1. Field of the Invention
The present invention relates generally to the field of analyzing wear particles in used lubricants. More specifically, the present invention discloses a sample preparation system for separating wear particles from such fluids by size and magnetic characteristics.
2. Statement of the Problem
The present invention is designed to filter and separate wear particles suspended in used lubricants or hydraulic fluids by particle size and magnetic characteristics. These samples can then be analyzed qualitatively or quantitatively using a conventional energy dispersive x-ray fluorescence (EDXRF) system or other analysis techniques.
More specifically, the present invention is designed to meet the particular needs of the Joint Oil Analysis Program (JOAP) laboratories. These laboratories belong to the Army, Navy, Air Force, and other Department of Defense (DoD) agencies. All of these laboratories are part of an interagency cooperative effort to implement an effective condition monitoring response to threats, and to increase safety of service personnel and the longevity of the hardware transporting the personnel. It is the responsibility of the JOAP Technical Support Center (TSC) to set the equipment standards for analysis for each of the individual condition monitoring and oil analysis programs operated by the Army, Navy, Air Force, and other DoD agencies. If a piece of equipment is to be used in the condition monitoring program of any DoD agency, the analysis system or technique to be used must first receive approval from the JOAP-TSC in Pensacola, Fla.
Current atomic emission spectrographs used by the JOAP are most sensitive to particles having a size of approximately 10 microns or less. Particles larger than 8 to 10 microns in size cannot be vaporized by the high-voltage arc of the atomic emission spectrograph and therefore are not part of the sample analysis. A growing number of people in the engine condition monitoring field are now of the opinion that analysis of a wide range of particle sizes, including larger particles of 10 microns and up, is far more indicative of abnormal wear and provides the best indication of impending, possibly catastrophic failure. This seems reasonable because small metal particles present in the oil are the result of both normal wear and large particles being ground into small particles by the mechanism. Therefore, any analytical technique that is capable of analyzing only small particles is going to be less effective in predicting a need for engine maintenance, and will only occasionally be able to predict the impending catastrophic failures that are most hazardous. It is estimated that current atomic emission spectroscopy techniques detect abnormal wear only an average of once in every 5,000 analyses performed on used oil samples. There have also been several instances where an aircraft has had an in-flight failure shortly after having an oil analysis by atomic emission spectroscopy indicating no unusual quantities of wear metal. Visual inspection of the oil filter and other interior portions of the engines after the crash revealed numerous large particles, chips, and chunks of metal debris. An atomic emission spectroscopy analysis of the used oil collected after the crash still showed nothing abnormal.
An analytical technique that is sensitive to a wide range of particle sizes, including large particles, is advantageous and would allow detection of impending failures that are not observed with the current technique. This translates to a reduction in maintenance costs, increased safety for personnel, and fewer in-flight failures. EDXRF is sensitive to all particle sizes and therefore offers an opportunity to significantly improve the early detection of abnormal wear in aircraft. As a result of these concerns, there is a need for a system to prepare filtration samples in which particles are separated into multiple categories by size and magnetic characteristics. In addition, the system should allow the operator to easily identify any samples containing significant quantities of oversize particles.
Although the present invention was specifically developed to support aircraft engines used for helicopters and jet fighters, it should be expressly understood that the invention is also applicable to analysis of used lubricants and hydraulic fluids from commercial aircraft, ground-based equipment such as heavy construction equipment, trucks, power generation stations, ocean liners, other types of ships, and high performance automobiles.
A number of particle filtration systems have been used in the past for analysis of used oil and lubricants, including the following:
______________________________________ Inventor Patent No. Issue Date ______________________________________ Thornton et al. 4,555,331 Nov. 26, 1985 Cox et al. 4,550,591 Nov. 5, 1985 Luria 4,169,677 Oct. 2, 1979 Westcott 4,047,814 Sep. 13, 1977 Vobach et al. 2,105,851 Jan. 18, 1938 ______________________________________
Thornton et al. disclose a semi-automatic quantitative filtration assembly having means to measure and present a known quantity of fluid for filtering. An in-process fluid holding tank (e.g., moat) adjacent to the filter medium receives any excess fluid during filtering to prevent excess fluid from intermixing with the known quantity of fluid to be filtered.
Cox et al. disclose an apparatus for monitoring particulates in a fluid. The fluid flows through a filter 28. A pressure sensing means 46 senses the fluid pressure difference across the filter. A processor evaluates the rate of change of the pressure difference in order to give an indication of the particulate matter levels in the fluid.
Luria discloses a system for analyzing used oil in which a plurality of samples are separated according to the different mobility rates of its particles through a liquid medium. The samples are separated by passing them through a large mesh screen at the bottom end of a tubular holder in which the centrifuging is effected.
Westcott discloses a system for detecting and analyzing particulate matter suspended in a fluid. The fluid flows over a collecting substrate in the presence of a magnetic or electric field having an intense gradient. The particles are deposited on the substrate in accordance with their size with the larger particles being deposited first and the smaller particles being deposited last.
Vobach et al. disclose a system for measuring contaminants in lubricants. A magnetic field is used to separate magnetic metal particles suspended in the lubricant.
3. Solution to the Problem
None of the prior art references uncovered in the search show a sample preparation system for analysis of wear particles in lubricants that produces filtration samples in which wear particles are separated into multiple categories by size and magnetic characteristics. In addition, the system allows the operator to easily identify any samples containing significant quantities of oversize wear particles.