Tobho's HT1-Inspired Cement Mixer Muller Build

Discussion in 'Sand Mullers' started by Tobho Mott, Mar 22, 2018.

  1. Tobho Mott

    Tobho Mott Silver Banner Member

    Got the basic ingredients picked up:

    "Quik Gel" sodium bentonite (that's the western type I believe), which appears to be in powder form though I have not opened the bag yet:

    20180510_153340-780x1040-390x520.jpg

    75 mesh silica, 200 pounds:

    20180510_153246-780x1040-390x520.jpg

    I would have liked to find finer, but silica seems hard to find here at all, I tried various companies including local sand blasting media providers (no silica) Opta Minerals which was recommended, and they don't sell silica at all anymore either apparently. So back to the pottery supply company where I got the fireclay for my original Gingery charcoal furnace back in 2013. My office just moved to right around the corner from there, so that was handy. It was this or 140 mesh. Or even higher (200), and I was hoping for something in the range of AFS GFN 115-130 as recommended by my foundry products supplier. That is what they (Smelko) use for their aluminum casting sand blends. They also said they use coarser sand for cast iron, and I want to do some more bronze which is also higher temperature work than aluminum, so I decided to go a little coarser rather than a little finer. (not that I know how to translate GFN to a mesh size anyhow, or even if a conversion is possible). This seemed logical, hopefully I am not overlooking or misunderstanding something.

    In any case, I got the guy to let me see and feel a handful of 75 mesh sand before placing my order and it seems quite fine to me, at least compared to big box store sand. Seemed like the best option that would not involve paying for shipping bags of sand from Southern Ontario.

    If I find it too coarse once the sand has been mixed and mulled and tried out, I will use my existing purchased Smelko sand as facing sand, since it seems to give a really fine finish, and the hope is that as it slowly combines with the new sand until it makes up about 1/3 of my whole heap, that it will improve the new sand along the way. We'll see in due time, I guess...

    Still gotta finish working on the scrapers for now anyhow, but when the muller build is finally done I am glad I will be ready to start making new sand ASAP.

    Jeff
     
  2. oldironfarmer

    oldironfarmer Copper Banner Member

    I bought a bag of bentonite from my local well driller today. $18US for 50# bag.

    IMG_3535.JPG

    It does not list the contents.
     
  3. Tobho Mott

    Tobho Mott Silver Banner Member

    Aside from "Highest Quality Wyoming Bentonite" you mean? :D

    Mine is from Wyoming too and it is sodium bentonite if that helps.

    Jeff
     
  4. oldironfarmer

    oldironfarmer Copper Banner Member

    Why would that help? I have no idea whether one is better than the other.:( My ignorance is only exceeded by my enthusiasm.

    I do think I paid a higher price (it's a small business, back when we had active oil drilling rigs they would give you a bag)
     
  5. Tobho Mott

    Tobho Mott Silver Banner Member

    Thought it might help because you said it didn't list the contents, and I was able to figure out which type you've got. Plus it is my understanding that a mix of both types is supposed to be a good thing. They each have different effects on the sand's properties. I'm really not sure how big of a difference it would make to use both as opposed to just the one type, maybe you would have to really be nitpicky or build a sand analysis lab to see the difference, I'm really not sure. I have just got the one kind as well to use, when I get to that point.

    Jeff
     
  6. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    OIF, discussed here:

    http://forums.thehomefoundry.org/in...ount-of-moisture-for-greensand.232/#post-3799

    but also discussed several times in the thread. 2:1 and 4:1 blends are those you see referenced the most. Short story is to achieve the most favorable compromise of green/hot strength and minimize the water necessary to achieve same.

    Best,
    Kelly
     
  7. Petee716

    Petee716 Silver Banner Member

  8. oldironfarmer

    oldironfarmer Copper Banner Member

    Thanks for those responses! I guess at my level of expertise 100% Western would be OK, although I have not a clue if Wyoming is Western other than apparent location.
     
  9. Tobho Mott

    Tobho Mott Silver Banner Member

    When I was looking inio benseal vs quik gel I learned that both come from Wyoming and are sodium bentonite. And that sodium bentonite is western bentonite.

    Jeff
     
  10. oldironfarmer

    oldironfarmer Copper Banner Member

    Thanks!

    I think I understand green strength, but am having trouble finding why dry strength is important. Just can't find it.
     
  11. Tobho Mott

    Tobho Mott Silver Banner Member

    I took a quick look and found this...

    From C.W. Ammen's The Complete Handbook of Sand Casting:

    "A mold must not only hold it’s shape in the green state, it must also hold it’s shape in the dry state."
    ...
    "If the molding sand has too high a dry strength it will not give or break down as the casting shrinks during solidification. This will cause hot tearing of the casting."

    Jeff
     
  12. oldironfarmer

    oldironfarmer Copper Banner Member

    I'm guessing I need to read his book again. However, I'm still feeling good about 100% WB. Especially for the stuff I'm currently doing. I could see needing to adjust sand to fit a particularly tough casting.
     
  13. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    It's just fine tuning OIF. If you are able to get the mold strength and detail you need without defects, good enough. Besides the strength, for a given mesh size, lower water content usually means better surface finish too.

    Best,
    Kelly
     
    oldironfarmer likes this.
  14. Tobho Mott

    Tobho Mott Silver Banner Member

    Yeah, this western stuff is all I could find too, so I'm not gonna worry about it. Unless I come to believe I have poor dry strength, I suppose.

    Jeff
     
  15. Melterskelter

    Melterskelter Silver Banner Member

    I have found the Naval Foundry Manual (thanks to those that have pointed it out) to have some of the most "scientific" information on sand casting It is well worth a review.
    Here is what it says indicating dry strength is greater for western compared to southern bentonite:
    http://archive.hnsa.org/doc/foundry/index.htm#pg40
    "The effects of blending western and southern bentonite on the green strength and dry strength of a sand with an AFS Fineness Number of 50 to 60 are shown in figure 56. There is a rather uniform decrease in dry strength with a changeover from western to southern bentonite. The green strength increases slightly from 100 percent western bentonite through the various mixtures and then increases rapidly as the 100 percent southern bentonite bond is used. This shows the difference in properties that result from the use of the two different bentonites, or mixtures of the two bentonites. The low dry strength of southern bentonite is especially advantageous when a sand mixture having good collapsibility is required, for instance, when casting alloys that are apt to hot tear easily."
     

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