Segmental Thin Plastic Refractory/Wool Furnace Build 14" Dia Bore

I am setting out to make a iron melting furnace heated with a diesel. What will distinguish this furnace from other hobbyist furnaces is that it will use a thin plastic refractory hot face divided into four keyed segments. At this stage all details are not fully worked out. But I plan to use an approximately 1/2" thick Blu-Ram (proprietary phos-bonded plastic) refractory hot face wrapped in 2 inches of 2600 degree wool. Whatever space is left between the wool and furnace shell will be "backfilled" with perlite. The whole works will be set into a shortened 55 gallon drum with a bore of about 22". I will loosely band the wool circumferentially with steel wire at several levels to compress the wool onto the hotface thus helping keep the hot face segments engaged. The floor will have a hotface of four pie-like segments about 3/4" thick overlying insulating board and perlite. The pie segments will have a raised center with a 7" radius and will likely be about an 8" radius to their outer edge. The raised center should help maintain the registration of the vertical segments on the floor. Floor joints will occur at the middle of the vertical segments---sort of like typical staggering of brick joints.

I plan to thicken the segments to about 7/8" at their edges. The vertical edges of the of the segments will somewhat key together in that the left hand edge will have a convex profile and the right correspondingly concave. The hotface segments will be 19" in height and each segment will span an arc of 11 inches.

The furnace lid will be the segmental lid I recently built and reported in another thread.

I have been fabricating the single-sided form to be used to generate the segments.

This is the backbone of the segment form. I simply cut arcs of 2X4 material (recycled from a discarded flask) with a 7" radius and screwed them to a 3/4" plywood base. I expect to do a fair bit of pounding on my form to coalesce the refractory and I wanted it to be plenty solid. I expect to have to use the form for this build and for future replacement of segments that are bound to fail eventually.

Over the backbone I stretched 20 ga steel sheet with 3/4 square tube skip welded alon it long edges. The choice of square tube was fortuitous as its shape helps direct the clamping force s to help the sheet fully conform to the backbone.

The arched top and bottom edges will be built up to 3/4" thickness and these laminated sticks will provide barriers to the refractory and a sort of thickness gauge. Not shown are wood inserts that will be screwed to the long edges of the form. Those inserts will impress the key profiles in the long edges.


The general plan will is to lay the refractory slabs into the form, pound it into one solid sheet, and then remove the wood components and use a weed burner to heat the refractory to a few hundred degrees. Based on some testing I have done to this point, I think the refractory will then be hard enough to be self-supporting. At that point the refractory will be slipped out of the form and more fully fired with the weed burner. I think I will try to raise its temp to 1000 F with the burner. At that point the refractory should be quite hard and ready to be placed into the furnace. Full firing will happen in the furnace, perhaps with the burner turned to a lower intensity for the first 15 minutes and then likely it will be time to "go for it."

I hope to pack my first segment and weed burner it tomorrow. I also have a large mold to pack for a Sunday pour. So, most likely the other segments will have to wait.

This design is somewhat novel and therefore its performance and durability are uncertain.

Questions still in my mind are whether it is necessary or even desirable to thicken the top and bottom edges of the segments. But it seems like the right thing to do. The possible down side is the increased thickness could increase expansion stresses. I also have not fully decided how to bring the tuyere into the furnace through the wall of a segment.

Denis

 

Nice work so far Denis. It looks like you've really thought this through. I was up against some similar challenges when I built my reverb.

Although it was made with castable my point here is still the same. The challenge was how to get my refractory into the concave body sections at a uniform thickness. The forming was opposite of yours- mine was concave where yours is convex- but again the idea is the same. I made a sheetmetal form and put some blocking into the furnace body to support it. I made a rectangular form out of plywood strips of the desired thickness and laid it flat on the bench with stiff plastic underneath. I poured/rammed the refractory into the form on the bench which allowed me to screed off each section to a consistent thickness (you could use a rolling pin), remove the forms, and lay the sections one at a time into the curved furnace form. I worked the sections together once they were placed in order to form a continuous surface. Once the refractory air dried for a couple of days I was able to lift it out, remove the forms and blocking, place my , kaowool, and finally fire it. It worked like a charm.
You may have a similar plan in mind, or maybe something different, but I thought I would throw it out there. Oh, and don't forget mold release!

Pete

 

Pete,

I am surprised you were able handle the castable that way. Cool. I think your suggestion of “ planking” the mold with rolled strips is a good one. I’ll have to learn what width of strip is most manageable but doing it that way should be faster than just randomly hammering the refractory and checking areas for thickness. If I recall, Kelly mentioned that he had, at one point, thought about trying to roll out some plastic refractory as well. The slabbing device I made is intended to make it easier and faster to slice slabs off the wet refractory bricks as it is supplied. And I should be able to get the slabs near the desired thickness from the start. http://forums.thehomefoundry.org/in...blu-ram-or-any-other-plastic-refractory.1118/

Your release paper point is a good one. I have found simple brown paper bag sheets to work well in general. But, for areas where some detail rendition is desired, waxed paper seems better. The slipperiness of the paper seems to help the refractory slide into place and settle into depressions. Without release paper, this stuff would stick but good to steel or wood.

Denis

 

I'm glad you found the suggestion helpful. Keeping my castable on the dry side and treating it more like cookie dough than cake mix allowed for the handling of my "planks". It didn't need to flow, so drier was better.


I think one of the advantages this planking technique would have for you is the soundness of the ramming, i.e. ramming into a confined space as opposed to a wide-open one which will provide for more solid compaction.

Pete

 

The end pieces are secured. So next comes refractory. But first, I have to pack up a 450 pound sand mold for pouring tomorrow. Gotta keep priorities straight! Weather looks pretty good for a pour tomorrow.



The shiny coating on the straight piece is thin cyano glue that I often apply to “case-harden” wood.


Denis

 

I figured on just using a piece of pipe and a couple 1/2” thick rails to get me in the ballpark. Rolling is pretty optional, really. Putting pre-cut slabs as they are into my form would work pretty well based on my lid experience. I will make at least one panel in the next 24 hours. I just put the finishing touches on a 30” square mold—-ramming them up, drawing them, cutting gates, venting, cutting a pouring basin, and then getting every last bit of loose sand out takes a while. Hopefully I’ll be pouring in an expected weather window tomorrow afternoon.

Denis

 

As I started reading Melter's post ... my mind was thinking slip roll. Back off the 3rd roller and run it through like a pasta roller.

 

I got a segment formed in about a half hour tonight. I simply place slabs on a piece of wax paper on my table saw table. I arranged them more or less in a 10x19 array and laid down on each long side a 1/2” thick slat. I then use a 2x2 to bridge the slatsand used a mallet to smash the refractory slabs into a Single approximately 10x19 slab of 1/2 thickness. I used egg or smaller sized blobs of refractory to “heal” areas where slabs were joining incompletely and varied the inclination of the 2x2 from level to sloping somewhat forward or reversed to coax the migration of the refractory. Once the sheet was formed, I slid it off the table onto a conveniently-sized piece of 1/4” plywood using it like a serving tray to carry the slab to the form. It was easy to slide the slab onto the form with the wax paper still under the slab. Then I took care to press the refractory into the convex and concave forms. I left the edges of the segment about 3/4” thick and tapered it to 1/2” over a distance of 1.5” approximately.

Next I warmed the slab up to 150 or so to drive off some of the water and harden it a little. Then all the wood blocks were removed and the metal form with the slab resting on it was lowered to the floor. At that point I turned on the weed burner with a orange to almost blue flame and warmed it up to 220F or so. Then I turned up the burner to a strong blue flame and warmed the slab to 600F . At that point I turned off the flame and tapped on the slab. It rang with a pretty hard sound and was free of cracks. I’ll examine it more tomorrow after it’s cooled.





BTW, I checked to see if the slab was stuck to the metal form. It’s not. Whew.

Denis

 

Kelly,

The above thoughts are much appreciated.

I really like the idea of splitting the shell of the furnace. I had not considered that possibility. The one downside is that my furnace lives outdoors in the Pacific NW. Very rainy here. So, I’ll definitely be tossing ideas around in my head. Right now I drop a metal “hat” onto my furnace to act as an umbrella. The one-piece side sheds rain. Rolling it indoors is not impossible, but is undesirable. A shed is out of the question.

You’ve talked me out of the perlite idea.

The base will be stepped.

The moly wire is also new to me. I see a whole lot of it on eBay in very thin gages. Do you have a favorite source or two for heavier wire?

Denis

 

The segment is off the mold. It seems to be good and strong. Final firing will take place when three more are laid up and wrapped in wool with a metal shell to make a furnace.


The inside surface



The concave key


The convex key.


Denis

 

Believe me, I’m being as careful as I know how.

Panel #1 weighs just exactly 10 pounds. I am hoping that this will provide a furnace that is lightish weight and durable. Only one way to find out. I think my first 2/3 the volume castable furnace made following the usual thickness suggestions for the hot face weighed 2.5 times what this one will.

Thanks for the kind words.

Denis

BTW, I just cooked panel #2

 

Well, half a hot face...



Denis

 

Denis, I love your idea and I love the tongue and groove. But I'm not sure about the perlite. The perlite will have great performance but I think it will slowly migrate crashing the ceramic wool. Maybe more ceramic wool or Rockwool. I know my brakes get a little loose as I only have them lightly held using mechanical hose clamps. The hose clamps must be growing a little bit but when the furnace cools they become tight again. My ceramic wool is held in place by 70 feet of 0.035" stainless steel MIG wire. There is about 19 to 20 loops (every 3/4 of an inch apart, one continuous piece). The wire compresses the 2 inch thick ceramic wool about half inch per side. My thought was this is a little bit of a spring to hold the bricks in location if the wool doesn't break down over time.

 

Incidentally, Kelly wished me good luck on a pour I had hoped to make today. It came off without a hitch.
It was a 30” square. 65 pounds in the pot.



Denis