Casting Aluminum Bars. Cement and Steel Mold

I prepared some scrap of aluminum, so it was time to melt it. Not long time ago, I’ve made a steel mold and several days ago a cement mold. The thing that I called “a cement mould” is a mixture of cement (45%), sand (45%) and graphite dust (10%). Therefore, I’ve decided to make 2 aluminum ingots from the scrap.

During the pouring a crack appeared in the cement mold but it didn’t effect on the bar quality.

When I tried to extract the ingot, cement mold was completely destroyed. No surprises with the steel mold. It worked perfectly. When ingots started to cool, aluminum bubbles appeared on both of them. I’m not sure why that happened. May be that was because molten aluminium started become solid but in the center it was still hot and liquid.

It should be that I need to warm molds before casting though it may be not a solution of a problem.

In conclusion, I'd like to summarize the information. Steel mold is grate because it could be used unlimeted time. It's easy to extract metals out of it. Cement mold is disposable but could be used if you need to get an ingot or something else of a complex shape.