Multiwavelength Pyrometer for Galvannealed Steel Sheet Temperature Measurement

Abstract

The multiwavelength pyrometry problem of inaccuracy in determining the true temperature has been analysed in detail. The results of this analysis and a comparison with numerical simulation results show that a proper calculation method of a temperature and a certain knowledge on the emissivity of the target surface are indispensable to an accurate temperature determination. On the basis of this study a new multiwavelength pyrometer for the use of the galvanneal process is developed with a careful design. In spite of the greately changing characteristics of the target surface emissivity in the galvanneal process, where zinc-coated steel sheet is rapidly annealed to produce desirable intermetallic coated layer and the surface of the zinc layer changes from highly specular reflectivity with emissivity near 0.1 to a nearly diffuse reflectivity with emissivity as high as 0.7, this new pyrometer is effectively applied and the measurement accuracy is confirmed to be ±10% for temperature and ±10% for emissivity by laboratory simulations and on-line tests.