Vacuum casting Yellow Brass spitting out of mold

[TimW]

Hi,

I have some small, fine parts that need to be cast in Yellow Brass and have been using Rio Grande Yellow Brass casting chunks in a JR-2 vacuum casting machine.

Everytime I do a pour, about a dozen or so attempts, I get the same issue, the metal seems to “spit” out of the mold, only filling half the mold with the rest spilling outside the flask.

I cast a lot of white bronze and never have this issue, but the yellow brass does it everytime.

I am casting at 1950F in a 950F flask that has had a long burnout with steam dewaxing. Using nitrogen at full pressure during the cast with a good solid vacuum on the perforated flask.

Has anyone had experience casting Yellow Brass and seen these issues? It’s driving me nuts!

[pft1045]

Sounds like you’re doing everything right. I’m putting my money on the sprue. I think that your central sprue is way to small. Without seeing what’s on the tree it’s hard to tell. Remember that you want your tree to cool top down, outside in with your button to be the last to cool.

[wmiles]

I pour Rio Grande Yellow Brass at 1040C (1904F). White Bronze at 1020C (1868F).

You might be too hot? Both these alloys have zinc that can boil and smoke. The yellow brass more than the white bronze. But mostly I agree that your flask temperatures seems about right for small fine objects. If you are not getting a good fill it might be sprues.

Also, you might be short on metal? I don’t see a button in your picture? Multiply your wax weight by 8.4 density to get your metal weight in grams and add 50 grams for the button.

I don’t use a JR2 machine so I don’t know anything about that.