Feb 22, 2009

I tried loading the furnace with charcoal tonight and forcing air in through the 1/2 inch pipe.  The results were better.  With the soup can crucible sitting on the coals, the bottom of the can reached 900-1000 degF (dark red glow).  The sides of the can were still below 900 degrees.  Neither temp is the 1400 degrees that I need to melt and pour aluminum.  The position of the can seemed to prevent decent airflow through the coals.

I tried a different approach..  With the furnace packed with charcoal and lid on, a high temperature stream of flame comes out of the hole in the lid.  Neato!  I set a strip of aluminum across the hole and it began to sag within about 2 minutes.  To check the temperature, I set an 18 gauge copper wire across the gap.  The wire was small, thin, and would heat very quickly to the temperature of the exhaust gas.  Copper has a melting point of nearly 2000 degF, so it was safe to assume that we would not melt it.  The wire glowed a bright orange color, indicating a temperature of around 1600 - 1700 degF.  The wire was still solid when I removed it, so we didn't hit 2000 degrees.

So this proves that my cheap furnace can produce temperatures in excess the 1400 degrees needed to melt and pour aluminum.  I need to find a way to hold a crucible in the path of that hot exhaust gas.  The insulation on the furnace held up very well.  During the 90-minute firing, the furnace was able to sit on my wooden workbench without scarring the wood.

Copper wire glowing red  ~ 1600-1700 degF

Feb 21, 2009

My propane-fueled coffee can furnace seems to be a lost cause.  I was hoping that the application of the ITC-100 coating would hold in enough heat to reach melting temperature.  It kept the outer walls cooler, but the soup can crucible inside was far below 900 degF (except for the edge near the torch).  Looks like I will need to look into a charcoal design instead.  Photos below showing tonight's setup.  The ice cube is there because the torch head gets hot, and I'd rather not deal with an overheated propane tank :)