- Joined
- Jun 27, 1999
- Messages
- 804
I apologize in advance for the long-winded discussion, but I think it could be helpful to others trying to cast.
I've been working on casting nonferrous metals for some time. I have my forge and a furnace made from the plans in Dave Gingerys book series "How to build a metal shop from scrap" by Lindsay publications. Check eBay, they're there. My furnace is made from a 55 gallon drum, rather than the 5 gallon that he suggests. I like to have more power available if I need it.
My project that I've been working on lately is bronze. Aluminum is easy. I've melted many, many pounds of aluminum. I've melted several ounces of brass, but I didn't like what the zinc did, and I really needed bronze for some other projects. The real reason is that you can forge bronze, you can't forge brass. It crumbles under the hammer.
I decided on a 9.5-10% ratio of tin, mostly because it made the math easy, and it seems to be the median for the period of items that I want to reproduce. I took 5lbs of copper cable that someone gave me for the use of my shop, and 1/2lbs of tin ingots purchases off of eBay, and cut them all into pieces that would fit into my largest crucible. It's around a #10. I should have used the #5, but it's too late for that now. I set aside these items, the crucible, two sets of long tongs, my stainless stirrer, a stainless hook(long), and about 4 gallons of casting sand on my ad-lib casting table. It's some aluminum shelving with a 1 1/2" lip, inverted. I also set aside two bags of Kingsford briquettes. (Don't panic, this furnace is made for them, read the book.)
I filled the furnace with briquettes and set it afire, then started working on tempering my sand, since it had been sitting in a bucket for a year and a half. It was pretty dried out. I rammed up the flask somewhere in there, too, but I don't remember when. The form was a simple 2" sphere, using a 2" styrofoam ball from Wal-Mart, with a 1" sprue. I put some ingot molds in the sand with the bottom of a cup for the excess.
When I had a good bed of coals, I put the crucible in, already filled with the copper. I kept the tin set aside, since its melting point is MUCH lower than the copper, and it would slow the copper from melting by insulating it from the heat. I let the crucible warm up to the ambient heat of the BBQ from hell, then turned on the blower, slowly ramping it up.
After many adjustments of fuel and air, I reached what I knew to be well beyond the melting point of copper, yet my cables were still sticking up at me like a hundred middle fingers, mocking my efforts. My crucible has no lid, and the lid of my furnace is pretty high from where it sits, so I thought that maybe the heat needed was being radiated away from the copper out the top, so I put a firebrick on top of it. This obviously helped, from the color of things, but still no liquid. I reasoned that the oxidization layer on the outside of the copper may be holding it together. This happens in Al all the time. All you have to do is scratch the surface a bit, and it starts to flow. I tried this with the copper, and it just reoxidized. I could swear that I heard the blower laughing at me. I had been rotating the crucible in the coals to keep the heat even, as it has a tendency to heat up the tuyere area faster. I did this a final time, and the handle broke free. We had reached welding temps, and still no molten copper. Just to make sure I was committed, I added the tin. I know, I should only do that once the copper was molten. I was ready to try anything, and it was easy to rationalize to myself that the tin would conduct the heat to the copper at this point. It melted just like a popsicle, before it even reached the crucible. Then I remembered that foundries use fluxes. I've never heard it said why, and I never remember steps if I don't know why, but I was getting desperate, and racking my brain produced this.
I dropped a handful (about 1/2 cup) of Borax into the mix. Raw Borax, not anhydrous. I watched it foam up and coat the copper. Then I watched the copper melt. Just that quick. The parts that hadn't been touched by the borax had to be pushed into the pool or fall into it, as physics dictated. I was ready to run naked through the streets, I was so happy.
Then the crucible broke and I bronzed my shoes.
I've been working on casting nonferrous metals for some time. I have my forge and a furnace made from the plans in Dave Gingerys book series "How to build a metal shop from scrap" by Lindsay publications. Check eBay, they're there. My furnace is made from a 55 gallon drum, rather than the 5 gallon that he suggests. I like to have more power available if I need it.
My project that I've been working on lately is bronze. Aluminum is easy. I've melted many, many pounds of aluminum. I've melted several ounces of brass, but I didn't like what the zinc did, and I really needed bronze for some other projects. The real reason is that you can forge bronze, you can't forge brass. It crumbles under the hammer.
I decided on a 9.5-10% ratio of tin, mostly because it made the math easy, and it seems to be the median for the period of items that I want to reproduce. I took 5lbs of copper cable that someone gave me for the use of my shop, and 1/2lbs of tin ingots purchases off of eBay, and cut them all into pieces that would fit into my largest crucible. It's around a #10. I should have used the #5, but it's too late for that now. I set aside these items, the crucible, two sets of long tongs, my stainless stirrer, a stainless hook(long), and about 4 gallons of casting sand on my ad-lib casting table. It's some aluminum shelving with a 1 1/2" lip, inverted. I also set aside two bags of Kingsford briquettes. (Don't panic, this furnace is made for them, read the book.)
I filled the furnace with briquettes and set it afire, then started working on tempering my sand, since it had been sitting in a bucket for a year and a half. It was pretty dried out. I rammed up the flask somewhere in there, too, but I don't remember when. The form was a simple 2" sphere, using a 2" styrofoam ball from Wal-Mart, with a 1" sprue. I put some ingot molds in the sand with the bottom of a cup for the excess.
When I had a good bed of coals, I put the crucible in, already filled with the copper. I kept the tin set aside, since its melting point is MUCH lower than the copper, and it would slow the copper from melting by insulating it from the heat. I let the crucible warm up to the ambient heat of the BBQ from hell, then turned on the blower, slowly ramping it up.
After many adjustments of fuel and air, I reached what I knew to be well beyond the melting point of copper, yet my cables were still sticking up at me like a hundred middle fingers, mocking my efforts. My crucible has no lid, and the lid of my furnace is pretty high from where it sits, so I thought that maybe the heat needed was being radiated away from the copper out the top, so I put a firebrick on top of it. This obviously helped, from the color of things, but still no liquid. I reasoned that the oxidization layer on the outside of the copper may be holding it together. This happens in Al all the time. All you have to do is scratch the surface a bit, and it starts to flow. I tried this with the copper, and it just reoxidized. I could swear that I heard the blower laughing at me. I had been rotating the crucible in the coals to keep the heat even, as it has a tendency to heat up the tuyere area faster. I did this a final time, and the handle broke free. We had reached welding temps, and still no molten copper. Just to make sure I was committed, I added the tin. I know, I should only do that once the copper was molten. I was ready to try anything, and it was easy to rationalize to myself that the tin would conduct the heat to the copper at this point. It melted just like a popsicle, before it even reached the crucible. Then I remembered that foundries use fluxes. I've never heard it said why, and I never remember steps if I don't know why, but I was getting desperate, and racking my brain produced this.
I dropped a handful (about 1/2 cup) of Borax into the mix. Raw Borax, not anhydrous. I watched it foam up and coat the copper. Then I watched the copper melt. Just that quick. The parts that hadn't been touched by the borax had to be pushed into the pool or fall into it, as physics dictated. I was ready to run naked through the streets, I was so happy.
Then the crucible broke and I bronzed my shoes.
....(it scared me too!)