Reverb. Furnace Part Two

Finished the lid (it went about the same as the hearth molding process), while that was curing I spread some furnace cement on the inside of the hearth to smooth over and fill in the air pockets. Yesterday I stuffed both blocks into the oven, baked at 350°F for about four hours, this is how they looked after:

Open Face Lid and Hearth

That's sheetmetal from a microwave I took apart, in case you were wondering. It shouldn't get hot enough to discolor or burn the paint, but since I built this at night, you know, when you're tired and bored, I didn't have the foresight to cut the half-holes in the sheetmetal for where the flues (exhaust ports) cross the base, so that'll probably char up pretty nice. Oh well, poisonous fumes are why you do this stuff outdoors...

Burning it out

Burning it out. This is uh, maybe 20 minutes or half an hour into it? I started at about this level of propane, turned it up (at which point the internal temperature, as measured by a coat hanger, got to near 2,000°F), then eased it back down to this idle level. Here the walls are about 1,500°F. Heat is concentrated at the rear (left side in the photo), opposite the burner, and it's a bit cooler just below the burner port, but only 200-300°F below average from what I can tell with the coathanger probe. It's also hotter and more powerful just in front of the opposite side's flue, here getting a good orange heat faster than on the near side flue. You can also see a sparkle on the upper right of the lid, that's condensation from moisture that didn't come out from the baking. I guess four hours wasn't enough...


Kinda hard to see exactly what this is. The black outer edges of this picture is the side face of the lid seen above. The dim red/orange part at the top is the cool flue; it's not running enough power right now for it to be incandescent itself. The two orange edges on the left are the lid (upper) and hearth (lower) corners respectively, opposite the flue this picture was taken through. The right side glow is the other corner of the far flue; the space between here and the upper-left corner is that far flue. The orange haze seen between them is the flame from the burner, orange from contact with hot surfaces. If it weren't for that, you would be seeing clear across the furnace at this point.

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