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

Reading about bubble alumina, it is designed to be cast into tiles. Should be great for hearths.

 

My thinking is if the curved hard bricks are reasonably priced, and rated at least 3,000 F, it would be foolish not so snag a few, because sometimes these places go out of business, and then when you need them, you can't get them.
Another big benefit of buying fire bricks locally is you can avoid the often exorbitant cost of shipping.

With 110 lbs of patching compound, chances are I may not need them any time soon, but I am also contemplating a mini-iron furnace with perhaps a #5 crucible for small stuff.

Every time I have passed over an opportunity to grab some good foundry supplies for cheap, I have regretted it later, so I think I will grab them while the grabbing is good, whether I use them or not.

And perhaps grab some of two different radii.

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I think it might be worthwhile to do some creative thinking about how one could design decent sized segments that could be fired in an ordinary-size pottery kiln and that might stack well and interlock or key together well. So then furnaces of say 1, 2, or 3 courses high walls and varying diameters could be assembled. Maybe curved segments 3/4” thickness could be pressed into service. Being segmental, portions that fail could be replaced. Relatively low mass hot faces could be assembled. OIF’s segments keyed together vertically. The dreaded cracking of the hot face would be prearranged and now accepted.

Ordinary dense refractory would be satisfactory for his application.

Denis

 

I think that if I had more time this year I would pursue this route, but maybe next year.

It would take time to make a mold or molds.
I would really want to ram up a 55 lb bag or two of Mizzou at the same time, which means multi-molds.
I need to look at oldironfarmer's mold again, but I would probably make molds out of sonotube that was slit and spread out to the appropriate radius.
I would make a new furnace 14" inside diameter.

Here is oldironfarmer's castable segment thread:
http://forums.thehomefoundry.org/index.php?threads/segmented-castable-furnace.588/#post-11727

I am reviewing what he did, and then will decide how to proceed (which may be next year if I go with castable segments).

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After looking at oldironfarmer's thread about castable segments, and then looking at the MIFCO furnace thread that Denis posted
http://mifco.com/B & C Manual-2014.pdf

there are two sizes of interest, which are the B-301 which has an interior diameter of 13" and an interior height of 15",
and the B-702 which as an interior diameter of 17" and an interior height of 20".

The B-301 has a 4 piece lid, two sets of 4 side segments (total of 8 sides segments), and a 1 piece bottom.

The B-702 has a 4 piece lid, two sets of 6 side segments (total of 12 side segments), and a 4 piece bottom with 4 bricks below the bottom.

The furnace I would build would have a 14" interior diameter, and would be 16" in height (or maybe 17" for good measure).
If the hard curved fire bricks are 9" tall, then I will use a dual stack, and let the hot face be 18" tall. I could always set some bricks on the floor to make the interior more shallow, and remove the bricks for a taller crucible.

I would set it up for two burner tuyeres at 180 degrees, but probably only use one oil burner (maybe two oil burners if I got into the larger crucible sizes on a regular basis).
One tuyere would be plugged when using only one burner.

So the bottom line is that a MIFCO furnace is going to have fewer side segments than a furnace made from hard curved fire brick, but I don't really see the downside to having more segments.

I am not positive I could get an accurate 1" thick refractory form, or rather not sure I could compress the refractory into the mold into an exact 1" thickness (without a lot of trouble).
Making multiple molds would be rather time consuming.

And the flip side is that if I did cast tall segments in refractory, they would probably crack horizontally at the center.

So it seems to me that a consistent 1" thick prefabricated curved brick would a good way to do almost exactly what MIFCO is doing, and would be a quicker and far less labor intensive method.


Its executive decision time:

Not being retired, and not having any free time on my hands at all, the choice is simple for me.

I am definitely going with the curved fire 1" thick fire bricks, assuming they are rated a minimum of 3,000 F.
The Plastic A will basically patch any crack, and it is cheap (like $1.00/lb without shipping), so I am not worried about joints.

I would think a hard fire brick would be rated higher than 3,000 F, but I will check before I buy.




Edit:
And good luck trying to understand fire brick ratings.
The ratings are listed using acronyms, but no definition of the acronyms.
I think P.C.E. refers to a pyrometric cone rating, which is tied to a temperature, such as Cone 31-32 is 3,ooo F per one of the reference sheets.
I see one product with a P.C.E. rating of 41 +, so a pretty good fire brick, but not sure exactly what 41 is rated at.

http://www.jmdrefractories.com/high-alumina-bricks.htm

http://firebricks.com/techData.asp

If the price is right, I will buy some curved hard fire bricks and try them.
Proof is in the pudding as they say.

 

Got a quote on the curved fire bricks this morning.
While the Plastic A is very resonable, the curved hard fire bricks are not.
They are rated at 2,800 F, and are $30.00 each.

Casting my own furnace segments in Mizzou just became a much more reasonable (reasonable = affordable) idea, LOL.
Not going to happen this year, but I will put that on my list for next year.

I would give the furnace a 14" interior bore, and a 16" interior depth, and would use perhaps 5 segments on the lid, 10 segments on the sides, and one monolithic piece on the bottom.

And I would ram the segments vertically between two forms that are spaced 1" apart, not horizontally as oldironfarmer did.

It would actually save time to just ram the shell in one piece between two enlarged sonotubes, and then use a diamond saw to cut some relief slots in the outside surface.
Alternately, some dividers could be installed between the sonotubes to provide the breakpoints.
I am not sure exactly what the dividers would be made of; perhaps aluminum angle flattened a bit for a more shallow angle.
Post-casting saw cutting would be an easier and quicker method I think, as long as the diamond cutter disk would go through the aggregate in Mizzou (it may not go through it easily, that aggregate is very hard).

It really would be a slow and time consuming process to ram one segment at a time, and I don't think I would do it that way.

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I started to comment on the expected price of curved brick but deleted it, you were so eager. My experience is that specialty shapes are expensive, curves, copes, wedges, etc.

I cast my segments horizontally because it was very quick and easy. Any voids wind up being on the outside rather than on the inside hot face. 1" thick 16" deep is a long way down to see what you were doing while putting wet refractory in. Not saying it won't work, but troweling on a 1" thick layer is much easier. The Greencast 84 I used is rated for 3,400F service temperature but slumped much more than I expected so I had to make the external forms.

 

My current furnace was that way, and so I added about 2" of refractory at a time, and used a 1/2" wood dowel rod to pack it after the addition of each layer.
With careful packing, voids and air bubbles can be avoided, and no, a vibrator is not needed, however it may make things easier if you happen to have one laying around.
If you know how to pack refractory, you don't need a vibrator, unless you get into a situation where you cannot reach all areas with a packing rod, in which case vibration is pretty much the only good method.
I still have concerns with a vibrator settling out the aggregate in the mix, and after seeing a sectino of my cracked Mizzou, I would definitely not want to settle out the aggregate.
Probably would be ok if one did not over-vibrate the mix.

I am eager, but not that eager.
That is just outrageous for a backyard setting.
For an industrial setting where productivity is critical, curved hard fire bricks may be the cheapest money ever spent.


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Two inches at a time sounds like it would be slow. Using a vibrator also takes judgement and skill, like hand ramming. Pneumatic rammers are routinely used in industry for locations which cannot be vibrated, but with each the skill level of the craft is important. There are no foolproof easy methods. You can also over ram and get aggregate separation. Moderate vibration does not settle the aggregate, and too little vibration does not get the trapped air out.

 

Is it possible with vibration to get rid of nearly all the little bubbles on the surface? I usually end up with a lot of 1/4" and smaller surface bubbles on my molded refractory. I do vibrate a, seems to me, moderate amount. But it is hard to get a perspective on too little, just right, too much. I've never seen any hint of aggregate separation and feel like I have to really vibrate to do that. I don't think those small bubbles do any harm. I usually oat with satanite anyhow and that closes the holes.

Denis

 

I think the number of bubbles on the surface of the form is partially dependent on the form surface finish. However I seem to recall that to get all the bubbles out you have to over liquefy the mix so you don't want to do that. Dispersed fine bubbles are common in good refractory jobs I've seen. They are beneficial for insulation so long as there are not so many they weaken the refractory and obviously surface bubbles make for a nice surface to grip a coating.

 

OK, I'll relax already and not worry about it! ;-) Good to know.

Denis

 

I think you all are just going for the giggles, and trying to make me do an internet search for vibrators.
I am onto you guys.
God knows I would be getting pop-up adverts for all sorts of exotic stuff for years to come courtesy of Big-G.
Try explaining to the wife how it is all for the good of casting refractory.
She would give me "that look" and say "yeah.......right".

Is there a (safe) link to a cheap one (the thing whose name shall go unmentioned) ?
No wild goose chases now !
And don't anybody send any weird stuff in the mail either (I won't mention any names Jason).

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I think Jeff's reciprocating saw is a great idea. Surely you already have one.

 

Ok, if this thing does not work well, you will never hear the end of my whiny ass.

 

I'm confused. Would that be a change?