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

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Pat I cannot thank you enough for the help and the Drawings especially. I will be going down the furnace road soon with a build for everyone

 

Hope the drawings help.
Thank me if it all works well.
If it does not work well, then I am changing my name and moving out of town.

I am very pleased with the speed at which it melts iron, and a replacement hot face is only a bag and a half of Mizzou away.
Hot face and lid replacement is about 2 bags of Mizzou, so less mass and less money too.

I did cast a tuyere extension to allow the burner tube more length along which to seal, but I do not show that on the drawings.
The tuyere extension is also 1" thick refractory, and protrudes out perhaps 6" from the furnace (3"-4" would really be sufficient).
And I would cast the tuyere extension integral with the hot face and bottom, all in one piece.

I rammed the hot face about 2" at a time, using a 1/2" wood dowel rod to thoroughly ram each level.

Edit:
And as I mentioned, if I made another lid, I would omit the lip and see how that worked.
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The lip on the lid is turning out to be a very bad idea, at least with the clearances I gave it, perhaps 1/4".
My furnace shell is expanding when heated and jamming the lid so I cannot get it open, in spite of me grinding on the refractory to give more clearance.

I am going to build up fire brick around the top of the hot face to make a flange for the lid to rest on, so that the lid lip does not have to engage the furnace refractory.

Live and learn.

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I am having some issues with the thin hot face cracking.
(this is a long post, and is basically my checklist of things to do/try, so you can skip to the end and read the last paragraph to save a lot of boredom).

When my lid got stuck last fall, I pulled up on it hard, and sheared the refractory horizontally at about the center of the hot face shell.
I saw what was happening, and let the lid back down carefully before the crack opened up more than about 1/4".

I ground on the refractory at the top outside edge the other day, and supposedly added enough clearance to allow the lid to open easily when everything was hot, but it was not to be.
I fired the furnace today, and the lid stuck solid as a rock again to the refractory shell.

I was due to take the furnace down to the F.I.R.E. show today, however the demonstration is not until Saturday night, so I have a little time to rework things.

The 1" Mizzou is cracked horizontally and vertically.
The bottom of the shell is cracking/separating from the vertical refractory wall.
The refractory shell is still solid, and I am guess that the stainless needles are holding it together.


So I have some issues:

1. I need to remove the lip from the lid and just let the lid rest on the top surface of the hot face, but there is no way to do that without recasting the lid refractory.

2. I wrapped the stainless lid shell under the bottom of the refractory, instead of anchoring the refractory with screws from the sides, and so there is a danger now of hot gasses escaping a flat lid joint and overheating the lip on the lid shell, and the entire lid refractory falling out.

3. I need to elevate the fire bricks that are around the refractory shell so that the lid can rest on those without dropping the lid lip down over the hot face.



Some observations:

1. All refractory cracks at iron temperatures.
There is no way around this, and so basically the refractory has to be contained in place.

2. I don't think a cement bond between cast refractory and insulating fire bricks will hold up, and I think this joint would crack.
So I am refraining from cementing the insulating fire bricks to the hot face shell, although it is a tempting thought.
Cementing it all together would prevent it from being rebuilt in the future when it starts to crack.

3. Since all refractory cracks at iron temperatures anyway, I am starting to think about casting individual curved pieces for the hot face (from refractory).
I am reminded of what the concrete man told me about 25 years ago when he replaced my driveway.
He said "My driveways don't crack. I use an expansion joint every 10 feet."
He was right, my driveway has never cracked.
So perhaps the same approach for refractory; ie: use curved individually cast refractory pieces, and seal the joints from the inside.
I have to seal the cracks as they occur anyway, so no different than keeping joints sealed (at least I think that logic holds).

And individually cast refractory pieces could be replaced individually too.
I am not sure if individual pieces could be cast as thin as 1" though.

4. An iron furnace hot face and lid are going to be a high maintenance items, and a rebuild can be expected every "X" number of iron pours (I am not sure what the value for "X" is).

5. The stainless steel bands that I put around the hot face are scaling badly, and will not last forever.


Changes:

1. I added a heavy steel plate tonight under the furnace to better support the insulating fire bricks.

2. I will cut another set of upper row insulating fire bricks tomorrow, and let them extend up flush with the top of the hot face shell.

3. I will probably cut a ring of hard fire bricks to go around the top, to create a flange at the top of the hot face shell.
The bottom lip of the lid will rest on these hard fire bricks.

4. The cast refractory tuyere extension is a problem to keep in place, and I need a better solution for that.
I may core drill through some insulating fire bricks that are supported from the base.

5. At some point the lid refractory may have to be re-cast so that the stainless shell does not turn under the refractory at the bottom of the lid.
I obviously cannot change this before Saturday, so I will have to make do with perhaps a temporary ceramic blanket gasket around the lid, but the ones I used in the past tended to fail, so that is a short term solution at best.


Some aggravating issues that are occurring late in the game, but fully to be expected from an unproven prototype furnace design.

One of the reasons I kept the pieces modular and not cemented together in one big monolithic block was to allow adjustments as necessary to change/adjust the design.

The siphon nozzle burner and associated fuel system operated well today without problems.

More work tomorrow.
Perhaps I can salvage the demonstration pour.
That is the plan anyway.
I think worst case the ceramic blanket gasket will get me through one melt.

If the lid fails, I will toss it to one side and finish the melt.
Damn the torpedoes, full speed ahead !!!



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In the MIFCO furnace whose plans I posted a while back it is noteworthy that they cast their liner refractory cement in 3 individual pieces each about 1/3rd the circumference of the the hot face. Might just be a reason for that.

I tried casting a full-circle vent liner of dense refractory and low density refractory.The first one was low density and it cracked on the first firing eventually developing many cracks and threatening failure. It lasted a fairly large number of firings but eventually failed. On my second liner I made it with a thin (1/16th?) expansion joint. Eventually it developed one other crack opposite the joint but no more cracks occurred. On my next liner, I think I will cast it as two hemi-circles.

My conclusion is that fully circular refractory componenets will crack if driven hard. Using control joints makes sense.

Denis

 

Too bad about the lid. That's especially hard right before a show.

 

I have reached that conclusion too, and almost certainly I will use a refractory liner in the future that is in multiple pieces, but not sure exactly how many.
I have become a believer in control joints.

I think I am going to buy a sack of refractory, and separate the fines out from the aggregate, and use that for patching compound.
ITC products are just too expensive.

That is what I get for waiting until right before a show to test things out.
I have been busy with work stuff, and so my foundry time this year has been limited.

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Did you see the four piece tongue and groove shell I cast? I've never completed it. But it shouldn't crack.

Have you thought about Satanite to patch the liner? I think it's rated for 3,200F or so. It sure is friendly.

I bought a can of ITC-100 and have put some on but really can't tell it is any better than Satanite, which is almost free by comparison.

 

I need to see that (not sure if I have seen it before; I don't recall it).

I will buy some as soon as I can get it.
Who is a good supplier?

I can't afford any more ITC, so satanite it is.

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Here are the photos; the good, the bad, and the ugly.

I think I have fired this furnace at least six times, with four serious iron melts.

Removed the outer stainless shell and one brick.



The upper and lower row of insulating fire bricks look good.
A little scorching, but very solid.






This is the 1" ceramic blanket, and it is in good shape.
A little scorched, but not at all melted or brittle on the side that faces the hot face.



The lid has a few hairline cracks, but nothing major.





The stainless bands are not fairing well.
The upper band is to minimize vertical cracking that begins at the top of the hot face.
The lower band holds on the tuyere extension.
Lots of scaling.






The interior of the furnace looks good.
I have been patching it with ITC200.

 

The exterior of the refractory shell is cracked badly.
Surprisingly it is still very solid, and can be handled without breaking.
My guess is the stainless needles are holding things in place.

I think this hot face is usable as long as the interior is kept patched, and it is contained.
I will patch the cracks from the outside tomorrow, and it will look much better (not that looks matter, and not that I care about looks either).

The horizontal cracks are caused by the lid sticking, and me trying to force the lid open while the refractory was hot.
The vertical cracks were caused by expansion of the refractory, which I think gets hotter at the top than at the bottom (the cracks always open at the top first, and then migrate down).

I am just glad the shell is solid and not crumbling.
When I ground around the top of it, it was like grinding diamond.
The aggregate in Mizzou is very hard stuff.

 

Here is the layer of insulating fire bricks that the hot face sits on, and they have some very thin strips of ceramic blanket on top of them.
The bricks were in great shape.
The ceramic blanket strips were scorched, but not brittle at all.





No problems with the frame.

 

I decided to add a steel plate, in lieu of the inverted aluminum water heater pan.
The pan did not provide as good of support of the insulating fire brick as I wanted.

 

The fix planned for tomorrow is to cut some 1" thick hard fire bricks in a circle and install them around the top of the furnace.
The upper layer of insulating fire bricks that are standing vertically will have to be replaced with new ones cut to the exact height.
Of course there will not be gaps between the bricks.

The lid will rest on top of the hard fire bricks.

I will probably cut outside of the hard fire bricks round, and band around those.
I have quite a few very long stainless hose clamps.

This is sort of a cludge, but about the best I can come up with on short notice.

I am considering omitting the 1" ceramic blanket, and banding around the outside of the insulating fire bricks, with some thin strips of ceramic blanket under the bands to allow for expansion without cracking the IFB's.

I may put the ceramic blanket over the bricks, with the intent of the bricks being right against the hot face to perhaps add a bit more rigidity to the hot face wall.
I could cement the bricks to the hot face wall, but that would only crack, and would not allow a rebuild/replacement of the hot face without replacing all the IFB's too.
If the bricks degrade from being up against the hot face, then they will have to be replaced one day.
The outside of the 1" thick hot face does get bright red, and I was not expecting that.

I think this would get me through the demonstration, and hopefully allow a lot more iron melts.
At least there will be no way for the lid to stick closed.

Edit:
I could potentially change the upper layer of vertical bricks to a taller set, and let them come up to the top of the hot face, and call it done.
That may be all I have time for tomorrow, but hard fire bricks up top will last longer over time, because a flat lid joint always leaks.
My lip joint did not leak, but I did not allow enough space for expansion and refractory shifting, and so that did not work out.

 

Here are all the pieces to the jig saw puzzle.

 

Since the subject of segmentation of castable furnace components is being discussed, I looked again at MIFCO’s user manual, this time with the perspective of more experience in furnace use. Studying the manual shows their segmentation ( 4 or more not my recalled 3 parts) strategy of refractory division. They do mortar their parts together. If interrsted, start looking around page 30 of this manual.

http://mifco.com/B & C Manual-2014.pdf

Denis

 

Wow! It sure came apart nicely!

I think your stainless bands are a detriment. They are against a hot face and are only good for about 1,800F max in short term service. And expect them to actually melt at 2,500F. What they do is hold the Mizzou from expanding as it's heating to make it crack, then when they get hot they expand faster than the concrete so they offer no support while at temperature. You really should only use banding in cool areas.

You're seeing lots of gas leakage, maybe from around your tuyere. I think that is what is getting your shell hot, not a lack of insulation. You can see the black on the edges of the brick. Maybe your furnace is pressurized. If you're putting in enough air to burn 3 gph cleanly your flue opening may not be large enough. Pressure inside will cause hot gasses to flow through cracks seeking an outlet, around the tuyere and up the sides of the shell.

I vote for extending the height of the vertical brick. If you're worried about wear smear some mortar on top. Don't mortar things together, they have to swell with the heat and if you get a good mortar joint you'll get breakage between the brick.

You know temperature drop across insulation is all connected with energy flow, it's about like an electrical circuit. In this case you have three resisters in series - Mizzou, wool, brick. If you have, DC electrically, a low resistance (Mizzou) in series with a high resistance (wool), in series with a higher resistance (brick) you have low current flow (heat) so the voltage (temperature) will drop only a little through the first (Mizzou), then a lot through the second (wool) and more through the last (brick). You also have loose connections at the end (steel shell with convection to take away the heat). So if you have 2,800F inside, the outside of the Mizzou could easily be 2,500F (almost to melt the banding) because you have low current flow and almost no voltage drop. If you put more and more layers of insulation around the furnace you cut the heat loss and everything eventually comes up to temperature. One inch of wool is not going to be a good as 2-1/2" of brick. I did some quick calculations and you could assume 1" Mizzou is 130 ohms, 1" of 6# blanket (if not compressed) is 1,100 ohms, and 2-1/2" of 2,600F brick is 1,250 ohms. Pick your voltage, say 28v for 2,800F inside, and 8v (800F) outside and easily calculate the voltage (temperature) at the intermediate faces. Outside of the Mizzou will be HOT.

Fine cracks are, fine, big cracks like you have will pass gas and artificially heat what's outside. Your stainless needles won't stand up to a lot of heat. Personally I don't like them because I've found them to inhibit expansion and tend to crumble the hot face. They're great when thing don't get too hot. About the only metal which does not melt around 2,500F is titanium at about 3,000F.

Extend your side brick, let everything float inside the cold outer shell, and don't try to set records the first few firings. Good luck!!

 

Their segments look rather heavy, but I am going to contemplate this.
I guess a lot will depend on if my 1" hotface holds up after cracking.
Thanks for posting.

Edit:
I have seen some furnaces made from vertical hard fire bricks standing in a circle, but it does not make for a round shape exactly, and I have noticed that combustion inside the furnace is sensitive to irregularities.
The entire combustion process in the furnace is easily disturbed with something as simple as the paper towel that I put in the furnace initially to light it.
I have read (forget where) that a round furnace is important for complete combustion.

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That was from the drip-style burner tests, where there was raw fuel running out the tuyere.
That burner did not work well at all.

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