Mixing up K-Bond Sand (Similar to Petrobond)

Discussion in 'Sand Casting' started by Melterskelter, Jun 9, 2021.

  1. BattyZ

    BattyZ Silver Banner Member

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  2. I’ve run into exactly the same issue. I mixed up some with glycerol in place of the alcohol. I used it a few times but it wasn’t cohesive enough, would just fall out of the flask moving it. I successfully poured last night and the castings look good, but I can’t use this sand mix for long term. I don’t have any Bentone left and don’t think I can get anymore, it’s pretty difficult to get where I am in Canada. I’ve been trying to find a better sand mix than I’ve been previously using (bentonite, sand, water). I want to avoid water in my mix to reduce pinholes in my castings as I polish what I make. I was hoping to use this sand mix, but tracking some of the stuff down seems really difficult, and Petrobond is really expensive and shipping would be expensive as well.
  3. Tom Cobett

    Tom Cobett Silver

  4. Tom Cobett

    Tom Cobett Silver

    My bad. When I suggested using glycerin (glycerol) as the polar additive or catalyst for K-KOND, I must admit that I have never tried it. It seems that glycerin is not a strongly polar molecule. I still prefer using propylene carbonate as the "catalyst" for K-BOND. And yes, Propylene Carbonate is sold as an industrial solvent. It can also be used to harden sodium silicate bonded sand. In that application, use the PC at 10% by weight of the liquid sodium silicate. It will set up rock hard in 10 to 30 minutes, depending on which type of sodium silicate that you use. You can mix it with the sand using a kitchen mixer and a tupperware bowl.

    Some organo-bentones do not require a polar additive to get them to swell in oil. Bentone 34 still requires the polar additive.
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  5. Melterskelter

    Melterskelter Gold Banner Member

    Well, I am even more confused as in the following table:
    glycerin is listed as having a polarity less than water but greater than methanol, ethanol, and propanol and is actually second only to water of the agents listed.

    I am frustrated to be 1000 miles from my foundry and unable to mix up a test batch of K-bond using glycerin because I THINK it worked well when I did so. Maybe my memory is faulty on that point. I used bentone graciously supplied by Mach which has yielded results at least as good (I think a little better) than the commercial petrobond I purchased. On Friday I’ll be home and I intend to mix up a test batch using glycerin. If folks have used glycerin and the feeling is methanol or ethanol might be a better additive, have they tried mixing it to the batches of poorly-performing sand?

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  6. Tops

    Tops Silver Banner Member

    I have not tried to fix my batch yet. I was not having green strength trouble, but my new K-Bond sand was more sticky than newish P-Bond and the parts looked like they were 'fried in grease' in comparison texture-wise. I am hoping either straight methanol or propylene carbonate would be more polar and allow the bentone to take up the oils that makes things seem sticky or greasy.

    I appreciate everyone posting!
    Last edited: Apr 2, 2023
  7. I haven’t tried anything yet. I’m also wondering if my friend possibly gave me some regular bentonite thinking it was the same as Bentone. I can get methanol fairly easily here, I’ll try that and go from there. I’m gonna see if I can source some Bentone in the meantime. Other then the lack of strength, I was very happy with the castings and they have the best rough finish I’ve had yet. I definitely want to move to an oil sand if I can find a mix that works for me with ingredients I can get.
  8. Melterskelter

    Melterskelter Gold Banner Member

    The Bentonite/bentone confusion is very common. Perhaps someone ( I’m thinking Tom Cobett) who has enough experience might know a simple test to distinguish the two by doing a simple test on the stuff you think is bentone.

    Too bad that shipping across the border is senselessly expensive. We know Mach has the real bentone.

  9. rocco

    rocco Silver

    That should be pretty easy, bentone is organophilic whereas normal bentonite is hydrophilic so, what happens if you mix a sample of each in water compared to what happens if you mix them in oil? Maybe somebody here has both on hand and could give that a try and report back the results.
  10. Melterskelter

    Melterskelter Gold Banner Member

    Exactly. If I were not remote from my foundry I would have experimented along those very lines.

  11. BattyZ

    BattyZ Silver Banner Member

    Had a couple of minutes to add water as the polar agent to a part of my botched batch. Added green strength quickly.
    20230403_161427.jpg 20230403_161818.jpg
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  12. Melterskelter

    Melterskelter Gold Banner Member

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  13. Tops

    Tops Silver Banner Member

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  14. Tops

    Tops Silver Banner Member

    I added another 7.5# (3.4kg) of my sticky-mixed K-Bond sand and about 6ml of Propylene Carbonate to the above batch.
    Mulled, still sticky. Added 5% dry sand and mulled and then another 5% more dry sand, still sticky. Did a couple castings and they still have that 'fried' look.
    Wondering if burning in this same batch in through a few more castings would help.
  15. Tops

    Tops Silver Banner Member

    Noticed some shrink effects in the star castings. Drag sides opposite of risers, tops of risers, and backs of pattern behind star. This is the modified match plate (smaller risers and gating) than featured previously upthread. casting1.jpg casting2.jpg
  16. Tobho Mott

    Tobho Mott Administrator Staff Member Banner Member

    Update, I finally came back to my batch of K-Bond that (I thought) I made using glycerin as an activator. I thought it worked ok when it was just made but that was more wishful thinking than anything else, the castings were not that great (just ok, nothing to be proud of) and after a month sitting in a bucket it lost all its strength. Now that we have heard from Tom Cobett that glycerin isn't a suitable activator after all, this all makes more sense.

    Added 15g of presumably propylene glycol (labelled as catalyst for the sil-bond sodium silicate core sand system) to my appx. 40# batch of sand and wow, what a difference it made. Bogged my muller down just like new petrobond and molded really well. Test pattern that I faced with the K-bond had a lot of coping down but the K-bond held up great, no crumbly edges or anything. Haven't poured it yet but will update in a few days once I do.

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  17. Tobho Mott

    Tobho Mott Administrator Staff Member Banner Member

    Nothing unexpected. I'm very happy with the K-bond as mentioned, now that I have the right activator. But I promised an update, so...



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  18. Nice finish too!.
  19. BattyZ

    BattyZ Silver Banner Member

    This sounds quite promising! I put all of my 'experiment sand' away in a box as well and hope to enjoy similar results. When I get around to needing it again.
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  20. Seemann1972

    Seemann1972 Copper

    good morning everyone

    I have now read a lot of interesting things about the production of formsand here. I was very impressed by all the experiences we had.
    I now need a larger amount of molding sand in the future and here in Germany there are apparently delivery problems with oil molding sand. delivery times up to 30 days. and I don't want to torture my postman with a 200 kg package ‍

    What I now understand is that there are differences in clay. So does that mean you shouldn't use "cat litter with bentonite"?

    In short, is there a very clear recipe for formsand for brass casting?

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