Protective Atmosphere for Furnace

[langchop]

Hi All,

I am in the throes of deciding on either buying a furnace or making one from scratch.
At the moment, making it from scratch seems to be the most cost effective and practical route to go.

Having given the design some thought, I realised there are many furnaces out there that dont cater for any protective or carbon balanced atmosphere in the furnace.

From my business dealings with many heat treaters, the carburising/ decarburising issue seems to be one of the bigger concerns in HT.

For those of you that do have simple (Andy Gascoigne type, not salt bath) furnaces where you have kitted it out for atmosphere control, I would be grateful if you could give me some hints as far as:

1. How you feed the atmosphere into the furnace
2. At what sort of rate you feed it into the furnace
3. How you prevent the 'throughfeed' excessively draining heat out of the furnace.
4. What gas is used, or what combination.
5. If a combination of gasses, how do you monitor/control the carbon concentration levels

Thanks
Lang

 

[SteelSlaver]

I have thought about trying argon in mine. Argon is inert and heavier than air. I have a stainless tube plumbed in the top of my oven and a kao wool "seal" in the door. The 3/8 stainless steel tube has a needle valve on it. My argon bottle regulator has a flow meter on it that I could set to very low flow. I would think that once the oven is flooded with argon just a little bit of flow would keep a positive pressure in the ovens small chamber and oxygen out.
Thing is I have lots of 309 stainless foil and it works well. Plus even if I keep the oven inert what happens when I remove a piece of D2 at 1850f and expose it to the atmosphere from oven to quench plates. Another thing is I often do batches of up to 5 blades at a time when doing D2. Keeps the cost down when I do the dry ice/kerosene bath. With batches every time I open the door to get a blade I would lose my inert atmosphere. Argon isn't cheap either. Just doesn't seem worth it.

You could maybe use nitrogen, which is cheaper. Mild steel wire welders use CO2, as an inert gas. (the carbon is already tied up with oxygen) some use a mix of argon and CO2. A good sized bottle, flow meter, hose and argon is going to set you back well over $200, maybe $300 to start and that would by quite a bit of foil. I already have all the pieces and I save my argon for welding aluminum.