Sensor Wire Protection via Local Cement Barrier
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Solution Overview
Problem
High-temperature strain gauges and thermocouples on turbomachine parts experience significant oxidation and reduced mechanical resistance due to porous alumina coatings, leading to measurement errors and shortened lifetimes under high-temperature conditions, posing risks to turbo-engine certification and incurring financial losses.
Innovation Solution
Applying an impermeable and thermally insulating cement around sensor wires before a denser alumina cover layer is deposited, to prevent oxidizing atmospheres from reaching the wires and reduce porosity, while maintaining coating ductility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If alumina flame spraying is used to create an electrically insulating coating on the substrate, then electrical insulation is provided and the substrate can bear the gauge, but the coating develops a porous coarse-grained structure that allows oxidizing atmosphere to reach the sensor wires
Solution Approach 1:
The patent applies a denser alumina-based material specifically around the sensor wires to create a localized barrier against oxidation, while the rest of the coating maintains its porous structure for ductility. This local modification provides targeted protection where needed without compromising the overall coating properties.
Solution Approach 2:
The patent uses a composite coating structure combining two types of alumina materials: a standard flame-sprayed alumina coating for general insulation and ductility, and a denser alumina-based material applied locally around sensor wires to prevent oxidation. This composite approach leverages the advantages of both materials.
2Object-affected harmful factors
If a dense impermeable coating is applied to protect sensor wires from oxidation, then oxidation resistance is improved, but the coating loses ductility needed for hot deformation of the instrumented parts
Solution Approach 1:
The dense alumina-based material is applied only locally around the sensor wires where oxidation protection is critical, while the bulk of the coating retains the porous flame-sprayed structure that provides necessary ductility for hot deformation operations.
Solution Approach 2:
Instead of making the entire coating dense (which would eliminate ductility), the patent applies the denser material partially and locally only where oxidation protection is most needed, achieving sufficient protection without excessive densification of the whole coating.
3Ease of manufacture
If standard flame spraying is used to deposit alumina coating, then the coating process is simple and fast, but microcracks and pores form that connect to the sensor wires and allow oxidizing atmosphere penetration
Solution Approach 1:
The patent applies the denser alumina-based material around the sensor wires before the final flame-sprayed alumina coating is deposited. This preliminary protective layer ensures that even if microcracks and pores form during subsequent coating processes, the sensor wires remain protected from oxidation.
Solution Approach 2:
The denser alumina-based material serves as a preliminary barrier that cushions the sensor wires against the harmful effects of oxidation that would otherwise occur through microcracks and pores in the flame-sprayed coating. This prior protection prevents oxidation before it can penetrate through the porous structure.
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 increases the lifetime of sensors and stabilizes their electrical properties during high-temperature trials, minimizing measurement errors and mechanical stress, thus ensuring reliable turbo-engine certification.
Implementation Method 1
an impermeable and thermally insulating cement is applied locally on connection wires of said sensor so as to encapsulate the wires of the sensor
Implementation Method 2
an impermeable and thermally insulating cement is applied locally on connection wires of said sensor
Implementation Method 3
depositing, by alumina flame spraying, an electrically insulating sublayer on the substrate
Implementation Method 4
depositing, by alumina spraying, an electrically insulating sublayer on said substrate
Implementation Method 5
the alumina layers have a porous coarse-grained structure, which gives the coating a ductility suitable for hot deformation
Implementation Method 6
the alloy of commercially available gauges is strongly oxidized
Data Source
AI summary
The method consists in depositing, by alumina spraying, an electrically insulating sublayer on the substrate, then in placing the sensor on the electrically insulating sublayer and finally in depositing, by alumina spraying, a cover layer on the sensor and the electrically insulating sublayer. It further includes, before the cover layer is deposited, a step in which an impermeable and thermally insulating cement is applied locally on wires of the sensor.