Subsea Corrosion and Abraision Resistance

this may be off topic, but... here goes.

A few years ago, in Ottawa, a group of engineers were updating an hydroelectric facility, and they pulled out turbines that had been in the water, and still operating for just over 100 years. As bearings, they used a type of wood called Lignum Vitae, which is perfectly suited for this application, apparently, and was all still in great shape, and could have gone for another 100 years... an excellent underwater bearing material. It is from south america. I don't know how well it stands up in salt water, but obviously has no problems with fresh water. Of course, as a bearing material, it must have a low Fc. I don't know the numbers. maybe this will help.

Chris

Here is some information... very interesting.

properties

http://www.plantservices.com/articles/2005/469.html

friction

http://www.diracdelta.co.uk/science/source/f/r/friction/source.html

"Under certain conditions, the Bearing surfaces of Lignum-Vitae become glazed and slick after usage. This causes a lower coefficient of friction, which is in turn, reflected in decreased power consumption.

Lignum-Vitae has an unusual resistance to many acids and harsh chemicals, in comparison to various other industrial materials."

"The combination of density and high resin content of the wood is responsible for its extreme resistance to friction and abrasion and its remarkable property of self-lubrication. Under certain conditions lignum vitae wears better than iron. Consequently, it has been used for pulley sheaves, bearings, casters, and even in the construction of propeller shafts of steamships."

"Lignum has a long history of being used in sea faring cutlery handles as well as other tools for sailing and marine uses also because it did one thing other woods didn't do in those environments: It held up and lasted around salt water. "

You might be restricted on the steel you can use, but a very interesting surface conversion process I recommend you investigate further is "NITROTEC".

Look at www.nitrotec.co.uk for more info.

I read once that the pistons fitted in the first petrol engines designed by W.O.Bently were made of Lignum Vitae which gives some idea of its wear properties.

The idea of using Lignum Vitae is very interesting and worth further investigation however my application requires rings approximately 120 inches in diameter. there will also be several million pounds of axial and bending forces involved.

Thanks for input.

Where will you find any material to withstand those kind of forces? Are you saying
"several million PSI" ??? good luck! What you need there is some good old fashioned "Scrith"!

Scrith would be great but I would settle for some Unobtanium!

The contact stresses will be close to the yield strength of the 4130 base material (75-80 ksi). I thought of putting a strip of the lig on the faces but I'm afraid there is too much shear in this application for wood of any kind. Do you know about any flame spray or other process that could handle the shear?

Thanks

Carey

You might try plasma spray of a ceramic material to provide a thin, somewhat flexible coating on the steel, including Al₂O₃ , TiN, WC. These last two are quite common on cutting tools to provide abrasion resistance (from metal chips pitting the relief angles, not so much protectin the cutting edge, which does require a certain amount of friction to separate chip from base metal. However, be sure to check the thermal expansion co-efficients of the coating and the base metal to see if they are compatible.

Thanks,

Does this process involve heating up the substrate?

Would you know a vendor that could apply this to a part 120" in diameter, hopefully in Texas or surrounding area?

You might try plasma spray of a ceramic material to provide a thin, somewhat flexible coating on the steel, including Al₂O₃ , TiN, WC. These last two are quite common on cutting tools to provide abrasion resistance (from metal chips pitting the relief angles, not so much protectin the cutting edge, which does require a certain amount of friction to separate chip from base metal. However, be sure to check the thermal expansion co-efficients of the coating and the base metal to see if they are compatible.