Transcript A new System for Single Particle Strength Testing of

DIAMANT
A new System for Single
Particle Strength Testing of
Grinding Powders
Einar List
Joerg Frenzel
Heiner Vollstaedt
AfraTest – not only for diamond
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Abrasive
Powders
Fracture
Strength
Tester
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Content
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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
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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
Computer
Analog data acquisition
Actor interface
Digital image acquisition
Force transducer
Actors
Cameras and lighting
Planar drive
Focus
Anvil control
Crushing unit
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Digital image processing
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Particle size
(whatever this
means)
Particle Shape
Position
Proximity to
neighbours?
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Particle size
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Minimum feret
diameter
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Particle size
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Minimum feret
diameter
Maximum feret
diameter
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Particle size
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Minimum feret
diameter
Maximum feret
diameter
Area
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Particle size
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Minimum feret
diameter
Maximum feret
diameter
Area
Area equivalent circle
diameter
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Shape
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Compactness
calculated from
Perimeter and Area
P2
4   A
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Shape
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Roughness
P
Pc
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Convex Outline
Pc 2
4   A
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Position
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Centre of gravity
Surrounding box
Surrounding box +
safety distance must
be empty
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Shape
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Moments of inertia
Minimum and
maximum moment of
inertia
Ellipticity
Momentmax
Momentmin
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Images ready for processing
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Find and pick the particle
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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
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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
700
Force / N
600
500
400
300
200
100
0
0
100
200
300
400
500
600
Time / ms
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Crushing corundum
350
Force / N
300
250
200
150
100
50
0
0
100
200
300
400
500
Time / ms
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Which fracture force?
350
Force / N
300
250
200
150
100
50
0
0
100
200
300
400
500
Time / ms
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Which fracture force?
350
Force / N
300
250
200
150
100
50
0
0
100
200
300
400
500
Time / ms
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Influence of the anvils
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Footprints of 55µm diamonds
on WC anvils (z~10 µm)
Indentation of the
anvil
Lower anvil hardness
causes higher
fracture forces of the
particles
Usage of different
anvils for the same
powder?
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Fracture forces vs. size
200
blocky diamond
fracture strength / N/mm²
180
160
irregular diamond
140
120
black cBN
100
80
orange cBN
60
40
corundum
20
0
sintered corundum
0
50
100
150
200
250
300
350
400
450
particle size / µm
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Do we know the fracture stress?
F
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A
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true Area A under stress is unknown!
don´t know the true stress!
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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
10000
fracture strength / N/mm²
blocky diamond
irregular diamond
1000
black cBN
orange cBN
100
corundum
10
sintered corundum
0
50
100
150
200
250
300
350
400
450
particle size / µm
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Conclusions and outlook
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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!
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