Any good forced air burner designs?

[Killerace]

First thing is I'm not looking for a ribbon burner, this is just the only section I could find for any kind of burner. I know if you're getting a Venturi burner a solid choice is the frosty t. However I am at a high altitude and overall think a forced air burner would be better. Are there any tried and true forced air burners that I can buy or are not to complicated to make.

[ThomasPowers]

How high an altitude; I've tried a NA burner out at 7000' with no issues, and also used a forced air ribbon burner running at forge welding temps at around the same altitude.

Using my browser's search function I found 728 hits hunting on: forced air burner site:iforgeiron.com

A couple of the ones I found:

Forced air burners?? - Gas Forges - I Forge Iron

Set up my first forge, forced air burner question - Gas Forges ..

Forced air burner design - Gas Forges - I Forge Iron

 

[Frosty]

Welcome aboard Ace, glad to have you. If you'll put your general location in the header you'll have a better chance of hooking up with members living within visiting distance.

The belief a Naturally Aspirated (NA) burner isn't effective at high altitude is pretty well debunked. Most of the problems were guys who didn't know how they work making adjustment based on false assumptions. Most were for some reason closing the chokes and complaining the burners were running rich. That's like pushing the gas pedal to the floor because your car is going too fast. Exactly the opposite of what's needed.

However, a gun / blown, burner is easy to make, there are lots of proven plans in the "Gas Forge" section of Iforge.

And we'll help. 

Frosty The Lucky.

[Killerace]

With all do respect to this forum, and the people in it it's a mess. On a related note, and I probably should have been more clear on this. I am looking for something of a diagram or name of a proven burner. I can look again at the gas forge section ( I looked through the first 10 pages pages or so of burners 101 and got no where). Or would you suggest a different section of gas forges?

 

As for why I was looking at a forced air it was not just due to altitude which I was unaware has been debunked but also  I'm assuming a forced air burner would tolerate high humidity and wind better than a Venturi. 

[Buzzkill]

It's well known that the search function on this site is less than desirable.  That is covered here:

https://www.iforgeiron.com/topic/53873-read-this-first/

You'll have much better results by using your favorite search engine with the site name and some key words.

I'm not sure how much of a difference humidity would actually make, but a forced air burner will typically have fewer issues dealing with wind than a naturally aspirated burner.

Forced air burners are probably the easiest to build so you most likely won't find a lot of detailed information.   You need a constant air source, some pipe with at least one bend (for mixing purposes) between the point where the gas is introduced and where the fuel/air mixture enters the forge.  You also need a way to control the air and gas flow independent of each other.   That's about it.   You tune the burner by sight and sound using the air and gas inputs. There are no particularly tight tolerances to worry about or alignment issues like there would be with a naturally aspirated burner.

 

[Killerace]

Thank you buzzkill you know I went into that expecting forced air to be just as if not more complicated than Venturi with tight tolerances and everything. But just to make sure what you're saying is so long as I can meet the requirements you specified and adjust the air and fuel I should be able to get the correct fuel air mixture right?

[Buzzkill]

Yes.  I ran a forced air burner for a short time (I didn't like being tied to electricity to forge), but I would tune by adjusting the gas or air to get the loudest roar then back the air off just a bit to get a slightly reducing atmosphere in the forge.   Of course your air source does need to provide enough volume of air to ensure combustion of the gas.  An air compressor is not ideal for instance.  You want low pressure high volume air as opposed to low volume high pressure air.   You should also use the correct size for the final length of pipe to your forge.  You would not want a 1 inch diameter pipe in a tiny coffee can forge, nor would you want a 1/2 inch diameter pipe feeding a 750 cubic inch forge.  The larger the diameter of the delivery pipe, the more space is needed for complete combustion before the flame impinges on the opposite wall.

[Goods]

Also, for a force air burner, you may want to add a normally close solenoid valve for the gas. That way if you loose power for some reason you won’t have gas without air. Safety first!
 

David 

[Killerace]

Ok I was planning on using a dust blower for electronics which from what I found has plenty of air, I was unaware you need a certain size pipe my forge size would be around 350 cubic inches after all insulation is installed. So pretty small what I want for a Forge that size? 

[Buzzkill]

350 cubic inches is pretty much the recommended size for starting out, give or take a little.  A 3/4" delivery pipe should be about right for that volume.  A flare can help keep the flame on the end of the burner, or you can run your burner turned down until the forge stats to glow and then bring the heat up.

[ThomasPowers]

 I used a forced air propane forge for about 10 years.  Built it in a forge building workshop put on by SOFA.  Pretty much what is shown at: https://www.spaco.org/Blacksmithing/PipeForge/PipeForgeAndPropane.htm

Of course we built them with Hans standing over us providing instruction...10" grain auger pipe and 150 cfm blower; gas was controlled by the regulator and air by a sliding piece of sheet metal in a cut in the air pipe. (I prefer a thicker pipe than grain auger, my next NA forge was made with Oxy welding tank and is much nicer and easier to tack weld stuff too.)

I've melted steel in mine so it can get plenty hot.  Blown forge burners are  much easier to build and adjust and not as sensitive to construction issues, wind, etc.  Being able to separately adjust both air and gas give you a lot of control over the internal forge temps and atmosphere. I only switched to a NA forge when I moved and didn't have electricity to my shop; been using that for 16 years now and just replaced my old burner's with Frosty T's.

I'll be offline till Monday; but will check in then.

 

[Frosty]

Oddly enough the same general rule of thumb works for NA or gun burners. A properly tuned 3/4" burner will bring 300-350 cu/in to welding temp. 

As far as the flame is concerned the air source doesn't matter. X cu/ft of flammable air fuel mix per second WILL develop X BTUs and the closer to a stoichiometric mixture the closer it'll be to the highest ambient flame temp allowed by the fuel.

The above doesn't change depending on the air source. Both types have their plus and minus sides.

NA burners require no electricity and induce combustion air in a ratio according to the fuel injected. It's a pretty flat curve but does lean out the higher the psi gets. So a NA burner just needs to be hooked up and lit, you adjust temperature by adjusting the propane pressure.

The down side of NA burners is the precision required to make them work properly. There are ratios of length, intake area, shape and jet that make very real differences. The direction of the air intake makes a BIG difference in induction. The real downside that messes lots of folk up is back pressure, a too closed forge or too many burners. Breezes have disturbingly too much effect on home built NA burners. The surprising exception is the NARB, for some reason it doesn't seem to care about breezes and is more tolerant of back pressure.

A gun burner requires hardly any precision, if you can: measure accurately, drill and tap a hole, operate nuts and bolts or screws you're golden. No fooling they're crazy easy to make. There are only a couple simple rules of thumb. Another good point is they work in a more closed forge and don't care spit about breezes. 

The down sides are: it's tied to electricity. You have to adjust the fuel air ratio every time you want to adjust the temp. BOTH fuel AND air, you'll need a valve on the air, intake or output doesn't matter so long as there is one. Adjusting the pressure at the regulator OR with a needle valve, is the easy way to handle fuel. Pressure isn't so important with a gun so long as it's higher than the air flow in the pipe. This makes a needle valve a pretty good idea it lets you run higher PSIG propane and lets you adjust it. 

I'm known for the T burner but I don't really have a dog in the fight as to superiority of one over the other. Both have their good and bad sides. 

See your happy AVATAR Monday, Thomas.

Frosty The Lucky.

[Killerace]

Thanks that makes a lot of things make a lot more sense, frosty when you say forced air works better in a closed Forge does that mean I can't use them if I want to weld two really long pieces of steel together?

[ThomasPowers]

No; blown burners are just not as sensitive to back pressure as NA burners are.  You close up a NA burner forge tight and it can't induce any air to mix with the propane.  The blown burner pushes the air into the mix and so does better.  The amount of heat produced is just based on gas being burned correctly so a NA burner does well in a more open forge and a blown burner does well in either.

[Killerace]

Okay that makes sense.

[FlatLiner]

You can hit up Jymmie Hoffman. I built a blown burner off his design. It's dirt simple but works great. It consists of 3; 1 1/2 T's, 2; shorter 1 1/2 nipples, 1; 5" long 1 1/2 nipple with one side smashed down to an 1/8" opening, 1; 1 /2 plug, 1; 1 1/2 by 1/2 bushing, 1; 1/2 by 3/8 bushing, 1; 3/8 needle valve, 1; 3/8 quarter turn gas valve with the apropriate ntp connectors to attach to your propane tank. You will need a blower with some sort of gate valve also. Here is a pic of his burner design.

[Killerace]

Thank you flatliner, been working on a design myself working around what I can get in town needle valves are hard to come by here but I think I've got something that should work. I can't draw but here's what I have.

 

A 3/8 flare ball valve connected to my regulator, connected to a 1/2x1 1/2 pipe nipple connected to a 1/2 inch tee. 1/2x1 1/2 nipple connected to a 3/4 to half reducer, connected to a 3/4x1 1/2 nipple, connected to a 3/4 glove valve duct taped to a coleman air mattress pump. On the other side of the tee will be a 1/2x 1 1/2 nipple connected to a 1/2 inch elbow, connect to a 1/2x1 1/2 nipple, connected to a 3/4 to 1/2 reducer 

[Irondragon Forge ClayWorks]

14 hours ago, Killerace said:

needle valves are hard to come by here

Where in the world might that be? I can show you three places near me to get all you need and I live in the boonies. If you edit your profile to show your location, we won't have to bug you for it when answers require knowing it, as outlined here.

READ THIS FIRST

[Killerace]

My apologies for not giving my location, this was an account I originally made to use for a couple of days since I couldn't log into my other account. As for why needle valves are hard to come by, I should probably be more specific, I can find needle valves here, they are just the wrong size. You see given the covid-19 situation store assistance can not confirm stock over the phone, so I have to use websites.

[FlatLiner]

Most propane refilling stations have a "work shop" that you can buy the size of needle valve you need.

[Killerace]

I did not know that.  Is there any reason to have a needle valve on the propane side if you have a regulator? Also. Is there any reason the design I specified wouldn't work?

[Latticino]

You can certainly use the regulator instead of the needle valve.  I feel they are typically more accurate and linear throughout the modulating process (i.e. one turn varies the flowrate a more fixed amount regardless of where in the adjustment you are as opposed to the needle valve where the amount of change of flow/turn varies depending whether you are close to open or not).  However needle valves are typically cheaper, act faster, and can be located in close proximity to the air valve so you can adjust your air/fuel proportion easily.  On my forge I bypass the issue altogether by using a zero pressure regulator.  This has a diaphragm that can be set to adjust the gas flow in a direct proportion to the air pressure.  So I have a setting for air/fuel ratio and a butterfly valve to modulate the forced air.

[Killerace]

Wait a second are you saying you don't even need a regulator with a forced air burner or do you mean the needle valve is cheaper than a globe valve? Because I bought a 0-20 psi regulator back when I was planning on using a Venturi burner.

[Buzzkill]

I would recommend using a regulator regardless of whether you install a needle valve.  Ideally the regulator is directly attached to, or as close as possible, to the propane source.  The reason for this is it drops the pressure in the lines going to the forge.  If something unfortunate/catastrophic does happen, do you want the full pressure and as much volume as the fittings and lines can carry from the tank spewing into your work area or a significantly reduced pressure and volume? The reduced pressure also somewhat decreases the chance of a line or fitting failure between the source and the forge.

I'd set the regulator for slightly higher output than you are likely to need and fine tune with the needle valve if you are using both.  Just my 2 cents.

[ThomasPowers]

The regulator regulates. I had a friend try to run his gas forge without one before using a valve to get the flow he wanted.  He was always having to fiddle with it as the pressure in the tank varied with use due to the chilling effects.   Meanwhile I set my regulator one time and used it all day.  A change in how things were running meant it was time to swap out the tank!