Sodium silicate recipe: The good stuff

I have been able to wash out the SS on aluminum cast, i pour between 1350 to 1425, I did one pour at 1550 that had some thin spots the SS in that one all but took an act deity to get it out.
Art B

 

I think it must be the high heat that bakes the SS into glass. I forgot the sugar one time with iron. There was NOTHING I could do to remove that core. I tried boiling it in water, acid, lye, chipping etc. In the end I just junked the casting and remelted it. If I use the sugar, the core crumbles out and separates very very easily. The difference is amazing to me. I learned about the sugar from a monograph by Tom Cobett, professor emeritus of Kent State, who was in on the develpment of K-Bond there.

Denis

 

At aluminum temps, the cores crumble with light force or disintegrate in warm water.
If we haven't already, Cobett's essays should be put in the useful links page.

(Link and local copy added here: http://forums.thehomefoundry.org/in...-silicate-for-core-making-by-tom-cobett.1334/)

 

ok more free tips, if you have a core being a PITA, soak the entire piece in water. the water will desolve the SS , and then you just have sand , other ideas that work, we have sand blasted them out , you of course then have sand in the sand balster, which may be an issue depending on your normal agragate, we ran steel shot, the dust collector would get all the sand out in no time,

lastly, pressure washer

V/r HT1

 

From that Tom Cobett article:

 

Funny, Some of my Cores from an aluminum cast were outside in the rain and snow for 6 months before I ran over them with the truck ....still hard as a rock. Maybe I poured that one too hot

 

Just some additional information for people using sodium silicate: I was in my workshop today and noticed a stain under one of my bottles of homemade sodium silicate with a 1.3 specific gravity. The PET plastic had crazed and cracked all around the base where there's some bumpy high stress blow moulded features. The leak was slow enough to kind of cure and seal well enough to be very slow. The main bottle full of 1.7 S.G. sodium silicate is a two litre HDPE milk bottle which has held up fine despite being filled a few months earlier than the leaky PET soda bottle.

 

Just a short note to add some more info about making sodium silicate from silica gel/kitty litter: I found that by using Nurd Rage's video as a starting point and then adding excess silica gel until no more dissolves into the hot solution you can end up with a high specific gravity sodium silicate that seems to be much less hydroscopic and cured sand will stay dry even after months of tropical humidity and wet weather. Sodium hydroxide/caustic soda is very hydroscopic so an excess of silica gel with consume all of the caustic in the chemical reaction. Also I have found a very common dry powder sodium silicate from a local chemical supplier that makes cleaning supplies: sodium metasilicate pentahydrate which sells for under $4 Australian per kilo. It's a dry powder you mix with water and I found I could increase the silicate ratio by again heating the solution and dissolving more silica gel into it until no more gel dissolves.

While either solution cools, you have to be ready to dilute it as it can go solid when cool if the S.G. is much higher than 1.7

https://en.wikipedia.org/wiki/Sodium_metasilicate

https://bosca.com.au/products/sodium-metasilicate-anhydrous-25kg?variant=39363606020138

 

So Mark,

You are routinely using your silicate, I assume. What is your current recipe and process?

Denis

 

Hi Denis, I haven't made any since about July last year when I made a couple of 5 litre batches for casting copper: Nurdrage mentions the recipe ratios at the 3:56 minute mark and shows that the sodium metasilicate granules has half the silica needed to be waterglass which is what we'd need, so by adding extra silica gel kitty litter to a hot solution until no more dissolves, it's being upgraded to something like Non-stoichiometric sodium silicate. So I dissolve enough weight of sodium metasilicate to get an SG 0f 1.7 maximum (so it doesn't solidify) and then add silica gel until no more dissolves. I then follow the sodium silicate instructions for SG, dilute it with water and add sugar according to instructions and gas it with CO2.







Moulds clamped and glued with Dow Corning clear silicone, the mould on the left next to the aluminium is used as an end cap and not poured.

 

Mark, I guess I asked as I felt that just having someone say how to make sodium silicate in a video is interesting. But, I was more interested in a long-term use report to see how it actually fits into a foundry process and if there are certain caveats to consider.

Denis

 

The only differences I've noticed to date with this home-made sodium silicate is that it's almost impossible to overgas but then I am using a regulator. Secondly I'd heard from at least two people that sodium silicate cores absorb water over time and need baking dry if stored for a long time, so far that hasn't been the case for this stuff with samples over a year old and still seemingly dry. For the small amounts I use it's easier to make the stuff rather than have it shipped 1800 kilometres from a foundry store that may be closing at any time.

 

I can say the the silicate cores I make from RU Silicate also store well. Though, the longest time I've kept them is probably a month to six weeks in relatively low humidity conditions. Right now I have a five gallon pail orderd to start to use after the prior fiver is empty. That amount has lasted about 3 or 4 years. So, as long as I can buy it and get it delivered free from a source 90 miles away (I have them drop it when thjey are servicing "real" customers in the area.) Being able to get SS of consistent compostition and known analysis I consider to be a luxury that I hope does not end in the near future.

Denis