Use of argon in heat treating oven + going from 120V to 240

Folx,
I've been using home made kiln (omega PID + SSR + nichrome wire + some refractory bricks) to heat treat A2 and similar for some time
now and it all works great.
I am thinking about moving up - expanding the internal volume somewhat and that will require going 240V (I want to be able to reach reqd temps in minutes and with my 9x4x4 cavity 110V @ 15A barely makes it).
I will keep most of electronics - only replace the spiral to longer one. About wiring - do I get it hooked up between 2 hot legs of 240 ( in series with SSR of course) ? I will use the ground to ground the oven . Otherwise I'd need to use 2 spirals in parallel (hots to neutral) and doing that will require 2 SSRs (what pros/cons of these 2 methods ?). Was thinking about getting an electrician to give me a dedicated 240V in garage, with 20A breaker .
And about argon: for now I use tool wrap steel and it works OK, but I do get some scaling and softer decarb in the outer layer - which I grind off. Even using the paper-in-the-foil-bag trick. Assuming I have a top-load oven and it's rather air tight below the lid, can I simply flood the interior with 2-3 CF of argon before starting the heat treat cycle ? Being heavier than air , will it stay "put" inside of the oven - even when heated up to 1800F-2000F ?
I know some people keep moving inert gas through the oven throughout the cycle (at slower rate), might need to do the same. Drill a smallish hole through firebrick, stick some time of copper tubing with connector to attach the argon hose to - am I correct in my thinking ?
What are typical prices for smaller argon bottles (need pure argon I reckon, not the CO2 or Oxy mixes) ? Will also need a flow meter . Also am I correct in assuming that argon is 100% to use ?
Any advice's most appreciated :)
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You would hook the heating element between the two hot legs to get 240 volts. You could get another element exactly the same as your existing one and hook the new element in series with the old element. Or get a new 240 volt element. I have not used argon for an inert atmosphere, but I don't think you can put some in and have it stay put. Since it will be hot, it will expand and probably become lighter than air. I think you will have to keep putting in some gas to keep any oxygen out. I expect you could use CO2 just as effectively. I don't know if CO2 breaks down at 1800 to 2000 F but if it does part of it is C. So might work anyway.
If you have a place that is really fireproof, like outside in a car port, you could use natural gas or propane. You would need to supply the gas and drive out all the air before getting the temperature going. You probably ought to light the gas as it escapes from the kiln too.
I have seen commercial melting of alloys ( not steel ) at Westco where they used natural gas for the heat and to have an inert ( well non-oxygen anyway ) atmosphere. The gas burned supplied to the inside of the ovens burned as it escaped.
Dan
rashid111 wrote:

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effectively. I don't know if CO2 breaks down at 1800 to 2000 F but if it does part of it is C.(clip) ^^^^^^^^^^^^^^^^^ CO2 is used in shielded arc wire-feed welding, so it ought to work in your kiln. (And its cheap.)
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You and I have about the same setup. I tried using argon from my welding setup in my furnace I set the argon to 5 cubic feet per min the oven had a few cracks in it so I set the flow high just to see if it would work.Well it did'nt work and it used alot of argon expensive .
I had a freind he was a dentist he had an oven about the size of yours it was in a steel box and had about a 2 inch air space between the oven and the box.
He used a compressor from a refrigerator to create a vacum .He would heat the oven up to about 2000 deg. and but some kind of dental work in it close the doors and turn on the vacum pump. I noticed the tempature would drop a few hundred deg. when he turned the pump on but it would quickly go back up.
I was wanting to try the same thing but never got around to it. Another thing i was woundering about is when the part comes out of the atmosfere controled furnace would it get the scale on it cooling down? And how high of a vacum does it take? TIM
http://metalworking.com/dropbox/_2001_retired_files/furnace.jpg
http://metalworking.com/dropbox/_2001_retired_files/furnace-control.jpg
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But you also know, what really is happening with the CO2? At welding temperatures: If you have, say, SS, it will absorb C (CO2 <-> CO + O AND CO <-> C + O). On the other hand, if you have a high carbon steel, it will loose it's C! There is a balance between the C-content of the gas, the C-content of the wire and the C-content of the material. If you add C through the wire, it has to be removed by the gas. And vice-versa. You can observe this happening with Ar+18%CO2. And it surely will happen with 100% CO2. You will add C to the steel (at 2000°C). Also the O will catch some of the Cr (+Nb), if there is any in the steel.
**But** I don't have the temperatures at hand, when CO2 dissoziates.
Nick
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I think you need to make a retort. This is a container that is sealed shut except for your gas input and output. This might be more complex than a home shop justifies.
A friend of mine worked at a place that used hydrogen as their gas, and they burned off the exhaust. They did mostly furnace brazing there. They had two types of retorts. one was a metal can about the size of a common trash can. It had a flange formed on one end and the other end had a pipe flange welded on. A flat lid with another pipe flange was then welded to the flange to seal the retort and then an electric furnace was lowered on the base.
These had to be ground open after each heat and were tossed after about 10 heats.
The other style had the can inverted and was sealed against a water cooled gasket.
I don't think hydrogen would be good for all material as in some cases it may cause imbrittlement.
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I don't think that you want H in an environment where steel is heat treated of hours. Hydrogen will diffuse into the steel and will make it brittle.
Nick
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wrote:

Isn't that what I said?

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Roger Shoaf

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Herr Mόller,
I accept your Ooops.
It is nice to know I am not the only one that does these kind of things.
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Roger Shoaf

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In doing argon replacement of the atmosphere in the furnace, the lower the flow rate, the better off you will be. The problem here is that you have to heat the gas to the temp of the oven in order to allow the gas into the chamber. Failure to do so makes the surfaces you are heating cool. Note that the sealing doesn't need to be inside the furnace but can also be outside the furnace. Extra insulation followed by even just a styrofoam sealing/insulation layer can help things immensely. Excellent would be a nice sealing door for the furnace with a pressure limiter so the oven doesn't blow out and you loosen a valve during purge and then shut it and keep the pressure to some value after that.
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