Mixing up K-Bond Sand (Similar to Petrobond)

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

  1. Melterskelter

    Melterskelter Gold Banner Member

    ADDED LATER: See post 17 below concerning better formulation options.

    I followed as closely as I could the K-bond formula published online to make my own K-bond. It was easy to do and the resulting sand mix is promising. It does seem very similar to petrobond. It has good green strength, breaks cleanly and has excellent cohesion.

    The instructions are as follows:
    How to make K-Bond sand
    Named for Kent State where it was developed, K-Bond is an almost smokeless oil-bonded foundry sand. Typically, it’s used for casting zinc, aluminum, brass, bronze and iron.
    What you need:
    • 100 lbs. sand - 100 mesh or finer
    • 6 lbs. bentone clay (such as Bentone 34 or VG-69)
    • 3 lbs. synthetic 2 cycle motor oil
    • 0.2 lbs. (3.2 fluid oz) Methanol (dry gas)
    Mix the sand and bentone clay first (wear a dust mask), then blend in the oil thoroughly. Small batches (less than 10 lb.) can be done by hand with good results, but a muller is preferred. The small batches can be done with a cheap kitchen electric mixer.
    Add the alcohol and mix thoroughly.
    • The sand won't seem like much until the alcohol takes effect and become like stiff cookie dough.
    • The sand will be easier to handle the more you use it over time.
    • If the sand gets powdery after sitting, mull or warm it before use.
    • When green strength starts to fade, add in some alcohol.

    Instead of methanol I used denatured ethanol as it was more easily available to me. And I used inexpensive semi-synthetic 2-cycle oil since the only fully synthetic oil I found locally cost 75 dollars per gallon. What I bought in a quart size was 7 dollars. I used 100-mesh olivine sand. I got the bentone from member Mach. I apreciate his kindness and diligence in running the material down, packaging it superbly and shipping it to me.

    Here is a 30-sec video of 50 pounds of the mix in my muller:

    K-bond Alcohol.JPG K-bond oil.JPG

    I have not yet molded with the new sand. I expect to do so very soon---in the next couple days. I will report back on the cast results. I'll be using it on a pattern I have cast many times in petrobond. So, it should be possible to make some comparisons with respect to smoking (K-bond is supposed to smoke less), molding qualities, and mold filling.

    Overall, mixing it up was very simple once the ingredients were in hand.

    Last edited: Jun 11, 2021
  2. I'm very keen to see the result despite the bentone not being available here.

    A lot of oil makers are very coy about the actual PAO content of their synthetic oil, I see yours is labelled "Synthetic blend". I found that the MSDS had to be looked at as even "Full Synthetic" oil was mostly mineral oil.
  3. Melterskelter

    Melterskelter Gold Banner Member

    “Coy” indeed. It is still unclear to me how much real difference there is in performance of synthetic motor oils vs conventional oils. But, for purposes of making this mix and hoping it would be less smokey, I wanted to follow the developers’ recommendation as closely as possible. The part mentioned above in the notes about the tiny amount of added alcohol making a huge difference in consistency of the mix is very true.

    I plan to do some molding with it today.

  4. HT1

    HT1 Silver Banner Member

    what clay did you source??? I have never seen a petrobond, not be orange ,

    Olivine is going to make some difference over silica sand, though I admit it has been too long for me to remember what, I suspect you may not ne able to get as thin of castings, because olivine transfers heat faster the silicia ... It's been 30 Years since I had to have all that indepth stuff memorized

    Best of luck, keep sharing please

    V/r HT1
  5. Melterskelter

    Melterskelter Gold Banner Member

    I think the red color is due to an added iron compound.

    This material molded every bit as well as Petro.
    85833327-5893-43B4-8E5D-EAEFEC6FC59D.jpeg CCCE6D06-64D0-43B0-AE17-850F14EDB930.jpeg 221394A8-36FA-4443-8C63-6BEF08B82929.jpeg

    Proof will be in the pour. Tomorrow?

    Two more of the same to do in petro.

  6. Melterskelter

    Melterskelter Gold Banner Member

    The same pattern Petrobond

    F5E6A50E-71A4-4AEF-A606-A32FBAAA3EB7.jpeg F5A916A9-9EF6-4D8A-A7DF-7A307BF62DDD.jpeg

    BattyZ likes this.
  7. Melterskelter

    Melterskelter Gold Banner Member

    Mold 3: Also petro.

    49AC2D0F-98E4-49A3-AD00-C9934E5C1264.jpeg 58AE4689-8DD9-4DD0-BF7A-2178E14784F2.jpeg

  8. spelter

    spelter Copper

    I've never seen a source to clearly state the reason for the red color, but some have hinted that it is included to make the oil/catalyst ratio less fussy. I add some red ochre (325 mesh red iron oxide at the pottery supply) to my K-bond. Never tested the sand extensively in its absence, so I'm operating on faith.
  9. Melterskelter

    Melterskelter Gold Banner Member

    Here are the ingredients to Petrobond. It is a somewhat different formulation as it does use a "modified clay" (what is that---probably an organophilic clay?) process oil, and propylene carbonate not alcohol. A process oil could be any oil used as an ingredient as opposed to use as a lubricant. So, would the rust help K-bond? Who knows, but Tom Cobett, who very deliberately developed the K-bond at Kent State is a pretty capable fellow and likely would have included it if it would do anything beneficial:

    Petrobond MSDS.jpg

  10. rocco

    rocco Silver

    Compared to the K-bond, those petrobond the sand/clay/oil ratios look off, with around half as much clay and up to twice as much oil and also, a huge range on the amount of catalyst. I have absolutely zero experience with oil bounded sand so I'm not really in any position to judge but it just seems weird to me that the recipes would be as different as they are and yet as Denis notes, the performance of the sand is similar. Something funny is going on there, I don't think whoever produced that SDS for the petrobond is being completely candid.
  11. Melterskelter

    Melterskelter Gold Banner Member

    Well, it looks like the Kb has 6% oil and 3% clay. That is in the range shown for PB. And no catalyst is used for Kb. I was surprised that, evidently, all the ingredients in PB were listed in the SDS. Seems like often “inactive ingredients” are an often-used catch in a lot of SDS’s for things as obviously benign as clay and iron oxide.

    Bottom line is they do feel very similar in use. I think the sand in the PB is probably slightly finer than my 100-mesh. It will be interesting to see if that makes a visisble difference. My guess is that it will not. I base that guess on having cast aluminum using my green sand a few times that is composed of the same 100-mesh Olivine. The finish was little different from the PB in those cases.


    BTW, some might be puzzled by the grey cast of much of my molded sand. That greyness is the result of using graphite and talc as parting agents. I have a feeling I use more than is truly needed. But these molds are fairly sensitive with pretty steep and deep portions and I wanted to minimize any risk of cope sticking to drag.
  12. rocco

    rocco Silver

    Okay, it's still early and maybe I'm not reading things properly. The Kb recipe as you posted earlier has 91.5% sand, 5.5% clay, 2.75% oil and the catalyst is the methanol at ~0.2%. whereas the Pb (according to the MSDS) has less than 3% clay and up to 7% oil, that's a pretty significant difference!
  13. Tobho Mott

    Tobho Mott Gold Banner Member

    Interestingly, I believe propylene carbonate is also the catalyst for sil-bond, a brand of sodium silicate core sand binder.


    For what it's worth, somewhere in one of these petrobond alternative threads, I seem to recall someone posted a link to patent document where it is stated that some sort of alcohol can be used as an alternative to the official petrobond catalyst.

  14. rocco

    rocco Silver

    I vaguely remember reading that somewhere too, I think it might have been in one of the articles by the aforementioned Tom Cobett.
  15. Tobho Mott

    Tobho Mott Gold Banner Member

  16. rocco

    rocco Silver

    I haven't yet found the article I was referring too but I did find a slightly different version of the K-bond recipe that has propylene carbonate catalyst and mentions methanol as a viable substitute.
  17. Melterskelter

    Melterskelter Gold Banner Member

    I just communicated with Cobett. He had a couple interesting points:

    He does not know why Petrobond includes iron oxide. He says he can only surmise it is used solely for its coloring properties as historically popular naturally bound sands like he used to use in the 70's (Tennessee Red brand was common) were naturally red in color due to their iron content.

    The oil I used above is not said to be "smokeless." Evidently that distinction has some real meaning and, according to him, smokeless 2-cycle oil will generate less smoke than semi-synthetic oil will. I have to admit to having been skeptical as to what real difference there might be between 'Smokeless" oil and oil for which that claim is not made.

    Second he suggested use of glycerin as a polar activator instead of ethanol or methanol as glycerin has a boiling point of 554F "Try using glycerin (glycerol). About $25/gal. at Walmart."
    Methanol boils at 148F
    Ethanol Boils at 173F

    So, I had some glycerin already in stock (did not previously know it was a choice let alone a better choice) and will use it in the next batch. And I bought some Lucas 2-cycle smokeless oil.

    I will make another 50 pound batch of K-bond with those ingredients and will see what difference they make. I will not be able to segregate these two batches long term, unfortunately.

    Mark's castings and HT1 like this.
  18. HT1

    HT1 Silver Banner Member

    just record your data, even empirical well, we appreciate the effort
    a sand that does not smoke would be very adventitious to me ,

    Many Thanks in advance

    V/r HT1
  19. rocco

    rocco Silver

    As do many others here! And if you're in contact with Tom Cobett again, please express our gratitude for his willingness to correspond with lowly hobbyists like us.
  20. Melterskelter

    Melterskelter Gold Banner Member

    Thanks for the kind words. Believe me, I have let Tom know how much we appreciate truly expert input.

    I JUST pulled a casting out of the KB mold. It is excellent. Yes!

    Here is the mold hinges open.

    Here is the casting BDA8E885-45DB-4AAD-94A6-C46A39E49C9B.jpeg

    More later including smoking hot videos—-hang onto your seats. Okay, okay. I’ll try to cool it. ;-)


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