Help with tuning blown forge

[jsurgeson]

Posted a few days ago my new blown forge, added the blower with adjustable air gates.
As you can see below although the burners run stable, however they do not appear to burn right.

The images below are after 30 min's, and as you can see it it still no where near even
forging temp net alone welding temp.

I ran from 15kpa (2.2psi) to 30kpa (4.4psi) with little difference.
The air gates are almost closed, probably only 3mm open, any more and flame out.

I am using 0.6mm (0.02") tips.

There is obviously something very wrong with this design as my 2 burner (reil style)
made out of stacked loose fire brick got to temp in 15 min.

1. Is internal vol too big (1028 cubic inch) for 2 x 1" burners?
2. Is thick cast-able liner absorbing all the heat?
3. How to tune these forced air burners.

[Nakedanvil - Grant Sarver]

I suspect you still have way too much air. Are you able to cut the air back to where you have a lot of "dragon breath" coming out the front?You could make new throttle plates like this:

[jsurgeson]

I suspect you still have way too much air. Are you able to cut the air back to where you have a lot of "dragon breath" coming out the front?You could make new throttle plates like this:

It does not look like it but my plates are as you describe.
If I close the air completely the burners is fairly unstable, the flames burns at least
4 inches from the end of the burner tube.

[kcrucible]

2. Is thick cast-able liner absorbing all the heat?

What castable? Is it insulating? Is it backed by wool? Do you have ITC-100 on the face?



Have you tried going up to 10 psi?


Heat build up is determined by how fast you add BTUs vs how fast BTUs leak through your insulation. If it's poorly insulated then you need to supply more heat.


Firebrick has better insulation value than insulating castable from what I've read. Backing the castable with wool would have slowed down the loss too.

[jsurgeson]

What castable? Is it insulating? Is it backed by wool? Do you have ITC-100 on the face?

Firebrick has better insulation value than insulating cast-able from what I've read. Backing the cast-able with wool would have slowed down the loss too.

It is a South African product called "Verokast 1300"
It is not solid castable, it has heavy furnace bricks for insulation encased in cast-able.
The 1300 denotes its temp rating and is designed specifically for furnace use, so i have to assume
it is insulating.

Have you tried going up to 10 psi?

No only about 5psi

[kcrucible]

It is a South African product called "Verokast 1300"
It is not solid castable, it has heavy furnace bricks for insulation encased in cast-able.
The 1300 denotes its temp rating and is designed specifically for furnace use, so i have to assume
it is insulating.

That's not a good assumption. many people combine a solid refractable over wool, etc. For use in furnaces just means that it can take the heat. The fact that it contains "heavy furnace bricks" makes me think that that it's not especially insulative. Heavy bricks mean a lack of air pockets that give insulative firebricks their qualities.

I can't find your brand online to look up the specs. For comparison though, here's a vendor that sells 3 different castable refractories.

http://elliscustomknifeworks.hightemptools.com/castablerefractory.html



The top is basically not insulative..

- Density = 141 lb/ft^3
- This material has a thermal conductivity of 7.4 btu-in/hr-F-ft^2 at 2000 degrees F



The lower is called "insulating castable"

- Low thermal conductivity = highly insulating compared to Mizzou
- Density = 90 lb/ft^3

- This material has a thermal conductivity of 4.54 btu-in/hr-F-ft^2 at 2000 degrees F and conducts almost 40% less heat through the forge shell at 2000 degrees F!



Much better than the top refractory at retaining heat. You'll notice that it's much less dense. The reason that this is so is that the insulating refractable includes elements that will burn up when you fire it, leaving air pockets that increase the insulative qualities, that also makes it less dense.


You can take a "non-insulating" refractory and add your own bits that burn out (foam beads, sawdust, small fibers, etc.) I've heard a 3:1 ratio of insulative volume to refractory is good, but can't vouch for it myself.


I did an experiment (click here to read more) where I added additional shredded styrafoam and sawdust/coffee grounds to the already insulative one, and so far it seems fine though I haven't brought it up to max temperature yet. I did this at both a 2:3 and a 1:2 ratio in various parts. They both worked, but 2:3 required a lot more post-cast doctoring by "glazing" it with more binder so I'd recommend 1:2.

In my own furnace I'm surrounding this mixture with ceramic wool also, to further improve heat retension (when the heat soaks through the castable it'll hit the wool and slow down even further, keeping the heat in the center.)


The ITC-100 reflects heat, so that less enters the refractory to start with.

No only about 5psi

Try cranking it up and see what happens. I suspect it'll improve things.


If so, then you can consider whether you want to redo it with more insulative materials to cut down on gas usage.

[Nakedanvil - Grant Sarver]

Do you have some sort of orifice on the gas? With blown you don't need any. When it's running as shown, is there dragons breath out the front? Like actual flame at the door.

[jsurgeson]

That's not a good assumption. many people combine a solid refractable over wool, etc. For use in furnaces just means that it can take the heat. The fact that it contains "heavy furnace bricks" makes me think that that it's not especially insulative. Heavy bricks mean a lack of air pockets that give insulative firebricks their qualities.

The heavy brick are kiln bricks so must be insulate, in any case i have used them on their own just stacked together in one layer no cast-able and after 15 mins it is at 980 deg C, you can still put you hand on the outside, just very warm. So yeah they are insulative, and combined with castable furnace cement, i assume even better, not so?

The high tech light weight high temp board is very expensive here, as is any of the wools. Brick and cement although not ideal, was the most cost effective way.

Are you saying that I can not achieve a working solution using brick and cast-able?

[jsurgeson]

Do you have some sort of orifice on the gas? With blown you don't need any. When it's running as shown, is there dragons breath out the front? Like actual flame at the door.

No there are no openings, I built this as a blown burner not as a atmospheric type.

Except on initial ignition with low air pressure when you get a belch of soft flame, I cant get any flame to exit no matter how I adjust the gas/air.

[kcrucible]

The heavy brick are kiln bricks so must be insulate, in any case i have used them on their own just stacked together in one layer no cast-able and after 15 mins it is at 980 deg C, you can still put you hand on the outside, just very warm. So yeah they are insulative, and combined with castable furnace cement, i assume even better, not so?

The high tech light weight high temp board is very expensive here, as is any of the wools. Brick and cement although not ideal, was the most cost effective way.

Are you saying that I can not achieve a working solution using brick and cast-able?

No, not at all, I just wasn't sure the nature of your castable. As I was trying to illustrate, there's a huge difference in performance possible, and outlined one method to turn non-insulative castable into highly-insulative castable yourself... no need to buy it.



Here's one group working on creating low-tech insulative bricks by hand to aid villages that could use better cooking stoves, etc.

http://www.bioenergylists.org/stovesdoc/Still/VC%20Stove/vcstove.html

The following slide show details how to create a 6 brick combustion chamber made from inexpensive and locally available materials. Light weight, insulative, heat resistant bricks can be made from:

vermiculite 85% and clay 15%
pumice 85% and clay 15%
sawdust 50% and clay/cement 50%
charcoal 50% and clay 50%
perlite 85% and clay 15%

When you're pouring castable, you're basically making your own custom-shaped bricks. Whether they're insulating or not depends on the composition. (and how high a temperature they can take before breaking down also.)




The point still stands though, that you may want to ask your supplier for the insulation specs on the cement and compare to the two I listed. If it's edging toward the first, then it is going to take a lot more heat than the latter.

If you have half insulative brick, half no-insulation concrete, the net effect is roughly half insulation of the brick.



But if you're confident that energy loss isn't the problem, then you can move on to other things. Since you suggested the idea yourself I thought I'd give you some things to consider/research.


Best of luck! I know very little about blown burners, so can't be of much help there.

Do you have some sort of orifice on the gas? With blown you don't need any.

No there are no openings, I built this as a blown burner not as a atmospheric type.

Miscommunication here I think. He means anything that would restrict the gas flow, like a mig tip.

I am using 0.6mm (0.02") tips.

My 1" atmospheric pipe burner uses a .045 tip, just for reference. .02 is way too small for that (and apparently isn't needed at all for blown burners anyway... no point in accellerating the gas to draw in air, etc.) This could be the problem... I think .02 tips are in the 1/2" burner range and heat-class. Sounds like you may just be able to pull the tip out and try it there.

[jsurgeson]

No, not at all, I just wasn't sure the nature of your castable. As I was trying to illustrate, there's a huge difference in performance possible, and outlined one method to turn non-insulative castable into highly-insulative castable yourself... no need to buy it.

The point still stands though, that you may want to ask your supplier for the insulation specs on the cement and compare to the two I listed. If it's edging toward the first, then it is going to take a lot more heat than the latter.

But if you're confident that energy loss isn't the problem, then you can move on to other things. Since you suggested the idea yourself I thought I'd give you some things to consider/research.

No thank you, the very detailed info is more than helpful.
It makes sense to check with supplier as you suggest, either way it is not the best but \
unfortunately will have to do.

Miscommunication here I think. He means anything that would restrict the gas flow, like a mig tip.

My 1" atmospheric pipe burner uses a .045 tip, just for reference. .02 is way too small for that (and apparently isn't needed at all for blown burners anyway... no point in accellerating the gas to draw in air, etc.) This could be the problem... I think .02 tips are in the 1/2" burner range and heat-class. Sounds like you may just be able to pull the tip out and try it there.

Sorry i misunderstood Grants post, I think he has possibly hit the nail on the head when he asked the question "any orifices"

I think also the fact that I have the tip in the throat of the burner does not help as well.
Strange posted images of the burner a few days ago and none commented on that?

I will remove the mig tips tomorrow and try without..good one guys, thanks :D

[maddog]

Generaly, solid refractories are not good insulators by design. They need the heat to spread as evenly as possible to avoid mechanical stresses due to expansion. That said, what you have in your forge should be good enough.

I agree with Grant. You arent putting enough heat in to the chamber and there is too much air. You ought to see orange flames at the mouth of the forge and when its heating up it should sound loud. And you dont need an orifice. The blower is moving air for you. Try cranking up the heat, and if you dont have an air gate, for the moment you can partially choke the blower input with a piece of cardboard.

When people fire up their first forge ever, they are often timid about putting the pedal to the metal. Thats a fairly big forge. It's going to need some serious burn in there.

[jsurgeson]

Yeah well it was as you said, removed the mig tip, pulled the 6mm pipe which held the tip back to about where the air is injected and vooma!

Questions?

1. The gas oriface is now 6mm, too large?
2. Gas pressure at below 2 psi, hardly registers on gauge, if I raise, flame out.
3. Flame at burner blue, lots of orange dragons at rear and front, is this correct?
4. Is there a correct (or best) start up procedure for 2 x blown burners? had a lot of problems starting.
5. Is there a right and wrong position/order/distance between the forced air in/ gas in?



This is what i currently have, position of gas in is B, any advice on position and orifice size?

[ciladog]

Yeah well it was as you said, removed the mig tip, pulled the 6mm pipe which held the tip back to about where the air is injected and vooma!

Questions?

1. The gas oriface is now 6mm, too large?
2. Gas pressure at below 2 psi, hardly registers on gauge, if I raise, flame out.
3. Flame at burner blue, lots of orange dragons at rear and front, is this correct?
4. Is there a correct (or best) start up procedure for 2 x blown burners? had a lot of problems starting.
5. Is there a right and wrong position/order/distance between the forced air in/ gas in?



This is what i currently have, position of gas in is B, any advice on position and orifice size?

From the pics you posted, I take an opposite opinion from most of the responders thus far. It has nothing to do with the refractory lining. And, you have too little air being forced through the burners not too much. That hose connecting your blower to the burner manifold looks to be about 1 ½ inches in diameter connected to a 1 inch pipe. Then you split that down to two 1 inch burners. Lots of static air pressure but very little volume.

The dragon’s breath is excess fuel looking for oxygen so it can burn. It doesn’t find it in the forge so it burns outside of the forge. A little dragon’s breath is a good thing because it means you have a reducing atmosphere in the forge. Too much means not enough air or too much fuel.

By the time you adjust your gas to get a stable flame for the amount of air you are blowing in, you are not putting in enough fuel and you get very ‘soft’ flames. Just not enough heat for that volume of forge.

Turn the blower on, gas off, and put a lit match in the forge near the burner and see it the match gets blown out. I think you will be surprised or I will be.

[jsurgeson]

From the pics you posted, I take an opposite opinion from most of the responders thus far. It has nothing to do with the refractory lining.

Agree with you, it has nothing to do with lining.

And, you have too little air being forced through the burners not too much.

Hmmm don't think so, that blower chucks out plenty air, and yes it does blow out any flame put near it, even on 90% choke.

By the time you adjust your gas to get a stable flame for the amount of air you are blowing in, you are not putting in enough fuel and you get very ‘soft’ flames. Just not enough heat for that volume of forge.

My previous post when I said "removed the mig tip, pulled the 6mm pipe which held the tip back to about where the air is injected and vooma!"

I meant that it was now working almost perfect barring the few questions I just asked. So I have to say that the guys were pretty much on the nail for what the problem was.

I need to learn how to adjust my mix correctly, it might be that due to the design of my burners i am not getting a "proper mix" and as a result am battling to adjust without killing the flame. Also why I cant increase it above 2psi, this I suppose could be as a result of what you say not too sure.

1. Will increasing pipework from 1" to 2" from start to finish increase volume?
2. Would I then take a 2" pipe all the way into chamber?
3. How much air do you need to work with?

[kcrucible]

Yeah well it was as you said, removed the mig tip, pulled the 6mm pipe which held the tip back to about where the air is injected and vooma!

Questions?

1. The gas oriface is now 6mm, too large?
2. Gas pressure at below 2 psi, hardly registers on gauge, if I raise, flame out.

Is this inside or outside the forge? It means the velocity of the exhaust is too high when you crank up the pressure. You could try dialing back the air pressure and see if it stabilizes. Sounds like your fuel-air ratio is ok-to-too-rich as it is though, so even if it's interesting from an experimental standpoint it'd just be wasteful and wouldn't increase temperature anyway (all the extra fuel is going to burn OUTSIDE the forge.)

You could always try adding a flare to the burner output to slow down the gas, but I don't think that's common with forced air, particularly inside a forge. If your burner inlet isn't expanding as it enters the forge, you could always dremel out a tapered cone. This would serve as a functional flare, and should make it easier to get a stable flame at the higher velocities.

3. Flame at burner blue, lots of orange dragons at rear and front, is this correct?

If you're trying to keep your piece from oxidizing rapidly, yes, I think that's what you're looking for. There's not enough oxygen to fully combust. Ideally you want just-a-little orange/yellow if you're trying to maximize fuel-efficiency though since the longer the yellow flame the more fuel is leaving the forge without getting combusted, basically pushing the heat to the outside air instead of in your forge cavity.

4. Is there a correct (or best) start up procedure for 2 x blown burners? had a lot of problems starting.
5. Is there a right and wrong position/order/distance between the forced air in/ gas in?

No idea. For #5, I don't think it really matters a huge amount on a blown burner. I think your B position is just fine... I've seen other schematics that do that. If you push it too far in you're reducing the cross-sectional area that fuel-air can occupy to get into the tube. Too far back and you may have a harder time getting them mixed.

Orifice doesn't matter except as it may block off some pipe depending on positioning, etc. You're just dumping propane into the tube. Volume and speed of propane is dictated by the regulator and blower vs tube diameter.

1. Will increasing pipework from 1" to 2" from start to finish increase volume?
2. Would I then take a 2" pipe all the way into chamber?
3. How much air do you need to work with?

The larger the pipe is for a given quantity of gas/air, the slower the gas moves. At a given magic-velocity your flame stabilizes. Going up to a larger pipe would slow down the gasses exiting from the burner, making it easier to get a stable flame. You should probably experiment with different tube diameters. That's functionally what the flare is doing, but again, as a blown burner the dynamics of the tube are a lot less important. maybe start with a reducer jumping up to 1.25" and see how that changes things.


But again, I'm no expert... just my understanding of things. I'm happy to be corrected in the particulars!

[jsurgeson]

Thanks kcrucible, I need to play a bit now and see what happens.
Going forward i might just re-plumb the burners with 1 1/2" straight through and get proper gate valves for finer control.

I cant find any plans for blown burners like there are for atmospheric (reil, mod side arm etc etc), any links you know of?

[kcrucible]

Not a whole lot of that that I can see. I guess they're so easy to get running that no one bothers documenting things in detail. You can eyeball some people's works though.


http://www.jamesriser.com/Machinery/GasForge/PropaneForge.html

http://elliscustomknifeworks.hightemptools.com/burners.html

[Dodge]

FWIW, I'm using 1.25" pipe with a .06" gas orifice. One blown burner brings my forge to temp in about 10 minutes. I can weld at 7 or 8 psi and it will idle at 3 or so. Chamber is 6" x 15" Inswool covered with refractory mortar. No ITC 100 like coating. Just the mortar. I made my air gate, just a blade that slips in the air pipe, so it can go from essentially closed to wide open but generally is only about 1/4 way open. Sorry, I have no idea what the fan's CFM is.

[edge9001]

here are the plans used to build mine. works pretty well so far, only have one problem with a few deviations the builder had made. I hope this helps

[pkrankow]

Jymm Hoffman's proven design. Blown burners are very simple but require electricity.



Phil

[kcrucible]

Very nice, edge. I tried a ring based flame holder with my atmospheric and it did not work well at all because of the back pressure killing the venturi action of pulling in combustion air. The blown shouldn't care about that.


Just found another link that documents several forges/burners, including some blown ones.


http://forgegallery.elliscustomknifeworks.com/

Indian George's and Michael Birche's look useful to you.


Sorry I can't post direct links.. they're doing some funky html stuff.

[jsurgeson]

Thanks guys, that should keep me going for a while :D

[ciladog]

Agree with you, it has nothing to do with lining.



Hmmm don't think so, that blower chucks out plenty air, and yes it does blow out any flame put near it, even on 90% choke.



My previous post when I said "removed the mig tip, pulled the 6mm pipe which held the tip back to about where the air is injected and vooma!"

I meant that it was now working almost perfect barring the few questions I just asked. So I have to say that the guys were pretty much on the nail for what the problem was.

I need to learn how to adjust my mix correctly, it might be that due to the design of my burners i am not getting a "proper mix" and as a result am battling to adjust without killing the flame. Also why I cant increase it above 2psi, this I suppose could be as a result of what you say not too sure.

1. Will increasing pipework from 1" to 2" from start to finish increase volume?
2. Would I then take a 2" pipe all the way into chamber?
3. How much air do you need to work with?

Well, I did say one of us would be surprised so I guess it’s me. I’m no guru when it comes to gas forges but over the years I have bought some and built some. All of the forges that I bought, I returned after trying them out. I don’t like atmospheric burners. They roar like jet engines and I can’t here the radio in the shop. So now all my propane forges are forced air. But I did learn a little along the way.

There are three things that have to be right for a forced air forge to work correctly.

The first is that you need to be able to burn enough fuel for the size of the forge to get it up to heat. Fuel consumed equals BTU’s. In order to do that, you need enough air to burn the fuel efficiently. You need to be able to control the air fuel mix as precisely as you can.

The second thing is to make sure that you can overcome back pressure in the forge. Ideally there should be no back pressure. What flows in by volume should flow out without any restriction.

The third thing is that the fuel and air need ample time to mix before they enter the forge for good combustion.

I just finished building a new forge for knife making. It’s long and narrow. I made a manifold that branched off into two 1 inch burners that came into the forge from the side. Well, after futzing with it for a few days, I could not make it work. So I decided to go radical and make a side blast ceramic ribben burner for the forge. I could not be happier with the results. Forty minutes after a cold start I had a pool of metal in the forge.

[jsurgeson]

I just finished building a new forge for knife making. It’s long and narrow. I made a manifold that branched off into two 1 inch burners that came into the forge from the side. Well, after futzing with it for a few days, I could not make it work. So I decided to go radical and make a side blast ceramic ribben burner for the forge. I could not be happier with the results. Forty minutes after a cold start I had a pool of metal in the forge.

Well it sure burns great, and appears to support what you say about "more" air and not "less"

Do you have any other images/details of the "side blast ceramic ribben burner"

I dont have a needle valve on my gas, which also makes it hard to tune.