浸入式水口吸入空气机理及吹氩量控制模型

 连铸过程浸入式水口本身及其与上水口连接处容易吸入空气,导致钢水二次氧化,随之可能造成水口结瘤及断浇,导致严重的连铸事故。通过向水口内部吹入氩气可以防止空气吸入,吹氩量控制不当容易引起铸坯缺陷。基于伯努利原理和质量守恒定律建立了从中间包到结晶器的速度-质量模型,探讨了以上部件吸入空气的机理。首先研究了理想与考虑压损2种情况下水口直径、水口浸入深度、中间包液位、铸坯宽度和拉坯速度对水口入口的钢液横截面积与出口的钢液横截面积之比(A_A/A_P)的影响,然后对水口结构进行了优化,并建立了吹氩量控制模型。结果表明,为防止水口吸入空气,应尽量减小水口直径、降低中间包液位和水口浸入深度的高度差、增大拉坯速度和铸坯断面宽度。其中水口直径提高10%,A_A/A_P从2.15增大至2.62;铸坯宽度和拉坯速度对A_A/A_P影响略低于水口直径,同样提高10%,A_A/A_P均从2.15降低至1.96;中间包液位和浸入深度对A_A/A_P影响最小。基于此研究结果,水口结构优化为符合钢液流束的圆台形,并结合水口内真空区体积确定了吹氩量控制模型,使得水口内始终保持微正压。本研究结果为减小甚至消除水口的空气吸入、控制氩气吹入量提供了理论基础,对高品质钢的生产及节能降耗具有重要意义。

Mechanism of air aspiration and control model of argon flow volume for submerged entry nozzle

The submerged entry nozzle and its connection with the upper nozzle are easy to inhale air in continuous casting. Air aspiration leads to the oxidation of molten steel,nodule at the nozzle and serious continuous casting accidents. Argon injection inside the nozzle to prevent air aspiration,improper control of injecting argon is easy to cause defects in slab. Based on Bernoulli's theorem and law of conservation of mass,a velocity-mass model from the tundish to the mold is established,and the mechanism of air aspiration by the above components is discussed. Firstly,the influences of nozzle diameter,nozzle immersion depth,tundish level, slab width and casting speed on the ratio(A_A/A_P) of cross-sectional area at nozzle inlet to cross-sectional area at nozzle outlet are analyzed in both ideal and pressure loss cases. Then,the nozzle structure is optimized and the control model of argon flow is established. In order to prevent air aspiration into the submerged entry nozzle,the diameter of the nozzle should be reduced,the difference between the liquid level in the tundish and the nozzle immersion depth should be decreased,the casting velocity and the width of the cast slab should be increased. Among them,the nozzle diameter has the greatest influence to A_A/A_P. When the nozzle diameter increased by 10%,A_A/A_P increased from 2.15 to 2.62. The effect of slab width and casting speed was slightly lower than that of nozzle diameter. When the slab width and casting speed increased by 10%,A_A/A_P decreased from 2.15 to 1.96. The liquid level and immersion depth of tundish have the least influence on it. Based on the research results,the nozzle structure is optimized in accordance with the flow beams of liquid steel. Combined with the volume of vacuum area in the nozzle,the control model of argon blowing quantity is determined,which keeps the slightly positive pressure in the nozzle. The results provide a theoretical basis for reducing or even eliminating the air aspiration and controlling the argon flow rate,which is of great significance to the production of high-quality steel and energy saving and consumption reduction.