Segmented Castable Furnace

Not much here but Kelly asked about it so I thought I'd post, maybe something someone can glean.

My first attempt at a castable furnace I decided to cast four wall section with tongue and groove joints. Four segments to allow for expansion and tongue and groove to limit hot gas escape.

Used a piece of 12" pipe (12-3/4" O.D.) and formed for a quarter of the wall.



Then poured the first segment. Pretty stiff mixed per instructions. These expired bags of 3,500F abrasion resistant refractory had been given to me as expired materials.



But it sure flows. I could not pile it up like mortar and had a thin pour.



So after a little head scratching used scrap lumber to step it up.



And the second one was much better.

 

Then for a tuyere. This is hard refractory so it seemed best to cast rather than drill. I turned the appropriate shape then band sawed a curve to fit the pipe.



Coated and ready to pour.



I cut a concave into a 2x4 to make a boss for the tuyere and continue the curve around the boss.



It came out OK.



They assemble into a circle.



My burner is stuck into the tuyere and the pattern is laid inside to match. Pretty much a tangential entrance.

 

Used a farm implement disc to get a dished shape in the hearth or floor of the furnace.



Poured it is flat on the bottom (shown) with a dish on the top.



Made a large plug for a flue in the arch and poured right side up for a dished inside and flat top. There's a 1"x1" dado on the underside for a lifting and tension ring.



Assembled. You can see the tuyere boss. This will go through a layer of ceramic fiber for insulation.



Then each part was given a dryout, 26 hour ramp, soak, and cool down to 1,500F in my large kiln.

 

I built this 12-3/4" ID as a melting furnace, planning to fire scrap aluminum and have it run out the bottom.

First firing was with my small propane burner with no insulation and no satanite in the joints, out in the wind. Not enough heat. I believe now it will not melt and run out the bottom like I envisioned unless the furnace is hot before charge is added, and preferably there is a plug in the bottom to let liquid accumulate and get some superheat.

The furnace has sat like this since July of 2017 while I did more productive things like build an oil drip burner.

When first fired the lid cracked from the flue to the edge. Not unexpected.

I have to build a lid lifter, including a tension ring, a suitable base, and add insulation with an external shell. The Greencast 94 has very little insulation value and moderate heat capacity so it will take a while to get it hot but once hot it should met added scrap readily.

I also envisioned using a crucible in it but my subsequent firebrick furnace works so well this may never see a crucible.

A first furnace.

 

Thanks for that video link. Interesting furnace. I like his design. It looks like air leakage would be an issue. The loose brick furnace has the same issue and it's minor but still an issue.

After firing the segmented furnace the first time I quickly realized the low insulating value of this refractory. That was discouraging and I like to make efficient designs.

Holding the segments together is intended to be via compression of ceramic fiber. The segments stand well on their own but since the outside of the refractory will be very nearly the same temperature as the inside, any wire will expand more than the refractory as the temperature increases and will be loose so wire is really only useful before the shell is installed.

Now that I'm burning used oil efficiency is no longer an major issue. It may take the furnace a half hour to come up to temperature but should be very thermally stable after that, like dropping cold charge into a hot crucible. The mass of the furnace should heat the charge quickly. If I put a shell and fiber around this furnace I'll seal the seams with Satanite. It will crack along the seams but still seal gas. The goal of this design was to allow refractory movement without refractory failure.

I definitely like my brick furnace better. Brick is light and replaceable, and not that expensive, I'm surprised more people don't use it. I don't think that not having a smooth circular interior is an issue at all, I'm nearing 250 melts on my brick furnace with no brick replacement.

Thanks for the comments!

 

I am going to have to try this method.
It seems like the main cracks are vertical, and this would give the refractory somewhere to move without cracking.

.

 

The Greencast 94 is a 3,500F refractory used for things like burner tile and high abrasion areas. Less insulating than Mizzou but tough and good for flame impingement.

 

MIFCO’s segmented furnace user manual could have clues around page 40 to 46 or so that might be informative for assembly of segmented firing chambers.

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

Nicely made and explained fabrication of your segments, OIF!

Denis

 

Very detailed manual. Thanks for providing that!