Measurement of Paint Coating Thickness by Thermal Transient Method

This paper is concerned with the accurate laminary determination of the thickness of coatings on metallic surfaces. The development goal was to devise a system that allows for highly spatially resolved full-frame 2-D scans that conventional systems are not able to provide. Furthermore, it is able to allow for a sufficiently large physical separation between the measuring head and the inspected surface to accommodate industrial environments that provide a high operating velocity and is able to detect quality problems of square millimeter in size. The system consists of a heat source that introduces a thermal transient to the surface layer of the specimen, a thermal imaging system to acquire the time-dependent cooling behavior, and an image processing system to determine thermal parameters indicative of surface quality and/or coating thickness. The results clearly show that a thickness resolution of better than 50 microns can reliably be obtained at a scanning velocity of 0.37 m/s, covering a field of view (FOV) of approximately 200 mm × 140 mm.