Improving Wear Resistance of Valve Rods 1

[TCallahan]

Hello all,

This is my first post here, proud to be doing so. I've been googling through this site this afternoon, and it's been very informative.

I'm working with a metered mix system with a worst-case kind of application, dispensing an aluminum oxide filled thermal compound. The compound itself is insanely abrasive, and I've been trying to improve several parts of it.

The cup seals it originally came with were made of EPR (god knows why), so those have been swapped for polyurethane (I should be seeing some improvement in wear resitance), I'll be stepping up to UHMW Polyethylene with a steel spring if that doesn't work.

The next improvement on the list is replacing the valve rods in contact with the seals mentioned above.

As provided, they were stainless steel with some kind of superficial gold-colored coating. Completely inadequate in terms of wear resistance.

I did some drawings, and sent it out for quotes specifying fully case-hardened 8620 steel.

Was this a good call?

Is there a better option?

Take it easy,

Toby

 

[Artisi]

Have you considered ceramic coating.

 

[MintJulep]

Titanium nitride coating?

The question mark has two meanings:

1. Have you considered it?

2. It's gold-colored is that what was already on the original?

 

[vc66]

MintJulep-

If it was TiN coating, and it was "superficial", then it must've been done by a bad supplier. But I agree, TiN or AlTiN is definitely a good option for wear resistance.

V

Mechanical Engineer
"When I am working on a problem, I do not think of beauty, but when I've finished, if the solution is not beautiful, I know it is wrong."

- R. Buckminster Fuller

 

[TCallahan]

The color is a pretty good match for the TiN tools we have in the shop, and I can't think of any other reason for it to be this color. Good point.

I think the decision then was, lets make it stainless steel for corrosion resistance (which, in our application, doesn't matter, the compound is silicone based, excludes air and moisture, and is pretty chemically friendly, at least as far as metal goes), and then coating them for wear resistance (which didn't work).

I think overall, perhaps replacing the seal material may have a bigger impact on the problem. If the seal is better, then there's less chance of material getting in and abrading the rods.

We'll see how expensive making these is going to be.

 

[TCallahan]

By superficial, I mean that it didn't stand up to a caliper blade.

 

[TVP]

There are a number of ceramic coatings that are applied by thermal spray methods (HVOF, etc.) which you can investigate. They have outstanding wear resistance. Sulzer has a good website for obtaining background on materials, coatings, etc.

http://www.sulzer.com

 

[israelkk]

From my experience the seal may be the abraser. The aluminum oxide doesn't have to pentrate beyond the seal. What usually happens it that the aluminum oxide is attached/embeds itself to the rubber seal which in turn becomes abrasive.

 

[arunmrao]

8620 may not be a good choice as the wear resistance is controlled by the case. You can try 430 stainless steel rods with a ceramic coating on the work surfaces.

Save water Drink Beer

 

[TCallahan]

Just got off the phone with our local machine shop.

He recommended A-series steel fully hardened, with a note that 60-62 Rockwell C is attainable this way.

I'm comparing prices as far as that versus 8620.

 

[tomwalz]

always been impressed by Balzers for coatings.

http://www.oerlikon.com/balzers/

I have seen solid TiCN valves.

Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessors.com

 

[eromlignod]

If you don't need stainless, can't you use alloy steel and carburize or nitride it?

Don
Kansas City

 

[hydtools]

What about hard chrome plate?

If you use 8620, be sure to specify the case hardness and depth after grind so that all the case is not removed by finish grinding.

Ted

 

[unclesyd]

I would look at solid ceramic rods/plungers or get in touch with Saturn Ceramics and discuss your problem with them.
We use solid ceramic plungers on a variety of PD pumps.
We have used Saturn Coatings on some on very tough problems.

http://www.saturnceramic.com/abrasion.htm

 

[EdDanzer]

It may be best to use a ceramic or metal face seal so the shaft material is not used as a seal surface. Try this link.

http://www.skf.com/portal/skf/home/products?maincatalogue=1&lang=en&newlink=4_2_1

Ed Danzer

http://www.danzcoinc.com

http://www.dehyds.com

 

[TCallahan]

Good Lord, that's a lot of options:

- Ceramic Coating on steel
- Hard Chrome Coating on steel
- Fully hardened A-series steel
- Case-hardened 8620
- Solid Ceramics instead
- Alter design to change seal mechanics.


I think the first step is definitely to replace the seals with something tougher.

 

[TCallahan]

The decision has been made (barring extreme cost) to go with case-hardened 8620 with a TiCN coating.

Thank you all for your input.

 

[unclesyd]

A lot of optiosn are better than you have got to live with what you got.