Forge welding

R

Rob Greene

Joined
Jan 4, 2019
Messages
11
Ok why can I bend a piece of rebar back on itself and weld it but can't forge weld a multi layer billet of bandsaw blades together lol. Different alloys of metal I am guessing? I am learning it only takes one thing to make it not work but I have done 4 pieces of rebar and welded each one and 3 billets and couldn't get any of those to weld. Kept thinking I needed a longer soak and would end up with a big ball of metal lol. I'm burning a lot of coal trying to figure it out and unfortunately have no one around me to learn from. Thanks
 
Hey Rob, where are your at? I thought I was in the middle of nowhere out here in w. Tx but there’s a guy an hour down the road that has helped me out a bunch! Fill out your profile, and who knows there may be a forge welding expert right down the road from you too!
 
Band saw blades most times are a high nickel content and nickel steels don't like to weld to each other. It can be done, but it's not as easy as mild to mild, or simple high carbon to high carbon. You need a good flux and or have the metal clean and in close contact and some way of keeping any oxygen from getting to it, such as a sealed can or arc welded edges. Also sounds like you might be over heating, easiest way for me to forge weld high carbon steels is in the gas forge, partially from not worrying about overheating and also because it's easy to see what's going on, with coal I have to be a lot more careful to not overheat or burn the steel. With mild steel and wrought iron it's easier for me to forge weld with coal because of the harsher heat.

Also, what kind of coal are you using? For good forge welds I prefer either charcoal or soft, bituminous coal. I do use a good bit of anthracite for general forge work, and have managed to weld mild steel with it, but it's not good for high carbon steels or forge welding.
 
Thanks will for the reply. I use anthracite rice coal and it does well it seems but I'm no expert. I cleaned the blades with a buffing will and used acetone on them and then squeezed them together in a vice and welded them together but still no luck. I figured it was because of the nickel content
 
How is your coal tending? I use bigger coal (half inch chunks?) because that's what I have. My method for welding damascus in a coal forge is:

- Grind the surfaces clean, stack, weld (just enough to keep the stack together and put on rebar for a handle, don't close off the gaps). I usually sprinkle some borax between the layers during stacking, just a bit.
- Start the forge, build a good mound and apply a constant low flow of air. Continuously push coal in from the side for coking (burning off all the bituminous crap), creating a steady influx of cokes. Wait until you're running a nice clean fire (I always watch for transparent blue flames).
- Stick the billet into the middle of the mound (Make sure the stack is covered with cokes to contain the heat) with the laminations running vertically. In my experience this gives more uniform heating of the inner layers because the heat coming from the bottom supposedly doesn't have to jump the gaps between the layers that have higher thermal resistance. Maybe this is nonsense, but it's the way I learned and it works for me. The middle of the mound is the most neutral location oxygen-wise, minimizing the amount of oxide buildup.
- At a dull red heat, pull out the stack (close the gap in the mound) and apply Borax to the edges. It doesn't have to drenched in Borax. Put it back the same way and cover with cokes.
- Ramp up the heat, periodically peeking through the coal (you can poke the occasional peeking hole and close it back up) to judge the temperature of the billet. When it gets to yellow start watching the flames. When you hit welding temps (with high carbon steel) you'll see an occasional spark floating up through the flames. When you get to that point, pull out the billet, put it on the anvil and gently but firmly tap it with a hammer (I use a either a 1.5 or a 2.5 pound ball peen with a slight crown on the flat side, don't use the ball end). I always go along the center from handle to end (squeezing out the borax along with the oxides and contaminants) and then around the perimeter. You can massage the billet a bit with the hammer, but in principle your welds should now all be set.

Again, there are other ways to do it, but this works for me. Never used a vice for setting welds.
 
Rody, that is a very good write up and it makes a LOTS of sense. While I've never used a coal forge (well, since childhood anyway) your method sure makes sense. Thanks for sharing.
 
Thank you Rody for taking the time to share that info. I couldn't have explained my process any better. I do it exactly how you explained. I noticed last night while I'm messing around. I'm waiting for this white heat color and I think that's why I was burning things up. In my building under my lighting it's not a white looking color at welding heat because of my lighting I think and I learned a trick from an old timer last night that is spot on. Take a coat hanger and flatten the end of it. As you're coming up to welding heat stick the coat hanger through the coal and touch the steel. If it's ready to weld the hanger will stick to it. Works perfect! You were asking how the coal is tending and it seems to do pretty good. I'm sure it's not lasting as long as the bigger chunks would. I didn't want the rice coal but it's easy to get here and cheap. I have to run constant air on it to keep it going but I guess that's a drawback with anthracite so I hear.
 
1DCB4C0F-189B-45D9-94B8-C191921448F1.jpeg Here’s a pic of a wrap&weld hawk head inside a bee hive coal fire near welding temp. You can see your work pieces clearly
 
No Kentucky I haven't but I do like how you can see what's going on. I think that is my main problem. I just made me some charcoal and I'm getting ready to play with that after alabama clemson game lol. Do you leave the top open like that? Seems you would lose a lot of heat like that.
 
It’s actually the front that’s open.. it ends up being an open chamber with the shell being cooked down coal. You wet it as it burns to form the hard crusty shell
 
Ohhh ok makes sense. I'm assuming I probably can't do that with rice anthracite and surely can't do it with charcoal. I'm getting ready to go out now and try it lol. Thanks for your help!
 
What Kentucky is describing only really works with bituminous coal, to the best of my rather limited knowledge, you can't do that with anthracite coal as it doesn't coke and won't wet clump like soft/bituminous coal will. Anthracite is also a lot dirtier than than bituminous coal. Fortunately it works OK for ironwork, and is easy to get. Bituminous is about a 1 1/2 hour drive for me, only worth while if I'm getting a half ton or more. I haven't tried the rice size coal, but use a good bit of the "nut" sized anthracite and that seems to work well. My understanding is the "rice" size really isn't that good for smithing, but sizes may vary from location to location.

For forge welding damascus, I really can't recommend a gas forge enough. That said, it's possible, just not easy in anthracite coal.
 
Yeah I tried it Will and it doesn't wet and clump lol. I did manage to get my billet to weld all but a half inch hairline. I also tried the charcoal tonight and didn't like it at all. The heat was good but went through a small feed sack full of charcoal in about an hour lol. I'll stick to starting my coal with that. What I buy here at tractor supply is called rice coal but is about the size of pea gravel. I'm starting to think I made my fire pot way too big. It is 12" long by 7" wide by 4 1/2" deep and when I get it going good the whole fire pot full of coal is orange hot. I don't think I need that much coal but not sure. If I knew how to post pictures I would lol.
 
That sounds too big. Of course, I don't know the size of your billet. My fire pot is (guessing) 7*7" and about 2" deep. The coal mound typically reaches 2-3" above ground level. I have an "extender" for larger pieces, which is basically 4 pieces of 2" angle iron, welded into a square with the corners pointing up.

Sometimes I wet the sides of the mound (blocking the air flow) to focus the air to the center. Don't know if that works for anthracite. I also continuously break up the clumps, kind of an ongoing process. By the time the fire runs on clean cokes there isn't that much clumping, but still.

BTW white is waaaay too hot, regardless of the lighting situation. High carbon steel welds at much lower temps than mild. And by coal tending I was actually referring to your fire tending skills ;-). For me, properly maintaining the fire is key to good, reproducible results. When I watch FiF I cringe at seeing contestants trying to take a heat in a yellow flame, smoking, clumpy spread open fire...
 
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Hey Rody! I'm green at the whole process lol but this is how I tend my fire and I may totally be wrong. I start with lump charcoal and put a little coal on and let it heat up really good then continue that until I'm probably 5" above top of the fire pot. I then turn air on high and let that get really hot and then stick my billet level with the table into the mound of coal and then I keep pulling my green coal on top to hold in heat. There is no to very little coking because of it being anthracite I presume. Thank you guys so much for your help.
 
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