(click on the images for larger pictures)
I decided to start by trying to build a small electric foundry. Unlike something that used gas or coal or oil, I could safely operate it in my garage. It would be cleaner, quieter, and simple to operate. I used the "Lil' Bertha" book by Dave Gingery from Lindsey Books as a source for ideas and inspiration. I was also inspired by this guy's project, although I didn't buy his plans (maybe I should have).
I started in January of 2007. Some of the materials took me quite a while to track down. I took numerous diversions from the project for house maintenance, other projects, related experiments, and my lousy job which had me work more than a few too many 7 day weeks. I'm assembling this web page in December of 2007.
Not being good at working with sheet metal, I started with a 6 gallon stainless steel trash can purchased at a local hardware store. I used a section of duct to make the inner form.
I used a chimney cap to make a vent, and cut a hole in the lid to install it. I removed the handle from the trash can and attached it to the top of the vent cap. I used some black iron pipe through the trash can for handles.
Since refractory cement is notoriously brittle, I used 1/2" hardware cloth as 'rebar'.
I bought the refactory cement locally (Columbus, Ohio area) at Adrian L. Wallick Company.
I used rope to make the grooves for the heating element and dowels to form up the through passages as suggested by Gingery.
Hand mixing the refractory with a stick was a lot of work. The nature of this material is such that you add "just enough" water to wet it, you don't make a soup. This makes it much harder to stir.
At this point I made a critical mistake. I'd had two bags of Noxcast and they were about 1/2" short of filling up the foundry. Rather than try to get some refactory cement at the last minute while the first two bags were already curing, I just mixed some regular cement I had lying around in with the top 2 or 3 inches. This made the mix very crumbly after I heated it. It also makes me nervous about spilling melt in the foundry itself. You can see the two colors of cement mixed together, curing in this picture.
I bought a small "tea cart" from Harbor Freight and filled it with play sand. I set the foundry in the sand (actually on a few quarry tiles). The wheeled cart, in theory, would give me the flexibility to kick the entire assembly out of the garage if it burst into flames or started smoking really bad. It also lets me move the rather heavy (well over 100lb) foundry around and out of the way when I have other projects to work on. The large red tin is filled with an extremely fine grained sand I got at Columbus Builders Supply. My plan, if I ever get that far, was to try lost foam casting of the small objects, in the sand there. I left enough room between the foundry and the casting bin so that I could set the crucible in the play sand and switch the tong grip for the pour.
One of the trickier things is to come up with a way to install a bolt through the foundry wall without shorting it against the internal rebar or the side of the can. With the help from a good friend, we broke up a couple of quarry tiles and drilled holes in the pieces to act as an insulating washer. (The washer had to be non-conductive, and able to withstand considerable heat. Commercial ceramic washers are wicked expensive. We made these for a few pennies. -- well, except for the one tile drill bit that I ruined experimenting with making them.)
I put a "cage" over the bolts to keep from accidentally bumping into them. The teflon coated chicken wire is quite stiff. It would take a pretty hard bump to accidentally touch the bolt.
I attached the ground wire with a short bolt to the spot where the trash can handle used to go.
I purchased a temperature controller and solid state relay from Auber Instruments. They were very friendly and helpful and answered my questions very quickly and patiently. I wired it in an electrical box. I set up a seperate power cord for the controller and the heating element.
The wire pair with the white ceramic insulation coming out the top of the circuit box is a Type K thermocouple I bought on eBay (which was rated for the temperature range I hoped the foundry would operate at).
I gave the heating element a seperate cut-off switch, so I could shut it off while working in the foundry without having to shutdown the temperature controller and reboot it.
The relay got very hot. I mounted it on a small piece of aluminmum, and then attached another piece of aluminum on the back side, and added an old computer heat sink. I smooshed it all together with heat sink paste. I also directed a small fan to blow in the box while it was in operation to keep the controller and relay a little cooler.
I bought a spool of kanthal wire on eBay and made my first element. I carefully studying the kanthal engineering guide, and triple checked my resistance measurements. I even went so far as to buy a new multimeter that had much more accurate resistance readings so I could be sure I had it right. As soon as I fired it up, it jumped out of the grooves and shorted itself out and broke into about 6 pieces.
The next attempt, I took little pieces of oven baked clay, and packed them in the grooves with the kanthal wire. This lasted a little longer. The clay eventually exploded, and the wire broke again. You can see the bits of clay in this picture.
Ok, so next I wove three strands of kanthal wire together like a rope. I pressed it in with clay, and made sure it was firmly attached and the clay was really dry. Again, the wires moved, shorted, and broke. (Arrggh!) This time it also burned up the solid state relay.
Next I bought a "real" heating element, again off of eBay. I got a new relay from Auber, and installed it. This one wasn't rated for as much current as I'd been hoping for. It had a nice coil to it. It pressed into the grooves fairly tightly. Again, it moved when I applied current it moved, and burned out. (double Arrggh!)
(You can see the thermocouple in the bottom of the foundry in this picture.)
Next I found this stuff called "Ceramic Putty". I bought it from McMaster-Carr. It is made by Cotronics. It is really cool stuff. I bought another element and attached the heating element. You can see it in the picture here. This time it worked. It held the element in with no explosions, no movement, or anything. And it wasn't expensive.
I carefully cured the foundry and the crucible, and then came the time for the real tests. Could I melt bronze?
Unfortunately after 11 hours, the foundry temperature was only up to 1200°F. It appears I need more insulation and more heat. Back to the drawing board. I didn't want to leave it unattended overnight, and I didn't think it was going to get to 2000°F n any sort of realistic timeframe to stay there watching it any longer.
Next I tried drilling a hole in the side (the refractory really doesn't like that much), and I stuck a butane pencil torch in. The torch itself doesn't do much to heat up the foundry. I'll probably try wrapping the whole thing in regular fiberglass insulation, and then running the torch and electric at the same time. I'm not optimistic. I am starting to plan a waste oil powered foundry and will probably move forward to give that a try soon. [ early December, 2007 ]
For the past few months I've been experimenting with Pewter casting to get some of the basics and ideas of metal casting down by working with a more forgiving and easier to melt material. I've been experimenting with carving and casting. These last two pictures are of a pattern I was carving into "smooth foam", a very tight grained polystyrene specifically made for crafts. (I purchased it at a local craft store.)
Pewter doesn't get hot enough to do the lost foam casting method.
This celtic weave will hopefully become the tailpiece on my banjo.
I'll try to make up a web page with some of my pewter experiments and post it soon. Meanwhile, thanks for stopping by. I'll hopefully have some happy updates on this endeavour soon.