Frontal Link Nut Unscrewing in Twin-Spool Turbine Overhaul
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Solution Overview
Problem
The existing methods for dismantling gas turbine engines, particularly removing the nut connecting the high-pressure rotor to a bearing in a twin-spool, front-fan turbine, are challenging due to the central location and inaccessibility of the nut, leading to potential damage or the need to cut the nut, which contaminates nearby gearing.
Innovation Solution
A method involving prior heating of the nut to soften coked oils and allow differential expansion, followed by using a tubular wrench with complementary teeth to unscrew the nut from the front of the engine without engaging the nearby gearing, utilizing a support and anti-rotation tool to prevent rotor rotation and apply controlled torque.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the standard procedure is used to unscrew the connecting nut via the central passage, then access to the nut is possible, but the torque that can be applied is limited and the nut may not be loosened
Solution Approach 1:
The tool is divided into two separate functional components: a wedge for immobilizing the rotor and a tubular wrench for unscrewing the nut. This segmentation allows each component to be optimized for its specific function while working together to solve the overall problem of nut removal with sufficient torque.
Solution Approach 2:
The tool transitions from accessing the nut through the central passage (one-dimensional approach) to accessing it from the front of the engine (different spatial dimension). This allows the application of much higher torque through a frontal approach rather than being constrained by the central passage geometry.
2Force
If the fan and low-pressure compressor are removed to access the nut from the front, then larger torque can be applied, but the procedure becomes more complex and time-consuming
Solution Approach 1:
The wedge is inserted and positioned in advance to immobilize the rotor before the unscrewing operation begins. This preliminary action ensures that the rotor remains stationary during torque application, enabling effective unscrewing without requiring removal of surrounding components.
Solution Approach 2:
The wedge acts as an intermediary device between the rotor and the unscrewing tool. It mediates the interaction by providing a reliable immobilization mechanism that allows the tubular wrench to apply high torque without causing rotor rotation or requiring disassembly of the fan and compressor.
3Productivity
If the connecting nut is cut when it cannot be unscrewed, then removal is achieved, but the nut must be replaced and nearby gearing is contaminated
Solution Approach 1:
The tubular wrench is designed with teeth that complement the nut's teeth shape, providing gradual engagement and torque application. This cushioning approach prevents sudden failures or damage to the nut teeth, allowing controlled unscrewing without resorting to cutting that would contaminate the surrounding gearing.
4Strength
If maximum permitted torque is applied to prevent nut deformation, then the nut is protected from damage, but the torque may be insufficient to loosen seized nuts
Solution Approach 1:
The invention replaces the conventional approach of applying torque through the central passage with a frontal application mechanism. The tubular wrench positioned at the front of the engine can apply substantially higher torque forces while maintaining proper engagement with the nut teeth, overcoming seizure without exceeding deformation thresholds.
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
This method reduces the risk of damaging the nut's teeth and eliminates the need to engage the IGB gearing, allowing successful unscrewing without cutting the nut, thus avoiding contamination and ensuring efficient dismantling.
Implementation Method 1
prior step of heating the nut and introducing a tool for unscrewing the latter along the axis of the engine. Prior heating to a moderate temperature makes it possible to soften the coked oils gluing together the thread of the connecting nut and that of the journal and also to allow a differential expansion between the cylindrical elements in contact with one another
Data Source
AI summary
A method for unscrewing a link nut of an HP rotor of a twin-spool turbine, including a front fan, an intermediate casing, a HP module with a HP rotor, and a LP turbine module, the intermediate casing including a support bearing for the HP rotor, the rotor being retained in the bearing by the link nut, the method including: placing an unscrewing tool in front of the link nut after having removed the fan and released access to the nut from the front; with rotation of the HP rotor locked and the frontal unscrewing tool including a socket spanner including teeth having a shape that complements that of teeth of the link nut, attaching a mounting for the socket spanner to the intermediate casing, the socket spanner being rotatably mounted on the mounting, and applying an unscrewing torque to the socket spanner. An unscrewing tool implements the method.