I am putting together ideas for a 5" system and want to cast the entire thing, but am unsure on the refractory. Can you just use high temp castable refractory? Does it need a steel liner on the burn side of the tunnel and riser, or will exposed refractory be OK?
I found this "recipe" for a crucible furnace, does it sound ok, or any other suggestions?
Here is the recipe: The refractory mix is composed of Portland cement (1.5 parts), silica sand (2 parts), perlite (1.5 parts) and fireclay (2 parts). The first three components are mixed together thoroughly.
Or, should I just use refractory cement mixed with perlite to lighten/insulate it?
Another question, if this system is entirely cast, is there a minimum thickness? I planned to use 5 gallon steel pails like paint thinner or something comes in for the riser. This would be about 2.5" wall thickness with a 5" round riser. For the tunnel, I planned to make it 5" wide x a little under 4" high rectangle. This is close to the 19 cu/in to match the 5" round riser.
Also, it sounds like this cement is gooey and won't pour, so I will have to plan my assembly of this to fill the outside steel form?
Seems to me that if it's good enough for a metal casting furnace, it's good enough for a wood stove. Either of your ideas might work just fine. I would be looking for a more insulative mix, even though it will be fragile around the wood box area. Perhaps you could cast the wood feed out of the heavier, heartier stuff and the burn tunnel and heat riser using the insulative mix.
I don't really know about minimum thickness in your castings. peterberg's opinion would be valuable here.
I've found that the intuition can get it roughly right more often than not. If you don't get a decent answer from someone, just make your best guess and go for it.
Minimum thickness would be 1 1/4 ", this will heat up very quickly.
My opinion about Portland cement in refractory: it won't hold. Normal cement and sand contains silicium. This is changing christal structure at about 1000 F and expands at the same time. I've been using proper refractory castable which contains aluminum cement and ground porcelain. Specification: 2190 Fahrenheit and it's still intact. Instead of elephant grey it's color has been changed to vaguely pink. Tapping it, it do sound fragile.
Post by carllittle on Nov 19, 2009 13:02:52 GMT -8
It appears great minds.... Yesterday I cast a burn tunnel and the beginning of a heat riser using the refractory mix Dave mentions. My idea was to have one piece that would serve as the burn tunnel and the base that would hold a stainless 8" heat riser. My plan is to build Peterburg's initial rocket/bell heater. I have a section of double walled stainless stove pipe left over from when I built my house that seems perfect to build a heat riser. Here is a link to a couple of pictures. picasaweb.google.com/Carl.Little.law/Desktop?feat=directlink I'm not sure of this cast will work, especially after Peterburg's warning about Portland in refractory. ( I wish I would have seen it before i did this.) If I were to do it again, I wouldn't. I think the few extra bucks for firebrick would be worth it. This thing weighs probably 200 lbs and I greatly underestimated the amount of fireclay that I would need. Therefore, the top of the firewall is just at 1 1/4 inches, but I imagine it will need more insulation. The reason that it is the shape and size it is, is to fit just inside the brick tower that will act as the bell. It will also sit on concrete fireplace foundation, so I wanted plenty of refractory between the bottom and the concrete.
Wow carlittle that is huge looking! Perhaps you can shell out the money for some proper refractory cement and plaster your burn tunnel with and inch or so to take the high temp shock (or precast some that slide in)? Might even need an expansion joint or two? I don't know, just ideas.
Well after researching the weight and cost (incl shipping) of refractory cement, I'm wondering if it is worth it considering I want this to be somewhat moveable, plus the expense.
If I used heavier walled steel tubing for the burn tunnel and riser, with an outer sheet steel shell, could I just fill it up with perlite? I understand that it greatly expands when heated above a certain temp, but does it stay in that form? Perhaps build the thing, fill it with perlite with open tops, fire it, then cover the tops with steel again?
I am greatly interested in hearing how this works out. I've seen refractory recipes, but they all seem to require a high temperature kiln firing. Sculpting the entire innards of the stove seems like a good thing, but all the mud stoves I've seen are fragile and vulnerable to water and cracking. (the banana stem form and such) Could something like a two-part cast work: the inner lining out of more durable cement mix, but not thick. Surround that with the mostly perlite insulative mix. And then finish with a coating of cement to make the outside durable.
I'll go off and do a lot more reading on such things.
ericvw: Got that right, sista Daryl!
Apr 10, 2015 16:57:57 GMT -8
Daryl: I'm off on a hike...everyone have a good day!
Apr 12, 2015 7:40:50 GMT -8
ericvw: So Daryl, to where did you hike?
Apr 13, 2015 14:21:38 GMT -8
Daryl: Along the French Creek. Ok, it was more of a walk...but still! I got outside!!! And it was in the 60s, cool, and breezy! If it doesn't rain tomorrow, then I am going to try to get over to a lake. Just smelling the fishy water will be a buzz!
Apr 13, 2015 15:38:28 GMT -8
ericvw: Everyone in the states doing there taxes or something? Perhaps Spring has sprung... Boards are quiet!
Apr 15, 2015 16:18:19 GMT -8
Daryl: Warm and the sun is out = quiet boards.
Apr 16, 2015 5:08:56 GMT -8
ericvw: We've been in the rain for DAYS! And not warm rain, either
Apr 16, 2015 14:57:18 GMT -8
Daryl: You are two states south of me! You're supposed to be warm! Stop it!
Apr 16, 2015 16:14:09 GMT -8
ericvw: Talk to the hand, Daryl! You can handle being two states above me, this I know! Did you catch that buzz off the fishy creek, or is that what u youngsters call it these days?(rofl)
Apr 17, 2015 17:44:41 GMT -8
Daryl: Ooooo snap, Eric. Nah, I get high on nature...and ice cream.
Apr 17, 2015 18:16:53 GMT -8
Daryl: Well, I got a growing pile of sticks in the back getting ready for burning. Windy here.
Apr 21, 2015 12:03:16 GMT -8
ericvw: I got a growing pile of logs and buckable limbs in the back- windy and intermittent rainy here, going back down into hi 30's- lo 40's overnight. Guess I'll be firing up the old iron box! Need to get that batch box built this summer!
Apr 21, 2015 17:52:25 GMT -8
Daryl: Yep, 30s overnight here too this week. Crazy. We will be lucky to get 4 months of steady weather over the 60s. I only burn in the summer so I am looking forward to cooking outside soon.
Apr 21, 2015 20:55:27 GMT -8