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Forge welding, how to see when it's ready?


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I tried to forge weld a ring last night but it failed. It didn't need to be welded though to work and I don't have flux, it was a spur of the moment thing. But it prompted some questions.

I noticed the thing I had most difficulty with is telling when it's ready, I use coke and a side blast jabod, it gets up to welding heat as I've done that by mistake before. The way I understand fire management and smithing with coke is to mound the coke over the piece being heated. I shove the piece in from the side trying ot keep it level with the "floor" of the forge and use the coal rake to mound it up even more. With the ring I had to use the rake to break up the mound though and then put it in the center while rebuilding the mound over it.

Anyway the result is that I have a very hard time seeing the object in the fire and it's almost impossible to look for that transition when the surface starts looking liquid. Just how do people with side blasts and coke forge weld? With bituminous coal I understand the coal naturally forms a sort of hollow cave of coked coal that is nice for forge welding and also for easily seeing the piece inside. The only way I get to see what's going on with the piece I built was to partially disassemble the mound I made.

I am also a bit paranoid of looking into the fire too much, since it's not good for the eyes. I use glassesa but don't know if they give any IR protection.

I'd love to hear from people who forge weld using only coke, or perhaps charcoal and coke, I tend to mix in some charcoal whenever I start a fire, it makes it so much easier to get going than using just wood or paper. 

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I use coal, but when I'm doing any welding everything in the fire pot is already coke so I think what I'll share will be relevant.

First off, I would pick up some flux. While it isn't strictly necessary if you have good fire control and know what you're doing, it is very helpful. I use Borax since I can buy it at just about any store here. There is a difference between getting up to welding temperature and your turning steel into a sparkler. 

When my welds fail it's usually one of 3 things..

First, my fire is too shallow/dirty. An oxidizing fire will result in an excess of scale formed on the surfaces, which acts a barrier. Flux helps to dissolve and flush out that scale, but it can only do so much. In an oxidizing fire, you're also more likely to start burning your steel once you get up to welding heat. Generally, if your steel is a sparking while you're trying to weld it, that's not a good thing since you're loosing material and degrading it to boot. A little bit of sparking is fine, on the toe of a scarf for example, but that's not the goal. Note: If there are sparks coming out of the fire, chances are you have either melted the steel or you have an oxidizing fire. Those sparks should really only be appearing once the steel comes on contact with oxygen.

The second reason is that I'm not prepared. Lets just say I'm making a ring out of 5/16" (8mm) round. When that comes out of the fire I only have a few seconds before it drops below welding temperature. If I don't have everything ready to go it's going to cool off before I get anywhere.

The last reason (which ties into your question) is some form of impatience. I'll try to bring it up to a welding temperature too quickly or I'll remove it from the fire before it's ready because, like you said, it can be hard to see what's going on inside that ball of fire. Something that Mark Aspery said that seems to work well for me was once you think you're at welding temperature, wait 10 more seconds. If you have a good fire going you can even kill the air and just let the heat soak into the material.

So how do you know when you're at or near welding temperature if you can't see? Part of it is feel. The more you weld in your forge, you'll get a feel for about how long it takes to get stock of a certain size up to welding temperatures. Even when you get a feel for it, you still need to see what's going on. To do this I will sometimes shimmy it up toward the surface of the fire until I can see it just below the top layer of coke. I also have a poker, which is just a long relatively thin taper that I can slide into the fire and move the pieces of coke that are obstructing my view of what's going on. Even if the coke doesn't stick together like coal does, you can still make yourself a little peephole into the fire. I agree, you shouldn't be staring into it for extended periods of time, but a little peek here and there is fine

I don't look for the "wet" surface so much. Once the flux is on there everything looks wet. I am usually using color as my reference for when it's ready to weld. With borax flux yellow flames start coming out of the fire one the flux is at a welding temp. Note that flame is an indicator of the temperature of the flux, not the steel, but it is still a useful indicator that you're getting close. 

I also use a ~1 lb hammer to set pretty much every weld I make. Anything heavier is unnecessary and causes more problems than it solves IMHO.

Hopefully that helps. I'm sure you already knew much of this, but I figured I would give a more complete answer.

Also, here's my favorite post regarding forge welding (you may have to scroll down to read it).

 

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Another trick you can use to get a feel for things is to have a wire (straightened out coat hanger) or sharp poker of the same material in the fire with your work piece and when you think your close to the right temperature lightly touch/rub the end of the wire/poke to the weld area. If it sticks it’s at the right temperature at least on the surface.

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We all fall for the heating to fast trap. Think of it like roasting the perfect marshmallow. When the outside is toasty tan and the inside is hot and gooey. 
So I find that bringing things to a good forging temp before upping the air to the welding temp. Not to hot, just to welding temp. 
another trap is thinking that A36 is homogenized steel. It isn’t 1018 but what ever mix of scrap will make the engineering spec. Not much better than medium grade rebar. So if their is a spot with a hard to weld steel you will fight it, I have even seen Steve Sells fight a spot. After folding and welding the same bar half a dozen times he hit one spot that wouldn’t weld. 
 

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Welding in an open fire like you describe is based a lot on experience: you know how long it takes to get a piece of that size to welding temp.  

I have a trick I use for billet welding in my bituminous coal forge:  I run the forge way up in temp and stick the cold billet in and immediately turn off the air supply and go get a drink in the house; or use the facilities; or... Then when I get back I turn on the air and quickly take the billet out, and thoroughly wire brush the surface and flux with a borax/boric acid mix (3:1 appx) and put it back in.  This allows the entire billet to come up to fluxing temp in a reducing atmosphere.  When the center is nice and hot it doesn't take as long to get the entire billet up to welding temp. I also use a slowly climbing amount of air to bring the fire and billet up to welding temps.

I realize that with a totally coke fueled forge you will probably need a small amount of continuous air to keep it from going out; but try to keep it very reducing as it heats!

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5 hours ago, Frazer said:

First, my fire is too shallow/dirty. An oxidizing fire will result in an excess of scale formed on the surfaces, which acts a barrier. Flux helps to dissolve and flush out that scale, but it can only do so much. In an oxidizing fire, you're also more likely to start burning your steel once you get up to welding heat. Generally, if your steel is a sparking while you're trying to weld it, that's not a good thing since you're loosing material and degrading it to boot. A little bit of sparking is fine, on the toe of a scarf for example, but that's not the goal. Note: If there are sparks coming out of the fire, chances are you have either melted the steel or you have an oxidizing fire. Those sparks should really only be appearing once the steel comes on contact with oxygen.

That was exactly the behavior I got last night, so good to know something is working correctly!

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That's a good sign then. It seems to me like some flux will make a big difference for you. I know some people can weld without flux.. I am not one of them. I use a lot of it :D

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Getting a hold of borax was a little tricky but I am trying to order from a shop in Sweden, getting a proper blacksmiths brush too, only had a simple steel bristle brush and it hardly does anything.

Getting 1kg or 2lbs> of borax, which hopefully lasts a while.

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Try this, it works every time 

With your poker, gently move a piece of coke out of the way and look, then move the piece you moved back where it was.

You can also, depending on shape, quickly pull it back to you and look, then slide it back in. Don't disturbed your fire when you do this, just move it quickly in and out.

I'm not sure what some above are implying, so to clarify about what you burn in a coal fire: if you are burning bituminous coking coal, the green coal stays around your fire and you should only have coke in your firepot heating your iron. Coal mixed in the firepot means you have a dirty fire. Basically, when the green coal burns, it turns to coke. This gets moved into your firepot and you move the coal into the space that turned to coke.

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Dennis, when you get the Borax put on an old cookie sheet in the oven on low heat for a couple hours. Then store it in a sealed container. I use an ammo can. Borax contains water and when you put it on hot metal the water will boil and cause it to foam. Baking it will evaporate the water but borax will absorb water from the atmosphere hence the need to keep it sealed.  Not as good as anhydrous borax but better than just borax. 

It is not that hard to make anhydrous borax but involves melting then grinding it to a powder and i am to lazy so i just put it in the oven.

Edit: forgot to add, if that is the standard size i am on about year 4 of mine and still well over 3/4 of it left. 

Edited by BillyBones
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Chances it will be anhydrous if it's sold as flux. It's available from welding supplies as torch welding and brazing flux. It'll be easy to tell heat a piece of flat stock to high red, take it out of the fire and sprinkle a little flux on it. If it melts and covers the steel in a layer of clear sticky goop its anhydrous. If it foams up and doesn't cover the steel in goop immediately it's NOT anhydrous it's equivalent what we call laundry borax.

In short, anhydrous just melts and covers. laundry borax foams up and can run off.

Frosty The Lucky.

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In what way is it too low a temp for welding steel? I've been welding with borax for decades. I've also been silver soldering and brazing with borax flux since Jr. high school, metal shop 1, around 1963 to now.

I've recently started using Peterson #1 blue flux for forge welding, it's similar to more expensive "forge welding fluxes" sold by blacksmith supplies but for about 1/4 the price. It's anhydrous borax and boric acid with something proprietary to turn it blue. Peterson has another that contains iron oxide if you like Black Magic etc.

Either of these commercial fluxes are used routinely for hard solders of all types, torch welding stainless steel, steels, aluminum, copper and bronze amongst others. 

Frosty The Lucky.

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This is one of the ways I was taught to recognize when steel is at welding temperature in the coal forge. After making sure I had a clean coke fire (no clinkers) and the stock has soaked so the heat is through and through. I know this is risky, I watch for the first few sparklers and quickly remove the stock and set the weld.

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10 hours ago, Frosty said:

In what way is it too low a temp for welding steel?

I think he was saying flux melts at a temperature that is too low for forge welding. Which is true. 

From Wiki: Melting point of Borax = 743 °C (1,369 °F)

~1400F is well below welding temperatures. So to answer mcostello's question, no. The flux melting does not indicate that you're at a welding temperature. Frosty, to your point, that does not mean it's not a suitable flux. 

--

Now I'm thinking if the yellow flames that come out of the fire are from the flux beginning to boil, which happens at 1,575 °C (2,867 °F). 

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On 6/26/2021 at 12:24 PM, BillyBones said:

Dennis, when you get the Borax put on an old cookie sheet in the oven on low heat for a couple hours. Then store it in a sealed container. I use an ammo can. Borax contains water and when you put it on hot metal the water will boil and cause it to foam. Baking it will evaporate the water but borax will absorb water from the atmosphere hence the need to keep it sealed.  Not as good as anhydrous borax but better than just borax. 

It is not that hard to make anhydrous borax but involves melting then grinding it to a powder and i am to lazy so i just put it in the oven.

This is explained in greater detail on THIS THREAD. The short version is that baking the borax only removes the water on the surface of the borax crystals and not the water trapped inside them. Even baked borax will still foam.

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You WANT your flux to melt at a lower temperature than welding temp as you want the melted flux cover to protect the surface of the metal from oxidizing(scaling)  and scaling starts way below welding temp!

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10 hours ago, Frazer said:

I think he was saying flux melts at a temperature that is too low for forge welding. Which is true. 

From Wiki: Melting point of Borax = 743 °C (1,369 °F)

This is a problem with looking up specific numbers without really understanding the process. It's easy to lose what's going on when we see something that doesn't make sense. As Thomas says the flux MUST melt well before the steel/iron gets close to welding temp or it can't do it's job. 

We all get caught by these little bits of mental discontinuity, no big thing. 

Frosty The Lucky.

 

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What iron dragon said is gold, as is just moving a piece of coke and looking at your iron,,, in a constant light. When I was starting out, I'd look for the early sparks, slow my hand crank a bit, and count thousand 1, thousand 2, thousand three and pull it out. That pushes the burn envelope a bit, but it worked for me til experience kicked in. 

I tried the "high priced spread" for borax, but not for long. I just use good ole 20 mule team mixed with a bit of boric acid for bragging rites. 

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Boric acid keeps the roaches from eating all your flux. It's okay Anvil you can let the gang in  on the secret. ;) 

Price is a thing, so I just did a search and darn if prices haven't come down a lot. Seems most fluxes are running between $18/lb and $30/lb. 

Peterson #1 blue was $27 for a lb. can on the shelf in the welding supply in Wasilla. 

I've used plenty of 20 Muleteam and it worked a little better when I started adding boric acid. I still like the Peterson better. 

The thing to remember though is it's NOT the flux it's the guy doing the welding.

Frosty The Lucky.

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No kidding Fosty. I saw on of the young guys that just joined our group last year before things got crazy pull off a weld I never thought would happen. He was set up perfect, the drop the piece found the drop tong part. Well, he picked I up and proceeded to weld it. I only looked like a low orange heat to meet, but the tack weld took and it ended up seem less after a second welding heat.

For those that want the answer to good forge welds, most of it is practice. He said ever time he lights the forge he does a forge weld. Well in the year I’ve know him his welding skills have grow significantly!

David

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