Noncontact measurement of the exit temperature of sheet metal in an operating rolling mill

Abstract

In order to monitor the temperature at the exit end of a hot rolling mill, the Aluminum Association and NIST entered into a Cooperative Research and Development Agreement to use the sheet itself as the basic element of a resistance thermometer. The non-contacting requirement can be satisfied by using eddy current techniques, and the temperature can be deduced from the basic relationship between electrical resistivity and temperature. To convert the measured resistivity to temperature, the temperature dependence of the resistivity of pure aluminum is obtained from laboratory calibration measurements and a temperature independent contribution characteristics of the alloy being produced. The latter is determined from the nominal alloy composition or by making a direct measurement of the resistivity and the temperature at an upstream location when the particular alloy being processed is temporarily held stationary for a contact thermocouple measurement of its temperature. The results of on-line measurements with the eddy current noncontacting thermometer in an operating rolling mill are discussed. These measurements consist of data taken from an entry eddy probe, a contact thermometer, a precise resistivity meter, an exit eddy probe, and a thickness gauge. The entry eddy probe was designed, built, and calibrated by the NIST.