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Underwater Bearing Application

Underwater Bearing Application

(OP)
We have a unique project coming up that will require the use of bearings underwater. The bearings will be supporting a shaft rotating at approximately 1800 rpm. I expect thrust load to be approximately 50-100 lbs, and I expect a radial load of no more than 500 lbs. The system is intended to remain underwater for up to 20 years with little or no maintenance (intermittent use - under 1000 hrs of operation). This is conceptual right now, so I don't have much more detail, but I can may be able to tweak the design if we need to.

My question: Does anyone here have recommendations for bearings being used underwater? I can select and size bearings in other applications, but I've had trouble finding bearings that are rated for underwater use. I have seen large custom marine bearings, but I'm looking for something a little more standard if possible.

Thanks is advance!

Jim Breunig P.E.
XCEED Engineering
Mechanical Engineering
FEA Consultants

RE: Underwater Bearing Application

Of the materials that my company makes bearings from, I'd probably recommend something like N360 (AMS 5898, nitrogen enriched corrosion resistant steel) or L-605 (AMS 5759, cobalt alloy). We use those for aerospace bearings and they're probably our most corrosion resistant materials, though I'm more used to worrying about high temperature issues than aqueous corrosion. I'd have to do more research to actually check their performance in that type of environment but those are the ones I'd start with.

As always, calling a reputable bearing company and asking to speak to their applications engineers is probably your best course of action.

Aidan McAllister
Metallurgical Engineer

RE: Underwater Bearing Application

When you say the bearings will be used underwater, I'm assuming they will be mounted in some type of housing with seals preventing direct contact with the water. You also did not mention the shaft size. But unless the shaft is very small diameter the axial/radial loads and duty cycle should not pose a problem for any good quality corrosion resistant steel currently used for rolling element bearings. For your combined radial and axial loads, you can use a pair of angular contact ball bearings. Most manufacturers offer these bearings in 440C which should give acceptable service with suitable lubrication. If cost is no concern, you can use bearings made from silicon nitride, which tolerate poor lubrication conditions better than other materials.

RE: Underwater Bearing Application

(OP)
Thanks for the feedback. The shaft size is about 1" diameter. I'm actually now considering a bushing for this application. To answer some of the questions, we can't use soft goods due to radiation, so sealing the bearing from the water environment is extremely difficult. We were hoping to find a bearing that was either sealed itself, and/or find a bearing that can operate while exposed to water.

NSK got back to me, and they have ceramic and resin bearings that may work, but there are some drawbacks. I'm not sure that resin will work in this environment, so I'm between ceramics and bushings. Leaning towards bushings due to high cost/complexity/risk of ceramic bearings.

I think I got the answers I need. I appreciate the responses!

Jim Breunig P.E.
XCEED Engineering
Mechanical Engineering
FEA Consultants

RE: Underwater Bearing Application

(OP)
Thanks for the information everyone! This has certainly been interesting. I actually found out that similar applications used bushings, so I'm going forward with that design. I'm keeping some of these other designs in mind for later!

Jim Breunig P.E.
XCEED Engineering
Mechanical Engineering
FEA Consultants

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