furnace and crucible construction

[dan610324]

hello all cannon maniacs , and especially you who cast in bronze .

as Im planning for an new furnace build of middle size my idea was to exchange ideas and experiances in this area , the furnace I planned should be for approximately 70 kilo ( 155 lbs ) .

I will use an drum what will be to compare to your 50 gallon drums as an base to build from , they are for free and have an suitable size     cheap is nice , but free is better   

the dimensions are : inside diameter 22,5 inch , inside height 33 inch
heat source will be an boiler burner .
my idea now is to build totaly without fireproof refractory , just use ceramic insulation type kaewool .
as this small things aint used continious they are hot cold hot cold and the refractory cracks more and more , if using an high temperature ceramic insulation only  you dont have that problem .
what I can remember since I worked with those things there are ceramic insulation that can handle 1600 degrees celsius , I will probably never come close to those temperatures .
even if it will wear and tear from use , its easy to just change the damaged layer when needed .

my idea was to use 50 mm ( 2 inch ) rockwool first , then put 4 layers one inch thick with kaewool ,
I believe that would give an very well insulated furnace with small heat losts , and extremely easily repaired when needed .

but this is probably nothing new and revolutionary , but I got an idea of an new design for the lid that it will use the exhaust gases  one more time inside the crucible before they go up the chimney .
I think it will be both enviromental and wallet friendly , and thats no bad idea today   

please check out the sketches I did earlier today ( pictures below )
Im very interested to have comments and ideas about this .
maybe someone more who have plans in an similar direction .

Ive had some furnaces before , some ok and some of very poor functionality and quality   
but now I decided to build the last furnace in my life , now I will try to find the ultimate in relability and function .
please show what you other use for your cannon castings , and describe what you think of your equipment .
I made an small calculation on this and I believe I can build it for less then $300 ,
ok then I have the boiler burner already .

what experiances do you have of the crucibles for bronze melting ??
what do you use ?? whats the most cost effective ??

my idea for this build was to talk to an local ceramic producer , she believed when I talked to her earlier about this that she had good clay that would take this kind of temperature without any problems .

[Eyes Of Death]

The design of the kiln look sound just be sure to inject the burner off center to induce a spiral around the crucible. The next thing would be how you gonna lift and pore the crucible. Most kilns of this size tilt the kiln and crucible together. I don't know if I would trust a 55gallon drum to hold the weight and pivot on it's sides. Remember  most metals lose most of their structural properties at 600c. Would depend on the insulation keeping things cool.
some help  http://www.charlesahones.com/

[dan610324]

of course the burner will be off center , as in both sketches .
it aint my first build , but hopefully my last   

it will not be an tilting furnace , the 70 kilo is with totaly full crucible .
that will probably never happened , I would believe 35 - 50 kilo will be max  what I will use it for .

the 6 inch insulation would be enough to keep the outside below 100 degrees celsius I believe .

but so many have read it already and no comments so far of my idea to try to use the hot gases one more time inside the crucible .
I dont know how this will work , but in teory it feels right to try it .

[Eyes Of Death]

OK i was looking at the circle in the corner and wondering. On the hot gas flow the concave lid can't hurt. But more than likely will build a high presher zone on top of the bronze and not circulate into the crucible far enough to help.

[dan610324]

do you know anyone who have tried something similar ??
it would be nice to know
why do the same mistake as someone else if its tested without success ??

[GGaskill]

My concern is that the low exit will trap gas that is cooler than the melt at or near final termperature.  It would probably accelerate melting while the metal is still solid, so if you could figure out a way to pull it up flush near the end, you should get the best of both worlds.

[dan610324]

as it is now in the sketch its 2 inches below the lid , how about cut it in half ??
just have it go down 1 inch into the chamber

it will be difficult to produce an moving chimney

[GGaskill]

I am just theorizing, not speaking from experience.  When one treads the unknown, one must expect surprises.  I suppose you could always cut off the inside extension if it proves to be a problem.

[dan610324]

yeah probably the best solution

but all other people are so silent , please comment this and tell a little about your experiances

[Max Caliber]

Dan, The lining using Kaewool sounds like it should work fine. Are you going to put a protective coating on it? I have only used Kaewool in a forge furnace but it works well even with using just one thickness. I use refractory material that I make in my small propane furnace and 1.25 inch thick fire brick in my two coke fired furnaces that get little use. For a furnace that is not going to see a lot of use you don't need a lot of lining unless the furnace is inside.

I would think that your lid design would constrict the exhaust gasses to a point that you would not get very good output from the furnace. The exhaust vent needs to be carefully matched to the input of the burner. A little fuel and air generates a large volume on gasses that need to move through the furnace cavity quickly or the process gets choked down. You could go ahead and try your idea with the lid and maybe you will discover a new and improved way of furnace construction. If it doesn't work you can use a conventional type lid.

I would not try using a home made crucible for a furnace this large. The graphite crucibles work great and are cheap and last a long time. They are also strong and not prone to breakage as one might think. I have been using (and abusing) graphite crucibles for 40 years and have never have had one fail on me. The newer silicon carbide crucibles are better but more expensive, I have just one silicon carbide crucible and I really don't see much difference in it and a graphite crucible.

Max

[dan610324]

ok maybe I must start looking for an graphite crucible ,
but I hate all long unneccessary transporting .
I prefer localy produced things .
it would probably be much cheaper to buy an chinese graphite crucible . but I still dont like it