Machinery Lubrication magazine published by Noria Corporation
Issue link: http://www.e-digitaleditions.com/i/730290
COVER STORY maintec-show-catalogue-150x109.indd 1 05/07/2016 16:11:36 changes. Begin preparing a maintenance plan (order materials, define the job scope, etc.) for executing corrective action for either a planned event or unplanned failure. Use care when lubri- cating any bearing in an alarm condition, as lubricating (especially greasing) can elevate the operating temperature and even lead to failure. Shutdown Conditions In an equipment trip/shutdown condition, the bearing temperature may be more than 300 degrees F. Bearings at this temperature are likely in the final stages of failure. Depending on the equipment design, failure can be rapid and catastrophic. The time to react may only be hours, not days. At this point, the bearing is gone, so your actions should be focused on minimizing a secondary failure of the remaining components (shaft, housing, etc.). An immediate equipment trip/shutdown may be recommended to prevent catastrophic failure and additional damage. The bearing integrity and geometry can be severely compromised at this temperature range, as the heat stabilization temperature for many bearings is between 300 to 400 degrees F. Do not attempt to grease a bearing in a shut - down/trip condition, since this is likely to result in an immediate failure. Cooling Methods If the bearing temperature is severely elevated, spraying with water could cause it to explode. Do not put water on the bearing or bearing housing. Water can migrate into the bearing and lead to a breakdown of the lubricant film. Corrosion can also occur. Cooling the housing of a hot bearing can remove bearing clearances when the outer race cools, as the inner race will still be hot. The reduction in radial internal clearance will increase bearing friction and drasti- cally reduce bearing life. The potential of catastrophic failure is also increased. Smaller bearings have a greater risk of this occurring due to their small radial internal clearances. Using a fan on a bearing housing can be an acceptable cooling method for a bearing in an alert or alarm condition. If the bearing is on a circulating oil system, increasing the oil flow may also cool the bearing. However, too much oil flow can cause oil churn and increased friction inside the bearing. Expert Help If a bearing continually operates in an alert or alarm condition, you may need to consult an expert to evaluate the risk of continued operation and to identify possible changes for improve- ment. These bearings that persistently run at elevated temperatures have a chronic problem and require analysis to determine the root cause. While bearing temperature monitoring can be relatively simple, the decisions that result will necessitate an evaluation by trained profes- sionals to ensure the best course of action is taken to maximize equipment reliability. About the Author Randy Riddell is the reliability manager for SCA at the Barton Mill in Alabama. He has more than 25 years of industrial experience with a career focus on equipment reliability. Randy has a bachelor's degree in mechanical engineering from Mississippi State University and is a certified maintenance and reliability professional by the Society of Mainte - nance and Reliability Professionals. Contact Randy via email at Randy.Riddell@sca.com.