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Want to lower HIGH horiz vibe readings !

Want to lower HIGH horiz vibe readings !

Want to lower HIGH horiz vibe readings !

(OP)
Greetings -


      -               pulley
fan  - -------------|||---shaft  
   -    /\       /\      |          
    -  brg4   brg3   | belt
                          |
                motor|||pulley
           
What could cause high horizontal readings on the motor bearings? Pulley misalignment? Belts too tight? Belts too loose? The motor bearings are sealed and not regreasable. Shaft guard prevents getting horiz readings on fan shaft bearings at this moment. What course of action is recommended to bring down the horizontal vibe?? See numbers below. Questions are welcome. Answers are too.

ODE motor bearing .75 in/sec peak at 1XRPM (3750)
 DE motor bearing .57 in/sec peak at 1xRPM (3750)

RE: Want to lower HIGH horiz vibe readings !

Is it 1x rpm of the fan showing up on the motor?  I assume this is the case since 3750 is not likely a motor speed unles you have an electronic drive.

Does the belt lie horizontal between sheaves, vertical between sheaves, or at an angle?

Did you check axial on the motor as well?  How about fan readings? Did you leave 'em out because they were much lower?

Was there a sudden increase?

RE: Want to lower HIGH horiz vibe readings !

(OP)
Most likely the fan RPM *is* showing up at the motor.
Motor RPM must be 3600 RPM. Belt is at an angle. Here are all readings at the biggest spike.

                            H               V              A
Bearing 1(RPM)  .748(3750)   .171(3600)
Bearing 2(RPM)  .569(3750)   .215(3600)   .089(3750)
Bearing 3(RPM)                     .062(3750)
Bearing 4(RPM)                     .39 (3750)

New vibe program. First time readings taken on this fan.
I'm thinking fan shaft imbalance?? ---Nisqually--

       
             




RE: Want to lower HIGH horiz vibe readings !

I wouldn't think fan unbalance would create vibration at the motor.  I would think more likely pulley misalignment or eccentric fan sheave.  Other opinions?

RE: Want to lower HIGH horiz vibe readings !

also check belt tension

RE: Want to lower HIGH horiz vibe readings !

is the unit mounted on anti vibration mounts i have had many cases where where the drive motor has been running at 10-15mm/sec(mainly vertical and axial planes ) and the fan bearings have been no more than 4-5mm/sec after further investigation i found that some of the av mounts were worn.
i agree with electripete and would suggest check the pulley arrangement

RE: Want to lower HIGH horiz vibe readings !

Nisqually - Did you solve your problem?
Is there a reason to use a pulley instead of a flexible coupling at 3600 rpm?
Anyway, I always first ask:
1. Are readings taken using a magnet mount? - If so, is hand-pressure also used - especially for horizontal readings as you won't stop the vibration, but will get more accurate readings.
2. Is a flat surface used for magnet or glued-on mounting, and are readings at bearing centerline-not at a long overhang?

We usually recommend tripping at 0.62 ips peak velocity.
I like to pass along this great on-line calculator:
http://www.wilcoxon.com/calculator.html

RE: Want to lower HIGH horiz vibe readings !

Nisqually - Did you solve your problem?
Is there a reason to use a pulley instead of a flexible coupling at 3600 rpm?
Anyway, I always first ask:
1. Are readings taken using a magnet mount? - If so, is hand-pressure also used - especially for horizontal readings as you won't stop the vibration, but will get more accurate readings.
2. Is a flat surface used for magnet or glued-on mounting, and are readings at bearing centerline-not at a long overhang?

We usually recommend tripping at 0.62 ips peak velocity.
I like to pass along this great on-line vibration unit conversion calculator:
http://www.wilcoxon.com/calculator.html

RE: Want to lower HIGH horiz vibe readings !

(OP)
Franko,

Thanks. I will try out the vibe calculator. I wish it could tell me how to lower the vibe on my equipment :)

Did you look at the picture? How do you use a flexible coupling with a belt driven fan? I thought that is for direct coupled fan/motors. I am new at this. Please explain. A link to a vendor website would be welcome.

I don't understand why the horizontal vibe is so high at bearing 1. The belt is attached at bearing 2 so I would expect the vibe to be higher there. But then again I am a rookie at this.

We took readings using a hand held "stinger" type probe tip. The readings are probably at bearing centerline for the fan shaft pillow block bearings but may not be so close to centerline of motor bearings. We we looking at overall vibration levels, not shock pulse although we have that information also.

Our vibe values are zero to peak. I am familiar with zero to peak, peak to peak and rms. What is ips? I thought that was iron pipe size. :)

Nisqually-rookie

RE: Want to lower HIGH horiz vibe readings !

Ooops - forgor - ips is inches per second.

RE: Want to lower HIGH horiz vibe readings !

nisqually,
I have to agree, to an extent, with pete. check pulley runout (taperlocks are bad for this if not properly torqued) and alignment, one question though, doesn't pulley misalignment tend to show higher in the axial direction with the dominant peak on driver being the driven and visa-versa ( just asking).

Roy Gariepy
Maintenance and Reliability Dept.
Bayer Corporation  Dorlastan Fibers Div.
Goose Creek, South Carolina  USA

RE: Want to lower HIGH horiz vibe readings !

(OP)
hi micjk,

I would very much like to understand what you are asking about pulley misalignment and the axial direction and driver versus driven but I don't. Can you please rephrase and try again? What do you mean driver being the driven and vice-versa?

-nisqually

RE: Want to lower HIGH horiz vibe readings !

if memory serves me correctly, often times with belt drive pulley misalignment axial data on the motor will show a dominant peak at the 1x frequency of the driven component and likewise the driven component will show dominant peak at motor 1x frequency. I added "just asking" in case other experts in this forum had different thoughts and could add some added input for educational value. i am also working on a fan with similar problem. Mine however has a few more forcing funtions involved. We defintelay have unbalance, along with looseness ( I have multiple harmonics of 1x driven component and found that the pillow block bearings have a .020 gap between housing and bearing support structure from center of housing to hold down bolt.) Hope this clears up my former post for you.

Roy Gariepy
Maintenance and Reliability Dept.
Bayer Corporation  Dorlastan Fibers Div.
Goose Creek, South Carolina  USA

RE: Want to lower HIGH horiz vibe readings !

It's a good point that Roy makes. A typical symptom for pulley misaligment would be 1x fan speed vib on the motor  axial reading, and 1x motor speed vib on the fan axial reading.  Still we probably shouldn't rule out misalignment based on the absence of axial vib.

RE: Want to lower HIGH horiz vibe readings !

I should add that I don't have a bunch of experience with belt drives... we've only got a few at our plant.

RE: Want to lower HIGH horiz vibe readings !

Nisqually,
    My suggestion would be to take phase readings. This will help to eliminate extensive time associated with the trial and error approach.

J MacK

RE: Want to lower HIGH horiz vibe readings !

(OP)
Excellent idea jmack. What I have is a "balancing kit" with the ability to take phase measurements and an instruction manual with the Commtest instrument vb1000-T.

OK then. Will the phase measurement tell me how much the sheave is wobbling, that is, rotating through an angle perpendicular to its axis of rotation? Am I making any sense?

RE: Want to lower HIGH horiz vibe readings !

Hi nisqually i am using the commtest vb2000t kit and found help with phase @ universal technologies inc. interpreting unbalance/misalignment using relative motoion diagrams
any problems ill try to help

RE: Want to lower HIGH horiz vibe readings !

Checking phase will certainly give good info.  

I would like to take a moment to mention that there probably is no right approach for all situations.  Depends on your situation.  (Availability of the machine for running-tests, for shutdown maintenance, availability of maintenance vs predictive manpower etc).  

I don't think that going after the belt/pulley system based on what you have already is trial and error. What else (besides belt/pulley system) is going to cause highest 1x-fan rpm appearing on the motor?  And since pulley alignment and belt tension cannot be adjusted independently there's not much sense in discriminating between those.  Add on a pulley runout test adds another 10 minutes.  

OR... you could spend another week gathering and analysing data. And how much more conclusive will your diagnosis be?  And by the way is that motor still shaking at 0.75ips the whole time your analysing?  Just some food for thought. As I said, there is no single right answer.

RE: Want to lower HIGH horiz vibe readings !

(OP)
thank you very much Franko. Millwrights replaced shaft bearings and belt and the readings are even worse at the motor and shaft bearings. also the motor mounting bolts are actually in the horizontal direction! I should have noticed that last time.

I notice robinson doesn't differentiate between horizontal and vertical, they just use radial. I find that interesting.

RE: Want to lower HIGH horiz vibe readings !

You say the motor mounting bolts are in the horizontal direction. Can you explain that some more.  

(Typically on fan applications I have seen vertical bolts mounting the motor to a light metal frame/baseplate and vertical jacking bolts which move the light metal frame/baseplate with respect to the pedestal.)

RE: Want to lower HIGH horiz vibe readings !

(OP)
sure. what I mean is the motor is bolted to the wall, not the floor. and it's bolted to a flimsy mounting plate that has no real jacking bolts so they can't get the proper tension on the belt for one thing.

I would very much like to figure out a new mounting arrangement for the millwrights if you know where I can look on the internet for mounting suggestions.

The readings are worse than last time.
4/09/03 in/sec rms overall machine vibration
3/26/03 in/sec rms (in parenthesis)
_____________
                                 H               V               A
Bearing 1(RPM)         .81 (.61)    .23 (.13)
Bearing 2(RPM)         .67 (.48)    .30 (.17)      .30 (.11)
Bearing 3(RPM)         .31            .06 (.06)
Bearing 4(RPM)         .19            .36 (.28)


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