Experimental study on low-speed lubrication characteristics of large tilting pad bearings

Large generator sets may experience boundary lubrication between the bearing and the shaft during startup, shutdown, or low-speed cranking. This can lead to localized wear or damage to the bearing and rotor surfaces, potentially causing safety accidents in the unit. In this paper, the lubrication properties of the unevenly distributed six-watt tilting pad bearings in an in-service unit are analyzed through theoretical calculations. The analysis focuses on parameters such as film thickness and temperature rise under low-speed operating conditions. Subsequently, a full-size test rig is set up to examine the lubrication properties of bearings made of two materials—Babbitt alloy and polytetrafluoroethylene (PTFE). The tiling pad temperatures, film thicknesses, and vibration characteristics of the bearings are tested under actual operating conditions. The test results show that: The designed bearing does not exhibit wear under low-speed conditions (40 r/min); the bearing made of PTFE material has lower temperatures compared to those made of Babbitt alloy, with higher pivot film thickness than that of the Babbitt alloy; the bearing pivot film thickness value using VG68 oil is larger than that of VG46; and the values of the temperature of the tilting pad measurement point are larger than that of VG46. This research paper validates the feasibility of the bearing design scheme for this unit and provides data support for the design and safe operation of similar units.