advice on repairing cracked coal forge

[Khukuri Monster]

Today I picked up a large coal forge from a neighbor. It appears to be the first model (Cannedy-Otto) that is listed on this page: http://www.beautifuliron.com/factory.htm.

Here's a picture of the one I bought:

It came with a blower (which needs a hand crank) and this tee-shaped thing which sits beneath the firepot and catches the ash. (sorry, I'm new to this so I don't know the terminology).

Here's the problem, the cast iron forge has a crack (actually, two cracks) in it. It looks like somebody did a repair on it. Here's a picture of the crack. The other crack is similar but much, much smaller and is repaired in the same way.

I would like to know if this sort of repair will be sufficient to hold the thing together. It didn't fall apart when picking it up and transporting to my house.

I could try to braze or weld the crack. I am not sure if this would be a good idea. I'm not an experienced welder and I haven't welded cast iron before. I read a few online articles about the precautions you have to take in welding cast iron.

My neighbor told me that this forge also needs a ring which sits in the hole in the body, and the tee-shaped thing is bolted on to this ring. I was planning on making one out of 1/2" mild steel plate - would this be OK? I also need to make a grate to go over the ring, and an arm to hold the blower.

Thanks.

 

[Matt Shade]

Brazing won't do you much good, the forge probably gets hotter than the melting temp of the brazing rod. It'd probably be really hard to get the crack cleaned out well enough for the brazing rod to really flow the way its supposed to anyhow, doubt you could get a good joint.
You could probably weld it. Its not too hard to find the right kind of electrode for a stick welder (high nickel content IIRC). Don't know what it takes with a wire feed though. So welding will depend on the equipment you have. And like you I don't have any experience welding cast iron, so I can't tell you whether its overly difficult or give you any pointers.

I'd guess that as long as that patch job holds the peices together you don't have much to worry about with the cracks, other than whether or not they will spread to other places. The forge only has to be structurally strong enough to hold the coal, and whatever hunk of steel your trying to heat. Not necessarily a real heavy load.

I've never used a coal forge before so I can't give advice on finding parts or what you need

 

[FlaMtnBkr]

Well I am not what I would consider a knife maker but I am trying to get into it...but would all the trouble you put into fixing it be worth it? I know some people like the nastalgia of using old equipment like how it was originally done. But do you have a good supply of coal or real charcoal? If you are willing to build some parts to get that one running you could just make a propane forge for not too much money. I was quoted 5 bucks for a piece of 8" diameter pipe 16" long from a local steel place. Another $35 for some inswool, couple soft fire bricks, and satanite along with a few various pieces here and there and your ready. Propane is a lot easier for me to get and it will get plenty hot very quick. Just a thought. Hopefully I didnt :foot: too bad.

Ryan

 

[Khukuri Monster]

Matt, I have a stick welder. I was thinking that braze would be OK because I was told that you have to use some sort of refractory coating over the cast iron anyways. I thought the refractory might protect the braze. Although, if I'm going to bother welding it I might as well do it right and use the nickel electrodes.

Ryan, I have a couple of nice propane forges. I really like them for forging out straight blades. However, I recently tried making a sickle-like blade and had to stop halfway through, because the blade was so curved that it wouldn't fit into the tube anymore. I want to try forging a couple of khukuris and anticipate similar problems with fitting them into my propane forge.

I have a supplier of blacksmithing coal within a 30 minute drive so that's not a problem.

I guess those are the practical reasons that I want the coal forge. The other reasons are hard to explain rationally, nostalgia as you say. Thanks for the advice though.

 

[T Blade]

I’m not an expert at repair welding cast iron, though I’ve done it in the past using heli-arc welding.

Cast Iron needs to be preheated to at least 400oF, which must be maintained throughout the welding process. This is required as to prevent cracking of the weld (at toe of the weld, heat effected zone). It requires a SLOW cool down when the welding is complete.

Due to the heating/expansion and cooling/contraction cycles a forge goes through, a complete penetration weld will be needed to prevent re-cracking.


Preparation: I would first grind a bevel along the crack on one side of the piece, about half way through the thickness of the iron plus clean down to shiny metal 1” either side of the bevel to remove rust and grease, this will allow you go get a good penetration on the root pass. Preheat before striking your first arc and maintain heat throughout the job.

Bead planning: On this particular repair, I would use a back stepping technique weld both ends first (weld beads 3 to 4 inches long). You will have an un-welded area of about 8 to 12 inches. Start your next bead 3 to 4 inches from the end bead from the direction you weld in. Do this till you have completed the first pass.
Back stepping helps prevent warping and stresses from building into the work pieces by distributing the heat more evenly. Cast Iron, brittle by its nature would not react well to warping. If more weld is required to bring the surface up to flush, back step till you’ve reached at least flush with the base metal.
When side one is complete back grind the other side to clean metal, maintain preheat, and use the same weld technique to finish the job.

Cooling: Immediately after welding, reheat the work about 3” on either side of the weld evenly with a torch to approx. 500oF then wrap it with Kaowool for a slow cool down.

If you have a stick welder, go to the weld shop and get wire specialized for cast iron. If you’re using MIG, I believe you will need a wire that has high nickel content.

The few times I repaired cast iron, I used to TIG weld with 70%Ni/30%Co, wire RN80 with good results.

You will probably need to enlist help from a friend in this effort.

Good luck in your efforts to resolve this problem.

Larry T

Member of NECKA, NCCA & ABS

 

[Jon Christensen]

Stick with a Ni rod. I'm not sure exactly what brazing rod is made of but it looks like it should have some copper or brass in it (bad news if you want to weld with it).
Jon