Well, it was a success all around. The small burner took some adjusting -- I found 8 psi was about right. The gusty wind did put it out a few times while I was trying to find the right settings of pressure, throttle valve, and flare position.
This is one clear drawback of an atmospheric torch -- it's definitely subject to wind gusts.
Eventually I found that if the furnace heated up sufficiently, it was less affected -- that took maybe the first five or ten minutess of heating -- it is still a small torch and there isn't the power to make the walls glow right away.
I also found that using my piece of stovepipe as a chimney on top of the furnace lessened the effect of the wind changes, and probably drew air around the torch, as well as keeping the torch drawing better.
Once the torch was drawing well and the walls starting to glow around the crucible, and I could see the crucible bottom starting to look dark red, I inched both the pressure and throttle up until I was at 10 psi and an open throttle. This sounded a little more ragged with the wind as it was. It almost blew out at one point, but reducing the throttle got it back on track.
When the aluminum appeared to start shifting and crumbling in the pot, I lifted the stovepipe off to give it a stir, but doing this allowed a gust to snuff out the flame. I closed the throttle, re lit the torch and inserted it back in the tuyere. The stovepipe stayed on after this. And the furnace was restored in a couple minutes to full throttle near 10 psi.
When the aluminum had melted and the pot and walls were glowing orange, I shut off the gas and skimmed the dross -- there was very little, and then poured small size muffin ingots. without incident.
Hard to say what the exact time to melt was because of the flame outs, re-starts and pressure adjustments, but it was roughly 15 to 20 minutes with this burner and furnace. As a comparison, the store bought charcoal took 12 minutes to melt the same amount aluminum in the same furnace with the same crucible. That was after it was lit, which takes maybe ten minutes, or so. So roughly similar total time.
One thing was obvious -- the furnace was unecessarily tall for propane melting -- charcoal takes up space, so needs a taller bore. I'd say a 20 lb cylinder would be plenty for a strictly propane furnace, though i still like an 8" dia. bore.
The ingots poured very clean, and look good. Since they are small, I'll probably use one at the bottom of other melts to start the molten pool in the crucible.
Here's what the setup looked like after the pour:
