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Geoff Keyes

Blown burners, the care and feeding

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I'm not fond of square forges. The way you have the burner tube coming directly down onto the bottom of the forge creates a hot spot. I also recommend that you coat the inside with something like an infrared reflector or those soft bricks aren't going to hold up long. For safety reasons I would also move the propane tank a bit farther away from the forge. If that's a propane grill regulator on that tank it's not going to do the job for you. It's not going to have the range of adjustment that you'll need. Putting a pressure gauge on the regulator wouldn't be a bad idea. You could go to a welding supply store or the somewhere like High Temperature Tools and Refractory, or Zoeller Forge and get the regulator, pressure gauge, and regulator all in one package.

 

As far as the flame goes, the first part of the video shows a pretty good flame. In the latter part where the forge just barely has a flame floating out of it you are you're not getting enough air pressure. I'm not sure if the blower is adequate.

 

Doug

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The screws are to hold the top part of the burner on the forge- there's the 1 inch reduced pipe inside that 1.5 inch coming off the top of the forge. The flange/1.5 inch is how I mounted everything on the brick assembly.

 

The fan is 50cfm- and I'm adjusting the amount of air with that dimmer knob next to the fan.

 

It is a grill regulator- a high PSI one, up to 10 psi.

 

During the video I'm adjusting the gas and fan- the beginning was what I thought was the best I was getting out of it- then I adjust the gas, then air, then gas again. Just to show what could be done. I didn't have the fan blowing full speed at all in that video.

 

I'll keep the ITC in mind- will probably pick some up when I have some cash to spend. The tank will be moved farther away- just had it up there for testing. Have to rearrange some stuff for permanent location.

 

Thanks!

Edited by Doug Crawford

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Try cranking the fan all the way up and adjusting via the needle valve. I use a dual gauge regulator, like the kind you use for a welding torch. That means that I've got tank pressure (100 psi +/-) up to the regulator and whatever I want on the burner side. I hardly mess with the air once I get it set. I do all of my adjusting with the regulator and the needle valve.

 

Geoff

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Thanks for the feedback, and the original post. This is going to make moving metal much easier!

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Here's my 2 cents:

Reverse the fan and gas locations (unless there's a hidden piece of pipe that extends the gas to the bottom of the Tee in that photo). On blower assisted forges, you pretty much always want the gas inline after the blower. You could also use a longer pipe between the Tee fitting and the forge body. You will get a better mix of air/gas with these two minor changes. The flame will be much more even and steady too.

 

Adjustable regulator and pressure gauge as Doug suggested, yep set somewhere around 3 psi for that size forge.

Add a 90 degree ball valve as a safety shut off as the first fitting inline after the tank. Then go into the needle valve.

Figure out how to limit the air from the blower. A gate valve works pretty well and is extremely adjustable. A ball valve works as well.

Here's where I differ on the set up and mixture tweaking. I get my needle valve where I want it and never touch it again. It is acting as an orifice and should not be used as a gas adjuster.

Set the ball valve wide open and close the air blower valve down to about 50%. Play with the needle valve and air mix until you have a great burn. This forge probably won't get to welding heat, but it might. Once you have the gas and air mixture burning at its hottest, you can control the gas by closing down the ball valve and matching the reduction of air with the gate valve to limit oxidation and keep a reducing flame. This will lower the heat to regular forging levels and not make your steel scale up from too much air. The air adjustments are pretty small. 1/4 -1 turn usually does the trick. When you need more heat, open the valves back up.

Edited by Joshua States

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Reverse the fan and gas locations (unless there's a hidden piece of pipe that extends the gas to the bottom of the Tee in that photo). On blower assisted forges, you pretty much always want the gas inline after the blower. You could also use a longer pipe between the Tee fitting and the forge body. You will get a better mix of air/gas with these two minor changes. The flame will be much more even and steady too.

I have to disagree with this, in the friendliest way possible. I've built a lot of these and I haven't seen any difference in the burn depending on where the fan and gas input locations are. You want some turbulence in the flow, to mix the gas and air. Whether it comes from the gas bouncing off the side of the "T", or the air bouncing off the side of the "T", I don't see any difference. I have tried putting a "swirler" in the tube downstream of the "T", and it just seems to make the burner burn in the tube, too much blockage of the flow.

 

I know that this design works as is, but YMMV.

 

On my forges I set the gas pressure from the tank (1-3 psi for my everyday forge, 7-10 psi for the HT and welding forges), choke off the air to a point I know works for that forge (a bit of trial and error). I turn the fan on (always first), open the valve to the manifold (I run all of my forges off a single manifold fed by a single tank), light the torch and open the needle valve until the forge lights, then adjust the needle valve until I have the burn I want. Pretty much I don't fuss with it after that. Welding and HT'ing take a bit of adjustment while they are running.

 

I need to scoot to PT, I may have more comments after.

 

Geoff

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Did some work today with it- started with the fan going full blast, and adjusted the needle valve just until it wasn't sputtering and there were a few blue flames coming out of the front. This thing is HOT. I was testing a piece of an old saw blade to see if it would heat treat, and the I could feel the tongs I was holding the piece of metal with start to bend a little. Heated up some o1 and was able to move more metal heating it twice than I got done in a couple hours with my old POS setup.

 

A coating of ITC will be coming in the near future, possibly with a layer of kaowool around the top and sides too.

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Let your forge run for a while and then carefully check to see how hot the sides of your forge are. You may not need the Kaowool/Inswool for more heat retention. If you do you will probably want to make the bars on the top and bottom a little longer to allow for the one inch thickness of the ceramic matting so that it's not compressed. You might want to sit the forge on a blanket of ceramic matting, however, just in case a jet of burning gas pokes through a joint in the brick. I had this happen with a soft brick forge that I built once. It ate a hole in the bench that I had the forge sitting on.

 

Doug

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Little update- have been putting some more time into improving the forge. I mixed some soupy Satanite and smeared it into the pores on the firebrick, then mixed some thicker and started to round out the corners with it. Sanded it a little and mixed another wetter batch for the last coat, then gave it a coat of ITC. It goes from completely off, to lit with hot metal on the anvil in about 45 seconds now. I think if I wanted to go hotter at this point I would need a more powerful fan. The fan is wide open and I still have the gas on very low to get a good mix.

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Well, I've been talking to Mr. Keyes who helped me a ton with materials and my barrage of dumb questions. Just got the last of the parts in the mail and the next two days off, so its time to start building my first gas explosion, i mean, forge. Wish me luck and I'll have pics soon.

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The forge I made with Geoff Keyes' help. Works great, didnt explode ;) just have to work out temps and fine tuning and such

I know my blower and such is in a dumb spot, im gonna mess with that, dont worry. And yes, im gonna build a stand for it too lol

Thanks again to Mr. Keyes for all his help!

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Quick question, been playing around with my air/gas mix and such, got everything pretty well controllable, but my flame is a little sputtery. Its not particularly bad, doesnt try to go out or anything, just a mild but incessant sputter. Doesnt go away no matter what mix or fan speed or whatever that i do.

Theres nothing blocking airflow, inside of forge where the pipe goes in is pretty smooth, the flames kicking out the front are generally the right color and size.

Any ideas?

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My phone wont pick up the noises. Its a dull whomp, but it seems to slowly be getting better, i guess it has something to do with the internal temp and the really fine tuning of gas/air mix. Ill keep playing with it.

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On 4/1/2017 at 4:06 PM, ethanknott said:

My phone wont pick up the noises. Its a dull whomp, but it seems to slowly be getting better, i guess it has something to do with the internal temp and the really fine tuning of gas/air mix. Ill keep playing with it.

I think you nailed it there. Mine "putts" a little 'til it heats up.

Also, it took me a while to realize how minute adjustments would effect the burner.

And too, mine will require gradual fine tuning as it heats up.

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Thanks Don, its nice to know I wasn't just goin crazy... Also found I was using WAYYYYYY too much gas so theres that...

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Ethan, If you recall, I run my setup on about 1 psi, at the needle valve.  That means that the burner is running at .5 psi (more or less)  That's why I like to have a gauge on the main line.  You don't need much.  I like to set the main gas line so that the needle valve is open about 50%, that way you've got some head room if you need to really blast it, or some space at the bottom of the travel, for finer control.

 

Geoff

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Newbie here!

I want to move on from my coal forge...I have a couple propane venturi forges. One is a single burner and the other is a custom 6-burner I wanted to heat larger quantities of small pieces and occassionally completed units. However, I actually like a scaled finish on some of the items I am making...not the loose scale but the "pre-scale" (for lack of a better term) and feel a blown forge can get this done. Not to offend anyone but I don't make knives so scale isn't a big deal to me. My venturi models don't get the desired results. My coal forge does this well but I want to move away from coal as much as possible. 
Question is just that...will the blown forge produce this effect better?

This is a great thread and I enjoyed reading and viewing the pics! From the info gleened here, I hope to make a nice unit but am having trouble locating the blowers you show...any tips on these, what type they are and where to order them online would be excellent and most appreciated! I am willing to dig deep for the right blower. 
Thanks,
Morris

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I believe the "pre scale" you are talking about is the result of overheating, in knifemaking, the steel and a blown forge will certainly do that. Other scaling, since it is a function of oxidation, heating the steel in an oxygen-rich atmosphere, is right in the blower's wheelhouse.

Sorry, I'm no help with fan shopping.

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This is very close to what I use. 

https://www.zoro.com/dayton-blower-75-cfm-115v-045a-3016-rpm-1tdp3/i/G2510164/

I got a deal on mine at Surplus Center, but they haven't had any in quite a while.

Someone here had a short tutorial  here about building a blower out of a PVC pipe cap that I thought was very interesting.  That is something that needs exploring.

 

Geoff

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Quick question for anyone reading this. I made a new forge w/ a blown burner about a month or two ago. Works good, got the performance I was hoping for. Wanted to do some pattern welding so I cranked up the air and fuel and had the metal shooting sparks at me. Problem was that this burner was drinking propane, I ran through a tank in a matter of hours. Even before when doing some basic forging my 30 lbs tank seemed to go a little faster than normal. I'm getting about 5 hours of forging with this burner where before with my venturi burner I was getting 8+. The burner is 2" or 2 1/2", I forget exactly which. Would reducing the burner to about 1 1/4" or 1 1/2" help with fuel consumption while also delivering enough heat to the forge?

Forge is circular 350 cu in with 2" insulation, furnace refractory, ITC-100 coating with the burner aligned to get a swirling flame if that helps with the question. 

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