Diagnostics and control in the thermal spray process

Zheng

Plasma Chem Plasma Process

et al. 2007

This paper investigates the influence of particle injection angle on particle inflight behaviors and characteristics at different primary and carrier gas flow rates through an integrated modeling and experimental approach. Particle in-flight status such as temperature, velocity, size and their distribution are analyzed to examine particle's melting status before impact. Results from the experiments and numerical simulations both show that, when carrier gas flow rate is fixed, a small injection angle favors the particle melting and flattening. This behavior is independent of primary and secondary gas flow rates, spray distance and carrier gas flow rate. When both carrier gas flow and injection angle vary, a high carrier gas flow rate and a small injection angle are recommended for high particle temperature and velocity. Nomenclature a isStoichiometric coefficient of the ith species in the sth reaction b is Stoichiometric coefficient of the ith species in the sth reaction c Concentration, mol m -3 C p Specific heat, J kg -coefficient, m 2 s -1 F Momentum source due to particles, kg m -2 s -2 h Convection heat transfer coefficient, W m -2 K -1 h i Specific enthalpy, J kg -1 I Unit matrix J i Mass flux of the ith species, kg m -2 s -1 k Thermal conductivity, W m -1 K -1 L m Latent heat of fusion, J kg -1 L v Latent heat of evaporation, J kg -1 M i Molecular weight of the ith species, kg mol -1 N p Number of particles in a computational grid P Pressure, Pa Pr Prandtl number, dimensionless _ Q Energy source due to particles, W m -3 r, R Radial coordinate, m Re p Particle Reynolds number,q f D p jṼ þ V 0 À V p j=l f ; dimensionless Sh Sherwood number, dimensionless t Time, s T Temperature, K T m Melting temperature, K ũ Favre average velocity vector, m s -1 ũ 0 Velocity fluctuation, m s -1 Ṽ p Particle velocity vector, m s -1 _ W Source term in momentum equation due to particles, W m -3 x, y, z Coordinate, m Y iMass fraction of the ith speciesGreek symbols j Turbulent kinetic energy, J kg -1 e Turbulent dissipation, m 2 s -3 e Emissivity, dimensionless U Viscous dissipation, kg m -3 s -1 l Viscosity, kg m -1 s -1 l t Turbulent viscosity, kg m -1 s -1 h Coordinate in the circumferential direction q Density, kg m -3 r Stress tensor, Pa x s Progress rate of the sth reaction, mol m -3

Section: Experiments and Diagnosticsmentioning

confidence: 99%

Study of Injection Angle and Carrier Gas Flow Rate Effects on Particles In-Flight Characteristics in Plasma Spray Process: Modeling and Experiments

Zheng

Plasma Chem Plasma Process

et al. 2007

Plasma Chem Plasma Process

“…Integrated sensor setup consisting of DPV 2000 (Tecnar Automation Ltd, Quebec, Canada) [6,7], Control Vision (Control Vision Inc, Boise, ID) [8] and Torch Diagnostic System (TDS) (Inflight Ltd, Idaho Falls, ID) [9,10] was used in this study (Fig. 2).…”

Section: Sensors and Diagnosticsmentioning

confidence: 99%

Particle Injection in Direct Current Air Plasma Spray: Salient Observations and Optimization Strategies

Srinivasan

Friis

Vaidya

et al. 2007

External injection of high-melting point low thermal conductivity ceramics orthogonal to a typical direct current thermal plasma jet plays a vital role in determining the in-flight state of the particles and the process downstream. The interactions between low density ceramic particles and high temperature plasma jet is quite complex, which influences the spray process and associated deposition. Detailed in-flight particle diagnostics as well as spray stream visualization have significantly enhanced our capability to diagnose and control the process. In this paper we present some salient observations on the role of key variables on particle injection. A number of experiments were conducted using a 7MB torch (Sulzer Metco, Westbury, NY) with both Ar-H 2 and N 2 -H 2 plasma gases, where the carrier gas flow to inject Yttria Stabilized Zirconia (YSZ) was varied systematically and the resulting in-flight particle state was captured using an array of particle and spray stream sensors arranged in a 3D set-up. A notable observation is the existence of a ''sweet-spot'' in the plasma jet where the particle temperatures and velocities achieved a maximum. This sweet-spot can be characterized by the plume position (location of centroid of the spray stream) rather than carrier gas flow rate and is independent of primary gas flows and other process/material conditions. This result suggests a possible approach to optimize particle injection independent of plasma-forming-torch-parameters. Controlling particle injection at this sweet-spot has shown to benefit the overall process efficiency (in terms of melting) and process reliability (both in-flight measurement and coating build-up) with concomitant application benefits.

Pure and Applied Chemistry

“…Using appropriate particle sensors makes it possible to detect any out-of-normal spray conditions and, eventually, adjust spray parameters to ensure constant particle conditions during spraying [29][30][31].…”

confidence: 99%

Diagnostics for advanced materials processing by plasma spraying

Moreau

Bisson

Lima

et al. 2005

Advanced coatings deposited by plasma spraying are used in a large variety of industrial applications. The sprayed coatings are employed typically in industry to protect parts from severe operating conditions or to produce surfaces with specific functions. Applications are found in many industrial sectors such as aerospace, automobile, energy generation, and biomedical implants.Coatings are built by the successive deposition of molten or partially molten particles that flatten and solidify upon contact on the substrate, forming lamellae. The coating properties are intimately linked to the properties of these lamellae, which in turn depend on inflight particle properties as well as substrate temperature during spraying. Consequently, the development of diagnostic tools for monitoring and controlling these spray parameters will help provide the necessary information to study the coating formation process, optimize the coating properties, and, eventually, control the spray process in production.In this paper, a review of some recent developments of optical diagnostic techniques applied to monitor plasma-sprayed particles is presented. In the first part of the paper, two different sensing techniques for in-flight particle measurement are described. First, time-resolved diagnostics on individual particles is described. This technique is used to study the instabilities of the particle characteristics associated with the plasma fluctuations. Secondly, a technique adapted for use in an industrial production environment for measuring the particle jet characteristics as an ensemble is presented. In the second part of the paper, the use of an optical system to study the influence of the substrate temperature on the flattening and solidification of sprayed particles impacting on a flat substrate is described. The last part of this paper describes the optimization of nanostructured coatings based on a tight control of the temperature and velocity of the plasma-sprayed particles.