Evaluation of reflectivity of metal parts by a thermo-camera

Abstract

All objects, apart from black-bodies, reflect a part of the incident radiation.The reflected fraction of incident radiation is termed as "reflectivity".The reflectivity of surfaces is often a function of the wavelength, the material, the quality of the surface, and the incident angle of the radiation.In order to evaluate the specular reflectivity of a surface at small incident angles, a method, based on thermal radiation measurement by a thermo-camera, was developed.A quasi black-body, a so-called "Hohlraumstrahler", was realized and used as thermal radiation source.The temperature of the source was continuously monitored by temperature probes at 3 different locations inside the source, while the radiation flux of the source was measured by a thermo-camera.During a calibration process, the temperature data from the probes and the radiation flux measured by the thermo-camera were simultaneously recorded and evaluated.In a next step, the radiation from the source was reflected by the samples and measured by the thermo-camera along with the temperature data from the probes.Using the calibration data, the reflected radiation flux could be calculated.The surface profiles of the samples were also measured by a stylus instrument.The calculated reflectivities were evaluated together with the surface roughness of the samples.The results showed good coincidence with the theoretical model of Bennett and Porteus [1].