Metal Casting Zone

Hello everybody, I am new here, and have a question about alloying. A friend and I wanted to try our hands at bronze casting, but we didn't have any bronze to melt. We thought we could make our own, melting some copper and tin in a small electric kiln that I have. We didn't have a crucible that would fit in the kiln, so we used an iron pipe cap as a makeshift crucible, figuring that the kiln wouldn't be able to melt the iron. We put in some small pieces of copper pipe and some tin fishing weights for our alloy ingredients. Having never done this before, we didn't know if there was a specific way to mix the metals; we planned on going with trial and error. We tried, and got error. The tin melted very quickly, as we expected, but the copper never liquified. It glowed and slumped a bit, but that was all. We let the kiln run for almost an hour, but glowing slumpy copper pipe was all we could get. If the iron pipe cap had not been damaged by this process, I would assume that the kiln was just not hot enough; however, the iron cap got hot enough to oxidize extremely, breaking apart into flaky scales.

I suspect that our mistake was the use of the iron pipe cap instead of a proper crucible, but I don't understand the physics of what happened. The copper pieces should have absorbed the heat more readily than the iron, shouldn't they? Was the iron cap simply reflecting too much heat away from the copper inside it?

Also, were we correct to put the copper and tin into the "crucible" at the same time? We knew the tin would melt much more quickly, but we were scared to melt the copper first and then put cold tin into it. That just sounded... unsafe. Should we have melted the metals separately, and then poured them together? (Our copper never melted, so we couldn't confirm if our test method would have worked.)

Any advice is appreciated. Thanks!

Hi atomicchicken,

I have no experence with bronze but as no one else has ansered I will have a go.

1. Are the sinkers tin? I have only seen them in lead, and lead copper is not a bronze like alloy.

2. If the copper slumped but did not form a puddle your kiln is not hot enough. It may melt bronze but copper has a higher melting point.

3. At red heat the oxygen in a kiln becomes very reactive, oxidising steel and copper. A furnace uses much of the oxygen and may reduce this efect but it still hapens. To reduce this hamer your copper scrapes into as smaller nuget as you can befor melting, and use a flux.

4. There should be no danger adding cold metal to a melt. Wear apropreate gloves and use tongs.

5. A steel crucible should be fine for melting cupper, however I would line it with ganister which will reduce the oxidising/flacking, and prevent iron contamination of the alloy. (Ganister is simply a sand clay slurry sloped on the crucible and left to dry.)

A point you need to know when casting the metal dosnt need to be just melted, it needs to be hotter otherwise it will solidify before completely filling the mold.

Hope this helps.

Good luck.

Peter.

I haven't tried this either but I've been told you can melt Aluminum and then disolve copper wire or plumbing pipe into it. I think wire works better. Keep adding the copper until you have about 10 to 15% Aluminum and the rest copper by weight. So 1 to 1.5 pounds of Al to 9 to 8.5 pounds Copper. This is an Aluminum Bronze and is very golden in color.

Or, you can make Brass by melting copper and zinc together. I'm not sure of the order you have to melt these but you have to be careful, the zinc will burn and make some nasty fumes. Don't breathe it.
You can get zinc from water heater anodes or boat anodes, I got some of these from e-bay and it seemed like a fair price. 20 to 30% zinc with copper is a normal brass. Newer pennies are zinc but it's probably illegal to melt them.

I had not thought of trying to make aluminum bronze; I may have to give that a go. Sounds like a fun experiment.

The fishing sinkers were tin; most sinkers are lead, but these specified on the package that they were tin, so as to be more environmentally friendly. They were a slight bit larger and bulkier than the lead sinkers of the same weight, but not by much. I bought them several years ago at Wal-mart; I have no idea if they are still available. (I think the brand name was "Gremlin Green" or something like that.)

Aha, so the kiln oxidized the steel quickly because it was at red heat and oxygen-rich, but not hot enough to melt the copper. That explains what happened. Sounds like I need to finish making my furnace so I will have a hotter, oxygen-reduced environment.

Thanks for the good advice, everybody. I think it will help. Anyone know what makes a good flux for use while melting copper?

Hi atomicchicken,

The usual flux for copper alloys is borax however table salt or glass can be used.

In my previous reply I forgot to say you should alloy your metals in aproximatly the right proportions even for a trial and error experiment. Bronze is roughly nine parts cupper to one part tin.

Good luck with the furnace.

Peter.