Multispectral radiation thermometry
Abstract
Quality control during the processing of materials at elevated temperatures requires accurate measurement and control of temperature. However, in processes such as the continuous annealing of steel and the extrusion and rolling of aluminum alloys, temperatures must be measured using methods that do not require physical contact with the metal. As radiation thermometry does not require contact during the measurement of temperature, the aim of the present study was to measure the temperatures of specimens of steel and aluminum in simulated processing conditions and to use the results to develop and test multispectral radiation thermometry emissivity compensation algorithms that would accurately infer temperature. The study involved measuring the spectral radiance of selected specimens; developing and evaluating emissivity compensation algorithms (experimentally and numerically), and examining the extents to which the algorithms reproduced the measured temperatures. The spectral emissivities of the aluminum alloys studied (1100, 2024, 2224, 5052, 7075, and 7150) were typically metallic in their behavior, decreasing in value with increasing wavelength in the 1.9 and 5 μm range. An algorithm adapted from the Hagen-Rubens emissivity relationship (HRR) gave inferred errors of ±7 K with specimen temperatures in the range 600 to 740 K. The emissivities of the steels, heated to temperatures up to 1000 K in a reducing atmosphere to simulate continuous annealing, were also metallic in their behavior. Use of the HRR algorithm for the entire set of steel specimens gave the largest error of 27 K and an average error of −8 K with a standard deviation of 8 K. These results demonstrate the viability of the HRR algorithm for the processing conditions and metals examined and the success of the application to aluminum alloys prompted the development of a new radiation thermometer, which, when tested in and extrusion mill, gave results similar to those obtained in the present laboratory study.
Degree
Ph.D.
Advisors
DeWitt, Purdue University.
Subject Area
Mechanical engineering
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