Gas Turbine MTF Case Boss Sealing Interface Design
Solution Overview
Problem
The Mid-Turbine Frame (MTF) assembly in gas turbine engines faces challenges due to high thermal and pressure stresses from combustion gases, leading to potential failure and the need for frequent replacement of the inner MTF case, particularly due to the high diametric tension experienced by tie rods and service lines.
Innovation Solution
The proposed solution involves a case assembly with a thicker peripheral wall case boss to maintain acceptable stress levels, including a raised boss with a machined surface and a bushing system that allows for the enlargement of the inner diameter to accommodate a piston seal, enabling a sealed interface and reducing the need for full case replacement through reworking methods like inserting a bushing or applying a coating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If the inner MTF case is designed with a thin peripheral wall to minimize weight, then the weight of the case is reduced, but the case cannot withstand the high thermal and pressure stresses from combustion gases, leading to frequent failure and replacement
Solution Approach 1:
The patent applies local quality by making the peripheral wall of the case boss thicker only in the specific region where the piston seal interfaces, rather than thickening the entire case. This localized thickening provides the necessary stress resistance at the critical sealing interface while maintaining lightweight construction in other areas of the case.
2Reliability
If the inner MTF case is designed with a thick peripheral wall to withstand high stresses, then the reliability under thermal and pressure stresses is improved, but the weight of the case increases significantly
Solution Approach 1:
The patent applies local quality by making the peripheral wall of the case boss thicker only in the specific region where the piston seal interfaces, rather than thickening the entire case. This localized thickening provides the necessary stress resistance at the critical sealing interface while maintaining lightweight construction in other areas of the case.
3Reliability
If the inner MTF case is replaced completely when wear occurs, then the reliability is restored, but the maintenance time and cost increase due to full case replacement
Solution Approach 1:
The patent applies segmentation by separating the case boss (which experiences wear) from the rest of the case structure. The removable wear ring fits into the case boss, allowing only the worn component to be replaced rather than the entire case. This modular approach reduces maintenance time and cost while restoring reliability.
Solution Approach 2:
The patent applies discarding and recovering by designing the case boss to be reworkable. Instead of discarding the entire case when wear occurs, the case boss can be machined or fitted with a new wear ring, recovering the functional integrity of the sealing interface while discarding only the worn surface layer.
4Ease of repair
If the peripheral wall thickness is increased to allow for reworking and bushing insertion, then the reparability is improved, but the manufacturing complexity and initial cost increase
Solution Approach 1:
The patent applies local quality by concentrating the additional structural features (thicker peripheral wall, bushing insertion capability) only in the case boss region where reworking is needed, rather than complicating the entire case structure. This localized approach improves reparability while minimizing manufacturing complexity.
Data Source
AI summary
A case assembly for a gas turbine engine, includes a case with a case boss, said case boss including a peripheral wall that defines a first inner diameter in a first condition to receive a piston seal, and a second inner diameter in a second condition, the second condition including enlargement of the first inner diameter to form a second inner diameter and a bushing mounted within the second inner diameter, an inner diameter of the bushing defines a bushing inner diameter about equivalent to the first inner diameter to receive the piston seal.