Perlite/Satanite Brick Furnace Lid Trial (by Fire!)

I have this crazy idea to try bricks cast from a combination of perlite (garden amendment or hydroponics material) and Satanite. I have played around a bit making "cow-pies" of this mix and think that it just might hold up as a lining for furnaces. I am very impressed with the durability of Satanite as a refractory coating and perlite is also very heat/atmosphere resistant. A cow-pie made from them and fired to 1500 degrees to set the Satanite resists a Mapp gas flame for a period of time evidently unfazed (where insulating wool will degrade).

My furnace lid made of IFB coated with Bubble Alumina started to gradually fail. So I kicked out the IFB and am going to set in cast bricks of S/P. Incidentally, I do not think the failure is due to inherent "weakness"
of the IFB. I think rather it is due to my design

http://forums.thehomefoundry.org/index.php?threads/my-attempt-at-an-ifb-domed-furnace-lid.740/

In which the bricks are set at a low (too low) angle and wedge between the metal lid outer ring and the chimney liner mad of dense castable. With each melt I think the outer ring heats and expands allowing the bricks to settle just a bit. Then with cooling they get jammed really hard together and into the liner as the outer ring cools and contracts. A higher angle of inclination may have helped that situation and not using a liner, but rather coating with Satanite might have been much better---the retrospectroscope analysis. Might be right. Dunno for sure. In the picks below you can see the liner is badly cracked and falling down in one segment. This late failure allowed hot gas to hit the brick ends and melt those ends.


I noted and you can see that certain repaired areas of the IFB coating where the BA fell off has retained the Satanite very well and it appears to provide excellent protection to the IFB. I have taken careful note of that for future reference.

I am also thinking of building a larger furnace and am thinking S/P may be an ideal lining material. Before making the big step to actually constructing that furnace, this lid project will provide a very good test bed to see just how durable S/P bricks are. I will say in advance that there is a very good chance the bricks will not hold up. But there is just one way to find out.

Here is how the bricks are formed:

I use paste wax to coat the steel form prior to packing it with wet S/P. Then I bake out the water at 400F deg for 2 hours. The brick is so porous that a slow ramp of temp does not seem necessary. After the bake out the bricks are fairly strong. Then I cook them in my kiln at 1500F for a couple hours. All this by guess and by golly.

The mix for one brick is 1.5 yogurt containers (about 60 fl ounces total) perlite mixed with a half cup of Satanite powder combined using a drill-powered paint mixer paddle with 13 ounces of water. This makes a more or less cohesive mass of coarse material that will sort of pack together. I pack the S/P into the forms shown (I made two of 16 ga material) using a tamper being careful to press it well into the ends, sides, and corners just like you would pack sand in a mold but using far less force.

The bricks are shaped so that they will stack in a ring of 12 bricks angled 20 degrees from horizontal. My HOPE is that this angle will be at a low enough angle to keep the bricks pressed together but a high enough angle to allow the "teepee" to expand outward with heat and not wedge to tightly on cooling. All unkowns, of course. I plan to spray on Satanite on the f inner and outer faces of the bricks to improve there abrasion resistance and to liberally soot the apposing edges to prevent them from fusing and allow some movement. More by guess and by golly.

Anyway, I should have the bricks low temp cooked by days end.

I hope to try this mess before the end of the week. Fingers crossed. I figure it might work and celebration will be called for. Or it may well fall in a heap and lesson learned. But if it holds up in a lid, then I think I can certainly rely on it as vertical walls. I believe it will be inherently more durable and heat resistant than my current (pretty good) wool/satanite walls.

Denis

 

So many unknowns here. But I can say that I have subjected blocks of the Satanite/Perlite mix to direct Mapp Gas flame (3770F) for several minutes and not had breakdown of the aggregate material. There are so many factors in play as we read about inswool rated to 2600 but really being much more refractory if coated with Satanite and much less refractory if in direct contact with molten iron. I will soon find out what an hour and a half at iron melting temps does. I am hopeful but far from certain. In some ways the perlite is forming a matrix for the Satanite, so that even if the perlite softens the Satanite may be providing some structural support. (Or not!)

I have argued with myself for quite a while over whether to try it out. But, it was an intriguing idea that I hated not to test. So, we shall see.

The bricks themselves are very light weight weighing only a pound each.

Denis

 

Yup, either brush it on or spray by using drywall texture gun.

Denis

 

Why don't you try soaking wool in a Satanite slurry and firing it.

 

That is an interesting idea! You haven't done this?

Denis

 

I've soaked paracord and hardened it but no reason to do anything else, coating works for me.

 

There's a 3040 deg F melting point mortar the pottery guys use on their electric furnaces that could be used to repair that furnace lid: 3 parts Wollastonite with 2 parts 85% phosphoric acid. It chemically reacts and gets hot while setting solid in minutes with heating to 550 deg F to cure fully. I've used it to repair my small electric lab furnace and the resulting mortar is not super strong but is lightweight and insulating with a high melting point similar to dense castable refractory of 1670 deg C.
https://cone6pots.ning.com/photo/wollastonite-phosphoric-acid

 

Very interesting product! I was previously unaware of it. Thank you for pointing it out.
Denis

 

I can tell you from experience. Perlite in you hot face leads to a green glass like material that easily melts/eats everything around it! My furnace has a mix of perlite and refractory and it actively tries to destroy it's self. The lid likes to sluff off and falls in as it melts. I will not be using it again.

 

Ohhhh. How did you use it---mixed with what?

Denis

 

Hmmm. Sounds like a change in course is indicated.

So, i did try mixing a 1/4 cup of Satanite and water to make a very thin suspension of Satanite. I tried dippiing the insulating wool into it and repeatedly compressing it to try to get the Satanite to soak into the wool. I could not get over 1/8" penetration either on the cut end of the wool or on the flat of the wool. That does not mean it might not be helpful to apply a first coat that way to help ge good ahesion of the Satanite. But, a through-and-through soak does not appear likely at least by the crude attempts I made.

But, as I mull this over, especially given crazybillybob's experience, I think that I need to try a lid of book-stacked wool. By that I mean not flat-stacking two or three layers of wool in the lid but rather book stacking short strips of wool on end side-by-side. Then I'll coat the wool with a very thin coat of Satanite and weed torch it and then apply two more coats of Satanite, each heated with my weed burner.

I think I will try wire stitching some of the pieces of wool to the lid to help suspend the chimney end. The lid will be about 3" thick and the wire will be kept back an inch or more from the face. The wire will skewer the wool and be tig attached to the lid where it exits. The lid is 20" diameter and I'll make a 5" vent.

Thoughts?

Denis

 

I woke up about 2:30 this morning and lay there thinking about this. What went through my head was using 1/2" wool, laying it in a shallow pan and pouring the devil juice over it like pancake syrup. Then sliding the wool into a foodsaver vacuum unit and squashing it flat. The reason for 1/2", if it soaks in, you would have a 1/2" hot face covering 2 inches of uncoated wool.
Twenty years ago, I would have jumped up and headed to the shop. Now, it's... I hope I can get back to sleep.

 

My early experimental furnace used fireclay-cement-silica sand-perlite rammed mix and while I had oil combustion issues of soot down low, the upper part of the chamber had a foamy green glaze forming. Of all the refractory ingredients I listed, perlite had the lowest melting point.

 

If the sand-perlite melts it seem you will be left with a Satanite closes cell foam/matrix. It sould have good thermal insulation properties. I didn't know about it structural properties.

 

Shop vac pulling it through Hmmmm

 

I used a type of refractory that is meant to fix furnaces or stove fireboxes. Where the perlite doesn't melt it's held up well. But the areas that take the most heat (flame impingement zone, lid) the perlite has fluxed out and eaten everything. I have been patching it with a sand and waterglass mix till I get around to building a new furnace (too many projects not enough time).