melting and casting basics
plain notes on melting metal at home. safety comes first, so it's first on the page.
this is general information, not professional training. molten metal can injure or kill. if you melt or cast, you do it at your own risk.
safety
- work outdoors or with serious ventilation. never in a closed room.
- wear leather gloves, a face shield over safety glasses, long sleeves in natural fiber (cotton or wool), leather boots and a leather apron. no synthetics: they melt onto skin.
- keep a class d extinguisher (rated for metal fires) and a bucket of dry sand within reach. never put water on molten metal.
- never leave a melt unattended.
- never let wet or damp metal or tools touch the melt. trapped water flashes to steam and throws molten metal: a steam explosion. preheat anything that goes in.
- don't work over concrete. moisture inside concrete flashes to steam when molten metal or a hot crucible touches it, and the surface can spall explosively. work over a dry sand bed or a steel plate.
- use proper crucible tongs and a pouring shank that fit your crucible.
- keep kids and pets away.
- check local ordinances, fire codes and air quality rules before you melt anything.
- never melt or cast firearm parts. AxiomZero doesn't take those jobs.
melting at home
furnaces: a propane furnace, an electric melt furnace or a kiln that's rated for melting metal, or a charcoal furnace.
melting points: aluminum about 660°C, zinc about 420°C, copper about 1085°C. you pour hotter than the melting point so the metal stays fluid while it fills the mold. how much hotter depends on the alloy and the mold, so check the alloy's datasheet.
crucibles: clay-graphite or silicon carbide, sized for your furnace. never a galvanized, painted or improvised steel can: zinc coatings give off toxic fumes, and improvised crucibles can fail and dump molten metal.
the process
- preheat the crucible.
- start with a dry, clean charge. nothing wet, oily, painted or sealed.
- stir gently once it's molten. hard stirring folds dross and gas back in.
- skim the dross off the top.
- pour into a preheated, fully dry mold.
molds: steel or cast iron ingot molds, sand, or graphite. preheat them and make sure they're completely dry. moisture in a mold turns to steam and can throw metal.
removing impurities
- skim dross while the metal is molten.
- aluminum uses a commercial aluminum flux: chloride/fluoride-based cover and drossing fluxes. borax is not the standard aluminum flux.
- borax is for copper, brass and precious metals. borax with soda ash is fine for copper.
- commercial fluxes give off fumes. read the safety data sheet (sds) before you use one.
- let the melt settle 5–10 minutes so heavy junk sinks and dross rises.
- degassing: molten aluminum picks up hydrogen, which leaves porosity. use an argon or nitrogen purge, or commercial degassing tablets. the 'dry wooden stick' trick is folk practice and unreliable, since wood adds moisture and hydrogen. the best defense is less hydrogen to begin with: a dry charge, dry tools, and don't overheat.
what you can't fix at home
tramp elements (iron, lead, cadmium, zinc, or copper in aluminum) don't skim off and you can't see them. only lab analysis finds them, which is why recycled ingots get spark oes testing before we buy. how we test recycled ingots
alloys blend, but they don't un-mix. melt cans with 6061 and you get neither, just a mixed alloy that matches no spec.
can scrap
cans are mostly 3004/3104 bodies with 5182 lids, which carry more magnesium. melted together, they match neither.
don't try to strip coatings or liners with chemicals at home. the coatings burn off in the melt, with smoky, toxic fumes, which is one more reason to melt outdoors. cans must be bone-dry and crushed, and fed into a molten heel already in a preheated crucible. never drop wet cans into a melt.
recovery is often poor and can-only melts are low yield. dross losses around 30–40% are commonly reported, but it varies a lot with the cans, the furnace and the technique. treat that as a rough range, not a promise.
this is general information, not professional training. molten metal can injure or kill. if you melt or cast, you do it at your own risk.