A machine manufacturer rediscovered the old axiom regarding extrapolations after experiencing many bearing failures in its 40-hp air blowers. The design incorporated life-time lubricated (sealed) blower bearings in rotors that spun 20-mm shafts at 22,000 rpm, and the bearings did not last very long.
The designers knew that mechanical components are designed for a range of application. If a passenger car tire has a rating of 115 mph, it would not be advisable to operate the vehicle at 150 mph. Decades ago, some bearing manufacturers published the recommended re-greasing intervals as a function of bearing bore diameter, shaft speed (rpm), and bearing type. Others factored-in the load imposed on the bearing. Grease lubrication for 20-mm bearings at 22,000 rpm may be possible only if new grease is continually injected and a path is created to continually dispose of the spent grease.
Although we argued against grease lubrication with sealed bearings at extreme speeds, the equipment manufacturer didn’t seem interested in abandoning the clearly out-of-range grease application. Nevertheless, our out-of-the-box solution was forwarded to the manufacturer; our advice was to explore two courses of action without procrastination:
1. A small volume of air could be diverted into air bearings. The power losses may be no different than the frictional losses of rolling element bearings
2. The self-contained fully Air-Driven Intermittent Oil Spray (“ADIOS”, see attached Book List, Item 21).
The point of this story is quite simple: Serious inefficiencies and backward thinking still exist today. At some plants there is no budget for solving serious problems, but there is time and money available to debate, defer, and finger-point. No money for lasting reliability improvement, but time and funds to fix each of the many repeat failures. Thinking “out of the box” would be better than tinkering with marginal improvements and approaches that are mere extrapolations of outdated designs.TRR
Editor’s Note: Click Here To Download An Updated (May 2020) List Of Heinz Bloch’s 22 Books
ABOUT THE AUTHOR
Heinz Bloch’s long professional career included assignments as Exxon Chemical’s Regional Machinery Specialist for the United States. A recognized subject-matter-expert on plant equipment and failure avoidance, he is the author of numerous books and articles, and continues to present at technical conferences around the world. Bloch holds B.S. and M.S. degrees in Mechanical Engineering and is an ASME Life Fellow. These days, he’s based near Houston, TX. Email him directly at [email protected].
Tags: reliability, availability, maintenance, RAM, grease lubrication, oil mist, professional development
