Re: Casting Aluminum Brackets for Kayak
Posted: Wed Nov 06, 2013 1:05 pm
I don't think you're understanding the suggestions I've offered. You know for a fact you're overheating the metal... then don't! Melt slower, watch for the pinkish hue, shut down, degas, and pour like I suggested. Learn to read temp by visual clues. Do some research on it. How else do you think they cast metal before there were pyrometers? They made a literal science out of reading metal temps based purely on visual clues. For instance, if you see your metal vibrating inside the crucible you've gotten the metal to a point of boiling. Vibrating "IS" boiling. Metal doesn't bubble like water when it boils... it vibrates, beginning with very mild quivers (which is simmering). When metal gets to a near state of boiling it loses it's pinkish hue inside the furnace due to the radiance of yellow heat from the furnace wall. If you see your crucible inner wall bubbling at the metal's edge you can pretty much assure yourself that crucible's temp is at 2000 degrees. This is extremely too hot for aluminum. All you want is an even PINK hue to your crucible (not pinkish, but PINK) inside the furnace. Once all the aluminum is liquid it, too, will develop a hue... that pinkish hue I'm referring to. At this point you need to shut off the flame, purge and skim (if you're using scrap with manganese, high zinc, and magnesium additives), then watch for that hue to disappear and pour.
I also don't think you understand what contaminated metal is... dirt will not harm your metal, and oils will flare off... contaminated means, you're using metals with alloys you're totally unfamiliar with and are prohibitive of producing a quality of cast you desire using the methods you have at hand. Those wheels are chocked full of magnesium and manganese, both will give you problems if not dealt with under strict controls. Not to mention the cast product you do end up getting not only will have gas bubbles but will also be extremely brittle. Pistons and crank case metals will give you similar issues, as well. But... degassing and lower temps with pistons and crank cases will give you a workable product. Those blue cakes will work for these metals. I've suggested you to try that blue cake and yet you adamantly affirm what you're using will do the job... or should, at least, which implies you're not going to go that route. Learning this trade requires experimentation. What won't work every time for you should give you a clue it just may not be what you ought to be using. Those blue cakes are cheap as candy... it won't hurt you to try it.
Inside that furnace you need your crucible encircled by the flame and your melt not exposed to the combustion of gas and air, this is why I suggest to leave the skin on the melt till you're ready to pour, this helps keep the metal protected from the furnace combustion elements. This is true regardless what metals you're melting down. And as for melting wheels to cast into ingot, expecting them to be "cleaner", does not eliminate the difficult alloys, nor does it purify the aluminum. The ingots you make will have the same properties as the metal you've been casting. Shit in... shit out... in other words. Don't know how to explain it any clearer than that...
I also don't think you understand what contaminated metal is... dirt will not harm your metal, and oils will flare off... contaminated means, you're using metals with alloys you're totally unfamiliar with and are prohibitive of producing a quality of cast you desire using the methods you have at hand. Those wheels are chocked full of magnesium and manganese, both will give you problems if not dealt with under strict controls. Not to mention the cast product you do end up getting not only will have gas bubbles but will also be extremely brittle. Pistons and crank case metals will give you similar issues, as well. But... degassing and lower temps with pistons and crank cases will give you a workable product. Those blue cakes will work for these metals. I've suggested you to try that blue cake and yet you adamantly affirm what you're using will do the job... or should, at least, which implies you're not going to go that route. Learning this trade requires experimentation. What won't work every time for you should give you a clue it just may not be what you ought to be using. Those blue cakes are cheap as candy... it won't hurt you to try it.
Inside that furnace you need your crucible encircled by the flame and your melt not exposed to the combustion of gas and air, this is why I suggest to leave the skin on the melt till you're ready to pour, this helps keep the metal protected from the furnace combustion elements. This is true regardless what metals you're melting down. And as for melting wheels to cast into ingot, expecting them to be "cleaner", does not eliminate the difficult alloys, nor does it purify the aluminum. The ingots you make will have the same properties as the metal you've been casting. Shit in... shit out... in other words. Don't know how to explain it any clearer than that...