Development of an emissivity compensation algorithm for radiometric temperature measurement during the galvanneal process

uring the galvanneal process, zinc-coated steel sheet is rapidly annealed in order to improve the characteristics of the final product. The zinc layer changes from highly specular liquid zinc with a spectral emissivity of approximately 0.2 to a largely diffuse intermetallic layer with a spectral emissivity as high as 0.8. These rapid emissivity changes preclude standard radiometric measurement techniques. The objectives of the research were to explore the behavior of the spectral emissivity during the process as influenced by the heating cycle and metallurgical properties of the product and to develop an appropriate dual-wavelength emissivity compensation algorithm to accurately infer temperature.;The galvanneal process was simulated in the laboratory for 63 samples, and in situ emissivity and temperature data were obtained using a dual-wavelength radiation thermometer at spectral bands of 2.18 and 2.4 ;Iron analysis results indicated that emissivity increased with increasing iron content. Final iron content varied from 5-13%. Optical and mechanical roughness measurements indicated that surface topography is not the dominant mechanism affecting emissivity changes. Arithmetic roughness values varied from 1-3...