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.

Step 1: Pouring

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

Step 2: Extraction of Ingots

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.

Step 3: May Be It's Important to Warm Molds?

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

Step 4: Conclusion

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.

Comments

[NoelA11]

i have found the best option is to use a section of heavy angle the hight of the crucible yoiu use. stand on its point and weld a couple of ends out of the same angle with flat facing down as feet. after poring the alloy tends to shink a bit so a light tap with a hammer will pop out perfect ingots. the other idea that Grant Thompson "The King Of Random" uses old muffin tins with sucess. cement is hydrosopic so even when dried completely and stored it will take water from the atmopher and this means the mold made from it could exspode with little warning.

[DuralM]

Thanks for the tips NoelA11. I should say that I thought about using angles but decided to try U-section. In my opinion, it allows to make ingots with more "natural or traditional shape" :) I've just made the second bigger mold using U-section. I'll upload the whole process here. Of course there is nothing hard but I think that some moments could be useful for home melters. :)
Could you explain me when is the moment when I need to tap an ingot? As I understand right after it started shrining?
I think that old muffin tins are good for aluminum but there could be the problem with brass and copper. During my first attempt I casted aluminum into a tin can and it worked fine. When I tried the same with brass than it welded with tin can and became one whole. :) The temperature of brass is 300-350 C higher than aluminum, so tin is not good for such purposes. It's good only for aluminum, lead and so on.
I understand about the cement but I dried it into the oven in addition right before casting. Anyway I think that for some specific shapes cement as well as plaster could be used. :)

[NoelA11]

i have fabricatored a few billet molds out of plate but found the angle was a simple mold that will handle alluminium and brass and verious other mix. i tended to tap them out when i could do so with a welding guaghlet with minimal smoke, hope that makes sense. the problem you had with the bake ware is easy to understand when you consider the brazzing method of welding. i often dusted my ingot molds with casting sand ot aid seperation. one of my favorit little mold is an old cast iron jem iron used in the days of coal ranges.keeping it simple is a good rule of thumb when finding the best option, differing enviromental factors will make some good one place but no good elseware in the world. im no expert but have 30 years of playing with metals. Knowledge is useless unlesss shared.

[DuralM]

Yeah. I fully agree about knowledge. :) I'm not sure that I have described the situation about welding brass and tin can clear. Please look at my instructable: Brass Casting - Got nice ingot This is how it happened!

[Black Beard Projects]

Hi mate! I would like to point out that molten aluminum and concrete are very dangerous together if there is any amount of moisture in the concrete! If it's the case the molten metal will literally EXPLODE. This happens because the water inside concrete become steam and expand. I really suggest you to use steel mold if you can't get casting sand :) Have a nice holiday :)

[DuralM]

Thanks for the cautions and the comment Black Beard. :) I try to do everything safely. I dried cement mold 2 days on the air and some time in the oven! In addition, both molds were heated in the oven before casting . I've made green sand long ago (you can check my notes about "Green sand formula" and several green sand casting videos which are on instructables and YouTube) and it's good for making some stuff but not ingots. That's why I had to make a steel and a cement mold. Shure in the future I am planning to use mostly steel molds for scrap melting but concrete as well as plaster could be used for some unique shapes. And of course, thanks for the greetings! Merry Christmas and Happy New Year! :)

[Black Beard Projects]

Oh nice :) Looks like you know what you are doing! You know it just came my mind that I saw in a mall some rectangular cake mold that look just like ingots but maybe they are on the big side :) Keep it up mate! See you

[BeachsideHank]

From time to time I too get small bubbles, but the are never to a size that matters for my projects, a typical treatment may be a degasser like washing soda, but again I cast for utility, not looks . ☺

[DuralM]

Yes, you're right. As I wrote about lead ingots I don't want them look very beautiful but it's strange :) I read that degassing is important during melting aluminum only if you have a large quantity of aluminum and melt it for a long...long... time. Only than degassing is demanded. Nevertheless, I tried once soda for degassing and salt as flux. I didn't see the difference but that time I casted things and not ingots. May be those bubbles appeared because the shape of the mold, the temperature inside and outside or both. When I poured aluminum the first time into the can I saw shrinkage and no bubbles. Now I have no shrinkage and big bubbles. :)

[BeachsideHank]

As I watched the video again, the "burp" just reminded me of a moisture reaction, I'd expect that with a concrete mold, but the metal one- all I can think is maybe some condensation formed in it, and a simple preheat would be the fix for that.

[DuralM]

Good idea. Thanks. I've decided to heat a mold the next time little more. In fact, these two molds were heated but started to cool. I heated both molds into the oven to 200 C before casting but some time passed before I could start the process. May be 5-10 minutes and it was cold enough outside :)