Removable Borescope Plug for Gas Turbine Thermal Expansion

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Solution Overview

Problem

Existing borescope plugs for gas turbine engines face issues such as cracking, bending, buckling, and installation difficulties due to thermal growth and expansion, leading to leakage and increased complexity and cost.

Innovation Solution

A borescope plug configuration that includes a removable plug with radial movement capability through bushings, allowing for thermal expansion compensation and reducing erosion wear, while also providing structural load-bearing functionality and access for inspection.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a solid borescope plug is used to seal the inspection path, then leakage is minimized, but the plug is limited in movement and must be located near the center of thermal growth locations to minimize deflection, leading to cracking and bending

Engineering Contradiction:

Improvesealing effectivenessVSAvoidplug integrity

Core Design Contradiction:

ReliabilityVSStrength

Solution Approach 1:

The plug is divided into multiple sections: a fixed portion anchored in the outer case and a movable portion that can move radially and axially. This segmentation allows the movable portion to accommodate thermal growth while the fixed portion maintains sealing effectiveness, resolving the contradiction between sealing and structural integrity.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The plug transitions from a static solid structure to a dynamic system where the movable portion can adjust its position in response to thermal expansion. The spring mechanism enables the plug to dynamically adapt to changing dimensional conditions while maintaining both sealing and structural integrity.

Inventive Principle:

Principle #15Dynamics

2Adaptability or versatility

If a flexible borescope plug with spring or thin section is used to allow radial or axial movement, then thermal growth is accommodated, but cracking, bending, buckling, and installation and withdrawal difficulties occur

Engineering Contradiction:

Improvethermal expansion accommodationVSAvoidplug structural integrity

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The plug is segmented into fixed and movable portions, with the movable portion containing the spring mechanism. This allows controlled flexibility for thermal accommodation while the segmented structure prevents uncontrolled bending and buckling that occur in fully flexible designs.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The spring acts as an intermediary element between the fixed and movable portions, providing controlled elasticity. This intermediary mechanism enables thermal accommodation through controlled deformation rather than uncontrolled bending, preventing cracking and buckling while maintaining structural integrity.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Device complexity

If the removable plug is made structural to provide load-bearing functionality, then part count is reduced and cost is decreased, but the plug must withstand thermal transitions and erosion wear

Engineering Contradiction:

Improvepart countVSAvoiderosion wear and thermal stress

Core Design Contradiction:

Device complexityVSObject-affected harmful factors

Solution Approach 1:

The material properties of the plug are optimized to withstand thermal transitions and erosion wear. The plug is made from high-temperature resistant materials with appropriate mechanical properties that maintain strength under thermal stress while resisting erosion, enabling the structural plug to survive in the harsh environment.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The spring mechanism provides beforehand cushioning by absorbing thermal stresses before they can cause damage to the plug structure. This pre-compression system allows the plug to withstand thermal transitions without experiencing damaging stress concentrations that would lead to failure.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

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 seals the inspection path, reduces part count, and enhances reliability and cost-effectiveness by allowing radial movement and structural load transfer, addressing the limitations of prior art borescope plugs.

Implementation Method 1

due to the very high temperatures at which gas turbine engines operate, the engine casings undergo thermal growth and expansion

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Data Source

PatentEP2831378B1Dual-intent locator pin and removable plug for gas turbines

Publication Date: 2018.10.31 UNITED TECH CORP

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AI summary

A borescope plug configuration is disclosed. The borescope plug configuration comprises an inspection path defined through a bore in a first engine structure, a second engine structure, and an opening into the gas path of an engine. The borescope plug configuration further comprises a removable plug for sealing the inspection path. The removable plug is adapted to couple the first engine structure to the second engine structure.