Development Of Testing System For Nozzles And Optimization On Secondary Cooling System Of Billet Continuous Casting At NanSteel

The secondary cooling system has an important status during continuous casting process, it not only relates to the product quality directly, but also affects caster output. Therefore, establishing a proper secondary cooling system (including choice of nozzle type, arrangement manner and control model for water distribution) has a significant role in continuous casting.This paper introduced the new equipment developed for testing characteristic of nozzle by improving the existing testing system. Through a series of improvement, the testing system has increased the accuracy of the water flow density testing, and decreased the testing error of system. The cold state characteristics of water nozzles and air-water nozzles from NanGang billet caster were tested. The flux characteristic, spraying angle, water flow density and impacting force distribution of the nozzles were present. Through the comparison of four different type air-mist nozzles, the best air water ratio in a condition and the relation of water flow density and water flow were obtained based on the testing results.The solidifying heat transfer model of billet has been established, and its boundary conditions have been optimized according to the circumstances of NanGang billet caster. The results of temperature and billet shell thickness testing indicate that the calculating results of model were in good agreement with testing results, and the solidifying heat transfer model was feasible. The dynamic control model of secondary cooling water adjusts the water distribution by casting speed, uses the straightening point temperature to feed back in order to make proper water adjustment in unsteady state condition. Through the comparison of the straightening point temperature and target temperature, there is a feed back signal to adjust the water distribution so as to guarantee better quality of the billet, until the straightening point temperature in a range of target temperature.In addition, the paper analyzed the problem of the existing secondary cooling system according to the billet quality defects of different types of steel which contains free-cutting steel, high-carbon steel, medium-carbon steel, low-carbon steel at NanGang. Optimizing scheme of secondary cooling water distribution has been put forward on the basic of water rate cooling request of different types of steel and the straightening point target temperature. Then low-carbon steel has been chosen for temperature proof and macroscopic billet quality survey. The results indicate that the quality of billet has improved greatly, and the optimizing scheme has effectively settled the quality problem related to the secondary cooling.