Blown Forge VS. Atmospheric

[Jon Brown]

Hello All!

I've been lurking around this forum for a little while but this is my first post, so be gentle!

I'm looking to build (or probably less likely, buy) my first forge and I'm having a tough time deciding which would better suit my needs, blown or atmospheric burners. I'm primarly plan to use it for forging blades, and I would like at sometime in the future to at least try forging some damascus in it. I think I've about settled on a horizontal design if that makes any difference.

So, I was wondering what insight you folks could provide as far as your own experience since mine is limited having worked mostly on a blown forge and only on one old NC Forge. What I mainly want to know is how the two compare as far as controlability, Fuel comsumption, longevity and anything else you may think is relevant.

Also and general forge building tips would be great.

Thanks in advance,

Jon

[Grisly Atoms]

I'm starting to build an atmospheric this weekend, copied from the ones we used in a class I took with my daughter in May. They worked well in class, get about 9 hrs out of a 5 gallon bottle of propane.

I'm definitely NOT speaking from any extensive experience, but the man who taught our class, Gordon Williams, uses them and he is very good at what he does.

I'm working off of a rough sketch he made right now, but I promised him I would draw up up a detailed CAD drawing for him to pass out in his classes. I'll pass it on here when done if there's interest.

They're relatively simple to build, mostly welding, grinding and drilling, and I should have under $200 in it when it's done. (I have a pretty good scrap pile though....)

These units are made from 10" dia. tubing, 8" long, not real big, but good enough for what I want at the moment.

[Jymm Hoffman]

The search engine here works pretty well. If you take a look at these previous posts, you might find your answer:

[jake3330]

with blown u use alot less gas but im pretty sure forge welding is easier with less air beacause it contaminates the weld area so its up to u

[BIGGUNDOCTOR]

As they say in drag racing. Injection is nice, but I would rather be blown. Just like cars, more air, more fuel, more power ARRRR ARRRR ARRRR :D

[ThomasPowers]

With a blower you can more easily use *less* air than with an atmospheric burner; I don't see what Jake is saying?

Blown are easier to make and tune but tie you too a power cord.

Both types can get to welding heat if designed right.

Blown has less problems with wind if you are in a windy area.

I have one of each and am working on a ribbon burner currently for a welding forge.

[youngdylan]

with blown u use alot less gas but im pretty sure forge welding is easier with less air beacause it contaminates the weld area so its up to u

I'm never quite sure about this. For a given volume of gas there is an optimum volume of air needed and a set amount of heat energy is released. Does it matter how this air is got, forced in or drawn in by the venturi? Equal amounts of gas in either burner need the same amount of air, if they're not running weak or rich they should release the same amount of energy ............. I think!

Perhaps the advantage of a blower is that that you can force in a lot more air, this means you can squirt in a lot more gas and so get the forge a lot hotter .... but you're using much more gas ....... I think

[ThomasPowers]

Aspirated forges need a certain amount of gas going through to actually work as it's what entrains the combustion air and so they tend to get less efficient in their burn as pressure goes down. With a blown forge the blower does the work of providing (and the mixing force) the combustion air and so you can turn them way down and still tune the burn as you like.

You are right in that per unit of gas the BTUs should be the same if they are efficiently mixed and burnt.

[Robert Simmons]

I'm starting to build an atmospheric this weekend, copied from the ones we used in a class I took with my daughter in May.

This is something of a religion debate in most smithy circles. There are advantages and disadvantages to both. However, the atmospheric forges are safer. If there is a power failure or the failure of the blower on the blown forge, the flame will soon go super rich and then blow out from lack of O2. The propane will then pool in the shop and wait for someone flicking on a light or throwing a grinder spark to make the evening news. An atmospheric forge is aspirated via the venturi effect and requires no electrical help. You can walk away from it for 20 min if you want, I wouldnt walk away from a blown one. Just make sure you have lots of airflow in the shop with either, they both eat oxygen like candy and thats oxygen not available to your lungs.

On the other hand there are advantages to blown forges. I just prefer to err on the side of safety and simplicity.

My personal opinion only, not to be taken as gospel on anything.

[Robert Simmons]

Aspirated forges need a certain amount of gas going through to actually work as it's what entrains the combustion air and so they tend to get less efficient in their burn as pressure goes down. With a blown forge the blower does the work of providing (and the mixing force) the combustion air and so you can turn them way down and still tune the burn as you like.

You are right in that per unit of gas the BTUs should be the same if they are efficiently mixed and burnt.

Thomas, not trying to be a snipe or anything but I have had my regulator so far down on my regulator that you cant see the diff between 0 and where it is at and my regulator goes down to 1 psi markings. The burner was still stable and the flame was still neutral. So I can run it at vanishingly small amounts of propane. I was trying to test how low can the burner go and it only flamed out when I had the gas completely off.

[youngdylan]

Thomas, not trying to be a snipe or anything but I have had my regulator so far down on my regulator that you cant see the diff between 0 and where it is at and my regulator goes down to 1 psi markings. The burner was still stable and the flame was still neutral. So I can run it at vanishingly small amounts of propane. I was trying to test how low can the burner go and it only flamed out when I had the gas completely off.

I take it that is when they are burning in free air, it it the same when you have them running in the forge?

Mine run lovely at almost zero psi in air but splutter and f**t when used in the forge. It's none to small a chamber .... 200 by 200mm by 600 long; 3 off 3/4" burners, usually runing 2 occasionally 1 or 3 burners at once.

[Robert Simmons]

I take it that is when they are burning in free air, it it the same when you have them running in the forge?

Mine run lovely at almost zero psi in air but splutter and f**t when used in the forge. It's none to small a chamber .... 200 by 200mm by 600 long; 3 off 3/4" burners, usually runing 2 occasionally 1 or 3 burners at once.

Yeah, it works in my brick pile forge well. As for the new one I am building, we will see.

My question would be what is the distance between the burners and the piece in the forge or the opposite wal the burner is pushing into. The back pressure may be causing problems for you. I am not an expert or anything but I know the orientation was important. When I had it firing down into the brick pile, it had a hard time, when I fired it sideways and a tiny bit up, it did fine. It was angled to hit the roof, just before the wall opposite the burner so that the gas would bounce around and not merely reflect back. Maybe tinker with your angles and see what you get? Took me a bit to get just the right spot.

[ThomasPowers]

Funny my blown forge doesn't go out if the power is cut---just burns rich out of the door.

OTOH the aspirated one can start burning badly if the wind picks up and burn up in the burner tube. A pain at an outdoor demo as we commonly get high winds out here. (Last campout we had 60mph winds at night and I would DRENCH my charcoal set up long before they started to be sure!)

Guess which one is safer to walk away from?

Of course these forges were both built in Forge building workshops put on by SOFA about 10 years ago and at least one of them the designer, Hans Peot, stood over us making sure we did it right!

Seems like there is great variability in these things and nobody should make blanket statements about them!

[Jon Brown]

Thanks guys for all the advice, and sorry if kinda kicked a hornet's nest with that question. Seeing as if/when I build this thing I will be working out of my garage with the door wide open, it seems that the blown forge would fair better in the wind. But I'm thinking if I did this I would set it up with a normally closed solenoid to shut off the gas if the power goes out (like the setup seen here about halfway down the page.) Has anyone done this?

Thanks again for all the feedback

Jon

[Dodge]

This is something of a religion debate in most smithy circles. There are advantages and disadvantages to both. However, the atmospheric forges are safer. If there is a power failure or the failure of the blower on the blown forge, the flame will soon go super rich and then blow out from lack of O2. The propane will then pool in the shop and wait for someone flicking on a light or throwing a grinder spark to make the evening news.

As stated above, there are solenoids available to shut the gas off in the event of a power outage, but even without one, I can't see how a safety conscious smith would leave the forge unattended long enough to allow the pooling effect to occur. I run my forge outside so the pooling would be minimal, but a forge should never be left unattended inside a shop or out. Its just an invitation for disaster and tragedy; Not just the danger of explosion but injury to innocent bystanders un-aware of the dangers. In the past, I have left mine running for brief periods, i.e. quick trip to the toilet, but then realized how bad that could end. Now I shut he gas off when I am going to leave visual contact with my forge. Just my 2 cents.

[Francis Trez Cole]

first of all I would hope you would be right there working and not walk away so if there was a power outage you could just shut the gas down. I have a Mankel with a blower love it I have used atmospheric they work well but have there heat limitations. I will in the future build a single burner atmospheric for my self some times the mankle is to big and heats up about 2' of steel at one time. The only advice I would offer is get one bigger than you think you will need you will grow into it.

[Nakedanvil - Grant Sarver]

We can think up dangerous scenarios all day long, any one have a real life experience along these lines? Forges should not be left running and unattended PERIOD.

[Nakedanvil - Grant Sarver]

I think people who build atmospheric forges like to tinker. There are tons of "how to's" on atmospheric forges and the assemblage of parts. With blown forges you just slap em together and go. We built one at a conference during lunch one time because the hosts monster forge sounded like a jet engine. Started with a five gallon bucket with a double layer of kaowool, poked a hole in the side for an 1-1/4" pipe, burned a little hole in the side of the pipe for a 1/4" copper gas line, stuck a hair dryer in the end and we were heating steel in 45 minutes, start to finish! Host used that forge for years. K.I.S.S.

[Marc]

I've accidentally turned off the blower on my forge and it also keeps burning, but mostly outside the forge. There's no pooling, however it's just as dangerous. Now, the flames will lick up and I can see how it might catch fire to the joists above it. A sheet of cement board up top might make it safer, but I'd rather not chance anything.

[KTB]

I would strongly recommend a CO detector for anyone using a gas forge indoors. I first used my small forge in a garage with the overhead door wide open and was feeling a bit funny afterward. A few days later I purchased and used a meter and it was screaming at me in no time. Now I roll it outside before firing it up. More recently it alerted me to an acetylene hose leak.

[Dave Hammer]

I use my propane forge inside my garage (near the door) without any problem. I check the carbon monoxide level by hanging a detector at head level on an electrical cord in the center of the garage. I do, however, have a 24 by 48 inch opening in the center of my garage for access to the attic. I always leave it open. The heat generated by the forge facilitates air movement from the garage into the attic (natural convection) and out the attic vents. In the summer time, my garage door is fully open. During cold weather, I usually have the garage door open about 4-6 inches.

Unless there is active venting, I would consider it unsafe to run a gas forge anywhere near an unvented building door (courting disaster if running in the building). A detector will verify this.

If I had a large shop, I would have exhaust fans drawing air from the building whenever I was using a gas forge.

[Marc]

I strongly agree with the CO warnings. I have a monitor near head height in the shop, which is a 2-car garage. I swapped out the "normal" overhead doors with some homemade swing-outs and put open-able windows in each door. While the forge warms up it puts out enough CO to be dangerous. But opening a couple windows and putting a dept. store fan in front of one of them clears out the CO fine. Once the forge is hot, I can usually turn the fan off with no problems.

[Robert Simmons]

I would strongly recommend a CO detector for anyone using a gas forge indoors. I first used my small forge in a garage with the overhead door wide open and was feeling a bit funny afterward. A few days later I purchased and used a meter and it was screaming at me in no time. Now I roll it outside before firing it up. More recently it alerted me to an acetylene hose leak.

That is a common misconception. A huge open door doesnt necessarily mean you have airflow. Without air flow there is no ventilation of gasses.

[Robert Simmons]

I use my propane forge inside my garage (near the door) without any problem. I check the carbon monoxide level by hanging a detector at head level on an electrical cord in the center of the garage. I do, however, have a 24 by 48 inch opening in the center of my garage for access to the attic. I always leave it open. The heat generated by the forge facilitates air movement from the garage into the attic (natural convection) and out the attic vents. In the summer time, my garage door is fully open. During cold weather, I usually have the garage door open about 4-6 inches.

Unless there is active venting, I would consider it unsafe to run a gas forge anywhere near an unvented building door (courting disaster if running in the building). A detector will verify this.

If I had a large shop, I would have exhaust fans drawing air from the building whenever I was using a gas forge.

Ya can snag an exhaust fan from home depot for 50 bucks. All you nneed is a bir of roof mastic and a reciprocating saw and it will take an hour to install and wire.

[Nakedanvil - Grant Sarver]

Wonder what kind of detector I need with my induction forge? Probable cooking my bratwurst with electro-magnetic neutrinos. But then if you live next door to a radio station.............