Wednesday, April 19, 2017

New Crucible and Casting Brass

I had never really gotten around to buying a "real" crucible for melting anything hotter than aluminum.  The one time I made it to the foundry supply store, I forgot that they closed at 3 PM, and it was 3:15 or something. 

2 Years later: I got invited to American Foundry Society/ North American Die Casting Association annual vendor's night.  This is an event where people from the industry get together and showcase their products, hang out, and have a good time.  Personally, I was just there for the free food.  Long story short, each vendor booth had a raffle prize, and judging by the proximity of this crucible to the ticket jar, I thought it was the prize.  I asked if it was because I had been in the market for one, but it turned out they were only giving away $100 cash.  Still, I bet most of my tickets on them since it seemed like one of the better prizes compared with all the alcohol, golf accessories, and gift cards for restaurants that don't have enough vegan menu items... But I really wanted the crucible!  At the end, I didn't win any of the drawings, but the nice people at Advanced Ceramics and Crucible decided to give me the crucible anyways!  I guess when you're young and have your own foundry, people treat you differently or something (it's because in an industry like this, they're hard pressed to find young people interested in it, there's actually quite a shortage of people to replace those retiring).  Hey, it worked before when I accidentally got a free lathe.  This goes along with a discussion we had there was about "what got you interested casting?"  Of course for me it was the concept of being able to melt and recycle your own metal, and cast seemingly unlimited parts from a single pattern, and in the case of a vegetable oil furnace, for practically free.  Going back even further, it was probably the "Foundry" level from Tony Hawk's Pro Skater 3 where I first learned the word "foundry".
OSHA's gonna sue somebody
Anyhow, it's a silicon carbide crucible which, if I remember correctly from chemistry class, is nearly identical to diamond in its molecular structure and almost as hard, but who cares?  Let's melt some metal!
Grapefruit for size reference
Wow, that's convenient!  It's the perfect size to fit my lifting and pouring equipment!
I've been given specific instructions to not try melting cast iron in this crucible or else it would dissolve the carbon binder.  I guess I'll just have to save that for the next free crucible I get... but in the meantime, I've collected enough scrap brass to have an excuse to light up the furnace!
My oil hose had gotten really hard from sitting around with rotting oil inside.  Not wanting to repeat the mistakes of the past, I decided to replace it.  I also mixed in some leftover diesel I had from the early testing to thin out the oil a bit since it had been sitting around for at least a year.
A picture of the crucible after the melt and skimming it once.  This stuff certainly behaved differently than aluminum.  For one, brass is a mixture of copper and zinc; but zinc vaporizes at a lower temperature than copper melts which means zinc fumes come off this when melting it.  Also, certain brasses have lead in them too, which adds to the list of reasons why I don't want to breathe this.  I could tell there was zinc vapor because on the opening of the lid I could see a white substance appear when I turned the oil low enough to not char it black.  This is the same substance that comes off when you weld on galvanized (zinc coated) metal, and it smells like burning popcorn or something.  Either way, don't breathe it.  There was this really eerie effect when I was skimming the slag; the metal started flaming and glowing green.  This actually made sense since I remember seeing green flames when doing torch brazing.
It did seem like a lot of slag for such little metal, but I wasn't using the cleanest scrap either.  There were rubber inserts and chrome plated parts mixed in there too.  The brass slag looks much more crumbly than the aluminum type.
I went ahead and tried casting some familiar shapes, though there wasn't enough metal to fill the Aku-Aku pattern.
Here's a 3rd mold I didn't get a chance to use.  I made this metal flask since my wood ones are just about falling apart.
A shot of the junk left in the bottom after pouring.
The finished parts.  What can I say?  I'm actually quite surprised at how unimpressed I was with casting brass.  I left with the impression that brass is every bit as cool as aluminum except a bit heavier, expensiver, and a more yellow.  Other than that, the toxic fumes are a real turn-off.  Scrap aluminum is so much easier to find anyway, it will probably take me another 5 years to find enough brass for another melt.

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