Another 20lb propane tank forge

[rhitee93]

I wasn't very happy with the fuel consumption and temperatures of the off the shelf forge I purchase this fall, and decided to build my own. the bladesmiths on this forum have been a bad influence on me and I decided to build a forge that I could try my hand at pattern welding blades in.

 

I based the burner and forge off of the plans int Porter's book.  The only major changes I made were to go with a total of 3" of ceramic blanket, and to use a castable refractory for the floor instead of a kiln shelf.  I also lined the inside with a layer of bubble alumina.

 

Here are some pics after I got done playing around with it a bit today:

 

 

 

Here are a couple of pics of it running at 12psi.  I am still trying to figure out how to tune the burner at different pressures.  I don't really know what I am doing but this seemed to be the sweet spot.

 

 

 

Of course, I had to try to weld something.  This is apiece of 1/4" square mild steel I had laying around.  I folded it over and welded a 4" section.  Then I cut the folded end off and ground one side to see the results.  I have only done a few welds and this is the first one in a gas forge.  The results seem as good or better than what I have been able to do in coal. (Not that I claim to be any good at it yet)

 

 

 

I used a 0.030" welding tip for the orifice.  The forge will run stable from 3psi to where my regulator caps out near 30psi.  The weld was done at 12psi.  I don't know how the gas consumption will be, but the tank I was using was nearly empty when I started playing around, and based on my experience with my other forge, I expected to run out in just a few minutes, but it is still going strong.

 

I still plan to do some sort of door like Porter has in his book, but I couldn't resist playing around with it for a while  :)

[WayneCoeArtistBlacksmith]

Brian, you might want to move the box of matches further from the dragon's breath. :o

[Frosty]

Not bad Brian. Extra insulation is one of those can't hurt, might help things, I generally call it good at 2" but wash mine with zircopax/kaolin. The bubble alumina won't hurt but adding another very thin and fragile bit of insulation is pretty marginal. A proper kiln wash will protect the ceramic wool far better and reflect more heat back into the chamber.

 

You don't say what diameter the burner tube is but assuming you used Mike's basic design and used a 3/4" tube you need a 0.035 mig tip, then you can open the choke more.

 

One of the benefits of using a naturally aspirated burner is in not needing to keep tuning it every time you turn it up or down. Mike's burners induce air efficiently enough just tuning with the choke will put you in the groove. The induction curve is pretty flat between minimum psi and around 25-30psi. so once tuned just adjust the fire with the regulator.

 

You don't show or mention a gauge, a good one is a good thing. Don't worry about what psi other guys run for what, there are too many variables for their results to mean a whole lot to you. What the gauge will do is allow you to repeat temperatures with minimum hassle. Keep notes too, they'll really flatten the learning curve.

 

By the looks of the pics your forge is running pretty cool, a good welding temp forge will be white the camera out yellow. That's Incandescent yellow. The dragon's breath isn't excessive, looks pretty good if a little too orange. All in all, just a little tweaking and it's going to ROCK. For right now, I'd open the choke up a LITTLE, say 1/4" or less and test it. Write it down in the note book.

 

Change ONE thing at a time or you'll never know what did what.

 

Frosty The Lucky.

[rhitee93]

Wayne, Good call on the matches, not sure how I missed that :rolleyes:

 

I was hoping you would chime in Frosty,

 

I don't know much about burners, and I don't seem to get it when people talk about what to look for when adjusting the flame.

 

The pic you think looks a bit cool was actually stopped down 3 f-stops to keep from washing the picture out.  In reality it looks like a butter white/yellow, but maybe not as hot as you describe.

You are right in that I used a 3/4" pipe for the main tube.  Porter says to use a 0.030" or 0.035" tip, but doesn't really explain why to use one over the other.  I can make another injector with an 0.035" easily enough if it would be better.

 

My choke adjustments don't seem to be as flat as you describe.  Would the smaller orifice cause that?  I have to have the choke much further open at 5psi to keep the flame at the same point as I do at higher pressures. (There is a gage down by the propane tank)  There is a point where you can start to see green in the flame, I have been finding that point and opening the choke up a bit more until it is all blue.  

 

Thanks for the help. You are right about the notebook.  I need to start taking some notes...

[VaughnT]

Very nice build.  I'm jealous that you can get to welding heat at just 12psi.  My forge doesn't even get into the yellow spectrum at 12, and forge welding doesn't happen until, I'm told, around 25psi.

[timgunn1962]

Vaughn, please pardon my ignorance, but what is felt to be the advantage of hitting welding temperature at low pressure?

 

I can understand it for those in the higher latitudes, where low ambient temperatures might keep cylinder pressures low, but it's not obvious to me how it is advantageous for those nearer the equator.

[Frosty]

Wayne, Good call on the matches, not sure how I missed that :rolleyes:

 

I was hoping you would chime in Frosty,

 

I don't know much about burners, and I don't seem to get it when people talk about what to look for when adjusting the flame.

 

The pic you think looks a bit cool was actually stopped down 3 f-stops to keep from washing the picture out.  In reality it looks like a butter white/yellow, but maybe not as hot as you describe.

You are right in that I used a 3/4" pipe for the main tube.  Porter says to use a 0.030" or 0.035" tip, but doesn't really explain why to use one over the other.  I can make another injector with an 0.035" easily enough if it would be better.

 

My choke adjustments don't seem to be as flat as you describe.  Would the smaller orifice cause that?  I have to have the choke much further open at 5psi to keep the flame at the same point as I do at higher pressures. (There is a gage down by the propane tank)  There is a point where you can start to see green in the flame, I have been finding that point and opening the choke up a bit more until it is all blue.  

 

Thanks for the help. You are right about the notebook.  I need to start taking some notes...

 

Stopped it down that explains the color, so she's hotter than she looks. Good, that burner should be a lot hotter than the pic looked.

 

Mike specs a 0.030" - 0.035" mig tip as a good working range, his burner will work as drawn with either so for all practical purposes you don't need to worry about it. Using the larger dia jet means putting more gas into the fire per psi. per second. If your forge is hot enough there's no reason to mess with it unless you like to tweak the most you can get out of things. Ron Reil is that kind of guy.

 

So, if you put a 0.035" jet in you'll need to open the choke plate more and you'll be running at lower psi for a given forge temperature. Don't quote me on this but a larger jet should flatten the adjustment curve for the choke. Smaller jets need a higher psi. per given volume of propane/second. The gas stream is moving proportionally faster per psi and entrains air proportionally as well. A larger jet's velocity will vary less vs. psi. meaning the entrainment curve is more lineal, "flatter."

 

The short answer to your small vs. larger jet vs. intake/choke adjustment is. Yes. Unfortunately the short answer means I can't ramble as much. <grin>

 

Vaughn's statement wishing his forge would weld at such a low psi. is an example of why I said not to take psi as such into account. I've been  making burners that work well enough I have to be careful to not melt the 3,000f fire brick in my forge floor and it's operating range is 15-25 psi.

 

There are just too many variables for such a simple number to mean much, my burner's operating range changes day to day, sometimes during a session. Especially during winter here, the air is dense when cold and dry so, as the shop warms up the fuel air ratio changes and I tweak the reg to keep it where I need.

 

Folk like to be able to control their stuff and if there's a simple method so much the better, like setting the thermostat in the house or the knob on the range or cruise control. You bet, I like set it and forget it, I may be weird but not THAT weird. We just aren't making devices with brains in them, even if it is just a bimetal spring and mercury switch like the house thermostat. Our burners will always require a little hands on control to hit the balance between hot and economy we need.

 

After all that if you can weld in your forge and that's what you need, don't fix it it ain't broke. <grin> OR if you want to tweak it till it sings and dances, keep us in the loop and take pics, please.

 

Frosty The Lucky.

[VaughnT]

what is felt to be the advantage of hitting welding temperature at low pressure?

 

My forge, for example, gets extremely hot on the outside after just a few minutes of forging.  This is because I'm losing a lot of heat through the insulation.  As such, I have to crank the psi higher to compensate for the rate of loss, meaning that I have to burn more gas to get the same effect as someone with a more efficient forge lining.  

[JimsShip]

Pics don't display for me, just little red x's. :(

[Frosty]

My forge, for example, gets extremely hot on the outside after just a few minutes of forging.  This is because I'm losing a lot of heat through the insulation.  As such, I have to crank the psi higher to compensate for the rate of loss, meaning that I have to burn more gas to get the same effect as someone with a more efficient forge lining.  

 

Yeah, your liner needs some rethinking, the outside of the forge isn't where you want the heat.

 

What kind of liner are you using?

 

Frosty The Lucky.

[Frosty]

Pics don't display for me, just little red x's. :(

 

That's how forum the vote went: Red Xs for Jim.

 

Of course you might just want to check your preference settings but that'd sort of make it harder for me to poke foolishment at you.

 

Frosty The Lucky.

[Dodge]

Just a little trivial(?) fyi while orifice sizes are being discussed:

The hole in a *.035" mig tip* isn't actually .035" in diameter. Otherwise, the .035" diameter wire would drag. I don't recall the exact figure and I assume it may vary slightly from manufacturer to manufacturer, but, IIRC, its closer to .039" or .040". (#61 or #60 drill) For a 1" pipe T-burner, I drilled a *.035* mig tip to #57 (or .043") and I have to choke it a bit to control scale some. Its the same tip I used previously in a 3/4" Reil burner and it worked great there. Point I'm making is that ".035 mig tip" isn't .035"

 

Hope this helps,

Scott

[timgunn1962]

As close as I can measure using drills as Go-NoGo gauges, my cheap noname MIG tips are between .006" and .007" bigger in diameter than the nominal wire size.

[WayneCoeArtistBlacksmith]

My forge has 1" of Inswool and 1/2" of Kast-0-Lite then a coat of Metrikote.  I can forge all day long and when I shut the forge down in the afternoon I can reach out and touch the outside.  Now, I don't hug it but I can touch the shell and not leave my fingerprints.

[Frosty]

Right you are Scott, it's easy to forget a 0.035" mig contact tip is a designation not a size. Differences in manufacturer could explain some of the variances in working tip sizes too. Dang, I thought I had it down to a by the numbers thing. <sigh>

 

I must . . . ponder this development. Ohmmmmmmm.

 

Frosty The Lucky.

[LastRonin]

 

Frosty

Posted Today, 07:10 PM

Right you are Scott, it's easy to forget a 0.035" mig contact tip is a designation not a size. Differences in manufacturer could explain some of the variances in working tip sizes too. Dang, I thought I had it down to a by the numbers thing. <sigh>

 

I must . . . ponder this development. Ohmmmmmmm.

 

Frosty The Lucky.

 

Is that patchouli I smell? :huh:

 

[VaughnT]

Yeah, your liner needs some rethinking, the outside of the forge isn't where you want the heat.

 

What kind of liner are you using?

 

Frosty The Lucky.

No telling, Frosty.  It's a cast OEM insulation, the floor is just 1" hard fire brick.  How hot does it get?  Well, it will make a pine board smolder after just a few minutes: the wood tabletop it was sitting on got hot enough to turn to charcoal after just a few minutes, and that was through a 1" layer of hard fire bricks I put down as a barrier between the two.

 

I'm thinking a coat of metrikote or the like would help, but there's nothing much to be done with the size of the box it's all in.  An overbuilt shell that underperforms as a forge.

[JimsShip]

That's how forum the vote went: Red Xs for Jim.

 

Of course you might just want to check your preference settings but that'd sort of make it harder for me to poke foolishment at you.

 

Frosty The Lucky.

 

Wow, I didn't even see this jab until I my search for firebrick sizes led me back here! It's not my computer settings wise guy, but the filters at the hospital where I work that's blocking me. :)

 

So, since i'm here-  firebrick for a small forge, is the standard replacement bricks for a wood stove (4 1/2" X 9" X 1 1/4" ) enough for the floor and doors?
 

[Mikey98118]

Brian,

Listen to Frosty's advice, but if you want to see that forge enteior go from yellow up to yellow-white use ITC 100, or a homemade equivalent in it.

Porter

[Mikey98118]

Brian,

Listen to Frosty's advice, but if you want to see that forge enteior go from yellow up to yellow-white use ITC 100, or a homemade equivalent in it.

Porter

[Mikey98118]

Brian,

MIG tip sizes are listed for the welding wire they are meant to handle. An .030" MIG tip actually has an .035" orifice, and an .035" tip has an .040" orifice. I recommend buying both tips because neither is a perfect orifice diameter for this burner size; the smaller tip will put out a better flame in the lower gas feed pressures, and the larger tip is needed for best performance at higher gas pressures. Somewhere in the book I mention using torch tip cleaning file sets (about $2 at your local welding supply store), to ream the smaller tip out a couple thousandths if you want perfect gas accelerator performance. Most people just buy both tips. I mean, it isn't as though you're going to be running the burner up and down its range just for something to do, is it?

Porter

[Mikey98118]

Brian,

Listen to Frosty's advice, but if you want to see that forge enteior go from yellow up to yellow-white use ITC 100, or a homemade equivalent in it.

Porter

[Mikey98118]

Brian,

I recommended two MIG tip sizes: For .030" welding wire and .035" wire. The reason is that this burner size "sits on the bubble" the smaller tip works better at lower pressures; the larger tip at higher pressures. I sand bagged a lot of my figures and recommendations. Actually, I tested out every burner in the book up to 60 PSI, and then listed their limits as 30. You need to remember that this was a brand new burner design and my legal exposure lasts as long as the book goes on being read.

 

So, when guys wrote back then that I must be bragging, I laughed out loud, knowing the burners would actually do far more than I'd claimed.

 

But, I did play fair; the book also recommends using a set of torch tip files (about $2 at your local welding supply store) to ream out the smaller tip size a couple of thousandths to get perfect performance out of this burner. Most people would rather buy two tips; after all, it's not like you're going to be changing them back and forth much.

 

Here is another tip that didn't go into the book: On any of these sizes the builder can cut the amount of air openings down to three by simply widening the air openings and have room left over to widen (and therefore strengthen) the ribs between the openings. The other result of this change is a more powerful burner, so why didn't I mention that in the book? People hadn't built thousands of these burners back then. The extra air openings made the burner run a little smoother out in the open air, and I wanted all the extra safety I could get.

Porter

[Mikey98118]

To timgunn1962

The gas pressures they are talking about have to do comparisons to other gas pressures out of the same size of orifice; so 12 PSI versus 25 PSI means less than half as much gas used to produce a desired result, assuming that the same size orifice is used in someone else's forge, and if the same sized burners are being used, it is also likely that the same size gas orifices are being used.

Porter

[timgunn1962]

That would make sense Mike.

Except there seems almost never to be a jet size mentioned when I see pressures quoted in relation to welding temperatures.

 

Like Frosty says, the wide variety of burner designs out there seems to make the likelihood that apples are actually being compared with apples pretty small. That's before we even start on the differences between forges.

 

Personally, I'd rather build a Venturi burner to give welding temperature at around 30 PSI and take as much turndown as I can get for when I don't need to run that hot. To use half the gas, I am fairly sure I'd need to drop from 30 PSI to 7.5 PSI, as pressure vs flow through an orifice follows a square law. Going up from 30 PSI to 60 PSI would give around a 41% increase in gas input on that basis, but I think the flow chokes somewhere around 30 PSI so the increase would actually be less. 

 

Unless I've completely misunderstood the physics, turning down from 25 PSI to 12 PSI actually reduces gas consumption by only around 30%.