Reliability Engineering Snapshot TM

Illustrated Case Studies in the Maintenance Reliability Engineering World of Failure Analysis, Predictive Maintenance, and Non Destructive Evaluation

Did someone say that the "L₁₀" design life on this bearing was 14 years, or 14 weeks? Any bearing designer will tell you that I must be referring to 14 years, and any maintenance engineer will snicker and tell you that I must be referring to 14 weeks. That's because we truly are our own worst enemy when it comes to lubrication failures.

Look at this nightmare to the left. This is the second bearing on this equipment. The first bearing lasted 14 years while the second bearing lasted only 14 weeks.

The housing of the second bearing was so full of product that it welded the roller cage to the outer raceway and bearing housing. In the picture to the lower left can be seen white product between the labyrinth seals and the clamp rings. This region should be chock full of grease, but it wasn't. Even the rollers have product all over them. This bearing is a large 10" diameter split bearing. When the first bearing failed, it was completely empty of grease. We hadn't worked on the equipment it was on for all of those years.

Why did the first bearing fail? Because the lubricator that used to take care of this bearing retired three years ago. Along with him went all of his tricks of the trade. Regardless of what the preventive maintenance sheet told him, he use to keep the bearing housing completely full of grease. The unit only turned one to five RPM, so churning of the grease was a non-issue. He use to do one thing more, he use to pump the housing with grease until it came out of the labyrinth seals big time.

AAAAAAAAAAHHH you say? It goes against everything you were ever taught about the proper greasing of bearings? Well step right up my boy into the ugly world of product contamination. In the mining industry you can't get away from it, it's all around. Most of the time equipment gets buried in product that is leaking out of elevators, screw conveyors, mills, screens, you name it we leak it. Yes there are parts of the plant that don't leak yet, but give it time, we'll make it leak soon enough. Stuff wears out, things get altered, and altered again and again and again. New stuff gets put in where it can't fit and then we make it fit. Then someone talks about a bearing "L₁₀" life! Not in this world!

Over the years I have looked at the effectiveness of various sealing devices in "buried service." None of them hold up. Lip seals are a joke, the product abrades them away in nothing flat. Labyrinth seals are an open invitation to death by firing squad. The product gets inside them and locks them up. Then the labyrinth seals lose their grip on the shaft, but the set screws on the seal become milling tool bits that cut into the shaft. Now you have an undersized shaft and a larger opening for product to get into the bearing housing. Sealed bearings don't fare any better than lip seals except that the product takes a little bit longer to do its dirty deed. Deflectors, who came up with that idea? Deflectors are great until wherever they are deflecting to becomes filled up, and then they get buried too.

With regard to equipment that has run fine for years and years, whenever I have dug out the bearing housing from underneath a mound of product I have always found the seals blown out and tons of grease encased around the blown seal. The outer regions of the grease react with the product that makes a crusted but pliable shield. When the crust is broken there is good grease inside waiting to react and "heal itself." The bearing housing seal is untouched by the product.

So how does one survive in this Jurassic Park? There isn't a lubrication consultant that will tell you this, but if you have grease lubricated equipment that operates under 30 RPM and is routinely buried in product, blow the seals out and bury it in grease. Honest to God I thought that I would never ever hear myself say something like that, but its true.

That was the trick that the old lubricator used to make the first set of bearings last so long. Excuse me, do I sense someone out there thinking of the word "good-housekeeping?" That might be the name of a company, but it has no relevance in an industry that leaks like a sieve. Trying to keep up on leaks in this industry is like a Chinese water torture. It's never ending, and you will go crazy.

Here's some good housekeeping for you in the picture above. This is a picture of the rest of the equipment that is below the bearing housing shown in the middle picture. Notice how clean it is so that maintenance can work on the top bearing in the middle picture. Notice the standing water on the lower bearing housing in this picture. With a one inch hose going full blast on both of these bearings that have useless labyrinth seals in them, where do you suppose the water went?

I will title this picture "Just Shoot Me Please."

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