EXPERIMENTAL AND THEORETICAL-STUDY OF SUR FACE POLLUTION INFLUENCE ONTHE RADIATIVE PROPERTIES OF ROLLING STEEL SHEETS - APPLICATION TO CONTINUOUS ANNEALING FURNACE

Experimental and theoretical study of surface pollution influence on t he radiative properties of rolling steel sheets. Application to contin uous annealing furnace. The purpose of this research is to study the s urface pollution influence on the radiative properties of rolling stee l sheets. The surface pollution resulting from rolling operations is c onstituted of oil and thin particles of iron and is similar to a semit ransparent medium. This residual film modifies the infrared absorption of the iron sheet and its heating kinetics during its thermal treatme nt within the continuous annealing furnace. We developed an experiment al device to measure the directional spectral emissivity of sheets und er industrial thermal treatment conditions. This device is composed of a spectroradiometer and an annealing simulator. It allows to heat the samples up to a temperature of one thousand Celsius degrees and to de termine the radiative properties in a spectral range between 2 and 14. 5 mu m. This device also allows transmittivity measurements of the sem itransparent medium in order to determine its absorption coefficient. We elaborated a model to calculate the radiative transfers in an isoth ermal semitransparent medium, for an unidimensional geometry. This mod el uses the discrete ordinates method which offers the advantage to ta ke into account the high anisotropies of the radiative properties at t he interfaces. The polluted sheet emissivity increases strongly compar ed to a clean sheet, even for thin films. The modification of these ra diative properties causes an important over-heating of the strips with in the annealing furnace.