Building vaccum heat treat oven

vilts

vilts

Joined
Mar 23, 2007
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This is probably crazy idea, because I don't know enough about what could happen and what are the problems, but that is exactly the reason I ask here.

Soon I'll get vacuum pump with rating of 0.1 mbar, which should be 29.92 inches Hg, 3 CFM. Probably pretty good.

Now, can I use this pump to build a small vacuum oven for heat treating? Probably the oven itself is not such a problem, but how do I solve the cooling?

Can I just fill the oven with some gas, like nitrogen, argon or CO2 to cool the blades and avoid the oxidizing (that's the whole point of it)? I'll be using air-hardening steel, of course.
 
Pulling a vacume at 1500+ will be interesting to say the least. I am pretty sure your pump is not up to that task.

Maybe others could discuss how in a electric kiln you can get much oxidizing when the amount of oxygen in the chamber is so low. You could get rid of all the oxygen by placing a match stick in the oven and let it burn out the oxygen.
 
I worked on some home made vacuum ovens in school. It's pretty straight forward. You need to drill a hole in a oven and have a metal tube going in and leading to a metal box inside the furnace that is kept under vacuum with the pump a few feet from the actual furnace. The pump is far enough away from the heat that it will stay cool if the chamber is evacuated of air, since then the only way heat can travel is along the surface of the pipe.

The hardest part is opening and closing the box, because you'll need all metal fittings if the thing gets up to 1500+ or 1700+ for A2 steel.

If you want to go electric think about making a tube furnace using an alumina tube. This will make things easier when making the vacuum connections, since you will be able to use a long alumina tube and then use viton vacuum fittings at the ende. viton is good to about 200C.

greg
 
As Greg mentioned, hardening temps are going to be real high...
Then you have to figure out how to cool evenly and fast enough to quench properly.
If you're thinking of plate quenching, which has been recommended a lot here for air hardening steels, foil wrapping is the way to go.
This will eliminate the need for a vacuum or non-oxidizing atmospheres.

Vaccum... think stabilizing...
I've got a Napco vacuum oven, but it will just go to 200°C. Good enough for drying woods, and removing air from laminates.
 
Thanks for your answers! Actually my initial thought was to suck out the air from the oven before I even start the heating process. That way I won't have to deal with high temp air in vacuum pump. I don't know if and how that would work.

Actually I bought the pump for stabilizing, but the idea processed and thought why not use it for heat treating as well.

But probably plate quenching foil wrapped blades is the way to go at first. Just got the foil too.
 
If you're worried about the heat, make a heat sink in your vacuum line. Easiest would be a coil of copper in a bucket of cold water. You could get as creative as time and $$$ allow.

Airtight oven would be your primary challenge, I would think if you're hoping to hold the vacuum during the whole heat treat.

J-
 
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