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Thread: microscopic glass beads?

  1. #11
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    Just checked, were too big.

    VDX, can you please tell me how you decide what size sandblasting media to get? They are sized in grits and I can't find anything in the 800-1000 grit range which corresponds to about 20 microns. Do bigger ones have some small ones mixed in them? What grit should I get?

  2. #12
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    ... I've got a "standard distribution", which was specified in the range of 50 to 100 microns ... but found all sizes from <1 to 500 microns! ... and even some with >1mm!!

    Viktor

  3. #13
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    Hm, that is interesting. I'm going to get some from ebay, where did you source yours?
    I wonder why the sizes are mixed up so much. If the smaller ones weren't spherical I'd then assume its just broken bigger beads but if the smaller ones are beads too then they are probably just not perfectly separated during production.

    By the way, is this a correct conversion between grit to micron? https://www.gessweincanada.com/category-s/11328.htm
    There are some different charts with "US Grit" and the numbers are wildly different to this.

  4. #14
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    ... I'm used to metric -- so mm and microns, not mesh or grit ;-/

    Got the 50-100 micron glass beads from a German company, which sells different types for sand-blasting.

    Here an image with some beads from a "300 microns" size type, I have some remnants from:

    Click image for larger version. 

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    This was from the top of the box, so more the "bigger" fraction ... more to the bottom there should be more "smaller" beads ...

    Viktor

  5. #15
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    mixedgas is offline Creaky Old Award Winning Bastard Technologist
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    Patents usually contain deliberate errors in their exampes... At least in the US...

    I'd start with tumbling it for a few hours in a slow rolling bottle mixer(think commercial gas station rolling hotdog cooker) , or a very short burst in a Vortex Mixer.

    Trying to remember numbers from a summer job in the 1990s is futile.
    ~
    We did spincoat the polymer at ~ 3000 RPM for 2 minutes 40 seconds... How I remember that is juvenile but interesting:
    ~
    We have a nearby amusement park that had a standard speech for safety warnings before getting on rides...
    Everybody went to that park or the one in Sandusky every summer, so they knew where the parody came from.
    My take on it... Usually had my colleagues rolling on the floor the first time they heard it...
    ~
    "Ladies and Gentlemen welcome to the Spin Coater at Crystalloid!
    "Until you have been safely mounted on a platter please stay on the precoat table behind the yellow safety line"
    "Please keep your arms, legs, and any of your possible fragments inside the coater chamber at all times"
    " When the ride begins we will ramp your speed to 3000 PRM in 30 seconds... and maintain that thrilling speed for 2 minutes forty seconds.."
    "When the ride ends we will decelerate your rotational speed to zero in sixty seconds and the lid will rise..."
    "When done please exit thru the top of the coater and proceed to buffing after post inspection for smears and particles at the light table"
    "We hope you have enjoyed your evening here at Crystalloid's Spincoater..."
    ~
    Yes, I was that bored, a college student handing glass for eight hours of time in a bunny suit in a ultra dry clean room, on evening shift, with three other oddball people like me.
    I hated that job, because every night I drove home smelling like rotten fish from the DMF solvent and the polyimide or whatever nasty polymer mixture was used for coating the glass".
    DMF is not something a young person should be breathing anyways, so leaving was a blessing.
    ~
    BTW, the glass needs cleaned in a smelly, chilled, Freon type vapor degreaser, too... after ultrasonic cleaning in a nasty organic that I can't remember, then baking to remove water vapor that adheres to the glass. You sure you want to be around these nasty chemicals? The one is liquid cancer for all practical purposes, and the other drags any available poison thru your skin into your blood stream. I don't even want to know what was in the "forbidden" ETCH room for etching the ITO coating on the glass. I now know most of those chemicals probably diffused right thru the latex gloves and finger cots. We were constantly changing gloves, latex dried and ripped after exposure to those chemicals. That should give you an idea of the processes involved, and there were some steps I did not see, like masking, photo etching, computerized diamond scribing, adhesive application, annealing, and incoming glass screening.
    ~
    The charging of the glass from the electrostatic field generated in the buffing machine will shock the $**T out of you, because ITO + Glass + Poly coating + dry air = supercapacitor. The grounding probe did not always work on the coated glass. That is one of the ways production yield went down, breakage plus electrostatic field attracting crud on the glass. Cuts from the diamond cut glass are VERY bad too, as latex doesn't protect you. (Hint, you need a balanced ionizer aka charge neutralizer and a e-field meter to be professional, true and dull the edge on the damn glass to protect your fingers)
    ~
    BTW, identifying the ITO side of the glass is extremely difficult on a production basis, you need to build a Kelvin probe, and its even more difficult after coating. Now you know all I remember except the name of my very mean and cruel supervisor and the temp company I worked for.
    ~
    Remember to never put a net DC field on a LCD, it will kill most types quickly. Careful electrode design and square wave AC signals are/used to be/ used for a net zero balance on the liquid crystals. I know there are some DC tolerant designs now, but that is beyond the scope of my knowledge.
    ~
    Steve




    Last edited by mixedgas; 03-21-2018 at 15:16.
    Qui habet Christos, habet Vitam!
    I should have rented the space under my name for advertising.
    When I still could have...

  6. #16
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    Don't worry about me. The process may have changed from the 90s to be less hazardous, or I'm just using chemicals and environment which works for my lower quality results compared to hi res lcd screens.
    https://www.youtube.com/watch?v=_zoeeR3geTA

  7. #17
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    VDX I want to thank you for your suggestion.
    I managed to find a supplier of glass beads of <=50 microns and a seller of 5,10,15,20,25 micron stainless steel mesh sieves for USD 25 each.
    This saved me so much money as the professional glass bead spacer prices were astronomical, I probably wouldn't be able to fund my experiments without doing it this way, so thank you again.

  8. #18
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    ... good to hear! Click image for larger version. 

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    Viktor

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