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welding heat, or not? it's got to be...


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i just recently stated using my gas forge for welding my billets. i also just made the biggest billet i've ever made (6 x 1 1/2 x 2 inches, 44 layers. 15n20, 1095, & mild carbon) with this forge. it's a single burner with forced air forge. the quesyion i have is, it doesn't get as yellow-wight as it does in the coal forge. it gets pretty yellow- orange, but not as bright as the coal. i just did my first weld tonight and it seems to be pretty damn solid. i'm pretty sure that i got a good weld. it just puzzles me that it doesn't seem to be near as bright at welding temp as the coal forge, i guess if it works then i shouldn't worry about it. right? anyway, does anyone know if the color is different from coal to gas and why?

thanks, chris

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My first question is what psi are you running your gas at....to low and not enough fuel to get the heat needed to weld. So the higher the psi the more fuel the greater the heat...It also depends on the quality of the regulator you are using, I found the standard regulator from any propane shop did not give me the psi needed to achieve good welding heats, so I bought a rather expensive regulator and did not have a problem. Now that I moved to a vertical blower forge the psi is a tad useless but for when I switch back over to the atmospheric forge. So more psi equals more fuel greater heat.

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My first question is what psi are you running your gas at....to low and not enough fuel to get the heat needed to weld. So the higher the psi the more fuel the greater the heat...It also depends on the quality of the regulator you are using, I found the standard regulator from any propane shop did not give me the psi needed to achieve good welding heats, so I bought a rather expensive regulator and did not have a problem. Now that I moved to a vertical blower forge the psi is a tad useless but for when I switch back over to the atmospheric forge. So more psi equals more fuel greater heat.

i have a great regulator that goes up very high for propane, and i have it up to 15-20 psi and the air open all the way. it's a pretty decent sized blower as well. it seems to have welded. i'm just puzzled on the color of the billet at welding heat.

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I have run across this problem with at least one of my coal fired friends. My CFF swore up and down that you could not weld in a gas forge, never seen it done, couldn't happen. We trotted out to the forge and I fired up my forge. At that point I didn't have the either the press or the hammer set up. I took a small billet that I had ready to go and brought it up to what I know is a welding heat for that forge, and with his help as a striker, welded it. The look on his face was worth all of the trouble.

 

So my question to you is; How do you know when you've got a welding heat in your coal forge? DO you just heat it up until the pieces start to spark? That is probably 200-300 hotter than you need, perhaps more. Welding heat for carbon steel is about 2300F (I think, anyone know for sure?). If you've got sparks flying off the surface, that is carbon burning. You don't need to be that hot, and you don't want to lose carbon. You really want to weld at the lowest temp that will do the job.

 

Another couple of things I have noticed. First, blacksmiths often work in mild steel. Mild steel seems to weld at a higher temp than carbon steel. Second, coal fires can be dirty, and it's harder to weld in a dirty fire.

 

The simple test is to take a piece of steel rod, heat it in the same fire as you welding pieces. You touch this rod to the surface of your pieces, when it it starts to feel tacky, like contact cement, you are at welding heat.

 

I can get a welding heat in my blown vertical forge at less than 1 psi of line pressure. My welding forge takes a bit more, it's a bigger space and it has a brick floor which eats btu's getting to a welding temp. After the welding forge has been running for an hour or so the interior is a bright yellow white (I don't have a pyrometer in that forge) and that is a good temp for carbon steel. It's interesting to watch the forge color drop when you stick a big chunk of steel in the box :lol: .

 

These are just my observations.

 

Geoff

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There shouldn't be a noticeable color difference at a given temperature based on the theory of black body radiation. However ambient lighting can affect how you perceive the color. If the coal and gas forges aren't in the same place (i.e. the gas inside and the coal outside) it may be difficult to judge if you have the same ambient lighting. Or even different spots in the same shop can have different enough lighting to cause a perceptual difference in the color of the hot steel.

 

ron

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I run mine at 3. It used to be ran at 2, but I changed part of the burner, if I switched it back I could run it at 2 again.

if your welding a large billet does it get real yellow? because mine doesn't. it did seem to weld though. it gets up to a orange-yellow. more orange than yellow though.

Edited by tormentchris
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same here... bright yellow, with steamy smoke coming off it when i go to set the weld..

 

in the forge... it'll have have the flux all bubbly and dancing around on the top of the billet..

 

for me.. i tune the forge by watching the flame coming out... if its a big puffy lazy orange flame... then you need more air ( too much propane can cool it abit )

- no flame, then you have not enough fuel going in

 

- flame coming out that is perfect... but heat is low..... ( after runnin for awhile )

then you need to increase both fuel and air

 

its easy to get a weld heat on a very small forge... my little box forge will easily weld at 2 to 3 psi ... with a hairdryer blower... and thats in our crazy cold winter..

 

 

and.. once you get weld heat in there... after awhile you can often dial back the forge in gas and air... as it seems it'll maintain this heat with lower pressure after its run form awhile.. (some extra propane savings )

 

 

what kind of lining do you have

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"the quesyion i have is, it doesn't get as yellow-wight as it does in the coal forge."

 

By "it" do you mean the billet, or the interior of the gas forge compared to the coal fire?

 

If you're talking about the color of the forge interior versues the coal fire hot spot, it seems likely that your coal fire was actually running somewhat than you needed to weld, and you were just pulling your billets before they started to burn.

 

If it's the billet that you're talking about, I would guess that you were heating your billets hotter than you really needed to in the coal forge.

Edited by Matt Bower
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ok, my forge is pretty small. it says in the plans that i bought it should be ran at @ 8 unless welding it says 15-20. this is the round forge made frome an old propane tank with the top and bottom cut off. i'm using kaowool for insulation. it's about an inch thich and i have a hard fire brick on the bottom. the actual forge gets that orange color as well as the billet. i swear it seems like iv'e had it up to a nice yellow- white before. when i ave it up to a supposed welding heat the flame is a nice bright orange and is coming out the front about 4-6 inches. i have the back closed and the front halfway closed so i can work out of it. the front and back are sealed with fire brick as well. i'm going to go out and mess with it he in a little bit and i'll take some pics. i'll also use a smaller billet. the one i've been talking about is a quite large piece of steel. oh yeah, the flux does get all bubbly and does dance around on top of the billet too.

i'll let you know, chris

Edited by tormentchris
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8 and 15-20 psi sound more like atmospheric burner numbers to me.I could be wrong.At present I weld with a venturi burner in a freon tank forge(horizontal)2" of wool,at about 6 psi.Im almost finished with my upright forge and will be switching to a blown burner for better efficiency.Another layer of insulation would probably help you some too.

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Well, if you're welding with it then by definition you're getting a "welding heat."

 

By the way, pressure really doesn't mean anything without orifice size. 5 psi through a 1/4 inch orifice is vastly more propane than 20 psi through a 0.030" orifice. And even if we knew orifice size, there'd be a dozen other things that influence the temperature inside the forge. So "I run mine at 20 psi, how about you" conversations have always struck me as kind of pointless, unless they involve two people with identical forges and identical burners.

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Well, if you're welding with it then by definition you're getting a "welding heat."

 

By the way, pressure really doesn't mean anything without orifice size. 5 psi through a 1/4 inch orifice is vastly more propane than 20 psi through a 0.030" orifice. And even if we knew orifice size, there'd be a dozen other things that influence the temperature inside the forge. So "I run mine at 20 psi, how about you" conversations have always struck me as kind of pointless, unless they involve two people with identical forges and identical burners.

matt, i have a propane tank forge. my orifice is .048 it's supposed to be a 3/64's but that was close enough. i got the plans from david robertson at artist blacksmith in ontario. it calls for 2 layers of kaowool which would be 2" of thickness. i just got back in from my shop and realizes as i was out there that i took off a layer of my insulation. i'm pretty damn sure that that is the problem there's too much space to heat for my one burner. it's got to be that. i usually weld at 15-20 and i run at 8 for general forge work. i'm going up to get more wool now. i'll post the results later.

thanks, chris

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That's a good sized orifice. I would think it'd flow plenty of gas for a propane tank forge. I bet you'll see a huge difference with the extra insulation.

 

Is this a naturally aspirated burner, or a blown burner?

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That's a good sized orifice. I would think it'd flow plenty of gas for a propane tank forge. I bet you'll see a huge difference with the extra insulation.

 

Is this a naturally aspirated burner, or a blown burner?

no, it's a blown burner. i'm sure it will. that is what the plans call for. i'm sure there's a reason for that.

Edited by tormentchris
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