The Shop > Metal Stuff

Foundry Furnace for the Tiny Shop

(1/27) > >>

vtsteam:
I hadn't planned on doing a thread on this little furnace, because it's not much different than many others online. But it's come up a couple times, so I'll just show what I'm trying.

I've run a charcoal briquet aluminum furnace since 2002 using the recipe set out by Dave Gingery in his book (highly recommended) and built my lathe with it back then, a complex milling attachment, many accessories, and a disk turbine (whose blades were actually cast from aluminum melted in a ordinary campfire -- no furnace at all). The furnace was of sand and fireclay construction, but finally deteriorated after ten years when rain leaked through a metal cover over a winter and the shell rusted out.

Then a couple years ago I tired building a sawed off single charge cupola as an experiment. That failed (with wood charcoal, at least -- didn't have coke, which might have worked). That was re-fitted with an oil burner and I was able to successfully cast with iron after much trial and error.

So now with my new tiny shop, I find i need to cast an aluminum pulley to upgrade my Gingery lathe spindle to 1" dia. And I want something less massive and involved than the oil burner -- which is overkill for that purpose. Also located by my distant and unheated big shop, and outside, under snow.

Anyway, those were the reasons for a new furnace. I also hoped to have alternate metal capability -- small capacity iron would have even been possible if I was able to follow Ironman's small furnace design. But I wasn't able to find the very expensive rigidizer he uses, here in the States. So I dropped back in my expectations to maybe being able to melt the red metals.

Instead of fireclay and sand, this time, I wanted to try Plaster of Paris and sand. A recent video post here showed another furnace made from a galvanized bucket using the same refractory, but I'd been thinking about poP for a long time before that. Steve Chastain's books refer to commercil pouring liners of that material, and show data that it has a high insulative ability as well as refractory qualities. Bronze statuary casters have long used it for lost wax molds, flinging it onto the armature to prevent bubbles.

Anyway, wanted to try it and see how refractory, insulative, and long lasting it was. I still want to make Ironman's furnace some day, and will when I can find the right materials. If the plaster doesn't last long, I can always replace it with blanket and rigidizer. So this is a pure experiment, with little to lose.

Materials were sand, a bag of plaster of Paris ($14.95 at the local hardware store), and an expired 30 lb propane tank (a little taller than the 20 lb size) for a  casing.

I had some left over 8" dia. Sonotube (cardboard form used for casting concrete pillars) and I used that for a form inside the furnace. It actually measured 8-5/8" wide so I cut a 1" strip out of it and taped it back together to reach 8".
The seam made it easier to remove when the plaster was cured, too.

The mix was equal parts of sand, plaster, and cold water, and I mixed about 2 quarts at a time. Actually, the first pour was about half that in size, and used a little less water to make a heavier pasty mix which I used to "glue" the outside of the form to the propane cylinder.

This stuff sets off in literally 3 minutes, even with cold water and cold materials (very -- they were stored in a cold shop) so you have to work very fast. DO NOT use warm water!

As soon as that kicked, I ddn't have to hold the cardboard form any more, and could pour the rest of the refractory with no leaks. The proportions I used makes a good pourable mixture that self levels. Within an hour, I peeled out the cardboard form to a nice clean interior. Then I poured the bottom inside the furnace cavity -- about 2" deep.

Finally I found a cardboard mailing tube of exactly 3" diameter and used that to form the lid hole form. in a similar way to the furnace cavity. And then poured the lid.

Today, after 3 days of drying, I brought the furnace outside, and put a double layer of charcoa briquets in and lit it off. This applies gentle heat, and will help me drive off the water from the plaster -- it will probably take all day, and I'll be adding charcoal as needed. Moisture is obvious as steam this time of year!

dsquire:
Good to see you underway with this one Steve. I'll be watching over your shoulder.  :D

Cheers  :beer:

Don

awemawson:
Good stuff Steve BUT

 :worthless:

vtsteam:
Sorry, I didn't take any pix of the construction. Here it is after running an hour with charcoal. Sorry also -- I couldn't paint the furnace this time of year -- too cold, but plan to make it nicer when things warm -- if they ever do.

vtsteam:
I added more charcoal to about 3 layers deep after three hours and a piece of old stovepipe on top to increase the draft a little. Still way to early to get out the blower. The brown residue inside the barrel and under the cover will burn off once the furnace is in use at high temps. For now, sorry about the Grapes of Wrath appearance here! You can tell I'm suffering from cabin fever to be doing this at this time of year.....

Navigation

[0] Message Index

[#] Next page