Development of hard secondary cooling by high-pressure water spray in continuous casting

Cooling intensity in secondary cooling is an important factor for achieving high-speed casting. In this study, we investigated the effects of the hydraulic pressure and water flow rate of a cooling water spray on cooling intensity, and developed a more efficient secondary cooling system with a high-water pressure spray. In laboratory experiments, a test plate was heated to 1 273 K and then cooled below a certain temperature by one nozzle under various experimental conditions. The heat transfer coefficient was estimated using the temperature data from thermocouples 3 mm below the cooled surface. The average heat transfer coefficient with a hydraulic pressure of 5 MPa was 2.8 times larger than that of a conventional water spray nozzle at the same water flow rate. On the basis of the laboratory results, plant trials were carried in the Kurashiki No. 2 CCM at JFE West Japan Works. A high-pressure water supplying device (maximum 5 MPa) with high pressure type nozzles was installed in one segment at a position from 2.5 to 4.0 m below the meniscus and the water flow rate of the high-pressure spray was the same as that of the conventional one. It was confirmed that casting speed was increased by 30% without any inner cracks or surface cracks for several steel grades. In addition, the measurements of slab surface temperature were in good agreement with the thermal calculation results from the laboratory heat transfer coefficient data.