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

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

19 Crushing corundum

20 Which fracture force?

21 Which fracture force?

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!