According to TestOil Field/Data Analyst Matt McMahon there are important considerations for choosing the best bearing lubricant such as speed, load, and temperature —how fast the bearing is spinning, how much pressure is on the bearing and the operating temperature range.
Matt mentioned some general rules of thumb:
1. The faster the bearing spins, the “thinner” the lubricant.
2. The higher the load, the “thicker” the lubricant.
3. The higher the temperature, the “thicker” the lubricant.
Generally, bearings perform best with a minimum amount of the thinnest lubricant that will keep the bearing surfaces apart.
Additional considerations for bearing lubricant selection include:
- Housing type
- Individual requirements for specific bearings
- Environmental conditions
Oil analysis tests for oil lubricated bearings that Matt recommends include; water content, particle count, FTIR spectroscopy, elemental spectroscopy, viscosity, acid number, and ferrous wear concentration. He recommends advanced testing in some situations, such as an unusual amount of foaming.
“For oil in an anti-friction bearing: the two most important tests would be particle count and water content,” Matt explains. “The reason being that the cleaner and the drier the oil, the more life you will get out of that bearing. Those two physical properties should really be on everyone’s radar.”
In some bearing applications, grease is used instead of oil for lubrication. Using grease as a lubricant poses additional considerations.
In a high speed/low load situation, if grease is selected for lubrication, some factors to consider are base oil viscosity, oil separation and pumpability. While a multi-purpose grease would be suitable for moderate speeds and loads, it may contain a base oil too thick for an application at higher speeds. Improper grease selection can result in increased operating temperatures and shorter bearing life.
Also, once a specific grease has been selected for an application, proper identification of the grease in use is extremely important.
“There is a misconception that bearing greases are all interchangeable,” Matt says. “That’s just not true—in some situations, swapping out one grease for another without checking compatibility can lead to lack of lubrication and damage the machinery.”
The Building Blocks Guide to the Fundamentals of Lubrication & Analysis gives a great overview and understanding of lubrication.
With more than 30 years of experience in the oil analysis industry, TestOil focuses exclusively on assisting industrial facilities with reducing maintenance costs and avoiding unexpected downtime through oil analysis program implementation. As industry experts in diagnosing oil-related issues in equipment such as turbines, hydraulics, gearboxes, pumps, compressors and diesel generators, TestOil provides customers with a guarantee of same-day turnaround on all routine testing. With in-house, certified training professionals, TestOil offers lubrication and oil analysis training, private onsite training, certification training and exams, and educational webinars. For more information on partnering with TestOil on oil analysis programs or training opportunities visit www.testoil.com.