What makes a good, quality bearing, and what causes bearings to fail?
Rolling bearings come in many types, including ball, cylindrical, spherical, and tapered types. Most are designed to support a combination of radial and axial (or thrust) loads simultaneously, plus they reduce rolling resistance and power consumption. The tapered roller bearing is most suited to conditions with large loads that experience a significant axial load component, which makes them the obvious choice for heavy truck wheel hubs.
To produce a high quality bearing, you need extremely clean steel and excellent control of geometry. Prior to 1945, you may have called bearing manufacturing and material technology an art; there was a wide variation in quality. Today bearing steel quality is much improved and modern manufacturing techniques can provide greatly improved accuracy of bearing geometry and smoother rolling element surfaces.
To identify quality differences in bearings, we first look at the accuracy of the geometry and secondly at the material cleanliness. The playing field for bearing manufacturing technology has become fairly even, but there are quality differences between manufacturers (especially some from developing countries) and specific design enhancements can be made to the internal geometry to improve the robustness of the bearings. It is important for manufacturers of mechanical equipment to understand and check these features.
The predicted life of a bearing refers to metal fatigue resulting from surface stress. If a bearing is kept clean, is properly adjusted, has adequate lubrication, and is sealed against the entrance of dirt and water, metal fatigue will be the only cause of failure. But metal fatigue is rarely the reason bearings fail in truck wheel ends today.
In reality, commercial truck wheel ends typically fail due to inadequate lubrication (not enough, or contaminated with dirt or water) or improper bearing adjustments. There are some other failures related to bearing rings moving around in their mountings, but those tend to come and go due to other issues. Contamination can be from internal sources or a result of a seal or hub cap failure. (We could add pictures to identify a few of these if we want that type of article or not)
Today’s truck wheel end systems and components contain many design improvements that eliminate the occurrence of many of these premature failure causes, like bearing adjustment and seal installation damage. The best way to avoid bearing failures is to check for a few things during pre-trip inspections and during preventative maintenance intervals:
- Make sure the lubricant is clean and at the correct fill level,
- Check that seals and/or hubcaps are not leaking, and
- Check for improper bearing adjustment by ensuring that the wheel end spins freely and smoothly and that there is no excess movement or “chucking”
The frequency of these inspections depends on the service conditions in which you run. The tougher those are in terms of mileage accumulation and severity of conditions (heavy loads, dirty, extreme temperatures, heavy braking, etc.), the more often you should conduct thorough inspections.