A Novel Principle for Molten Steel Level Measurement in Tundish by Using Temperature Gradient

Molten steel level is difficult to measure as a result of high-temperature medium and the covering flux. The characteristic of the steelmaking process is that a strong stratification of the temperature gradients is formed between different layers. Thus, temperature gradient is proposed as the principle for measuring the molten steel level. According to the new principle, a refractory material sensor is inserted into the tundish to sense the temperature distribution of the different layers. After adequate heat transfer, the sensor is lifted, and an area charge-coupled device camera is used to capture the temperature distribution of the sensor through radiation thermometry. Then temperature gradients for the different layers are extracted from the sensor and utilized to identify the molten steel level. However, there is a problem that lifting of the sensor destroys the original temperature distribution and gradients before lifting. For this issue, finite element method software ANSYS is adopted to theoretically analyze the temperature decline of the sensor during the lifting process. Due to radiation, the decay rate of the temperature on the sensor surface is the fastest, disabling the acquirement of the original temperature gradients for the different layers from the sensor. A temperature field restoration method is proposed by extracting the highest temperatures of all the thermal images during the lifting process. Based on the restored temperature gradients, sequential clustering is utilized to identify the molten steel level. Verifications with numerical data and thermal images from the actual on-site applications demonstrate the effectiveness of the new principle and measuring method.