Machinery Lubrication

Machinery Lubrication September October

Machinery Lubrication magazine published by Noria Corporation

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Page 13 of 69 | September - October 2016 | 9 Measuring Bearing Temperatures Before any action is taken, the question of how hot the bearing is should be answered. Hot to the touch might only be 130 degrees F, as 120 degrees F is gener- ally the threshold temperature where you can still hold your hand on the surface. While there may be gray areas for identifying the appropriate action at certain temperatures, some guidelines can provide consistency and help plant personnel make better decisions. The first step should be to determine the actual temperature of the bearings being monitored. Keep in mind that the temperatures measured are only the skin temperatures of the bearing housings. The actual bearing temperatures will be 15-25 degrees hotter. Observe the surface condition and type when measuring temperature. Also, ensure the measuring device's emissivity is correct for the surface being measured. Most dark carbon-steel surfaces will have an emissivity setting around 0.95, while shiny stainless steel or aluminum will have a much lower setting. A typical infrared camera shot is shown below. Process buildup on bearing housings can result in lower measured temperatures when the actual bearing temperatures are much hotter. Buildup will insulate the bearing and not allow it to dissipate heat, which will in turn make the bearing run even hotter. Temperature checks should be performed in the same locations on the equipment and the bear- ings. Variations in bearing temperatures can be expected when different locations are measured due to load zones, ambient temperatures, lube levels, etc. Consistency is also important when different individuals are taking the measurements. Bearing Temperature Conditions Most precision installed and lubricated equip- ment will operate at less than 180 degrees F. A bearing temperature that is less than 180 degrees F is typically considered acceptable (see the chart below). Of course, there may be other consequences for operating in this "good" range. A higher operating temperature will cause the bearing lubricant to deteriorate at a faster rate. At more than 150 degrees F, the lubricant life can be cut by 50 percent for every additional 18 degrees F. A higher operating temperature also means a lower operating viscosity for the lubricant, which may hurt the overall reliability of the equipment. The chart on page 10 shows how the maximum temperature for a specific lubricant (viscosity index) and bearing type may limit the maximum operating temperature s. Caution Conditions In a caution condition, the bearing temperature may be between 180 and 200 degrees F. While this is slightly higher than desired, it may be a typical operating temperature for some equipment. Therefore, it is essential to have an operating temperature history for equipment in this range to determine if the temperature is normal. For gearboxes, sump temperature limits are less than 200 degrees F, as defined by the American Gear Manufacturers Association (AGMA). A C3 clearance ML | September - October 2016 | 9 An infrared image of a bearing housing Bearing temperature condition chart <180°F Good 180-200°F Caution 200-250°F Alert 250-300°F Alarm >300°F Trip/Shutdown

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