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1493 |
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Wednesday, June 04, 2008, Room 08 12:00 PM Diagnostics and Sensors 1 Modern process diagnostics offer a lot of possibilities for gaining data for both quality control and process knowledge. The recorded data is the base for process models and enhances the process knowledge |
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Analysis of plasma spray particle state distribution for deposition rate control |
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Michael Gevelber* / Boston University
Manufacturing Engineering, USA Donald Wroblewski/ Boston University, USA Onomitra Ghosh/ Boston University, USA Michael VanHout/ Boston University, USA Annie Lum/ Boston University, USA Soumendra Basu/ Boston University, USA |
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The plasma spray process for depositing thermal barrier coatings is characterized by large distributions of particle states (temperature and velocity) that result in significant variations in coating quality (thickness and structure). These variations are due to the distribution of particle sizes, large spatial gradients of plasma thermal-fluid fields, and temporal variations of the arc and plasma jet. This paper describes the relation of the particle state distributions to the powder size distributions, torch inputs, arc fluctuations, and the implications for developing improved deposition rate monitoring and control. Two models have been developed: a torch model that relates the torch inputs to the plasma jet that exits the torch, and a plasma-particle interaction model. The torch model captures the fluid-thermal spatial gradients of the plasma within the torch and the results are compared to experimental measurements of torch operation. Based on the plasma torch exit conditions, the spatial thermal and velocity gradients in the plasma jet have been modeled by the growth of the turbulent shear layers around the laminar core, the mixing transition region, and the development of the similarity region. Plasma-particle momentum and thermal interactions, particle phase transitions and collapse of in-flight hollow particles have been modeled using a multi-lumped particle model flowing into the jet. Variations resulting from the distributions of particle size, torch and injection conditions have been parametrically studied. In order to develop a better understanding of the deposition characteristics and the requirements for deposition rate control, the effect of different operating conditions on the molten particle states (volume, velocity, centroid) has been analyzed, and implications for implementing measurements and control of particle states that relate to deposition rate has been analyzed. |