Tundish refractory

(1) Structure and overview of tundish

Tundish's function is to stabilize the temperature of molten steel and make the molten steel inclusions float up. When the cylinder water is short or the ladle is replaced, continuous casting can be guaranteed to run smoothly. The capacity of tundish is 15%~30% of ladle. Each continuous caster is equipped with 7~12 tundish. Tundish comes in two forms, the T-shape and the boat shape.

The temperature of molten steel of tundish is 1510~1570℃, and the service life of permanent lining is 200~1000 times, more than 1000 times abroad. Erosion lining to achieve a continuous casting and easy to turn the bag. The service life of ordinary special steel tundish is 2~10h, while the service life of ordinary carbon steel tundish is increasing, and has reached 20~40h, and now some have reached more than 70h. Thermal insulation lining with clay brick or thermal insulation board, there are many steel mills do not use thermal insulation lining, permanent lining is generally used for 60%~80% alumina content of low cement or ultra-low cement castable. Erosion lining with magnesium coating, insulation board and dry ramming material. The tundish is covered with an aluminum-silicon castable containing 60% alumina. High aluminum castable prefabricated blocks or high aluminum bricks for impact zone. At present, there are also magnesium prefabricated blocks or magnesium carbon bricks. Slag weirs are made of magnesia prefabricated parts and high aluminum prefabricated parts, but nowadays high aluminum is used less and less. In this respect, slag buckets and air curtain retaining walls have also been developed. More importantly, the development of tundish metallurgy, including the development of CaO tundish. The plug rod is made of aluminum carbon as a whole, but may also be mounted in segments. The sizing nozzle is zirconium, and there is a tendency to combine the brick with it. The upper vent is aluminum-carbon and calcined mullite. The slide plate is aluminum carbon or aluminum zirconium carbon.

 

(2) Development of continuous casting technology

In China, the continuous casting level is getting higher and higher, and the drawing speed is also getting faster and faster. With the development of the market, the requirement of steel quality is higher and higher, so the proportion of producing clean steel and special steel is also larger and larger. In order to reduce the cost and improve the yield, the service life of continuous casting tundish is longer and longer, and the near-terminal continuous casting represented by thin slab and strip is developed, and the proportion will be higher and higher. China has langang, Handan Steel, Zhuzhou steel and other steel mills began thin slab continuous casting, and some steel is also in the planning. Development of the tundish metallurgical technology for the purpose of ensuring that the molten steel is not polluted in the tundish and further improving the purity of the molten steel. In order to meet the needs of clean steel production, high drawing speed, near terminal continuous casting development and tunplate longevity, continuous casting refractory materials with high corrosion resistance, thermal shock resistance, no coalescence, no pollution of molten steel, and even can improve the purity of molten steel must be developed. This puts forward stringent requirements for refractory materials for high alkaline tunic lining and cladding wall immersion nozzle and sliding nozzle systems.

In the production of construction steel - based long - process production lines, steel supply is adequate. In order to reduce costs and improve benefits, the service life of tunic is required to be better and better. For the longevity of tunic, the development features of the tunic refractory are as follows :(1) zirconia content and volume density of the diameter nozzle for billet continuous casting reaches 94% and 5g/cm, which can be used for more than 30 hours. Domestic this respect still has certain gap. However, the rapid replacement technology of nozzle has been developed in Our country, which plays a promoting role in improving the service life of tundish and promoting the development of tundish refractories. (2) In order to meet the requirements of longer and longer service life of tundish and clean steel, tundish working lining is developed from silicon insulation board to alkaline coating of tundish. In alkaline coating, magnesium calcium coating is more suitable for the production of clean steel. At present, magnesium casting plate with high density can be used for more than 50h. Some high performance coatings, service life can be up to 2.70g/cm of high density tundish coating, service life can be expected to achieve better results. Now some steel mills and refractory plants have also developed the dry tundish ramming vibrating material, and the results of continuous casting 77.5h, 147 furnaces have been achieved. This kind of dry tundish ramming vibrating material is actually added solid resin or some inorganic solid binder. After preventing the mould and vibration from ramming, the binder in the dry material is liquefied or solidified by heating the inner mould to improve its strength. Then the mold is removed and the oven is heated for use. The method is troublesome to heat with mould and with mould. Although its density and other properties than the current general coating is higher, but than the casting board and high density coating still have a certain gap. So there may be more room for high density coatings and cast alkaline magnesium plates to increase the working life of tundish liners. But the dry tundish is easily made into magnesia-calcium tundish with vibratory ramming materials, and very good results have been obtained. And general wet magnesia-calcium coating CaO is more in the form of CaCO3 and slushies, CaCO3 should be in 1000℃ above to ensure decomposition, which is adverse to the baking and service life of tundish. (3) Refractory for tundish permanent lining. It mainly plays the role of safety and insulation. The longer service life of tundish castable is required whether it is longevity tundish or not. At present many steel mills permanent layer use clay brick, its service life is low, generally in 200 times or so, safety is not enough. Therefore, permanent layer castable is currently developed. Al2O3HANLIANG generally USES 60%~75% al si castable. In order to facilitate the construction, there is a tendency to develop from vibrating castable to ultra-low cement self-flowing castable. After maintenance, its service life reaches 1500 furnaces.

Most of the damage of tunic permanent layer is due to :(1) insufficient thermal shock resistance. In the course of use, the crack and spalling are caused by temperature fluctuation or the steel slag penetrates into the crack and the steel slag is embedded in the castable, which causes the difficulty of turning over; (2) Poor slag penetration resistance. In the process of use, the slag penetrates into the castable and promotes sintering, which results in structural spalling under temperature fluctuation. (3) High temperature performance of castable is poor. It may be sintered at a lower temperature, which will cause the spalling of the castable sintering layer near the coating layer. (4) Some tundish slag erosion is very strong, the working layer erosion, and erosion of the castable layer, so that it will be difficult to turn over the bag and the service life of the decline. According to these conditions, the solution of slag penetration, thermal shock resistance and erosion resistance is the key point to improve the service life of tundish castable. Through acting U, we developed Al2O3 about 70% aluminum-silicon castable. When the service life of 35T tunnage of Baosteel reaches 639 times, the surface is very smooth and seldom corroded. If the maintenance work is done well, the service life can reach more than 1000 times. When the castable lining before improvement is used for 200~300 times, the surface will be seriously sintered and spalling, and the service life after repair is only about 440 times.

 

(3) Refractory for purifying molten steel

A Tundish slag dam

In order to prevent slag from forming nonmetallic inclusion in molten steel, a slag weir is set up in the tundish. High aluminium materials were used in the early stage of development, and magnesium slag weir has been widely used now. In order to make the slag dam itself adsorb molten steel inclusion, it tends to develop towards magnesium-calcium slag dam. Experiments are also being carried out to bubble up molten steel inclusions by blowing argon in tundish furnaces. Once this method is successful, it is possible to remove the slag dam.

B Filter

Its material has mullite, rigid jade, zirconium, CaO, and so on. No matter what the material of the filter, have a certain purification of the role of steel. Relatively good quality of CaO. By installing the filter, the flow field of molten steel is changed so that the impurities float up, which is more effective than the filter itself to absorb the inclusions.

C Magnesium calcium coating for tundish

The oxygen and sulfur in molten steel and inclusion index decreased by 37% with magnesium calcium coating

D tundish nozzle

Corundum - mullite and aluminum - carbon materials are commonly used. In order to prevent clogging when casting aluminum-killed steel, aeration nozzle with argon blowing is provided. In the aspect of the tundish nozzle for long life, some internal zirconium compound is used to insert the diameter nozzle into the tundish nozzle, so that the service life can be greatly improved.