This is the foundry in it’s current incarnation after more modifications, a new burner, and a coat of black grill paint.
For this modification it wasn’t necessary to rebuild the entire lining since it was still mostly intact. All I did was trowel in a thin (approx. 1/8″) layer of a product called “Everset”. Everset is a fireplace mortar that is rated to about 2100 degrees F. I got the Everset from a brick/masonry supplier (Acme Brick is the name of the place if it turns out to be a chain). The five pound bucket cost about $15 but since I only used a little bit to coat the inside, I have plenty left in case repairs are ever needed. Once dry the Everset protects the perlite/drywall from further degradation while still allowing it to be a really good insulator.
This iteration of the foundry also got a new burner as the old burner was just too slow. This burner is based (read: almost exact copy) on the “Oliver Upwind Burner”. One of the major advantages to this burner (besides faster melts) is that it does not require a fan or blower.
Being unable (like a lot people) to find a #57 drill bit locally I decided to improvise. I just went to the local welding supply place and got a .045″ contact tip from a MIG welder (the contact tip is basically a copper tube with a .045″ hole drilled through) and cut a slice off the end with a hacksaw. I then soldered the slice onto the gas feed tube (the horizontal copper tube in the pic) and turned the excess off on a lathe so it would fit through the hole in the burner tube (I could’ve just used a file but the lathe was more fun).
The reason this burner does not require a blower is because the jet of gas from the tiny hole in the gas feed pipe is moving so fast that it sucks in air through the holes in the burner pipe (this is the same way hand held propane torches work). To accomplish this, the burner needs to be supplied with gas at a much higher pressure than can be supplied by a regular grill regulator. Not wanting to have to buy a special regulator I realized that the regulator from my Oxy/Acetylene torch would fit the valve on my propane tank. However the outlet on the regulator has reverse threads as some sort of safety feature (heh, I’ll fix that real quick), and Lowes/Home Depot doesn’t sell any reverse thread fittings (and the welding supply place guys aren’t about to help someone like me defeat a safety feature for compressed fuel gases). So to solve this, I hose-clamped a piece of 3/8″ reinforced tubing onto the regulator followed by a 1/2″ brass barb fitting connected via an adapter fitting to a 1/4″ hose barb. Then a 10′ length of 1/4″ hose goes to the burner. I usually run the burner at about 4-5 psi.
On it’s first burn, besides a small part for the Gingery Mill, the refurbished foundry was able to melt down enough scrap for 20 ingots in a little over 2 hours from cold start (the scrap was not preheated before going into the crucible). Each ingot above is 6 inches long.
Here are a couple of videos of foundry run where I was using the lost foam method to make some prototype parts for a future CNC machine: