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Journal of Thermal Spray Technology

, Volume 16, Issue 4, pp 512–523 | Cite as

Clogging and Lump Formation During Atmospheric Plasma Spraying with Powder Injection Downstream the Plasma Gun

  • Isabelle Choquet
  • Stefan Björklund
  • Jimmy Johansson
  • Jan Wigren
Peer Reviewed

Abstract

This study aimed to numerically and experimentally investigate lump formation during atmospheric plasma spraying with powder injection downstream the plasma gun exit. A first set of investigations was focused on the location and orientation of the powder port injector. It turned out impossible to keep the coating quality while avoiding lumps by simply moving the powder injector. A new geometry of the powder port ring holder was designed and optimized to prevent nozzle clogging, and lump formation using a gas screen. This solution was successfully tested for applications with Ni-5wt.%Al and ZrO2-7wt.%Y2O3 powders used in production. The possible secondary effect of plasma jet shrouding by the gas screen, and its consequence on powder particles prior to impact was also studied.

Keywords

influence of spray parameters shrouded spraying spray deposition 

Nomenclature

Latin notations

cp

specific heat capacity of the powder particle, J kg−1 K−1

C, C, Cμ

constants of the RNG k-ε model, dimensionless

Di,m

diffusion coefficient of species i in the mixture, m2 s−1

eT

total specific energy of the fluid \( e_{{\text{T}}} = h - p\uprho ^{{ - 1}} + \raise0.5ex\hbox{$\scriptstyle 1$} \kern-0.1em/\kern-0.15em \lower0.25ex\hbox{$\scriptstyle 2$}u^{2} \), J kg−1

\( \ifmmode\expandafter\vec\else\expandafter\vec\fi{F}_{{{\text{ext}}}} \)

external forces applied on the fluid, N m−3

Gk

rate of turbulent kinetic energy generated by velocity gradients, kg m−1 s−3

h

specific enthalpy of the fluid \( h = {\sum {Y_{i} h} }_{i} \), J kg−1

hi

specific enthalpy of the species i, J kg−1

\( \ifmmode\expandafter\vec\else\expandafter\vec\fi{J}_{i} \)

diffusion flux of species i in the mixture, kg m−2 s−1

k

turbulent kinetic energy, m2 s−2

p

static pressure of the fluid, Pa

Prt

turbulent Prandtl number

r

radial position (at nozzle outlet), m

r0

nozzle radius at the plasma gun exit, m

Rε

rate of dissipation rate ε generated by rapid strain and streamline curvature, kg m−1 s−4

Sswirl

ratio between the flux of angular and of axial momentum, or swirl coefficient

Se

energy source term due to the interaction between fluid and powder particles, J kg−1

Sm

mass source term due to the interaction between fluid and powder particles, kg m−3 s−1

Sct

turbulent Schmidt number

T

temperature of the fluid, K

Tmax

maximum temperature T (at nozzle outlet), K

Tmelt

melting temperature of the powder particle, K

Twall

wall temperature, K

u

velocity norm of the fluid, m s−1

\( \ifmmode\expandafter\vec\else\expandafter\vec\fi{u} \)

velocity vector of the fluid, m s−1

umax

maximum velocity norm (at nozzle outlet), m s−1

Yi

mass fraction of species i

Greek notations

αk

inverse effective Prandtl number for the turbulent kinetic energy k

αε

inverse effective Prandtl number for the turbulent dissipation rate ε

Δhmelt

latent heat of fusion of the powder particle, J kg−1

ε

dissipation rate of turbulent kinetic energy, m2 s−3

κ

laminar thermal conductivity of the fluid, W m−1 K−1

κt

turbulent thermal conductivity of the fluid, W m−1 K−1

κeff

effective thermal conductivity of the fluid κeff = κ t  + κ, W m−1 K−1

κp

thermal conductivity of the powder particle, W m−1 K−1

μ

laminar dynamic viscosity, kg m−1 s−1

μt

turbulent dynamic viscosity, kg m−1 s−1

μeff

effective dynamic viscosity μ eff  = μ t  + μ, kg m−1 s−1

ρ

density of the fluid, kg m−3

ρp

density of the powder particle, kg m−3

\( \overline{\overline \uptau } \)

laminar viscous stress tensor, kg m−1 s−2

\( \overline{\overline \uptau } _{{\text{t}}} \)

Reynolds stress tensor, kg m−1 s−2

\( \overline{\overline \uptau } _{{{\text{eff}}}} \)

effective stress tensor \( \overline{\overline \uptau } _{{{\text{eff}}}} = \overline{\overline \uptau } _{{\text{t}}} + \overline{\overline \uptau } \), kg m−1 s−2

Mathematical symbols

\( \overline{\overline I} \)

unit tensor

t

partial derivative with respect to time

\( \otimes \)

tensorial product

\( \nabla \cdot \)

divergence operator

\( {\overrightarrow{\nabla }} \)

gradient operator

Notes

Acknowledgments

The authors wish to acknowledge Mats-Olov Hansson, Carina Karlsson, Svante Magnusson, Peter Mårtensson, and Raymond Zakrisson, Volvo Aero Corporation, as well as Mats Högström and Fouzi Bahbou, University West, for their valuable contribution to the experimental investigations.

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Copyright information

© ASM International 2007

Authors and Affiliations

  • Isabelle Choquet
    • 1
  • Stefan Björklund
    • 1
  • Jimmy Johansson
    • 2
  • Jan Wigren
    • 2
  1. 1.Department TMDUniversity WestTrollhättanSweden
  2. 2.Volvo Aero CorporationTrollhättanSweden

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