By Kevin O’Brien
The number one reason for bearing failure is excessive lubrication. The grease gun can be a greater enemy than one might think. Greasing bearings is necessary to maintain bearing life. Lubrication minimizes friction between contact surfaces, protects against corrosion and the entry of foreign matter, and dissipates heat from the bearing. However, maintenance personnel often apply too much grease. The misuse of the grease gun can cause premature failure of the bearing and cancel out any benefits the grease had in protecting the bearing.
Grease Gun Pressure and Bearing Seal Failure
A grease gun has an average rating of 6,000 pounds per square inch (PSI). This can go up to as high as 15,000 PSI. Bearing seals fail around 500 PSI. Many service technicians often “go by feel,” but with an extreme difference between the grease gun pressure and the bearing’s seal failure, the damage may occur before they “feel” anything.
Once the seals are purged, the bearing is prone to contamination. Moisture and other debris can enter the bearing, corroding the bearing surfaces. Any grease that was purged from the bearing will be drawn back into the bearing after it cools, bringing outside contaminants with it.
Over greasing also causes heat buildup in the bearing. This occurs because there is nowhere for the heat to dissipate. A “full” bearing will hold a higher temperature than a properly filled one. Also, if a bearing is hot to the touch, it is not necessarily overheating and in need of more grease. The heat—along with the internal churning of the bearing—will force the grease to the outside of the bearing. The grease will then break down and harden, blocking any future grease from getting to the contact surfaces, working against the main function of minimizing friction between contact surfaces.
One solution to this problem is to determine how much grease is expelled with every pump of the grease gun. A service technician can measure the number of ounces of grease that are expelled per pump with a scale. Every grease gun varies.
A second solution is to look at automatic lubricators, which are made to the bearing manufacturer’s specifications. Automatic lubricators distribute a measured amount of grease to the bearing at a timed interval. Maintenance personnel only need to determine the interval at which the lubricator empties itself. They then change the lubricator once it empties.
Benefits of a Proper Greasing Schedule
Following a proper greasing schedule can not only save the company money but also free up time that could be better spent by the maintenance personnel. Bearing manufacturers publish lubrication charts for their products, and most are willing to train staff on the proper lubrication practices.
For more information or help with bearing failure, contact the power transmission and motion control experts at IPEG.