ADVANCED PARTICLE CHARACTERIZATION FOR IMPROVED UNDERSTANDING OF SPRAY COATING QUALITY

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ADVANCED PARTICLE CHARACTERIZATION FOR IMPROVED
UNDERSTANDING OF SPRAY COATING QUALITY

• E. PirardUniv. Liège (Belgium)
• F. Campana, J-P JanssenAdvanced Coating, Liège
  (Belgium)

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Introduction

• The interaction between the gas and the
  individual particle plays a key role
• A better understanding of the way individual
  particles are affected, will allow for developing
  more accurate powder specifications
• Existing norms provide only limited insight into
  particle characteristics
• Use innovative single particle digital imaging
  and analysis to access pertinent information

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Metal Powders

• High velocity oxy-fuel (HVOF) spray coatings with
  four (Cr3C2-NiCr 75/25) comparable powders

A B C D
Supplier Sulzer Metco Sulzer Metco Sylvania Deloro Stellite
Size Range µm -4515 -4515 -5310 -5310
Flowability 50g sec. N.A. 18,26 26 23
App. density g/cm3 N.A. 3,67 3,6 3,62
Carbon () 9,64 9,48 9,11 9,45
Manuf. Process A/S A/S/P.D. A/S/P.D. A/S/P.D.
supplier data
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Standard Characterization

• ISO 3923/2 Determination of apparent
  densityPart 2 Scott volumeter method

Density A B C D
Test 1 2,77 3,82 3,79 3,84
Test 2 2,75 3,87 3,79 3,8
Test 3 2,76 3,82 3,78 3,78
m 2,76 3,84 3,79 3,81
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Standard Characterization

• ISO 4490 Determination of flow time by means of
  a calibrated funnel (Hall flowmeter)

Flow A B C D
Test 1 29,59 22,15 29,29 21,78
Test 2 29,73 22,23 29,37 21,18
Test 3 29,66 22,28 28,75 21,79
m 29,66 22,22 29,14 21,58
Suppl. data N.A. 18,26 26 23
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Digital Image Analysis ofIndividual Particles

• Three essential steps requiring dedicated
  solutions

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Powder Dispersion

• Patented vacuum disperser
• Cylindrical chamber
• Pinhole with plastic membrane
• Settling onto circular glass slide
• Advantages
• Perfect dispersion (1500)
• No breakage / deformation of particles
• Controlled (symmetrical) segregation

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Particle Imaging

• Automated Digital Microscopy
• Diascopic illumination _at_ 439nm (LED)
• Superzoom telecentric lens
• Hi-resolution digital video
• Fully motorized glass plate
• Advantages
• Typ. 10.000 particles/min
• Controlled particle position and velocity
• Dynamic range 0,5 µm 200 µm

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Particle Analysis

• Accurate estimation of a sieving diameter
• ISO TC24SC4 Sizing by methods other than
  sieving
• Application oriented shape characterization
• Computation of a wear index
• Computation of a satellity index

W 46,18 64,14 65,71 82,55
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Results on Cr3C2-NiCr 75/25 particles

• Size Distributions
• By Number of by Volume
• Sub-sieve analysis capability

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Results

• Morphostatistics
• Quality control statistics
• Discriminant statistics

DINµm W Roundness El Elongation
A 33,66 65,67 25,68
B 33,35 74,83 21,70
C 28,97 58,29 21,70
D 30,02 79,00 16,10
Mean values
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Results

• Coating Deposition Efficiency

Q Fl Th/r Th/p/Fl
g/(m²x0.1mm) g/min µm µm/(g/min)
A1 Mean 1.184 39 11.8 0,3
A1 Std Dev 70 5.4 1.8 0,03
A2 Mean 1.252 38.1 11.4 0,3
A2 Std Dev 244 2.1 1.6 0,05
D Mean 1.381 45.5 12.2 0,27
D Std Dev 142 7.3 1.3 0,05
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Results

• Coating Deposition Efficiency

Th µm Porosity Porosity Porosity Hardness HV0,3 Hardness HV0,3 Hardness HV0,3
Th µm Mean Min. Max. Mean Min. Max.
A 183 2,6 2,1 3,8 1041 845 1255
D 159 1,1 0,4 1,4 971 856 1173
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Discussion Conclusions

• Image analysis provides very accurate size
  distributions
• Perfect correlation with sieves
• Number weighted distributions are unique (e.g. A
  contains 90 lt15µm)
• Image analysis provides unique shape information
  that correlates perfectly with flowability tests

DINµm W Roundness El Elongation Scott Hall
A 33,66 65,67 25,68 2,76 29,66
B 33,35 74,83 21,70 3,84 22,22
C 28,97 58,29 21,70 3,79 29,14
D 30,02 79,00 16,10 3,81 21,58
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Perspectives

• Image analysis offers a unique insight into metal
  powder properties (direct measurement !).
• It opens the way to a better understanding of
  coating qualities with respect to powder
  properties
• This new analytical technology allows to optimize
  powder specifications.