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Epoxy

Discussion in 'Misc Electronics' started by Esther & Fester Bestertester, Mar 20, 2008.

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  1. See no n.g. for adhesives & epoxies, so if there's a better forum for this,
    just point me to it.

    I need an epoxy that is strong to the point of brittle. I want no flex; it
    has to transmit vibration as close to 100% as possible.

    Am I looking for a high Shore Hardness value? That's what Devcon uses in its
    data sheets to specify hardness.

    Is this something that I can achieve by changing the mix of the 2 parts? If
    so, what do I lose if I use more hardener?

    Any personal experiences with epoxies that you found to be harder than
    others?

    Thanks.
    FBt
     
  2. Guest

    For spacecraft vibration testing we use Dental cement. It's extremely
    non-compliant so it is good for transmitting vibration from a
    structure to an accelerometer. It is brittle so we remove them by
    just taping them with a hammer and breaking them off the surface. We
    first put a layer of thin tape on the surface to protect the surface.
    the tape does not affect the vibration response.
    bob
     
  3. try searching for
    sci.engr.chem
    or sci.engr.*




    martin
     
  4. Dave Platt

    Dave Platt Guest

    I need an epoxy that is strong to the point of brittle. I want no flex; it
    Sounds to me as if you're actually looking for stiffness, not
    necessarily strength?

    I think you'd want to look for (or make) a filled epoxy. A
    high-strength epoxy which is loaded up with (e.g.) chopped or milled
    fiberglass would be very stiff.
     
  5. Didi

    Didi Guest

    Any personal experiences with epoxies that you found to be harder than
    I cannot suggest a harder epoxy but you pressed a sensitive button on
    me
    so here I go.

    Many years ago (1991, to be precise) I opted to epoxy-fill my first
    5kV
    coils I did for my then employer in Cologne, Germany. I used no
    multiplier,
    straight flyback @ 5kV; about 1000 windings on an RM8 core, winding
    and insulation layers being an art of their own. I located some very
    liquid
    epoxy meant for that purpose, then the whole module went filled, using
    vacuum to make sure there were no cavities. Everything worked fine,
    the filling
    was perfect - I got asked how come the space between the *windinds*
    was
    not filled (0.05 wire, mylar foil between each layer) by my then
    employer...
    Some years later I had founded TGI in Bulgaria and did the first HV
    source
    making the coil more or less the same. However, I used off-the-shelf
    epoxy;
    it did not get as hard (although it was by far not as liquid before
    hardening),
    and after some warmup it began to conduct just enough to make the
    thing
    noisy... I wasted more than one coil (wound with a lot of work) until
    I
    got what was going on, I spent days if not weeks on that nightmare...
    Eventually I learned I needed no filling at all, just a few drops of
    melted
    silicon at the right spots did the job (still does) quite well.

    And on another occasion I had a guy from a detector repairshop in
    Sofia
    use the same effect trying to cheat on me... The HPGe gamma detectors
    are very sensitive things, the front FET is cooled to -90C or so for
    lowest
    noise. The bias is a few kV (3.5 in that case), and the HV input is
    filtered
    through a 1Gohm/0.47uF group. Well, he had had the detector in his
    hands
    to "check it" for me and had put a stripe of such epoxid along the
    resistor
    between its pins... (The resistor is a rectangle, say 20x5mm, 1mm
    thick).
    After some warmup - the preamp consumes not so little, they have not
    changed its design for >20 years - the detector begins to behave like
    when it needs repair. Well he did not get it for repair because I
    looked
    and discovered what he had done and cleaned the mess up -and the
    detector
    worked fine. A few years later he got the same detector in his hands
    directly from customers and did the same, this time he had added a
    stripe
    across the capacitor, though, and had scratched the paint of the
    resistor between the pins. Mind you, I had told him I knew what he had
    done the first time and he had done it again. I guess the epoxy must
    have
    had braindamaging effect as well.... (and I had refused to believe
    other
    people telling me he was sabotaging detectors before I got burned, the
    epoxy must have worked on my brain as well - perhaps while dealing
    with my coils... :).

    Dimiter
     
  6. TT_Man

    TT_Man Guest

    If you can afford it, Araldite 2014. 4-6 hrs grab, 24hr set.It's a grey
    paste two part.-
     

  7. With the way you worded this, it would seem that a technical response
    would go right over your head.

    Epoxy mix ratios are NEVER meant to be altered. You need to find an
    epoxy that matches your needs. The only time I ever saw mix ratio ranges
    to alter behavior, it was with an epoxy branded as "stycast". Which,
    would oddly meat your needs.

    It will not likely be cheap, however.
     
  8. Al

    Al Guest

    sci.materials is good.

    Al
     
  9. Tim Williams

    Tim Williams Guest

    Don't let your meat loaf ;-)

    Tim
     
  10. If you have been letting it cure at room temperature, try about 15 minutes
    Does it matter when the heat is applied? Right away? Or after it seems to
    have cured as much as it is going to at room temp?
     
  11. To those who offer help even to the misguided, thank you for the benefit of
    your knowledge.

    To those who offer directions to the appropriate forum, thanks for the
    (index) finger. :)

    FBtf
     
  12. Rubinno cement made by Singer Kearfott in the 70's was used on
    guidance systems for the Sram missile, PC3, and A7 navey fighter
    jets. It is the best there is.
     
  13. Rubinno cement

    Google turns up zero hits. Is the correct spelling? Any web references you
    can give?

    Thanks,
    FBt
     

  14. It is probably $50 a quart. Minimum.
     
  15. It is probably $50 a quart. Minimum.

    But that doesn't help me know *where*.

    FBt
     

  16. Try this one:

    EPOTEK

    http://www.epotek.com/categories.asp?ID=1

    There are several that would easily fit your needs, and some that are
    sold at small qty tube level.
     
  17. JeffM

    JeffM Guest

    I saw something on Blue Whales the other day
    that mentioned they are the loudest creature.
    I looked it up and the figure is 188dB (like being next to a rocket)
    ....and there is great controversy about SONAR use
    because it is thought (due to weird behavior
    like healthy-appearing specimens beaching themselves)
    that it is so loud that it damages the hearing of whales.
     

  18. Metal filled epoxies pass thermal as well as vibration quite well.

    http://www.epotek.com/SSCDocs/datasheets/H20E.PDF
     
  19. The other thing to consider is the mass of the sensor, the flexibility
    The "flexible coupling" provided by the epoxies I've tried is causing issues.


    It's been suggested that I try silver-filled epoxy and potting compound.
    Dental cement was also a suggestion. I'm looking at all of these.

    FBt
     

  20. The silver filled is used to attach IC chip dies to their heat sinks
    inside the chip package.

    It is quite firm... brittle even, and is also conductive.

    Requires 4 hr 80 C cure, however.

    There are cooler, longer schedules.
     
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