GDR 99 - Airborne Systems

Wear-Debris
Analysis made Easy


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Top: The EDAX Eagle micro-probe EDXRF system is specifically suited to the individual measurement and analysis of larger wear-debris particles

Wear-debris particles provide a very early indication of possible critical wear damage

The EDAX Eagle Micro-Probe EDXRF system provides a fast and simple method for the component identification of wear-debris particles.

Since 1962 EDAX has led the way in the development and supply of elemental analysis instrumentation based on the method of energy-dispersive (X-ray) spectrometry (EDS). The EDS method utilises the simple spectral information produced as a result of electron transitions deep within an atom. These X-ray spectra (so called because of their energy/ wavelength) obtained from a sample under investigation within a suitable analysis instrument, provide unique information about the type and quantity of the elements present. Hence in the case of a metal alloy sample, for example, the resultant spectrum also will provide a fingerprint representation of its composition and thus its identity. EDAX introduced the first commercially available EDS system for electron microscopy applications in 1969 and has been a major supplier of such systems to microscope manufacturers ever since. It is here that EDAX's technical achievements are second to none.

The EDS technique is a familiar elemental analysis attachment to a scanning electron microscope (SEM) where electrons are used as the primary energy source to excite the X-ray spectra. SEM-EDS methods are used for wear-particle analysis for both their morphological and compositional properties, and are particularly useful where the study of very small particles (approximately five microns or less) is necessary. On the other hand, the radiation output from an X-ray tube may also be employed as an energy source. The resultant benefits for systems using an X-ray energy source include greatly simplified specimen handling/presentation needs, less sophisticated instrumentation, simpler and faster operation and lower cost. Such a standalone system is called an energy-dispersive X-ray fluorescence spectrometer (EDXRF), of which the EDAX Eagle is a specialised example.

For over 10 years EDAX EDXRF systems have played a vital role in ensuring the success of the engine-health monitoring programme implemented by British Airways Engineering at London Heathrow and also by South African Airways. As well as the analysis of oil-filter deposits, the technique was used in particular for the analysis of wear-debris particles as collected on magnetic plugs (chip detectors), strategically located in turbine aero-engine scavenge oil lines. Experience has shown that such particles, typically from 50 microns up to a millimetre-plus, provide a very early indication of possible critical wear typical of, for example, ball-bearing raceway failures. The EDAX Eagle is admirably suited to analysis of these particles.

Ease of analysis


The EDS technique is a familiar elemental analysis attachment to a scanning electron microscope

The magnetic plugs are degreased prior to the transfer of the debris on to a clear sticky tape (the traditional method used for debris archiving and/or optical examination). Without the need for any further sample preparation, the tape/debris is presented to the spectrometer for analysis where, in typically less than two minutes, its analysis may be obtained. Also the measured spectrum can be compared (using spectral pattern-recognition methods) to stored reference spectra of the monitored assembly's component parts and hence to identify the component that has worn or been damaged.

Substantial amounts of time and money have been saved in terms of aircraft serviceability as well as in the assessment of a component's approximate useful lifetime and minimisation of secondary damage. Because the EDXRF technique is non-destructive, the tape/debris sample may be archived for re-investigation any number of times.

With the needs of the aircraft engineer in mind, recent developments in X-ray focusing optics have enabled the development of the EDAX Eagle micro-probe EDXRF system to be specifically suited to the individual measurement/analysis of larger debris particles. The Eagle incorporates a capillary optic to define a very fine, high-intensity beam of X-rays as the energy source with a diameter down to tens of microns. This enables individual particles present on the surface of the tape to be quickly located at the analysis position via the system's point-and-click controlled X-Y-Z stage in conjunction with the internal CCD video camera. Where it is suspected that the debris sample may contain wear particles from more than one distressed component, automated measurement sequences are easily implemented for any number of pre-selected particle locations.

It has always been EDAX's policy to listen to the analytical needs of its customers and to define its development programme accordingly. The development of the Eagle system serves as an example of EDAX's response to satisfy the unique demands of single-particle (small-area) analysis as specified by condition-monitoring engineers in particular for the analysis of magnetic-plug debris. The applicability together with the ease of use of the Eagle system for such monitoring tasks has been recognised by the Defence Evaluation Research Agency (DERA) fuels and lubrication laboratories in conjunction with the service they provide for British military and civilian aircraft.