Ceramic Shroud Attachment via Wave Spring and Aft Tabs

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Solution Overview

Problem

Ceramic shrouds in gas turbine engines face challenges due to low ductility and thermal expansion, leading to attachment issues with metallic structures, and existing support methods like elastic springs and tab-and-slot designs suffer from thermal stress and assembly complexities.

Innovation Solution

A ceramic shroud attachment system utilizing a shroud support ring with aft tabs that engage through slots on the ceramic shroud, combined with a wave spring and aft ring, provides controlled preload and minimizes thermal stress through soft metal foils or coatings, allowing for radial growth and maintaining concentricity with the turbine.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If ceramic shrouds are used to control gap and minimize losses, then thermal distortion is reduced and energy loss is minimized, but attachment to metallic structure becomes difficult due to low ductility and thermal expansion mismatch

Engineering Contradiction:

Improveenergy loss from tip clearanceVSAvoidattachment to metallic structure

Core Design Contradiction:

Loss of energyVSEase of manufacture

Solution Approach 1:

A metallic transition piece is introduced as an intermediary between the ceramic shroud and the metallic turbine support case. This transition piece has a ceramic-facing surface that interfaces with the ceramic shroud and a metallic body that interfaces with the metallic support case, thereby mediating the attachment between dissimilar materials with different thermal expansion properties

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The attachment system employs composite construction by combining ceramic material for the shroud portion that interfaces with the ceramic turbine, and metallic material for the support portion that interfaces with the metallic engine structure. This composite approach allows each material to be used in the environment where it performs best

Inventive Principle:

Principle #40Composite materials

2Stability of the object's composition

If tab and slot approach is used to support ceramic shroud, then thermal constraints are minimized allowing free growth, but thermal stress at tabs becomes sufficiently high to cause local damage

Engineering Contradiction:

Improvethermal growth freedomVSAvoidthermal stress at tabs

Core Design Contradiction:

Stability of the object's compositionVSStrength

Solution Approach 1:

The design changes the geometric parameters of the tab and slot interface, specifically making the slots longer in the axial direction and positioning tabs to engage at multiple locations. This parameter change allows the ceramic shroud to expand axially without concentrating stress at single tab locations, reducing thermal stress while maintaining growth freedom

Inventive Principle:

Principle #35Parameter changes

3Force

If axial tabs engage through axial slots in shroud, then support is provided, but assembly becomes difficult and prone to error due to limited access inside turbine support case

Engineering Contradiction:

Improvesupport loadVSAvoidassembly accessibility

Core Design Contradiction:

ForceVSEase of operation

Solution Approach 1:

Instead of assembling the ceramic shroud inside the turbine support case from the interior (which is difficult to access), the metallic transition piece is first attached to the interior surface of the support case, and then the ceramic shroud is assembled to the transition piece from the exterior where access is easier. This inverts the traditional assembly sequence

Inventive Principle:

Principle #13The other way round (Inversion)

4Temperature

If ceramic materials are used for turbine blades and vanes, then high temperature capability is achieved, but large gap between rotor blade tip and shroud results from low thermal expansion

Engineering Contradiction:

Improvehigh temperature capabilityVSAvoidgap between rotor blade tip and shroud

Core Design Contradiction:

TemperatureVSLength of stationary object

Solution Approach 1:

The metallic transition piece and metallic portions of the support structure are designed to undergo thermal expansion that compensates for the low thermal expansion of the ceramic turbine components. As the engine operates and temperatures rise, the metallic components expand to reduce the gap between the rotor blade tip and the ceramic shroud, maintaining optimal clearance

Inventive Principle:

Principle #37Thermal expansion

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 system ensures reliable attachment and reduced thermal stress, maintaining a nearly constant clamp load across engine conditions, enhancing engine performance by minimizing energy loss and assembly errors.

Implementation Method 1

a wave spring positioned adjacent the gasket ring and between the shroud support ring and the aft ring

Methodology Applied

Scientific EffectElasticity: Elasticity

Implementation Method 2

Soft metal foils or coatings may be provided at the aft tabs to reduce thermal stress

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Data Source

PatentEP2543825B1Gas turbine shroud arrangement

Publication Date: 2018.04.04 UNITED TECH CORP

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AI summary

A system for supporting a shroud (18) used in an engine (10) has a shroud (18) positioned radially outboard of a rotor (20), which shroud (18) has a plurality of circumferentially spaced slots (40); a forward support ring (26) for supporting the shroud (18); the forward support ring (26) having a plurality of spaced apart first tabs (36) on a first side for functioning as anti-rotation devices; the forward support ring (26) having a plurality of spaced apart second tabs (38) on a second side; the second tabs (38) engaging the slots (40) in the shroud (18) and circumferentially supporting the shroud (18).