Building a stainless forge

[Kevin Powers]

Forge size: 10"x 18"
Chamber size: 6"x18"
Burner type: propane ribbon
After spending a ton of time researching, designing, and getting input from friends, I decided to build my first forge. I still need to make some minor changes but I got the body built, lined, and the first coat of satanite on. The body is 16 ga 304SS that I rolled into 10" diameter. The feet are 10ga 304 plates, and 1x1x18" 304 angle. Everything was tig welded. I haven't finalized what I'm going to do for doors yet. I did 2-1" layers of kaowool. I didn't have enough time to finish my burner. I am hoping I can cast it tomorrow. I'll update with progress.
Rendered my parts in solidworks, then cut them out on the waterjet. The Q looking piece is a choke plate.

Starting to roll the body. This took a while as the roller is rated for 16ga steel, not 16ga stainless.

Body all welded up and my "too small"burner plenum. I had hoped to build everything completely out of stainless but couldn't source a tapered tee fitting in stainless so I ordered a ward tee.

Base all fit and tacked.

First lining.

 

[Lieblad]

Nice, That should last longer than you will !

As far as doors, We build without doors. Just stack firebrick to close off or accommodate opening to fit whatever the workpiece consists of. (we make more than just knives)
Both ends are open to fit long pieces thru, or two Smiths, one working small stuff at each end.
Also durability, we make solid floor.

 

[kuraki]

I thought about doing this since I'm swimming in stainless but I was worried about hexavalent chromium. Maybe that's not a concern?

 

[Josh Rider]

Man, you don't play around! The forge looks great.
I like the opening on the side. Especially if you had an odd shaped piece like a tomahawk or something like that.

 

[kuraki]

I think that's where he intends to put the burner plenum.

 

[Kustom Kutz]

Wow I hate you!

Seriously it looks amazing good job! I have been researching forges and I am about to build mine when I am off this next rotation from work.

 

[Stacy E. Apelt - Bladesmith]

I thought about doing this since I'm swimming in stainless but I was worried about hexavalent chromium. Maybe that's not a concern?

I think with good planning on ventilation and fumes evacuation, this isn't a problem unless you do it daily for years.

 

[kuraki]

I think with good planning on ventilation and fumes evacuation, this isn't a problem unless you do it daily for years.

You're probably correct. Especially since the wall temperatures never really get to the point they need to be. The doors/end covers would be about the only real concern.

I built a sheet metal wood stove for a wall tent and thought about doing stainless and didn't because of it, but that's a different story with no insulation, and like you said, probably still a non-issue for a few days every few years.

 

[Stacy E. Apelt - Bladesmith]

I thought you were talking about the welding of the forge shell in concern with hexavalent chromium. If you are talking about operation of the forge, or a wood stove, then I would say it is no concern at all. The temperatures needed to convert the chromium to hexavalent state ( most likely chromium tri-oxide) is far higher than either will operate at. Hexavalent chromium is mostly a concern with drinking water contamination from chemical compounds in wood treatment, anti-corrosive paints, and other applied chemicals getting into either the air of the ground water.

For it to be an issue in a forge of stove, it would require the trivalent chromium ( Cr3+) to be heated to the melting point and then it converts to hexavalent (Cr6+). This happens at or above 2500F. Even upon this melting, most will convert back upon cooling, and the retained hexavalent chromium would be bonded in the steel, thus making it not an exposure issue.
A blown forge can reach the 2500F inside the chamber with some serious gas and air blown in, but the metal shell will never approach half that. The internal temperature of a high temperature wood stove burning a really hot type of wood will likely never reach even 2000F. The outside will stay below 1000F in most cases. Wood starts to burns at around 500F and the gasses created burn at 1100F. The heat from the burning gasses gets to about 1400-1500 usually as the max internal chamber temperature.

 

[Kevin Powers]

Nice, That should last longer than you will !

As far as doors, We build without doors. Just stack firebrick to close off or accommodate opening to fit whatever the workpiece consists of. (we make more than just knives)
Both ends are open to fit long pieces thru, or two Smiths, one working small stuff at each end.
Also durability, we make solid floor.

I may do this on the front. The back will more or less be sealed off with a pass through.

 

[Kevin Powers]

I thought about doing this since I'm swimming in stainless but I was worried about hexavalent chromium. Maybe that's not a concern?

if I get the forge body hot enough to convert to hex chrome, I'll be running away from the forge and calling the fire department haha.

Man, you don't play around! The forge looks great.
I like the opening on the side. Especially if you had an odd shaped piece like a tomahawk or something like that.

I think that's where he intends to put the burner plenum.

Thanks Josh, and yes that is where the ribbon burner will enter the forge. I'll see if I can get some progress done today and it will make more sense.

Wow I hate you!

Seriously it looks amazing good job! I have been researching forges and I am about to build mine when I am off this next rotation from work.

I have been researching forges for over a year and a half. It took me this long to decide on what I wanted to do with it.

 

[timgunn1962]

I'm not sure why it would be, but I'm not a chemist.

I have made a few stainless steel forges using scrap tubing.

It is obviously prettier and less rust-prone than most alternative candidates for forge shells, if you have the ability and equipment to use it.

In my case, the available alternative is usually a compressor receiver: painted mild steel.

I do not have a "special" design that relies on the material used being stainless steel, so it is only subject to the same temperatures, etc, as the painted steel. Under the circumstances, it seems unlikely to present any great health hazard, as it only forms a stable Oxide layer. I understand the Chromium Oxide in the stable Oxide layer is Cr2O3: Trivalent Chromium Oxide.

When used for a burner "flare" or flame retention cup, the temperatures involved are high enough to cause stainless steel to form scale, which usually spalls off on cooling. I have not researched the hazards associated with this scale to any degree, but understand it also to be primarily Cr2O3: Trivalent Chromium Oxide. Trivalent Chromium is not usually considered hazardous and is in fact required, albeit in tiny amounts, by the human body.

I've no intention of reacting the scale with anything likely to Oxidize Trivalent Chromium to Hexavalent Chromium and it does not seem to be something that is likely to happen naturally in an environment I am likely to encounter. I tend to view it as being of no great concern. I certainly feel more concerned by the fumes from the hot paint when I use a compressor receiver.

If you have better information which shows that Hexavalent Chromium exposure is a Hazard in this application, please post a link.

 

[Kevin Powers]

I went in to work this morning and redesigned my burner. I really love solidworks, it makes it so easy to get stuff planned out and right.

All the pieces of the burner cut out.

Some bending on the finger break.

Everything all tacked together. Got my crayons and .308 shells so hopefully I can get the castable refractory. Poured today. Then bu the time it's cured I should be receiving my ward tee.

 

[Kevin Powers]

Mocked up on the forge body.

Got the .308 casings and crayons in place. I painted some wax on the shells and crayons to help release when the kastolite sets up.

 

[Kevin Powers]

I just got done pulling the shell casings. I locked onto them with vice grips and gave them a twist back and forth with downward pressure. They all popped out easy. Now I need to get the crayons out and I tried melting them with my map torch... what a mess. So I just put the burner assembly into the heat treat oven upside down over a disposable baking tin. I'll let this bake for a while and see what progress I make.

 

[Kevin Powers]

Test fitting the burner into its spot in the forge. Had to move a little satanite out of the way and also do a little finish sanding on the castable.

 

[Kevin Powers]

My tee finally arrived. Did some work on the burner before I go out and get some final items to finish up this build.
My stainless supply company only had sch 40 1/8" nipples so I cut an end off of it and tapped it with a 5/16-24. The mig tips that I use are Bernard ceterfire tips. They're non-threaded from the factory and are thicker than normal mig tips. It got threaded with 5/16-24 as well. I then cleaned up the choke face on the T. Drilled and tapped the choke with a 2-56 and used one of the stainless screws from my folder hardware. I like the tab I put on my choke plate.

 

[Kevin Powers]

Got the burner all plumbed up. Using an LP regulator for welding/cutting. Acetylene hose, check valve and flash arrest or. Using a needle valve off an oxy/acetylene Y. The advantage of this valve is that it has right hand thread on one side, left hand on the other. Makes for an easy transition from hoses to pipe fittings.
Venturi ribbon burner first fire video
https://youtu.be/TmbnVvm3gXg

 

[mete]

Nice project ! The only question would be possible problems with thermal expansion as it's different from carbon steel.

 

[Kevin Powers]

Nice project ! The only question would be possible problems with thermal expansion as it's different from carbon steel.

Stainless has about 3x the rate of thermal expansion as carbon steel. I'm not worried about it at all. I just had the forge glowing orange on about 5 psi and didn't notice any issues at all.