Lubrication of bearings 1

[pdmou]

Hi
I got a question regarding how often a bearing needs to be lubricated for example in flight controls and what determines how often it needs to be done?
Best regards
Peter

 

[tbuelna]

Need to know exactly what type of bearing you are asking about, the specific application the bearing is used for, the installation arrangement of the bearing, and the operating environment the bearing is exposed to.

If you post these details I can provide some guidance on how to determine the service interval for this bearing yourself.

Regards,
Terry

 

[WKTaylor]

pdmou...

Too many variables, as tbuelna indicated.

In addition to what tbuelna mentioned...

Grease [zerc, etc] fitting provided in the mount with passages thru to the rolling elements [balls, rollers, needle-rollers, etc] for routine servicing; or does the bearing have to be manually cleaned/re-packed ['classic hand-packing, or needle injection, etc]?

Type of grease [synthetic, petroleum, etc]?
NOTE. Some greases are highly durable; some more prone to early break-down.
Grease '%fill' in the rolling elements?
NOTE. Control system bearings typically have a 20--40% fill to ensure absolute minimum friction... even from lubricants; while other bearings have a much higher fill requirement [60--80% etc] for highly loaded parts in high-force hydraulic systems.

Exposure to drip or condensation or direct water [rain, wash, etc]; or solvent like fluids [hydraulic/oil, fuel, cleaners, etc]?
exposure?

Exposure to high heat or continuous air-flow [outside mold-line or in vented cavities, etc?

Bearing orientation relative to debris/moisture/fluids intrusion/entrapment?

Etc.

May pay to peek at AMMs for similar acft/systems.

IF You have access to standar overhaul practices manuals [any major OEM], then there is typically one dedicated to bearings and one for general lubrication.

IF you have access, there are several amazing USAF T.O.s for every aspect of bearings, inspection, installation, repair, relubrication, etc as follows...

44B-1-2 GENERAL MAINTENANCE INSTRUCTIONS AIRFRAME ANTIFRICTION BEARINGS
44B-1-3 AIRCRAFT WHEEL ANTIFRICTION BEARINGS AIRCRAFT WHEEL BEARING CUPS AND GREASE SEALS
44B-1-15 JET ENGINE ANTIFRICTION BEARING HANDLING, REMOVAL, CLEANING INSPECTION, AND INSTALLATION AT JET ENGINE BASE MAINTENANCE (JEBM) FACILITIES
44B-1-16 GENERAL INSTRUCTIONS FOR INSTALLATION AND REMOVAL IN AIRBORNE ACCESSORIES ANTI-FRICTION BEARINGS44B-1-102 MAINTENANCE INSTRUCTIONS - ANTIFRICTION BEARINGS
44B-1-18 GENERAL INSTRUCTIONS FOR INSTALLATION AND REMOVAL IN AIRCRAFT INSTRUMENTS - ANTIFRICTION BEARINGS (PRECISION INSTRUMENT BALL BEARINGS)
44B-1-102 MAINTENANCE INSTRUCTIONS - ANTIFRICTION BEARINGS
44B-1-122 MAINTENANCE OF AERONAUTICAL ANTIFRICTION BEARINGS FOR ORGANIZATIONAL, INTERMEDIATE AND DEPOT MAINTENANCE LEVELS

and for giggles...
MIL-HDBK-275 GUIDE FOR SELECTION OF LUBRICANT FLUIDS AND COMPOUNDS FOR USE IN FLIGHT VEHICLES AND COMPONENTS [out of date but certain elements informative]
Exxon Mobile Aviation Lubricants:

http://www.exxonmobil.com/lubes/exxonmobil/emal/index.html

AeroShell 2012 Lubricant handbook:

http://www.shell.com/content/dam/sh...ownloads/AeroShell-Book/theaeroshellebook.pdf

AeroShell Knowledge center:

http://www.shell.com/global/product...sses/aviation/aeroshell/knowledge-centre.html

Nation Lubricating Grease Institute [NLGI]:

http://www.nlgi.org/

[good technical info on lubricating greases].






Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true.
o For those who believe, no proof is required; for those who cannot believe, no proof is possible.
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion"]
o Learn the rules like a pro, so you can break them like an artist. [Picasso]

 

[tbuelna]

wktaylor-

Great post. Designing a proper arrangement for re-greasing bearings/bushings is not as simple as adding a Zerk fitting someplace convenient.

With aircraft bearings that are lubed in place, ideally you design the installation so that the new grease charge can completely displace the old grease. It is of little benefit to just mix new grease with the old grease, so besides having someplace to inject fresh grease you should have some means for discharging the old grease. Preferably somewhere it can be collected and easily removed. Displacing all of the old grease will also ensure any debris and moisture in the bearing cavity is flushed out.

With rolling element bearing installations the sealed volume should be kept to a minimum, and the fresh grease charge should fill as much of the bearing cavity as possible. If there is excessive air space in the sealed volume around a grease lubed rolling element bearing, condensation can form from heating/cooling cycles. Any condensation that collects on steel race/element surfaces can produce surface corrosion if the bearing is not cycled regularly. These tiny surface corrosion pits will quickly lead to larger pitting, and ultimately spalling, if they are located on the rolling element/race contact areas.

Interesting topic. Too bad pdmou disappeared.

Regards,
Terry