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Improving the Forge Heat


Ross Jones

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I'm having a problem getting my forge to welding heat. It's made from a 5 gallon paint can, has a 2 inch think layer of durablanket, several coats of satanite and 3 coats of Plistix 900f. I have 2 burners, but running both kills my propane tank in an hour or two, so I have to stick with one. I get to welding heat at about 15 psi. With the setup that I have, is there anything else that I can do to lower the psi needed to get to welding heat?

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If your using a 20 lb propane tank and killing it in an hour sounds like orifice in burner WAY to large or inside of forge to big. Can try adding fire brick or kiln shelf for floor to reduce size. Pictures would help

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Can you post pics?

 

It's quite difficult to suggest what can most usefully be shown by photos with no prior information. Best approach is to give it a run, take photos of everything you can and post the long shots first. If the guys that know what they are doing ask for specific details after that, you have the photos ready.

 

The most useful shot is usually taken in the dark from a distance off to the side and shows the Dragons Breath from both the front and rear ports. Long shots in bright daylight don't normally show the Dragons Breath at all and are of limited help when it comes to diagnosing the overall problem.

 

Close shots into the chamber can sometimes be useful, but digital cameras usually mess about with the white balance so badly that the color in the photo is nothing like the color in the forge. They are most useful for showing temperature distribution: is the color even, or are some parts hotter than others?

 

Sometimes video is better than a photo, particularly when trying to capture images of flames.

 

If pics are not an option right now, what are the burners? Atmospheric or Naturally Aspirated? Whose plans did you follow (a link helps)? What changes/improvements did you make? What jets did you use? What is the actual ID of the forge and what size are the openings?

 

The burner to forge volume thing seems to be a rule-of-thumb, rather than an absolute thing: A forge that is well-designed and well-constructed to "normal" proportions from the appropriate materials will work with X burners of Y size per Z cubic inches. The surface area and particularly the opening area seem to be the most important factors affecting the heat retention and these are accounted for in the rule-of-thumb by the "normal proportions" bit.

 

If you just stick a brick in the forge to occupy some of the volume, you still have the same size forge, but with a brick in it. It will not help much. If you add another layer of insulation to reduce the inside dimensions, it may help quite a lot.

 

Reducing the size of the openings usually helps and that's where the brick might do most good.

 

I'm not a smith and you'll get better advice from those who are. I do mess about with gas burners for a living though.

 

One of the things I see when I visit smiths is lots of Dragons Breath and not enough temperature. This is often easily fixed by going to a smaller gas jet.

 

It's easy to lose tight of the need for enough air to burn the gas in the forge and think in oversimplified terms of "more gas = more heat". As soon as there is more gas than the amount of Oxygen present can burn, adding more gas just reduces the temperature in the forge and increases the DB outside it. This may or may not be part of your problem. Pics would help, particularly the one from the side showing the DB.

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Sorry

Was not specific enough about the brick in forge. I was thinking raise the floor with extra layer of brick not just add brick to reduce volume. Brain better than fingers at times.

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The apology should be mine: It didn't read the way I intended at all.

 

I tend to be somewhat anal and pedantic about stuff like this, partly because it tends to get picked up and taken out of context when someone has a problem and Googles it months or years down the line. It was with such a future Google-jockey in mind that I posted.

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There are a few things that could be hurting you here. If you have venturi burners, there are a handful of things that could be wrong with them, but without details it wouldn't be much help to throw out suggestions. For blown burners, you could be using too much air for the amount of fuel or too little, both are equally likely. Having too much air will cause the temperature to drop dramatically because, depending on your setup, might be blowing in unheated air that didn't have a chance to undergo complete combustion with the fuel. I suspect the burner isn't the sole problem, however. How large is the interior chamber? Follow up question, how much of that chamber size are you actually utilizing? Unless you are routinely forging large masses like axes or hammers that need the extra space (height, most likely), it is just more unnecessary volume to worry about. The fire brick suggestion might help a little, but you might want to consider lowering the ceiling instead, using some castable refractory or even another half layer of the blanket. I have built a few forges and that is the first thing I do to cut back on the volume I need to heat. Don't get carried away though, there should still be a bit of space! Something else to consider is burner placement. How is the atmosphere circulating? Is there some sort of natural circulating happening around the interior? Possibly try lowering the entry angle to improve heat distribution. Finally, without more info to go off of, how large are the openings on the front and back? This alone might be the source of the problem. You will still need space for the forge to breathe, but the openings could be haemorrhaging all your heat away if too large. Possibly consider closing them off a little or using a firebrick as a door to close off what you don't need for whatever you are working on. Hopefully some of this helps, but as others have said, pictures are worth a thousand words for helping understand where the problems might be coming from.

 

John

Not all those who wander are lost. -J.R.R. Tolkien

-Shards of the Dark Age- my blog
-Nine Worlds Workshop-
-Last Apocalypse Forge-

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The interior volume of my forge is 460 cubic inches. I'm using the 3/4" side arm burner (venturi) sold by Zoeller Forge. I built my forge using the plans on Zoeller Forge's website for the "Simple Gas Forge", that being making the body from a 5 gallon steel bucket, though I tried to improve the design by adding a back door with a hinged cover and a front door with a 4" 3/4 x 3" 3/4 opening. I'll admit that I'm not very well versed in the language of burner parts, so I have to make some assumptions on what is meant by certain terms. If by "jet size", you mean the mig tip that goes into the pipe, then that's a .035 contact tip. I'm assuming the mixing tube is the 3/4" x 8" pipe that's connected to the 1 1/4" x 3/4" x 1 1 1/4" Ward reducing tee. The pictures I took of it it running don't show the true color, as it appears to be bright white when it was really a darkish orange. I noticed some gaps between the front cover and the forge body that I could plug up with durablanket. I also noticed that towards the back of the forge was heating up much slower. I could probably put a fire brick in there to reflect that heat back, but I doubt that there's enough room for one. Is there anything you guys can think of with this new info?

 

Link to burner (I'm using the normal one, not the mini)

http://www.zoellerforge.com/sidearm.html

 

Link to forge plans

http://www.zoellerforge.com/simplegasforge.html

IMG_20160425_201208863.jpg

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One thing I'm noticing right away is that you are running your tanks individually. Are you sure they are empty, or are they freezing? I made that mistake once and when I took it to get it filled I still had 4 pounds of propane left. One thing I would try would be to run off of both tanks at the same time.

 

Also, what is the size of the opening of your forge? It's hard to tell, but it looks like it might be a bit small to run two burners. You need at least a 3.5" square for each 3/4" burner. So you would need about 7" worth of opening for a two burner set-up. Atmospheric burners need to breath to function properly. If you have too much back pressure it has a hard time bringing in sufficient amount of air and cannot expel the rapidly expanding gasses. Don't box your forge up too tight around the openings. That blow out around the opening is not hurting at all.

 

It could be the angle of the pic, but it seems that your back burner is pretty far forward which may explain why the back of your forge is slow to heat.

 

Finally, what are the actual measurements of the inside of your forge?

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Is there any opening in the back when the door is closed? That could be part of the problem. Like Josh said, forges need to breathe. Having that closed off (can't tell if it is or not) might also be part of the reason the back is heating slower. Too much back pressure choking the burner. Also, it's hard to tell, but how tight is collets that hold on the burners? You might be drawing in more air than you need, having a sort of double venturi effect going, one from the gas inlet and another drawing air at the body of the forge. I don't see any dampers on the air inlet on the top end of the burner, but that isn't necessarily a bad thing. I've never had them on that style of burner I've built, but I also have the burners more secure on the body of the forge. Since you can't tune the air intake with a damper, try sliding the mig nozzle in farther towards the burner pipe if you can (not sure how yours is set up). That might be a cause for lack of proper combustion at the receiving end. Rarely have I had a burner that is tuned perfectly straight out of making it, and that can have a significant effect.

 

I built a few simple venturi burners a handful of years back, maybe it will be of some use to you- relevant blog post

 

I also noticed that your orifice diameter is .035", if I'm reading that right. The holes in all mine have been drilled with a #57 bit, which is .043" diameter. I've been able to weld in forges running these burners no problem at around 15 psi total for a pair. I'd bet that your tank is freezing running that much gas. Try sticking the tank in a bucket of water, it'll fix that problem for you straight away.

 

Finally, I think it might be your forge volume that's killing you. 460 in3 is massive. Looking at those plans, the interior is way more than you would ever need with a door that size. I've been tempted to make larger interior volumes before, but every time I regret it and end up lowering the ceiling by a fair amount. The most recent forge I've built has a volume less than half what you have. All that extra space is not doing you any favours. If you have any left, I'd take some of the insulation blanket and lower the ceiling by about 1/3 of the total height, making sure that the path from the burner inlet is solid and unobstructed. Unfortunately, now that you have a solid lining in there it will be challenging to have it come out sturdy and durable, but if that's what it takes, it's what it takes.

 

Anyway, hope this helps some.

 

John

Not all those who wander are lost. -J.R.R. Tolkien

-Shards of the Dark Age- my blog
-Nine Worlds Workshop-
-Last Apocalypse Forge-

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Other than the obvious things pointed out already (too much burner for a single grill tank, etc.) one thing I can recommend based on other forges with this type of burner is to add a choke plate on each burner. Simply drill and tap a small (say #10-24) hole on the rim of the reducing elbow like so:

 

post-41924-0-26677600-1461630594.jpg

 

and cut a circle of sheet metal big enough to cover the opening, drill for a sliding fit on the #10-24 screw near the edge, tighten just enough for a sliding fit and viola! You now have an adjustable choke plate. Or in a pinch duct tape works fine too.

 

The choke will allow fine adjustment and less pressure to get the job done. Most burners like this run great choked halfway down at half pressure, and a 3/4 closed choke gives a good reducing heat-treat atmosphere.

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Another way to do the choke plate is to get a piece of the magnetic sheet they make signs and fridge magnets with (the hobby/craft stores all carry it). You can cut it to shape with scissors and just stick it right to the burner.

 

Geoff

"The worst day smithing is better than the best day working for someone else."

 

I said that.

 

If a thing is worth doing, it is worth doing badly.

- - -G. K. Chesterton

 

So, just for the record: the fact that it does work still should not be taken as definitive proof that you are not crazy.

 

Grant Sarver

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I like the idea of using magnetic strips as a choke plate and will definitely be using that method. Guess it's a good thing I already have some that I got as an impulse purchase when I had the idea of using them to make etching stencils. I misspoke before when I talked about running both burners killing propane too quick. What I meant was that it uses more than I need when the front burner can get me to forging temps just fine. I did have a problem for a while with my tank freezing up when running both burners, so I decided to only run the front one to avoid this and half my fuel consumption. I can try leaving the back door open if this is choking the burners, or putting some kind of heat reflector in the back of the forge (durablanket, firebrick, etc.). I would like to be able to run both burners on two tanks at once, but I'm not at the moment to try to conserve fuel. I'm starting to sell more knives and picked up a second job, so hopefully the funds will be there shortly.

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What do you spend most of your time forging? John is right, 460 is a lot of forging area. My forge is 150 and I can do a lot of forging. I have been able to some mild steel welding at around 12.5-13 psi. If most of your forging work is blade related you could cut your chamber size in half and still have a lot of space to play and could consistently use only one burner and save fuel by not heating a lot of space you'll almost never use. I'll take some pics of my set-up this evening. I have a choke plate just like Alan is talking about.

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I do mostly blade work, but I forge guards and pommels of varying sizes. I also do some axe work and hardy tools. I'd rather put some sort of heat reflector in the back of the forge then build a whole new forge body. Trust me, it took long enough the first time.

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I can understand not wanting to rebuild. Do you have any wool left? If so you could possibly wash it in a thin coat of satanite and use it as a way of reducing the size of your forge chamber when you are doing smaller work. That would help in reducing the size of your chamber but leave your with the ability to have more room if needed. Here is a pic of my burner set-up:

 

image.jpeg

 

This is how I have my choke plate mounted, but I like the magnet idea Geoff had. One big difference I note is that my jet goes a bit farther into the burner tube than yours does. Mine runs great with this set-up. I have almost no scale at wide open choke, so getting a reducing flame is pretty easy with minimal choke.

 

image.jpeg

 

This is a pic of my opening. It's approximately a 4" circle. This is an old freon tank FYI. If you are only running one burner the opening you have is sufficient, but if you try to use the second one, you need to open the back at the very least, and adjust it from there. I close the back of mine with a fire brick cut in half after it warms up and it seems to do a great job of keeping the heat in.

 

image.jpeg

 

This is how I have my tanks connected. It keeps me from having to put them in water, and get the most out my tanks.

 

image.jpeg

 

This may seem like a weird pic, but I noticed your set-up is at least partially exposed like mine. I was having a problem with small gust messing with the sidearm intake. This kept the intake protected while still allowing a free flow of air. Since I did this I keep a nice consistent burn and small gust don't seem to effect it at all.

Edited by Josh Brannen
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i don't want to highjack this thread, but i have a similar project build in progress and i'm having a little trouble finding 1.5" black pipe. home depot only seems to carry up to 1" while other vendors mostly stock galvanized. what is an easy source for the proper product?

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You can use the galvanized, just soak off the zinc plating by leaving the pipe in a tub of distilled white vinegar for a couple of days, or in muriatic acid for a couple of hours. It's easier and faster to use black pipe if you can find it, though. Check out real hardware stores, not the Despot. My local Ace Hardware has black pipe up to 2".

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thanks all. looks like Alan's tip might work out:

 

http://www.acehardware.com/product/index.jsp?productId=29375766

 

or heck, I guess I can save a trip and gas:

 

http://www.amazon.com/Anvil-8700143608-Fitting-Nipple-Length/dp/B0058PRD52/

and use this for attachment (not sure where to find "conduit lock rings" described on the zoeller forge site, which seems like a simpler, cheaper option):

 

http://www.amazon.com/Anvil-8700164059-Malleable-Fitting-Flange/dp/B0058DQLAC/

not always easy to tell if it's galvanized or zinc plated or whatever, but these seem to be coating free.

Edited by joe pierre
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Try plumbing supply houses before you do Amazon. I have had great success going that route and saved a lot also. Check for a Ferguson supply.

thanks for the tip -- there was a Ferguson on the way to work and I picked up the pipe.

 

I have to say though that I only saved $0.03 on the pipe compared to amazon and they didn't have anything -- conduit rings or wall/floor bracket/flange -- to attach the pipe to the forge wall.

 

so I still need to a trip to home depot or an amazon order to find a suitable mount, a tap for threaded holes, and some other nuts and bolts...

 

 

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