Ultrasonic thickness testing

Discussion in 'Gold' started by goldpelican, Apr 4, 2012.

  1. goldpelican

    goldpelican Administrator Staff Member

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    [youtube]http://www.youtube.com/watch?v=tVjRSye8z-c[/youtube]

    Using an ultrasonic thickness meter to test the thickness of a gold bar based on expected sound velocity.

    Note I misquoted the metric weight of the bar - it's 1.555kg, not 1.67 :rolleyes:
     
  2. selfcentered

    selfcentered New Member

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    That was pretty cool GP,

    You mentioned tungsten would show a lower reading, how much smaller are we talking 2 or 3 mm or a greater difference?

    At first I thought you had little hands, but then I realized it was a massive gold bar!

    Made me smile!
     
  3. goldpelican

    goldpelican Administrator Staff Member

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    Say it was solid tungsten, 14.1mm thick, and using 3240m/s for gold and 5170m/s for tungsten, the thickness would have calculated at 8.8mm. So a considerable difference.

    Even if there was a tungsten insert only half the thickness of the bar, the reading would be in the 11mm range. I would say anything more than 1mm out (which is a 7% discrepancy!) would be very suspect.

    We tried some silver bars as well - it tests bang on (once you calibrate the device). Tested a 15mm thick 100oz silver bar at exactly 15.0mm - that's using 3650m/s for silver.
     
  4. silvertongue

    silvertongue Member Silver Stacker

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    This works well for both gold and silver, multi-reflection types also work well. The glycerine used for the transmission coupling can cause some minor errors, and again, a multi-reflection type can be useful if the item under test has a rough surface that doesn't couple well with the transducer.
    IMHO, this, in connection with a transient magnetic flux test, is almost as good as an XRF in determining the authenticity of gold and silver.
     
  5. Macros_The_Black

    Macros_The_Black Member Silver Stacker

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    Very nice GP, thanks very much for taking the time to demonstrate & explain!

    (I did get distracted quite a bit finding myself looking at the $80k-worth of gold bling and wiping the drool from my chin ;))

    And of course, it makes sense to test on something similar to that "altered bar".

    How accurate is this on very thin gold bars eg 1oz and also even the Valcambi?

    Cheers!
     
  6. rbaggio

    rbaggio Active Member Silver Stacker

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    So ..... where do we get one? Ebay?
     
  7. goldpelican

    goldpelican Administrator Staff Member

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    Tried it on a Peace dollar - came back 2.5mm, they're supposed to be 2.4mm - but the resolution of this particular meter is only 0.1mm - which in itself is ~5% variation on the thickness.

    Coins can be tested with XRF quite well - this is more aimed at testing bars that could conceal an inclusion deeper than the ~20-40 microns an XRF machine can penetrate.

    Yep, sourced this on eBay, ex Hong Kong.
     
  8. Macros_The_Black

    Macros_The_Black Member Silver Stacker

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    OK thanks GP - makes sense to me!
     
  9. EJAM5

    EJAM5 Active Member

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    Does GS provide testing services of PMs?
     
  10. goldpelican

    goldpelican Administrator Staff Member

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    Not really - we're not set up as a retail operation, our office is more operational and for pickup only. Happy to demonstrate the technology at a future meetup though (with a silver bar!).
     
  11. alex.ross

    alex.ross New Member

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    Thanks for the video GP. I echoed other posters who would like to see it tested on fake bars. Perhaps one of the milled silver bars?

    Can you please provide the link/price to the equipment? Also does the glycerine is included in the purchase?

    Cheers.
     
  12. goldpelican

    goldpelican Administrator Staff Member

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    Only fake bars we have on hand are in the 1oz size - the resolution on this meter is too coarse to provide a valid test.

    Have contacted the seller to see if it's possible to get a bulk discount, but everything pictured was included.
     
  13. ShinyStuff

    ShinyStuff New Member

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    Get glycerine in the cooking aisle of your local supermarket if you are not sure where to source it. Next to the food colouring. About $3 or so.
     
  14. RomanControl

    RomanControl New Member

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    does monkeyboy supply the fake bars for analysis?
     
  15. rbaggio

    rbaggio Active Member Silver Stacker

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  16. THUCYDIDES79

    THUCYDIDES79 New Member Silver Stacker

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    Speaking of Ultrasonics, ALDI currently is selling ULTRASONIC CLEANERS of jewellery and the like for $20.

    Should be able to be used for coins too.

    Its in a cube-shaped box of around 25cm
     
  17. Peter

    Peter Well-Known Member

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    HI
    bought one.
    But only good for small coins as they are low wattage
    I used on a sixpence successfully,but no good on 2 bob(2 shillings)
     
  18. goldpelican

    goldpelican Administrator Staff Member

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    This model is a TM8812 - I'd previously seen a TM8811 used to test silver, some I stuck with the same brand.

    Coincidentally I found an Australian equipment company selling these rebranded locally for $580 - I paid under $175 delivered. Figured if they were being sold at that price locally they must be acceptable for use.
     
  19. Kansas21

    Kansas21 Member Silver Stacker

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    Thanks GP quite interesting.
     
  20. pmbug

    pmbug Active Member

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