Here are some pics from Larry, a caster from the Azores.
Here's everything on the living room floor ready to get started. The cardboard circle is going to be the form for the center cavity of the furnace. We wanted a drain hole in the center, that's what is in store for the wooden dowel in the upper left of the picture. The little white thingy by the dowel is a balloon. It is intended to stiffen the center cavity form. It worked ok, but something a little more solid would definitely have been better.
Here we are getting started. The cement is actual refractory cement that is used locally for fireplace masonry. On the advice of some websites, we added perlite to the cement. Perlite is sold for gardening purposes, you mix it into the soil to improve oxygen and water retention. Supposedly, plain cement will conduct too much heat to the outside of the can. This will make working around the furnace difficult, and it will also make it harder to build up sufficient heat in the furnace to melt metal. The perlite acts as insulation, keeping the heat in the cavity where it's needed to melt metal. Perlite feels and looks like little Styrofoam beads. We put about a 2 inch layer of cement on the bottom with a piece of wooden dowel in the center for a drain hole. Then we put the form on top of that and started working the cement in around the form. The balloon in the center is the only stiffener we used for the center cavity. It was quick and easy, but didn't give us an entirely symmetrical opening.
Below, Brad is doing manual labor. Mixing the perlite and cement is pretty tedious. You can't add any more water than necessary, so you add just a little, mix a while and add a little more. It's slow going and the mixture is really stiff. It's hard work.
Here's Brad doing some more manual labor. He's mixing cement and perlite in small batches and then we're packing it in around the balloon/cardboard form. The cement is in the orange and yellow bag, the perlite is in the blue and gray bag by his left knee. The cement is almost to the top of the can. This is about the 6th batch he's mixed up, and he isn't having a lot of fun anymore. At this point, he'd rather be playing soccer!
Here's our furnace, filled with cement and set aside to cure. We still need to cut a hole in the side for the burner. We should have done that before filling it with cement, but we were so anxious to get started on the build of the furnace, that we forgot about it till about this point. We cleaned up and had set it aside and were admiring it, when I remembered the burner and said oh no?..
We need a lid for the furnace to keep the heat in. This is a piece of steel about 3 inches wide. It is salvaged scrap, it came off some kind of electrical conduit. The loops of wire behind it are for reinforcement in the cement. The plan is to bend this into a circle, put some bolts into it that will protrude into the cement, and run several lengths of wire inside to act as a kind of rebar. I was worried that the cement would not stay inside the metal ring, I didn't want it to drop out after going to all the time and trouble of putting it together.
Here's the lid off to a good start. We started to bend it into a circle, and discovered a problem. There's a small lip on the top and bottom, about 1/8? wide. I liked it because I felt it would help hold the cement in place. Unfortunately, it was creasing up as we bent it. I love my dremel. Small notches cut every couple of inches with an abrasive wheel let it bend very nicely.
Here it is coming together nicely. A couple of bolts hold it together, and extra long bolts for the handles that will hopefully help reinforce the cement. A few extra bolts for no other reason than to round it out. Don?t want it looking lopsided. We drilled holes in all the bolts to thread the wire through, I didn't want to just wrap it around the bolts.
Here we go with more cement. The reinforcing wire is in place, the pipe in the center is for a vent hole. We've got it about half-way full and are packing the cement in tight. It's surprising how much cement you use when you pack it in. It really compresses a lot. Probably because of the perlite added for insulation.
Here's the lid packed full and left to cure. It's on a piece of plywood with nails around the outside to hold it in place.
After about 48 hours of curing, we flipped it over and were very surprised at the finish. It isn't really wet here, it is very smooth from the finish on the plywood.
Here's the furnace after about 4 days of curing with the hole for the burner cut in it. It still looked damp, so we set it up in the school room with a butane torch blowing in it.
Here's a look inside the furnace. You can see the grey spot on the back wall, it's starting to dry. You can also see how the cavity isn't entirely symmetrical. Michele wasn't entirely pleased with the fact that we were drying cement in the school room, but she's been very lenient, letting us do much of this project in the house.
Here's a look down the pipe with Brad in the background. We've got the burn pretty good here, more blue flame and less orange. It was still a long way from right though, it took about an hour before aluminum would melt, and that was just barely. Aluminum melts at around 1200 degrees, it needs to be about 1300 to pour. We just couldn't get there with this set-up. We were also using soup cans for crucibles to melt the aluminum in, and they failed after a couple of melts.
The mixture is wrong, I didn't have a small enough drill bit to make a good 'jet' in the gas tube, but it was pretty neat with the flames dancing out of the top. The mixture is way too rich, there's a lot of unburned gas escaping in that orange flame, stinking up the backyard pretty bad. Some flowers nearby even turned brown and sort of died. It didn't do a lot to sell Michele on metalcasting.
Here we go with some more trial and error, starting over with a new burner. This is a brass 'T', with one end capped off, the center section has another cap in it with a hole drilled in it for a jet, and the other opening has a nipple for the hose to feed the gas. Decided to splurge here and spent about 6.00 euros (~=$7.44 USD when published)
Trying different size holes for jets. This turned out to be a case of smaller being much better. The smaller hole on the left burned much hotter and more stable.
Here's Brad doing more manual labor. He?s crushing cans for melting. Our crucible is pretty small, so he has to crush them flat and then roll them up. Even then, only a few will fit in the crucible. We had to let them melt and then keep adding a few at a time until the whole batch was melted.
The fruit of Brads labor. The cans are melting nicely in the first picture. He crushed and rolled 15 cans, it was hard to get them small enough to fit in our crucible. This is a new and improved crucible, made out of a piece of pipe with a piece of steel welded on the bottom. Very ugly welding, but it doesn't leak molten aluminum. In the second picture is an ear of corn aluminum ingot made from the cans. 15 cans made one small ingot, and almost as much dross as good aluminum. Almost more trouble than it was worth. Dross is at the bottom of the second picture.
First, before we cast anything substantial, we need some substantial aluminum. Cans just aren't going to cut it, we got way too little return on our labor investment. So, it's off to the Auto Hobby Shop, where we find these jewels in the scrap metal bin. All of the kids get in on the fun here and have a good time breaking these up into smaller pieces with hammers so they will fit into our tiny crucible.
Bailey is keeping watch over our ingots. They make a really cool sound when you dump them onto the floor or roll them around. I like it as much as the kids. Below is a little closer shot of an aluminum muffin and ear of corn. Don't eat these, they're bad for your dental health.
Here's a foam pattern buried in the sand in a stainless steel bowl. The sprue is simply a leg of foam attached to the pattern and extending through the top of the sand. The rolled up soda can is to provide a head of aluminum that add pressure to fill the entire pattern. We forgot to take a picture of the pattern before burying it.
This is shot of the furnace running full tilt at dusk. The crucible is full of aluminum, the foam pattern is ready in the sand, and we have a muffin tin handy for the excess aluminum.
This is a shot down the top of the furnace, the aluminum is melted and ready to be poured. It still surprises me to see cement glowing red hot.
Brad makes the pour. The can idea for a head of molten aluminum was a good idea, we just should not have used an aluminum can. It melted immediately and the aluminum ran across the top of the sand. The foam flares up and burns away quickly, it's a little distracting. It's important to keep a steady flow of aluminum into the pattern until it is full.
Pour the excess aluminum into the muffin pan to form ingots for the next melt.
Brad waits impatiently for the casting to cool. Since the pour didn't go quite as planned when the can melted, we are afraid this will be a failure. Waiting is hard.
Here's the finished product. We had some failures before this, so Brad didn't spend much time on the pattern, just roughed it out with a dremel. That's one of the drawbacks of lost foam, if it comes out bad you've lost your pattern and have to really start over.