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:


    75 mesh silica, 200 pounds:


    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.

  2. oldironfarmer

    oldironfarmer Silver Banner Member

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


    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.

  4. oldironfarmer

    oldironfarmer Silver 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.

  6. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    OIF, discussed here:

    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.

  7. Petee716

    Petee716 Silver Banner Member

  8. oldironfarmer

    oldironfarmer Silver 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.

  10. oldironfarmer

    oldironfarmer Silver Banner Member


    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."

  12. oldironfarmer

    oldironfarmer Silver 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.

    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.

  15. Melterskelter

    Melterskelter Silver

    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:
    "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."
    Tobho Mott likes this.
  16. Tobho Mott

    Tobho Mott Silver Banner Member

    Thanks for some good info. I have read the navy manual but I keep forgetting what's in there!

    edit - holy carp, looks like I forgot to post the part 5 video on both forums somehow...

    Shows first scraper being built and installed using those lost foam clamps, and a quick test with dry sand and one scraper and no spring on the wheel.

    ok, back to the real reason for this post:

    Got the second scraper installed and added a trampoline spring to the wheel to keep it pressing down...


    I know you guys all said the greensand will plug the gap around the edge of the wear plate, but I sealed it up with some high temp epoxy putty anyhow. This reflects not at all on how much I value all of your advice, but rather on how much I doubt my own ability to cut out a wear plate that fits as well as other people's...

    After watching the footage a bit more, I'm about 3/4 convinced the wheel angle is ok but that the whole wheel assembly should be moved in toward the center a little bit, even just an inch or so. Should mean just some more drilling and bolting, not too bad.


    I don't like the angle of the new scraper that much though. Thinking about sawing the left 'ear' off the lost foam clamps that hold that scraper onto the pipe so I can start the curve in it closer to the center end of the scraper... Right now it has too much of it uncurved, so some of the sand is actually getting pushed the wrong way. This can be seen clearly in the video at around 14:40 - easier to understand by seeing than it is to explain.


    (this sketch may be somewhat exaggerated)

    But bending that scraper even the small amount I did was lots of fun - my first blacksmithing experience! So I don't really mind having to do a little more of that.

    Last edited: May 31, 2018
  17. Melterskelter

    Melterskelter Silver

    Jeff, looks like you are making great progress. you asked about the noise the mixer makes. I don't know what normal is as I have limited experience with these mixers but the few I have been around have been NOISY. I wear headphone ear protection when running mine.

    I think you will find moist green sand behaves quite differently than the dry sand. I have an idea your mixer/muller will work well as it is. I'd be tempted to put it to the test and see what happens.
  18. Tobho Mott

    Tobho Mott Silver Banner Member

    I'm hearing the same about using real sand from multiple posters in my muller thread over at AA too... And I agree. So I guess that is the next step.

    Feedback about the noise has been more mixed, so I'm planning on opening up the motor cover just to have a look and make sure nothing is loose or misaligned in there.


    Last edited: Jun 4, 2018
  19. Tobho Mott

    Tobho Mott Silver Banner Member

    Ok, I finally ran some greensand through it and it seems to be working well.

    Maybe not perfect, but it is mulling sand.

    The one change I made to the muller before doing that was rotating the center scraper a bit to improve its angle.


    So far I've only used it to recondition my sand from Smelko Foundry Products here in Ontario, so no new greensand yet. I put way too much water in the first batch and maybe a little too much (not sure) in the second.

    Mixing it dry to break up lumps:


    Mulling with way too much water:


    Super sticky not quite soggy squeeze test:


    Next batch was still maybe a touch too wet, but much closer:


    Seems to handle half a 5 gallon bucket of greensand just fine, though 3/4 of a bucket was too much for it when it had way too much water in it, it got so sticky it just sat there in a big clump when I tried to dump it, the drum kept turning but the sand held together and let the drum just spin/slide under it and would not turn over. :D

    Still getting used to just pouring the water in I guess; I always used one of those little pump-up garden spray bottles before this.

    What do you guys think? Olfoundryman says I should ease up on the spring tension because he thinks my wheel is pushing sand to the side instead of rolling over it; Chirpy thinks I need a wider wheel; Jason says I was right about moving it over an inch so the whole wheel I've already got is rolling over the area where the sand was sticking to the wheel as it stands.


    I'd like a wider wheel and IMO that would accomplish the same thing as moving the one I have over a bit as well as making it harder for sand to get pushed to the side... I would cast one if I had a lathe to finish the job. Or I could buy another wheel like I have and put them side by side, though they would have a gap between them.

    I think it is working pretty well, so any more changes would be to make it work a little better, or rather, work just as well only faster.

    Mind you I haven't tried making new sand yet, possibly I will learn about more flaws in my build when I try that...

    I appreciate all the suggestions and advice so far, keep'em coming and thanks to everyone!

    Last edited: Jun 4, 2018
    Jason and Melterskelter like this.
  20. Melterskelter

    Melterskelter Silver

    It is working! If you add a wheel, I like that idea, place them side by side with no gap. A gap will just fill up with sand.

    I don't think new sand will present any special problems compared to prepared sand.

    When I am getting near correct moisture, I add water in very small increments. Maybe a 2-3 ounces at a time. After each addition I squeeze it a couple times and also pound some into a corner. Both give me an idea where I am. FWIW. Once you get to where you think you are right, I would suggest taking some inside and baking out the moisture to get another fix on where you are with the moisture. Smelko may have guidelines for their prepared sand mixture with respect to moisture.

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