everyone knows my furnace failed, the lid crumbled, really it was my fault when I built the furnace I did not order enough refractory, So I used some lower temp light weight stuff I had for the lid, combining that with a poor design for the supports and after ... 5 years!!! my furnace lid failed. Ok I was looking through McEnglevans furnace literature to figure out what size to make the hole in my lid, and noticed them going on about their hemispherical lid ... I though to myself ... That would be easy to do so why not.. so when I made the form for the Hole I included a 10 inch hemispherical lid ... 10 inch is my furnace bore. I fired the furnace for the first time today, and I dont have any specific data. But the furnace sounds better and seems to have heated significantly faster... I'll chime in when I have some data... in the mean time, any thoughts??? V/r HT1
I have noticed a couple of successful iron guys raising the crucible up as high as possible in the furnace on a tall plinth. A domed lid would give more space for an elevated crucible. And a domed lid tends to stay intact better than a flat one, since you can band it at the bottom and basically have a arch that is self-supporting even if it cracks. I bought a cheap bbq grille that has a domed lid, and I will be using that as a pattern next time I make a furnace lid.
I wonder if the arch adds a reverberatory effect. I think it was Old Iron Farmer who built an arched lid recently and its form and fitting were discussed, but the dynamics of the heat distribution didn't really come up. Pete
interesting thought, mine was in the same area, I thought it might encourage the heat to swirl around the furnace more times before exiting allowing more time for thermal transfer to the melt
Domes and arches have been de rigueur for masonry structures since sometime between the old kingdom Egyptians, who did not use them, and the Romans, who did. The Romans perfected the dome, and no one has improved on it. They used a heavy iron chain around the periphery of the dome to take the force. The weight of the dome was transferred down to the embedded chain, and it ended there. Those iron chains are still in place in the old Roman buildings. Why the history lecture? I have learned the hard way about flat furnace lids. A flat furnace lid gets what little strength it has from embedded steel rods, and from the integrity of the refractory, which in both cases is temporary: the steel oxidizes rapidly from the intense heat, and the refractory cracks. Whereas a dome, even if it is cracked, maintains its structural integrity as long as it has a "chain" around the edge. In our case this chain will be a solid piece of steel of some sort, out on the edge, away from the intense heat, and thick enough to withstand years of oxidation. Richard
I fired the furnace up today to heat a new crucible, there is definitely a difference totally outside of structural integrity, the furnace came up to cherry red much quicker then I'm used to, and has a different sound much more steady jet roar, and the flame extends significantly farther around the furnace wall... I'm very excited to get to run a heat through it to see if I get an improvement of melt times V/r HT1
That's why I made my conical furnace lid with a band of sheet metal around it. The brick is all loose, held in by gravity. I have mortared some open joints just to seal them.
Gotta be the nicest furnace lid I'e seen! When my current furnace gives up, I plan to use lightweight bricks rather than refractory cement (like I did this time) hoping for more rapid heat up and reduced heat conduction. I will be copying your elegant design, for sure.
