Why is proper radial clearance important?

When presented with an opportunity to resolve a noise issue, VNC proceeded with a systematic approach in order to determine the root cause and solution.

It all began when elevated noise levels began to be reported in approximately 20% of the customer’s assemblies.

During the initial investigation, the shaft and housings were measured and found to be within tolerance.  Bearing inventories were also measured and individually tested for noise and were found to be good.

Forensic Examination

The forensic examination began by carefully disassembling the bearings. Microscopic investigation of the bearing races yielded evidence of brinelling in about 20% of the inspected bearings.

Brinelling is a material surface failure caused by excessive contact stress. When the contact stress exceeds the material limits, plastic deformation occurs and small indentations can be seen.

In addition to the signs of brinelling, small axial scratches were observed on the raceways at ball spaced intervals. The combination of the axial scratches and brinelling pointed to the failure originating during the installation process.

At this point VNC contacted the customer in order to verify proper installation procedures were being used in the assembly areas. Once the team confirmed that all technicians were using acceptable installation procedures, the focus turned to the suitability of the assembly fits.

The Hypothesis:

Although each of the components were meeting their print specification, the resulting assembly fit, including the statistical variation of each component, must be considered. Even if nominal dimensions yield a desirable assembly fit, the statistical variation of each component must be included in order to consider every possible assembly scenario.

This type of situation, where only a portion of the potential assembly scenarios create undesirable results could explain why only 20% of the customer’s assemblies were exhibiting brinelling.

After detailed calculations, it was determined that brinelling could occur when the shaft was at the high end of the tolerance range and the housing and the bearings were at the low end of the tolerance range.  In this scenario the resulting assembly fit completely removes the radial clearance within the bearing and gives the bearing excessive radial preload. This excessive radial preload correlates to excessive contact stresses which in turn, cause brinelling.

After more calculations, VNC advised that the issue could be resolved up by changing the bearing’s internal radial clearance specification to a “C4” rating.

The Solution:

Working with the customer and their subcontractors, VNC supplied 200 bearings with the new C4 radial clearance specification. These bearings were specifically numbered and special attention was paid to each bearing’s radial clearance and noise measurements.

Before assembly, the other assembly components were also measured, numbered, and tracked. By tracking each component in this manner, the resulting fit of each assembly could be accurately identified and recorded.

Over the next several weeks, the performance of the assemblies was monitored and the results were recorded.  Testing proved that the “C4” radial clearance specification successfully eliminated the brinelling and noise issues seen in the previous assemblies. With the root cause and solution identified, the customer changed their drawings to require the “C4” radial clearance on all bearings for future production.

Contact VNC Bearing today to find out how we can help you.

Grease Caps: Why Do Grease Caps Lengthen The Life Of Bearings?

When it comes to bearings, there’s a delicate balance between over-greasing, and not greasing enough. Doing one or the other may end up ruining your ball bearings, or drastically cutting its life-span. Sound like a tricky issue? It may seem that way at first, but once you come to understand why your bearings need grease, the easier time you’ll have with your bearing maintenance.

Grease caps are the peg-like covers found at the center of a wheel and are a necessary component of keeping your ball and roller bearings in tip-top shape. Often time’s grease caps go ignored until your bearings are already cracked and broken. If you want to increase your bearings designed lifespan, then you’re going to want to start paying attention to grease caps.

One of the hard-hitters in taking down your bearings are the elements: dirt, debris, water, salt, and sand that can be transferred from the road into your vehicles bearings. Bearings need lubrication, and using grease caps will ensure your bearings are running smooth and clean while reducing the odds of debris and other contaminants getting stuck inside your bearings. Grease caps improve the function and lifespan of your bearings by ensuring that they receive proper lubrication and come in all different varieties to fit every possible application. These caps can be either threaded, or press-on.

No matter which type you choose, keeping a grease cap on your vehicle is an absolute must. To ensure the best possible protection of your ball bearings, clean and repack your bearings with grease at least once a year. This is essential in wheel bearing maintenance. For more information on bearings and grease caps, or to request a personal quote, feel free to call VNC Bearings at 800-862-3211.