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Influence of the Injector Head Geometry on the Particle Injection in Plasma Spraying

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Abstract

In plasma spraying, the particle velocity at the injector outlet has significant influence on the particles’ penetration into the plasma jet. The geometry of the injector and the flow rate of the carrier gas determine the particle velocities. Based on numerical simulations, it is evident that higher particle velocities and thus, a deeper penetration of the particles into the plasma jet, can be realized with an injector geometry which is significantly longer than the standard injector. This results in a higher melting degree of the particles, especially for operating parameters leading to high-speed plasma jets. In order to verify the results of the simulations, injectors with different diameters and lengths were manufactured and their influence on the particle velocities at the injector outlet was measured via particle diagnostics. The injectors were furthermore used to apply alumina coatings with a multi-cathode plasma generator. The resulting coating thicknesses were determined. Based on these results, it seems feasible to influence the injection behavior of the particles positively by increasing the injector length. By comparing the relative intensities of the α- and γ-alumina peaks in the XRD patterns, it is shown that these changes in injector geometry did not affect the phase composition.

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Abbreviations

C D :

Drag coefficient

d inj :

Diameter of the injector head

d p :

Particle diameter

e :

Coefficient of restitution

I:

Electric current

l inj :

Length of the injector head

\(\dot{m}_{\text{p}}\) :

Powder feed rate

µ g :

Dynamic viscosity of the carrier gas

Rep :

Reynolds number of the particles

ρ g :

Density of the carrier gas

ρ p :

Density of the particles

s :

Coating thickness

σ p :

Standard deviation of the particles’ size distribution

T inlet :

Gas temperature at the injector inlet

v g :

Gas velocity

v p :

Particle velocity

\(\dot{V}\) :

Plasma gas flow rate

\(\dot{V}_{\text{inj}}\) :

Carrier gas flow rate

XRD:

X-Ray diffraction

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Acknowledgments

The presented investigations were carried out at RWTH Aachen University within the framework of the Collaborative Research Centre SFB1120-236616214 “Bauteilpräzision durch Beherrschung von Schmelze und Erstarrung in Produktionsprozessen” and funded by the Deutsche Forschungsgemeinschaft e.V. (DFG, German Research Foundation). The sponsorship and support is gratefully acknowledged. Simulations were performed with computing resources granted by RWTH Aachen University under project rwth0315. The authors would like the thank Jannis Künzer and Dirk Ortmanns for their efforts in manufacturing the injector heads.

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  1. Surface Engineering Institute, RWTH Aachen University, Aachen, Germany

    K. Bobzin, M. Öte, M. A. Knoch & H. Heinemann

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  1. K. Bobzin
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Bobzin, K., Öte, M., Knoch, M.A. et al. Influence of the Injector Head Geometry on the Particle Injection in Plasma Spraying. J Therm Spray Tech 29, 534–545 (2020). https://doi.org/10.1007/s11666-020-01009-6

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