Junk muller (but it works!)

Discussion in 'Sand Mullers' started by Funkster, Jul 20, 2018.

  1. Funkster

    Funkster Copper

    Hi folks,

    I figured it was about time I built a muller, and in keeping with my general cheap-ass MO, I decided to build it almost entirely out of crap I had lying around. Here it is:

    muller_1.jpg

    Costs so far:
    £10 Oil drum (okay, I only used half but I wouldn't have bought it otherwise)
    £5.70 V belts
    £8 screws
    £5 propane to cast the wheel
    £2.50 bearings
    £3.20 a spring

    The motor and VFD are borrowed from Cider Club's apple scratter, so in ~October I'll have to temporarily swap that back but I can cope with that. Everything else (including the V belt pulleys) is made out of wood that had no other purpose and was getting in the way in the garage.

    And it works!




    It needs a stand to get it high enough to discharge into one of my sand boxes. Optimal load seems to be about 15Kg of sand - less than a whole box, but to be honest my boxes are too heavy to be easily manageable so I was thinking about finding smaller boxes anyway. The scrapers are pretty poor, but I can improve on them later.

    muller_2.jpg

    I made the wheel:
    whale_2.jpg

    And the thrust bearing that takes the vertical load is also homebrew:
    muller_3_thrust.jpg
    muller_4_thrust_in_place.jpg

    Overall, infinitely better than no muller. Any constructive criticism welcome ;)
    --
    Olly
     

    Attached Files:

    Last edited: Jul 20, 2018
    Jason and oldironfarmer like this.
  2. oldironfarmer

    oldironfarmer Silver Banner Member

    Looks like it works!
     
  3. Melterskelter

    Melterskelter Silver

    It looks like it is also significantly quieter than my (and most) cement mixer-based mullers. I have to wear hearing protection and worry about annoying the neighbors when mine is running. Nicely done on the casting you made for the wheel. Side ejection of sand is a definite plus.

    Denis
     
  4. DavidF

    DavidF Administrator Staff Member Banner Member

    Looks like it works like a champ!
     
  5. Funkster

    Funkster Copper

    Yes it's pretty quiet, certainly a lot quieter than an unmodified cement mixer. I don't have an SPL meter at the moment but I was thinking about buying one, maybe I'll take a measurement at some point!
     
  6. Jason

    Jason Silver Banner Member

    You can download a fairly accurate meter for your phone for free. Ya calibrate them in a quiet room.
     
  7. PatJ

    PatJ Silver Banner Member

    That is a very clever arrangement.
    Plywood is very strong, and there is a lot you can do with it, and it will do more than you would imagine (think Spruce Goose).
    I think I read that pound-for-pound, wood is stonger than steel.

    Its good to see such ingenuity, and that ability helps a lot when trying to build a backyard foundry.

    The wheel is a nice casting too.
     
  8. Funkster

    Funkster Copper

    I have a bit of a love-hate relationship with wood. It's so easy to work with and the tools are cheap, but finding quality timber is a pain in the wossname and I'm always cursing the timber merchants when joists show up looking like bananas. Even decent plywood has to be ordered in special, the merchants don't keep any good stuff in stock at least near me.
     
  9. Funkster

    Funkster Copper

    So, a bit of a performance update - I put all my sand (100Kg or so) through it yesterday just as a tune-up and to mix in some dextrin, and the muller worked fine. Definitely need stiffer scrapers but I'll need to scare up a thicker bit of metal for that.

    Today I did a big casting (I'll do a separate thread when I've edited some pics), and optimistically threw some of the large, hard chunks of used sand straight into the muller in the hope of turning it back into powder. Sadly the wheel ended up just skating when there was even a tiny lump of hard dry sand in front of it, and nothing got mulled. Is this something most mullers can cope with, or do people throw some water on the hard bits and leave it to soften for a bit?
     
  10. Melterskelter

    Melterskelter Silver

    I can only speak for my muller, but it manages to smash up even fairly large (4 to 5" on a side) lumps of hard sand post casting. Larger ones than that I smash with a shovel or walk on. For convenience, I think you will want to tune your muller to deal with moderate lumps. However, turning your sand out onto the floor and walking on it might be a pretty good interim measure for now.

    Denis

    Added: I got to wondering if your wheel is free to move up and down as it encounters more and less sand and lumps of sand. If it is fixed in height, then I can see how it could act more like a plow than like a roller and similarly if it is free to move up and down but its spring loading is too great, that could cause plowing. Also wonder if adding some sort of "tread" to the wheel might help it want to roll rather than skate. The tread could be pretty crudely added with an angle grinder cutting diagonal grooves to make a sort of diamond pattern on the wheel. Sort of thinking out loud here.
     
    Last edited: Jul 28, 2018
  11. Melterskelter

    Melterskelter Silver

    BTW, as far as scraper sheet metal weight is concerned, I used 11 ga (.120) steel and that seems about right. Just supplying that info as a data point. Might get by with lighter, but I kinda doubt it. FWIW.

    Denis
     
  12. Funkster

    Funkster Copper

    Thank you for the data points! Yes I'd definitely like to make it cope with the chunks. The wheel is hinged and spring-loaded downwards, with a bit of pre-load as it sits on the bottom of the drum when it's empty. Maybe I've put too much pre-load on... and maybe the spring force goes up too fast with distance. Both parameters can be tuned by moving the spring ends which are just held on with wood screws so it should be fairly easy to try some adjustments.
     
  13. Melterskelter

    Melterskelter Silver

    One more data point: my wheel is about 4” wide 7” diameter and weighs about 22 pounds. As it is unsprung, it’s own weight provides downforce. It seems like (by luck) that is in the neighborhood of the pressure needed to crush lumps but still ride up when needed. It has no tread as it is simply smooth cast iron.

    Denis
     
    Last edited: Jul 29, 2018
  14. Funkster

    Funkster Copper

    Although I have the spring, there's no way I have 22lbs of pressure with the drum empty. Maybe somewhere between 3 and 6 at a guess. And yet it still wouldn't ride over even a small hard chunk... it seemed like it was the bottom of the drum that was too slippery.

    I did manage to get it rolling at one point by adding water in front of the wheel (I guess it made the small chunk grip the drum) but I ended up with sand that was too wet.

    For reference, the wheel is 80mm wide (slightly crowned due to pattern draft) and 200mm in diameter.
     
  15. Melterskelter

    Melterskelter Silver

    I imagine you have tried increasing downpressure on the wheel to no avail.

    One thing I have noticed that will slow wheel rotation on mine is have too much sand in the muller. If the "wave" of sand impacting the wheel is deeper than about half the wheel diameter, then sand trying to go over the wheel reduces the rolling moment induced by sand going under the wheel.

    I also assume the wheel has a freely turning bearing and sand has not somehow gummed up the works. My wheel is mounted on a sealed standard trailer axle hub and bearing. (When I mention how mine is set up, I do not think it is the standard to which all other mullers should be built. Just giving comparative background info.)

    Sorry if I am stating the obvious above. But, I am a bit non-plussed as to why your wheel doesn't roll.

    Denis
     
  16. Funkster

    Funkster Copper

    I haven't tried any pressure adjustments yet, it was 11pm when I found it didn't work properly so I just chucked all the sand in the f*** it bucket and went to bed :D

    The wheel runs on roller bearings... only small ones (6200) but they're rubber sealed and haven't failed yet. I'm sure they won't last forever but they were only 65p each. The wheel isn't *perfectly* concentric on its shaft as the axle hole was drilled by hand... runout is maybe +/- 1.5mm or so, I thought given the free-running bearings this wouldn't be a big problem.

    Not stating the obvious at all, I was quite surprised when I found it skating on a 15mm diameter chunk of sand.

    Thanks for the help!
     
  17. Funkster

    Funkster Copper

    Another quick update, I wound up the spring pretension as high as I could get it without dismantling the machine. It doesn't get stuck on small chunks any more. It still can't really handle baked-dry chunks bigger than about 2" but I think this is at least partially the outer scraper's fault as big chunks don't get put fully in the path of the wheel so they just get patted back and forth.

    By breaking up the bigger chunks by hand while I'm waiting for each batch to mull, it seems to work fine so I'll run it until something big breaks and then maybe make some refinements :)
     
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