View Full Version : heat treat environment

12-16-2003, 09:55 PM
It seems that every time I torch something to silver solder it, I think of making an oven to heat the piece(s)in. Most of what I do will fit in a 6x6x6 cube, so I'm toying with the idea of rigging an electric heating coil within a suitably sized firebrick lined steel box. My question has to do with the atmosphere within the box- can I exclude oxygen by valving in CO2, and what would the result be? Would a different gas be better? I have a tank of CO2, I don't have, or have other use for, other gasses. (except helium, on birthdays). My thought was to have a slow continuous introduction of the gas to help purge other outgassing products, which would vent through the inevitable leaks in the box. A window would be nice, some clear tungsten, perhaps?

12-16-2003, 10:05 PM
CO2 should work OK although it is an oxidising gas. It is a good heat conductor so that should actually help. For a window use a sheet of mica.

BTW, what clear tungsten?

[This message has been edited by Evan (edited 12-16-2003).]

12-16-2003, 10:46 PM
I read a book on nitriding using a nitrogen atmosphere,K&T used it to make thier gears and several of the larger shops around use it.

I have been wanting to experiment for awhile now but haven't had the time.

For heat treating a small Duncan ceramic kiln will work,others here can tell you how to build a control for the temperature.Also Linsay has a book by Gingery on a small electric furnace that can be adapted for treating.

12-17-2003, 01:46 AM
Clear tungten is just something on my wish list. Like clear aluminum, which is something that does exist, so I have read. Mica is the answer for the window, that I didn't think of.
The idea of using the gas was mainly to prevent oxidation, so-- having thought about it more, maybe the tig or mig gasses would be better. Argon? I need to check out the books. Thanks.

12-17-2003, 01:54 AM
Argon is normally used as it is enert. Nitrogen can affect the hardening process and should not be used. There is no such thing as clear aluminum or tungsten (at least in the real world - science fiction, yes).

Small electric ovens used for jewellery work (Newell computer controlled) are commonly used as they can also be set for a tempering cycle immediately after air hardening. (A-2 steel, etc.)

12-17-2003, 02:11 AM
I stand corrected, it's not aluminum that can be clear, it's alumina, aluminum oxide, which is clear, or nearly so. Yeah, only on 'Trek' was the aluminum clear, a tank to transport whales, something like that.

12-17-2003, 02:32 AM
Tin oxide is totally clear and does conduct electricity well, unlike most oxides.

However, There is one very common "alloy" that is extremely transparent. Anyone know what it is?

12-17-2003, 03:04 AM
Succinonitrile(SCN) acetone?

12-17-2003, 04:06 AM
Lead glass. Amazing to think that a transparent material may contain up to 35 percent lead (70 percent lead oxide) and be totally transparent.

Forrest Addy
12-17-2003, 05:39 AM
It's helpful to place a charcoal briquette or two in a small furnace to make a reducing atmosphere. This will stop scaling but not some discoloration.

Btight anneals and non-discoloring heat processes are wrought in fully controlled atmosphere furnaces usually containing a sealed muffle an intert gas with an optional small non-flammible percentage of hydrogen.

12-18-2003, 06:05 AM
Tin Oxide is a white powder. I haved used it when faceting gemstones and has the consistancy of flour. Titanium Oxide is also white.


Aluminum Oxide used as a chemical barrier on carbide inserts can be clear but is normally black. The clear form is known as Sapphire. It prevents leaching (chemical erosion) of alloys from the insert to the swarf under the high temperatures and pressure of machining. It is also used as a binding agent for some coatings such as TiCN as it bonds more readily to the Aluminum Oxide than the Carbide itself.

12-18-2003, 01:28 PM

Most substances that look white in powder form are clear. Think of sugar, salt, and numerous other crystalline materials. Funny thing about that, my daughter observed that fact and commented on it to me when she was about 2 years old.