A Novel Structure of Blackbody Cavity Sensor for Continuous Measurement of Molten Steel Temperature

Abstract

For continuous measurement of molten steel temperature, this work proposed a novel structure of blackbody cavity sensor to overcome the shortcomings of the traditional sensor. The traditional sensor had slow response speed and poor thermal shock resistance, which was due to its double layer tubes and thermal stress concentration in the closed bottom of an inner corundum tube respectively. The double layers included an outer protective tube of Al2O3-C refractory and the inner tube which formed the blackbody cavity and isolated the fume generated by the outer tube. The novel structure was composed of a measurement cavity of an Al2O3-C tube and a fume exhaust system. The fume exhaust system, including an inlet, an exhaust pipe and two outlets, eliminated the fume influence of obstructing the optical path. Furthermore, the fume exhaust system was based on the relationship between the fume and temperature distribution. Results showed that the fume formed below approximately 1 320°C, meaning the fume existed in and above the slag layer in the internal cavity of the sensor. The open bottom of the exhaust pipe should locate at the interface between the slag layer and molten steel to remove the fume. Additionally, the sensor should dip into molten steel up to 220 mm for high accuracy. It improved the response time from 340 to 240 seconds and enhanced the thermal cycling times from about 4 to beyond 10 times.KEY WORDS: blackbody cavity; molten steel temperature; novel structural sensor.

A Fast Response Sensor for Continuously Measuring Molten Steel Temperature

“…A fume exhaust system uses N 2 to remove the fume generated by the support unit, which has been investigated in previous work. 9) The temperature measuring unit of the cermet tube only should suffer the thermal shock and molten steel corrosion. It avoids the molten slag corrosion that is suffered by the Al 2 O 3 -C support, which has been solved in the development of the traditional Al 2 O 3 -C sensor.…”

“…This temperature measuring accuracy is equal to that of the traditional sensor. 9) The response speed of the fast sensor is tested in Nanjing steel factory (in China) as illustrated in Fig. 11(a).…”

“…(2) In order to solve the cost problem, a blackbody cavity sensor has been developed, which is currently the most widely applied technology. [8][9][10] In detail, it dipped a measurement tube into molten steel with a certain depth, and then reached thermal equilibrium with molten steel to form an online blackbody cavity approximately. Meanwhile, it generates a stable infrared signal that is received by a probe for representing the temperature.…”

“…Meanwhile, it generates a stable infrared signal that is received by a probe for representing the temperature. To meet the demands of strong thermal shock resistance and corrosion resistance in the destructive environment, both of the above sensors almost use carbon-containing refractories, [5][6][7][8][9][10][11][12] such as Al 2 O 3 -C, MgO-C, and ZrO 2 -C. Al 2 O 3 -C refractory is the optimal practical material, which hasn't the hydration problem of MgO-C refractory and has lower price than ZrO 2 -C refractory.…”

Design and analysis on fume exhaust system of blackbody cavity sensor for continuously measuring molten steel temperature

“…1 (c)), 11 which is composed of a measuring cavity with single layer tube (Al 2 O 3 -C) and an active fume exhaust system. The fume is removed as the arrows: a gas enters into the inner cavity from the inlet and passes the exhaust pipe with an open bottom, then takes away the fume out of the sensor through the outlets.…”