Finally, yesterday the bottle of sodium silicate arrived so I could try making the sand core for the shaft tunnel!
I mixed 6% by volume of sodium silicate with fine grain silica sand and packed the core pattern full of it, I also poked a hole through the center to get the CO2 into it properly.
Lucky me for having a Soda Streamer at home.
Bugger, that didn´t end up as expected. The core sand didn´t solidify much at all and crumbled when I tried to remove the pattern halves.
After some good advice from a friend I tried it again this evening, this time by baking the sand core in the microwave instead of using CO2.
Now we are talking! The sand quickly became very hot and was near melting the PLA pattern when I removed it from the sand core, I gave the core another hit of microwaves without the pattern around it so now it is very solid. It must have been near cracking before it solidified as can be seen but it seems to hold together just fine now.
I´ll make the petrobond sand pattern and see if the core will fit, if so I will try to find me a quiet evening for some more aluminum casting!
Cheers!
/Anders