Part I of our e-zine on ball bearings covered what can happen to a bearing due to lack of lubrication. In this e-zine, we will discuss what can happen when the bearing itself fails.
The ball bearing elements can also fail. Balls bearings are "hardened" during manufacture and then "tempered". This makes them very hard on the outside and, due to the softer inner core, not too brittle. The result is a ball bearing with a tough, polished, low friction outer shell and a durable, but strong inner core. The outer surface of a bearing is not too thick.
If a bearing is carrying a load but not rolling or turning, the entire load is being carried by only a few of the bearings. When this happens, the load can pound up and down on the very small areas where the balls contact the races. Repeated contact in the same spot can damage the metal in the same way you can repeatedly push your thumb into an orange and create a soft spot.
When this happens, the hardened skin layer actually bends just a little as it pushes down on the core and then relaxes. If too many cycles happen, the skin layer may start to crack away from the softer core. If the crack continues to grow, a small section can finally break off as a separate piece. This type of fracture is called "spalling." When this happens, two problems start occurring. The first problem is the damaged area ruins the perfectly round geometry of the ball bearing resulting in a depression, similar to a pothole on a highway. If the hole is shallow, the bearing can roll over the first edge, falling into the hole, and then hit the second edge, climbing back out of the hole. This repeated up and down pounding will gradually destroy the bearing. The second problem is the loose piece that separated from the bearing. This piece can fall into the track on the race and either jam under the next ball bearing or, if it is small enough, the next bearing may hit it and roll over it. If the part jams under a bearing, it will be pushed along scratching and scoring the bearing raceway. This will result in more friction. If the ball bearing rolls over the piece, the bumpty-bump movement over the hard little piece of metal can now start to damage the other ball bearings.
As the damage progresses, the perfectly held alignment of the shaft is lost. The shaft starts to wobble from side to side. If this was your lawn mower, the blade might start to smash into the blade cover. In a ceiling fan, the fan blade might start to wobble. This is just one example of how a bearing can go bad. There are many other ways a bearing can fail, so, next time you have a "bad" bearing day, call us at The Warren Group. We're here to help you figure out why your bearing went bad.