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Real-Time Wear Measurement Using Radioactive Tracer Technology™Radioactive tracer technology (RATT®) is an important tool for measuring component wear on a real-time basis, and is especially useful for measuring component wear in operating engines, or other complex mechanical systems. Two radioactive test methods are commonly used in engine wear studies, namely, surface or thin layer activation (SLA/TLA) and bulk activation (BA). The choice of method depends on specific test objectives, component metallurgy, configuration or site particulars, or other factors that may favor one method over the other. Much of our recent work has been accomplished using the bulk activation method because of increased sensitivity, which allows better definition of cause-and-effect relationships and shorter test times. The responsiveness of this method is illustrated below. Here, changes in wear and wear rate are observed almost simultaneously with changes in engine operation. This is a major advantage of the bulk activation, radioactive tracer, test method, and would not show up during conventional wear testing, where hundreds of hours of testing and physical inspection are required to obtain a new data point, with no intermediate information. Radioactive tracer technology, bulk activation and SLA, is not limited to engines, but can be used with many other mechanical components, such as pumps, fuel injectors and transmissions, as long as suitable metallurgy is present to provide measurable radionuclides after irradiation.
The radioactive measurement technique, using bulk activated tracers, is illustrated below. To facilitate these measurements, new parts, for instance, connecting rod bearing sections and compression rings, are exposed to thermal neutrons in a nuclear reactor, and then installed in the test engine. Simultaneous irradiation of each group of parts produces artificial radionuclides that are separately characteristic of the ring and bearing wear surfaces. Gamma rays emitted from radionuclides of irradiated wear particles abrading from these parts during engine operation serve as detectable tracers as the particles circulate in the lubrication system. Measuring the level of radiation associated with these particles using a gamma ray spectrometer provides a direct measure of the mass of wear particles present in the oil at the time of measurement. When corrected for natural radioactive decay and compared to calibration data, these measurements give the specific amount of wear suffered by the parts during a given test period. With this technology, it is possible to measure ring and bearing wear simultaneously, in real-time, without disassembling the engine for inspection.
Because the bulk activation radioactive tracer method is highly sensitive, very small changes in wear can be accurately detected and quantitatively measured. This allows meaningful tests to be accomplished over very short test periods so that many test conditions and combinations of variable can be investigated simultaneously, in days rather than months. The amount of wear measured per test (typically micrograms) would not be detectable by physical inspection. Furthermore, since physical inspection of the parts is not required, possible changes in material clearances and in the engine's wear state are avoided, thus test-to-test continuity is maintained such that sequential testing provides meaningful results. Radioactive tracer wear testing can significantly reduce product development time and cost, and the ability to perform these tests often determines whether a particular program can be undertaken or not. We have conducted numerous RATT projects, from measuring wear as a function of lubricant chemistry, engine operating condition (speed, load, coolant temperature and duty cycle, for instance), component design, material properties, and internal and external environments; to corrosion studies, and the evaluation of anticontamination materials, particle transport and filter performance, to name a few. In many cases, meaningful results could be obtained in relatively short time periods by investigating wear and performance degradation under accelerated test conditions, or by direct exposure to specific environmental conditions. For instance, engine ring wear was measured while feeding dust of specific sizes, composition and concentration into the air intake, with and without filtration, for specific periods of time. Particles actually entering the engine were measured for size and concentration, while engine wear was monitored continuously.
Martin B. Treuhaft, Manager Filtration and Fine
Particle Technology |
