Downloaded from https://www.everyspec.com ADS-79D-HDBK Oil condition and wear debris monitoring should keep pace with these changes in order to provide reliable condition monitoring information. Monitoring the viability and usefulness of testing techniques for determining condition indicators should be an on-going process. M.5 GENERAL GUIDANCE The focus of oil condition and debris monitoring is to detect engine or gearbox behaviors indicative of degradation or an incipient fault that leads to component failure or performance changes in the oil-wetted components. Data from oil monitoring is trended over time to determine component performance or fault initiation.
See Appendix G, section G.6.2, for further discussion. For accurate oil condition and debris trending, the part‘s usage should be monitored as appropriate for that platform. See Appendix A for further usage monitoring discussion. Time- on-oil is typically used for oil analysis diagnostics (rate trending). M.5.1 Lubrication and Debris Monitoring: Lubrication is essential to the operation of many rotorcraft components. Lubrication carries the load and maintains wear surface separation; removes the heat of friction; provides oxidation stability and neutralizes acidic by-products formed; controls corrosion, rust and varnish deposits; and flushes away debris.
Maintaining the proper lubricant film thickness through the operating regime of the equipment is essential for long life. This requires keeping the lubricant free of contaminants and degradation, otherwise, metal-on-metal contact may occur resulting in component wear and eventual failure. For instance, the high operating stresses in a gas turbine engine pose challenges to maintaining effective lubrication during extended operation. The operating conditions inside the engine as well as environmental factors (dust, humidity) can introduce contaminants into the oil. M.5.1.1 Oil Condition and Contamination Monitoring:
Oil condition and contamination testing includes monitoring the oil for base stock degradation, additive depletion and contaminants (water, fuel, dirt and incorrect fluids). The degradation and additive depletion may be trended over time providing oil change-out guidance. Contaminants generally have a finite allowable quantity (limit) and once reached, the recommendation is for an oil change. M.5.1.2 Wear Debris Monitoring: Debris monitoring is performed to determine the presence, size and possible origin of both metallic and nonmetallic debris. Trending provides information on the component wearing and the rate of wear for remaining useful life (RUL) estimates.
Wear generation is typically divided into break-in wear, normal rubbing wear and abnormal wear cycles. a. Break-in wear is the polishing of the load-bearing surface during initial run-in while generating the shear mixed layer. This process removes build debris (micro swarf) left over from the machining process. Break-in wear generates a spike in measurable wear debris until the shear mixed layer is generated and normal rubbing wear begins. b. Normal rubbing wear generates small metal particles due to the normal exfoliation of the shear mixed layer (wear of surface metals due to the constant working of the surfaces by a sliding or rotating load).
Normal rubbing wear occurs throughout the life of the component until a fault is initiated. 241