Have you got an airplane but dont know how to fly?

by John C. Robertson

Imagine wanting to fly so badly and saving money for years to buy that special airplane. When you finally get it, you realize that it takes a whole lot more than investing in an airplane to get the benefits and pleasure of flying. No matter how hard you try, there is much learning and practice and certifications to master before getting behind the controls by yourself.

As a consultant who specializes in precision maintenance, I am appalled at the number of informed and meaningful companies that have invested thousands of dollars in analytical instrumentation and computer programs to enhance their maintenance and operations program. Unfortunately, many of them still do not know how to use them to their full advantage. In this day of sophisticated diagnostic programs, it is very common to see major faults happening because the analyst did not use the analyzer to its full extent.

In a recent in-plant investigation, I looked over vibration data sheets that contained no spectral data, only numerical values, and these were all recorded by a contractual source in only the horizontal direction on all of a machines bearings. Wake up! This kind of data collection was the only way to go when we had nothing but the good old IRD 350 analyzer to rely on. The engineers concerned were puzzled about why an intermediate gear drive shaft had "suddenly" sheared. Without the data taken from the vertical and axial points on the machine, they were blind. This disaster was giving out early warning signs that something was amiss, but nobody thought that it was necessary to take data because of the vibration analysis report received. A root cause failure analysis revealed the cause of the shear was created when a keyway was machined in the shaft without a stress-relieving radius at the root of the keyway.

Because some management have lost faith in their in-house predictive maintenance program, they have often turned to contractual help and shelved their existing analysis program. This does not always resolve the problem, as the previous example shows. Regardless of who collects the data from the machines, there has to be someone from the engineering staff who can read the data and make informed decisions. After all, no one wants to think that their maintenance program is still in a reactive mode. But in many cases, this is still apparent from the number of machinery failures studied.

Having a good diagnostic program does not necessarily mean you have a good precision maintenance program. An analyzer will detect faults if the data is read correctly, but it cannot effect the repair needed to get the machine back into long-time service. That part of the solution is not so readily available. This takes skill and experience, commodities that are in short supply across the United States. Certification of analysts has become a hotly debated subject as to whether it is reducing the number of failures across industry. This may be responsible for a greater number of failures being detected, but not corrected. These failures repeat because a lack in skills cannot correct the fault, and in a short time, the analyst successfully points the same finger at that same fault again.

An effective precision maintenance program must rely heavily on both a good diagnostic program and hands-on skills. Todays mechanics/millwrights must be skilled and knowledgeable people who can translate the analysts findings into reality at the machine. Too many times, someone who has done the same job before creates a fault that is considered too trivial to rework.

But without that mechanic having an understanding of how the machine works, that action can cause a major fault because someone trusted that persons experience. This type of maintenance must not be tolerated. Use procedural guidelines that clearly delineate responsibility, offer step-by-step detailed instructions to ensure accuracy, provide hold-points where test results are needed, and show condition alert and alarm warning levels. Procedures also provide consistency, accuracy, and accountability. Never rely on "experienced" people to set undocumented standards. They could leave you tomorrow, and new people must have company-approved guidance if they are to contribute to a good precision maintenance program.

Unfortunately, the technical manuals issued by the equipment manufacturers are not necessarily the greatest guidelines in the world. Many manufacturers are still issuing instructions on shaft alignment using a straightedge and feeler gauges, which is pretty archaic in this day of laser alignments accuracy to approximately 1/460th of a millimeter. Many problems can be directly traced to components that were substituted for the original designed part because there was no spare available, or delivery lead times were too long and nobody thought to record this as a "get-me-home" fix that would soon be replaced with the design specified part. When the failure happens again, the rogue part is considered to be the real thing and the problem compounds. This may cause resonance that can destroy machines even when they are not operating because the new operational frequency was not taken into consideration for the design of the machine.

I have also seen cast iron motors replaced with new motors that are made of much lighter materials and meet all of the other operational set-points except the frame size. On startup, vibrations are so severe that the unit must be shutdown. When the problem is investigated, in many cases, it surely couldnt be that new motor that has caused the problem, so more downtime is experienced looking for the gremlin. Always check back on what work was done on any job before hunting for gremlins!

Substituted anti-friction bearings are another source of problems associated with resonance. When the newly created operational frequency gets within +/- 500 cycles per minute of a machines natural frequency, it will cause vibration because of resonance. A vibration analyzer with either a strobe light or phototach provides phase angle relationships that are helpful in determining resonance conditions. Get to know what an analyzers capabilities are before you purchase one by having the sales engineer demonstrate it fully. Dont accept the first one you try as too many people have finished up with a glorified digital stethoscope. Most manufacturers offer specialized training, but none of them guarantees to make experts. That expertise can only be achieved in the field.

If you really want to fly that airplane, then next time you fly any commercial aircraft, observe what is going on in the cockpit before take-off. Both pilots, the engineer and cabin crew thoroughly check out every system that is going to keep that airplane flying to get you safely to your final destination. They diligently stick to their procedures and check sheets, and even with a small hop to the next destination, they repeat the same process before departing again. These crew members are also very highly skilled people and do not leave things to past experience.

Doesnt that make you feel better?

When we apply this approach to our jobs, there will be no need to go back to the same job again to try to effect any corrections. There is an approximate 25 percent chance that you will create a problem on each successive return to the same job. So, it behooves us to do the job right the first time, every time to make sure the equipment does its job the first time, every time.

John Robertson is the maintenance reliability specialist for Strategic Work Systems, a consulting firm with offices in Greenville, S.C., and Mill Spring, N.C.  For more information, call , e-mail or visit www.swspitcrew.com.

MRO Today.  Copyright, 2000.

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