Roughness Measurements at Small and Uneven Surfaces of Ceramic Foam Filters

This study investigated the possibility of roughness characterization of ceramic foam filters using a laser scanning microscope, examining the influence of magnification, measured area, cutoff wavelength ( λ c ), measured roughness parameter, and position within the ceramic foam on the measured roughness data. Firstly, the effect of magnification on roughness was examined using a Jenoptik RNDH 3 roughness standard, which showed that magnifications of 20×, 50×, and 100× are appropriate. Next, plane samples coated with slurries used to adjust the roughness of ceramic foams were investigated. These samples demonstrated the importance of using a sufficiently large measuring surface, particularly when using line roughness. When surface roughness values are applied, even measuring surfaces of only 1.1‐mm 2 deliver comparable results to larger measuring areas. In addition to the small measurement area, measuring ceramic foams presented another challenge: the high waviness of the samples. To remove the waviness, the cutoff wavelength ( λ c ) should be chosen to be between 0.25 and 0.5 mm. This implies that the proposed roughness measurement procedures do not follow standard procedures. The analysis showed that roughnesses could be differentiated, and the authors suggest relative measurement approach, meaning to use a reference foam filter. Finally, industrial foam filters were investigated, showing differences in roughness depending on the measurement position.