Furnace #2

After building my first furnace, I found a very cool online shop here in Japan (Zairyo-ya.com) that sells a bunch of useful casting supplies in small quantities. I ordered a #2 crucible, some green sand, and some "official" parting dust (3kg - I think I have enough parting dust now to last a couple of lifetimes). Even though I only got a #2 crucible, I decided that my next furnace should have a chamber at least big enough to hold the next available size crucible at Zairyo-ya.com (a #4).

Another problem I had to address was the burner. I didn't expect my faithful handheld torch to provide enough fire so I convinced myself that building a burner myself was a worthwhile challenge. I decided to leave the problem until after building the furnace, but I chose to make the hole in the side of the body big enough to fit a 1/2" galvanized pipe (the outer diameter is about 3/4").

I also really wanted to try building a furnace using some commercial refractory instead of a homemade version. I looked around for refractory at a lot of places online (refractory is basically just called "caster" in Japanese). I finally found some at Asahi Glass Ceramics Co., Ltd.
Next I needed to build the "shell" that holds the refractory (a lot of people use some kind of metal can). I didn't really want to piece together cut up clam chowder cans again so I looked around for some sheet metal. I found a nice piece of galvanized sheet metal, but I read a little bit about heat causing unpleasant zinc vapor. I think the outside of a furnace probably doesn't really get hot enough to cause this problem, but I want to be safe so I spent a lot more money and got a much smaller sheet of expensive stainless steel. Nice and shiny though, isn't it?
I cut out the body part and the lid part and crimped the edges down so they wouldn't be so sharp. I cut up my hands quite a bit on the edges of the clam chowders cans for my first furnace. I really should have been wearing gloves when building that one, but sometimes careful preparation loses out to that urge to just get things up and running... This time I was much more careful.

I rolled up the sides and locked them into place with little machine screws. I used a few U bolts for the handles because they were a lot cheaper than any of the handles I could find. I opened a small hole for the burner in the side of the body. I made the hole so that it would put the burner right at the top of the refractory making up the bottom, but in hindsight I should have made it a little higher up so the fire would come out a little above the bottom of the chamber.

I drilled a whole bunch of little holes in the sides so that I could put a wire mesh in the lid and bottom to support the refractory. I got a bit anal and calculated the spacing of the holes so that the mesh would be nice and square.

Finally I mixed up the refactory a little bit at a time and packed it into the shell. I tried to follow the manufacturer's directions, but I think I didn't quite add as much water as recommended. It seemed to come out OK though (later on I noticed a few cracks, but no problem yet). I remembered the problem of not packing my first furnace enough and used the handle end of my hammer to really pack this one as well as I could.

A couple hours after ramming in the refractory, I went to check on the furnace and noticed that the outside was very hot. Apprently the water caused some kind of chemical curing reaction in the refractory.

The funny black spot in the bottom of the chamber is a bit of burnt cardboard. I made little triangle pieces and poked them down into the wet refractory so that when they burned out, they would make little troughs for any accendental spills to flow out the spill hole in the bottom of the furnace. I also made a little "plinth" block out of the refractory to stand my crucible on.
Here's the furnace with my crucible inside. In the end I decided to skip the plinth block because the flame from the burner basically blasted straight into the block (the plinth block does make a nice support for the burner outside the furnace). My packing method wasn't great and the bottom of the chamber didn't end up very flat so the crucible wobbles just a bit. Not a big deal, it just means that I'll have to take the lessons I've learned and build another furnace!

Finally, here is everything all together with some fire! I ended up making two burners and this image shows the second burner. The details of the first burner are here and the details for the second are here. The picture doesn't show all of the blue flame that I could see looking in, but there's enough to show that it works!

I had to do a bit of experimentation with the gas orifice size on the burner. At one point I ended up with a nice, huge yellow fire that I left going too long. It made all kinds of smoke and left the black marks on the top edge of the furnace body. Now I have to learn about reducing, oxydizing, and neutral flames.

Home | Gingery Lathe Last modified at 2004/02/07 14:10:09 JST
Questions? Comments?