Design of ball bearing to operate in water?

[geesamand]

I'm thinking about using a ball bearing in an application where the bearing would run immersed in fresh pond water. I'd like to hear from anyone who has a similar application: what are the load conditions, bearing material (stainless, ceramic, etc?), type of water, and the real-world vs. calculated life.

In my case, shaft speed is 1200rpm and the load would be 100lb radial. Bearing will be in the 6018 to 6020 range. My basic L10 estimates are very high due to the low load which means with contamination and material adjustments this may be feasible.

 

[MikeHalloran]

There are two schools of thought on lubricating axles for Everglades swamp buggies.
One school seals them up and vents them through long hoses to high parts of the structure.
The other school cuts the top of the banjo open, and runs them 'mud lubricated' for as long as they last. They start with regular axle lube, to which is added whatever spills in as the unit travels through mud/ water/ whatever.
Speeds are generally very low.
Everglades 'muck' is definitely _not_ fresh pond water.



Mike Halloran
Pembroke Pines, FL, USA

 

[geesamand]

Interesting. I take it that these are not stainless bearings, and corrosion and particulate contamination quickly eat them up.

 

[MikeHalloran]

Definitely not stainless, and I'm told they last a season or two, which surprised me. It's certainly not continuous duty. The particulates are probably quite fine



Mike Halloran
Pembroke Pines, FL, USA

 

[geesamand]

What I do know is most stainless bearings are made of 440c hardened stainless steel. And it will rust if exposed continuously to water.

Ultimately I would use one of the more corrosion resistant stainless grades but any stainless bearing in water would be a valuable datapoint.

 

[unclesyd]

In your application could you use a wooden bearing. Lignum Vita, or if you have a little water flow a Cutlass Bearing.

http://www.lignum-vitae.com/

http://www.duramaxmarine.com/bearings.htm

 

[MikeHalloran]

More than a decade ago, Shamban was marketing a limited selection of bearings with glass balls and plastic races. They apparently found few applications, and Shamban has been been absorbed twice. I couldn't find a contemporary reference to the bearings. The load ratings were _much_ lower than those of dimensionally equivalent metal bearings.





Mike Halloran
Pembroke Pines, FL, USA

 

[geesamand]

I'm pursuing this in an effort to avoid a soft material that can trap abrasives. We have some past experience where the Cutlass style bearing got contaminated with an abrasive and ground through the ceramic coated sleeve on the shaft. I'm concerned a plastic or lignum vitae element would do the same.

So I'm thinking a bearing made entirely of hard materials might be more robust against an abrasive contamination event and flush free without retaining the abrasives. Ceramic or stainless ball bearing is an interesting answer(?) to the problem.

 

[Tmoose]

1200 rpm might be centrifugally useful to clean the fresh pond water . Then again, a fine screen or coffee filter could clean things up a bit too.

 

[caoimhin1]

NSK have a "molded oil" bearing which has a solid polymer lubricant which resists the washout that you get with greased bearings. Sealed and martensitic stainless.

http://www.nskamericas.com/cps/rde/xchg/na_en/hs.xsl/innovative-607.html

However, although your life may be doubled, if submerged and running at 1200rpm, you might be doubling it from 1 day to 2 days....

 

[caoimhin1]

As well as this, my advice on submerged bearings is always to make a housing to mount the bearing in, fit good shaft seals, and completely fill any free space in the housing with a water resistant grease. Long bearing life and water just don't mix, regardless of ceramics, stainless, solid lubricants....

 

[diskullman]

Jilson makes bearings with plastic races and glass balls, but I doubt they would make something quite so large.
I was with Unique Technologies for a while, and they would sned bearings out for additional heat-treating for corrosion resistance, then fill with solid graphite lubricant. They called this process "Cobra Blue",

http://www.uniquetechnologies.com/literature.htm

They do not mention the "Cobra Blue" on their website.

Russell Giuliano

 

[geesamand]

Thanks for the input everyone. It seems like the only way to get any kind of practical service life is to seal the bearing and keep it oil or grease lubricated. And given the environment of dirty water, that means Isomag type seals.

 

[DLite30]

Lignum Vitae...wow, I haven't heard those words in almost 20 years, from back in A school.

 

[4JawChuck]

I second the Lignum Vitae wood bearing for this usage, you will not find a longer lasting bearing for a submerged application like yours with as high a load rating.

We use them on hydro turbine shaft bearings with very high loads and they can last 50 years or more, stainless steel shafts are common...simple 304 is fine.

Machine and clearance it as though you were installing a plain babbit bearing and it will nearly last forever...just don't let it ever dry out once its wet since they must stay wet or they decompose.

Typically the wood is shipped encased in wax to keep it moist from the initial cutting, once you immerse the wood it must stay wet.

 

[unclesyd]

With the limited information another possibility you might want to consider is a Thordon bearing for your application. You can use someone like LM-Tarbell for help with your specific application.

http://www.thordonbearings.com/

http://www.lm-tarbell.com/plain_bearings.htm