Another cement mixer muller

Discussion in 'Sand Mullers' started by Melterskelter, Mar 25, 2018.

  1. Melterskelter

    Melterskelter Gold Banner Member

    This problem seemed to begin after running a few hundred pounds of petro through the muller over two or three sessions. It’s oiliness and heavy consistency may encourage sliding of the sand on the floor of the muller AND polish the floor as well. Interesting to know I’m not the Lone Ranger on this problem. I do think scuffing the floor and wheel will keep it at bay. Thanks for letting me know. Too bad the traction tape did not hold up, Pete, as that seems like a clever fix.

    Denis
     
    Last edited: Mar 11, 2021
  2. FishbonzWV

    FishbonzWV Silver Banner Member

    I have the same problem with the unmodified HF mixer. The greensand kept a little surface rust on it. PB shines it up. I have to give the rock a little nudge every now and then to keep it tumbling.
     
  3. Tobho Mott

    Tobho Mott Gold Banner Member

    When I was navigating through switching from mulling greensand to petrobond in a cement mixer muller, HT1 suggested I mull the sand while it's hot and avoid overloading the muller. I wasn't having sliding sand problems, it was hard patches of compressed sand stuck to the wear plate jamming the pushed wheel so that it had to bounce over them. But after (just) a dozen or so pours it does seem like the muller generally has a much easier time turning the sand over and rolling over it smoothly while the sand is still hot and soft.

    By the time I got my PB, my greensand had just about already put a mirror shine on the donut of the wear plate that the wheel passes over... Guess I better keep an eye out for sliding sand!

    Jeff
     
  4. Billy Elmore

    Billy Elmore Silver

    I dont have that issue with mine...it doesnt get used enough to ever get any wear on it.LMAO Mine is much more complicated than most of the ones I see on here though. A hollowed out cement mixer with a huge pinion gear rolling around smashing the sand. It actually worked much better than I anticipated so I never finished the build I started on a typical one.LOL
     
  5. Melterskelter

    Melterskelter Gold Banner Member

    Earlier I mentioned adding a sand deflector in front of my muller wheel and I had mentioned scuffing the wheel to aid rolling action. Today I removed the wheel from the muller and welded on the dflector. While the wheel was so accessible, I decided to hit it with the angle grinder a bit more. Here are a couple pics---not particularly pretty but pretty functional.

    Wheel Deflector.JPG Wheel Tread.JPG

    Denis
     
  6. Melterskelter

    Melterskelter Gold Banner Member

    Let it Rust!

    I have been trying a "natural" texturing method for the wheel and floor of the muller---rust. It is working very very well. Rather than reflexively cleaning all the sand out of the muller at the end of a session, I have been shoveling a third of a bucket of green sand and then adding enough water to make it pretty wet. That is significantly wetter than you would want to get the sand for molding. I then spread it more or less evenly over the floor and mound a bit up around the wheel. That does the trick. In my well-used green sand there must be some residual chemicals (acids?) left over from the heat and coal interaction so that the sand really promotes rusting. That rust provides excellent traction to the floor and wheel of the muller so that sliding of sand under the wheel and consequent stalling of the rotation of the wheel does not occur no matter how overloaded the muller is. So, now I have an excuse to be sloppy with the muller. What's not to like about that?

    Denis
     
    Billy Elmore and Tobho Mott like this.
  7. Tobho Mott

    Tobho Mott Gold Banner Member

    Mine's doing it now too. Anytime before this that the wheel has stopped turning, it's been the sort of event that stalled the whole drum and made me jump for the off switch, because the floor wasn't slick enough to let the sand just slide - it's always been bad bearings in the wheel or a hard lump of compacted sand stuck to the floor that caused it. This time the muller looked and sounded like it was running normally, except the wheel wasn't turning because the pile of sand sliding on the wear plate in front of it was holding the wheel just up off the floor in place. Like the sand found it easier to stay put and slide than get rolled over. Maybe the oil in the petrobond really isn't letting the wear plate regain a slight patina of rust that is needed to give it a bit of grip.

    20210703_003722.jpg

    I like the idea of leaving some greensand in the muller to rust it, other than having to keep cleaning it out every time to use for petrobond again after. I may try seeing what happens if I lay some damp paper towels on the shiny doughnut overnight...

    Jeff
     
  8. Petee716

    Petee716 Gold Banner Member

    My muller always handled green sand differently than petrobond. I had very little trouble with greensand but pb was always troublesome. The sliding on the bottom was always the problem. So we're all on the same page here. I put an 80 grit flap disk on my angle grinder and hit the floor with a swirling motion. Just enough to disrupt the surface. No need for any full-on gouging which is desirable because I like to sweep the muller clean before and after use. The muller invariably has chipmunk poop scattered in it every time I go to use it, and the bottom still sweeps up cleanly.
    The difference has been night and day.
    It makes sense that petrobond would be worse than green sand in terms of slipping:
    Its getting scoured with fine abrasive, the smooth steel is getting lubricated with oil while in use, and its left with at least a residual film of oil on it. Those conditions seem perfect for keeping it slick. I'll post a pic when I get out to the barn.

    Pete
     
    Melterskelter and Tobho Mott like this.
  9. Tobho Mott

    Tobho Mott Gold Banner Member

    Maybe I should have welded the wear plate in there diamond side up, for some long lasting texture... Or used an inflatable wheel with some kind of treads on it, like HT1 has.

    Jeff
     
  10. Melterskelter

    Melterskelter Gold Banner Member

    The rust method continues to work fine fo me. When I switch from green to PB I just turn the muller on and smack the drum with a hammer a few times which knocks loose most of the crispy dried residual green sand from a prior session. I have a wire brush sort the size and shape of a 4” paint brush that I let ride on the walls and floor of the muller to clean off the rest and whack the wheel a few times. There us always a very little bit of green that mixes in with the PB but an ounce or two in 50 pounds can’t matter I figure. And the rust doesn’t need to be deep to do the trick. Just etching the surface seems to do the trick. And, yes as you guys have observed, it does seem to be the oiliness of the PB that is at the root of the problem.

    Denis
     
  11. HT1

    HT1 Gold Banner Member

    sand sliding is a plow issue , lets see pictures of the offending plows

    V/r HT1
     
  12. Melterskelter

    Melterskelter Gold Banner Member

    Interesting to specifically blame the plows. When I look at my muller and consider the relative frontal area of my plows compared to the wheel, the wheel has considerably more area than both of the plows put together not to mention the fact that both plows impact the stream of sand at an angle. The wheel, on the other hand, faces the sand dead on. When I am mulling the standing wave of sand is also much large in front of the wheel. So I think in my muller the wheel impedes the sand the most. Regardless, the solution to the problem is to roughen the base of the muller chamber and the wheel. That “gets things rollin.” And the easiest way to roughen the wheel and wear plate is to rust it.

    Here is a brief video of the interior of my muller.


    And here it is with sand


    Denis
     
  13. Petee716

    Petee716 Gold Banner Member

    Here's the scuffed surface. It has started rusting since I scuffed it.
    20210704_175527.jpg


    Here's a video of the action.



    The wheel would turn pretty reliably before but any variation at all of the height of the stream of sand going under the wheel (addition, stirring, etc) would jam it up. Now the problem has been completely resolved. I've had plows setup all kinds of ways and although I can see them being a potential showstopper, until this slipping issue was resolved moving or reconfiguring the plows only made the situation more or less bad. Now I'm in a better position to reconfigure them to make them perform better in terms of circulating the sand. As you can see there is no hesitation.
    Incidentally that flat spot is of no consequence. I think it came off of one of those under-floor-pulled trollies you see in warehouses. A bearing probably failed in use. It just rolls around in the muller with a limp now.

    Pete
     
    Melterskelter and Clay like this.
  14. Melterskelter

    Melterskelter Gold Banner Member

    Pete, how full do you fill your muller?
     
  15. Petee716

    Petee716 Gold Banner Member

    I shake out my flasks into a 20gallon(?) round galvanized washtub which sits on a 4 wheel dolly. I push that over to the muller and scoop the sand in with a military entrenchment tool positioned for scooping. I empty it the same way. There’s plenty of room to safely accommodate scooping out while it’s running. I sometimes just shake out into the muller like you see Ironsides do, but I mostly use petrobond and like to carefully open my molds and sort out the burnt up sand before mulling. How about you?

    Pete
     
  16. Melterskelter

    Melterskelter Gold Banner Member

    I dump the green sand from the flasks onto the floor for two reasons:
    1) The molds are too large for me to lift by hand so I usually have to shovel most of the sand out of the flasks and the finally tip the flasks over and tap on them to get the remaining sand out. I just did a 400 pound mold yesterday, for instance.
    2) I like to “precondition” the sand on the floor by walking on it to smash the big dry chunks and to use a flat shovel to mix the sand to get the entire pile to more or less s uniform moisture. I notice that the sand from a given used mold, depending on its location in the mold, varies a lot in moisture from bone dry near the casting to quite moist in remote areas of the drag. So, by shoveling it and walking on the pile a few times the pile evens out in moisture. That way I can figure out by trial and error how much water the first load takes. After that I can just pour in the same amount of water and I know it should be right. That seems easier and less hassle than adjusting each load differently.

    My question above to you Pete actually was more asking how much sand you mull per load as the vid showed only ten or 15 pounds. My muller will handle 75 pounds per batch—-about 1.5 5-gallon buckets. Breaking up the large chunks on the floor helps it finish the batch a lot quicker than loading it with sand straight from the used mold.

    Oil-bonded sand is a different matter. Mulling it takes so much less mixing and rolling and my molds are often smaller. So, sometimes I dump directly but still often just make a pile on the floor and shovel it. Since getting recommendation for various polar agents to add from Tom Cobett, I’ve favored adding glycerol as my “freshening agent” to oil-bound sand as it should evaporate much more slowly than methanol or ethanol. I seem to only need to add glycerol once every few sessions and then in only a teaspoon or so per 75 pounds. I anticipate needing to add a small amount of oil at some point, but have not yet done so.

    Denis
     
  17. Petee716

    Petee716 Gold Banner Member

    I generally run about 50lbs at a time. I only had a small amount to mull yesterday and wanted to show the basic flow of material in the video.

    That's alot of work for you to shakeout and prep your sand for mulling, but: big molds, big labor. Manhandling the molds like we do with smaller ones ( mechanically or otherwise) would be awfully hard on the flasks with that kind of weight. Your moisture strategy makes alot of sense.

    Pete
     
  18. Tobho Mott

    Tobho Mott Gold Banner Member

    I'm sure my plows and backwards facing wheel are wrong in several ways. I might have shot a few seconds of video of the sand sliding the other day, will try to get that online and posted up later today when I can.

    Jeff
     
  19. Tobho Mott

    Tobho Mott Gold Banner Member

    Well I found that tilting the cement mixer back a bit allowed some extra sand to tumble outside of the wheel's orbit and allow it to resume rolling.

    But when it's -20C out... the petrobond just gets too hard for even a very shallow layer of sand to allow itself to get rolled over rather than pushed back by the wheel on the near mirror polished wheel track. It's not hanging up on the plows and sliding around there like it used to do if I put in way too much greensand (or added too much water), the is sand literally preferring to get pushed backwards by the wheel than to hold its ground and make the wheel roll up over it. I copied Denis and got out my angle grinder to carve some nice details into the iris of the eyeball, problem 100% cured.

    Before:
    20210703_003722.jpg

    After:
    Capture+_2022-01-24-12-24-44_copy_454x270.png

    Jeff
     
  20. Melterskelter

    Melterskelter Gold Banner Member

    Good follow up, Jeff. Thx.

    With a 1hp motor and grooved surfaces my muller will now do 100 pounds of sand per load without complaint.

    in addition to the grooves, I still occasionally put in some wet sand at the end of a session and let it rust up. Also helps. Petro tends to polish too much and make it too slick as you point out.

    Denis
     

Share This Page