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open mold brass casting

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savarin

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#1
Can I pour brass into an open mold?
I need 2 brass blocks approximately 1.25 x 3 x 4 inches.
They will be machined square after.
 

benmychree

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#3
All too many people use the term "brass" entirely too loosely; if it is an alloy of copper and zinc, probably yes; if it has tin in it, the answer is likely no. Tin oxidises in the presence of air and makes a nasty casting, a two part mold reduces the tendency to a very minimal effect; I have not looked at you tube posts, but generally, they do not know their a-- from a bucket of hot rocks. I have done a lot of brass and bronze casting, brass is easy, bronze not so easy to achieve clean sound castings.
 

savarin

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#4
I am assuming its brass scrap not bronze due to its colour.
I hoped an open mold would work but was unsure.
I think I will gate them as usual.
My lost foam cast was horrendous.
 

benmychree

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#5
What happened with the foam?
 

Cooter Brown

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#7
this guy does an open pour with Brass.....
 

genec

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#8
an uptodate yellow boy
 

savarin

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#9
thanks, excellent video.
A few defects that I'm hoping to avoid.
 

savarin

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#10
I have done a lot of brass and bronze casting, brass is easy, bronze not so easy to achieve clean sound castings.
What are the main problems with bronze?
 

benmychree

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#11
The problem with bronze is that the molten metal picks up gasses from the furnace atmosphere that results in nasty porosity, the cure for it is to use a oxidizing flux during melting, then plunge in a degassing tube containing (I think) phosphor bronze pellets and mix it around; after that treatment, the metal, when the dross is skimmed off should appear bright and shiny, if it still looks dull it probably needs more; if you use too much, the metal gets super fluid and results in dirty castings where the fluid metal soaks out into the sand. This can be the result of re melting too much "returns", that is castings and sprues/gates/runners that were likely over de oxidized, along with new metal, then being re melted and re deoxidized. Been there, done that.
Brass, on the other hand has zinc in it; when melted, exerts a vapor pressure on the melt, excluding the contaminating gasses.
Another tip; do not add silicon bronze scrap to any other brass/bronze mixture; the result is a casting so brittle that it breaks like glass and chips/spalls like obsidian.
 

savarin

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#12
Thanks for that. Now I'm worried about that little bit of bronze I want to cast.
 

benmychree

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#13
It can be done, just study up on it and get the proper supplies to carry it off.
 
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