Jump to content
I Forge Iron

Current forge - Questions/Tips/Suggestions


Recommended Posts

Hi All,

I'm attaching pictures of our current "brick pile" forge with a blown propane pipe burner. I have some questions and I'm hoping some of the knowledgable members might be able to help me clear up some questions and/or make suggestions of how we can do more/be better with what we have until we have v3.0 planned and built.

This forge has an internal space of H4.5xW7xL27.5, so an internal measurement of about 866.25 inches^3.  We can and have forge welded in it, but we have to hold our tongue just right and turn the gas up quite a bit.  I know the burner, being a 1" pipe burner modified from a N/A venturi design and now blown with a leaf blower, is underpowered.  I have three big questions:

1) We make a lot of scale.  Like, ridiculous amounts.  People I see online don't make that much scale even in propane forges.  Is there something about having such a big space with not enough heat that causes us to make huge amounts of scale?

2) Is there any way, without adding more burners, to get a "short" heat on something?  I interpret this phrase to mean a heat that is located in a particular part of a piece, especially the end, that doesn't travel all the way up.  Right now, to get something say 12" long to have enough heat to be easily forgable (bright orange, dark yellow...ish) in the 2" at the end, the heat will be bright red at least 6-7" away from there.  It means that the whole things is very "floppy" as I call it, bends easy when stressed with tongs and moved etc, and makes everything take more heats to straighten up properly after you're done the forging on the portion you wanted to heat.  I want to focus on making more tongs, and lots of them call for "short" heats so that you can work just the bit without affecting the reins or boss too much.

3) What is the glittery scale?  Is that a sign of burning metal?  Most of the scale we make is essentially dark brown/black.  But sometimes, especially on smaller pieces, we get scale that looks almost like it is covered in sparkly glitter.  If it's brushed away the metal underneath is duller than normal, but it still seems to brush/file up fine.  I've never managed to get a good picture of this phenomenon and google as I might I can't find anyone talking about it.  I feel like it's a sign the metal is getting too hot and some part of the steel alloy is sublimating out and then solidifying or something, but I just don't know.

FWIW regarding safety.  The dragons breath is not very bad on this forge, probably because the burner is centered in such a long cavity.  The top gets hot, hot enough to melt wax, but not enough to cause beeswax to smoke.  You don't want to lay your hand on it after a couple hours, but if you brush it with un-gloved hands you don't burn.  The burner pipe has never (according to my IR thermometer readings) exceeded 33C, and the brass gas fittings and hose have never exceeded 21C when measured.  The forge is hard kiln brick sitting on concrete paving stones on a metal table.  The table does not get hot, it gets uncomfortably warm, but still touchable, directly under the center.  The square tubing around the burner is our DIY method of holding the burner in place to the top piece that holds the roof together.  

The burner nozzle is almost all gone now....it lasted years but is now losing pieces regularly. it used to be a black iron reducer.  Now it's...scale. The flame is a bit more jagged and not as smooth as in this picture, and we know it needs to be removed, refitted and replaced eventually.  There is no wool insulation or refractory cement in this build, just high temperature rated kiln bricks.  That means it takes a fairly long time to get to real heat, about an hour or more.  You can easily forge before then, but not attempt anything fancy like forge welding.

current forge 1.jpg

current forge 2.jpg

Link to comment
Share on other sites

17 minutes ago, JCloss said:

I know the burner, being a 1" pipe burner modified from a N/A venturi design and now blown with a leaf blower, is underpowered.

Not hardly. No leaf blower is doing to prduce insuficient air for a forge six times that size!


(1) You have too much air; that is why your getting heavy scale formation. BTW, oxidizing flames reduce flame temperature; just not as much as reducing flames do.

(2) Get control of your flames (see above), and then spot heating simply becomes a matter of flame size versus opening sizes.

(3) No clue at all...

Link to comment
Share on other sites

Hi Mikey, thanks for your responses!

I didn't mean the leaf-blower is underpowered, just that the single burner for that cavity space probably isn't generating enough BTU to raise the entire cavity to a proper temperature.

(1) Too much air - that's an easy thing to test and I'll make some modifications next forge night.  We have a ball valve in front of the leaf blower, I'll turn the blower down and close it off a bit more if needed to try and get the fuel/air mix richer. (Richer is right, right? Leaner means less fuel, richer means more fuel?)

(2) This becomes quite testable too as it's related to #1, so I'll try to fix the first problem and then work on this.

(3) This mystery has been bugging me for a long time...I can't find anything about glitttery forge scale anywhere....

Link to comment
Share on other sites

Hard firebrick or insulating fire brick?  Hard firebrick is a heat sink and saps BTU's  from heating the interior of the forge.  The excessive dragon's breath is do to excessive air blasting into it from the leaf blower.  Why do you need that large of a forge?  I've used larger but it was using a blown ribbon burner and would reach welding temps at appx 7000'. (I know it at welding temp as another smith repositioned their 3/4" diameter rod sliding it against my 2.5" sq stock  piece and it welded and we had to sledge it off.

Link to comment
Share on other sites

Hard Firebrick, which is why it takes so long to get to temperature. It's however stood up well and I'm looking to probably use it as a replaceable floor for the next forge.

We dont' have excessive dragon's breath, we have very little. I think that's because the burner is so far inside.  I try and adjust the mixture so that there is some dragon's breath, which I interpreted as extra fuel that was unable to burn inside the forge due to not enough oxygen to mix with, so I could absolutely be wrong about that.  (Meaning, I thought I had the atmosphere rich enough to be reducing)

Hmm, do we need one this big?  Probably not.  We don't use the back half much at all.  I'd be down for a smaller forge than we have, but I would like a wider and taller chamber, just not as long.  We often seem to end up doing projects that are curved, curled, or otherwise oddly shaped that take up the full amount of the opening in one dimension or another, and/or long projects that need to be passed through. (Twisting ladder rungs for a quilt ladder I built two years ago comes to mind.)

My buddy is the main driver of a new forge and was the one that designed this one, I was mostly just labour, realism and troubleshooting.  Evidently I didn't do enough of the last two. ;)

Link to comment
Share on other sites

We have considered a re-emmissive coating for a while. (If by that you mean a product like ITC-100)  The suppliers my friend has found have not had any in stock or available to purchase for over a year though.  He was on their email list to get notified when they re-stocked and they didn't email when they did, probably because it was all sold out in pre-sales.

Link to comment
Share on other sites

Last night we turned down the air a bit and turned the fuel down a little bit as well.  I think it helped with the scale.  We had more dragons breath, but it was softer looking if that makes sense.


I may have flubbed my testing because I also moved some half size slabs of fire brick inside the rear of the forge to cut the length down closer to 18".  This did seem to move the heat further out front and didn't get in the way of anything we were doing.i took pictures once it was hot, I forgot to take pics when it was running cold before it came up to heat.




Link to comment
Share on other sites

I notice the dragon's breath from the back of the forge appears to be burning burning rich, although the front is blue (which I understand to be ideal or possibly lean)  My understanding is that blue=gooder, yellow=badder, as yellow flames are an indication of CO formation?  Likely this difference is because of the difference in pressure between the two exhaust ports.  The front is further and as such the propane must mix with the rest of the hot air in the forge as it comes out the mouth, possibly resulting in a cleaner burn?  The rear, where I've moved those bricks closer means that some unburnt fuel is likely rising and burning off before it has a chance to mix with the extra air in the chamber and is combusting as soon as it finds enough outside air to mix with to allow it to burn.  I'm kind of just spitballing here as I try to understand - please anyone feel free to correct me.

I should qualify the blower I mentioned too.  I called it a leaf blower, but that might be generous.  It's a variable speed blower motor from Amazon, marketed as a small corded leaf blower.  It is running about half speed (I know that doesn't mean much) and has a 1.5"-ish outlet.  That is redneck gasketed to some 2" PVC with a ball valve set to about 1/4 open , then runs through about 8" of PVC.  The PVC runs into iron pipe for about 36", hits a 90* elbow and runs through a reducer into the burner nozzle.


Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...