Interesting builds you found there, Nelson.
I agree with the comments of using a plug door to help seal. The commercial unit we have, uses that method and does not require any gasket.
Obviously I got pretty carried-away with my thread on the home-built heat box... Sorry about that... The topic is pretty fascinating all-around to me. I loved thermodynamics and took several advanced courses in it way back when. My old college won a research grant with the DoD to build (on-site) one of the most advanced wind tunnels in existence at the time. I did some work on the air dryers and it was pure thermo. Big stuff -so big, the power company could not supply enough power so several on-site multi-megawatt generators were needed. -I digress... Anyhow, when building the furnace box, I re-did all the thermo calculations just to see if I still knew how. I just finishing researching heating element wire and ordered some different wire and will "roll my own". There's a lot more there than what meets the eye...
Then, there's the whole topic of metallurgy related to heat treating. Even more fascinating stuff... It never ends.
Top end is about 2200F and that is for a few types of air-cooled tool steel; however some of the A-type steels are down in the 1800F range. More commonly, 1500 to 1650F is needed for low, medium and high carbon steels and alloys. Most of my work is done at 1550 and 1575F. BTW, these are austentizing temperatures, not melting temperatures.
In addition to a decent heat treat oven, you need either a visual spectrometer or high-end IR thermometer. For accurate/critical treating you cannot just look at the color or use a magnet to determine proper phase changes. You also need some method of oxygen deprivation. I've had good luck using a small burn-off piece along with argon gas flooding. Stainless steel foil is very expensive and error prone (not to mention, sharp as a razor and hard to handle). And of course, proper safety equipment.
Be apprised that at these temperatures, you are not playing games. The kinds of burns you get from this cause primal screams and foaming at the mouth and nostrils -long before you get the first cuss-words out of your mouth...
As far as casting (which I have no experience) I tend to think these temps are best for aluminum and other metals in the temperature range mentioned above. The ovens I'm referring to are heated with nicrome or kanthal wire. Nicrome tops out with a usable temperature of about 2000F and kanthal will go up to 2200F (usable oven temp). Beyond that, you need to get into carbon arc and there's not enough electricity in your service panel to get to high volume melting of around 2600F for steel forging.
Hello Mr Nels ,
I am relatively new to this group and machining but a friend got me started and I love trying to setup and make as many or as much of the tools and equipment that I need cause I am disable and limited income. I saw your treatment oven and would like to copy it and make my own. So would you allow me to copy the PDF file of it? I would greatly Appreciate it if you would. Or tell me what I have to do to be eligible to see it.