Valve Orifice Erosion - resistant material? 4

[valvesrus]

A difficult erosion problem is handling a 10 kpsi pressure drop across very small (.005 in.) orifices created by sliding gate valve seats. Tungsten carbide is quickly eroded. The candidate material must slide at low speed as the valve opens with 20 kpsi contact stress without galling. The fluid is water or alchohol. Sealing surfaces are lapped flat.

 

[unclesyd]

What is the size of the gate?

What type WC are you using?

What form is the corrosion, IE wire drawing etc.

 

[TVP]

Are you certain that the tungsten carbide is eroded, or is it possible that it is fracturing?

 

[valvesrus]

The gate has .094 in. bore and is partially covered by a seal ring with a land width of .110 in. and a major diameter of .42 in.
Pressure can load the seal ring to the gate at 20,000 psi contact stress while dropping 10,000 psi through an orifice created by the valve position to control flow.
I have tried WC with 6% nickel binder and 1.3 micron grain size and also 5% cobalt binder and .5 micron grain size. Both WC part sets showed significant loss of binder (>.005 in.) at the point of highest velocity flow after 50 gallons total flow of tap water.
This is erosion of the binder as grains can be seen unsupported by the binder at the point of high flow velocity.
I have tried solid silicon carbide but hoop stress and difficult geometery causing stress risers led to fracture.

Thanks for your interest!

 

[TVP]

I am not an expert on this subject, but this appears to be an extremely challenging situation. It would probably be useful to spend some time looking at design and geometry changes that would preload a ceramic part in compression, thereby reducing the tensile stresses that develop during operation. Some German researchers are working on cold forging tools that use ceramic inserts with substantial compressive preloading to prevent fracturing.

 

[valvesrus]

Thank you TVP. We have looked into this and cannot remove all the tensile shock loading produced by the high pressure fluid. We tried saphire as well with immediate fracture results.

 

[unclesyd]

Here are two material possibilities.
I know of an application that is taking a 6500 psi drop across this material with apparently no problems.

The diamond material just looks interesting. My experience has been with diamond guides in spinning steel. Have seen diamond nozzles/jets in UHPW systems.

http://www.cerbide.com/s.nl/sc.2/category.16/.f

http://www.novatekonline.com

 

[EdStainless]

Since all of the erosion is on the binder, you need a system with no binder. This rules out most of the ceramic system.
What else have you tried?
First thought is a hot pressed SiN.
Diamond should also work. I have used diamond wire draw dies and I have seen them used in some extreem extrusion applications.

= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[lgearhart]

There are a few commercial ceramics, primarily those toughened with zirconia, that have much better fracture toughness than sapphire (which is essentially alumina). Check out the offerings of Saint-Gobain or CoorsTek- they're worth at least a phone call to chat about Transformation Toughened Zirconia or the less expensive Zirconia Toughened Alumina.

If the ceramics route proves unfruitful, consider the metals that work in cavation applications, like the Stellite series of cobalt based alloys.

 

[EdStainless]

I wouldn't think that either TTZ or ZTA would work. The binder phases in both are not real strong or corrosion resistant. The TTZ has better corrosion resistance in water, it is very tough, but not real hard.
The other thought is to look into TiCN coating an ultra hard tool steel. This coating is CVD applied and diffused into the metal (it reacts with the C in the metal). Maybe use CPM REX T15 or 121 as a substrate.

= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[valvesrus]

Thank you all for your well thought suggestions. I have enough new things to try to keep me busy for a long time. The Stellite suggested by lgearhart seems very promising. If anyone is curious the patent no. is 6,973,936.