Abstract
The contact behavior of an abradable coating (Al-Si 6%) and a labyrinth seal tooth (stainless steel) in a turbo-engine application was studied as a function of the incursion depth parameter, during labyrinth seal/abradable interaction. A controlled and a gradual increase of the labyrinth seal incursion (by step of 50 μm) is performed to obtain the chronological contact evolution under severe operating tribological conditions. The labyrinth seal/abradable contact experiments were conducted on a dedicated test rig able to reach high contact speeds from 0 to 130 m.s−1. To complete contact forces measurement during tests, a suitable instrumentation (acoustic emission sensor, accelerometer, thermocouples, etc.) is developed and coupled as close as possible of the interaction area. The experimental results from the both severe tribological conditions are presented by an analysis of signals recorded during contact tests. Macrographic and micrographic rub-groove observations of post tests samples, coupled with recorded signals from the contact complete the Al-Si 6% behavior study. A wear process description using the third body approach has been proposed to sum up the whole tribological results. Two different varieties of particles production have been identified; a ductile and an adhering layer on the rub-groove bottom and pulverulent fine powder particles, thus providing two different kind of third body and two different material flows.
Highlights
Additional experiments developed by Sulzer Innotec and Sulzer Metco [19] use a specific test rig adapted to the application of labyrinth/abradable interactions which consists of an alloy disc that accommodates four continuous seal trips on the outer circumference, a movable specimen coated with an abradable material and a heating device
The Al-Si 6% abradable coating behavior, depending on the incursion depth, is first studied by a recorded signals analysis from the different sensors fitted on the test rig
A single contact forces variation is composed of a fast increase up to a maximum followed by a decrease generating contact instabilities between the labyrinth seal tooth and the Al-Si 6% abradable coating
Summary
Acoustic Emission Abradable flow, mm3.s−1 Incursion depth, μm Feed-rate, mm.rev−1 Fast Fourier Transform Normal force component, N Tangential force component, N Test series No 1 rotational frequency, Hz Test series No 2 rotational frequency, Hz Rubbed length, mm Number of labyrinth seal rotation, rev Internal radius of the tube coated with abradable, mm Radius of the labyrinth seal tooth, mm Short-Time Fourier Transform Interaction time, s Labyrinth seal incursion speed, mm.s−1 Labyrinth seal rotational speed, rpm Labyrinth tip speed, m.s−1 Contact angular length, rad Friction coefficient Mechanical clearance, μm Labyrinth seal angular velocity, rad.s−1 non-metal phase that provide a high porosity rate and offer a good balance between the abradability and erosion resistance [6] The use of this type of abradable coating is widespread in other extensively researched turbo-engine applications such as use in blade tips and compressor housing [7, 8] and has encouraged turbo-engine manufacturers to characterize the abradable behavior subjected to rotor-stator interactions. A third body approach was considered for a more complete description of the whole wear mechanisms through the concept of tribological circuit
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