INFRARED MULTIWAVELENGTH PYROMETRY - APPL ICATION TO METALS

The aim of this work is the temperature measurement of welded metallic materials in order to study the cooling kinetic in solid phase during the welding. To take the constraints of the process into account, a f ast noncontact method is indispensable. Moreover, the emissive propert ies of the metal evolve during the process and cannot be known a prior i. The multiwavelength pyrometry can solve this problem: first the the rmal emission is simultaneously measured at N wavelengths, then a para meter identification technique using a physical or an empirical model for the emissivity leads to the identification of the temperature and the spectral emissivity. We adapted this method to a temperature range between 500 K and the melting/solidification temperature of the metal lic material. Various metallic samples have been studied (steels, tita nium, aluminium). For each sample, the results present a relative devi ation between the identified and experimental (thermocouple) temperatu res of less than 2%, for the more adapted theoretical models. This stu dy does not lead to objective rules for the choice of the emissivity m odel. On the other hand, for some groups of materials (austenitic stai nless steels, and carbon steels), it has been possible to select one o r several models giving suitable results for similar samples.