Browse Topic: Lubricating greases
Rotorcraft, like most machines, require periodic lubrication tasks to ensure continued safe and reliable operation. Optimal lubrication intervals are desired to maintain system performance while minimizing aircraft downtime and maintenance labor. Boeing and AMRRI conducted a Lubrication Optimization Study (LOS) on the H-47 Chinook helicopter to establish the necessary engineering artifacts to define the grease lubrication intervals for selected Drive, Rotor, and Landing Gear components. Grease samples were collected from these components by H-47 operators from multiple nations and submitted for a laboratory analysis to characterize how wear, properties and contaminants change as time and aircraft hours accumulate. The LOS also revealed opportunities to further evaluate and leverage the data produced in this study, including determining superior performance of specific lubricants within the Mil-Spec designation, testing of greases for compatibility5 when mixed, and enhancing new grease cleanliness to extend component life.
Over the course of a long-duration aging of helicopter drivetrain bearings to examine the consumption of grease life, both vibration and acoustic emission sensing was used to monitor the bearing response as the grease life was consumed through this aging. Acoustic emission is evaluated against vibration in terms of signal trends over the course of the experiment. Common signal metrics are calculated to yield condition indicators, and machine learning techniques are applied to the vibration and acoustic emission data. For the 862 hour duration test run equivalent to over 6700 hours on wing, features of these signals trend with increased degree of aging. Autoencoders were used to enrich existing set of traditional condition indicators and principle component analysis was effectively used for feature fusion. This measured trending shows promise for future onboard Health and Usage Monitoring Systems which may adopt new sensing and data analysis modalities to trend the condition of mechanical systems.
Slit lamp biomicrography is paramount to the practice of ophthalmology, allowing for an inside look at various areas of the eye with a range of magnification levels and light sources. The development of medical devices, such as the ophthalmologic slit lamp, brings about a number of design restrictions. The equipment must be able to perform the necessary tasks with precision to allow for patient diagnosis and proper treatment, and must maintain a high level of cleanliness, low levels of noise during operation, and, due to the typical high cost of medical equipment, have a high service life with as little required maintenance as possible. With these design requirements in mind, the development team from A.R.C. Laser GmbH, Nürnberg, Germany, was tasked with creating a new slit lamp for an already established marketplace.
NASA has an ongoing need for high-temperature solid lubricant coatings to reduce friction and wear in turbine engines, rocket engines, and other mechanical systems. Such lubricants must be thermally and chemically stable in air, vacuum, and reducing environments like hydrogen. Traditional lubricants like oil, grease, and PTFE (Polytetrafluoroethylene), and even more exotic solid lubricants like graphite and molybdenum disulphide, lack such capabilities. The key problem is to identify and formulate a material that possesses good mechanical properties, long-term environmental durability, and acceptable friction and wear-reducing characteristics while being practical to apply to bearings, seals, and other mechanical components.
The purpose of this experiment is to determine if the intermediate gearbox (IGB) grease service level can be characterized through existing condition-based maintenance (CBM) practices, which include vibration monitoring sensors and analysis algorithms, in the IGB of the AH-64D. A secondary objective is to quantify a common phenomenon in the gearbox–the expulsion of lubrication during different times of operation. If both goals are achieved then common maintenance practices on the aircraft can be changed to reduce workload. Three different gearboxes of similar condition were used for this experiment. Each gearbox was run in a two hour test under different loading conditions five separate times. In each iteration, the gearbox contained a different volume of grease that increased in 25% increments of the standard service level (0%, 25%, 50%, 75%, and 100%). The vibration data analyzed was collected through the modern signal processing unit (MSPU) to find a trend against the different amounts of grease. To complete the secondary goal, the amount of grease ejected during the initial parts of the runs was captured and weighed. This will be used to obtain a constant number at which to service the IGB and prevent the "burping" of grease during operation. . More research should be conducted to discover whether higher-order vibrations analysis will allow this fault to be detected.
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