Coating of cylinder bores using plasma spraying is a growing application of thermal spraying in automotive industry. The Sulzer Metco RotaPlasma manipulator provides continuous rotation of the internal diameter plasma gun and enables a cost-efficient and reliable coating of the cylinder blocks. The development towards more advanced quality control systems and closed-loop spray control systems requires an on-line measurement of the most important particle and spray parameters such as particle temperature, velocity and flux. However, the small dimensions of the plasma plume of an internal diameter spray gun together with the rotation of the gun makes the measurement difficult, if not impossible, for many traditional diagnostics equipment. In this work, SprayWatch, an imaging CCD camera based diagnostics system from Oseir Ltd. was used for measuring particle and spray parameters during the rotation of an internal diameter plasma spray gun. The results show that the SprayWatch camera system is a promising tool for both development and production monitoring of cylinder bore coating process, as well as for realising a closed-loop spray control system.

Imaging techniques have gained popularity in thermal spray diagnostics over the last decade. They provide large amounts of data for research, development and process monitoring. The most important measured spray parameters are particle temperature and velocity. The biggest advantage of imaging techniques compared to optical point measurements is that they provide instantaneous distribution measurements. We present the application of high-power diode laser illumination to detect weakly emitting particles in thermal spaying. This extends the feasibility of imaging diagnostics to several demanding environments, including cold spray, powder mixing region of a plasma spraying torch and low-pressure plasma spray.

On-line monitoring of two thermal spray processes by means of an imaging diagnostic technique capable of measuring several spray particle properties, such as individual and average particle temperatures, velocities and number of particles with spatial distributions, was studied by using the Spray-Watch thermal spray monitor. Aim of the work was to demonstrate the capabilities of this novel monitor in quick optimisation of certain spray gun parameters to obtain desired particle characteristics in-flight, and hence desired coating structure and properties with high deposition efficiency. Examples are given in plasma spraying of Al 2 O 3 and HVOF spraying of NiCoCrAlY.

A novel technique and an instrument for on-line, quantitative imaging diagnostics and process control in thermal spraying have been developed and tested in laboratory and industrial conditions. In-flight spray particles are imaged by their natural luminosity with a short-exposure, digital CCD camera system. Particle images are processed using digital image processing techniques in a PC computer. The number of particles per frame and the spatially resolved particle velocities are calculated from the images. Spectrally resolved image information is further used to determine pyrometric two-color particle temperature. A number of different modes of data presentation have been developed. The developed instrument can be used to determine particle number, velocity and temperature distributions of individual in-flight particles from the imaged region of interest of the plume. Dividing the imaged area into smaller sections, spatial distributions of these parameters can be studied. SprayWatch system provides a technically simple, easy to operate, single imaging instrument, which can provide a visual overview of the spray plume in combination with quantitative evaluation of the most important spray particle parameters. In this paper examples of using the monitoring system with plasma and HVOF spraying are presented. Preliminary test results of using a semiconductor laser generated light sheet to detect cold particles is also demonstrated.