Sodium silicate recipe: The good stuff

Discussion in 'Sand Casting' started by Mark's castings, Jun 1, 2020.

  1. Last week I used NurdRages's YouTube sodium silicate recipe that involves silica gel kitty litter and caustic soda. He gives the correct proportions of the two ingredients with water as well as the process of just heating up the water and adding the caustic soda to the silica gel (silicon dioxide/quartz). I found that there was a fair bit of heat released during the mixing as well as lots of bubbling, so do it outdoors as it's highly alkaline and will irritate your skin...gloves are a must and some eye protection. I made three litres of thick syrupy liquid which weighed 5 kilograms to give a specific gravity of 1.666. I looked up the density of concentrated liquid sodium silicate and found it was 1.7, so I was pretty close. After a few days the stuff crystallized into a solid lump that had to be smashed with a hammer and I plan to add some water and heat to dissolve again.

    So far I've tested it with aluminium castings but not iron or copper alloys. The end of the video describes making it with higher silicon content that may be more heat resistant.

    It works perfectly fine for making cores at 6% by weight as well as 15% water and 12% sugar relative to the sodium silicate from the Tom Cobett notes. After a day the CO2 hardened test cores could be thrown at the concrete floor and only suffered damage at the point of impact.

    Last edited: Jun 2, 2020
    Tobho Mott, Chazza and DavidF like this.
  2. Patrick-C

    Patrick-C Silver

    So you are using it to make sand cores?
  3. Sand cores and the sand mould too.
    Chazza likes this.
  4. HT1

    HT1 Silver Banner Member

    That sounds dangerously hard, as in a complicated part, you are seriously risking tears, consider adding something to the sand to add some collapsability ... and Vent, vent alot ALOT !!!

    V/r HT1

    P.S. well all that sugar should add lots of collapsability , with 15% water, I would bake those cores overnight, not let them sit

    P.P.S vent alot
  5. It's taken a bit of experimentation to get to this point, right now coming into winter the humidity is low so it all dries out in the sand mixer. My beach sand is "hungry" and needs nearly double the polyurethane resin compared to pure silica sand when using resin. I'm following the instructions written by Tom Cobett so I have to add water to thin the very thick sodium silicate to the recommended "olive oil" consistency. I found that unlike resin sand where you tip it into the pattern and give it a few pats with a trowel, this stuff needs a good hard ramming to get it strong enough with the fine sand I'm using....venting is going to be necessary. The two castings I made so far had the sand mould crack in several places during cooling so the sugar burns and seems to be doing it's job, strength would be on a par with concrete without it.

    I still have to get familiar with it all to get a good result.

    silicate mould.jpg
  6. Melterskelter

    Melterskelter Gold Banner Member

    I too have found ramming necessary when using SS to bind Olivine sand. I use a common dead-blow plastic hammer. It does not ram like green sand as the SS sand will push up in the mold near an area I might try to really pack hard. I sort of thought the ramming just ensured that all the sand grains were in direct contact with their neighbors prior to kicking off the SS with CO2.

    It sounds like you are making good progress. Glad to hear it.

    I do bake my cores at about 220 for an hour or so. I have stored mine for a month in some cases with no ill effects.

  7. It's slowly getting to a reliable point, the poor finish I had with the castings was likely due to poor ramming making the sand a bit crumbly, the latest cores were rammed better and still hardened fine with CO2. An earlier batch of sodium silicate was made with an excess of silica gel and I have baked only silicate samples made over a year ago that have survived humidity with no wetness problems, not sure why. They are supposed to react with atmospheric CO2 over time and harden.
  8. Jammer

    Jammer Silver Banner Member

    I had made some of that years ago. It was on AA but I guess it's gone. I'm glad Nurdrage made a distinction betweem the various types of Sodium Silicate. I still have about a pint of mine. I bake it and it makes very hard cores and is difficult to remove. If I don't bake it, the cores have very little strength.
  9. DavidF

    DavidF Administrator Staff Member Banner Member

    I was just given about 40 lbs of desiccant from a new transformer that was shipped to us.
    Plan on making myself some before too long

    @Jammer , that was back in the metal casting zone days I think. I reached out to Nurde rage and asked him how to make it...
  10. One thing I'm finding with sodium silicate is that the results can vary a lot, so consistent mixing and ramming is key to getting a good result and adding water seems counterintuitive but it seems to allow every grain of sand to get an even coating of sodium silicate. If I don't add water the mixed sand can get a dry crust after a few minutes, before I can get it into a pattern now that humidity is low. The sand seems to dry out and lose the water after several days drying. Gassing a big piece is difficult too, I just made a 30cm square board with dense foam glues to one side that I'll fit a brass barbed hose attachment to the middle of: it should let me get a better seal with the patterns so the CO2 can flow deeper into the sand. Like everything, it takes some time and practice to get it to work.

    Caustic soda is hydroscopic, so making the sodium silicate with an excess of silicate seems to minimize the effect of humidity/dampness with some test pieces still holding up fine.
  11. Melterskelter

    Melterskelter Gold Banner Member

    Rather than trying to gas an entire core, I just poked 1/8” dia holes deeply into it with an ice pick every3 inches or so. Then, using a CO2 cylinder with a plastic tube and metal tube tip, blew CO2 into each hole for 3 seconds or so. See this video at about 20 mins in

    I also show my ramming method etc.

  12. HT1

    HT1 Silver Banner Member

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  13. Jammer

    Jammer Silver Banner Member

    It was on AA too because I took some grief since it cost about the same to make as it did to buy some. Where's the fun in that. I might have to make some more.
    Mister ED likes this.
  14. DavidF

    DavidF Administrator Staff Member Banner Member

    Expensive ass cat litter huh???
    I only made about 10 ml, then just ordered a gallon...
    Last edited: Jun 3, 2020
  15. Melterskelter

    Melterskelter Gold Banner Member

    At the commercial foundry that mentors me they walk on the resin sand and also push it into place with their hands. Most of their molds weigh more than a thousand pounds and some of their molds weigh tons. I have never seen a vibrator used nor a tamper for that matter. It is dispensed from a hopper connected to the sand prep machine which breaks down the clumps of used sand into granulated sand and mixes in new active resin. It appears the resin sand does not rely on forceful compaction, just good general grain-to-grain contact. It sets up so strong and hard that it has enormous strength. I can not press a thumbnail into the set resin-bound sand.

    If you look at my video, you can see that I use a plastic mallet to tamp my Sodium Silicate molding sand more than ram it with consistent and accurate results. I have never used a vibrator, but I did machine some parts and did a little welding to repair one for a now-defunct, green sand, local, 3-generation-family-owned foundry.

    Last edited: Jun 3, 2020
  16. Melterskelter

    Melterskelter Gold Banner Member

    Why should vibration be better than tamping for SS cores or molds?
  17. It's worth a try if it gives a good result, I have the gear to try it at a later date.
  18. HT1

    HT1 Silver Banner Member

    you dont need to pack the sand, you need it to evenly fill the mold with no voids , a Pneumatic Vibrator does it perfectly with much less effort (it's what the Pro's do) it works well , it is litterally what a Drop jolt machine does but Gentler, which is good for flasks and patterns,

    V/r HT1
  19. Melterskelter

    Melterskelter Gold Banner Member

    Being curious about squeeze machines and vibration units, I decided to do a little Google-foo and find some videos of them in use. These two show squeeze only, with vibration used to aid sand separation from cope and drag

    Here are Jolt (vibration first to settle sand) followed by squeeze to compress sand and in one case vibrate sand while squeezing it.

    I could find none that used vibration alone. To me it looks like the vibration helps get the sand settled prior to coalescing it with a powerful squeeze. I think tamping is a combined vibration and squeeze.

    Interestingly, there stands a squeeze machine covered in dust in a corner of the barn in which I work. The now-deceased owner of the barn (now his kids') never put it to work. It has a platen on it about 14 by 14" but might be large enough for my smaller straight edges. I do not think it could handle my 30" square flasks. And I would probably have to make aluminum patterns as the squeeze would likely splinter my wooden patterns. Something to think about though.

    The vibrator I fixed was occasionally used to settle sand in the flasks prior to floor tamping. But, in general it sat on the molder's bench, gathering dust.


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