrate stress and initiate cracking under high-cycle loading, while still providing the necessary anti-rotation restraint.
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 significantly reduces or eliminates cracking and enhances the load capacity of the foil bearing, making it suitable for environments with high external vibrations or intermittent reverse rotation.
Implementation Method 1
thin foil, hydrodynamic gas bearing
Data Source
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AI summary
A gas bearing within a cylinder is provided. The gas bearing comprises an anti-rotation tab sitting within a key way of the cylinder. Further, the gas bearing comprises a first foil (320) forming an inner loop and an intermediary loop. The inner loop extends in a first direction from a first end (320A) to an intermediary portion (320B). The intermediary loop extends from the intermediary position to the anti-rotation tab.