Tagged With "isolated"

Topic

Test stand vibration

tcvib ·
We have a motor test stand that I have a question about. We have had a motor that is failing our vibration acceptance tests here. Our spec for overall in .06 in/sec. The motor in question has been sent to the shop and measured good. The issue is that we run this motor at 480V instead of 2300V nameplate voltage. We normally run these motors at low voltage with no issue. The test bed is "isolated", but we have vibration to the floor up to .08 in/sec. We have .03 in/sec Vert and Axial and .12...
Topic

Vibration Isolators

MarkSl ·
Hi Gents, I took some vibration data today from an overhung fan which is visually vibrating at all locations including the structure and floor. The spectrum shows very high 1xF which is worst at the fan locations (up to 37mm/s RMS) . The 90KW motor...
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Re: Vibration Isolators

Dan Timberlake ·
Any historical vibration data ? To know when the busted isolators may have finally failed, or how they were working last year. Are there complaints from the occupants about noise or vibration at any of the fan's frequencies? If the floor is vibrating, the isolators are not "isolating". Selection of isolators is way more complicated than looking up the weight capacity in a table. ESPECIALLY when the equipment is not on a slab on the ground.
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Re: Vibration Isolators

Ron Brook ·
The amount of clips on that fan does not sound right. If you want to try to balance the fan, I would recommend taking the belts off and seeing what the fan does statically. As far as the isolators are concerned, their job is to keep the residual vibration from entering the structure. They have nothing to do with quieting down the fan itself. Also, not a big fan of motors mounted on the side of the fan support. Usually end up with very bad belt stability, meaning the motor vibration on the...
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Re: Vibration Isolators

Alin02 ·
Its very difficult some of the time when such kind of things happens in the unit. And the situation becomes more complicated when you choose wrong isolators without knowing the working capacity or style, because it not only affects the machine even other things also as in your case happening. you should use machine removing the belt independently first and need to see what happen, it there any pulley problem because as the isolator is not concern with this.You should also check the alignment...
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Re: Test stand vibration

John from PA ·
I once consulted for a motor OEM that had similar issues. After taking data I simply asked them to drive some steel wedges around the test bed; perhaps three wedges on the long side and two near the corners on the short side. The vibration dropped dramatically. The test bed was supposedly isolated but was driven to resonance with the particular combination under test.
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Re: Test stand vibration

Shurafa ·
Structural resonance is possible but more data is needed to confirm. I remember a very similar case where the shop people dismantled the motor doubting an internal problem. They in fact, performed a very fine balancing job (for the second time) to reduce the vibration. The combination of that motor and test stand did not produce a happy marriage. I recommend in your case to conduct an impact test in both directions. Please share with us the plots if you can. With respect to the inspection, I...
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Re: Test stand vibration

Dan Timberlake ·
Does the vibration drop instantly when the power is cut? Got pictures and drawings? Do you have frequency info to understand why the overall is over .06 in/sec. ? Without frequency and phase info the battle is pretty much lost. Finding A solution will immense amount of trial and error, or an immense amount of luck Are you using peak or rms readings? I'd make a map of the vibration and phase horizontally from the shaft CL down to the floor. Also vertically at all 4 motor feet, and each...
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Re: how detect if isolation pads are bad?

Yousuf Masood ·
Measure the amplitude at the top and bottom part of the vibration mount and it should be same across all vibration mounts of the machine, so any deviation will give u the hint of a faulty mount Measure the overall height of all vibration mounts (ideally loaded ) any major difference is a telltale sign of spring or material deformation Look for the signs of high 1x peak in horizontal direction with comparatively thicker base (however this is not always a sign of bad vibration mount)
Topic

how detect if isolation pads are bad?

ramonruiz ·
Dear All, I would like to know how detect when the isolation pads (anti-vibration pad) are bad, how measure, what kind of test are necessary. Best Regards.
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Re: how detect if isolation pads are bad?

Becar ·
Good new anti vibration pads should have some obvious vibration amplitude difference between the upper and the lower part. But they can also be bad from the point of wrong choice not just worn out.
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Re: how detect if isolation pads are bad?

OLI ·
It is common for a bad selection and placement of these feet if you as normally are select them from the machine weight and in the chart of the supplier of the feet. This is then for a vertical load normally and if you have a vibrating fan in one end and it makes the frame wiggle-waggle (see-saw?) it may be due to a resonance made up by the feet... so if you gave hi vibration in one end and not the other plug in a pine wedge to short those feet in the vibrating end to verify the problem. In...
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Re: how detect if isolation pads are bad?

Walt Strong ·
Are those measurements on the photo in horizontal or vertical direction? What kind of machine and size and speed? Your OP question needs to specify the type of vibration mount/pad and the direction of vibration. Why do you suspect there is a vibration mount problem? Walt
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Re: how detect if isolation pads are bad?

ramonruiz ·
hello, the machine is lobe blower, direct coupling, (1500 rpm) both reading are horizontal. RRR
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Re: how detect if isolation pads are bad?

ramonruiz ·
Dear All I attached more details about vibration in base of Blower. Thanks for yours comments. Best Regards RRR
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Re: how detect if isolation pads are bad?

ramonruiz ·
Dear Walt, thanks for your comment, the motor is about 14kW (50Hz, 1500 rpm), I have checked the severity chart ISO 10816, and maximum permissible for normal operation condition is about 4,5 mm/sec for low power machine. based on this standard we consider to do some actions.. RRR
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Re: how detect if isolation pads are bad?

Becar ·
My advice: don't stick with the ISO10816 table. A 14 kW fan with vibration pads can be easily regarded as one ISO grade higher sometimes even two. The standard itself allows you to do it with some arguments.
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Re: how detect if isolation pads are bad?

Walt Strong ·
I'll ask again " Why do you suspect there is a vibration mount problem? " What indications do you have (observations or measurements) that the vibration mounts are defective or suspect? Rotary lobe blowers produce pulsation frequency and harmonics that can change with load (pressure differential) and may excite structural resonant frequencies. There are many indications of defective or failed vibration mounts depending upon type and if correctly selected and sized such as: loose/broken bolts...
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Re: how detect if isolation pads are bad?

OLI ·
If you follow ISO recommendations, collect data as the ISO describe, Hor, Vert, Axial on the bearings. In my book I follow ISO 10816-1 as it been mu follower for 40 years and the 2.8 is acceptance and 7.1 where you at least should do something. So verify the readings, H,V,A at both bearings and tell us the result. Next check if it is 1xRPM same both H and V, clean the fan and if it doesn't help, balance it if that is not feasible actually don't want to be balanced, look at the foundation.
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Re: how detect if isolation pads are bad?

Becar ·
Mr Ramon, where is your statement about the looseness coming from? Also at 5,7 mm/s I would not talk about any vibration excitation. Have I overlooked any bearings spectrum data? What are your motor and fan bearing values? Please send us all of your recorded spectrums otherwise you can't expect a quality answer. Your post started with isolation pads, now continues with bump tests..... I think you began to start solving your machine problem from the wrong side. Let's start from the beginning.
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Re: how detect if isolation pads are bad?

ramonruiz ·
Dear All, Today I did Dump Test in base of blower & motor, please check that we found two natural frequencies at 12.5Hz and 25 Hz, with motor in OFF position . may for that reason the system response at 1x rpm force excitation? now we can say the system has looseness with resonant vibration? RRR
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Re: how detect if isolation pads are bad?

Becar ·
I don't see any critical issues from your data sent. No obvious mechanical looseness, no critical vibration level. 1st peak amplitude is a little higher in horizontal and could indicate some residual unbalance on the motor-coupling-blower shaft line. I wouldn't say this machine needs some actions. It would be good to have some envelope/peakvue data for bearing evaluation. However if the vibration level still bothers you, you could try field balancing on the motor fan and on the coupling. I...
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Re: how detect if isolation pads are bad?

ramonruiz ·
Dear All, I attached vibration readings at higher vibration points of motor and blower, RRR
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Re: how detect if isolation pads are bad?

ramonruiz ·
Thanks so much at All.. Excellent comments, I will take in count all of them, thanks you a lote. RRR
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Re: how detect if isolation pads are bad?

William_C._Foiles ·
Anyone using ISO 20816 these days?
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Re: how detect if isolation pads are bad?

Walt Strong ·
" Today I did Dump Test in base of blower & motor, please check that we found two natural frequencies at 12.5Hz and 25 Hz, with motor in OFF position . may for that reason the system response at 1x rpm force excitation? now we can say the system has looseness with resonant vibration? " You did not indicate what direction and locations you did "Dump Test" (impact test), but I assume it was in horizontal direction. You have a curious choice of mixed vibration units mm/sec RMS velocity...
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Re: how detect if isolation pads are bad?

ramonruiz ·
Dear Member, we did some actions about the blower, please see the attached file. please after this results what actions we need to do? what do you recommend? RRR
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Re: how detect if isolation pads are bad?

OLI ·
Well, if you answer some questions it is easier to reply. So how old are the pads? OEM normally state 10 years op time and shorter in sun and chemical environ then they get stiff "change properties". So maybe the customer don't like beams in the machine and if the machine previously was ok, so change pads to new, correctly selected pads? Or make your own but blower foundations are tricky, not funny. Have you checked the bearing condition, greasing? Just asking.
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Re: how detect if isolation pads are bad?

ramonruiz ·
Thanks for your comments: Mr Walt , Mr Oli and Mr Becar. for continues supporting in this case, I asked to Operational people they told me that this pads have not been replaced since the plant started (more than 30 years). and I checked vibration in foundation and I found 0.39 mm/sec at down side of Vib pad. to replace all vibration pads will be good recommendation for our customer. RRR
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Re: how detect if isolation pads are bad?

OLI ·
You have some cracks in the foundation also. are they serious, if you measure vibration each side of the cracks is it the same vibration or do the cracks separate parts of the concrete? Isolation pads "seismic mount" are defined to have one side mounted on a reasonably stiff foundation, if that is not the case anymore they may not work as intended. Inject something if needed maybe?
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Re: how detect if isolation pads are bad?

Walt Strong ·
Ramon, Your "temporary" structural modifications was surprisingly effective! You demonstrated significant vibration reduction by adding mass to lower the natural frequency. I don't know if you thought the wood beam would add stiffness or not, but at least it worked quite well. I could make a suggestion for a more permanent modification, but I would like to see what you do. The blower spectrum now looks more "normal" with pulsation peaks higher than 1xSS. Good job! Walt
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Re: how detect if isolation pads are bad?

OLI ·
It may not do the miracle you are looking for there are a lot of things, cracks in foundation, any in the frame? Do they grease the bearings sometimes? If not,do that.
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Re: how detect if isolation pads are bad?

! ! Shabir Ahmad KHAN® ·
Check cross phase on vertical direction. Skid vertical and foundation vertical if found 180 out of phase then the pads not working properly.
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