Vibration Analyzer for mtr, Worth it or not?

Hi,
I just reported to the boss yesterday that one of our 150 H.P. compressor motors didn't sound right. I speculated that it might have a bearing or coupling problem. Damn guy had the gall to ask me what the plan was to fix it! I removed the guard & used a dial indicator to check the shaft runout & end play. I couldn't find any glaring reasons for the change of the "tone". Pretty hard to diagnose a rear bearing with a dial indicator in my experience. The bearing temperatures are normal. Maybe I just need to clean the old ears out. Maybe too much motorcycle riding over the weekend has "tweaked" my ear drums.

I mentioned that a vibration analyzer would be a good tool to have in the old tool box for these kinds of situations.

He is looking into the tool purchase. I was wondering if any of you guys used vibration analysis & had any success with it.

I suppose there are a lot of different types of analyzers. A lot different kinds of failure tolerance among bosses too! I suppose that if a bearing failure is prohibitively expensive, the monitoring costs are justified.

Feel free to leave opinions here!

Bd

Vibration analysis is good stuff. But the equipment is expensive and you'd have to use it alot to justify the cost.

A better way is to use a contractor to do the vib analysis. They do enough of it to justify the best equipment and good training. That doesn't mean that they all do good work. Check out there credentials first.

In my experience, motor repair shops generally have good vibration analysis people on staff.

Back in the dark ages when I was in the navy

I was trained to do analysis of sound in the ocean. Obviously we weren't listening for whales. Later I/we made a press monitor. We could easily see bearings start to go bad before the actually went bad. If you know how to interpret the frequency spectrum you can learn a lot.
However, for starters you will not have that training but modern systems can at least compare a good system with a bad system.

I would go with DickDV's suggestion to find people experienced in using the equipment and interpreting the data.

Peter Nachtwey said:

I would go with DickDV's suggestion to find people experienced in using the equipment and interpreting the data.

Click to expand...

+1

Whilst simplistic comparisons can be made between "readings now" and "readings then", proper interpretation of results requires proper training and the field experience to go along with it.

Vibration analysis isn't a "Black Art", but it comes pretty close.

Tag along with a guru for a day and you'll see what I mean .

Muz

I also saw the Navy and a few industrial operations get on the bandwagon for vibration and or sound analysis on installed motors. What seems to happen is they buy the package at 5 thou and do a few or even all motors and then that is the end of that and the gear sits in a closet. The whole idea is to do it regularly and compare this year to last year. The downside to this is a factory maintenance guy does not do it often enough to stay good at it.

I would also recommend having a good motor shop do two things
1. Balance all motors after rebuild
2. Do the first and maybe second year of your program and train your people while they are at it.

Like any other contractor or service the quality depends on the shop and their ethics.

Dan Bentler

I first used one back in the 80's. Prior to that we would put a screwdriver to the ear and pretend we could tell if a bearing was on its way out.
We marked each motor with several paint dots so that the readings would be taken at the same locations each time. The readings were taken about every 3 months and without even understanding what they all meant we were able to prevent catastrophic failures by plotting the readings on a graph and simply looking for variations from our baseline readings.
We were never that accurate at predicting failures with the screwdriver.

There was an article on Imotes which is a 1 cm computer waifer where each has its own operating system and individually were limited however when you place several hundred of these in the same area they gain in capabilities when one fails the others reroute their communication path to the next shortest route. Anyways one plant in Canada used these to record vibration and temperature on all their motors, gearboxes etc for thier predictive maintenance they estimated their savings in the range of 300,000 per year

Hi,
Thanks for all the ideas & opinions everyone.
Seems like the majority agrees that this should be left to someone who we can trust, who has the tools & experience.

BD

The critical thing for me would be to ask yourself "If I tell the boss the bearing is on the way out, what will he say?"

I was recently tasked with installing vibration and temperature monitoring equipment on rotating plant but am worried if the equipment says the bearing is critical it will get ignored as what my boss really wants is a system which tells him everything is fine. He's not a very bright boss!!!

Seems to me your boss needs to make the choice between preventive and breakdown maintenance, stay committed to his choice and be ready to pay the bill for it.

Dan Bentler

Another way is to use thermal imaging (not quite as good and takes longer (some times) to show compared to vibration).

And if you have a thermal imager you can use this on your panels as well for electrical PM.

See Flir

504b,
We have the thermal imaging done annually to all the panels by a service contractor. After 10 years he is still able to find some things that need cleaned tightened.

One time a few years back he shot us a picture of this particular motor I'm troubled with. The temperature of the fan end bearing was way hotter than normal. The image was taken in the first thirty days of operation. The bearing coooled down after a few days though so we never took the time to have it replaced. Seems like it may have started to act up again, only this time it sounds different. It's going to cost thousands to get it replaced. I just wish I knew for sure the bearing was bad because right now I can't feel any heat or see any play in it. If I called a "Vibration Guru" in to look at it, he may declare it to be one way or the other. That would just add to the cost of the repair it seems. I should probably just go ahead & have it replaced & re-balanced since it has over 12.000 hours on it. A lot of our motors run much longer than that though.

Most of our motors don't get this kind of attention. This one happens to be critical to the operation during the summer months.
BD

As a general rule, a good vibration program will result in fewer bearings changed rather than more. The bearing manufacturers publish vibration signatures for their bearings and you can predict with good accuracy just when the bearing will fail. Knowing that, you can schedule the repair at the best available time rather than wait for a breakdown, of course, right in the middle of your most important run.

Especially with high and premium efficient motors, the air gap between the rotor laminations and the stator laminations is so small that very little slop in the bearing will result in a "rotor rub". When this happens, your motor is toast, ie, not repairable, because all of the laminations are smeared together from the rotor rubbing on the stator. Restacking the laminations is only economical in the largest motors.

If vibration analysis only saves one rotor rub, you've probably paid for a lot of contractor time to do the analysis.

gphillips said:

...... Prior to that we would put a screwdriver to the ear and pretend we could tell if a bearing was on its way out........

Click to expand...

Don't kid yourself. The human body has great potential of detection.

I have no doubt that an experienced, concientious mechanic laying on of hands and listening to bearings through a screwdriver could detect an impending failure in plenty of time to schedule a successful intervention.

I'd suggest a stethoscope though... keeps yer beloved punkin a little farther from the spinning stuff.

The OP's problem seems to be more of a local version of the ubiquitous lunkhead boss syndrome, which tends to discourage the concientiousness of the mechanic.

Let's see:

Cost of vibration analyzer?
Cost of stethoscope?

Pay of mechanic reporting problem in time to prevent major shutdown?
Pay of mechanic ignoring potential problem?

Concientiousness trend of mechanics encouraged and rewarded for being concientious?
Concientiousness trend of mechanics rewarded with wise-assed answer from ignorant boss?

Cost of replacing 2 150 HP motor bearings on scheduled shutdown? $2600?
Cost of replacing 2 bearings after shaft goes bad and loss of production during unscheduled downtime? $ 2600 + much more.

Cost to nationwide (worldwide?) economy of supporting the sum total of ignorant, useless, dead weight morons in managements across the country instead of applying a fraction of that money to support those actually doing something useful?

No wonder the economy is in a shambles.

SKF has a "vibration pen" that will give indication for some types of impending bearing failures as well as things like imbalance and misalignment. It isn't as good as the signature analysis type of equipment described above, but it is a lot less expensive.