Poor lubrication is known as an important factor in the bearings failure. Therefore, it is very important to detect the lubrication condition. Hydrodynamic lubrication, mixed lubrication and boundary lubrication are the basic regimes of the fluid film lubrication. In a proper condition, development of hydrodynamic pressure is adequate to support the load and the bearings operate under hydrodynamic lubrication condition. However, in most situations, they operate in mixed lubrication or boundary lubrication regime and have metal-to-metal contact. To establish these regimes, using the so-called Stribeck curve is a useful method. In this curve, the oil film thickness is proportional to the lubricant viscosity and sliding velocity and inversely proportional to the applied load. However, distinguish of the exact range of hydrodynamic lubrication regime from mixed and boundary regime using this curve and relation related to the sliding bearings, due to high number of affecting design factors and operating parameters is difficult. The present study focused on the acoustic emission measuring method in order to monitoring the lubrication conditions in a type of journal bearings. Thus, condition monitoring of the journal bearing lubrication is provided and the numerical value of operating variables of the bearing for lubrication regime change from hydrodynamic to mixed is achieved. Using wavelet method, frequency features for each regime is identified. Then, for each lubrication regime, metal-to-metal contact detection is performed.

Keywords: Acoustic emission method, Journal bearings, Wavelet transform, Lubrication condition monitoring, Metal to metal contact

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