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D.J. Varacalle
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Proceedings Papers
ITSC 2005, Thermal Spray 2005: Proceedings from the International Thermal Spray Conference, 399-404, May 2–4, 2005,
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The primary purpose of grit blasting for thermal spray applications is to ensure a strong mechanical bond between the substrate and the coating by the enhanced roughening of the substrate material. This study presents statistically designed experiments that were accomplished to investigate the effect of abrasives on roughness for A36/1020 steel. The experiments were conducted using a Box statistical design of experiment (SDE) approach. Three grit blasting parameters and their effect on the resultant substrate roughness were investigated. These include blast media, blast pressure, and working distance. The substrates were characterized for roughness using surface profilometry. These attributes were correlated with the changes in operating parameters. Twin-Wire Electric Arc (TWEA) coatings of aluminum and zinc/aluminum were deposited on the grit-blasted substrates. These coatings were then tested for bond strength. Bond strength studies were conducted utilizing a portable adhesion tester following ASTM standard D4541.
Proceedings Papers
ITSC1998, Thermal Spray 1998: Proceedings from the International Thermal Spray Conference, 347-353, May 25–29, 1998,
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The high-velocity air-fuel process (HVAF) is an emerging technology used in the thermal spray industry. The Praxair HVAF process combines air and a liquid fuel (e.g., kerosene, diesel) to generate an energy source with extremely high gas velocities. Analytical studies were conducted to investigate gas and particle dynamics in the Praxair HVAF process for coating with WC-l2Co and stainless steel powders. The mass, momentum, and energy conservation equations were first solved, using the TORCH computer program. Typical output from the model includes temperature and velocity profiles as a function of radial and axial position. The PROCESS gas/particle computer program was then used to calculate from these temperature and velocity profiles the dynamics of particles injected into the gas plume. The primary result of the gas/particle code is a description of the injected particle temperature and velocity as a function of position in the plume. A thorough understanding of the process was obtained using this modeling technique. The results of the modeling were confirmed with process diagnostics. Particle temperature measurements for the WC-Co powder system were obtained with a two-color pyrometer; particle velocity measurements were obtained using particle imaging velocimetry. The coatings produced in the study exhibit superior quality, with high-density, high-hardness, low-oxide content, and high-bond strength.
Proceedings Papers
ITSC1998, Thermal Spray 1998: Proceedings from the International Thermal Spray Conference, 529-535, May 25–29, 1998,
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The High-Velocity Combustion Wire Process is a new high-velocity combustion process now being used in the thermal spray industry. This process combines air, oxygen, and a fuel gas to generate a high-temperature, high-velocity plume that is optimum for producing metallic coatings. Analytical studies were conducted to investigate gas and droplet dynamics for the spraying of three different materials: aluminum, stainless steel, and molybdenum. With the relatively low flame temperatures of the process, the feedstock wire is melted by convective heat transfer with no superheating or vaporization of the droplets. When the droplets strike the substrate, their temperature peaks as the high kinetic energy of the droplet is transformed into thermal energy. The conservation equations were solved using the TORCH computer model, yielding the temperature and velocity profiles as a function of location. The PROCESS gas/droplet computer program was then employed to calculate the dynamics of the molten droplets. The results of this modeling was confirmed with process diagnostics. Experimentation included droplet temperature measurements using a two-color pyrometer and droplet velocity measurements using particle imaging velocimetry for the stainless steel material system. The coatings produced in the study exhibit superior quality with high density, high hardness, low oxide content, and high bond strength.
Proceedings Papers
ITSC1997, Thermal Spray 1997: Proceedings from the United Thermal Spray Conference, 231-238, September 15–18, 1997,
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Statistical design-of-experiment studies of the thermal spraying of polymer powders are presented. Studies of the subsonic combustion (i.e., Flame) process were conducted in order to determine the quality and economics of polyester and urethane coatings. Thermally sprayed polymer coatings are of interest to several industries for anticorrosion applications, including the chemical, automotive, and aircraft industries. In this study, the coating design has been optimized for a site-specific application using Taguchi-type fractional-factorial experiments. Optimized coating designs are presented for the two powder systems. A substantial range of thermal processing conditions and their effect on the resultant polymer coatings is presented. The coatings were characterized by optical metallography, hardness testing, tensile testing, and compositional analysis. Characterization of the coatings yielded the thickness, bond strength, Knoop microhardness, roughness, deposition efficiency, and porosity. Confirmation testing was accomplished to verify the coating designs.
Proceedings Papers
ITSC1996, Thermal Spray 1996: Proceedings from the National Thermal Spray Conference, 251-255, October 7–11, 1996,
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Experimental studies of the subsonic combustion process have been conducted in order to determine the quality and economics of polyester, epoxy, urethane, and hybrid polyester-epoxy coatings. Thermally sprayed polymer coatings are of interest to several industries for anti-corrosion applications, including the infrastructural, chemical, automotive, and aircraft industries. Classical experiments were conducted, from which a substantial range of thermal processing conditions and their effect on the resultant coating were obtained. The coatings were characterized and evaluated by a number of techniques, including Knoop microhardness tests, optical metallography, image analysis, and bond strength. Characterization of the coatings yielded thickness, bond strength, hardness, and porosity.
Proceedings Papers
ITSC1996, Thermal Spray 1996: Proceedings from the National Thermal Spray Conference, 699-707, October 7–11, 1996,
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Air plasma sprayed tungsten carbide-cobalt coatings are being used at Kelly Air Force Base for a fretting application for convergent seals in aircraft engines. Experimental and analytical studies were conducted to investigate the plasma spraying of two powders for this application. Statistical processing schemes were accomplished in conjunction with analytical modeling of the air plasma spray (APS) process. Classical and statistically designed experiments (SDE) chosen to be conducted were determined by analytical modeling. The coatings were characterized for composition, hardness, porosity, surface roughness, deposition efficiency, and microstructure. Attributes of the coatings are correlated with the changes in operating parameters. Wear screening of the coatings from the experiments was conducted using an abrasion tester based on ASTM Standard Test B611-85.
Proceedings Papers
ITSC1996, Thermal Spray 1996: Proceedings from the National Thermal Spray Conference, 709-715, October 7–11, 1996,
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To enhance usage of the plasma spray process, a better physical understanding of the process is required, which entails a synergistic mix of analytical and empirical studies. Better understanding can lead to development of optimal thermal spray coatings for future applications. This study presents an analytical method that can be used for these purposes. Experimental and analytical studies were conducted to investigate gas, particle, and coating dynamics and the resulting coating properties in the plasma spray process for the Tribaloy 800 powder system. Historical full-factorial statistically designed experiments were the basis for the analytical-experimental comparisons. The thermal plasma produced by a commercial plasma spray torch was then numerically modeled from the electrodes to the standoff distance in the free plume for sixteen experiments. This information was then used as boundary conditions to solve the plasma/particle interaction problem for the experiments. The predicted temperature and velocity of the droplets at the spray distance were then used as initial conditions to a coating dynamics code. Multiple polynomial regression analysis was then used to establish the sequential relationship between the process parameters (i.e., power, total flow, hydrogen flow), the coating properties (porosity, oxides), and the coating mechanical performance properties (tensile strength, microhardness, superficial hardness). The equations derived from the regression analysis were used to construct a predictor code for the process. The code predicts the process and coating attributes reasonably well. The predicted coating properties exhibit excellent correlation with the actual properties obtained from the experimental studies in the range of the parameter settings.
Proceedings Papers
ITSC1996, Thermal Spray 1996: Proceedings from the National Thermal Spray Conference, 717-723, October 7–11, 1996,
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An experimental study of twin-wire electric arc spraying of zinc and aluminum coatings demonstrates the suitability of the process for anticorrosion applications. Experiments were conducted using Box-type full-factorial designs. Operating parameters were varied around the following process parameters: nozzle diameter, nozzle geometry, and system pressure. A systematic design of experiments displayed the range of processing conditions and their effect on the resultant coatings. The coatings were characterized with hardness and deposition efficiency tests, and optical metallography. Coating properties are quantified with respect to roughness, hardness, porosity, thickness, bond strength, and microstructure. The features of the coatings are correlated with the process changes. Selected analytical calculations and process diagnostics of the meltpool dynamics are presented.