Water lubricated ceramic roller bearings?

[TAPtechit]

Hi guys,

First time poster after reading the forums for years!

We have an interesting project that requires a seawater submerged rotating assembly. We need bearings, and plain bearings have too much drag loss for us. Long service intervals would be ideal so we're hesitant with using seals in this environment. The unit will be in high current flow areas near the bottom so there's likely to be a good amount of sediment.

I am thinking if we can go with a water-lubricated ceramic roller bearing we would be looking pretty. Does anyone have any experience with these bearings? We have low rpm, "moderate" radial loads, bearings will probably be in the 4" ID range for our requirements.

Looking for guidance here more than anything. We're currently using enviro-friendly lubricants and doing our best to seal out the seawater, but are looking for more robust solutions. Maybe a housing that is sealed with a mechanical seal and filled with fresh water before deployment..?

 

[MikeHalloran]

Ceramics + sediment = early bearing death.

Mike Halloran
Pembroke Pines, FL, USA

 

[TAPtechit]

Yes, I was thinking that keeping the ceramic bearing in a housing and using a mechanical seal would do well. Pre-filling the housing with freshwater or biodegradable oil would greatly reduce water ingress over time. Hoping for something like 3 years service interval.

 

[Tmoose]

Not sure about water lubed plain bearings, but when up to speed hydrodynamic oil bearings don't have to have much more drag than ball/roller bearings.


I think I'd look for buy-in from a bearing manufacturer for water lube.

 

[TAPtechit]

To get to hydrodynamic surface speeds we would need a prohibitive diameter, IE going from 8" to something like 20" diameter. We did have some buy-in from the ceramic guys but they seem to have very limited experience as compared to other types of water lubricated bearings, like cutlass or thordon types.

It is tough to find comparable examples as we have a large side load where most of the seawater lubricated bearings we are seeing are used in ship shafts. Maybe we need to hunt down a different industry, like seawater pumping instead of ships.

 

[Tmoose]

Were the ceramic guys from SKF or FAG ?

http://www.fag.com/content.fag.de/de/press/press-releases/press-details.jsp?id=23019584

have the unsuccessful journal bearings been made from something similar to this?

http://www.igus.com/iglide?WT.srch=1&WT.mc_id=gadUS49&c=US&L=en&gclid=CNyd1rq6_rsCFc07OgodLGkAww

 

[me66us]

you may try air bearings it s require no maintenance air may push out the sea water ...oav air bearings has list of product on there website

http://www.oavco.com/products/

 

[romke]

Have you considered sealed for life greased bearings? I guess when using a water repellent grease and maybe some additional sealing could do the trick. Ceramic bearings may be very susceptible to mud and sediment, also water and low bearing speeds will yield only marginal lubrication and may lead to premature failure and corrosion problems.

 

[geesamand]

In seawater, ships use rubber bearing or Thordon with a ceramic-coated bearing sleeve. But sediment that gets trapped in the rubber will eat the sleeve in a hurry.

Ceramic bearings with water lube and consistent flushing action could work better. I had an application where I pondered the same things. We ended up not even trying it because I couldn't get an all-ceramic bearing free of any carbon steel. Only one way to know for sure is to build it and try it.

 

[TAPtechit]

Our current solution is a sealed grease bearing. It does have ports for grease refill/purge on maintenance intervals.

There's an outfit called Champion Bearings that can provide large diameter, full ceramic bearings. You're right though, only way to know for sure is to test! Since we have a current design ready for testing, I would like to get a ceramic/water lubricated variant test in order. It would be interesting!

 

[Tmoose]

What were Champion's comments on bearing life when lubricated with sediment laden water?