Failure analysis of fluid machinery often focuses on the part that failed. If the bearing failed, it must be because “the bearing is bad.” Mechanics and machinists then often react by doing the obvious: Replace the bearing. However, if we replace parts without first determining why the part failed, we set ourselves up for repeat failures.
Best-in-Class (“BiC”) user companies teach their craftspersons that all failures have causes. Well-taught craftspeople are no longer just parts changers; they are individuals who find and eliminate failure causes. They realize that failures of mechanical components are always attributable to one of four cause categories: Force, Reactive Environment, Time, and Temperatures, “FRETT.” Whenever a part is subjected to an out-of-normal, or out-of-allowable “FRETT” contributor, the part will fail.
Technicians at BiC user companies may determine if the failed bearing shows signs of excessive interference fit = F, high force acting on rolling elements; a reactive environment (perhaps due to intrusion of contaminants) = RE; inadequate lubrication originating with flawed lubricant application, which would be evidenced by indications of high temperature = T; or the last letter in FRETT − T = Time. Operation beyond the design time of a component, or storage time of greases will show up in the chain of causes that led to parts failures.
Good texts will point to elusive failure causes. Consider this simple example: mounting constant-level lubricators on the wrong side of bearing housings. In fact, mounting a lubricator on the down-arrow side of shaft rotation will promote air ingestion and deprive the bearings of proper lubrication. So, if your technicians say mounting on the wrong side works just fine, you might learn (too late), that they tinkered with the height setting of the wing nuts supporting a lubricator’s transparent bulb. This would be a tough lesson.
Learning and understanding how parts, components, and entire machines perform is a key ingredient of dependable operation. Supported by perceptive managers, such learning will allow parts changers to join the ranks of true RAM professionals.TRR
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 at firstname.lastname@example.org.
Tags: reliability, availability, maintenance, RAM, bearings, fluid machinery, pumps, motors, constant-level lubricators