Removing sodium silicate sand

[kelvin2164]

I've just done some cast iron locomotive wheels, first time using sodium silcate. It has set like concrete and I'm having great difficulty removing the sand. Is there a solvent of some kind. Also perhaps next time I should dilute the sodium silicate with 50% water?

 

[bmac2]

Hi Kelvin
Ya . . . Been there, done that.:fan:
When I use SS for a cores I put in just enough for the sand to hold together while I gas it, around 5%. Remember that any water you add to the sand you have to get rid of before casting by baking it out. Soaking in water after casting (overnight) or better all day in the sun will help dissolve the SS.

Any pics of the castings?th_wwp

 

[kiwi2]

Hi,
I'd try caustic soda to get rid of the sodium silicate sand. I'd start of with a 10% solution (100grams/liter of water).
Add the caustic soda to the water while stirring and make sure you have at least safety glasses and rubber gloves with no bare skin showing - caustic soda burns hurt like hell.
Regards,
Alan

 

[kelvin2164]

Attached is pic as requested.
Kiwi2 suggests using caustic soda. I made my own Sodium silicate from silica gel and caustic soda. I was thinking that to reverse the reaction an acid would be better. I have gallons of sulphuric. I suppose I could try both. I'll try Bmac2 soaking first.

 

[GLCarlson]

Attached is pic as requested.
Kiwi2 suggests using caustic soda. I made my own Sodium silicate from silica gel and caustic soda. I was thinking that to reverse the reaction an acid would be better. I have gallons of sulphuric. I suppose I could try both. I'll try Bmac2 soaking first.

Kiwi is right.

You made sodium silicate from silica gel and lye. Presumably, you then gassed it with CO2 (or let it react with atmospheric CO2). CO2 is an acid anhydride, and the system was aqueous, thereby acidifying the silicate sand and making silica gel again. To dissolve the silica, you again need a strong base.

(All of this ignores the actual complexity of what really happened, but to a first approximation, it's close enough. Crude, but adequate).

Only use strong base with ferrous castings. Base and aluminum in particular react vigorously. That mixture is sold commercially as Drano.

 

[kelvin2164]

Wow!
Before reading this post I went out and put a wheel in a bath of hydrochloric acid overnight. I guess that was wrong. I'll remove that now! We can buy pure sodium hydroxide here in Australia, which I presume is the Drano? I'll mix up a strong batch and give it a go.
Thanks.

 

[kelvin2164]

I had another go using a watered down sodium silicate. Didnt really harden that much after gassing, so gave up and did it using green sand. Pic below. I would like to be able to do it though. I have some cylinders to cast using quite a few cores and I like the idea of being able to sand the cores down to make them fit.