Machinery Lubrication magazine published by Noria Corporation
Issue link: http://www.e-digitaleditions.com/i/730290
10 | September - October 2016 | www.machinerylubrication.com COVER STORY 10 | September - October 2016 | www.machinerylubrication.com bearing is typically considered for this oper- ating temperature. Continue regular monitoring and watch for any significant changes in temperature. Another factor that is just as critical as the absolute bearing temperature is a change in temperature, which is an indication of a condi- tion change. A temperature change of more than 50 degrees F is of concern no matter what condition range in which the absolute tempera- ture falls. Increased monitoring and investi- gating should be required with this type of change. Small temperature changes are generally of little concern. It may be normal for a recently greased bearing to increase in temperature 25-30 degrees F. Machine speeds and loads as well as ambient conditions (winter/ summer) will also affect absolute temperatures. Other factors that can cause higher temperatures include increased bearing friction (poor lubrication, high load, high speed, etc.), excessive lubrication (grease overpres - sure), high oil level (oil churn) and misalignment. Alert Conditions In an alert condition, the bearing temperature may be between 200 and 250 degrees F. These elevated temperatures may be due to a heated application, a recently greased bearing, oil level issues, early stages of bearing failure, etc. Be sure to verify the process condi- tions, recent greasing cycle or oil level. You may also need to increase the frequency of monitoring the temperature changes. The safe operating tempera- ture for grease is typically 75 percent of the dropping point. If the bearing is running in an application with heat through the journal, this elevated temperature range may be normal for operation. This would also call for a C4 clearance bearing. Alarm Conditions In an alarm condition, the bearing temperature may be between 250 and 300 degrees F. Bearings operating in this tempera- ture range likely are in some stage of failure. The amount of life left can be highly variable. Employ other predictive technologies (vibra- tion, infrared, ultrasonic testing, etc.) and increase the condition monitoring frequency until corrective action is taken. Also, minimize stress on the bearings by limiting startups/ shutdowns and reduce process speed/load Viscosity-Temperature Diagram for a Paper Machine Oil Temperature, °C Kinematic viscosity, cSt 100000 10000 1000 100 1 0 1 -20 0 20 40 60 80 100 120 The maximum operating temperature to satisfy the minimum viscosity (22 cSt) for a spherical roller bearing with this lubricant is 92 degrees C (197 degrees F). The ball bearing would increase the safe operating temperature to 110 degrees C (230 degrees F). Lube viscosity-temperature curve (Ref. SKF)