How Load-carrying Capacity Affects Bearing Service Life

Blog | July 1st, 2019

Rolling elements, just like human beings, are expected to handle stress. Now, people do succeed in dealing with such pressures, at least to some degree or other. For bearings, it’s a little harder. They can’t adapt, not easily. No, to properly deal with load-induced stress, their carrying capacity should be determined before they’re pressed into service. To think otherwise would be to court disaster in the form of rolling element fatigue.

A Speculative System Study

Hypothetically speaking, a heavy burden will accelerate bearing fatigue. The moving components experience plastic deformation, for a weighty load is pushing down way too hard. Micro-welds take place between ball contact points, then there’s race spalling to add to matters. The load-carrying capacity of the rolling elements is no match for the actual load weight, so the bearings age rapidly. Fatigue foreshortens the life of the mounts even though they’re well-lubricated and regularly maintained. No matter what the applied solution is, there’s no getting away from the fact that bearing service life is compromised because of the excess load.

Don’t Stress: Using a System Troubleshooter

Maybe the system designers and equipment fabricators should try a change of perspective? Perhaps the load is exactly as heavy as it needs to be, but the load-carrying capacity of the bearings hasn’t been properly assessed. The equipment shafts are within specs, so there’s little to no deflection issues to worry about. Meanwhile, despite maintenance, the system bearings are overheating. They’re also squealing noisily. Either when in motion or during the startup/slow down phase, the noise is penetrating the whole machine frame. It gets worse when load spikes are applied, so the lead maintenance tech immediately suspects the cause. On dismantling the system, on forcing downtime into a high-volume production line, the problem is revealed. Here’s what’s going on with the bearings:

  • Contact point microwelds
  • Alloy discolouration because of load overheating
  • Rolling element path spalling
  • Ball-induced race grooving

So, what’s the solution to the loading issues? One approach involves a load reduction strategy. That’s a workable plan, but now the system is hit by productivity problems. Output targets are missed, so profit bottom lines shrink. Getting inside the equipment frame, a preemptive mount redesign takes care of bearing service life. Still, what if the equipment is already in use? Perhaps the system payload has increased recently, so a matching load-carrying capacity needs to be injected into the equipment bearings. Fortunately, there are numerous load-bearing formulas and tables, but someone’s still going to have to do the dirty work and replace the failing bearings.

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