Forging with Venturi style burners.

[Zsartell]

I have never really had any problems forge welding in my coal forge, but I am determined for different reasons to forge weld in my newly built gas forge. I really like the idea of an even heat of a gas forge. This is something not easily obtainable in a coal forge. Also I want the ability to heat up larger billets with an even heat and be able to let it soak without having to worry about the ends getting too hot and burning off. I built a 7" x 12" round venturi gas forge with two sidearm burners just so I could forge damascus. I really didn't want to go with a blown style burner because I like the idea of not having to use electricity and it just seems safer to me. Ok, lets get to the problem. I have been unsuccessful at forge welding a 1/2" square bar to itself. I turn up the gas pressure so that flames bellow out and my flux (normal 20 mule team) indicates it's ready to weld. One thing I noticed the last time I tried is that my test piece got stuck to a scrap piece of 3/8" square that I had recently put in there to assist in propping pieces up. I had to do some twisting and banging inside the forge to get the thing to snap off my test piece. This made me sure that it was at welding heat. I took it out of the fire and gave it a few modest hits to set the weld. Then I welded it again just for kicks and when I tested it, it hadn't even come close to sticking together. Since I know it is getting hot enough, I must have a problem with scale forming inside the forge even though I have flames bellowing out. This is something my smithing friends and I have been pondering over for the past couple of months (we have been concentrating more on getting over 2400 degrees). I did notice that I actually was getting more scale buildup inside the forge at a higher pressure than with a lower pressure. What I haven't tried is using a larger mig tip to supply the same amount of gas at a lower pressure and therefore a slower speed. This slower speed should reduce the amount of air being sucked into the burner. Also I plan on placing the mig tip lower into the tube, closer to the bottom of the venturi to see if helps draw less air. At this time I am running the venturi openings wide open for testing purposes (and because I haven't made a choke for them yet) and my pressure settings are not very accurate and have had to rely more on what the forge sounds like than the pressure. Has anyone else come to this conclusion or am I making this much more difficult than I need to?

BTW: My forge is made with 2"s of Kaowool, a lining of Santinite and a lining of ITC-100. I'll post pictures later when I get a chance.

Edited May 16, 2008 by Zsartell

[keykeeper]

Maybe the flux is causing the problem, or misleading you to believe the pieces are ready to weld. Try adding some straight boric acid (roach pruf) to the mule team. I know a fellow that uses this with his propane forge, and makes some nice billets that are welded excellent.

Just my .02 worth.

[Zsartell]

I have thought about changing my flux ( and we have used a boric acid mix with my friends forge that is acting just like mine), but I have never had a problem with it when forging in my coal forge.

[Valentin]

I have heard that some people put a peace of coal in the forge to burn the exces air...The choke is simple to make...you just make a hole in the pipe weld a nut and than insert a screw in there.
BTW i was never able to forge weld in my gas forge...but i only tried a coule of times.

[Rich Hale]

Twenty mule team straight works fine in all three of my gassers. You sound like youi are on the right track with enlarging the tip size and reducing pressure. Have you pushed some water down the tip to see if it is delivering gas straight down the venturi? that can cause a poor mix if it is off. The other part That may be an issue is what was the metal you tried to weld? Mild steel is harder than most common higher carbon steels. Let me tell you what works for me. Preheat the forget and while you do that put a fair size chunk of metal in and heat it up. When the metal is a good red lay it on the anvil. A cool or cold anvil will suck the heat right out out the contact side of the metal you are trying to stick together. Oreperation is like gold grind all contacting pieces clean and shiny. Fold the piece over or tack weld one end only, wire it tight every two inches or so the rest of the length of your billet. When the billet gets a little bit of color pull it out and flux it on all sides. For very thick pieces I bring up to a red color and turn the forge off for a few minutes to let the heat soak through,,,turn forge back on and brush and flux again..let the billet get to the same color as the inside of the forge and bring it out quickly to the warm anvil and tap it a couple of times on each side, I weld about two inches at a time..cut the next wire wrap off,, brush and flux and repeat. After the whole billet is one piece you can be more aggressive with the hammer,,,,I run down the length of it a couple of times,Always at a welding heat, then I square it up hitting on the sides. Then draw and cut stack reweld etc until layer count is what you want. I work billets at welding heat and continue brushing and fluxing with every heat and for each weld I grind to clean shiny contact surfaces, This may be old stuff to you but it works for me.

[ThomasPowers]

I'd add a choke and retry.

I'd not suggest adding *coal*---big mess; but I have lined the floor of my gasser with coke before, found a big chunk near the RR track and wanted to do a heat treat with little oxidation, worked a treat for that.

Thomas

[Ken Kelley]

Here's a very simple choke for a sidearm burner. It's a piece of 1/8" aluminum plate attached with a small socket head screw and a little spring to keep it in place. Works like a champ and you can adjust the forge atmosphere as you please.

[Zsartell]

Twenty mule team straight works fine in all three of my gassers. You sound like youi are on the right track with enlarging the tip size and reducing pressure. Have you pushed some water down the tip to see if it is delivering gas straight down the venturi? that can cause a poor mix if it is off. The other part That may be an issue is what was the metal you tried to weld? Mild steel is harder than most common higher carbon steels. Let me tell you what works for me. Preheat the forget and while you do that put a fair size chunk of metal in and heat it up. When the metal is a good red lay it on the anvil. A cool or cold anvil will suck the heat right out out the contact side of the metal you are trying to stick together. Oreperation is like gold grind all contacting pieces clean and shiny. Fold the piece over or tack weld one end only, wire it tight every two inches or so the rest of the length of your billet. When the billet gets a little bit of color pull it out and flux it on all sides. For very thick pieces I bring up to a red color and turn the forge off for a few minutes to let the heat soak through,,,turn forge back on and brush and flux again..let the billet get to the same color as the inside of the forge and bring it out quickly to the warm anvil and tap it a couple of times on each side, I weld about two inches at a time..cut the next wire wrap off,, brush and flux and repeat. After the whole billet is one piece you can be more aggressive with the hammer,,,,I run down the length of it a couple of times,Always at a welding heat, then I square it up hitting on the sides. Then draw and cut stack reweld etc until layer count is what you want. I work billets at welding heat and continue brushing and fluxing with every heat and for each weld I grind to clean shiny contact surfaces, This may be old stuff to you but it works for me.

This is pretty much how I have done my billets before, except in a coal forge. I'm not sure I understand why you turn your forge off to let the heat soak in, but if it works for you that's great.

I have not bothered to put a choke on the burners because I had planned on building a heat exchanger system and adding the choke to the end of that. Since it might be a while before I build that, perhaps I'll come up with a quick and dirty alternative to test my theory.

Thanks all for the insight....

[Ken Kelley]

I was trying to upload a photo from the gallery but it didn't work. Went to advanced and loaded it from my computer.

Edited May 16, 2008 by Ken Kelley
lost my picture

[Zsartell]

I have a feeling I am making this more complicated than it needs to be. I tend to do that....

[metalmangeler]

Try just closeing down the air intake some with some duct tape (easy choke). It sounds like it should be welding.

[Rich Hale]

I shut the gas off on larger billets to let the heat sink all the way through, It it does not reach an even heat throughout you will almost always get a spot in the middle of the billet that does not weld. It is a simple precaution to avoid a problem for me. Sounds like you got a lot of things to try and work out your problems,,,,

[Ian]

Can't be 100% sure but my 2p's worth is to try to choke the burner first. I also think that having a ton of dragon's breath is no good either, seems to me thats combustion going on outside the forge thus wasting a lot of BTU's.

[Zsartell]

I had a few free minutes last night so I decided to try and cover a little less than half of each of my venturi's (with duct tape). It made absolutely no difference in how my forge sounded. I also kept the pressure down a bit and tried a faggot weld with 20 mule team and Boric acid. I got absolutely nowhere. Actually this time I believe that my temperature wat too low. I waited until the piece kinda disappeared in the lining of the forge, but it did not stick at all. I think I am going to finish my heat exchanger, put the air adjuster on that and go with bigger jets and put the jets closer to the burner tube. I built this forge mostly for forge welding billets and by golly I'm going to make it work and with the heat exchanger I'm hoping that it will be efficient as can be.

[Rich Hale]

I am not sure what you mean by a heat exchanger but there are a whole lot of basic venturi style gassers that weld just fine. Simple is sometimes the best way to go. You might even be well off to buy a premade gasser from a known maker or at least buy burners that you can use that are proven to work. Be safe..and have fun

[Zsartell]

I purchased the burners from a well known source. I did not make them myself. The heat exchanger is something that preheats the air coming into the burner. They have been proven to reduce the amount of gas needed to operate your forge. I understand that the heat exchanger has nothing to do with getting up to heat, it is just something I want to try out. I know that I am just dealing with an improper fuel to air ratio and that I need to do more tweaking. I know it will get up to welding temps easy, but there just must be too much air rushing into the chamber. I just need to "finish" my forge and get to know how it operates. One of these days I will get some pictures of it. for everyone.

[Steve Sells]

it stands to logic to get it working BEFORE you modify it with heat exchangers, turbo lifts. and transporters.

Add things later after you get the hang of welding temps. don't frustrate yourself, before you learn to have fun.

[Shane Stegmeier]

Try welding something other than AS36 hot rolled 1/2 square... A LOT of what we are getting is polluted remelt, and is Hard and sometimes impossible to weld unless your welding technic is just perfect. I had a boy who was working with me some and he could make chain link welds all day long (I think he was using cold rolled 3/8 round, but it might have be HR??), but could not get a simple faggot weld in 1/2" square. The mill scale on HR can give you problems too, ifn you don't take it off first. If you were sticking to something else in the fire, then it is more likely something wrong with you your material or how you are handling it would be my guess...

In our local group we have noticed and been talking about how hard it is to get the new remelt steel to forge weld one guy was guessing copper contamination as the culprit. Personally I have noticed that some of the AS36 seems to be hot short and will crumble because of excessive grain growth, especially on a narrow neck after you stop working that area. Modern materials have different characteristic than old wrought iron or even old steel. You need to modify your technics and your designs to avoid the weaknesses and play to the strengths of the materials you use. Good modern steel is very homogenious, and can be moved fast under the hammer. Old wrought iron isn't homgenious at all, and unless it is a Very fine grade of wrought it has a tendency to split if you push it too hard and too fast, but it forge welds beautifully, something that isn't true of mild steel;-) It is very interesting to note that some of the things from the past that we are so impressed with in our modern age were done simply to overcome the limits of the materials at hand, and to take advantage of some of the benifits of the material. Pattern welding in Europe, and Japanese laminated blades are prime examples... Of course forge welding was everywhere in the past... Sorry about the digression into a history lesson, I have been working in my head on some material for a demo at an up coming conference... ;-)