gas forge burner question

Let's see :
1. when you have a 3000 degree power cord for the blower 2. when you have to force more air than is reasonable
3. when you never have to be away from a wall plug.
Actually either way works just fine. Just be careful with the blower and power. Having a venturi it simply requires a gas source.
Might be nice to have it both ways - two torches. One for local work and another for use when you haul it over to charlies or to the club meet or ..... Sometimes those places are at the edge of a mountain where some ore is located, or other fun job.
Martin
Martin H. Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net NRA LOH & Endowment Member NRA Second Amendment Task Force Charter Founder IHMSA and NRA Metallic Silhouette maker & member http://lufkinced.com /
Rusty_iron wrote:

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Martin H. Eastburn wrote:

You can easily set up a car battery and a cheap inverter to run your blower when your "in the field"... I've done it, it's really not a big deal. I find the increased effeciency more than make up for the inconvienience.
Really, I think it's a matter of which is *more* inconvienient: filling up extra propane tanks, or running a blower. I haven't made any effort to measure it, but I get a lot more heat out of a blown burner than a venturi-style one. I haven't really tried to tune the burner to be totally effecient, either.
BTW, right now I'm running a poor-man's recuperative burner (w/blower). The recuperative burtner is loosly based on the Sandia recuperative one, just made with inexpensive Home Depot parts. Basically it's just a Riel-style burner run inside a "sleeve" of larger 2" pipe. The hot air from the forge rises up the "sleeve" and exits out a T- fitting. It's fairly basic, but seems to work well. If any one wants to know more I can send some pictures.
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snipped-for-privacy@rgs.uci.edu wrote:

I don't know about expensive, I use one 9kg tank (20 litres of gas) of propane in about 4 days solid effort running a 2 burner propane forge running at 15 psi. The same 9kg tank will last about 4 hours when running at 300kpa in a melting furnace. No air source, all naturally aspirated. To refill a tank costs $25 AUD, and refill 5 is free.
If I were to add air, I would definitely be able to get higher temperatures, with the cost of adding a lot more oxygen.

Pictures, yes please :-)
Regards Charles
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Rusty_iron wrote:

It depends on what you want the forge to do. There are ups and downs to both. I've got an old four hole Johnson that's set up for 'city gas' and forced air. It will get plenty hot enough to weld, about 3000 degrees on a cold winter day. It cranks out roughly half a million BTUs into a 24"x4"x 5" box. It has an 8" centrifugal impeller driven by a 1.5 hp electric motor at 1800 rpm.The fuel feeds into the compressor inlet through a 1/2" gas line. The upside is that I get absolute control of the atmosphere by controlling the fuel and the total air into the blower with a choke plate on the air inlet and a flow valve on the fuel. The down side is that it isn't portable. Methane, 'city gas', has more BTU potential than poopane, being a shorter chain hydrocarbon, and more reactive. Poopane has portability.
Atmospheric burners are limited in their output by several factors; fuel feed pressure, air inlet size, mixture jetting. Since air is entrained by the passage of the fuel through the venturi sectiuon, fuel pressure has a direct relation to how much air gets mixed, as well as jet size. Atmospheric burners are more 'finicky' about mixture, which has a direct beasring on flame temperature at trhe burner face. Even with a well engineered burner, you can get lass than desirable results if the box volume is not matched to the output of the burner, and this includes the design of the box exhaust as well. A fire that can't breathe won't get hot.
If portability is your more important factor, go with a venturi system that's been tuned by a professional builder, there are lots of good ones on the market. If you don't need portability, go with forced air and gain a wider range of operation parameters.
One word about forced air... don't turn your back on it until it's up to autoignite temp in the box. I've had flameouts, backfires through the compressor, hung starts, stuff like that. You'll want some sort of inline fuel interlock valve to cut the fuel flow if you lose power to the compressor. It's kinda like an early jet engine, sounds like one too. Air first, then add fuel, not the other way around.
Charly
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Good summary. My additions: 1.What Charly said about exhaust with a venturi forge is certainly true. But what this also means is that every time you move a firebrick around to close off the front door a little, you have screwed up the mixture somewhat. Many people don't realize the impact this can have.
2. Regarding flame-outs, etc. Some burners are more robust than others. SEE them work. See if they are fussy for the first couple of minutes. The one I use NEVER goes out unless there is an out of fuel condition. Even then, it takes many minutes of lower output before there is any danger of a flame-out. Once the forge is hot, even a temporary loss of fuel (someone steps on the hose) shouldn't be a problem because the forge should auto-re-light from the glowing insulation. Of course the safest system is one that shuts off the fuel if the pressure ever drops low, there's a drop of power, or if the heat goes down. And then the system won't resart without starting the lighting sequence from scratch, like a gas water heater.
Don't choose until you have seen both styles doing the heating the YOU want to do. Our group, the Guild of Metalsmiths is planning a "Gas Forge Clinic" to deal with this exact issue. It will be an event where the experts on both sides discuss (argue and hit eachother) why their way is the only way, and tell stories about their favorite designs. Actually, there are about a hundred different sides to this issue. The observers get to take all this in. ----We have been looking for people brave enough to head this up for about 3 years.
Pete Stanaitis ----------------------------
Charly the Bastard wrote:

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spaco wrote:

I mentioned the interlock because my unit feeds gas from the city main directly into the inlet of the comprrssor, and if the AC goes down there's nothing to stop a build up in the compressor housing and the manifold, other than the interlock. So far, I've been lucky, all I've lost are my eyebrows. Gas explosions can be catastrophic and deadly. Better safe than sorry, solenoid valves are cheap and reliable. Art is not worth getting blown up over. Since you mentioned low pressure conditions and someone stepping on the feed hose, I assume you're using Poopane.

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Charly the Bastard wrote:

'Compressor'? compressing the gas?
We're on a street where there is only low pressure gas (just a couple inches of water), the cost of a gas compressor and storage and compliance with all the regs was more than complying with the regs for coal.
Or are you managing welding heat with low pressure gas?
Or are you lucky enough to have a high pressure main?
- Carl
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I've never seen that. :/
IME just the otherside of the meter and its 4 psi pressure regulator, the natural gas is like 125 psi.
Did I miss something?
Alvin in AZ ps- poopane, huh? :/ pps- well then, NASTY GAS to you! ;)
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Carl wrote:

Yep.
Compressor, like the compressor half of a turbocharger for a car. Snail housing into a manifold to the box, burners are just holes in the box wall. Choke down the inlet and the gas gets sucked out of the pipe and into the inlet. The impeller will put up about six pounds above atmoshperic ambient boost, just like a turbo in a car. It sure makes the gas meter spin when it's running full out. Regs? What are those? This is a 'hobby'. I can make 12 Large a year on a hobby here. There are stringent regs for coal, EPA and all that, but nothing for natural gas. All the gas company cares about is that I pay the bill on time. They love me.
Charly
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