Sinking Deep Casting Aluminium

Hello Everyone

I am trying to cast this big block out of aluminum around 90 to 100 pounds worth and i been getting lots of sinking

I made this mold out of steel and it seams to be working well with the exception of the sinking hehe

The first time it sank into the part and made the part unusable, the second try i added 10+ inch to the
pouring basin thinking that it will sink but not as far as in the part, but it sank even deeper, i would say a good 6 to 8 inch

I have a few pictures of my setup i take my time and pour at a good rate and try not to make to much turbulence
I am not sure what i am doing wrong ??
Anyone know ??

Thanks
Biggs

Would it be worth making the feed tube from of something more insulating ? To keep the metal there molten for longer ?

This is just a guess, I have no experience of this, interested to learn.

Maybe,
I think feeding it from the bottom probably be better, but that's a lot of work hehe and it might be to much to be feeding it from the bottom not sure
I was hoping to keep it very simple so i can reuse the mold quick

It sounds like you're complaining about shrinkage. Aluminum shrinks quite a bit as it cools. The "sinking" you're noticing at the top of the piece is a sign of that. But in your last photo, it looks like the bottom part, which I'm assuming is the piece of it that you're interested in, came out pretty well. When you cut off the excess part on top, does it seem okay, or does the shrinkage porosity extend down into the part you want to keep?

In general, you want to create a reservoir of molten metal that the piece you're casting can draw from as it cools. This should be thicker than the part you're casting. If it chills too soon, it won't function correctly. As Zorbit suggests above, insulating the feed tube will help combat premature cooling. An easy way to do that is to bury the whole mold in dry sand, or something more insulating like perlite, with only the top of the feed tube sticking out, then pouring it and letting it cool for several hours before unmolding.

I am not sure how to approach this one,
I found this, sounds like I am pouring to hot, look at number 7 https://www.mechanicalbooster.com/20...g-defects.html

I think i will try a bit of everything
Build a wooden box and fill it with sand
a bit smaller pouring basin and kind of a L shape
and pour a bit cooler, i just orders a thermometer, they say around 725oC to 750oC
I was almost glowing red when i poured haha

in the picture the blue is the part that i need, The part in the picture of the part i made the sinking when down into the part,
i added more aluminum on the top but seams like it did not work, when i cut it, you can see it inside

Here is what the inside of one of the parts i made so far

That teardrop shape on the left fell out :-(
I might be able to save it if i tig weld the inperfections
After its machined

In your red and blue picture, the red part needs to be bigger; it has to stay molten when the blue part is mostly solidified. I don't think splitting it into two offset parts is helpful.

As for the "teardrop" it looks like some splashed metal got to oxidize on the surface before the rest of the metal filled in around it. Better pouring technique will help with that sort of thing.