The sizing nozzle is a functional refractory material for controlling the flow rate of molten steel by continuous casting of less than 120 mm. Since the size of the billet is too small, the long nozzle and the immersion nozzle are not suitable, and the sizing nozzle is used for the open casting in the tundish casting system of the billet continuous casting machine. The injection speed of the billet is adjusted only by the sizing nozzle. During the whole casting process, the aperture must be kept constant to ensure a stable casting speed. Therefore, the sizing nozzle must be safe and reliable during use, except that it cannot be blocked, cracked or peeled off. In addition, the aperture of the nozzle requires a small reaming speed. To meet the above requirements, the material of the nozzle needs to have good erosion resistance, erosion resistance and thermal shock resistance. Therefore, the use of high-grade corrosion-resistant ZrO2 material must be used.
The types of nozzles currently used are as follows:
(1) Fully homogeneous sizing nozzle: The nozzle is composed of ZrO2 (60%~95%). The study shows that the higher the content of ZrO2, the stronger the erosion resistance of the nozzle, the longer the service life and the higher the cost; It is characterized by uniform chemical composition, good integrity, high strength, corrosion resistance, long service life, safety and reliability, but high production cost.
(2) Compound sizing nozzle: The body is a low zirconium material, mostly zircon material, and the composite is a high zirconia material. The two are directly combined together, molded once and fired together. The amount of ZrO2 is greatly reduced compared with the homogenization, the production cost is low, the strength is high, and the corrosion resistance is good. However, since the zirconia content of the inner and outer layers is different, the linear expansion coefficient of the material is different, and the crack is used during use. The possibility is greater, so the zirconia content of the inner layer is not required to be too high, often in the range of 70% to 80%.
(3) Inlaid sizing nozzle: The inlaid sizing nozzle is divided into two parts: the outer casing and the inner core. They are respectively made of refractory mud and bonded together; the nozzle body is generally made of high-aluminum material; the inner core is made of zirconia. The nozzle has low production cost and good thermal shock resistance, and the content of zirconia can be produced according to different requirements, so the product has high cost performance and large usage.