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Thread: sieving microscopic glass beads

  1. #1
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    Default sieving microscopic glass beads

    Initially I wanted to PM VDX about this since he has done this before but thinking about it some more this info may be useful to others. Glass beads in the micron sizes (5,10 or smaller) can be used as spacers for DIY LCDs and PDLCs or maybe poured on your DIY projection screen paint to add some brightness gain to your dual laser show projector and video projector shows. https://makezine.com/projects/make-3...ection-screen/

    I purchased this electric shaker and the results are miles better than trying to sieve by hand. https://www.amazon.com/Electric-Auto...dp/B07K2XGGRT/


    It sieves glass beads sized <= 20 microns just fine from a <= 50 micron batch.
    Image of 20 micron beads:





    However, going lower than that it becomes very difficult (slow). I believe the electrostatic charge transfer in the glass beads is to blame.
    15 micron sieved amount:





    I sieve gradually, from 20 to 15, 10, then 5. The machine is too weak to shake more than two stacks of wire mesh frames at once properly.


    There is definitely even some <=5 micron beads coming out of the filters but very slowly, as seen here, so the glass beads batch is not to blame:





    I considered trying to alcohol submerging method but it will be difficult to modify this machine to prevent the liquid reaching the motor which is on the bottom.


    "ion blowers" could be added to a modded top cap but unless the air flow is very strong it just doesn't pass through the very fine steel mesh. And if it is strong there will be cloud dust from the glass beads potentially blowing out from the back of the blower to the room.


    I also connected the steel frame of the machine to ground but it didn't help either.


    Another issue may be air humidity. I cannot get it lower than 30% in my environment.


    VDX, Any ideas what I should try from here?

  2. #2
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    ... I've separated my glass beads by hand dry or with distilled water with etched steel sieves and much smaller volumes, so the problems were of much smaller orders too.

    Best bet would be to use smaller dishes submerged in water with a slow current ...

    Viktor
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  3. #3
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    Hi VDX.
    I sent you PM.

    Can you please mention whether you have any water leak with your ~5 micron sized etched holes? My sieves at these sizes barely leak water, only few drops per second. But I have confirmed both with a microscope and sieving machine that there are holes and glass beads do get sieved through those. I'm just not sure what you mean by dishes submerged in water with a slow current. I guess you mean the containers with the glass beads already in them get slowly submerged into a larger container with water in it so that the beads won't form a mixture in the larger container?

    I suppose since the beads only fill <10% of the dish I can first try adding as much distilled water without fear of water leaking into the motor. If it goes well I will let you know. These machines are quite cheap and can save a lot of time.

  4. #4
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    ... the surface tension from water to air is a problem with this geometries - for this you have to "submerge" the sieves completely and use a slow current and a "weak" ultrasonic sender, attached to the frame (or put the sieves into an US-cleaner, which gives more power), to force the throughput.

    My "tinkering" with microspheres (glass, PMMA and carbonyl iron) was maybe 15 years ago with etched steel or nickel sieves from different companies (most of them were closed since then) or R&D project groups and some "experimental" parts made from silicium with chip-manufacturing processes -- smallest possible "holes" were in the range of some ten nanometers, but this was not common made or available.

    You can ask Metaq for their smallest/finest etched structures - https://www.metaq.de/en/

    Viktor
    Last edited by VDX; 08-04-2019 at 13:14.
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  5. #5
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    ... hmmm ... found the Metaq spec-list (https://www.metaq.de/images/metaq_le...416_lo_web.pdf) -- their actual thinnest sheet is 10 microns, but smallest hole or slit is around 200 microns!

    When sourcing the sieves, I've got some "experimental" samples with "partial etching" ... and some polymer foils with "heavy-ion-puncturing" from GSI, where the foils were "shot through" with ions and then "widened" the ion traces to diameters of some ten nanometers to some microns with chemistry -- but too, only "experimental", not available for customers ...

    Viktor
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  6. #6
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    Quote Originally Posted by neilhrgd View Post


    Another issue may be air humidity. I cannot get it lower than 30% in my environment.


    VDX, Any ideas what I should try from here?
    Do you mean higher than 30%? If static charge is an issue, you need the humidity >60%.

  7. #7
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    Hi NobleGas, I'm aware that increasing humidity reduces ESD but here I'm concerned about condensation clogging the holes on the wire meshes. Should I not be worried about that?

    VDX, the sieves I have are made of wire meshes, not foils. I have no idea how they are manufactured at such high tolerances but inspection through microscope shows me they are pretty accurate. If you are interested in trying them out you can buy them both attached to a standard sieve machine dish or just the wire mesh in the link below. I payed 260$ for the 3 micron hole 300mm diameter dish and 152$ for the 5 micron one, excluding shipping. You can find the supplier here: https://wirecloths.en.alibaba.com/pr...5b862348UEuVGj

    1) I am still not clear on what you mean by slow current.

    2) And did I understand correctly that you are suggesting to use an ultrasonic cleaner as the container with water in it instead of mechanically shaking the sieves with a sieve shaking machine such as this one? https://www.amazon.com/Electric-Auto.../dp/B07KYFT3NM
    Have you yourself actually tried the ultrasonic cleaner approach or just by hand as you mentioned before?

    3) Finally any tips on drying the beads afterwards?

    Thanks again.

  8. #8
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    ... "slow current" means "slow water flow" ... my translater gives "current" for "Strömung"

    I've sieved/separated the micro-spheres by hand without ultrasonic -- but know others, which used US with low power or small amplitude for handling carbon nanotubes with even finer sieves.

    Drying was as simple as pouring the mess on paper, flatten, and let it dry some hours ...

    Viktor
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  9. #9
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    Interesting. I would have never thought of trying that. Thanks for the idea.

    But what water flow? Are you circulating water or having a continuous water stream? I assumed you meant ordinary container with water in it and submerging a sieve in it and shaking the sieve.

    I do not own an ultrasonic cleaner but can borrow one and test this. I will need to buy some more wire meshes though since these 300mm diameter sieves won't fit in an ultrasonic cleaner.
    Do you by any chance remember whether the people you knew who did this used ordinary distilled water or something else such as alcohol?

  10. #10
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    ... the carbon nanotubes were dispersed with alcohol ... for my glass and PMMA microspheres I've used distilled water ... dry for the carbonyl iron microspheres (tend to "rust" with water or alcohol).

    For "water flow" you can use a tube with (sealed) insets for the different sieves and an aquarium pump to circulate the water from the bath into the partially submerged tube.

    And/or move the tube by hand or put it with the pump into the ultrasonic cleaner.

    Last rinse it with fresh/clean water to remove the submicron "dust" from the bigger fractions ...

    Viktor
    Aufruf zum Projekt "Müll-freie Meere" - https://reprap.org/forum/list.php?426
    Call for the project "garbage-free seas" - https://reprap.org/forum/list.php?425

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