1200 Celsius press

[skeezybum]

Hello,

 

I am looking for material to make a screw type press, or maybe a wedge press. This has to fit inside of a 1200 Celsius oven for 12 hours. I'm pressing a carbon based material to cure it. The press atmosphere will be in a vacuum with an inert atmosphere (argon).

 

Thanks,

[CaptainPanic]

I think graphite or some ceramics. Both are far from ideal for equipment with moving parts, like a press.

 

To be honest, I would recommend any workaround solution you can come up with.

 

Make sure that the parts which are at the highest temperature don't need to move much (for example, they only press against each other), while the actual pistons or whatever causes the movement is far outside the hot area.

 

Disclaimer: I'm not an expert regarding process equipment at these temperatures.

[swansont]

What's the oven made of? It can apparently stand 1200 ºC.

[John Cuthber]

Not a trivial task, I think silica, sapphire and tungsten and maybe molybdenum would be OK (The metals might need carbide facings to prevent reaction with the sample) , but that sort of thing isn't a trivial engineering task.

Platinum is probably OK too, as long as you keep it away from the carbon.

On the whole, I don't think you are going to get a solution from a web page like this unless you are lucky and some passing expert in the field helps you out.

[Enthalpy]

What kind of pressure? "Pressing a carbon material" sounds like sintering, and then it looks bad!

 

For sure, all iron, nickel and cobalt-based superalloys are impossible.

 

Among alloys, you might look at molybdenum, niobium, tantalum, and if needed tungsten. You have to check in detail what alloy fits what temperature and stress for how long ("creep"). One company in Austria delivers Mo alloys, of which one alloy might fit 1200°C at limited stress. I have no opinion about reactions with your carbon-based material; the use is difficult enough that you have to split the design constraints and rely on a coating for that. Also beware many refractory alloys gall.

 

http://www.plansee.com/ I hope they still exist

 

Ceramic looks better but they're generally brittle. Alumina, zirconia are candidates; some must be stabilized (with yttria for instance) to withstand thermal cycles.

Edited October 26, 2012 by Enthalpy

[Enthalpy]

Plansee's web site doesn't respond, I hope the company is alive and well. Anyway, I had downloaded the doc for my needs. I wouldn't like to upload it here because it's several MB each, but:

 

- Among their Mo alloys, TZM is meant against creeping. At +1100°C the tensile creep resistance is 350 to 400MPa. At 1450°C it's 35MPa for 1% in 100h, 17MPa for 1% in 1000h (and the MLR alloy is better than TZM at 1450°C below 24MPa).

 

- Plansee gives no creep data for Nb nor Ta alloys. Ta's tensile strength is around 120MPa @1200°C, Nb is worse, and creep stress is always much lower.

 

- Plansee gives no creep data for W alloys. Yield and ultimate strength is around 200MPa @1200°C for sheet, rather 280MPa for rods.

 

As it looks, only Mo alloys were developed for serious structural uses.

 

Nasa's technical note TN D-3222 (Web) tells creep behaviour of Nb and Ta, where the alloy T-222 outperforms all others. At 1204°C (2200F) and 55MPa (8000psi) it creeps very little, like 0.5% after 8000h. That's not a different world from TZM.

 

======================

 

You get ceramic properties there

http://www.ceramics....ry/advmatdb.htm

 

They give a tensile strength, which could be as well a creep strength for ceramics.

Alumina (which one?) 140MPa @1200°C, sintered SiC (good in reducing atmosphere) 250MPa @1200°C.

My other docs tell a "maximum operation temperature" (at zero stress?) here in reducing atmosphere:

From Ceramtec: Al₂O₃ 1000 to 1500°C depending on the mixture and processing, ZrO₂ less, SiC 1350 to 1800°C.

From CTTC: ZrO₂/Y₂O₃ 1500°C, Al₂O₃ 1700°C, MgO 2200°C (must be structurally weak), SiC 1500°C in air

http://www.goodfellow.com/ gives still other data. I didn't check Matweb, often a good info source.

 

Pretty much inconsistent, as expected from ceramic, so you'd have to check with individual suppliers. SiC is promising.

Ceramic may well be cheaper and more common than molybdenum alloys, and SiC react less with carbonated compounds.

My doc is in varied exotic languages, so you'd better search the Web.

[Enthalpy]

TiB₂ is a strong candidate as well. From Nist: 1800MPa compressive strength @RT, creep data begins with 5*10^-12/s @1500°C and flexural 100MPa, or 0.1% in 6 years.