Instructables

Step 4: Steel Crucible

After the first two crucibles failed, we settled on using steel. A steel end cap and nipple with a 2" diameter was our choice. This worked for approx. 30 minutes before the end cap completely melted off and mangled the end of the nipple. We determined the cause of the too-high temperature was due to the high wall of insulating mud and brick, instead of just covering the holes, the wall was up to the top of the furnace.

We salvaged the nipple by turning it upside down and purchasing a new end cap. After heating it red-hot and using a hammer and chisel to knock off as much garbage as possible, the crucible was serviceable again. We also pounded a pour spout into the nipple for ease of filling smaller molds.

Its also interesting to note that when the steel was first placed into the furnace, it burned green. We believe its was the zinc used in the galvanization process that was causing the flames to turn green.
 
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kidharris2 years ago
You should not use galvanized steel for any thing to do with a furnace. At high temperatures the zinc burns off and emits zinc fumes which are extremely harmful to your health, including death. Same problem with welding galvanized steel. Lots of info on the net, read it.
yep, i agree with hailsteve. I'm a blacksmith and sometimes i will burn the zinc off of a galvanised piece of steel and that burns with a bright cyan(blue) colour. Love your little furnace though. It's just the very thing. Ps i think the big foundries use a clay crucible. All the best smithy
hailsteeve5 years ago
I don't think the zinc made it burn green. Copper is the chemical that burns green, so maybe there was copper powder on your pipe or something.
All cotton and leather clothing are definitely important when dealing with fire, no synthetics.