Help with fine tuning new gas forge

[jsurgeson]

Hi all

I recently completed my first gas forge, although it works quite well most of the time I am having problems getting it to work well all the time.

It starts ok and runs fine on both burners for 20 - 30 mins.

Back burner then starts to stutter, flame goes soft and burns inside burner tube, no adjustment of choke from full closed to full open makes any difference.

If I turn off gas to that burner and back on, it runs ok for a few seconds then goes wrong again. Front burner seems to run ok all the time by itself, although it appears to battle to run at pressures below 10psi once hot.

Can a faulty regulator cause this?

Please explain what are the conditions for stuttering, a soft flame that burns in the tube. Is it too much, lack of, gas/air etc.

If it starts and runs ok for a while what is changing to make it run badly?

I have used the water trick to make sure both jets are aligned correctly.

Both burners are identical in theory, specs of forge/burners below.

Dimensions are:
Internal:- 4.5" x 4.5" x 16" (115mm x 115mm x 406mm)
Burner:- overall 12" (300mm) 10" tube 2" reducer (2" - 1") burner has no flare
Jet:- 0.6mm mig tips

[Dodge]

When you said regulator, it made me think of the tank. What size is it? What is the air temperature you are working in. Is the tank frosting up? Looks like its getting nice and hot though :D

[jsurgeson]

Hi Dodge

Sorry for delayed response, was very late when I posted.

It does get nice and hot, image makes it look nicer than it actually is, but it definitely gets hot enough.

The tank is a 20lb (9kg) bottle, (It is marked as 11.2kg thats bottle incl)
Ambient is 20 - 30 degC very humid
Tank does not frost up

If I turn the pressure all the way up when full it max's out at about 16psi.

Why I thought possibly regulator, when you first turn it on you get a loud thud a fews seconds after opening bottle before regulator opens and allows gas, also pressure adjustments seems to be erratic, but thought it was more the gauge than the regulator.

But then if it was anything to do with bottle/reg etc it should effect both burners, not so?

[jsurgeson]

Ok this is what I have done so far to try and pin point the problem.

Problem:- Back burner starts to stutter after 10 - 20 mins
Action:- I reversed the burners so back is now front.
Result:- Problem moved to the now front burner.
Conclusion:- Problem is related to that particular burner, this then excludes position in forge, size of forge, back pressure, opening sizes back and front.

Further observations:-
Gas pressure, on starting 8-12 psi, on fault 4-5 psi.
One burner works fine at this pressure but the faulty one wont.
Burners are theoretically the same, but obviously not.
When left off overnight, next day pressure back up and all works ok again.

Questions:-
Why is pressure dropping?
Can a faulty reg cause this?
What causes one burner to not work at lower pressure while other will?

[jsurgeson]

I thinks I have solved 50% of the problem :cool:

I am no expert with regards gas, but here goes, the pressure is dropping after 10 - 20 mins because:

At 10 - 15psi the consumption is higher than the bottle can supply (vaporise), so after a while most of the gas is liquid and cant supply the required pressure. I assume a larger capacity bottle, say 40lb (18kg) min should solve that problem.

It unfortunately does not explain why the one burner works down to 4psi while the other wont.

Any help with a list of things to check or possibly reasons based on other experience with this problem would help.

[jimbob]

put the tank in a pail of water it sounds like its iceing up

[jsurgeson]

Hi jimbob

Thanks, I checked that and the tank was not getting cold at all.

I changed my 20lb tank for a 40lb tank and that has solved the loss of pressure problem but has not solved the stability on one burner problem.

I think that although the loss of pressure problem caused the one burner to run badly, even with bigger tank running at constant 12psi it still misbehaves, but not as bad. So I think that it still has something else that is causing it to run badly, but blowed if I can see what.

[Brian D]

Can you give a little more information of your burners?

You mentioned you have verified the alignment of jet along the burner axis... Are both jets positioned the same in relation to the intake opening?

What is the overall length of your burner tubes?
Tubes that are incorrect length will cause problems.

You mentioned you have not burner flares?
I have found that burner flares or flame holders provide for more flame stability. I use stainless steel for mine and try to set them back into the refractory material as far as I can and use the refractory material to continue the taper of the flare.

Did your burners perform well when outside of the forge? Mounted in vise or something...

[jsurgeson]

Hi /D

Thanks, first post has full forge spec, but quick version:

Overall Length:12" (Reducer + Tube)
Tube Only Length: 10"
Tube Dia: 1"
Reducer Length: 2" (2" - 1")
Jet:- 0.6mm mig tips

Both jets are positioned in throat pretty much the same position, within 2mm.
Tubes end at inside face of forge.

After reading many posts I came to the conclusion that flares did not seem to make much difference except when running outside of the forge. I have never run them outside, dont see the point as they are not going to work there. Also the fact that one burner works ok all the time seems to confirm no flare is needed.

[Brian D]

I asked for more detail on burners mainly regarding jet position related to intake.
It was a little tough to glean from photo.

I asked if you have run them free air outside of forge because they are a lot easier to tune and make adjustments outside of the forge.

You can get a burner to run without a flare......BUT.

You will get a burner to stabilize and behave better if it has a flare.
A burner with a flare will draw more air in the intake due to higher vacuum created from the burner tube to flared nozzle transition. (It creates a smooth pressure differential at the nozzle)

It sounds like you have a definite difference between the two burners.

Are both burner tubes exactly the same length?

Are there any restrictions or burs or obstructions on one of the burners?

Does the mounted height of one burner differ to the point where the refractory interferes with the gas flow?

When fired up initially, do the burners perform exactly the same until the forge gets up to heat? (is the burner performance affected by excessive heat)


Just a few questions you have probably already ran through the think tank....

[jsurgeson]

Hi Brian

Thank you for taking the time to answer my questions

What you say makes a lot of sense, especially with regards the flare, what do you suggest in terms of dimensions for a suitable flare, also does the flare reside inside the forge wall or protrude into forge?

The jet points for both burners are located as shown in image give or take some manipulation to aim them down the center, but they started off in approximately the same position.

How critical is the position? would say a 1/4" difference in position create this problem?

Do you think my position of the jets is correct in relation to the throat?

Burner tubes same length.
No restrictions or burs or obstructions that I can find.
The burners are about the same in terms of stability however the bad one requires the choke to be a lot more closed to run stable. The length of the blue flame is a lot shorter (1 1/2" or less) than the stable one. The good one I can adjust choke from almost closed, greenish flame (rich I assume) to soft orange flame with almost no blue flame (lean) and stable in between with a nice 2" - 3" blue flame extending from end of burner with softer orange filling space.

The bad burner only burns stable in one position (choke) anything else make flame unstable. This position changes very slightly as the forge heats up till it starts spluttering continuously.

I also have a 1/2" gap around the burner tubes and forge wall?

[Frosty]

Jeff:

There will always be minor variations in these things. Something's different obviously but you guys have already run through the most likely. I'll give it some thought and get back.

Frosty

[Brian D]

Jeff,
Sorry for the delay in getting back to you....Had some things to do to keep the peace with the wife..

what do you suggest in terms of dimensions for a suitable flare, also does the flare reside inside the forge wall or protrude into forge?

The flare should have a 1:12 internal taper and be made of stainless steel pipe or tube that will slip over the burner tube. Plan for a 3/4" to 1 1/2" (tuning range) section of the flare to protrude past the end of burner tube.

Stainless steel will help the flare to hold up longer to the extreme heat. Mild steel will deteriorate very quickly.

Do not allow the flare to protrude into the forge chamber! Even a stainless steel flare will not last long in the forge chamber. I like to leave the flare recessed into the refractory material (about 1") and then cut or form the refractory material to follow the taper of the flare into the forge chamber.


The jet points for both burners are located as shown in image give or take some manipulation to aim them down the center, but they started off in approximately the same position.

How critical is the position? would say a 1/4" difference in position create this problem?

Do you think my position of the jets is correct in relation to the throat?

I would say that 1/4" variation COULD make a difference, depending on how close to the edge of the Performance range the tips are positioned.

It looks to me from your sketch like the position of the jets or tips could move out slightly. (further away from the tube) But this may be difficult to do, depending on the way you have them mounted.



Burner tubes same length.
No restrictions or burs or obstructions that I can find.
The burners are about the same in terms of stability however the bad one requires the choke to be a lot more closed to run stable. The length of the blue flame is a lot shorter (1 1/2" or less) than the stable one. The good one I can adjust choke from almost closed, greenish flame (rich I assume) to soft orange flame with almost no blue flame (lean) and stable in between with a nice 2" - 3" blue flame extending from end of burner with softer orange filling space.

The bad burner only burns stable in one position (choke) anything else make flame unstable. This position changes very slightly as the forge heats up till it starts spluttering continuously.

I also have a 1/2" gap around the burner tubes and forge wall?

In my experience with burners, when they start to behave as your "bad" burner does (abruptly to minor adjustments) I have found a problem with the intake section of the burner.

Ensure the gas tip is axially aligned the entire length of the burner. (as best you can) Do not just check alignment at the end of the burner tube.

Check the tip itself for debris or damage.

How does the pipe joint at the burner tube to bell reducer look? Is the shoulder very abrupt where the pipe threads into the reducer? Try filing that shoulder down into a taper and see if that helps any.

From the way you describe your "good" burner operation, it sounds desirable. You definitely have something different with your other burner.

As you well know, building and tuning these burners sometimes turns into quite the science project......But that's half the fun, yes?

[jsurgeson]

Hi Brian

Thanks I know the feeling

I think you have probably hit the nail on the head with regards the bad performance of the one burner, and as it turns out, the only thing I can find different. :confused:

The jet, although centered to eject gas so it exits the burner centrally, is in fact not centrally located in the throat. This happened due to the threading not being 100% straight, so i had to offset slightly to get it to exit centrally.
So in fact it starts off exiting the jet from a off center position in the the throat of the tube and exiting centrally.

I will correct this tomorrow and see how it improves it, will let you know.

I think the flare I will add to improve performance one I have them both working the same and stable.

I think in the long run I am going to look at a modified side burner, which I think allows for greater adjustment of jet position, but needs perfect construction.
I also think that I am going to machine up intake reducer's as apposed to off shelf fitting as I thing that they are not 100% ideal.

Thanks again for the great info, much appreciated.

Edited April 5, 2009 by jsurgeson

[Brian D]

Sounds good Jeff,

Yes, let me know how things turn out.

I like the Sidearm style burner, they seem to work best for me and are more forgiving to breezes and drafts.

I do not have a shop and need the forge to perform outside when there is often a very stiff breeze or wind blowing.

Good luck.

[leroyk]

do you really need two burners in a forge this size i have one about the same size 4 1/2 by4 1/2 by 18 in and one burner seems to do real good for me

[Brian D]

do you really need two burners in a forge this size i have one about the same size 4 1/2 by4 1/2 by 18 in and one burner seems to do real good for me

That depends on what size the burner is and what you are expecting to do in your forge.

I would say that your forge is a little too big to expect to forge weld with only one 3/4" burner.

[jsurgeson]

Hi Brian

Thanks will do, yes I have a small shop and was outside but ran into problems with wind interfering with burners, so moved it inside but would like to be able to forge outside.

What is your take on judging color in daylight as apposed to shop light?

I mostly temper blades and one - 1" burner deals with that but battled to weld with just one, so went to 2 - 1" to be able to weld. I think it is more than capable of getting to welding temp but what I found was it tends to be very localized and on larger pieces more difficult.

I must say i wish someone would show me how to weld with only one as gas is very expensive for me, about $30 / 39lb bottle

Brian meant to ask before, how come when I try look at your profile it says you are not registered?

Edited April 6, 2009 by jsurgeson

[Frosty]

The jet, although centered to eject gas so it exits the burner centrally, is in fact not centrally located in the throat. This happened due to the threading not being 100% straight, so i had to offset slightly to get it to exit centrally.
So in fact it starts off exiting the jet from a off center position in the the throat of the tube and exiting centrally.

I'd call that a bingo.

If you have access to or own a lathe you'll be much farther ahead to build a Sidearm or "T" burner. They're much easier to tune.

Frosty

[jsurgeson]

Spoke too soon :mad:

It was actually the good burner that was slightly offset, so that was not the problem.

Just going to live with it till I can make up side or t burners, not prepared to waste anymore time on this as i have a few knife order waiting to be done.

Thanks for all the help :)

[Frosty]

The things that make you go Hmmmmm.

Sometimes it is better to cut your losses and move on.

Frosty

[jsurgeson]

Yeah thats for sure!

I am definitely rebuilding from scratch, forge with easier access, and t burners :D

[Brian D]

....
What is your take on judging color in daylight as apposed to shop light?

Brian meant to ask before, how come when I try look at your profile it says you are not registered?

I don't know, I have only been outside under my covered patio as I don't have a shop to work in. (It does seem easier at dark when I have the flood lights on though)

With any luck, I will be able to start on a shop this summer / fall. It will most likely be a several year project. I will just build it a little at a time as I can afford it.

I don't know why it shows me as not registered, I will have to look into that.

It was actually the good burner that was slightly offset, so that was not the problem.

Just going to live with it till I can make up side or t burners, not prepared to waste anymore time on this as i have a few knife order waiting to be done.

Thanks for all the help

Bummer....I think you will like the other style burners a lot better....

The things that make you go Hmmmmm.

Sometimes it is better to cut your losses and move on.

Frosty

Yea, it does get frustrating at times though.

Yeah thats for sure!

I am definitely rebuilding from scratch, forge with easier access, and t burners

But, think of how much better the next one will be due to all you have learned on this endeavor!

[Ken]

My melting furnace has similar problems but with only one burner. After an hour or two the fire pops back into the mouth of the flare. Breaking the gas flow with a piece of sheet metal passing in front of the jet works, but only for a few minutes. My current **answer** is that the pressure in the combustion chamber rises to more than the flow of the jet / gas mix allowing the flame to move back to the jet / orifice killing the venturi effect. ? can you make your exit hole opening larger? or move to a smaller burner tube?

[jsurgeson]

Ken

Makes sense, and I think that is where my problem lies, I think that I miscalculated originally the conversion from gauge to millimeter, ans worked out that #58 - #60 was about 0.6mm, how I got this I don't know.

Talking to some of the other knowledgeable guys on the forum and reading posts, it would appear that 0.8mm for 3/4" tube and 1.2mm for 1" tube appears to be the norm.

This also appears to backup what you are saying.

Thanks for the reply, I am going to remake my burners using one of the other designs, I am looking to machine the combustion chamber to improve performance.