TECH TIPS: Extending bearing life in rotating equipment
Like any mechanical device, bearings wear out over time. This is an unavoidable fact of life. Yet there are ways of getting the maximum life out of the bearings in your rotating equipment.To start wit...
Like any mechanical device, bearings wear out over time. This is an unavoidable fact of life. Yet there are ways of getting the maximum life out of the bearings in your rotating equipment.
To start with, there are five simple things one can do to maximize bearing life. These five steps are: keep your bearings clean, dry and cool, and keep your equipment balanced and aligned.
Clean, dry and cool means addressing the lubrication issues of the equipment. For instance, circulating oil systems are used when the heat buildup at the bearing is more than a static oil system can radiate away. In this case the system provides external cooling. However, just like in a car, circulating oil must be changed periodically. Oil will deteriorate over time from heat, oxidation, catalytic reactions, and dirt or water contamination. It is a good idea to change the oil whenever it becomes dirty or cloudy.
Grit and dirt contamination act as abrasives and over time will remove the hard facing of the bearing. Once the hard facing is removed, the bearing will quickly deteriorate to failure. Therefore it is important to keep the dirt contamination out.
In wet environments, keeping bearings dry can sometimes be difficult. It is also important since water will separate the lubricant. If you notice a milky look to the grease being purged from the bearings, it is an indication of contamination by water.
Balanced and aligned refers to minimizing the destructive energies present when imbalance and misalignment are allowed to continue. Keeping these forces to a minimum greatly adds to extending bearing life. Many companies use vibration monitoring equipment to determine the severity of these forces or shut down the equipment if these energies get too large. As an example of vibration levels seen in the field, it is not uncommon to see vibration velocities of 0.10 in./sec or lower for initial operation, 0.30 in./sec for an alarm setting, and 0.45 in./sec as the shutdown setting for a heavy duty fan. However, as there are many applications, it is always best to check with your fan supplier on these matters.
An example of using the five steps — clean, dry, cool, balance and align — to extend the life of equipment is a process pump in a paper mill application suffering repetitive failures. It was felt that the location in the process subjected the bearings to high impact from foreign material going through the pump.
Because of the frequency of repairs, the pump was not looked after as well as other pumps, since the service people knew another failure would be occurring soon.
As a repeat offender, this pump was singled out by the team in order to reduce downtime. Initial steps focused on paying close attention to the motor alignment. In this case the use of laser alignment equipment was employed. This one step had a marked impact and doubled the time between failures.
After this success, the team focused on improving the bearing seals to prevent suspected water and dirt contamination. Following these upgrades, the pump no longer experienced frequent failures.
In closing, clean, dry, cool, balanced and aligned are simple but important and fundamental steps to ensure that you get the most running life out of your equipment’s bearings.
This Tech Tip was prepared by Marcel Kamutzki, P.Eng., a partner at CH Ljungberg Inc., a company that specializes in industrial equipment. His background includes fan design and engineering at Novenco Canada. The Fan Guys include Jim Wywrot, P.Eng., Mark Bugdale and illustrator Richard Comely (creator of Captain Canuck). For more information, visit www.fanguys.com.