Casting help

[kadora]

Hello experts
Please give me an advice what should i do to improve my
AL castings.
On the picture are two castings left is AL right is zinc .
As you can see AL casting has not as sharp edges as zinc
and i do not why.

Could you tell me what i do wrong?
I am beginner all advices are welcome.
Thank you a lot

 

[old-and-broken]

I'm no expert. I'm not even a layman when it comes to casting, BUT

Aluminum shrinks when cooling, that, I know.

Castings are supposed to have a large extra piece of metal attached from where the metal is poured in to the mold. This extra metal forms a reservoir of sorts and provides a source of molten metal to the cast part that keeps it from shrinking in such a dramatic fashion as yours has.

Did your casting have this 'sprue' piece and you removed it before taking the picture? If not, then do some more research, or simply wait for a real expert to come along and answer.

I'll go back to my corner now. I seem to have misplaced the pointed cap I was wearing.

 

[aonemarine]

It looks like you cast it in an open face mold, bad idea!! You need a closed mold with a good sprue and rised height to give it head pressure to fill properly.

 

[mcostello]

Temperature too cold.

 

[kadora]

Thank you guys
how you know that temperature is low?
In simple gas burning kilns is difficult to meassure temperature.
Is there some way how to judge if liquid AL is hot enough ?
thank you

 

[aonemarine]

Kadora was this an open face mold??

 

[aonemarine]

Kadora... cant help you unless you answer a few questions.