My jewelry's site
And other metal melting techniques: And chemistry:
Site index

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.

Powered, developed under Linux linux and Mac MacOSX and hosted under Linux.
This site is best viewed with Firefox, Safari, Chrome and Opera. On a smartphone use landscape mode.