A thin hotface medium/low mass beer keg (drum size) furnace for melting Iron

(laughing) Yes, I post a lot of stuff, but I enjoy the often useful feedback, and sharing the trials and tribulations of backyard castings with others who have had/are having the same experiences.

And I also basically leave a paper trail for myself and others, so that if I have to build another furnace in a few years, I can look back and remember what the heck I did.
I have learned so much from scavenger's iron furnace builds (and many other's threads), so I know the value of long threads that go into a lot of construction detail (tedious to read, but chocked full of useful information).

Thanks much for the brick cutting and lid construction info. Very helpful stuff indeed.

Edit:
I am wondering what I have that I could cut up and bend into that round shape that you have for the lid.
I may go buy a trailer fender (or three).
I have used those in the past for a muller build, and they are the right gauge for this application.
Here are a couple that could be cut to the right shape and bent:
https://www.northerntool.com/shop/tools/product_200648942_200648942
https://www.northerntool.com/shop/tools/product_200648966_200648966

If I played my cards right, I could perhaps cut a fender down the centerline, and retain the rolled-over edges. That would save me a lot of bending.

 

Edit: This is a summary of scavenger's furace builds.

I am re-reading some of scavenger's furnace build.
It is a very long thread.
No sense repeating any of the mistakes scavenger made.

Johnson Furnace:
He started out with a Johnson commercial furnace, and roasted it to shreds.
It had a steel spider web in the thick cast refractory lid.

Furnace #1:
Scavenger's first furnace build (furnace #1) used a 55 gal drum for a shell, two 1" layers of ceramic blanket, then one layer of 2,800 F insulating fire bricks vertical with beveled edges, cement between the bricks, and 1/2" or less of cast refractory over the bricks on the walls, and only 1/4" thick refractory over the top of the bricks at the lid joint.
He notes that the bricks were not rigidly supported, and thus broke and moved back into the ceramic blanket, and the refractory broke off the top of the bricks.
Apparently he did a lot of patching on this furnace and got about 150 iron melts out of it, which is impressive for 2,800 F fire brick with a light coating of refractory.
The floor of furnace #1 had to be replaced after a few melts.
Furnace #1 had a 14" bore.

Lid #1:
The first lid he made for the #1 furnace used a piece of 55 gal drum, and had apparently 2" fiberboard at the top of the lid, with a thin cast refractory coating (perhaps 1/2" thick refractory), and this lid began to fail during the first iron melt, and completely failed halfway through the second iron melt.

Lid #2:
The second lid he made for furnace #1 used a 55 gal drum shell, and had a layer of 2,300 F, 2 1/2" thick insulating fire bricks on top the lid, then a metal fan guard (like from the top of a residential outdoor condensing unit), and then poured about 3/4" (+ -) of refractory. He used stainless needles for the first time in the lid refractory. He sculpted a slight dome into the interior of the cast refractory with a hand trowel.
The refractory was allowed to protrude up past the bricks in a short chimney affair, to protect the ends of the bricks.
He used a heavy steel mesh over the top of the lid, to protect the insulating fire bricks, and so he could set scrap on this surface for preheating.
He notes that this mesh began to disfigure over time.
He also notes that there needs to be some supports welded inside the lid drum section to prevent the refractory from sliding down in the steel shell.

Standard 55 gal drums are 24" in diameter.

Furnace #2:
For scavenger's second furnace, he used a heavy steel hydraulic tank, which was the same diameter as a 55 gal drum (24" dia).

He started inside the drum with 2.5" thick insulating fire brick (rated 2,800 F), using a double stack.
He installs these bricks hard against the heavy steel shell.
A 1.5" space was left at the top of the brick (1.5" less than the top of the steel shell) to allow for cast refractory on top the bricks.

He then pours 3" of refractory as the floor of the furnace.

The bore of furnace #2 is 16" dia.

He added a center form (16" dia) and poured refractory.
Both the wall and floor refractory included stainless needles.

The thickness of the wall refractory would be 24" - 2.5" - 2.5" -16" divided by two, which is a 1.5" thick refractory hot face.

This furnace used 275 lbs of castable refractory, 48 insulating fire bricks, and 8 lbs of stainless needles.

Lid #3 (for furnace #2):
The third lid was made with a piece of the heavy wall 24" steel tank for a shell, a cultivating disc welded onto the top, and a steel pipe welded on top the disk (to create a chimney to prevent flames from impinging on the top of the lid). The chimney pipe was approximately 8" diameter and perhaps 6" tall.

Inside the lid, a layer of 2.5" thick insulating fire bricks was added, cut into pie shapes, and following the dome shape of the lid.

He used the end of an air compressor tank as the inner form for the lid, to achieve the dome shape on the refractory.

He welded in a steel fan guard (beaten into a domed shape) to support the insulating fire bricks.
He also welded steel tabs inside the shell to retain the poured refractory.
He mentions vibrating the refractory in place.
The refractory extended to the top of the chimney.

The refractory was rated 3,100 F for this lid and furnace #2.
It looks like he may have used 1.5 bags of refractory for the lid (55 lb bags I assume).

Looks like he changed to a standard siphon-nozzle oil burner when he built furnace #2.
The first oil burner he used was a bit of an oddball.

He also mentioned that his first melt produced a lot of slag, and the crucible was on top of a 1" plinth. He claims the slag problem was resolved by using a 3" tall plinth.

Pour time for furnace #2 with iron is 1.0-1.5 hours, typical.
He mentions using an A-40 crucible, but I think he went larger than that as the thread progresses.

He notes that furnace #2 is still going strong after 15 months and perhaps 200 iron pours, but the interior of the furnace has a heavy coat of slag, and his crucible looks quite thin at the top.
30 melts per crucible before they must be retired.

He mentions that at some point furnace #2 had a lid failure, and he almost lost the entire melt.
I had the same thing happen to me in mid melt and I lost a new #30 Morgan crucible when I was unable to continue the melt, and unable to dump the iron out of the crucible.

He notes that sealing the furnace/lid joint is an ongoing problem, which is why I added a lip on the bottom of my lid.

Scavenger mentions a furnace #3, but the thread stops in January of 2017, and no more videos either (bummer).

It is a great furnace thread though.
I went through it all again because I was not exactly sure how many lids and furnaces he had built, and not sure exactly how each was constructed.

It looks like furnace #2 and lid #3 were a great success, and both used insulating fire bricks covered by a layer of 3,100 F castable refractory, and a metal grille cast into the lid refractory.

200 (+) iron melts on a furnace and lid is a successful build in my book.
Apparently no problems with imbedding the steel grille at the top of the lid refractory as far as expansion/cracking issues, else the lid would not have survived 200 iron melts.

The question still lingers though; what would/does furnace #3 look like?

 

Thanks for that writeup.

Unfortunately my drums have all shrunk, they are about 22" ID, and they are not very round.

Edit: I also wanted to comment on the impingement on the furnace wall, I'm getting a lot of buildup using used motor oil, I'm sure it's soot, metals, and other impurities. But the carbon is all gone.

Edit edit: I have also read that polycarbonate blocks UV-A, B, and C. That would make cheap face shields an effective UV protection. Anybody take issue with that?

 

I would stick with glasses that have an IR/UV label, otherwise how do you really know?
I have a clear plastic face shield, and it will blind you looking at the melt.

Wife wants to travel over the holiday weekend, so maybe after that I can get something going.

 

This reinforces what I have been saying about the bottom of the furnace being significantly cooler than the top of the furance; cooler enough that the iron does not melt completely/properly.
I have had this happen to me, and speculated about the plinth height since I noticed that both ironsides and porositymaster use rather tall plinths.

 

I see no evidence of cracking on my flat lid, and so I guess I will try using it again on the next melt, with perhaps a hard fire brick cemented over part of the lid opening.
May as well use it until it fails since it is already built.


I want to use water-based green sand for the next mold, and it was too dry for the last pour.
No time to finish the muller, so I will use a concrete tub and a hoe to mull it; crude but effective (poor man's muller).

 

Amen on that.
If the war department is not happy, then nobody is happy (she will make sure of that).

 

One thing that scavenger does not really mention about his furnace #2 is the height of it, but assuming he used two stacked 9" tall bricks, and allowed 1.5" additional space for refractory on top the bricks, minus the 3" tall refractory floor, then his interior furnace height would be about 16.5 inches (bore of the furnace was 16").

A Morgan A-40 crucible measures 9.12" top diameter, 6.25" bottom diameter, and 12.5" tall.

So if scavenger used a 3" tall plinth, then he had a 1" clearance between the top of the furnace refractory wall and the top of the crucible, but actually more clearance than 1" since his lid interior was domed.

Scavenger was asked about the thickness of the refractory wall, and he speculated that it was about 2.5" thick, but if you do the math, his refractory wall was only 1.5" thick.
So that proves that a 1.5" thick furnace refractory wall with stainless needles will withstand over 200 iron melts.

My refractory shell is only 1" thick, but I think it will work, and it also has needles in it.

At 275 lb, his furnace was 62% the weight of my first furnace.
One of my blunders was to use up the remaining refractory in the lid for my first furnace, so the lid by itself is perhaps 8" thick, maybe more.
I could salvage my old furnace by just making a new lid for it (to save on melt time).

The refractory shell of my first furnace is between 3" and 4" thick (it is not uniform due to the center form trying to float).

I seem to recall using at least 8-55 lb bags of refractory, so the furnace without all the metal work weighs at least 440 lbs.
My first furnace was an exercise in stupidity, but it does work very well as an aluminum furnace since you can melt aluminum without actually getting the refractory up to any significant temperature (unlike iron), and I am guessing that if someone finds my first furnace 1,000 years from now, they will be able to fire it up and use it easily, but will probably wonder what kind of dumbass would make such a monumentally heavy furnace.


Edit:
Porositymaster did mention that he has a lot of plinth failures, and that is probably the downside to using a tall plinth, but I bet the crucible lasts longer with a tall plinth since a tall plinth would absorb the brunt of the flame impingement.

 

I lay a soft firebrick over part of my flue when I want to close it up. Why cement anything down?

The advantage to having a large annular space is the flame can wrap all the way around the plinth so everything heats from the bottom up.



I can't seem to get a good picture of my flame but since I'm left handed my burner goes in for clockwise rotation but with it pointed down 10 degrees it really helps keep it on the floor for the first revolution. It also helps oil drips go into the furnace. I'm over 200 aluminum melts on this furnace now and see no deterioration. Melting aluminum bronze the other day I burned off the end of my steel dipper so it was good and warm. You guys have me wanting to melt cast iron.

 

I have seen many references showing polycarbonate UV transmission cutoff. That said, I have found it uncomfortable to bring my face within 3 or 4 feet of my open furnace when the iron is getting good and molten. So, clear polycarbonate glasses would not be enough for me. Not only is the visible light uncomfortably intense, but the radiant heat allows only brief exposure. For me, a very good and inexpensive solution has been a simple shade 5 welding shield like this:

https://www.amazon.com/gp/product/B015ZL1SS6/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

It protects my entire face from the heat and my eyes from the intense brightness and UV. It is not so dark that I cannot see surroundings in daylight though. (I also wear a Carhartt jacket and long cuff leather gloves. Even so, I can only work at slagging the melt for maybe 10 or fifteen seconds before needing to close the lid and cool off. Otherwise you will start to cook the gloves. )

Denis

 

That's exactly what I'm using. And the link you quoted does not mention UV protection. If it is polycarbonate I believe it offers excellent UV protection. You can damage your eyes using dark glasses without UV protection.

 

I am using safety glasses like these, which are listed for both UV and IR protection (basically gas welding glasses).
https://www.homedepot.com/p/Lincoln...IR5-Flip-Lens-Brazing-Glasses-KH965/205993212

5.0 IR
UV-A, B, C protection

 

No, the link I provided does not state UV protection. Then again it is intended for welding. And if you go to ERB's website it does state that all ERB's polycarbonate face shields provide 99% UV protection.

Here is a link specific to their shade 5.

http://www.e-erb.com/customer/erinin/customerpages/Specs/files/FaceProtection/FP_8168.pdf

Denis

 

I noticed that porositymaster (guy from Mississippi who runs his own commercial foundry) skims his iron with the lid closed.

I tried this with my current lid, and my glove tended to get cooked.
My lid opening is too large.

I was thinking about cementing a fire brick in place because when I laid one over part of the hole, the exhaust stream blew sideways onto my rigidized ceramic blanket, and began to break it up.

I am pretty sure I had a very high fuel flow rate the other day, and since I have calibrated the nozzle to 3 gal/hr and added the dump valve to the combustion air (leaf) blower, I think my air stream will be greatly reduced.
I think what I will do is just remove the ceramic blanket from the top of my current lid.
I need to be able to spot any cracks anyway, but my guess is the cracks will only be visible from the bottom of the lid, not the top.

And unsupported hard fire bricks tend to break when exposed to that much heat, so I don't want the brick to fall in the melt if it breaks.
Now that I think about it, I would need to use refractory instead of furnace cement, since the furnace cement I use is not rated for exhaust stream temperatures.

 

The darkened full face shield is not a bad idea, but it would limit peripheral vision for me at night I think, and my pours in the summer tend to run into darkness, in order to avoid melting in direct summer sunlight.
Direct summer sunlight around here will almost melt iron by itself.

 

I pay a lot of attention to what ironsides does since he has successfully melted and poured iron for a very long time.
After the above comment from scavenger about having to elevate the crucible in the furnace in order to reach iron pour temperatures, I went and looked at ironsides video located in this thread:
http://forums.thehomefoundry.org/index.php?threads/furnace-measurements.178/

and he gives some very useful information about his furnace dimensions, and also dimensions of his crucibles and plinths.

His furnace is 13.8" (350 mm) in diameter, and 14.8" (375 mm) in depth (interior dimensions).

The crucibles he uses are an A6, an A12 and an A20?, and the respective diameters and heights are (A6) 5.1" (130 mm) dia, 6.7" (170 mm) height, (A12) 6.9" (175 mm) dia, 8.7" (220 mm) height, (A20?) 7.9" (200 mm) dia, 9.8" (250 mm) height.

The clearances between the top of his crucibles (when in the furnace and on top the plinth I presume; I think his crucibles have built-in plinths?) and the bottom of his lid are as follows:
(A6) 4.5" (115 mm)
(A12) 4.7" (120 mm)
(A20?) 3.1" (80 mm)

The vent hole in ironsides furnace lid is 5.9" (150 mm) in diameter.

 

From the research I did last night on scavenger's first furnace build, where his used insulating fire bricks with a thin refractory coating, my guess is that your exposed 2,600 F fire bricks may not last very long at iron temperatures.

I made a small furnace from all insulating fire bricks, with no hot face refractory, and it lasted one burn with my oil burner.
I don't know what grade of insulating fire brick I was using, but my guess is that you would need something in excess of 3,000 F fire brick to use it exposed, and I am not convinced any insulating fire brick can be used without a protective hot face, when using an oil burner to melt iron (I could be wrong but I have never seen and IFB-only furnace survive an oil burner.

I ruined a perfectly good and new IFB furnace on the first oil burner melt, and wasted some good money and time too.
I did not save a photo of the disaster; it was just too much to look at; new bricks all crumbled into a big pile.