MULTIWAVELENGTH PYROMETER FOR GALVANNEALED STEEL SHEET TEMPERATURE-MEASUREMENT

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.