Forge from an air tank

[Ted Ewert]

I decided that this forge is a bit too long, so I decided to trim it by about 4". I figured all I would have to do is to cut the outer cylinder, the burn chamber, and then reassemble it.

I was taking it apart this morning and got an unpleasant surprise when the inner casting fell apart

I'm not exactly sure what caused this to happen, since it was pretty solid when I installed it. I may not have cured it properly, or it may have had internal stresses that caused it to fracture when high heat was applied. Had I just left it in there I doubt it would have been a problem since it was securely held in place by the insulation.

Anyway, looks like I'll have to pour a new one. I don't think crazy glue will quite make it here. I noticed that one site was offering some stainless steel "needles" as reinforcement for high temp castables

I may order some of these to use in the next casting.

[Ted Ewert]

I finally got the forge cut down and modified more to my liking. I recast the inner tube in a shorter version and made a few other changes.

 

Here is the rear of the forge:

The center 2" hole is the exhaust port. I want most, if not all, of the exhaust to exit the rear of the forge. I also added a cutout for longer stock and filled it with wool until I need it.

The idea is to keep the forge as much of an enclosed oven as possible. I can completely close up the front and still provide enough room for the hot gasses to exit and not build up much pressure.

I made a little cutout in these doors so stock can fit through. I'm going to build new doors with a sliding slot for wider material. My anvil is right in front of these doors so keeping the heat down is a priority. 

Here's a look with the gas on. I built up the side wall below the burner to protect it from the return flame.

The inside length is now 11" instead of the former 17". This version should be quite a bit more efficient.

 

Ted

[Ted Ewert]

One thing I didn't understand when it was suggested here at IFI that a rotational gas flow was optimal, is that it works for you in more ways than one. The most important is that it keeps the hot gasses in the forge longer, which significantly increases your heat and efficiency. The normal forge with a burner pointing straight at the floor sprays the hot gasses right out the open end as soon as it is deflected off the floor, wasting heat. It also heats a lot of your work which is close to the opening.

A rotational flow travels past your door, not straight at it. I can stick a piece of work into the forge and the only part which gets color is the part sticking past the door. You can heat only as much of your work as you need to, which is nice for a number of reasons. 

Even though I mentioned it, the amount of heat you can generate in the forge is remarkable. Even at minimal settings my forge remains at a bright yellow heat. Reheating a piece rarely takes over 30 seconds. If it's thinner I just hold it past the door with the tongs for 10 or 15 seconds and it's good to go.

Anyone who is thinking about building a forge should consider this type of design. It's a little more difficult to build, but well worth it.

[Ted Ewert]

I further shortened the inner chamber of this forge to 7" long. I'm only using 7 out of the original 13 holes in the ribbon burner. Smaller is better!

The cave down at the bottom is a nice place to put something like a leaf when you just want to heat up the stem for further refinement. Whatever is in there gets no color, and no extra scale. I'm trying to get this to be as much like a coal forge as I can as far as being more capable of heating select parts of the work. I can already heat as much of the end as I need to, but the middle has been a little more of a challenge. 

I also poured the first of two new barn doors.

The square thing on top is a handle (I'm tired of getting burned), which is tied into the door with some baling wire connecting it together . The notch is for material to stick through while the doors are shut.

I'm starting to reinforce all the cast pieces I make with steel, especially new parts added onto cured material. Kast O'Lite will not stick to the cured material, so a mechanical bond of some sort has to hold it in place. I used two 1/4-20 threaded rods to hold the new addition within the chamber in place. 

I haven't had any cracking problems since doing this, so I don't think the steel expansion within the material is an issue. I also don't use any thick steel: lots of thin stuff is better.