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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

A new System for Single Particle Strength Testing of Grinding Powders

Einar List

Joerg Frenzel

Heiner Vollstaedt

afratest not only for diamond
AfraTest – not only for diamond
  • Abrasive
  • Powders
  • Fracture
  • Strength
  • Tester
content
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
small and tough a challenge
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
digital image processing
Digital image processing
  • Particle size (whatever this means)
  • Particle Shape
  • Position
  • Proximity to neighbours?
particle size
Particle size
  • Minimum feret diameter
particle size1
Particle size
  • Minimum feret diameter
  • Maximum feret diameter
particle size2
Particle size
  • Minimum feret diameter
  • Maximum feret diameter
  • Area
particle size3
Particle size
  • Minimum feret diameter
  • Maximum feret diameter
  • Area
  • Area equivalent circle diameter
shape
Shape
  • Compactness calculated from Perimeter and Area
shape1
Shape
  • Roughness
  • Convex Outline
position
Position
  • Centre of gravity
  • Surrounding box
  • Surrounding box + safety distance must be empty
shape2
Shape
  • Moments of inertia
  • Minimum and maximum moment of inertia
  • Ellipticity
images ready for processing
Images ready for processing

1.2 µm per pixel

4.5 µm per pixel

find and pick the particle
Find and pick the particle
  • Particles on a glass plate
  • Monochromatic lighting
  • Autofocus optics
  • Sample holder mounted on a planar drive
place and crush the particle
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
which fracture force1
Which fracture force?

For now we take the first fracture.

influence of the anvils
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)

do we know the fracture stress
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

conclusions and outlook
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.