Electric crucible furnace

I stumbled on a nicely written article and plans for building an electric crucible furnace. It's built like a kiln, with resistance elements and firebrick and looks like it would be much easier to build and use than the traditional gas or oil fired furnaces. I have a few parts I've been meaning to cast, so this may be a good time to build one and try it out.

The 52 page article was written by Dan Hartman and he sells a PDF of it for $3.95 here. It's a pretty good deal at 7.6 cents a page.

Tom

That appears to be a variation of Dave Gingerys "Lil Bertha" electric furnace. (actually it looks a lot like Daves!)

I made Gingerys version -along with about every thing else he published - and honestly, was disappointed... I had been using the charcoal fired furnace of his and thought the electric would be great - could work inside, no smoke/fumes, clean, etc. But after being able to pour molten Al after 25-30 mins with the charcoal, waiting for about an hour & half for the electric to melt ... well, it just wasnt getting it. By that time in my casting ventures, propane furnaces were gaining popularity - and ease of building one, so I built me a propane furnace ... and have never looked back.

Yes the melt time is a definite minus, but not something that can't be worked around with a little planning. The ability to closely control temperature plus the cleanliness and convenience of electricity is what caught my eye. I've built with gas fired and charcoal furnaces as well, and wouldn't consider bringing either one into my shop.

Tom

I made an electric furnace about 10 years ago.
Sorry, no build pics, you will need to visualize.
I started with a 45kg propane cylinder and cut it down to suit.
There is a steel grate in the bottom giving about a 100mm air gap, then 50mm of kaowool, and two 35mm layers of alumina fire brick.
All the bricks were full size, (115 x 230 x 75mm) and I split them with a carpenters’ saw to get the thickness I wanted.
I built the lining with 13 bricks standing vertically and mitred all the edges to fit them together. I then drew a pencil line spiralling my way up from the bottom to the top, and numbered the bricks to facilitate replacing them.
After I took it apart I used a coarse round file to carve a groove for the element. I think it took about a day of filing. The bricks are easy to cut and file to any shape but they wear the tools badly.
Then 2 more layers of kaowool were placed in between the brick and the side of the tank. A layer of bricks on their flat to cover the top edges, and the kaowool.
The lid is a plough disc, with a couple of clay buttons and stainless wire to tie the kaowool to it. The centre hole made a handy inspection port so I just cut a brick to suit. I made removable handles so they are never too hot to touch. The 3 legs help locate the lid on the top and also keep it off the ground when it is removed.
I got the alumina bricks from a bulk supplier who had an open box that he couldn’t sell so I was the lucky duck on the spot and got them for a song. I bought a whole box of kaowool blanket and still have most of that left over.
The junction box is aluminium and stands off on a brass threaded pipe. The element wire is insulated in clay beads, (normally found on thermocouples) and joins to the mains flex at a ceramic terminal block. The flappy thing is just a heat shield/heat sink to keep the heat out of the jbox as much as possible.
The tongs fit neatly inside and grip the crucible gently but securely.
I made the shank from 6mm rod and crafted loops of slightly different diameters, (to suit the taper of the crucible), before welding them together. I just sit the pivoting end on a block of wood to suit the pouring height and tip it with the crank handle.
On the plus side, it is clean operating, BUT, I would still never run it inside, the fumes from molten metals need to be well vented. Temperature control is simple. Start up and shut down by 1 switch. Easily portable.
On the minus side, yes they can be a bit slow to heat, the elements are fragile, and difficult to repair, expensive to replace, although I am only on my 2nd after 10 years of intermittent use. And possibly more costly to run than a gas unit.
I melt mainly bronze, so I am operating in the 1000°C range. It takes about 5 hours to reach a pour temperature for about 5kg of bronze. I just switch it on, and go and have breakfast. I use a graphite crucible. You should preheat the crucible to glowing red, (takes about 1 hour), before adding metal in small amounts. As the melt gets deeper you can add larger pieces to the pot. As I am waiting for the metal to heat I use this time to ram up my mold and get everything ready. Usually end up having lunch while the metal has a last soak before pouring. I wouldn’t say the waiting time is a drag as there is always something to do in the shed. I have never melted ally so I don’t know how long it would take but I think the 1 hour preheat wouldn’t need to be quite so long at the lower working temp and certainly the actual melting time of ally would be much faster.

Cheers Phil