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I hope someboby can answer david's question.
I read an article saying that Z type shield can be grease but not RS because of the rubber lips. I don't know about the purge. Personnally I don't use purge plugs as they are not provide on many equipment except motor and they are often not accessible. I grease monitoring with a stethoscope until I hear the grease enter the bearing and on more critical equipment I grease taking real time demod readings and you see when the grease enter the bearing.
RM
quote:
I grease monitoring with a stethoscope until I hear the grease enter the bearing and on more critical equipment I grease taking real time demod readings and you see when the grease enter the bearing.


J-Marc,

1.Are you using a simple stethoscope for automechanics or an electronic one?

2.When monitoring the demodulated signal what kind of pattern change (noise reduction?) do you see in the spectrum/TWF as greese enters the bearing and what is the HP filter setting?

When I mentioned purging, I ment grease replacement inside the ZZ type shield bearing itself and I have hard time believing that this is actually taking place.
RM
Last edited by Registered Member
A double sided shielded bearing 2Z or 2RS is not supposed to be greased. They are lubricated for life, and keep the dirt out (and also the grease in). The term RS stands for Red Seal (rubber) and the Z indicates metal shields in the SKF terminology.


If the bearing has only one shield you should supply grease.
In most cases I would suggest, use double shielded bearings, they will not run dry, and prevent contamination of the grease.
If you change to double sided bearings, take out the grease nipples, because one could fill up an entire electro motor with grease, thinking he is doing a good job.
RM
David, there is what I do

1.Are you using a simple stethoscope for automechanics or an electronic one?
Yes I use a simple automechanic stethoscope. I tried an electronic one wich was only a sound amplifier and I found it to hard for the ears. The problem with stethoscope is that you sometime need a third hand.

2.When monitoring the demodulated signal what kind of pattern change (noise reduction?) do you see in the spectrum/TWF as greese enters the bearing and what is the HP filter setting?

I had one to do this morning and I tried to save the real time demod spectra to show you exactly without success. I came back with only the last reading. I don't use to save these datas. I will look to see how I could do that and I could post it later.
When I see a bearing frequency in demod spectra (like for this morning, I had a clear BPO), I start the real time demod collect, I start to grease and when the grease enter the bearing, the bearing defect peak disappear. I wait 48 hours and take a new data collection. If it still clean,it's ok the grease made the jod. If the defect come back mean for me that it was not only a lack of lubrication but a real damage that now need to be monitor until the stage where it will need to be plan for a repair. But usually, if you have it show only in demod, grease will do the job.
Where I don't collect demod and I see lack of lubrication in high frequency spectrum, I grease using the stethoscope but I do it the same way i.e, data collection than grease, data collection just after greasing and 48 hours after to compare. I have to mention that I never tried to grease using real time spectrum or waveform data collection. I have a feature where I could collect realtime wave forms and listen to the vibration while greasing but I never tried.
For the HP filter, I don't have the possibility to set it and I don't know its setting (talking about demod).

When I mentioned purging, I ment grease replacement inside the ZZ type shield bearing itself and I have hard time believing that this is actually taking place.[/QUOTE]

I did grease ZZ type to try after reading the article I mentionned and it worked(I heard the grease enter the bearing) but I do prefer when the grease side shield is remove. I also prefer greaseable bearings than life sealed bearings to be in control of lubrication instead of wait for a failure.
It's the way I work, I can be wrong but results looks good. I'm open to improve my techniques with any better suggestion.

J-Marc
RM
My observation is also that by and large the bearing manufacturers will recommend against greasing double-shielded bearings but some motor OEM's will allow it.

Then again, SKF has provided me a recommendation that the grease within a double-shielded bearing cannot be relied on for more than approximately 2x the lub interval we would calculate for similar unshielded bearing. How many of us are actually replacing bearings time based and at such a frequent interval? None I'm sure. We have confidence in our vib to help us identify lub degradation. But those bearing manufacturers have a little bit of incentive to bias their recommendation towards replacing bearings rather than extending life though lube, don't they? Motor manufacturer has no such incentive. Hmmm.

That was a good link provided above to an EPRI NMAC document. Unfortunately EPRI does not speak with one voice. The Chairman of the EPRI Large Electric Motor User's Group recommends that double-shielded bearings be greased, although only half as frequently (twice as long) and with 1/2 the quantity of grease as would be associated with the same application unshielded. This is because filling up the cavity on a shielded bearing will compress the shield and start making a lot of noise. I have seen it.

There is some discussion that older style shielded bearings have a bigger clearance (20 mils) while newer style shielded bearings have smaller clearance (10 mils), and this makes the difference in whether we can really relubricate. Heinz Block wrote an article where he soundly rejected this argument. The grease doesn't go through the shield, only the oil from the grease and there is still plenty of room for oil to seep. Heinz does recommend relubing shielded bearings with careful attention to cleanliness, providing a successful drain path, relubing while warm etc. If anyone wants the name of that article let me know.
RM
If the double shielded bearings are meant to be greased, why isn't there a grease port in the outer race. Why do motor manufacturers put double shielded bearings in their motor end bells complete with grease port and nipple? Why does a lubrication guy pump grease into a double shielded bearing until it pops the seal off? "There that's enough till next time........"
RM
Warning the following is my opinion, based on my experience. Big Grin
At my plant we have stopped trying to grease motors with double shielded bearings. Like many other plants, we had been greasing motors with double shielded bearings for many years. Vibes indicated lack of lube on a motor in the early 90's, that had been greased often. When we pulled the bearings we found nice fresh grease in the housings, and very dry old grease inside the bearings (once we popped a shield off). That same year we saw this on 3 other motors. Throughout the 90's I started looking at all of our bearings removed from motors, and without exception, all double shielded bearings were found dry with nice fresh grease in the housings. We quit trying to lube double shielded bearings in 1999, and instituted periodic bearing changeouts instead. We base our changeouts on SKF's formula's for L10 lube life (not L10 bearing life, which is different). SKF has a chart that has lines corresponding to bore size. The x axis is motor RPM, and the Y axis is in hours of operation for L01 life. Multiply the hours by 2 to get L10 life, Then multiply by 2 again for bearings operating below 160 degrees F, then we multiply again by a "fudge factor of 1.5 to get hours that are more consistent with what we have observed at our plant. Thus for most motor bearing applications you can multiply the L01 hours from the chart by 5.5 to get the real life of a double shielded bearings lubricant. Typical values for 1800 rpm motors is in the 10 to 12 year range and 6 to 7 years for 3600 rpm. Note that this is for continuous running applications, intermittant duty bearings typically last much longer.
I have had many conversations with motor manufacturers about their proclivity to install shielded bearings and then install grease zerks. The answers are varied but boil down to the fact that the manufacturers will typically install grease ports in every motor, it is up to the end user to recognize the bearing type installed and grease or not grease. One or two motor manufacturers are starting to do something about this... Reliance has started installing single shielded bearings unless other wise specified by purchase order... just so there is assurance that the bearing CAN be greased. We have started to change many double shielded bearings over to single shielded, unless the motor is in a harsh environment, because we have found that bearing life in a typical motor is almost infinite if they can be greased.

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RM
Several years ago I faced this same issue on some high speed spindles. Grease zirks were in place, but the bearings were double shielded. Once the bearing cavity was filled with grease, enough pressure might be produced to force some lubricant around the shield and into the rolling elements. However, as was mentioned earlier, you run the risk of collapsing the shield into the rolling elements. You also have the problem of the excess grease trapping heat around the bearing. It's been my experience that you should never grease double shielded bearings. I now work for a large motor repair/manufacturing company. Any motors that we put double shielded bearings in, we remove and plug the grease zirk ports. I've also had situations involving bearings with grease ports in the outer race. These bearings may have 1 shield, but should not have 2. The grease has to go somewhere. Typically the unshielded side of the bearing faces a grease cavity with a purge port.
RM
Sorry to add to the confusion but as we here have thought for a long time a sealed bearing is sealead, a shielded bearing is shielded and not sealed so we beleive grease can escape and if it can escape then it should be replenished at a regular interval with the ability to purge the old grease out.Having said that, is there a
bearing pro that can give us the proper definition of sealed and shielded.Cause as always myths are not fact but that does not stop
people from believing them.Hard facts from professionals are what we all require to do our job.when manufacturers fail us, experienced people are the ones i listen to for advice.
RM
quote:
Originally posted by lee:
...is there anyone that can give us the proper definition of sealed and shielded.


Some info you may already be aware of:
- AFBMA number is provided on the nameplate of motors.
- AFBMA Suffix PP stands for double shielded (i.e. 65BC03 JPP3) and suffix EE stands for double-sealed (i.e. 65BC03 JEE3)
- Manufacturer p/n's often identify seal or shield. For SKF it is ZZ for double-shielded and 2RS1 for double sealed.

All of the shields I have seen are metal. Seals by their nature require a rubbing contact so they will usually be at least partially rubber.
RM
David
We have three deep well effluent pumps in which we replaced the upper plain bearing for a flanged SKF bearing. The bearing is 2RS however the housing has a grease nipple fitted to which we fit a 6mm tube with a nipple at the assembly top plate. The path of the grease is into the bearing and out through the rubber seals. I understand how greasing outside of 2RS bearings would not allow grease into the bearing. In our case the force of the grease slightly distorts the seal but we know that fresh grease is arriving at the bearing.
Regards
Joe Mc Cormack
RM
Lee,
In answer to your question about sealed and shielded bearings. Sealed bearings typically have rubber seals on each side. These seals make rubbing contact with the inner race, there is no gap. Everyone agrees that these can't be relubricated. They are normally only specified for harsh environments because the rubbing contact of the seals actually shortens bearing life, so they will not last as long as a shielded or open bearing in a good environment.
Shielded bearings have metal or hard plastic shields on each side. The shields are affixed to the outer race and a small gap (10 mils)exists between the shield and the inner race. Double shielded bearings are normally installed in smaller motors (<50 HP) because the motor manufacturer does not know what type of environment the motor will be in. Shielded bearings were originally developed for use in dirty environments like coal plants, paper mills, etc... None of the major bearing manufacturers recommend trying to grease sealed or shielded bearings. Motor manufacturers are mixed on the issue, with some recommending greasing and some not. My experience is that you can't get new grease into a shielded bearing.
RM

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