Digital Diagnostics Based on CCD Imaging for Monitoring Thermal Spray Processes

This paper describes the development of a diagnostic system that monitors in-flight particle diameters, velocities, and temperatures during thermal spraying. The system is based on a low-cost CCD camera and user-developed software. The camera incorporates a 732 x 282 pixel sensor with high sensitivity in the near IR range where the only radiation is that of the particles. User-developed software modules handle signal processing, image analysis, calibration, and data visualization. In video images, particles appear as light tracks of varying length, width, and intensity, corresponding (respectively) to velocity, diameter, and temperature. A test case in which Cr₂O₃ powder is sprayed in a plasma jet demonstrates the capabilities of the diagnostic system. Paper includes a German-language abstract.