i just tried heating up a crucible using a butane burner, the one use use for striping paint. sounds daft now but i thought at the time with butane burning a 1300c that it would glow. but nothing. what did i do wrong?
The hotter it get the more energy is lost by radiation - (is it a square or perhaps cube function ?) the crucible needs very good insulation around it to stop the energy escaping and perhaps reflect the heat back.
AWEM
"Andrew Mawson" wrote: (clip)(is it a square or perhaps cube function ?) (clip) ^^^^^^^^^^^^^^^ It's the fourth power of the absolute temperture.
You need a bigger burner. A large burner runs at about the same temperature as a small one but delivers more heat. Larger objects dissipate more heat when they get hot, so they need more heat input to reach a desired temperature.
Depends upon the size of the crucible, the weight of what's in it, and the amount of heat going in to it(btu's per hour output), and the rate at which the heat goes away do to radiation and convection. A match gets up to well over 2000 degrees F, but you wouldn't expect it to make the crucible glow.
The burner you have may be outputing maybe 5000 to 15,000 BTU/hr. If the crucible and its contents weigh, let's say, 20 pounds, you'd probably need 50,000 to 100,000 BTU/hr to get it glowing in a reasonable time period, considering that the crucible is sitting in some sort of refractory "box". Propane powered "weed burners" generate up to around 500,000 BTU's. Some of our guys use them to heat a refractory "box" of about 5 or 6 cubic feet full of pots to around 2200 degrees F. Of course, you have to have at least a 100 pound propane tank to feed it, it you don't want it freezing up. You mention butane, but I use propane, which has a lot of similarities. Propane, properly combusted, delivers about 90,000 btu's per hour per pound. It you are use a one pound (net)cylinder for your burner, you have about 90,000 btus' available. If you can use it up in one hour, then you have a 90,000 btu/h burner. If it lasts 4 hours, hen you have a 22,500 btu burner. Get the idea?
H> i just tried heating up a crucible using a butane burner, the one use
Without knowing anything about your geometry, you can do a lot by partially surrounding your target with insulating material. For example, my paint stripping propane torch will quickly get half inch steel bar up to a good red heat for bending by resting it in the "vee" of the frog of an ordinary brick. If you make up a "corner" from three bits of brick you can easily melt gold (1064 C) with propane. Proper insulating bricks will do even better.
Btu's aka POWER, as Tim the toolman would saw, you need more power.
Wes S
when I was using my oil burner furnace I could raise a crucible full of aluminium to a molten pot full in just over 20 minutes.
to get there I had to get the walls of my furnace thermally saturated. they would glow white hot on the inside face and the oil would vapourise and burn instantly.
my understanding is that in the thermally saturated state the walls of the furnace would radiate back to the cruicible a lot/all of the lost radiant energy from the cruicible and flame. until I got the furnace walls glowing with heat I couldnt get the crucible full of melted metal.
your burner setup is radiating away so much heat that your crucible never gets to the melt temperature.
you need to invent the furnace.
Stealth Pilot
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