Over-lubrication in Bearings: Why Should This Be Avoided?

May 27, 2018

Is bearing over-lubrication a problem? It seems unlikely. After all, we’d expect more oil to improve the slippery effect that governs bearing utilization. Counterintuitively, that “more is better” approach can actually impair the rolling elements. At this juncture, the best advice we can give is to avoid this unwise practice. But why? What possible reason could there be for this admonition? Here, let’s put the overly greased component under a microscope.

Runaway Lubricating Films 

It’s fascinating, the effect the extra lubrication film is having on the rolling elements. When a lubricating film forms properly along the surfaces of a bearing, the balls turn while maintaining a protected contact area with nearby rolling elements. Now, however, the over-generous application of oil or grease is occupying too much areal space in the bearing cavity. Instead of spinning and running down the twin races, the rolling elements stall. They’re skating inside that cavity, not rolling. Help, trouble is in store for this overloaded ring of moving parts.

The Dominos Fall 

Like falling game pieces, the effects spread. The oil churns, it ferments and experiences chemical agitation. The lubricant is beginning to break down. Heat is no longer distributed throughout this intelligently formulated greasing agent, and the skating, formerly rolling, elements force the distressed fluid to one side. The lifespan of the greasy mix is rapidly coming to a premature end, which means the lubricant is oxidizing. All in all, the bearing is beginning to cook. Again, that phenomenon seems counterintuitive, especially after more oil has been added, but it’s the overly filled bearing cavity that’s responsible for that seemingly unwarranted action, not the oil’s formula.

Spotting Over-Lubrication Symptoms 

Basically, the pressure inside the bearing has increased to the point that something has to give. Clearly, the rolling parts aren’t about to break, at least not yet. No, it’s the lubricant that’s forced to compress. Expect to see liquid traces bleeding from the ring. The lubricant has oxidized and the oil thickener has separated. Oftentimes, a new tech will feel the waves of heat coming off the device, and he’ll assume a mechanical fault. In point of fact, the messy residue is a result of too much grease, not a frictional defect. Most tellingly of all, if the issue is taking place all over the factory, the problem isn’t a mechanical defect.

If bearing over-lubrication problems are plaguing equipment all over the factory, take the machinery out of service and test the automated feed systems for a pumping error. However, if the equipment is dotted with manually filled grease nipples, it’s time to retrain the responsible maintenance tech to use his grease gun properly.

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