Ceramic Bushing with Metal Jacket for Turbomachine Vane Pivots
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Solution Overview
Problem
Ceramic bushings used in turbomachines for variable-pitch vane systems face issues due to brittleness and low toughness, leading to breakage during mounting and operation, exacerbated by differences in expansion coefficients and shock absorption, particularly under vibrational stress and peening pressure.
Innovation Solution
A ceramic bushing design featuring a metal jacket with a brazed ceramic ring, which provides structural strength and accommodates expansion differences, and includes a ceramic washer for dry friction, enhancing the ceramic/metal bond flexibility and strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a ceramic bushing is used for a variable-pitch vane system, then wear resistance and dry lubrication performance are improved, but brittleness and low toughness lead to breakage during mounting and operation
Solution Approach 1:
The bushing is constructed as a composite structure with a ceramic ring (alumina or zirconia) bonded to a metal jacket (steel or titanium alloy). This composite design combines the wear resistance and dry lubrication properties of ceramic with the toughness and ductility of metal, resolving the contradiction between wear resistance and toughness by integrating two materials with complementary properties.
2Reliability
If a ceramic bushing is mounted on a metal casing, then wear resistance is improved, but differences in expansion coefficients cause breakage under thermal and vibrational stress
Solution Approach 1:
The metal jacket serves as a transition layer between the ceramic ring and the metal casing, creating a gradient structure that gradually bridges the expansion coefficient difference. This composite approach allows each material to expand at its own rate while maintaining overall structural integrity through the bonded interface.
Solution Approach 2:
The metal jacket acts as an intermediary element between the ceramic ring and the metal casing, mediating the thermal expansion mismatch. The jacket absorbs differential expansion stresses through its own elasticity and ductility, preventing stress concentration at the ceramic-casing interface that would lead to breakage.
3Reliability
If a ceramic bushing is used in a variable-pitch system, then dry lubrication is achieved, but brittleness leads to breakage under peening pressure and shock
Solution Approach 1:
The ceramic ring provides the dry lubrication surface with low friction and wear properties, while the metal jacket provides shock and peening resistance. The composite structure allows the ceramic to function in its optimal dry lubrication mode while the metal absorbs impact energies that would otherwise cause ceramic failure.
Solution Approach 2:
The metal jacket serves as a pre-positioned cushioning layer that absorbs and dissipates shock and peening pressures before they reach the ceramic ring. This protective envelope prevents sudden impact loads from causing brittle failure of the ceramic component.
4Reliability
If a ceramic bushing is mounted in a through orifice, then wear resistance is improved, but mounting shocks cause breakage
Solution Approach 1:
The metal jacket provides mechanical strength and ductility that enable the bushing to withstand mounting insertion forces and shocks. The ceramic ring can be mounted within the protective jacket, which absorbs mounting stresses and prevents breakage during installation into the through orifice.
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 breakage and wear by providing a stronger, more flexible ceramic/metal bond, effectively addressing the brittleness and expansion coefficient issues, while maintaining dry lubrication for improved part longevity.
Implementation Method 1
a ceramic ring (16) secured by brazing to the inside wall (11a) of the jacket
Implementation Method 2
the brazing acts as an interface between two materials having different expansion coefficients and serves to accommodate differences in expansion
Implementation Method 3
Only dry lubrication can be envisaged for improving contact conditions and for increasing the lifetime of the parts
Implementation Method 4
with the oxides of iron, nickel, or cobalt that are created during continuous contact between the vane pivot and the smooth bearing, acting as a lubricant
Implementation Method 5
it further carries an insert ring constituted of a metal material based on iron, nickel, or cobalt, and shrink-fitted onto the pivot
Data Source
AI summary
The invention relates to a ceramic-based bushing for mounting in a turbomachine casing to provide a smooth bearing for a pivot of a variable-pitch vane. The bushing is constituted by a metal jacket and a ceramic ring secured to the inside wall of said jacket by brazing. The invention also provides a turbomachine compressor having variable-pitch stator vanes with pivots mounted in the casing by means of such bushings.