Underwater wheel

[RobertCasey]

Hello all. I am currently designing a turntable that must operate underwater, but I am having a great deal of difficulty in finding a suitable support wheel. The wheel must take a load of 22kN and must be able to be continually submerged in freshwater. I have looked at stainless steel but the capacities are very low. I am aware of other projects that have used solid steel wheels but they became corroded quite quickly. I envisage the wheel running on a smooth stainless steel strip to keep the friction low, so I have the idea to use some form of engineering plastic. The only problem is finding the right material, and someone that can turn it into wheels. Id be very grateful for any help.

 

[gwolf]

The strongest plastics that I have designed with are Torlon From BP composites which has a yield of about 180MPa and Peek from victrex which has a yield of the order of 100MPa -the web sites will give you details of properties. I would be surprised if these are any better than the stainless in terms of strength.

 

[Beggar]

Have you looked at titanium?

--------------------
Bring back the HP-15

http://www.hp15c.org

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[Philrock]

What are your diameter and width limitations?

 

[Barry1961]

If this is going to be submerged at all times while loaded would it be possible to build in some air chambers to take some of the load off the wheels?

Barry1961

 

[RobertCasey]

I dont really have a size limitation per se, at the moment I have assumed a diameter of 250mm and a width of 60mm. Both can be increased if required.

A safety shoe will probably take some of the load off the wheel during the loading phase, but the problem is that I cant be totally sure it will always do this and so I have to assume the loadpath is always through the wheel.

To be honest, I hadnt realised it would be so hard to find suitable wheels - none of the usual wheel and castor suppliers want to know, maybe theres a market there waiting to be tapped ;-)

 

[BillPSU]

Could you make the turntable bouyant offsetting the loading thus reducing the support wheel loading. You could have enough bouyancy where the turntable actually had positive bouyancy and you would have to hold the turntable down in the unloaded condition.

 

[Barry1961]

There are several brands of mounted bearings that are designed for washdown and submerged duty. You may have to make your own wheel. SKF, PTI and Fafnir should all have washdown bearings.

Barry1961

 

[sreid]

A note; washdown is not IP68.

http://www.rlws.com/lit/load-cells/IP_ratings.html

 

[ccw]

Hi RobertCasey,
If your budget can stand it make two rolled, seamed, and machined unhardened 304L SST raceway rims and load it with 440C SST hardened steel balls (McMaster Carr). To see what it would look like go to:

http://www.rotek-inc.com/english/e_index2;

or download Kaydon's turn table bearing catalog pdf:

http://www.reali-slim.com/pdfs/catalog390.pdf.

Mount one side of raceway static to the underwater ground support and the other to the wheel. It will last a long time.

You can cop Rotek's design data because the 440C and 52100 Chrome steel balls perform about the same. In addition, you might ask Rotek, Kaydon, or some of the other turntable bearing mfg.rs if they would make you a stainless version. One thing you did not specify was overturning moments. Does your wheel support an axial load only (the 22kN) or is there an overhung load as well?

 

[GregLocock]

Or to go back to an earlier suggestion, titanium tyres shrunk fit to SS wheels.

To be honest I'd have thought some sort of rubber would do as a tyre, but have no great experience with rubber underwater.


Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[ccw]

Hi RobertCasey,
The two web site references for the turntable bearing references may require registration (name and e-mail address) before proceeding to the subdirectories. Sorry about the gaff.

 

[RobertCasey]

Thanks to everyone for their help . Im looking into getting rid of the wheels altogether, and replacing them with some form of low-friction sliding bearing. This would give more scope for using material that might be slightly hydroscopic, but for which the lower contact stress of a pad bearing would make it less of a problem. It would also allow me to get rid of all the bearings and shafts associated with a wheel. Does anyone have any experience of using "Nyloil" blocks underwater?