So I saw a video on youtube https://youtu.be/hHD10DjxM1g well I thought it might be fun and useful to build one of these at the trolley museume to melt brass and cast simple parts. Instead of mixing sand and plaster I was thinking of just useing foundry cement as it is pre mixed and made for this, I am also going to make it gas powered. I am just wondering if any one on here has expearence with this kind of stuff and could offer any tips.

I am not sure what you mean by "foundry cement." Any cement mixed with water will probably fail when exposed to molten brass or bronze. The reason is that the water mixed with the cement does not leave the mixture when the cement sets, but instead combines and stays in the mixture, when exposed to the heat if molten metal the combined water will flash to steam and things start popping. This is also why you do not use a cutting torch on a concrete floor. Foundry sands are mixed with a little water which can vent through the permeability of the sand. Investment castings are done in a refractory plaster that can withstand the heat.
Before the the metal can be poured into plaster mold, the mold must be baked at a very high temperature to chemical separate and drive out of the mold any traces of water. If the water is not completely removed from the mold the reaction of the mold when the molten metal enters the mold is dramatic

Hi,



This is new to me. I'm not arguing, just a little confused by the statement.

I learned how to design concrete mixes in college (1970s) and then went into electronics manufacturing so I am a book learning novice.

If was my understanding that the lime-based concretes such as Portland cement and water chemically reacted to form sticky substance that hardened with the addition of water.

Wikipedia


I think of it as a man-made stone.

Are you saying that at high temperatures this man made stone chemically reacts and Breaks down?

Asphaltic cement does remain in a plastic state and can move (for instance on a downgrade to a stop sign where tractor trailer have to stop), there are frequently ribs or waves in the road due to the plastic flow of asphalt.

I just want to learn more about something I've never heard of.

Thanks.

Doug vV

Wikipedia


Maybe this is what you are seeing - a different concrete mix and/or improper water purity?

Grant Thomson's videos are good for an amateur regurgitating google engineering. But his lack of practical experience shows. For instance his whole series on extracting sulfuric acid and lead from a car battery is horribly impractical. When these items can be purchased for far less money then he spent on materials to make his rigs.

Remember he is in the entertainment business first and foremost so he will only show you his successes and minor failures to get more views and advertising dollars.

I take his videos with a grain of salt, there are others on YouTube(and other sources) who actually know what they are doing and give much better advice.

My 2 cents anyways and I think I owe you change.

There is a lot of good practical information out there on building small brass foundries apart from this one video, so please do some research and see about more good designs, materials and sources.

Ditto to what Dave said. It seems the one presented in the video is exceedingly rinky-dink, with availability of materials at the local home center being the major criteria. Also please note that he is casting aluminum, not brass. Aluminum melts at about 1100 deg.F, if I recall correctly, while pouring temperature for brass is somewhere around 1800 deg.F, and some of the bronzes requiring pouring temperatures over 2000 deg.F.

Rollerman, did you watch the video? The plaster and sand mix is being used as refractory cement to line the furnace, not as mold material, and furnace cement of some sort is likely a better substitute. When I was a kid, the college boys next door ran one of these hobby foundries, and as I recall their recipe for the lining was a mix of crushed fire brick and foundry clay, the same material used to plug tapping ports on cupola furnaces. because the lining is directly exposed to the fire, the water of hydration is driven out as the furnace comes up to temperature; it doesn't explode.

In fact, the video doesn't go into mold making at all, it seems the whole purpose of this furnace is (other than being the subject of a video) to make old pop cans into slugs.

Foundry practice is interesting, and a lot can be done with a little backyard hobby foundry. I always wanted to build one, but just never got around to it. However, there is much, much more to it than is presented in the video.

Probably he meant 'foundry cement'. AKA "plastic cement" (which has nothing to do with thermoplastics, of course)

Here is a useful site, notable for the extreme brevity with which it addresses the "concerns" expressed in some of the preceding posted material. Note the variety of potentially useful comments following the material.

http://www.imarketingcenter.com/refractory.html

Dennis -- as usual -- has the right idea about how to proceed.

refractory cement