Motor Journal Bearing Oil Foaming
Motor Journal Bearing Oil Foaming
(OP)
I have a large horizontally mounted ac induction motor with journal bearings, mechanically oiled with oil rings. The free end or opposite drive end bearing is experiencing oil foaming. I am looking for possible causes and ramifications of this conditions. Any help appreciated.





RE: Motor Journal Bearing Oil Foaming
Possible Causes:
1 – Erratic oil ring operation. – Inspect in viewing window.
2 – Improper level – check.
3 – Oil contaminants – sample.
4 – Foaming tendency. (related to #3). Take a sample of oil. Shake it up vigorously for 10 minutes. Let it sit. Bubbles should be gone in an hour. If not, suspect, contaminants and investigate further with oil analysis or with ASTM foaming tendency test.
5 – Malfunction in oil supply. (is this a forced oil system or a simple reservoir?).
If bearing temperature and vibration remains normal and oil level and viscosity are acceptable, I would not be too concerned about the bearing in the short term.
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RE: Motor Journal Bearing Oil Foaming
-The oil ring appears stable, non forced system.
-The oil sample results have not come back yet, but I don't anticipate problems as the motor is freshly rebuilt and new oil installed.
-There are vibration issues with the motor. The vendors own data shows multiple harmonics of 1/2RPM in the shop. We are seeing multiple harmonics of runspeed though amplitudes are not excessively high at this point.
Basically we are trying to determine what we've got on our hands and how severe the problem is.
RE: Motor Journal Bearing Oil Foaming
1/2 times and multiples are definitely not a good sign.
Neither are multiples of 1x but not quite as concerning.
Either way it most likely adds up to looseness.
I am guessing you are monitoring on the bearing housing? You can miss a lot there on a sleeve bearing machine (prox probes are better but of course not always available).
Tough call. No-one can know for sure. My best guess would be the foaming is contamination and unrelated to any vib problem (other than they both may have their origins in your recent overhaul). Evaluate the vib problem on it's own. If you get an opportunity to do prox probe monitoring that can provide better diagnosis.
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RE: Motor Journal Bearing Oil Foaming
RE: Motor Journal Bearing Oil Foaming
rmw
RE: Motor Journal Bearing Oil Foaming
I disagree with that logic. Our feedwater booster pump motor and pump has forced lubrication from a common sump feeding bearing reservoir with oil rings on bearing. Oil pump feeds from sump to reservoir thru orifice, then overflows from reservoir standpipe and drans back to the sump. Keeps the reservoir cooler than a static reservoir. It's a common configuraiton.
I agree with your other comments.
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RE: Motor Journal Bearing Oil Foaming
12fish
As Iron sharpens Iron so does a man sharpen the countenance of his friends.
RE: Motor Journal Bearing Oil Foaming
I think the important words are "forced lubrication". Forced lubrication is not the same as a continous supply and overflow to maintain the optimum level in the bearing reservoir.
RE: Motor Journal Bearing Oil Foaming
My objection was to the following sentence:
“Ring lubrication indicates to me that you probably don't have forced lubrication from a common sump. If you did, your contamination would be uniform and would be occuring in both bearings.”
I agree there can be different interpretations of the term “forced”.
1 – “Forced” as you are suggesting meaning hydrostatic lubrication (as opposed to hydrodynamic) injected under pressure at the bottom of the bearing such as oil lift system (not common in motors) or turbine hydrostatic lubrication.
2 – “Forced” meaning a pumped supply of oil through an orifice to a vented reservoir.
I assume rmw meant definition #2 and I further clarified my assumption by describing in my reply what I understood him to mean by “forced”. This seems like a safe assumption since #1 is very rare on motors. If rmw thinks I am using the wrong meaning, he is free to correct me.
Either way, the main point of his comment had nothing to do with the lubrication method but whether or not there was a common lubrication sump. Once again, I do not agree that the presence of oil rings means there is no common sump. Do you agree?
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RE: Motor Journal Bearing Oil Foaming
You have explained your meaning very well and I accept your explanation. What is also important is that you have removed any possible confussion of those who are not directly involved but are following the threads to increase their knowledge.
I have seen descriptions of pressure prelubrication systems but I never have worked with one.
I (and four others) have had to "roll" large machines with oil ring lubrication to establish the oil film before starting. One machine was a 3000hp motor driving 5 ring lubricated single bearing DC generators. When dry, the breakaway torque was about. 2800 ft/lbs.
That was 2x200lb. men hanging from a 7 foot coupling spanner. After about 3 revolutions the oil film would be established and the rolling torque would be much less.
I wish that pressure prelube systems were more common with ring lubrication systems.
respectfully
RE: Motor Journal Bearing Oil Foaming
Also are you using flood lubrication system. What kind of motor it is Fincooled or Open type enclosure. Which side bearing drive end and non drive end bearing is showing foaming.