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A new System for Single Particle Strength Testing of Grinding Powders

A new System for Single Particle Strength Testing of Grinding Powders. Einar List Joerg Frenzel Heiner Vollstaedt. AfraTest – not only for diamond. A brasive Powders Fra cture Strength Test er. Content. The specimen General machine layout Find, measure and pick the particle

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A new System for Single Particle Strength Testing of Grinding Powders

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  1. A new System for Single Particle Strength Testing of Grinding Powders Einar List Joerg Frenzel Heiner Vollstaedt

  2. AfraTest – not only for diamond • Abrasive • Powders • Fracture • Strength • Tester

  3. Content • The specimen • General machine layout • Find, measure and pick the particle • Place and crush the particle • Interpretation of the force / time plot • Results • Outlook

  4. Small and tough – a challenge • Sizes from 1000 µm down to 46 µm • Extremely wide fracture strength range • Automatic handling, new anvil for every particle

  5. AfraTest structure

  6. Digital image processing • Particle size (whatever this means) • Particle Shape • Position • Proximity to neighbours?

  7. Particle size • Minimum feret diameter

  8. Particle size • Minimum feret diameter • Maximum feret diameter

  9. Particle size • Minimum feret diameter • Maximum feret diameter • Area

  10. Particle size • Minimum feret diameter • Maximum feret diameter • Area • Area equivalent circle diameter

  11. Shape • Compactness calculated from Perimeter and Area

  12. Shape • Roughness • Convex Outline

  13. Position • Centre of gravity • Surrounding box • Surrounding box + safety distance must be empty

  14. Shape • Moments of inertia • Minimum and maximum moment of inertia • Ellipticity

  15. Images ready for processing 1.2 µm per pixel 4.5 µm per pixel

  16. Find and pick the particle • Particles on a glass plate • Monochromatic lighting • Autofocus optics • Sample holder mounted on a planar drive

  17. Place and crush the particle • 300 mm moveable anvil bars • 2000 N and 200 N range • 16 bit force resolution • 10,000 samples/s • Offset and excitation compensation

  18. Crushing a blocky diamond 159.2

  19. Crushing corundum

  20. Which fracture force? ?

  21. Which fracture force? For now we take the first fracture.

  22. Influence of the anvils • Indentation of the anvil • Lower anvil hardness causes higher fracture forces of the particles • Usage of different anvils for the same powder? Footprints of 55µm diamonds on WC anvils (z~10 µm)

  23. Fracture forces vs. size

  24. Do we know the fracture stress? The true Area A under stress is unknown! We don´t know the true stress! As imperfect as it is:we calculate CFS using the particle cross section area or the area of the inscribed circle

  25. Particle „strength“ vs. size

  26. Conclusions and outlook • AfraTest can handle the size range from fine powder to coarse grit • The measuring range allows for testing superabrasives as well as conventional abrasives • The first fracture is suitable for comparing materials. • A compressive fracture strength can be derived, making different assumptions for the loaded area. • AfraTest produces results on a common scale for abrasives and superabrasives.

  27. Thank you!

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