To Do or Not to Do… That is the Question – Vibration Acceptance Testing

Mike Fitch, Ludeca, Inc.

Imagine buying a new car and not taking it for a test drive first. That might not be so bad, given the built-in protections covering the auto buyer these days. But what about buying industrial equipment? Purchasing a new machine and finding unexpected problems after installation and integration into your manufacturing process is the stuff maintenance and production nightmares are made of.

Of course, you will have a warranty, just like when buying a car. You might even be entitled to a loaner. But none of this is of any real use to you if your problems and production disruptions continue.

In most industries, the process of manufacturing is just slightly less expensive than the price received for the product manufactured; the margin is tight. This being the case, unplanned costs are unwelcome additions to the manufacturing process. Most modern industries have recognized the value of process engineering and are making sure that capital expenditures for industrial machines is spent on the right machines.

To meet that challenge, acceptance testing can be employed, and if properly designed and implemented, the likelihood of unplanned costs incurred after commissioning can be virtually eliminated. Most facilities don’t “design” their acceptance testing, but rather simply apply a standard overall measurement considered to represent a typical machine in “generally” good condition. This is much better than no acceptance testing, and means you probably get “generally” good results.

But if you prefer to ensure good results, then you might want to actually design your acceptance testing to do so. Here’s how:

1) One key component of acceptance testing will include gathering vibration data. Understand that an overall vibration signal is a conglomerate of numerous components. Among those components are:

Note that no mention is made of bearing defect-generated vibration. We assume acceptance testing will mostly take place on new or refurbished assets, hence, if there is a bearing defect it will contribute to the overall vibration measurement, but its contribution will be relatively small until the bearing is well on its way to failure. In fact, most early to mid-stage bearing defects will not, by themselves, cause machines to fail the generally used acceptance standards.

Consider that a vibration signal where the RF constitutes ¾ or more of the overall signal would be considered acceptable. This is the expected healthy percentage. The reason is, in a typically healthy machine, the residual unbalance is the dominant vibration. Unbalance to some level is always expected, and when the residual unbalance is reduced to a level that won’t adversely affect the equipment service lifetime, this is acceptable. Therefore, if the unbalance is limited to a healthy level and that level represents 80-90% or more of the overall vibration, then that machine is highly likely to be a healthy machine.