Classification of zirconia nozzle tundish nozzle insert

Classification of sizing nozzles for tundish

As a key functional refractory material for billet continuous casting, the sizing nozzle plays the role of controlling the uniform and stable flow of molten steel from the tundish to the mold, stabilizing the billet drawing speed, and maintaining the liquid level in the mold, thereby ensuring the quality of the billet. To improve the efficiency of continuous casting, the quality of its quality directly affects the length of continuous casting time.

The structural design of the sizing nozzle is divided into upper and lower parts, the upper part is approximately streamlined. When molten steel flows to the mold through the sizing nozzle, the approximate streamlined structure design can ensure that the resistance generated by the molten steel and the working face of the nozzle (flowing steel surface) is small. The effect of stabilizing the flow of molten steel to the mold will not cause steel leakage, and this structural design has little disturbance to molten steel, which can reduce and improve the erosion resistance of the nozzle product to a certain extent. Use the time, and improve the service life of the nozzle; the lower part is the sizing section, this design can ensure that the molten steel flows uniformly and stably into the mold from the tundish. During the casting process, the inner diameter of the sizing nozzle for the tundish should remain basically unchanged, because the sizing nozzle plays a role in controlling the flow of molten steel. It affects the production efficiency of continuous casting, so the erosion resistance and erosion resistance of the sizing nozzle is higher.

Classification of sizing nozzles

According to the different content of zirconia in the sizing nozzle, the zirconium sizing nozzle can be divided into two categories: ordinary sizing nozzle and zirconia type sizing nozzle. The content of ZrO2 in the zirconium mosaic of ordinary sizing nozzle is less than 85%; the content of ZrO2 in the zirconium mosaic of the zirconia type sizing nozzle is greater than 85%.

Due to different production processes, ordinary sizing nozzles can be divided into four types: full homogeneous sizing nozzles, direct composite sizing nozzles, vibration forming sizing nozzles, and inlaid sizing nozzles.

(1) Fully homogeneous sizing nozzle

The fully homogeneous sizing nozzle is mainly made of zirconia and a small amount of zircon in a certain proportion by mixing, molding, drying, and sintering at 1620-1650 ℃. Its structure is shown in Figure 2. Since the content of zirconia is 60-90%, its advantages are good uniformity of composition and structure, high strength, high corrosion resistance, and safe and reliable use, but the disadvantages are high production cost and short life.

(2) Direct compound sizing nozzle

The body of the direct composite sizing nozzle is made of zircon, and the working surface of the sizing end of the nozzle is made of zircon and 72%-78% zirconia. The composite part of the body and the working surface is formed at the same time. ℃ once fired, and its structure is shown in Figure 3. The advantages of this nozzle are that it has good integrity, is not easy to fall off when used, and has a much lower production cost than a fully homogeneous sizing nozzle. However, due to the martensitic transformation of zirconia and the accompanying volume change, it is easy to make the nozzle in an Explosion occurs during use. Therefore, this nozzle must use stable zirconia as raw material, but its content should not be too high. There is a difference in the expansion coefficients of zircon and zirconia, and it is easy to cause the nozzle to crack when making the nozzle. In order to avoid this problem, it is necessary to minimize the difference between the expansion coefficients of the two. Therefore, in the working face of the nozzle sizing end, The content of zirconia needs to be controlled at 70-80%, but this is not conducive to the improvement of the life of the sizing nozzle.

(3) Vibration forming sizing nozzle

Its structure is as follows shown in Figure 4. The nozzle is formed by vibrating and pressurizing the pre-prepared nozzle core, high-aluminum material, and iron shell. After forming, it can be dried without firing. The advantage of this nozzle is the simple production and preparation process, the lower production cost, and the disadvantage is that it is easy to cause a steel breakout accident after long-term use.

(4) Mosaic sizing nozzle

The body of the inlaid sizing nozzle is made of high alumina material, and the nozzle core is made of zircon and zirconia. The two are made separately, and then they are bonded together with refractory mud. Therefore, if the runner body and the runner core are not well bonded, the runner core will fall off after long-term use, which will lead to the failure of continuous casting production. it is good.

Ordinary sizing nozzles are prone to problems such as diameter expansion and cracking during use. However, zirconia sizing nozzles are widely used because of their good thermal shock stability and corrosion resistance. According to the particle size of the raw materials used, the zirconia type sizing nozzle can be divided into coarse particle type sizing nozzle, fine particle type sizing nozzle, and ceramic type sizing nozzle.

(1) Coarse particle type sizing nozzle

The zirconia particles selected for the coarse-grain sizing nozzle are larger (up to 2mm), so the advantage of this nozzle is that it has good thermal shock resistance, and it is not easy to burst during use, but the disadvantage is that the compressive strength is low. The porosity is high.

(2) Fine particle type sizing nozzle

The raw material particles of the fine particle type sizing nozzle are relatively fine (particle size < 50μm), so the microstructure of the nozzle is relatively uniform, the advantages are low apparent porosity, high strength, and good corrosion resistance, but the disadvantage is thermal shock The stability is poor, and it is prone to bursting at the moment of pouring.

(3) Ceramic sizing nozzle

The raw material particles used in the ceramic sizing nozzle are very fine (particle size < 5μm), so the nozzle has high strength and low apparent porosity (<5%), but its thermal shock resistance is poor, and it is formed and fired. The manufacturing process is more complicated, and it is easy to burst when used.