Babbitt Bearings, properly cared for and maintained will last much longer than anti-friction bearings. Properly set up and aligned there is no contact between the babbitt and the journal other that a scuff mark at the bottom that is caused by minimal contact at starting. As long as the motor is properly aligned to the load, the oil is kept clean and continually fed to the bearing the bearing will last a very long time. There are two simple checks that should be done to check if all is well on Babbit Bearings. The first one is oil sampling. Cheap insurance which will tell you what contaminants are in the oil. The second one is an annual check on the air gap at the bottom of the motor. If the air gap is found to be getting smaller your bearings are wearing.
Babbitt bearings are normally found in larger motors and almost always in direct coupled applications.
In high speed motors the replacement of anti-friction bearings is essential every 1-2 years depending on the severity of the application. It is not uncommon to find a 2-pole Babbit Bearing motor, 20 years old or more with the original bearings. These motors can be overhauled and the windings cleaned up on a regular basis but the original bearings are re-installed.
Babbitt bearings are also affected by shaft currents and we often find a NDE babbitt bearing insulated from the housing.
Babbitt Bearings are also much quieter than anti-friction bearings. Another area where sleeve bearings are very common is in the fan motors in home furnaces. If ball bearings were installed in these motor you would get and annoying clicking sound coming through your ductwork. The bearings in these motors are not made from babbitt, there are made form an oil-bronze material.
Babbitt Bearings are much more expensive than anti-friction bearings and you can’t buy them off the shelf like a 6316. If they are worn, (normally because of mis-aligniment or lack of proper lubrication), they need to be re-babbitted. For a high speed motor with a 3″ journal the re-babitting can cost in the region of $1,200.00 to $2,000.00 per bearing.
When a new motor is being purchased it will cost much more with Babbitt Bearings than it will wit anti-friction bearings and users should be aware that, in the event of a bearing failure, it will not be a 2-3 day turn around on the motor.
Babbit bearings have an initial high cost but properly looked after they are more economical over a long period of time.