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DIY gas forge - heat problem


Alcibiades

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Hi everyone! I'm new to the site and in need of some help.

I built the gas forge picture below. It's a paint can (never held paint) and the refractory material is sand and plaster of Paris 50/50 mix. I have a burner I built following the instructions on makingcustomknives.com. The burner works great, but I cannot get the steel yellow hot - only bright orange. I'm running the gas at about 12 psi, but i would prefer to be lower. What are some things I can do to improve my forges heat? I know that's a loaded question, but I would prefer not to buy Kaowool and itc-100, etc. I'm new to this and don't want to get financially overextended yet.
Is there a better forge design?
Would a door help?
Is the forge opening too large?
Is my refractory material no good?

Thanks in advance for the help!

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n readin the tons of posts on this site about refractory materials I have never,  near as I remember, ever seen sand and plaster of  paris suggested as working materials. If you go to where3 yoiu got that information they may be able to help youi out and may be able to post refereences that would help.

Colors of steel are really dependant on ambient lighting. Some steels may look almost dull red in sunshine but in shade look forging heat. And in a dark room may appear at welding heat. I never suggest colors of steel. I prefer to see  how it moves under a hammer. And that of course can be related to lyou ability to move it from forge to anvil with no delay which loses heat. It also depends on wot the steel is and how large it is. If you have tool steel it is harder to forge. If you are working with small diameter it loses heat rapidly.

Try  mild steel, if it is used and  has been used as something that requires a lot of strength,,,such as a lug wrench, spring etc it is  not likely mild steel. Look for something with minimum thickness of half inch,,,sq or rd.

And if you do not have a forging hammer...not a claw or something similiar, and if you do not support your work with something youi use as an anvil that actually works then that may also be a problem. You gave us little in the way of details...fill in the blanks for more help.

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Welcome aboard, glad to have you. Please put your general location in the header, you  may be surprised at how many IFI gang live within visiting distance.

 

I really wish you'd done more and better research before going to all the trouble represented by your forge. Plaster pf Paris and sand is sometimes used as low temperature investment for casting, I've never heard of it used for a furnace liner of any kind. I don't think it'd survive in a BBQ. Refractory it is not.

 

If you must make your own refractory liner go to the local concrete plant and buy a bag of fire clay and a bag of sharp silica sand. 2pts, fire clay - 3pts sand - 1/2 pt portland cement. Add only enough moisture to make it clump in a hard squeezed fist and break clean. If it crumbles it's too dry add a LITTLE water. If it leaves your hand dirty or damp, it's too wet add a LITTLE more dry mix. Once it's the correct moisture RAM it in place with a wooden  dowel or mallet.

 

The best way to ram up this shape liner is to place a smaller diameter form in the can. sono tubes are perfect. Figure how thick the liner needs to be, 1"-1.5" will probably do in your forge. If you just MUST have an insulating liner add fine saw dust to the mix, it'll burn out and leave voids that'll help insulate, this is how light fire brick is made.

 

Lose the nipple from the intake end of the burner, It's only inhibiting air intake. We see this little addition all the time, guys just have to add something of their own to things. This one only hurts the performance. If you want to see how a linear burner should be built find Ron Reil's site and read it. Don't bother trying to ask him questions though, he burned out on guys asking questions rather than reading the faqs ad stopped answering years ago. You can ask me though, I'll point you to the pertinent post or section here.

 

Frosty The Lucky.

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Let me rephrase this for you:   "I don't want to spend US$10 for kaowool because I would rather spend hundreds of dollars more buying fuel for my forge since it does not have an insulating refractory"  How does this sound to you?

 

 

 

 

If you were near me I'd give you enough scrounged kaowool to make a forge!

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www.axner.com sells superwool (bio-safe kaowool) for $8/foot - which for that forge two feet would be just fine - with some left over.

 

Your lining is a fragile heat sink. not an insulator.

 

Drop buy and I'll give you a cup of zircon frosting to finish the can forge.

 

J

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I appreciate the responses. I'm in SoCal on Camp Pendleton, if anyone is out this way. I guess I should invest in kaowool and itc-100. I do have an anvil and a cross peen hammer. I think my new forge will be made out of an empty ammo can. That will allow me to use the lid. The little nipple on the end of the burner is actually clamping the brass nipple/nozzle in place - I don't have a tap and die set so I can't put screws in the reducer to tighten down on the brass nipple. I'll look into Ron Reils design.
Hope I can reuse some of my parts. :(

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It does sounds like you have confused the insulation used for cheap "metal casting" with the insulation needed for a forge.

 

 

Depending on how it is made and what is in the sand, a sand/plaster of paris mix is likely to have high conductivity at low temperatures (so anything insulated by it will take a long time to heat up) and while it may even have a moderate to low conductivity at higher temperatures, it won't stand up to repeated heating that happens in a forge.

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My older sister used to date Marines from Camp Pendleton hen she was down visiting.

 

Okay, you'll bump the performance and still be able to clamp the jet if you cut the end off the nipple and use it as a threaded insert/clamp.

 

You guys have a machine shop on base, bribe the guys with donuts and coffee, I'll bet you'll get to use a tap and more. Tell the guys what you're doing, get them involved, make them a cool forged thingy. Good PR will carry you farther than a fat wallet.

 

Check large HVAC companies, ask about the outfits that build and maintain large industrial furnaces, etc. They use Kaowool by the ton, literally. Better yet for our purposes, even the sales guys in the office LOVE to talk fire and furnaces. Tell them you're building a forge and they'll be more helpful than you'd believe. Locally we have E.J. Bartell and they've adopted the Association of Alaskan blacksmiths unasked and give us the commercial rates and kick in a discount AND send me home with a boat load of Kaowool rems and different refractory bricks to experiment on. Not counting the freeby rems, the last I paid for 0oz. 2,500f Kaowool was $0.75/sq/ft.

 

If you're going to be welding, tell them you need a refractory that's resistant to hot caustics. Usually high phosphate or phosphate bonded refractories are what they'll have but it's been a while, things change.

 

I hope I didn't come on too abrupt, I'm into building burners and really hot forges. I'll be thrilled to help you as much as I can. It's the least I can do. Thank you for serving.

 

Frosty The Lucky.

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Ok, I rebuilt my forge based on the fire brick design on the Zoeller website. I cut back the nipple that holds the brass nipple in place to allow more air flow. I kept a flange to make it easier to twist in and out. I took off the 90 degree bend in the brass piping. I used regular soft fire brick for the body and placed half cut hard fire brick as a forge floor. I had to raise the burner in the floor plate so that the flame wouldn't sputter or cut out. I ran it at about 7 PSI for about 20 minutes and got a railroad spike light orange. I'm still shooting for yellow, but I can raise my PSI more if needed. I also got one of those little dollys from Harbor Freight so that i could move the forge around. If anyone has any suggestions, I would be glad to hear them!

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I take it your forge isn't developing scale in the fire. If it's making clean heat the burner's operating well enough for now. Just try raising the PSIG.

 

A lot of guys tweak till their burners run at really low pressure but that's largely bragging rights. It doesn't really matter what the gauge says so long as the fuel air mix is correct and getting into the chamber in enough quantity to develop the BTUs to do the work.

 

Running low psi isn't doing much in an important way unless you're operating a naturally aspirated burner off household natural gas. What counts is burning fuel and air fast enough to bring the inside of the forge to the heat you need in your steel. If you're getting orange at 7psig, try ramping it up one or two psig at a time till you have your desired temp. Go to 9psig and give it a session. Don't start jumping around, give it time to work, it isn't like the throttle in a car, it's a delayed reaction. However, once you learn what it sounds and looks like you'll be able to judge a finial temp pretty closely by the roar and flame shape.

 

Repeatably estimating desired temp is the main reason I use a gauge on mine at all and a good thing to keep in a notebook till you get a good feel for your forge. Unless there's something odd going on I don't ask what psig folk run their burners, I'm looking for flame shape, dragon's breath and effect. Seriously, we're doing this for the effect, not what a gauge says.

 

Frosty The Lucky.

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Too bad you're not out here at Bliss-ful west Texas; we could do some forging together!

 

Look into how to make bottle openers from RR spikes as "trade goods" with the machine shop; I expect someone there will be a beer drinker!

 

(then get them to make you a couple of snazzy high tech burners for you and go wild!)

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My guess is that you would like to be able to forge weld if you are not satisfied with an orange color in the steel you are heating. If so I have a couple comments that may help.

  1. It looks like your chamber is open front and back. If so you should be able to develop more heat by blocking off some of the front and back.
  2. Also my guess is that you have a 1/2" burner. (1/2" nominal size of the long pipe). I have used a 3/4" burner with the same brick forge set-up and got to a yellow forge welding temperature. However, I never succeeded in forge welding. I probably have numerous problems but I think a basic one was too much oxygen in the chamber. My burner needed to be turned up a lot/openings adjusted to try and get an excess of propane gas into the chamber to consume the oxygen. If flames are licking out the openings there shouldn't be much oxygen in the forge to interfere with forge welding.
  3. I suspect you will get tired of bending down to look into your forge. I built a roll around stand for my brick forge when I finally had enough of it.
  4. Probably all of your soft fire brick will have developed cracks in about a year. I bought a whole case a couple years ago and they are all broke in multiple pieces despite me trying to be careful with them. Don't try to use a soft fire brick as the support for what you are heating. They are too fragile for that abuse. Also if you try to forge weld and dump Borax flux on the metal it will get all into the porous brick and ruin it. Flux on a hard brick. (Personal experience)

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  • 3 weeks later...

I appreciate the advice from everyone. I just got a pint of itc-100 to coat the inside of the chamber and I hope that improves my heat.

I was also thinking of adding a blower (although that seems counter to what Andrew is saying above). I have blocked off one side of the forge when working small stock, but i still cant get to forge welding heat. I have even tried closing up the front openning and only allowing a small apeture for air, but no luck. I have an old a/c with a busted compressor and I can take out the front blower, box it, and put a variable resistor on it to control the out put. Has anyone worked with something like that before?

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Hey Alcibiades, could you possibly post a few pictures of your forge running?  I've used a similar burner in a few different incarnations of (something resembling) a forge and I keep noticing varying results in how the flame looks seemingly affected by what the forge is made out of.  It would be nice to be able to compare it to someone else's.

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