Abstract
The emissivity change due to oxidation is very important information to measure accurate temperature by a pyrometer in steel making process, for example continuous annealing line of cold rolled steel. We have measured the behavior of spectral emissivity in detail during oxidation process. The behavior is very complex and it is difficult to compensate for change in emissivity. In order to compensate for emissivity in steel making process, we have proposed a new method. This method depends on both Kirchhoff's law and the characteristics of surface reflection of cold rolled steel. We have measured surface reflection of cold rolled steel sheets which had three kinds of surface roughness. The angular distribution of reflection mostly concentrates in a normal direction even with the roughest surface steel. 85-93% of hemispherical reflection is measured by reflection from normal to 35 degrees. Emissivity can be accurately estimated by measurement of reflection intensity from steel sheet surface.
We have manufactured a compact and practical pyrometer, in which specular and diffusive reflection components have been measured by photodiode separately. The accuracy of emissivity is ±13%, and the accuracy of temperature is ±10°C with the temperature range of 650-900°C in both laboratory experiments and continuous annealing line.
