Application of Laser Optical Measuring Techniques in Coating Processes

Due to permanently increasing demands on the appearance and quality of car body finishes, there is a strong need to obtain much deeper insights into the physical processes during the coating itself and the subsequent film formation. One step to achieve this goal is to apply sophisticated measuring techniques supplying data and information. In the present contribution, the use of optical measuring techniques for the investigation of the spray coating process is discussed, including - Fraunhofer diffraction for measurements of droplet and particle sizes - Laser-Doppler Anemometry to obtain locally resolved droplet or particle velocities - Phase-Doppler Anemometry to obtain simultaneously droplet sizes and velocities In several examples, it will be demonstrated how these techniques can help to clarify the correlations between the properties of the paint spray (mean diameters, velocities, momentum etc.) on the one hand and the quality of the final layer and the transfer efficiency on the o ther hand. Furthermore, the potential for future process otpimisations that is inherent in these techniques is discussed.