Greasing a bearing once a week????

[drivewizard]

New AHU with an air foil fan turning 1970 rpm at full speed. On a VFD.
2 7/16" shaft , Dodge tapered sleeve pillow blocks, ball brgs.
Have replaced brgs 3 times now, 1st time FIB brg was toast. The nylon/plastic cage was gone, jsut theballs left in brg. The next two brgs didn't fail but were showing increasing amplitudes on Vibe data, and were replaced proactively. I found a resonant vibe at 1305 RPM in the axial direction, also laser aligned sheaves which were slightly out.
Replaced belts with a matched set, unmatched before.
Locked out VFD between 36 and 42 HZ.
Is running smoother now, but while researching brg info I talked to Dodge Rep and they are saying this brg needs to be greased once a week when turning these speeds, on this size shaft, and running 24/7.

This sounds to me like a sign of a cheap brg? AHU Factory says it should be fine, never had a problem before!!!! This seems like an unreasonable request to ask customer of their new fan.
Do you guys have fans turning this speed, do they need greased once a week?

[DeltaT]

You are probably picking up harmonics through the VFD and into the bearings.

[dgruber]

You may have something going on that we can all learn from! Please post future information.

[madhat]

I have several pieces of equipment with Dodge bearings. The lube interval is a 1000 hours which at 24/7 is 41.6 days. Go to a synthetic grease and you can double the interval. Suggest Mobililth 100. On a bearings that big I like to use a couple of drops of Blue locktite, between the shaft and bearing, after cleaning with primer or acetone. The proper locktite for bearings is green, but you have to use heat to break that bond. So I use the blue stuff.

[dgruber]

Madhat,

Great feedback!!

[drivewizard]

I have several pieces of equipment with Dodge bearings. The lube interval is a 1000 hours which at 24/7 is 41.6 days. Go to a synthetic grease and you can double the interval. Suggest Mobililth 100. On a bearings that big I like to use a couple of drops of Blue locktite, between the shaft and bearing, after cleaning with primer or acetone. The proper locktite for bearings is green, but you have to use heat to break that bond. So I use the blue stuff.



I have never heard of using loctite between shaft and brg? What does that do?

As far as lube freq I was going off brg literature that came with brgs, and also called rep and he called Dodge and they confirmed. Once a week!!!!
Not making it up!

[madhat]

I have never heard of using loctite between shaft and brg? What does that do?

As far as lube freq I was going off brg literature that came with brgs, and also called rep and he called Dodge and they confirmed. Once a week!!!!
Not making it up!

Keeps the bearing from moving around on the shaft which produces friction between the shaft and bearing and heats up the bearing, which will make the bearing even looser, as the shaft will dissipate its heat, because of its mass, and stay close to its static size while the bearing expands, due to the insulating properties of the grease.

That's for the worse case application of that bearing, go to the O.E.M. for lube intervals, not the bearing company. Also if you need lubrication that often, you need auto lube equipment.

[absrbrtek]

Do these bearings have a grease plug on them or is the grease just pushing out the seals? Over greasing is worse than under greasing a ball bearing. Are there grease reliefs installed on the bearings to relieve the excess pressure generated after greasing?

Madhat, I use the Mobilith 100, an excellent synthetic grease.

[drivewizard]

Do these bearings have a grease plug on them or is the grease just pushing out the seals? Over greasing is worse than under greasing a ball bearing. Are there grease reliefs installed on the bearings to relieve the excess pressure generated after greasing?

Madhat, I use the Mobilith 100, an excellent synthetic grease.
We use Chevron SRI-2 , I'll look into the Mobilith 100.
No plug, they said to just put enuff grease in till you see a bead around the seal. Seems very excessive to me to have to grease that often.
I am wondering if a different manuf, like Sealmaster, or?? would have a less frequent greasing schedule.
absrbrtek: I agree, usually less is better than over greasing. Especially on a brg with seals and shields!!!! I asked rep where grease went that it needs to be greased so often. His reply was that it " Vaporizes" when turning at those speeds!!!!!!!
Madhat: I will try the Loctite if we go back to change the brgs. I did notice a little bit of fretting between shaft and brg sleeve. I assumed it was due to running under high axial vibration from the resonace at 37-38 Hz. That speed has since been locked out so shouldn't be an issue anymore.

[absrbrtek]

Vaporizes to where? Looks like that Chevron grease is not synthetic. You need a grease that is extreme presssure, Lithium based and NlGI 2 rated.
https://www.cbest.chevron.com/generated/MSDS/PDS7668239.PDF

I just spent many hours researching greases several months ago as we had over 500 bearings on pumps, bearing assemblies and motors to grease. All using different greases. Many of them had never been greased or shot water out of the drains.

I wanted them all to be on the same grease. Took over 100 tubes of grease to flush out and fill the cavities. The average grease gun takes 33 pumps per ounce. 33 pumps x 14 ounces x 100 tubes is about 46,200 strokes on the grease gun. Needless to say I have a rechargable grease gun now. :)

We added .5 to 1 PSI grease reliefs on every drain and extended out every fitting while greasing. You can now properly grease the thermal plant in about 1 hour instead of 2 days.

I always figured grease was grease, just open the relief plug, pump some in until it comes out the relief plug and walk away. I googled "greasing pumps" and "greasing bearings". It is amazing how much information on properly greasing a bearing or a motor without destroying it there is to be read. I would be willing to bet that 95% of the people greasing bearings have no clue on the proper procedures after reading multiple hours on grease and greasing.

My preferred greasing interval and amount method would be Ultrasonic Listening Device but I can't see my company buying the equipment.

http://www.maintenanceworld.com/Articles/noria/greasing-bearing-3.htm

Mobilith SHC 100 http://www.grainger.com/Grainger/items/4ZF49

JMHO

[NWChicago]

I have several pieces of equipment with Dodge bearings. The lube interval is a 1000 hours which at 24/7 is 41.6 days. Go to a synthetic grease and you can double the interval. Suggest Mobililth 100. On a bearings that big I like to use a couple of drops of Blue locktite, between the shaft and bearing, after cleaning with primer or acetone. The proper locktite for bearings is green, but you have to use heat to break that bond. So I use the blue stuff.

You have to really like that Mobilith 100. It is Surprising how many techs do not use it.

[NWChicago]

Do these bearings have a grease plug on them or is the grease just pushing out the seals? Over greasing is worse than under greasing a ball bearing. Are there grease reliefs installed on the bearings to relieve the excess pressure generated after greasing?

Madhat, I use the Mobilith 100, an excellent synthetic grease.

The Grease will act as an insulator and keep the heat inside instead of disipating it if a bearing is over greased.

[JoeVibe]

The majority of the industrial customers I service have gone to Royal Purple lube products and they swear by them. I've been told that after switching to RP oil and grease they've seen dramatic reductions in operating temperatures, wear, and failure in bearings, couplings, gearboxes, etc. I don't have any personal experience with it but I've heard nothing but great things about their stuff.

[jayhawker]

You might try having it balanced and they can lock out on the VFD any HZ that are causing a problem

[DCSCO]

Wizard,
At 1900 RPM you should try a Labyrinth seal, standard seals are rated to about 1800 RPM. However with a VFD you may not approach this limit. Do you use a locating bearing on the drive side and a non-locating beating on the opposite end. This allows the shaft to flex, expand and contract without laterial stress on the bearing.

SKF makes an adjustable rate, screw-in, battery operated grease despensed, check out their web site for alot of good information.

Recently, during replacement of a 100HP motor, our local shop took pains to label the motor synthetic grease only. They claimed that mixing with non-synthetic grease caused the two greases to ball up seperately and starve the bearing of oil. I have not heard about this from any other source though.

I think all pillow blocks are self aligning, but worth a check to make sure the dodge bearings are. A coworker recently found a fan wheel that had the bore in the hub off center making for an out of round fan. Check out the SKF ConCentra bearings if you visit their site. They are spherical bearings as opposed to barrel or tapered.

[chillersandcontrols]

By DriveWizard:>>Madhat: I will try the Loctite if we go back to change the brgs. I did notice a little bit of fretting between shaft and brg sleeve. I assumed it was due to running under high axial vibration from the resonace at 37-38 Hz. That speed has since been locked out so shouldn't be an issue anymore.<<

It is also possible that electrical corona could be causing those marks on the shaft and bearings. Installing proper grounding might extend the life of the bearings also. Make sure you have a substantial, copper ground from the motor casing and also the VFD ground bar to a true, verified earth ground - not just the sheet metal of the unit. I have seen situations where a commutator was added to the shaft to dissipate coronal discharges safely to ground, away from the bearing path to ground.


It sounds as though the original bearings were not chosen correctly for the application of this fan.

[drivewizard]

By DriveWizard:>>Madhat: I will try the Loctite if we go back to change the brgs. I did notice a little bit of fretting between shaft and brg sleeve. I assumed it was due to running under high axial vibration from the resonace at 37-38 Hz. That speed has since been locked out so shouldn't be an issue anymore.<<

It is also possible that electrical corona could be causing those marks on the shaft and bearings. Installing proper grounding might extend the life of the bearings also. Make sure you have a substantial, copper ground from the motor casing and also the VFD ground bar to a true, verified earth ground - not just the sheet metal of the unit. I have seen situations where a commutator was added to the shaft to dissipate coronal discharges safely to ground, away from the bearing path to ground.


It sounds as though the original bearings were not chosen correctly for the application of this fan.

I am a little confused now, you understand I am talking about fan shaft brgs failing. Not motor bearings.
I assume you are referring to shaft grounding being applied to a motor.
I am unaware of any common mode voltages ever being transmitted through belts to driven components. I could be mistaken.
What do you mean by electrical Corona?

[chillersandcontrols]

My bad....I was referring to a motor issue; however, you could be having static electricity discharge from the fan through the shaft and bearings to ground. This coronal discharge causes pitting of the shaft and internal bearing surfaces.
Is the fan draw-thru or blow-thru? Airfoils move significantly more volume of air than forward-curved fans and therefore have a greater change of generating static(blow-thru).

If the AHU is for comfort cooling the temperature should not vary enough to cause significant lateral movement of the shaft through the bearings. I don't know how sophisticated your vibration analysis setup is, but I would suggest aiming for resonance levels as low as possible through-out the speed range. The loctite is a necessity at the fan and bearings!

The fan wheel may have been mis-aligned on the fan shaft upon build or shipping from factory. Start there and work your way out - fan wheel to shaft, shaft to bearings, bearings to frame, sheave to shaft, fan sheave alignment to motor sheave. If your blower is large this may require some rather long precision straight-edges and measuring instruments to measure run-outs. I have seen blowers three stories tall run for over 40 years without a bearing failure and no appreciable vibration. Sounds like a bear of a job, Good Luck!

[hvacker]

If you still have the failed bearings maybe you could open them up to see what the failure mode was.
Also is there any welding going on in the building? I had a bearing book once that showed bearings affected by this.

If the problem is wear then that would be really fast wear

[DeltaT]

harmonics can lead to failures on fan bearing, motor bearing and anything else that it can get into.

Here is an article by Fluke:

http://support.fluke.com/find-sales/Download/Asset/1260362_6001_ENG_K_W.PDF

[jayhawker]

this is a good article on the volatage that can induced on a motor shaft from a VFD http://www.hpac.com/Issue/Article/47488/Preventing_Damage_to_Motor_Bearings

[ZZZRSC]

I've had similar problems on new equip. The Mfg. used incorrect bearings for the load and the bearing rep. didn't want to start a war with one of their better customers. First thing, I would get some reps for other brands and get their recommendations. That is not normal from what you describe. I believe DCSCO made an important point on the two different bearings on the shaft, maybe someone put the wrong ones on. I don't care for Dodge myself. Synthetic grease-always, never mix brands or types without flushing thoroughly. Save bad bearings, as a last resort send them to a testing lab.
Send the shaft to a good machine shop to check if bent, send fan also and have it balanced. Do both bearings fail equally or does the one closest to the fan fail first? What is FIB? Is it airfoil centrifugal or airfoil axial?

[berg2666]

My vote is for bearing fluting due to VFD discharge...

[propmanage]

It sounds like something is wrong even if the manufacture is telling you to grease every week. You can have specially made bearings that can handle a whole lot more then what you have.
1) Start with getting an automatic grease fill you can get battery operated or spring wound. That should buy you time.
2) Request a bearing manufacture sales representative to come to your site and look over this equipment. They should be able to special order you a solution to this problem.

Please keep us updated
;)