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Furnace built for larger amounts of metal

I built this furnace in 1992 using Mizzou concrete which is still available today. It is rated 1650° but does not insulate very well. Hence, it takes 40 minutes to heat up a crucible with 1kg copper to melting. The inner diameter is 18cm (7") and height 25cm (10"). I fire it now with propane with forced air using a $10 air mattress inflator. When the furnace is running it makes a loud roaring sound like a low overflying airline or similar to the sound inside an airplane during take-off.
I used it many times in the 1990s but in recent years I used it rarely as I use only small amounts for which I have a much smaller furnace which melts 200g copper within 15 minutes. But in Oct 2014 I decided to refurbish it. I relined the inside and repaired the burner entry hole.
Finally I melted 1 kg of old water and gas pipes made from pure copper using a 500ml crucible (which I got in 1972 and used it a few times and was then left unused for many years) which took 40 minutes. So I think cast iron is beyond reach of this furnace as the inside gets not hotter than 1200°C.

SAFETY issues

warning As you work with flammable propane gas and hot parts you must be aware of the risk of fire and burns !
  • Perform these experiments outdoors or in a well-ventilated room. When using a fumehood be aware that the vent should vent off hot air and the vent and exhaust pipe can withstand air of over 100°C. Vents and pipes of PVC or other plastic are not recommended.
  • Check that all gas valves, regulator and burner connections are not leaking. Apply a detergent solution with a brush on all couplings and no bubbles should appear. There should be no gas smell as well. After use ALWAYS close the main valve on the gas cylinder.
  • NEVER let the furnace run unattended.
  • When making your own burner TEST IT THOROUGHLY that there are NO LEAKS !
  • Keep flammable stuff away from a running furnace.
  • Have a fire extinguisher ready or at least a bucket of cold water in case of burns or fire.
  • When pouring metals always use a face shield or at least goggles.
  • Use heat resistant gloves when handling hot objects. Burns are not fun !!
  • Use dark green goggles (available for about $10 at a welding or hardware shop) when looking at objects above 1350°C.

Run in 2010 Jul 25

play A test run melting brass in 2010.

Repairing the old furnace 2014 Oct 18

play Re-lining the inner walls with Blakite and repairing the burner entry.

Test run melting copper 2014 Oct 26

play Melting 1 kg of copper to test how the furnace performs.

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