High temperature bearing material recommendation/suggestions 2

[XL83NL]

As a follow-up to this post, I'm looking for material recommendations for a simple ring I intend to use between a nut and fixed component, where the nut, due to threads, will exert a force on the fixed component once the nut is tightened. Purpose of the ring is to act as a sort of sacrificial ring, that will prevent any wear on the twisting nut or underlying fixed component. Ideally, rings should be easy replaceable and cheap.

Nut and fixed component are of the same material, have a hardness ~ 180 BHN, and will see temperatures up to max ~ 950°C. The material I'm looking for should hence be soft, be able to withstand some bearing stress at temperature (albeit low), and can withstand high temperatures. The lubricating action of the ring's material is probably out of the question, and can be accomodated by other means (e.g. anti-seize).

Bearing bronze alloys (like RG7 or phosphor-bronze CuSn8) are ideal materials for bearing applications, but wont handle these temperatures.

Any thoughts?

Huub
- You never get what you expect, you only get what you inspect.

 

You don't ask for much!

I don't know of anti-seize compounds that would survive many cycles to that temperature. Actually there are not many metals that would survive prolonged exposure at that temperature.

The big question is, what is the environment; i.e., what is the potential for corrosion?

Ceramic maybe?

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[EdStainless]

The only thing that I know of that might work as a lube/anti-seize at that temp is HBN (hex boron nitride).
Do you expect your bolt to survive? What is it made of?
You are up in Ni alloy territory.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[XL83NL]

Yeah we’re in the Ni alloy territory. Items don’t need to last for typical plant life time, and welding of the nut after a cycle is a concern yes. There are other concerns I don’t need to elaborate into now, just looking for ideas on how you this specific topic.

Arent ceramic rings much harder than that, and very brittle?

Corrosion is less of a concern, it’s not in the process side but oxidation at the outer may be an issue yes.

Huub
- You never get what you expect, you only get what you inspect.

 

[TugboatEng]

Nitronic alloys have high resistance to galling.

 

[EdStainless]

I don't think that Nitronic alloys would handle this temp.
Ceramics are brittle, but handle compressive loads well.
There are also grades that will not care about this temp.
And using two different ceramics is a good practice, such as Zirconia on SiC.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[IDreamChaserI]

May be machinable glass ceramic ? 800C to 1000C.
I could supply Technical Specification

 

[MintJulep]

Graphite?

 

[XL83NL]

Thanks all for the input, I think I have sufficient leads to go from here.

Huub
- You never get what you expect, you only get what you inspect.

 

[WKTaylor]

For what it's worth... since I am familiar with cobalt alloys for turbine-engine hot section, mount self-aligning-bearings...

MIL-HDBK-62624 COBALT BASE ALLOY INVESTMENT CASTINGS

1.1 Scope. This handbook gives guidelines for chemical, mechanical and physical
properties for investment castings of the cobalt alloy commercially known as L-605, Haynes 25,
or Unitemp L605. This handbook is for guidance only. This handbook can not be cited as a
requirement. If it is, the contractor does not have to comply.

1.2 Purpose. The material covered by this handbook is primarily for parts requiring
strength at high temperatures up to 1500 degrees Fahrenheit (“F) (816 degrees Celsius (“C)) and
oxidation resistance up to 2000°F (1093°C).

I suspect this is 'a day-late and dollar short'

Regards, Wil Taylor
o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[XL83NL]

Thanks. In unfamiliar with that spec or material.

Can you maybe explain in more detail how that spec relates to my question? I understand from your post it’s for castings, whereas I’m looking for a simple flat ring.
Data I could pull of the interwebs for L605 is a hardness of about 25 HRC (

https://www.hpalloy.com/Alloys/descriptions/HAYNES25.aspx),

which seems to be far more than what my base material is (BHN 180), making it unsuitable.

Huub
- You never get what you expect, you only get what you inspect.

 

[3DDave]

Being a hard material it can be polished to decrease wear on the mating nut.

Is this the same joint as before and, if so, where is the washer? Between 1 and 8 or between 3 and 8? If 8 is turning, then that isn't good for the o-ring.

I'd suggest talking with Kennametal - some of these alloys look suitable (except for not wearing out)

https://www.stellite.com/us/en/products/stellite-family/stellite-family-stellite.html

However, they have others that may be more suitable.

 

[XL83NL]

Washer ring would be between 3 and 8. 3 is turning

Huub
- You never get what you expect, you only get what you inspect.

 

[TugboatEng]

How does hardness differential make it unsuitable? Typically in bearings a high hardness differential is preferred as it generally reduces the chances galling.

 

[XL83NL]

Hardness differential is indeed preferred/required. What I was hoping/looking for is a ring material that's softer than my base materials, such that it works as a sacrificial part that I can simply replace once worn. I dont want my expensive parts to wear out first. If, at this temperature, Im only left with harder (than my base) materials, than thats just it.

Huub
- You never get what you expect, you only get what you inspect.

 

[Compositepro]

Keep in mind that hexagonal boron nitride is an effective high temperature solid lubricant.

 

[XL83NL]

Do you maybe have a link to a datasheet or other reference, as an example for HBN?

Huub
- You never get what you expect, you only get what you inspect.

 

[btrueblood]

Suggest you google "boron nitride ceramic" for more information. Or just order a piece from McMaster -

https://www.mcmaster.com/boron-nitride/

We used to machine chunks of this for weld and braze tooling at the rocket factory (it machines pretty nicely with plain hss tooling, just go slow), it has a wonderful property of not wetting to molten metal. Also used it as dielectric/insulation spacers some high temperature tungsten heaters for resistojets and arcjets. Oh, and used cans of the spray-on powder as high temperature anti-seize, along with water/alcohol/powder solutions to swab onto fasteners prior to assembly, same idea.

 

[TugboatEng]

I believe OP is asking about powder, not bar stock.

https://www.bn.saint-gobain.com/products/powders/lubricant-additives

 

[XL83NL]

Thanks TBE. This HBN is relatively new for me so forgive me any dumb questions.
Is this applied as a powder just on the threads, or is the powder processed into some liquid to make it a lubricant, and then applied?

/edt: as per McMasterCarr’s info, I looked into Krytox XHT-BD. It seems, but again this may be me unknown with HBD, this lubricant is rated for 300-350 deg C. I assume that’s not an issue since I only require the lubricant for initial bolt-up, and not for any dynamic purpose?

Huub
- You never get what you expect, you only get what you inspect.