Phosphor thermometry technology is expected to bring remote, real-time, emissivity-independent temperature measurement in furnaces, hot or cold rolling lines, and processing vessels to better than 3 C (5 F) accuracy from 20 Kelvin to 3,000 Kelvin.

Fig. 1 Overview of the phosphor thermometry system.
Developed as an outgrowth of uranium refining efforts at the Oak Ridge National Laboratory (ORNL), phosphor thermometry is being examined as a non-contact temperature measurement technique to provide reliable, accurate temperature measurement in the steel industry. Temperature is the controlling factor regarding the distribution of iron and zinc during galvanneal steel strip coating, which in turn determines the desired metallurgical properties. Faster feedback on galvanneal quality will reduce product variability, resulting in reduced down-grading of product, which translates into higher operating profits and reduced energy consumption.

This new on-line tool is currently being utilized to monitor galvanneal surface temperatures in-process during the galvannealing operation. Project partners include ORNL, the American Iron and Steel Institute, Bailey Engineers, Inc., National Steel Corporation, the University of Tennessee, and Weirton Steel Corporation. Due to system robustness and its remote nature, it is appropriate for precise process control in hot, high electromagnetic interference (EMI) fields, or corrosive environments. It is also particularly well suited for abrasive and chemical reactive exhaust gas environments. Long term applications are thought to include monitoring refractory in furnaces, measuring melt temperatures, measuring roll temperatures on casters or in the hot mill, and monitoring various coating processes.

Fig. 2 This schematic of the phosphor thermometry system displays the major components and their relative positions.
The overall intent of this temperature measurement technology is to allow on-line, emissivity-independent temperature measurement of irregularly shaped or moving surfaces with temperatures up to 1500ÝC (2732ÝF). In galvannealing, the fluorescent phosphor material is applied to the surface of interest as the product exits the molten zinc bath (Figs. 1 and 2). By applying a thin layer (milligram quantities) of a phosphor whose fluorescence decay rate is a function only of its temperature. It is reported that the instrument is capable of measuring on-line temperature of galvanneal more accurately than any previously available technique.

After the phosphor materials is sprayed, the steel sheet then passes through the galvannealing furnace and the optoelectronics measurement head measures the temperature at the exit of the furnace. The fluorescent phosphor material has been demonstrated to attain thermal equilibrium in less than 0.5 seconds and has been successfully removed or overcoated with no residual damage to the steel surface.

Progress and Milestones

The initial plant demonstration took place in 1996 with the first prototype system providing on-line temperature data with 5¯F accuracy. The Phase II effort was initiated in the summer of 1998 and was aimed at significantly improving robustness and the accuracy of measurement, while reducing instrument size, weight, and ultimate cost. The Phase II demonstration project began in February 1999 and is currently underway.

Future Commercialization

While the technology is not currently available to the commercial market, as it matures, it is possible that the technique will become available in a very compact size at an affordable price. Alternative implementations might include a fiber optic probe device that will allow immersion measurements to be made with similarly high robustness and accuracy.

Gains from the project will be realized with the application of this technology where temperature measurement is important to the economics of a process. Other AISI member companies are working with the team to develop approaches applicable to casting, rolling and other steel-making processes. Other manufacturers, from paper to semiconductors, have approached the team members to inquire about the applicability to their industry. IH