When rolling element bearings are required in manufactured products, an installer on the production line is often responsible for final assembly of the bearing, and for greasing and sealing it. This assembly task includes adjusting the bearing carefully so that its internal clearances — radial and axial distances between its inner and outer rings — meet the application requirements.

At the end of the line, workers test the product. In many plants, testing consists of an experienced worker listening closely to the product as it operates. Often, this is the only way to check if bearings and other components were installed properly.

Though usually successful, this procedure is susceptible to errors. The sheer number of parts in a typical bearing arrangement requires OEMs to keep an extensive inventory on hand. The installation process is time-consuming, and with the number of tasks involved, even an experienced worker can make a mistake that later surfaces in the form of poor bearing performance. Also, the sound test is often not sophisticated enough to detect signs of a bearing problem.

Today, new bearing designs, improved installation tools, and monitoring devices offer manufacturers more reliable alternatives to traditional installation methods. These new methods take less time, reduce warranty costs, and improve the performance of the end products.

For example, pre-adjusted, pre-lubricated unitized bearings greatly simplify the installation process, decreasing the risk of costly errors. Tools equipped with pressure gages speed installation while providing feedback on the force required to assemble the bearing (drive-up force). Condition monitoring devices, such as vibration analyzers, present an electronic picture of machine health, so OEMs can detect problems before a product is shipped.

Large manufacturers using high-volume assembly line or batch manufacturing methods are most likely to use the new concepts. But smaller OEMs can also benefit. The investment in new bearing designs and equipment pays off by reducing the cost of assembly time, rebuilds, and warranty costs.

Unitized bearings

The use of unitized bearings — self-contained, pre-adjusted units — is increasing. This is especially so in the automotive industry, where unitized wheel bearing assemblies, called hub units, have become virtually standard in domestic cars.

Previously, assembly line workers collected and assembled wheel bearing components — inner and outer rings, grease, seals, spacers, and lock nut. They were responsible for adjusting bearings and lubricating them with the correct grease in the right amount. Errors could occur at each step of this procedure.

By contrast, a hub unit incorporates all bearing components. It arrives at the production line preset, greased, and sealed for life. Hub units greatly simplify the mounting process. Instead of handling many separate components, the assembly worker simply bolts the unit in place, reducing the number of installation errors. Since these units were introduced, auto manufacturers have seen a large drop in wheel assembly warranty claims.

Bearing designers are working to integrate related functions into the hub unit. For example, one type of hub unit, which is typically used in driven wheel applications, also transmits power to the wheel via a splined inner ring bore, Figure 1. Installers bolt the unit’s flanged outer ring to the suspension, a procedure that takes only a few seconds.

Other hub units incorporate a wheel speed sensor, an important part of the anti-lock braking system, Figure 2. Currently, in most vehicles, the sensor is a discrete unit that is mounted separately. After installation, the auto manufacturer must perform a diagnostic test to ensure that the sensor is sending the correct signal. Including the sensor in the hub simplifies installation. Moreover, the diagnostic check can be performed off-site by the hub unit’s manufacturer, saving time on the assembly line.

The auto industry is not alone in reaping the benefits of bearings with integrated sensors. Other companies, wanting to prevent machinery breakdowns, use sensor bearings to obtain feedback on critical machine functions, such as speed, load, force, and temperature.

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