Mathematical modeling of the gas and powder flow in HVOF systems

Tawfik, Hazem; Zimmerman, F.

doi:10.1007/s11666-997-0069-6

Cited by 20 publications

(7 citation statements)

References 3 publications

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“…28,29 From the exit of the nozzle to a position whose distance is not larger than the potential core length (L pc ), the gas velocity and temperature can be considered almost constant. 30 Further downstream, the gas velocity and temperature decay rapidly because of the entrainment of the surrounding air. This decay of the gas velocity and temperature can be described by the empirical formulas 30 and where x is the axial distance from the exit of the gun barrel (x > L pc ) and R and β are parameters obtained from experimental measurements.…”

Section: Modeling Of the Gas Thermal And Flowmentioning

confidence: 99%

Diamond Jet Hybrid HVOF Thermal Spray: Gas-Phase and Particle Behavior Modeling and Feedback Control Design

Shi

Christofides

2004

Ind. Eng. Chem. Res.

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This paper focuses on the modeling and control of an industrial high-velocity oxygen-fuel (HVOF) thermal spray process (Diamond Jet hybrid gun, Sulzer Metco, Westbury, NY). We initially develop a fundamental model for the process that describes the evolution of the gas thermal and velocity fields and the motion and temperature of particles of different sizes and explicitly accounts for the effect of the powder size distribution. Using the proposed model, a comprehensive parametric analysis is performed to systematically characterize the influence of controllable process variables such as the combustion pressure and oxygen/fuel ratio, as well as the effect of the powder size distribution, on the values of the particle velocity, temperature, and degree of melting at the point of impact on the substrate. (These are the variables that directly influence coating microstructure and porosity, which, in turn, determine coating strength and hardness; see the second article of this series for details.) A feedback control system that aims to control the volume-based average particle velocity and melting ratio by directly manipulating the flow rates of fuel, oxygen, and air at the entrance of the HVOF gun is developed and applied to a detailed mathematical model of the process. Closed-loop simulations show that the feedback controller is effective in driving the controlled outputs to the desired set-point values and is also robust with respect to various kinds of disturbances in the operating environment.

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Section: Modeling Of the Gas Thermal And Flowmentioning

confidence: 99%

Diamond Jet Hybrid HVOF Thermal Spray: Gas-Phase and Particle Behavior Modeling and Feedback Control Design

Shi

Christofides

2004

Ind. Eng. Chem. Res.

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“…It was assumed that adiabatic, isentropic and frictionless fluid flow conditions existed within this portion of the gun nozzle with a constant mean velocity and temperature. The mean axial gas temperature had the same functional form as the gas velocity (2) only with a larger exponential decay exponent (b T = 1.35), as proposed by Tawfik et al in 1997 [18]. It was also assumed that the predominant reaction product during the combustion of hydrogen and oxygen in the HVOF gun was water vapor, i.e.…”

Section: Hvof Gas Flow and Thermal Fieldsmentioning

confidence: 85%

“…Tawfik et al [18] proposed and experimentally verified empirical correlations for jet core length after the nozzle exit and the axial mean velocity (v (g) ) of an HVOF jet with a range of validity between Mach number 0.3 and 1.4. The jet core length is a function of the nozzle exit diameter (D NZL ) and local Mach number (Ma), as shown in Eq.…”

Section: Hvof Gas Flow and Thermal Fieldsmentioning

confidence: 99%

“…The predicted velocities of 30, 60, 90 and 120 lm diameter particles at the moment of impact on the substrate at a spray distance of 225 mm were 537, 497, 427 and 368 m/s. In general, polymer particles accelerate in HVOF jets much faster than similarly sized metallic or cermet particles [18,20]. This is due to the much lower density of polymers (900-1400 kg/m 3 ) versus that of metals or cermets ($2700-15,000 kg/m 3 ).…”

Section: Particle Velocitymentioning

confidence: 99%

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3D predictions of thermally sprayed polymer splats: Modeling particle acceleration, heating and deformation on impact with a flat substrate

Ivosevic

Cairncross

Knight

2006

International Journal of Heat and Mass Transfer

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“…For the external flow and thermal fields, empirical formulae are used for the gas velocity and temperature decay, [18] which are experimentally derived as functions of the distance from the exit of the HVOF gun.…”

Section: Modeling Of Gas Flow and Thermal Fieldsmentioning

confidence: 99%

Feedback control of HVOF thermal spray process accounting for powder size distribution

Christofides

2004

J Therm Spray Tech

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This work presents a novel formulation of the control problem and a feedback control system for the high velocity oxygen-fuel (HVOF) thermal spray process, which explicitly accounts for the effect of powder size distribution. Initially, based on model predictions and available experimental data, the control problem is formulated as one of regulating appropriate averages (with respect to the particle volume distribution) of the temperature and velocity of the particles at the point of impact on substrate (these are the variables that directly influence coating microstructure and porosity, which, in turn, determine coating mechanical and thermal properties) by manipulating the oxygen/fuel ratio and the combustion chamber pressure, respectively. Then, a feedback control system is developed and applied to a detailed mathematical model of the process. Closed-loop simulations show that the average particle velocity and temperature at the point of impact on substrate reach the desired values in a short time, which validates the feasibility of real-time implementation of feedback control on HVOF thermal spray systems. It is also shown that the proposed formulation of the control problem (which accounts for the effect of powder size distribution) leads to a solution of the control problem that is superior (with respect to the achievement of the desired control objectives) to a solution that assumes a monodisperse powder size distribution. Finally, the proposed control problem formulation and the feedback control system are shown to be robust with respect to disturbances in spray distance and particle injection velocity, and variations in powder size distribution.

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Mathematical modeling of the gas and powder flow in HVOF systems

Cited by 20 publications

References 3 publications

Diamond Jet Hybrid HVOF Thermal Spray: Gas-Phase and Particle Behavior Modeling and Feedback Control Design

Diamond Jet Hybrid HVOF Thermal Spray: Gas-Phase and Particle Behavior Modeling and Feedback Control Design

3D predictions of thermally sprayed polymer splats: Modeling particle acceleration, heating and deformation on impact with a flat substrate

Feedback control of HVOF thermal spray process accounting for powder size distribution

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