Tagged With "Overhung Fan"

Topic

shaft looseness

Hossam 2 ·
Dear Experts what is the best way to detect the shaft wear under the bearing inner race or under the sleeve specially i face many problems like that but the only frequency shown in the spectrum is 1XTS. Example Overhung Fan variable speed motor (rated speed 1485 rpm) dominant frequency 1XTS (H=10 mm./sec....Vertical=6 mm./sec.....A=4 mm./sec) after balancing the vibration dropped to 2 mm./sec but in two days the vibration reached 36 mm./sec at horizontal direction 1XTS dominant vertical 25...
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Re: Balance two stages overhung rotor

Ngo Dinh ·
This pump is vertical pump, small one using SKF 7311 BECBM, 6212 C3 with oil mist lubrication . The length of shaft is about 808mm (you can see file attached). You are right that rubbing could excite the natural frequency and sometimes it is very strange one. I also think about the resonance issue and intend to double check when the machine taken into service. Now, this pump is still repaired for some corrosion issues. Anyways, when you do balancing for rotor, have you put the cooling fan to...
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Re: Balance two stages overhung rotor

OLI ·
Normally the fan is a part of the motor rotor or in some cases not normally vertical it is also a part of the gbx. To cut it short, I would have the fan treated as a separate case and a thing to be balanced separately, normally just cleaning is enough unless any other damage occurs.
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Re: Balance two stages overhung rotor

Ngo Dinh ·
Yesterday, I do balancing for this rotor but it is very unusual when the appeared value of unbalance on machine is not the same with correction amount. It means that the balance is not linear. The machine showed that rotor got 34g at plane 1(near bearing) and 25.4g for the plane 2 but when I put 5g for plane 2 the unbalance reduce to around 20g plane 1 and 15g plane 2 but when I increase 2g of clays more, it make increase unbalance again. i also try static/dynamics to balance with static...
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Re: Balance two stages overhung rotor

OLI ·
Normal in such case is that something is loose alternative is that the speed selected for unbalance is "unlucky" test another speed. You can take away the fan to see if it makes a difference or package in plastic foil to avoid turbulence.
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Re: Balance two stages overhung rotor

Ngo Dinh ·
Hi Oli, I have thought about loose but after I remove the clay weight and recheck, the result show the same value as the original. I also require to turn rotor 180o to check phase shifting and the result is 180o shifting. I will take the fan out and see. Dear William, The radian for correction weight is correct.
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Re: Balance two stages overhung rotor

Ngo Dinh ·
Dear All, Now, this issue is solved. After doing two case, Case 1: balancing rotor with two planes at two impeller and Case 2: balancing rotor with one plane at fan and one plane at both impeller. I discovered that the balancing with two planes at two impeller is correct and it can eliminate the axial force due to couple unbalance of two impeller. And the reason for unsuccessful balancing is due to tolerance of connector which used to connect shaft end and universal coupling. Thanks for your...
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Re: shaft looseness

Hossam 2 ·
i have already balanced the fan two days before exhibiting high vibration ,but how should i anticipate the shaft wear specially during balancing the phase was stable horizontal to horizontal is there a way to anticipate shaft wear , we found it 0.07 mm wear thanks
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Re: shaft looseness

Walt Strong ·
Did you clean the fan rotor before balancing it? Did you weld weights on rotor for balancing? If yes, then was the electric welder properly grounded to the fan rotor and not to the case? I assume the bearing was destroyed to cause the inner race to drag over the shaft and cause all of the surface gouging; correct? Did you use any other means of bearing fault detection; such as high frequency acceleration or demodulation? Were the bearing housing grease seals in good condition and keeping...
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Re: shaft looseness

Hossam 2 ·
thanks for your attention yes the welding machine was properly grounded and the procedure of balancing and welding was correct. i used peakvue technique yes i always use peakvue using CSI 2140 the bearing seal was replaced two days before balancing as it was damaged. the balance job damage the bearing ??!!! i doubt. Regards'
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Re: shaft looseness

Walt Strong ·
So the bearing and housing and shaft surface were destroyed in two days from the balancing job! One of the early technical papers on CSI PeakVue presented in October 2001 stated, “the primary PeakVue parameter which should be used for trending PeakVue measurements is the parameter referred to as Peak-Peak Waveform”. I believe that the bearing was significantly damaged by contamination at the time of balancing and when the grease seal was replaced. The PeakVue waveform was already indicating...
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Re: shaft looseness

Walt Strong ·
Adding to previous comment: The photos of shaft do not indicate spinning of inner race on shaft due to a loose fit. The surface gouges appear to be from Galling as a result of the inner race/ring being forced (tight/interference fit) to rotate on shaft when bearing locked up. The presence of 1xSS and harmonics in the PeakVue indicate bearing looseness, and probably occurring within the damaged/worn rolling elements. The lack of bearing fault frequencies is probably the result of extremely...
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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balancing of overhung fan using SKF CMVA 65

Francis Kamuriwo ·
Hie buddies how are you.For those that have used CMVA65 Microlog for balancing purposes,how can you identify the correct position to put your trial weight. Is the phase angle the highest spot or the lightest sport. Thanks for you assistance.
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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...
Topic

high vibration on two stages vertical overhung pump.

Ngo Dinh ·
Dear All, I have a case which at the moment, I have not found what is the root cause. The problem of the pump is high vibration from 2mm/s to 5mm/s after 4hours of running (for information of the pump and drawing, please see file attached) and the dominant frequency is 83.4Hz (speed of pump: 2960rpm, sorry that I could not post spectrum here due to some reason, it still not available). No signal of unbalance issue, no frequency of bearing fault is found on spectrum. The drain oil after high...
Topic

Balance two stages overhung rotor

Ngo Dinh ·
Hi everybody, Anybody know the procedure to balance this kind of rotor in balancing machine CAB 700? Thanks,
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Re: high vibration on two stages vertical overhung pump.

Ngo Dinh ·
Please see spectrum here
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Re: Balance two stages overhung rotor

OLI ·
Is this the version where you need to take it a part when rebuilding in to the machine with bearings? If so take care to mark and put it back in the same angular position. You need a hold down bearing in the machine.
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Re: Balance two stages overhung rotor

Ngo Dinh ·
Thanks Oli, I know that the position should be marked to be sure the balance is the same with the balancing time. Actually, I do not have experience on balancing machine. So, could I: - Balance each impeller and then do it for assembly. (Difficulties: have to manufacture bushing to fix each impeller when do balancing, I do not know how to do the rotor setting, static or dynamic?) - Do it for whole assembly at one time. Pls see file attached. Thanks,
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Re: Balance two stages overhung rotor

OLI ·
I would do it all in 1 go with both discs, it will reduce mounting errors I think, are they not axially movable? Is it a defibrator of some kind for pulp processing so in operation the discs are close about 0.1mm or less? So I would balance it with discs close and that give you basically a 1 plane balancing and you could split the weights 50/50 on the discs if it is much weight. Are they worn? Or am I assuming to much and totally wrong? What would the operating speed be?
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Re: Balance two stages overhung rotor

Ngo Dinh ·
Thanks Oli, In the last balance for this rotor, I did it as assembly. I set static first and try to correct static unbalance at stage 2 and then set dynamic for final balance. I read in API 687 mentioned that for overhung type, it should balance for each impeller first and then do it as assembly. That why I ask for advice because I did not use balancing machine before. As you mentioned above, our procedure is not wrong, is it? As I know, on the balancing machine have compensation mode like...
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Re: Balance two stages overhung rotor

OLI ·
Oh so it's a petrochemical thing, it looked very similar to a defibrator for pulp. So it may be hi speed? Anyway, API apart I would do as you tried but I would part the static to be 50/50 on the rotors 1 and 2 if possible that is the only thing I do different. Unless you have a reason to put it on only one that is. You enter a lot of more unknowns regarding mounting etc. by doing it the other way but it is only my view. I don't think you really need to use the password protected features.
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Re: Balance two stages overhung rotor

Ngo Dinh ·
Thanks Oli for your sharing. This pump is small vertical pump with speed 2960rpm. I am try to get the residual unbalancing to G2.5 (almost the pump is applied G.5, some pump G.1 with speed around 8000rpm, turbine & compressor are applied API grade). you are right that It is not necessary to keep the compensation function password. But some guys do it and now i can not assess in. Normally, I am not a person in charge for balancing job on machine (the other guy do it) but I am in charge to...
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Re: Balance two stages overhung rotor

OLI ·
Yes my suggestion was not to use the builtin function but as you did, do it manually. I think this password is standard in the machine and always apply and maybe found in the manual it may be some random number but I don't remember. If I find a strange freq. that do not compute I look for a rub and that may also contribute to change in balance. A rub would excite a resonance at a random freq. and that is what you find in the data so balancing procedure may be ok. Would you have a water lubed...
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Re: Balance two stages overhung rotor

William_C._Foiles ·
Since you only note the grams for the balance weight, you must have the balance radii correct.
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Re: Balance two stages overhung rotor

OLI ·
Is that a soft or hard balancing machine?
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Re: Balance two stages overhung rotor

Ngo Dinh ·
This is hard balancing machine
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Re: Balance two stages overhung rotor

Pakhtoon ·
1. Check that the distances entered in measuring unit of balancing machine (CAB 700) are correct physically. i.e. a=distance of correction plane 1 on the rotor from bearing#1, b=distance between both correction planes, and c=distance of correction plane 2 from bearing # 2. Also check that there must be no loose component(s) on rotor. 2. Check again the radii of correction points on correction planes. 3. After balancing the rotor, mark the match mark, disassemble it, again assemble it...
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Re: Balance two stages overhung rotor

John from PA ·
If the OP is still balancing this machine, he should give and and look for another issue. [Original post is April 20 2017]
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Re: shaft looseness

Becar ·
Can you share cascade view of measurement history? For the same spectrum data as above?
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Re: shaft looseness

John from PA ·
I'd have to look carefully at the data to see if there are some subtle symptoms but if I have an undersize shaft ("looseness") that also means I have a shaft that can be eccentric in the bearing bore. What does eccentricity cause? Unbalance (1X). But if the shaft is undersize to the point where it can randomly take a position within the bore, I would anticipate a different phase every time the machine is stopped/started. In addition, attempts to balance might be unsuccessful.
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Re: shaft looseness

Hossam 2 ·
Re: shaft looseness
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Re: shaft looseness

John from PA ·
Depending on shaft size, I'm not sure that 0.07mm is a large amount of wear. More importantly, are you addressing the root cause, why is the bearing inner race spinning on the shaft? Can you add a drawing of this area of the machine?
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Re: shaft looseness

Becar ·
I think something is wrong with your cascade plot. You measured the highest vel. in december right? But on your cascade you have the highest levels in june. The spectrum order in cascade is random which also isn't the best. Can you sort these things above and also send cascade for Peakvue?
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Re: shaft looseness

John from PA ·
Based on date entries of "10/ 17 /2019" and "10/ 27 /2019" it appears as if the date format is month-day-year so the largest is December (12/6/2019).
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Re: shaft looseness

Becar ·
Sorry my mistake. I am used to day-month-year format. Now it makes sense. Although Peakvue cascade would be interesting to see I think.
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Re: shaft looseness

Walt Strong ·
Thanks for confirming a good balancing procedure and results. You did not mention if the rotor was cleaning prior to balancing. A material loss after balancing could explain the very high 1xSS two days after balancing. You did not mention the bearing condition when it was removed. Walt
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Re: shaft looseness

Hossam 2 ·
Re: shaft looseness
Topic

High 1X Axial Overhung Fan

Raul Rios ·
Hello friends! It is a combustion air blower of a boiler with 1X of 1784 cpm. The values of 1X radial direction with 4 mm/seg-rms in ODE and 6 mm/seg-rms in DE, but in the axial sense the 1X is 17 mm/seg-rms. There are no harmonics or BPF present in the graphics. What could be producing this high 1X in axial? Further information is needed and can be supplied. Thank you for your valuable comments. Regards, Raul Rios
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Re: High 1X Axial Overhung Fan

chary tatta ·
Greetings team, For overhung fans high Axial reading and good radial reading, as suggested carry out the phase analysis and a bend shaft can be expected for High axial reading on a overhung fan. regards Chary
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Re: High 1X Axial Overhung Fan

Nagaraja ·
As William suggested possible of resonance. How old is this fan, any overhauling carried out recently. Is it a VFD drive. . ??.if yes reduce the speed by 100-200 rpm and watch axial vibs. My cent of advice will be try to reduce 6 mm/sec on DE brg by doing insitu balancing and see what happens to axial vibs. It may come down as well. If it does not then do a impact test and check. ..
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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

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: balancing of overhung fan using SKF CMVA 65

stachu ·
Trial weight is a trial run, it can be anywhere. This is your starting point for balancing
Topic

Shaft Centerline Movement of Overhung Rotor

DuPlesis ·
What will be the normal shaft centreline movement for Overhung Rotor supported by tilting pad bearings? Particularly with reference to a light overhung rotor, like Power Turbine Shaft in twin-shaft gas turbine driving heavier centrifugal compressor rotor. I have attached shaft centreline movements for 2 different set of machines. In one case, power turbine is driving LP and HP rotors. In another case, Power turbine is driving only 1 HP Rotor.
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Re: High 1X Axial Overhung Fan

Ander ·
Probably unbalance of the rotor.Do phase analysis.
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Re: High 1X Axial Overhung Fan

Ngo Dinh ·
I agree with Ander that unbalance could be a case but using phase to confirm. If phase at both bearing in axial direction is in phase, the unbalance could be suspected.
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Re: Shaft Centerline Movement of Overhung Rotor

William_C._Foiles ·
If gravity is the main force, one expects journals in tilt pads to move up. I see different probe orientations, check that things are wired in accordance with the indicated probe orientations. On GTs thermal growth can complicate the shaft plots, but the ones going aT 45 degrees looks suspicious for thermal growth of the mounting. Check the wiring compared to the configured probe orientations.
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Re: Shaft Centerline Movement of Overhung Rotor

DuPlesis ·
The issue is that 3 identical trains have almost identical SCL and the other 7 identical trains also have identical behavior. All trains are Solar Titan 130. How likely is it that they have all been wired incorrectly. Also this is an overhung rotor. So journal at Bearing No. 4 will move up and move down at bearing no.5. Concerning thing is the side load and movement.
 
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