Hello Guys,
I have a vibration problem with a DC Motor
The vibration is around 8mm/s @ 8X RPM, only in tne outboard bearing in horizontal position.
The inboard bearin vibration is 1.5 mm/s without the 8X frequency.
The Motor is coupled with a Gearbox, but the vibration isn't relation with the teeth.
I think that is a problem with the conmutator or with the tacometer.
Do you know something about it?
Thanks in advance for the info.

I would expect a tacho problem show also in the other end of the motor and gbx if it gives jerky speed variations but you never know, DC motors are strange critters. Commutator could be likely but it´s hi level so it should be bad then. Is it eating the carbon brushes fast? What is the speed? Just so it´s not LF related. Anything else around? Cooling fans or other stuff mounted in that end?
Olov

The brushes wear are normal.
The Speed is about 1600 to 1700 rpm, and I checked any other equipment around and I didn't find nothing

We can increase or decrease the speed but the vibration is always at 8X.

Attached you can find a vibration report.

AV_MTR_YANKEE_TM_1_190907.ppt (248 Kb, 63 downloads) Yankee DC Motor

Be careful of a voltage leakage causing EDM fluting of a bearing race. We have found this at the number of balls times the ball spin frequency. Watch the Time Wavwform for increases in raw energy or impacting, versus the Baseline data.

Hello Guys, bad news, the vibration continues, in the last shutdown (October 11) we reviewed all the issues, conmutator, brushes, encoder, motor aligment, soft foot, and we didn't find nothing wrong.

I'll appreciate others tips that you can give me.

Thanks in advance

Tomas

Tomas, you have a bit rough resolution I think. Can you really be sure it´s 8x? Have you checked the bearing status with something? If it´s looseness from a bad bearing spinning in the wrong place you should hear it even with the yellow handel analyzer. Have you done the lube test? Eg. take a reading first, add some grease, take a reading, compare. Did adding grease influence vibration? Then you should look at the bearing. Olov

Hello OLI, Yes, the vibration is at 8X. We did the lub test and no change in the vibration.
Thaking the tip from Allen, I found that fluting problem isn't relationship with the rotational speed and is in high frequecy (2000-6000 hz).
The bearing noise is normal, all the motor outboard section fells like "stressed"

Now, I'm looking something in the drive. Do you think that the problem can be the drive?
Do you recommend review or change bearings?

Hi,
Reviewing your data is a little tricky because you seem to be using a zoom function on the two spectra. Hence they are not both looking at similar frequencies. Your MOH data has 5 peaks with the dominant peak at 229.37Hz (8x RPM) the other peaks appear to be sidebands ie 222.5 Hz (7.7x RPM); 228.12 Hz (7.93x RPM); 230.62 Hz (8.02x RPM); 305.62 Hz (10.63x RPM).
Your other spectra displays different frequencies altogether ie 28.75 Hz (1x RPM); 257.5 Hz (9x RPM); 305.62 Hz (10.6x RPM) 360 Hz (12.52x RPM) 486.87 Hz (16.93x RPM).
Consequently this is quite confusing because all the data looks like harmonics, where in fact they are not!
I would suggest that you increase your resolution for your data and pin point whether the 8x RPM is in fact a bearing defect!
The other frequencies at the inboard side are also non harmonic and may have some other bearing issues there also.
Note also that your peak indicating the 1x RPM (28.75 Hz) equates to 1725 RPM whereas your report indicates a motor speed of 1718 RPM (28.64 Hz); a difference of approximately 0.1 Hz. This could make the difference to the 8x peak, becoming either 7.9x RPM or 8.1x RPM! Again indicating a possible bearing defect.

UK Vibeguy, I agree higher resolution needs to be taken to ensure correct frequencies. But 8 mm/s is .45 in/sec @ 230 hz. That is a lot of energy at a very high frequency. I am assuming that this is a 60 hz line frequency with the motor running 29ish hz or 1790 rpm. Can you supply triaxial data? Like what is the amplitudes and frequency in horizontal vertical and axial direction on both ends of the motor. You state it is high on outboard end. A commutator typically has over 30 bars/slots not just eight, what about the tach? How is it mounted and what couples it to the motor? Is there a lot of vibration on the tach and is it directional. Where is the 8X with 8mm/s located on the machine? (HVA on motor endbell?) Did this just show up or has it always been there? Are you having trouble controlling the speed of the motor? Have you done any infrared scanning of the motor, brush holder assembly, electrical cabinet? Lots of questions I know but this helps narrow down the potential cause and solution...
Dave

Hello Guys,
The vibration outboard in horizontal now is 12 mm/s, the vertical is 6 mm/s and axial 4 mm/s.
In the inboard has 3 mm/s horizontal, 2 mm/s vertical, and 2 mm/s axial.
Reviewing the measures, we observed that the vibration is high in the outboard bearing housing, but we move the sensor about 4 or 6 inches to the center of motor and the vibration go down.

The Motor has 8 poles, 4 armature poles, and 4 field poles.
Can The problem has relation with the poles?
We haven't problems with the motor speed control.

Dave, I didn't make an infrared scanning, I'm going to do it today.

Thanks for your comments.
Regards
Tomas

Tomas, this seems to be serious for a yankee drive, since you did the greasing test it seems unlikely to be a bearing problem at least if there are anything left inside the bearing, if there is nothing left inside it´s silent, I have tested that before . But not at a yankee. Take a look around at the vibrating end of the motor is it firmly bolted down, no cracks, nothing out of the ordinary? With such hi vibration in one end and normal in the other there must be a doggy buried in that end, one way or another. If you check vibration from top side down the same way as you did towards the not vibrating end, does it stop vibrating at the floor/mount or does the floor also vibrate that much? If so go on and look further at the support structure. There are different drive designs for these beasts, is this a single motor drive? Also for my suspicious mind check the grease at the grease outlet port. Black with particles of steel or normal? Olov