DIAMANT

A new System for Single Particle Strength Testing of

Grinding Powders

Einar List

Joerg Frenzel

Heiner Vollstaedt

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AfraTest – not only for diamond

Abrasive Powders Fracture Strength Tester

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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

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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

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AfraTest structure

F orce tran sd u cer

A n a log d a ta acq u is it ion

P lan ar d rive F ocu s A n vil con tro l C ru sh in g u n it

A c to rs

A c to r in te rface

C am eras an d lig h tin g

D ig ita l im ag e acq u is it ion

C om p u te r

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Digital image processing

Particle size (whatever this means)

Particle Shape Position Proximity to

neighbours?

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Particle size

Minimum feret diameter

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Particle size

Minimum feret diameter

Maximum feret diameter

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Particle size

Minimum feret diameter

Maximum feret diameter

Area

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Particle size

Minimum feret diameter

Maximum feret diameter

Area Area equivalent circle

diameter

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Shape

Compactness calculated from Perimeter and Area

A

P

4

2

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Shape

Roughness

Convex Outline

A

Pc4

2

cP

P

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Position

Centre of gravity Surrounding box Surrounding box +

safety distance must be empty

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Shape

Moments of inertia Minimum and

maximum moment of inertia

Ellipticity

min

max

Moment

Moment

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Images ready for processing

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Find and pick the particle

Particles on a glass plate

Monochromatic lighting

Autofocus optics Sample holder

mounted on a planar drive

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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

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Crushing a blocky diamond

0

100

200

300

400

500

600

700

0 100 200 300 400 500 600

Time / ms

Fo

rce

/ N

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Crushing corundum

0

50

100

150

200

250

300

350

0 100 200 300 400 500

Time / ms

Fo

rce

/ N

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Which fracture force?

0

50

100

150

200

250

300

350

0 100 200 300 400 500

Time / ms

Fo

rce

/ N

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Which fracture force?

0

50

100

150

200

250

300

350

0 100 200 300 400 500

Time / ms

Fo

rce

/ N

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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)

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Fracture forces vs. size

0

20

40

60

80

100

120

140

160

180

200

0 50 100 150 200 250 300 350 400 450

particle size / µm

fra

ctu

re s

tre

ng

th /

N/m

m²

blocky diamond

irregular diamond

black cBN

orange cBN

corundum

sintered corundum

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Do we know the fracture stress?

A

F

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

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Particle „strength“ vs. size

10

100

1000

10000

0 50 100 150 200 250 300 350 400 450

particle size / µm

fra

ctu

re s

tre

ng

th /

N/m

m²

blocky diamond

irregular diamond

black cBN

orange cBN

corundum

sintered corundum

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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.

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Thank you!