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forced air vs. venturi?


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#1 Tristan

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Posted 11 May 2005 - 11:54 AM

whitch burner is to prefer and why is it so?

#2 Guest_TimCrocker_*

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Posted 11 May 2005 - 04:50 PM

I like forced air much better. More air + more gas = more heat. I've tried both and he forced air units get up to temp alot faster. It makes it easier to weld and if you also do stock removal the unit gets a more even heat for heat treating stainless. It shouldn't be hard to meet up with a couple of makers so you can see both.

I've seen some people who prefer not to use forced air on their portable units because you don't need power. More common for demonstrations and ferriers.

#3 Kristopher Skelton

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Posted 11 May 2005 - 05:59 PM

I use forced air, too. In fact, I just picked up a new blower from surpluscenter.com for my upcoming rebuild. it's pretty simple- don't make the pipes too short to get a good mix, don't have the blower up too high to get a good mix, don't have the gas too low to get a mix that will burn at the heat you want and don't have any leaks in your pipes. Like ^^^ said: more gas+more air = more heat. Kind of like making your car go faster :D

The problem I have with the Venturi style is that there's a lot of precision necessary. holes that are 0.065" aligned perfectly with the center of a piece of pipe I bought at Home Depot, and I need a flare at the end that's either 11, 12, 15 or 16 degrees (or whatever angle happened to work for the materials that the person writing the tutorial was using)??? No, thanks. It seems like people spend more time fiddling with the thing than they do actually using it. I'm probably grossly misinformed, but that's just what I've seen.

Also, the one person I know that uses venturis for regular blacksmithing has to use blowers to get to welding temp for his damascus anyway. So I'm thinking that they're not worth the trouble. If I had his setup, I'd run the blowers all the time but use less gas to get the same temps.

Edited by engineerboy, 11 May 2005 - 06:03 PM.

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#4 Tristan

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Posted 12 May 2005 - 01:53 AM

So with the forced air you get better heat with less propane, because of the higer air pressure? Or is it just that you actually can use both more air and propane?

/Trying to save some expensive gas

#5 Jesse Frank

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Posted 12 May 2005 - 06:42 AM

I just switched to venturi burners and am quite happy so far. I was welding yesterday with a VERY small 1/2" sidarm.

So far, these seem to be much more efficient than my forced air setup. Pressure readings can be deceiving, it also has to do with the size of the orifice; I will generally use more gas at the same pressure with my old forced air unit than with these sidarm burners. I also feel like I have more control now, and that is after only a couple months as opposed to several years with the forced air setup.

IMHO, I think alot of the problems people have with burners not being efficient has to do with the forge. A well insulated shell will work very well with very little in the way of BTUs being put into it. Also, look to the size of the forge. Many of the forges Ive seen around(and bult/used myself) are just way oversized for the work bring done in them.

If you are going to use kaowool, use at least two inches, three is better, and put some sort of hard refractory in the bottom to help hold the heat, minimize bounce, and catch flux.

Check out posts by Don, Mike Blue, and Randal Graham, lots of good info from them........

Edited by Jesse Frank, 12 May 2005 - 06:47 AM.

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#6 R.H.Graham

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Posted 12 May 2005 - 09:03 AM

Although it's true that generally more air plus more fuel means more heat, the idea that forced air nessecarily makes more heat, and gets hot faster than a proper venturi forge is just wrong.
Design of the forge as a whole is more important than how it's aspirated.

The forge pictured here has a casing 8 by ten inches long, a single 3/4 bore venturi burner, and will reach 2000 F in about 30 seconds. add more fuel and it will reach 3000+ in about 3 minutes.
Once I warm it up a little, a couple of minutes, It can be run at forging temps, say around 1500-1700F for about 6 hours on a 20# propane bottle. It very easily reaches welding temperature, and with the needle valve one easy adjustments stokes it up, or pulls it back to an idle.

In my expierience the biggest problems with burners and forges of any kind is the penchant for folks to over-engineer the system to the point of silliness. flares, screens, flame-holders,complicated mixing devices, gates on the air-lines, you name it, we'll try it.... and none of it is nessecary.

Before I got onto the forge and burner style I use now I used Don's design for nigh on 10 years... simple blower and flap valve, reducer on the end of the pipe, and a needle valve dumping directly into the tube. Still got it, it still works, 100%.

Biggest isssue with venturi set-ups is lack of pressure at the burners. Some won't, or can't, run the line pressure to high enough levels to get efficient use of the venturis... in which case, the blower burners are a much better set-up...needing volume instead of pressure. Venturis are exact opposite, don't need much volume, but require the pressure. You need to be able to get to at LEAST 50 psi, like you can with the regs that come with NCtool forges and stuff like that.
I prefer tank pressure on the line, around 80-120 psi.
yeah yeah yeah, I know, safety nazis say that's unsafe... whatever, I think that's bullshit personally, same guys got oxy-acet rigs in thier shops and probably never once in thier lives had thier regulators updated and checked....
anyway, I'm doing tutorials on forges as we speak, and will have them on my site in a month maybe. Simple venturi setups as well as forced air.

keep it simple, regardless of design.

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#7 Romey

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Posted 12 May 2005 - 02:56 PM

Im with you Randall, i think the reason first generation venturi burners didnt work was due to poor refractory as far as heating a forge,i.e. satinite. Using satinite you would need forced air but with the refractory we have now days my single burner adjustable venturi once up to heat which doesnt take long can hold welding temps at a very very low pressure,AND being my nozzle is adjustable i can easily control my fuel mixture as well. I just mashed a 2x2x12 billet with no heating trouble at all.
Good example is a buddy of mine who is a blacksmith had a first gen forge and venturi with burner coming in at the top straight down , he would have hell heating steel up and zero for welding temps also scale like a poorly run coal forge. I took it, brought the burner in at a tagent,relined with kaotuff-c instead of satinite and his first gen Rom Reil venturi burner welds like a big dog.
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#8 R.H.Graham

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Posted 12 May 2005 - 06:38 PM

Actually, the forge pictured above in my post is lined with a single layer of inswool and covered with satanite. I think satanite works just fine, or at least it has for me.
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#9 John Frankl

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Posted 12 May 2005 - 09:39 PM

Randall,

I am SO all over those tutorials!!!

Mouth watering,

John

p.s. Until they are up, please confirm:

3/4" pipe by how many inches long?

(4) 1/2" holes around top of pipe.

.030 orifice: TWECO tip, or simply drilled into a pipe cap?

Diameter of pipe going into top of burner and method of attaching pipe?

Thanks,

JOhn

Edited by John Frankl, 12 May 2005 - 09:44 PM.


#10 csc

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Posted 13 May 2005 - 08:55 PM

This is a pretty good looking burner from the tutorials section of the knifenetwork board. looks like something that could work with a tweeko tip. it seems pretty large with a 1 1/4 pipe going into the forge. I also am looking forward to seeing the tutorials from Randal as I have wanted to goto a venturi for welding but havn't found a burner that I have been really happy with, but I havn't experamented with it too much yet.
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#11 Walter Sorrells

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Posted 17 May 2005 - 10:58 PM

I like venturi burners for the simplicity. I can weld at 12 lbs pressure on my rig. 15 to 18 is better. I can forge at 5 or 6 lbs pressure. All the stuff is home-made, based (roughly) on Ron Reil designs with the Tweco nozzle. Black iron pipe with the venturi mouth made from an old oxygen bottle from my Mapp gas welder. I use a piece of tinfoil for the choke. The flare long ago scaled away. And it still works great.

Electricty goes out, no sweat, I'm still working. I walk out of the shop for a quick glass of water and the electricity goes out, no sweat, my shop doesn't explode. It's quiet, too.

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#12 R.H.Graham

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Posted 17 May 2005 - 11:35 PM

I started out with burners kinda like Ron's, and later used some of his pipe-fitting burners, and still got a couple of them I use occasionally and they work great.
Simple is good.

yeah, some venturis work on lower pressures too, especially if they have somewhat large orifices like welding tips ( which have much larger holes incidentally than the markings state... an .030 tweeco for example is made for .030 WIRE... it's much larger than .030, or the wire wouldn't go through it.) I find they don't have the range or the top-end that a high-pressure venturi will have, but the differences in practice are hardly noticeable in most operations.
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#13 josh powell

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Posted 18 May 2005 - 10:11 PM

I've been using a modified sidarm burner for a while now. The sidearm burner seems to eliminate a lot of the difficulty that I had tweaking the Ron Reil design venturi burners. With the burner design using ward tee's, things are a little easier to get adjusted properly. There are really only a couple of variables: the distance of the fuel jet from the mouth of the venturi, the apperature size in for the fuel jet, and the setting for the choke. Each is easily modifiable; the fuel jet size is swappable simply by exchanging MIG tips, the distance is held in check by a set screw, and the choke on my forge is just a rotating flap that covers the air inlet.

The only parts that are hard to find are the Ward tees and the flares, and I felt pretty okay about ordering them from Larry Zoeller, who publicized the burner design. The machining for the burners is easy, consisting of drilling about a 1/2" hole in a 1 1 1/2" pipe plug, and a couple of holes that need to be tapped, to hold the fuel inlet and the choke. If you are ok with a hand drill, you could do it that way, or a bit more precisely with a drill press.

http://www.geocities...ge/sidearm.html

I'm guessing that my two burners get the forge (6" diameter x 24" length, two inches of inswool and a top coat of satanite) to about 2400 degrees at 25 psi. I suspect that if I bumped up to a bigger regulator, or coating of ITC 100 over the satanite, I'd be pushing 3000.

I'm also getting ready to build some burners for a pair of forges for the local community college. I suspect that they will be a modified, modified sidearm design, using Don's basic burner design, and an assembly method similar to the ward burner. They are going to be constructed from a 1 1/2" tee and pipe nipple, with one end as the burner, one for air inlet, and one with a pipe plug for drilled out for the fuel jet.

I'm using them for a test bed for some burners for a bronze casting rig, also, which is the reason that they are blower powered, saftey concerns, you see. The burnout oven needs to stay at about 1100 degrees f for about 36 hours to burn out the wax and cure the molds, and I don't want to have to babysit it constantly. In conjunction with a solenoid valve on the gas line, I hope that this will give me a little bit better saftety and heat. I'm sure that I could accomplish the same thing with a venturi system, but I haven't built any blown burners yet, and I want to just for the sake of it.

Anyone know where to get a #20 pouring shank and lifting tongs cheap, or of a set of plans in a book or online? I'm probably just going to end up copying a smaller pair that I have access to, but a print would be nice to have.

josh

#14 Sweany

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Posted 19 May 2005 - 01:25 PM

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#15 Protactical

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Posted 20 May 2005 - 11:04 AM

Setting up with a burner is the same as setting up with a propane torch, or BBQ. If they are properly designed, there isn't any reason to have to use a fan to make them work. There is less risk of flashback if you use a jet system than one that depends on positive pressure from a surplus fan. On the other hand, both systems work, and they can also be combined, so there isn't any one answer.

Michael Porter has written an excellent book on making your own high efficiency venturi burners. The bottom line is that you need a narrow and long accelerator tube to get high efficiency in the gas jet, which in turn leads to a complete fuel air mix. My own experience with Porter's recipe, however, was that it cost a lot more to make his form of V burner, than to buy the superior Hybridburner.com T-rex, so why bother. Rex is basically selling his high efficiency burners for what an upper end propane torch cost, and they are an outstanding deal. While I enjoyed reading Porter's book, none of his stuff is really worth building.

I think a lot of the problems with V-burners come from trying to assemble them from plumbing parts. At least locally, the made in China crap we get is so inaccurate that it just becomes an exercise in frustration. If you have a lathe, it is far easier to fabricate these burners out of tubing. Making the rocket jets is a waste of money, and the best source or those is from Zoeller forge, he sells them for less than I can make them. Cutting up the OA torch parts as recommended by Porter would cost me more locally than buying a rex and importing it. Also, assembling the full Porter burner from Zoeller doesn't seem particularly cost effective compared to the Rex. I think you need to either make your own from just the Zoeller jet, or buy a rex. At my prices those are the only two options.

If Zowada's crucible is all it is cracked up to be, we have a pro parts forge, composed of his enclosure, and Rex burners, for under 500, that is way better than the Mankel's etc..., and with few of the hazards and maintenance costs of a lot of the products being used out there.

One o fthe ironies of making your own venturi is this:
1) One does it to save money (and have fun doing it), by by-passing the ready made Rex burner.
2) Success depends on sourcing a bunch of name brand parts. This particular plumbing fitting manufacturer's pipe, that particular welding tip.
3) The local suppliers are just as anxious to avoid spending top dollar for these name brand parts, so none of the required name brand stuff was actually available, and I spent more than a Rex-burner's worth on gas tracking down stuff, most of which I could never find. I never found the sidearm joint part that actualy lines up with the nipple center, for instance.

#16 John Frankl

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Posted 21 May 2005 - 11:22 AM

I agree. The T-Rex appears to be awesome. I play with venturi burners to learn and for fun, but I can't see building a better one for less money, to say nothing of time and effort. Reading Ron Reil's site mostly convinced me to try one, but after I read on old post by Howard Clark saying he used one in his salt pots, I had enough info to try one. I have it now and will test it soon.

I want to get my hands on one of Randall's too, but I am limited to under 20 lbs of pressure on my propane, so I'm not sure. Have to ask him.

The funny thing for me is I like venturis for their low end--I can't get my Fogg burner cool enough for heat treating :) For welding I really like forced air.

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#17 DFogg

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Posted 21 May 2005 - 12:40 PM

Smaller blower, smaller pipe.

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#18 Glenn Moulton

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Posted 22 May 2005 - 07:09 AM

I went to a new blower recently and had a little trouble getting the temp down to heat treat also.Just a slightly larger blower that I knew would do heat treating and be hot enough to do whatever else I wanted.Turned out the blower motor has vents for cooling it and the blower draws air through the blower motor increasing flow to the forge.Just a little duct tape over the motor vents made it to where almost all the intake could be choked off making it more controllable.A lot of blowers dont have a good seal between the blower housing and motor creating another place to draw unneeded air.A little caulking can help that a lot.Even the wiring junction box where the ac line goes may have a unused knockout that would allow more air to draw into the forge.

#19 John Frankl

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Posted 22 May 2005 - 12:10 PM

Thanks Don. I am building a couple right now--one with a 1" and another with 3/4" pipe. But I haven't been able to find a smaller blower than the 15 cfm from Surplus Center. Any ideas?

John

#20 DFogg

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Posted 22 May 2005 - 01:51 PM

Reducing the pipe size will have a big effect because any constriction reduces the air flow. You might also try running the pressure way down. I am using 1/2lb on the drum forge, running off a plain gray regulator.

It is simply a matter of btu's, reduce the amount of fire going in until you are in the range you want and vice versa.

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