bigger furnace

[HT1]

I have to build a bigger furnace, I'm killing myself with heat after heat in my hobby melter (10B) crucible.

I have a new 1 inch propane burner from Hybrid burner on the way, a 30 gallon drum, and local access to kastolite 2600 f refractory and kaowool.

I'm worried about insulation what is the best, way to insiulate, for heat loss, and for durability, or at least the best comprimise between the two. or if there is a reason to mess with kaowool at all in a commercial insulating refractory like kastolite

V/r HT1

[Harry]

I am a fan of the not worry so much about efficiency and build to last crowd. Kent (machinemaker on AA) has talked about his furnace as being made using concrete backing to a very thick refractory liner (2" IIRC) and he does huge bronze melts. Oldfoundryguy who was on the old forum for a short time also talked about this and it seems he said he had been using his furnace for 30 years.

I think the push for uber efficiency using ultra thin hotfaces over wool because the numbers say its best is over rated with suspect actual gains in fuel savings or ultimate top end temperature. That said the wool will do the most in keeping surface temperature of the shell down which might be a concern for you depending on your own situation.

I have two furnace I am soon going to be rebuilding, my small one is 2" of wool with about 3/4" of solid 3k* refractory over it. This furnace is still going strong after more than a year of service but there are some pretty rough spots on it. It fits a #10 in a 9" bore quite nicely. This one will be rebuilt last so I can keep one furnace running.

The other furnace is my lil scrapper which has all but collapsed due to the rough treatment of bouncing wheels around on the rim while melting them. This has about 2 1/2" of 3 foam to 1 refractory and a 1/2" shell inside of that. I did two things wrong with this furnace other than beating it with rims. One was I think 3:1 with the foam is on the edge for having a strong structure and two 1/2" for a hotface is just way to thin. When I rebuild both of these I will use 2:1 mix for the insulating layer and 1" or more for the facing layer. I have a whole box of wool but honestly I found it a pain apply the refractory to compared to the refractory foam mix.

My big scrapper will have even less insulation and thicker hotface as it will take a lot of abuse so I want it as strong as possible, I am really hoping I wont be rebuilding any of these furnaces in the next 20 years.

On the Kastolite, I dont have a clue... do you have any information as to the density of it? If it is more than half the weight of the dense castable I would go with the foam mix.

What size crucible are you moving up to? I just got a bilge shaped 20 and sitting next to the #10 A it really doesnt look much bigger so I think I am going to be very comfortable with it but then I am pouring aluminum which is a lot different from brass.

[dallen]

my own personal 2 cents worth, get yourself an insulating refactory that will take the heat that your going to be working at. with brass I would use a 2600 degree insulating refactory and forget the fiber and the foam. the Blue Pig or my big furnace has a four inch thick wall that at Cast Iron temps I can lay my hand on the wall and hold it there. another route you can go is to use the white alumina brick stand them up on end, make yourself a miter box to cut them so that they will form a circle 4.5 inches thick no hot face no foam, just the 2600 degree brick will melt Cast Iron so no problem with Brass, Bronze.

My first furnace was pour with a 2.5 inch wall of 3000 degree insulating refactory it melts Cast Iron been treated worse than an x wife and is still in operation I just don't use it much cause the lid flips up instead of swinging sideways.

I guess if money was tight I would probably try the foam route, but if your not worried about having to move the thing, 3000 High Strength castable is only about 35 bucks a bag here in OKC. the 3000 degree resco insulating lightweigh was like 80 a bag a couple years ago. Been a while since I did the first furnace.

Thats my nickels worth, you just have to figure out how you want to build it, what materials or how much you want to spend on them. take pictures so we all can see what you put together.

[Nudge]

my furnace is 1.5" hot face with a 2.5" k wool insulating layer. to make it easier to put the hot face in I added another steel liner to the inside (it is still in there) so I guess it would be a bit like not having the wool to keep the heat in. Iy is there so I dont cook myself on the outside liner.

[barryjyoung]

My crucible furnace accepts a #20 SC crucible. It has no Kaowool at all, just solid refractory walls 3 inches thick on all sides. I have run it full tilt for 8 hours where the inside is very bright yellow and the outside is barely above ambient temp. Why do you guys use Kaowool at all? I hope that doesn't sound stupid, I just simply do not know.

Thank you

Barry

[Nudge]

Cos it was cheaper than another 2 bags of refractory and made the furnace a crap load lighter. I move my furnace out into the middle of my work shop to use it and put it under a bench again once it is cold.

[Harry]

For me just about everything I read when I got started implied using an insulating layer was needed Barry. Good to hear you have done long runs at iron temperature and still not gotten the outside very hot with a solid refractory wall, was that something like kastolite or dense castable?

My rebuilds will use at least 1 1/2" of dense castable over a foam 2:1 mix because it is easy to do and still very strong. Not much worried about weight like Nudge because I dont move my furnaces but saving some dens castable wont hurt my feelings any.

[dallen]

If you have checked out the video in the blue pig thread that I posted my wall is like 4 inches thick way over kill for a furnace this size but the way I wanted it. It has been at iron temp several times and as you can see from the paint the only places that it gets hot on the outside is where the heat leaks around the lid and body, I can lay my hands on the wall on the back side where the flame inpinges on the wall and its not hot.

the wall was poured using a 2600 degree castable so that it would heat up faster the floor is 3000 degree high strength, and the lid is a combination of the two it was going to be all insulating, but I ran short so I covered it with 3000 degree HS while it was still wet so the two are like welded together.

Yea shes heavy and fat like a hog, but she works good and as long as the lawnmower can drive about it I'm happy. The inside is 12 X like 18, for my A10 Silicon Carbide I have to set it about 6 inches up so that the top of the crucible is close to the top .

Guess I could make a flame trainer and set it lower and let the flame work on the bottom half of the crucible in a more direct manner. You got any thoughts on how that would help with melt time Harry ???

P.S. I was going to use 2 inches of fiber in it, but the guy that owns the place I buy my refractory at ask why, I said because I have it, its still under the shelf, one day I gotta find a use for it, maybe a 2 inch fiber liner in a cupola, with a 1.5 face of HS, should hold up to melting iron you think.

[Harry]

The flame trainer makes for a superheated zone in the bottom of the furnace which is great for flashing oil and making for a really clean burning furnace. It also creates a bit of a cyclone around the crucible which makes the heat go where you want it to go into the crucible instead of out to the walls. Not sure what it does for heat times or overall temp but I would expect that it would raise the upper limit of the heat into the crucible.

I have a full box of wool (almost 50 sq ft) that I will most likely use in a kiln, probably mainly in the roof and door.

[Jammer]

I'll try this one more time, this makes 4 tries. keep losing the internet for some reason, always when I save draft or try to post....??




I cast the liner of my big furnace with 3100 F castable refractory using 2 pieces of duct pipe. I was going for a 3/4" liner but ended up with about an inch. I put the outer shell on and packed it with ceramic wool. The stuff on top is some ceramic rods I had, and pieces of fiberglass looking squares, both I found in an old foundry I was allowed to rummage through. I found out later the squares are actually filters for casting Aluminum. I capped this off and made the lid about the same with wool and then covered with refractory.



Come on and post this time...!!!