What are the refractory materials for continuous casting-part 2

Refractories for horizontal continuous casting equipment

1. Separation ring

Horizontal continuous casting of steel is a new technology with broad development prospects. It has the advantages of simple equipment, low investment and convenient operation. In addition, the tundish is directly horizontally connected with the mold, which can effectively prevent the secondary oxidation of molten steel (prevent the liquid steel and injection of ladle and tundish, and the contact between the liquid steel in the mold and air to produce oxide film or oxide slag scale), and reduce non-metallic inclusions and surface defects in the slab, So as to ensure the quality of continuous casting slab.

The advantages of horizontal continuous casting equipment compared with traditional arc continuous casting 

(1) Due to the horizontal layout of equipment, the fuselage is low and the infrastructure investment is low.

(2) High billet quality. Because the tundish is directly connected with the crystallizer, secondary oxidation is prevented, and inclusions in steel are easy to float on the tundish, which improves the cleanliness of steel.

(3) It can be directly cast into small billets (such as 70mm square billets) or even wire billets of several millimeters. Therefore, the end product can be obtained with a small rolling ratio, which greatly shortens the metallurgical production process.

(4) Good safety and reliability. Due to the horizontal arrangement of the equipment, once the leakage is pulled, the burning loss of subsequent equipment is small, and a special leakage monitoring device is installed in the horizontal continuous casting to monitor the leakage. At present, horizontal continuous casting is suitable for small and medium-sized steel mills and electric furnaces to produce small section billets.

In horizontal continuous casting, "separation ring" - the sealed connection between tundish and mould is a key functional refractory. The connecting part should be sealed to realize sealing pouring, and also serve as the starting point of solidification at the front of molten steel crystallization. The "artificial liquid level" starts to solidify around the molten steel from entering the separation ring, and then the condensate shell is separated from the separation ring to form a billet in crystallization. The main functions of the separation ring are:

(1) Sealing connection between tundish and crystallizer;

(2) Prevent the mold from being blocked by solidification due to the drop of molten steel temperature;

(3) Determine the solidification position of the primary shell of the mold.

2. Conditions for separating ring

The separation ring is located in the sealed connection between the tundish and the mold, which is easy to be eroded by molten steel. If an "inverted bell mouth" is formed, the billet cannot be pulled out. Therefore, the material used should not only withstand the impact of high temperature, but also be easy to process, so as to make it closely match with the copper sleeve of the mold. At the same time, the separation ring is in contact with the high-temperature molten steel and the low-temperature copper sleeve of the water-cooled mold under the working state, so it plays the role of bearing the thermal stress and the mechanical stress caused by the external load of the surrounding environment.

The separation ring and its material shall meet the following main conditions:

(1) It is not easy to be wetted by molten steel, so that the billet can be separated from the separation ring smoothly.

(2) High temperature mechanical strength, wear resistance and erosion resistance.

(3) The separation ring bears large temperature gradient and requires good heat shock resistance, anti peeling and stable volume. In addition, since both sides of the separation ring are immersed in molten steel, if the separation ring peels or cracks, the front shape of the cast-in-place shell will be unstable and uneven. In severe cases, the front edge of the blank shell is bonded with the separation ring, which can not be "separated", so that the blank shell is broken.

At the same time, the use of separation ring should also pay attention to:

1) Bake and preheat to prevent cracks;

2) Moisture proof, the separation ring contains B2O3, which will generate h3bo4 after moisture absorption, and release moisture during baking and use, resulting in cracking and damage of products;

3) Anti oxidation; The antioxidant capacity of BN Based separation ring is poor. If the preheating and baking temperature is too high or for a long time, the separation ring will swell or blister on the oxidation surface, affecting the service life.

3. Refractory material for RAM

The ram used for horizontal continuous casting is similar to the sliding plate of sliding nozzle. The ram used for horizontal continuous casting is double plate, that is, it is composed of two rams. One of the ram is connected with the tundish nozzle and the other is in contact with the mold nozzle. There is a flow steel hole in the middle of the two rams. Before pouring, the two rams block the steel flow holes of tundish and mold nozzle respectively.

During pouring, the two rams slide downward at the same time to make their copper flow holes consistent with the steel flow holes of tundish and mold nozzle. At this time, the copper water in the tundish enters the ram hole through the tundish nozzle, then enters the mold nozzle, and finally enters the mold through the separation ring. At this time, the blank drawing starts. When the pouring is completed, the two rams slide up at the same time, blocking the copper flow port of the tundish nozzle and the mold nozzle, so as to prevent the molten steel from entering the mold. Then the tundish is removed and one ram is taken away, and the other ram is connected with the mold nozzle to prevent the molten steel from flowing back from the mold. The ram connects the preceding and the following and plays an important role in safe casting and ensuring quality.

Its performance shall have the following points:

(1) Resistant to erosion and scouring of molten steel and slag.

(2) It has high mechanical strength and wear resistance.

(3) It has good thermal shock resistance.

(4) It has high flatness and smoothness.

At present, RAM materials mainly include ram containing 85% ZrO2, RAM containing 65% ~ 75% ZrO2, and high aluminum carbon zirconium corundum carbon composite ram. The price of zirconium gate is high. In order to reduce the cost, Al2O3-C and Al2O3-ZrO2-C composite gate are developed and tested in horizontal continuous caster in steel plant. The ram is not cracked or rarely cracked. The flow steel hole is smooth, there is no sediment, the erosion is very small, and the erosion amount per hour is about 0.3mm.