a new system for single particle strength testing of grinding powders einar list joerg frenzel...
TRANSCRIPT
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!