Sodium Silicate RU for core making in cast iron molding.

Discussion in 'Sand Casting' started by Melterskelter, Apr 12, 2019.

  1. Melterskelter

    Melterskelter Silver Banner Member

    I just wanted to report on a core making process I just used to make somewhat intricate cores for casting iron.

    The cores weigh 3.5 pounds and contain lettering and contours used to form the inside of my 18" prism straight edge.

    I used 100 mesh silica sand bound with RU sodium silicate.
    I used Tom Cobett's recommendations ( and some intuition.
    Per Tom's suggestion I used RU plus 15% water plus 12% table sugar for weakening. I added about 4% by weight of the silicate mixture to the sand and to that, based on intuition, added 5% sea coal to the sand.

    I molded the core and gassed it for 10 to 15 seconds penetrating the core every few inches until the core was quite solid and then removed it from the box and baked it at 220F for 90 minutes to dry it out. The resulting core is quite hard and reasonably strong. I will add pics in the next day or so as I have no pics of that core now. It is 18 inches long and is 1/2" inch in thickness in several places. So, it had to be handled with care. More on that later when I have pics of a newly molded core I will make in the next day or two.

    I just poured the mold with core this afternoon and the core sand behaved just as I had hoped. It held together nicely but was crumbly after casting making removal very easy. [ HUGE WORD OF CAUTION: do not forget to put in sugar for weakening. I accidentally left the sugar out of the mix with a similarly molded core earlier this week and the core has been a huge PITA to remove despite soaking in lye for several days.] I was able to get 99% of the sand out today by simply striking the casting lightly with a hammer. The rest of the sand brushed off easily. The surface finish was pretty shiny and and there was no burn-on or burn-in of sand.

    I will take some pics of the casting tomorrow---tired tonight.

    Incidentally I poured the pattern using a 3-layer flask/mold system and used a bottom gate and blind riser setup that is a bit more trouble to mold but gives better results than my prior setup. I also used my oversized pouring basin that allows dumping the crucible contents and letting the basin drain into the mold. I am really liking that system. More on that later too.

    Mark's castings and Tobho Mott like this.
  2. PatJ

    PatJ Silver Banner Member

    Sounds very promising.
    Thanks for sharing the details.

  3. Chazza

    Chazza Copper

    Top work Denis! Exactly what I need to know regarding core fabrication,

    Cheers Charlie
  4. Melterskelter

    Melterskelter Silver Banner Member

    0DCF8E67-8B7F-433C-8EC6-F09D4101617A.jpeg 4A40EF0E-E34F-4AD9-B936-D09960F621C8.jpeg 59AF89BD-A06C-4AFE-B6AC-BDEB77ABAE6C.jpeg B1FA0E52-0F41-4401-908D-4CD0121EF60F.jpeg 01F19FE3-2A0B-47EB-B51A-6CE0B97D8116.jpeg Here are a couple pics of the process
    Last edited: Apr 13, 2019
    joe yard likes this.
  5. Melterskelter

    Melterskelter Silver Banner Member

    195392CE-331B-4926-BCF1-DC127B2D1DEF.jpeg 38537455-417B-4D90-A0E6-30E860AE5510.jpeg 198CDA7F-A272-44F1-8891-56CE005BBC46.jpeg 7A04F3E0-F561-4E1B-9F5D-1EB6074A0105.jpeg 05B23136-3A78-45FA-BE8C-208D5F13ABE2.jpeg A few more. I use the threaded rod with internal threads to attach a temporary "strongback" of wood to reinforce the core so it does not break as it is lifted from the mold and is transferred to the mold. Into the insets I thread cap screws with fender washers to attach the strongback to the core. By using the inserts rather than fixed studs, the back of the core is clear of obstructions when it is placed in the mold and the screws are removed. The inserts are retrieved from the mold sand after the casting is shaken out.

    Last edited: Apr 13, 2019
  6. Melterskelter

    Melterskelter Silver Banner Member

    81A71977-32C3-41A6-A373-7D5042B52B7A.jpeg 49175D30-F1A3-407E-B284-27A2CF5A489A.jpeg

    This is my CO2 tank and the 1/8th gassing tip cross drilled as sand plugs the open end of the tube. So I soldered the end shut and cross drilled. A tank seems to last a long time.
  7. PatJ

    PatJ Silver Banner Member

    I bought 5 gallons of sodium silicate from Clay Planet, with catalyst.
    I have not used it yet, but it does not require CO2 to harden.

    For cores I have made with Budget Castings sodium silicate, I used 3% and gassed a maximum of 5 seconds.
    When I first started making SS cores, I figured more CO2 was better than less, and so in my ignorance I gassed the sand, and then placed the entire core in a ziplock bag full of CO2 (more is better right?).
    And so overgassing the cores ruined them, and they fell apart all by themselves.
    So using my infinite knowledge again, I increased the amount of SS up to 6% or more, and I made cores that were like granite, and impossible to remove from a casting.

    Then I was watching a video (myford I think) about core making, and he said "be sure you do not overgas", and while I did not believe him, I did give it a try and cut back to 3% SS.
    Low and behold after 5 seconds the cores were perfect, and more importantly they break down relatively easily with water after the part has been cast.
    And I have had some 3% cores on the shelf in the shop, and after a year they are still solid and completely usable.

    So I wonder if you need the RU and all the additives, or just need the regular SS at 3% with 5 seconds gassing.

    And the idea of using the Clay Planet SS with catalyst is that the core (or mold, I make entire molds from bound sand) will harden no matter how thick it is.
    And you don't need to keep refilling those pesky CO2 cylinders.

    Here is the link to what I purchased.

    I also bought some faster catalyst from another foundry supplier to use with the Clay Planet SS, since the fastest catalyst that Clay Planet sells is a bit slow.

    Your cores look great.
  8. Melterskelter

    Melterskelter Silver Banner Member

    I have a couple gallons of catalyst but generally don’t use it as I don’t like waiting half a day or more for it to kick.

    If you wonder about the additives you may want to go without and find out for yourself. I did and had poor finish and very hard and difficult to remove cores. But, I don’t think I said anyone “should” use the additives. That is up to them. I just reported what worked for me.

    So, the sugar additive recommended by Cobett has proven to be needed in my hands and to work as he found them to work. He did not speak to sea coal and I do not know if he was casting iron or non-ferrous materials. For me, the coal made a big positive difference. I do not know the ideal coal percentage, but 5% worked well. I have yet to come across a discussion of coal in NaSi cores. So, I landed on 5% based on a similar prrcentage being used and important in my green sand

  9. PatJ

    PatJ Silver Banner Member

    You can buy catalyst in varying set speeds.
    I have some that sets in 5 minutes.

    I am a believer.
    I am going to try them.

  10. Melterskelter

    Melterskelter Silver Banner Member

    Please tell me about 5 or ten minute catalysts. Where to get them. Cost. Etc. A fast catalyst would be very interesting.

  11. PatJ

    PatJ Silver Banner Member

    I am traveling at the moment, but will be back tomorrow and dig out the details of it.
    I think I bought it from Lancaster, but it not something you will see listed on their site.

    As I recall I got a gallon.
    5 minutes is probably too short, but I have the catalyst from Clay Planet (Chembond 210) that is about 75-85 minute strip time at 75 F, so I am thinking about mixing the two catalysts in an appropriate ratio (assuming the two are chemically compatible) to get more like a 15 minute set time.

    I have not used any of the SS catalyst, so I can't report on how it works.

    I tried to by Chembond 250 catalyst from Clay Planet, but they would only sell it in a 5 gallon container, which is several lifetimes of supply for me.
    250 has a 10-15 minute strip time, and the brochure mentions that the Chembond catalysts can be mixed to vary the strip time.

    A note about "set time" and "strip time".
    Set time is when the bound sand begins to set up and get hard.
    Once you get into set time, you should have completed any ramming of the mold, and should not move the sand again, else you will break the bond and crack the sand.

    After set time begins, and before strip time, the sand is not completely cured, and so you can still press an indentation into it with your finger.

    When you get to strip time, you can pull the pattern out of the sand, but you have to be careful to keep a flask on the sand for a little while (I use snap flasks), and keep the mold on a flat surface because it can warp a little if you pull the flask off too quickly after strip time and don't keep the mold perfectly flat.

    At some point the mold becomes completely rigid, perhaps 10-15 minutes after strip time, and the flask can be removed, and the mold will not warp at this point since it is very rigid.

    The above description is with resin-binder, but it should be about the same with SS and a catalyst.
    SS bound sand is not quite as rigid and durable as resin-bound sand, but not too far off.

    The set time is what I pay attention to, since the strip time is generally not too long after set time.

    It takes 2 minutes to mix the binder in with the sand, and another 2 minutes to mix the catalyst in with the sand/binder mix, so you lose 4 minutes of set time before you can begin to ram the mold, and that has to be factored in.

    I think 10 minutes is about the fastest I have used a set time in the past (with resin binder), and that allows a mold to be made about every 15-20 minutes, which gives you enough time to thing and start preparing for the next batch while you are waiting on the strip time.

    I try to ram the sand all around the pattern first, and get all the voids completely filled, and then if my set time is a little too short, the sand around the pattern will not be disturbed while the remainder of the flask is filled with sand that is a little over on the set time.

    Last edited: Apr 15, 2019
  12. Melterskelter

    Melterskelter Silver Banner Member

    4DA377AF-C49B-4DD3-8EFE-3B51BFC979DF.jpeg F565D02C-BD0D-4DAB-BF0E-E5A8D9CBEE8F.jpeg 326ACB5D-C100-4A13-ABB3-0E996934B121.jpeg AA617B12-DF11-4950-A35C-F89C792DCFAB.jpeg FD6EB225-BCBC-4CEB-8539-F1B44DE8D2D1.jpeg Here are a few more pics taken while packing up a mold today.
  13. Melterskelter

    Melterskelter Silver Banner Member

    And a few more.

    4DC1D693-E5C5-4BF2-91E4-91CE6478DA3F.jpeg 51534731-CF05-4DD6-BD0B-C088D5F26C86.jpeg

    This is the top flask sitting on mid flask shown above. The mold has been rotated 180 deg.
  14. Melterskelter

    Melterskelter Silver Banner Member

    Today I poured the mold with the core pictured above.

    Pouring temp was 2500F

    I was pretty happy with the results.
    Here is the core knocked out of the casting by simply striking the casting with a hammer. The very crumbly core sand is seen in the foreground.

    Here are a couple closeups of the lettering.
    7F7C32A4-2487-404F-8ED3-B05BD7C84A84.jpeg 3CDB3A88-98C6-4F12-8472-E933A7D26F48.jpeg

    I don’t think I’ll make any adjustments to the core formula for the time being. I like how easily it falls out of the casting, the finish and detail resolution.

    _Jason and Tobho Mott like this.
  15. PatJ

    PatJ Silver Banner Member

    Looks like it worked very well.
  16. DavidF

    DavidF Administrator Staff Member Banner Member

    Super nice finish...
  17. oldironfarmer

    oldironfarmer Silver Banner Member

    Very nice!
  18. Melterskelter

    Melterskelter Silver Banner Member

    I made a few retaining nuts for the core strongback that should have a little more holding power than the externally threaded inserts shown a few posts prior to this one. The inserts worked OK , can pretty easily break loose and spin in the core sand. The new ones will resist spin and pullout. They will be bedded broad end deep in the sand. 59C533CD-1D8F-46DE-93FC-3B95BEF24120.jpeg
    oldironfarmer likes this.
  19. Melterskelter

    Melterskelter Silver Banner Member

    2C9A1985-4CFD-430D-BDFA-BDBE4BED3415.jpeg I’ll add one other bit I’ve learned about using nuts and bolts in sandy conditions—-mold making. Sand easily contaminates the fasteners and tends to cause jamming of threaded fasteners. If you grind off a flat on the bolt or screw, it then tends to act sort of like a tap and cleans the threads out and jams a lot less. If you haven’t done this, you may be surprised how much it helps.

    Last edited: Apr 16, 2019
  20. oldironfarmer

    oldironfarmer Silver Banner Member

    Thanks for that tip. Easy to see how it will work.


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