Tagged With "Non synchronous"

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Non synchronous peak

Onderarslan ·
Appreciate if someone could clarify a non synchronous peak issue. Load is a cylinders that crushes rubber Motor's speed is 995 rpm and maximum peak occurs at 1763 CPM Transmission is done by reducer and coupling
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Non-clogging pump vibration limit

Ayman Gamal ·
does anybody has experience with Non-clogging impeller (sludge pump) vibration limit as i found in ISO 10816-3 the following statement "For pumps with special impeller for non-clogging or similar operation, higher magnitudes normally can be expected (e. g. up to 3 mm/s for single-vane impeller)."
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Non-Magnetic Pump Casing

Mile High_PumpFE ·
Hi Guys, I have to do a modal on a barrel pump with a 300 SS casing (non-magnetic).... what would you recommend for attaching accelerometers? Is there a wax or glue (for washers) that works best? I am assuming that if I were to use wax, I would remove my magnet and try to have the accelerometer itself "stick" into the wax? What would you recommend? Thanks, KB
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Re: Non synchronous peak

John from PA ·
First of all help us help you. The picture of the motor is fine but the data (one spectrum) you attached is almost useless unless someone takes the time to enlarge it using other tools. It is very difficult to see the scales on the plot. There is also, and this should be obvious, very little information above the 6th to 8th order so the meaningful data is in the left 20% of the plot. The horizontal axis should be scaled to about 10 orders, perhaps 6 to show better detail. I have manipulated...
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Re: Non synchronous peak

Onderarslan ·
John, Thank you for your edit and warning I will care next times. At this moment I could not reach tooth combination but I will share when I get.
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Re: Non synchronous peak

John from PA ·
Also, if rolling element bearings, I would check the anticipated frequencies generated.
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Re: Non synchronous peak

Onderarslan ·
But gE overall value is very less
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Re: Non synchronous peak

John from PA ·
You should still rule out the bearing frequencies and the only way to do so is to start by knowing what they are! This takes on more importance when you have a frequency that currently is of "unknown" cause/source.
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Re: Non synchronous peak

John from PA ·
By the way, is this a VFD?
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Re: Non synchronous peak

Onderarslan ·
There is no VFD, and please see gE spectrum. I still don't know the type of bearings since no name plate and waiting client's answer. As I said before gE values are very low and I see the same peak and 3 harmonics at gE spectrum but very less amplitude.
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Re: Non synchronous peak

Onderarslan ·
With bearing defect frequencies for two different motors. Their common point is non synchronous peaks
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Re: Non-clogging pump vibration limit

Rotating Guy ·
I don't specifically use the 10816-3 for pumps unless for my criticality metrix. For pump i use 10816-7. you can also check.
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Re: Non-clogging pump vibration limit

ivibr8 ·
We had a number of non-clogging pumps at our facility. Because these pumps were used to pump "dirty" water/fluids for various applications, they had an open-impeller design. I suspect (only a guess on my part), that they may be more susceptible to higher unbalance loads than other pumps (i.e. closed/shrouded impellers) used for cleaner applications. I am not aware of any pump specifications that require a more robust design of the casing, bearings, shafting, etc. to accommodate increased...
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Re: Non-Magnetic Pump Casing

John from PA ·
Some considerations for what you chose include the temperature of the mounting surface, the extent you can clamp the two materials during the bonding, and especially important, the range of high frequencies you desire to observe. Wax for instance may not hold up well to high temperatures and may attenuate high frequencies. Gluing on carbon steel mounting surfaces work well and enable the use of a magnet mount. “Speedy” type adhesives exist, but high quality epoxies that require some clamping...
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Re: Non-Magnetic Pump Casing

Mile High_PumpFE ·
Thanks John!
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Re: Non-Magnetic Pump Casing

John from PA ·
Added link, see previous.
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Re: Non-Magnetic Pump Casing

William_C._Foiles ·
I have used wax for higher frequencies. If the transducer is too large, wax may not work. John, I used wax on a gear in the Philly area with someone who worked for Philly gear at one time - you know them. It worked well until it warmed the wax and the accels fell off. But using cooler wax would work for a little longer. Should be good for high frequency, which may not be required for a pump.
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Re: Non-Magnetic Pump Casing

Mile High_PumpFE ·
Thank you!
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Re: Non-Magnetic Pump Casing

Walt Strong ·
I measured vibrations (normal operations, ODS, and impact test) on feed water pump with SS pipes for the seal cooling plan. I used a tiny triaxial 100 mv/g accelerometer on flat magnet base mounted onto 1/8"x1" zinc-plated steel fender washers attached to surface with FastSteel Epoxy Putty Stick. I tried several adhesives without much success. Petro-wax certainly does not work with high surface temperatures. The key for a good bond is to clean and dry the surface well and to properly mix the...
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Re: Non-Magnetic Pump Casing

ivibr8 ·
If your "modal" requires a lot of spatial measurements, seems to me using an epoxy would be very time-consuming. I have also used wax for ODS and modal tests with good success. It is not for long-term/duration testing and perhaps limited in freq response as discussed above but it held my accels on well enough for the few moments I needed to get data. Doesn't hurt to at least try it. It would also be advantageous to use as small (i.e. mass) an accel as possible. Jim P
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Re: Non-Magnetic Pump Casing

Mile High_PumpFE ·
Thanks Jim!
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Re: Non-Magnetic Pump Casing

Walt Strong ·
What is the required F-max.? What is the expected surface temperature? If the pump is in quick and short shutdown, the high temperature of 250-F plus could be expected. If pump is shutdown for a while to cool, then wax might be good. Here is a good overview reference, but without temperature data. http://www.modalshop.com/filel...c%20Test%20Setup.pdf A better comparison with temperature and frequency response: http://www.straintech.fi/pdf/G...dhesive_mounting.pdf Walt
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Re: Non-Magnetic Pump Casing

William_C._Foiles ·
If one is doing a modal analysis on the pump, one will get better results if the pump is down - unless using output only modal.
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Re: Non-Magnetic Pump Casing

Walt Strong ·
" one will get better results if the pump is down" good tip Bill! Walt
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Re: Non-Magnetic Pump Casing

fburgos ·
for modal I dont think you need the pump to be running
Topic

Dry Gas Seal Failures

Saad Ahmed ·
One of our centrifugal compressor 2 BCL 306/A of make GE houses the 3 rd and 4 th compression stages and is being used at our Urea Plant for feeding CO 2 gas into the Urea Reactor at 160 kg/cm 2 . Compressor is equipped with John Crane make Dry Gas Seals of type 28AT at its drive and non-drive ends. In the last two and a half months, we have experienced twice the failure of non-drive end dry gas seal of aforesaid compressor; details are narrated below: The compressor was overhauled in...
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High Vibration Problem at Raw Mill Motor

Abid.Khan ·
Dear Analysts, We are facing an issue on our cement plant. It's raw mill main drive motor of 4300kw. On no load condition, vibration is normal but as the feed come, vibration reaches to 4-6 mm/sec (fluctuating between 4 and 6) and whole vibration is on 85Hz (which is natural frequency of end shield bearing housing as told by manufacturer). According to manufacturer, this frequency is being excited by some forcing frequency which is unknown. Second thing which is observed is vibration...
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Re: High Vibration Problem at Raw Mill Motor

John from PA ·
Hmmm, load dependent. When is the last time you did a good look at the coupling? Alignment, lubrication, wear, etc.
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Re: High Vibration Problem at Raw Mill Motor

Abid.Khan ·
Thanks for reply. Coupling pin bushes are replaced with new, bearings are also replaced along with bearing housing. Alignment verified and found no issue of misalignment.
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Re: High Vibration Problem at Raw Mill Motor

Becar ·
Is level 4-6 mm/s really considered as high vibration for such a beast machine? And the second question: is this some recent vibration change or was there from the beginning?
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Re: High Vibration Problem at Raw Mill Motor

Abid.Khan ·
Yes BECAR, this is recent vibration change and it all started after activity mentioned in PS of initial post. Before it was running smoothly with vibration no more than 3. We want to dig for the cause of this vibration and this strange behavior. Specially its relation with Lf. Since it's 6 pole motor, if we consider maximum fluctuation in Lf, it brings 10rpm speed change at maximum. Vibration magnitude changes drastically with this difference. One other thing is, at no load vibration...
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Re: High Vibration Problem at Raw Mill Motor

Becar ·
Could the 85 Hz peak come from the gearbox? (Gearmesh frequency)
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Re: High Vibration Problem at Raw Mill Motor

Abid.Khan ·
Dear Becar, motor is coupled with a single stage gearbox (GMF~640hz) which then drives the sun of a planetary gearbox box. Details of planetary gearbox are unknown and we've requested the supplier to provide the details. Sun of planetary gearbox runs at 40rpm. If dun has even 50 teeth then it's GMF will be around 33 Hz which is far less than 85 Hz. We've collected vibration on gearbox body and it's noticed that two peaks of around 84.5 Hz and 86.9Hz with almost same magnitude i.e. ~1 mm/s.
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Re: High Vibration Problem at Raw Mill Motor

Becar ·
I didn't understand what do you mean by speed fluctuation of 10 rpm, how does it happen and how long does it last. How did you catch both case situations? What is the motor nominal rotation speed?
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Re: High Vibration Problem at Raw Mill Motor

Abid.Khan ·
Dear Becar, motor rated rpm is 995. We noticed from the display of control room where values of Lf and vibration values from installed vibration sensors are coming that fluctuation of Lf (which is almost between 49.8 and 50.2 Hz) causes change of vibration from 2mm/s to 4mm/s or even more. When Lf is 50.2Hz, vibration will be 4 or 5 mm/s and when Lf drops below 50hz, vibration values decreases to around 2mm/s. Maximum fluctuation in Lf is about 0.5Hz. Speed(RPM) = 120 f(Hz) / P(Poles) So...
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Re: High Vibration Problem at Raw Mill Motor

Abid.Khan ·
Thus phenomenon is quite strange for us and it only in load condition. This fluctuation is not observed in no load condition.
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Re: High Vibration Problem at Raw Mill Motor

Becar ·
I wouldn't say your situation is strange when you wouldn't say it was not present before. Speed and vibration fluctuations you are witnessing are nothing special at machines with changing load. And raw cement mills are definitelly in that group. When you are 100% sure it is a new phenomena, I would bet it is related to some motor's drop of power after overhaul and could be related to electric motor issues. I would also check if anything changed on the electric network this machine is...
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Re: High Vibration Problem at Raw Mill Motor

Abid.Khan ·
We'll check if anything changed on the electric network this machine is connected to. We also acquire current and flux data. This data you can see that data in attached file (file that is attached to starting post). Can there be any source of 85Hz in motor? Or if the source of 85 Hz is planetary gearbox, can a frequency from that far location excites motor outboard housing natural frequency? Motor and gearbox are coupled by flexible coupling and installed on separate foundations. And what...
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Re: High Vibration Problem at Raw Mill Motor

Becar ·
Or if the source of 85 Hz is planetary gearbox, can a frequency from that far location excites motor outboard housing natural frequency? Sure, it can. But there also comes the same question, why it appeared after motor overhaul. What type of bearings are there? I suppose fluid type? Motor and gearbox are coupled by flexible coupling and installed on separate foundations. I don't like the fact about the separate foundation. It also could be causing some problems.
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Re: High Vibration Problem at Raw Mill Motor

Abid.Khan ·
Bearings are roller and ball bearings.
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Re: High Vibration Problem at Raw Mill Motor

Becar ·
Than you should check bearing frequencies
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Re: High Vibration Problem at Raw Mill Motor

Abid.Khan ·
Yeah we did that. New bearing are installed after overhauling. Bearing housings are also replaced. Bearing frequencies were checked and no bearing frequency is seen in the data.
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Re: High Vibration Problem at Raw Mill Motor

Becar ·
Can you tell the bearing numbers to recheck?
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Re: High Vibration Problem at Raw Mill Motor

Abid.Khan ·
Yes sure, bearings are NU1048 and 6048M.
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Re: High Vibration Problem at Raw Mill Motor

Becar ·
You have ball spin fr. very close at 82 Hz for NU1048
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Re: High Vibration Problem at Raw Mill Motor

Becar ·
I must say I suspect two other options rather then bearing frequency: - something is exciting your motor from the side of the gearbox / planetary gearbox, 50 teeth for sun gear sounds a low number, you also have to check the planetary teeth rotation speed - or there is some electric fault weakness on the motor but I don't understand how is it possible that the line frequency is fluctuating?? OK, rotation frequency, but line frequency should be constant at 50 Hz
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Re: High Vibration Problem at Raw Mill Motor

Abid.Khan ·
But it could only appear when there is a fault on the balls. Secondly, it's higher harmonics appear first and as the fault grows, ores 3rd, 2nd and 1st start to appear. Even though be bearings were installed, I checked the spectrum, there was no any other other frequency. I will reconfirm on Monday as well.
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Re: High Vibration Problem at Raw Mill Motor

Abid.Khan ·
We are waiting for reply of supplier regarding details of planetary gearbox. As I mentioned in my earlier post that we have also seen two peaks i.e. 84.5 and 86.9 on the gearbox body. I'm sharing the spectrums here as well. I think there is a allowed range in which Lf can vary. Due to this variation, rpm variate.
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Re: High Vibration Problem at Raw Mill Motor

Becar ·
Rpm variates because of the variable load not because of the variable line frequency. It is similar when you drive a car from the city to the hills. You can have your gas pedal at constant but your speed changes. I am not an electrician expert, but I think the line frequency should be constant because it doesn't come from the machine but from the distribution network. Would wait for some other electric expert to tell the truth But the motor should be catching the line frequency not the other...
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Re: High Vibration Problem at Raw Mill Motor

Abid.Khan ·
Find below the vibration trend with respect to line frequency.
 
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