Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/1061099
4 | November - December 2018 | www . machinerylubrication.com AS I SEE IT 68% of lubrication profes- sionals say overheating has been a problem for the gearboxes at their plant, based on a recent survey at Machinery - Lubrication.com Develop a thermal lubrication chart (TLC) for critical equip- ment, especially bad actors (as shown below). Defi ne the points (A-F) for a specifi c location on the machine to be monitored (e.g., a supply line). e normal working range (zone 3) is banded by tempera- ture points C and D. Temperature excursions below point C are controlled by a heater and alarms. Temperature excursions above point D are controlled by a cooler and alarms. Sustained operation in zones 2 and/or 4 lowers the service life of the machine and/or lubricant. For instance, operating in zone 2 may retard lubricant fl ow to the bearings, raise energy consump- tion and increase the foaming tendency. Operation in zone 4 may accelerate oil oxidation, reduce fi lm strength and increase wear associated with particles. Operating in zones 1 and/or 5 will threaten machine reli- ability. Temperature points A and F are sudden-death extremes. Zone 1 is typically a partial lubricant starvation condition, while zone 5 is associated with fi re hazards, thermal-oxidative oil degradation, additive depletion, volatilization and high fric- tion/ wear conditions. e use of high viscosity index (VI) lubricants can lower temperature points A through C. e use of high VI and premium- formulated synthetic lubricants helps increase temperature points D and F. TLC for Critical Machines are monitored in real time, often at multiple points, such as guide and thrust bearings (typically imbedded thermal couples). A common example of bearing temperature monitoring is shown in Figure 1. Here, a tempera- ture excursion was noticed fi rst before any other symptoms. After inspec- tion, a lubrication issue (cake-lock) was found to be the root cause. e cake-lock issue was solved by converting to a softer grease and a faster delivery rate. Had the bearing lubrication been more closely monitored by an inspector, i.e., noticing that the drip pan had only oil (not grease), the trip could have been avoided. Temperature monitoring is a fundamental condition monitoring principle and one of the earliest forms of instrument-based condition monitoring. It is nearly impossible to have a serious or advanced lubrication problem and/or machine component failure without heat being involved as a root cause or symptom. It is often said that when a bearing is running hot, the usual suspects (causes) are misalignment and impaired lubri- cation. Likewise, the fi rst and most pronounced symptom of misalign- ment and impaired lubrication is excessive heat. Whether you're using a heat gun, infrared camera or thermal couple/ resistance temperature detector (RTD) to monitor heat in real time, you should have a game plan. For lubricants, the use of thermal lubri- cation charts (TLCs) or something similar makes a lot of sense. ere should be a normal working range (green), cautionary zones (yellow and amber), and red (hot and cold) for life-threatening (catastrophic failure) issues. You can read more about TLCs in the sidebar above. ML About the Author Jim Fitch has a wealth of "in the trenches" experience in lubri- c ation, oil a na lysis, tribolog y and machinery failure investiga- tions. Over the past two decades, he ha s presented hundreds of courses on these subjects. Jim ha s a lso published more t ha n 200 technical articles, papers and publications. He serves as a U.S. delegate to the ISO tribology and oil analysis working group. Since 2002, he has been the director and a board member of the Inter- national Council for Machiner y Lubrication. He is the CEO and a co-founder of Noria Corporation. Contact Jim at jfi tch@noria.com. Continued from page 2