Or the user may overgrease the bearing, forcing bearing balls to push through excess grease as they rotate. For example, when relubricating open bearings, users may inadvertently employ a low-temperature grease which does not provide adequate viscosity at the normal operating temperature. Overheating in electric motor bearings is generally lubricant-related. For electric motors used in high-temperature environments, special consideration should be given to the bearing lubricant. The grease provided in shielded electric motor ball bearings remains effective to approximately 200-210☏. If the outer ring is inaccessible, take the measurement at the housing and add 15° to 20☏ to estimate the correct bearing temperature. As in all bearing applications, this measurement should be taken at the bearing outer ring. Normal motor bearing operating temperatures range from 140° to 160☏. The ball bearings used in most electric motors are pre-greased, shielded ball bearings. Maintenance technicians should be aware of these differences – and should know the common causes of, and remedies for, bearing overheating.
Normal operating temperatures differ, depending on the application. Higher-than-normal operating temperatures, whether caused by ambient conditions or generated within the bearing itself, have the potential to harm rolling bearings. In addition, the “floating” bearing in the fan arrangement was offset in the housing, providing it with more room to travel axially to accommodate shaft expansion. The plant immediately took steps to shield fan bearings mechanically from the worst of this heat. But their efforts came too late: By the time the meeting ended, the grease inside the bearing had dried up and smoke had begun to emanate from the bearing, causing shutdown.įailure analysis quickly pinpointed a cause: process temperatures of 1000☏ or more produced in the glassmaking process and resulting in an ambient temperature of 220☏. While the fan continued to run, plant technicians consulted with a bearing engineer to devise a solution.
Bearing temperatures, which normally hovered around 170☏, climbed to 195☏. Bearings in a fan used to evacuate superheated air during the glassmaking process began to overheat. Maintenance technicians at a glass fabrication plant recently witnessed firsthand how high temperatures can affect and potentially damage rolling bearings.
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