Refractory for steel outlet

1. Characteristics of different steel forms

The ordinary eAF steel outlet is groove steel outlet. Because of the large tilt Angle of the arc furnace and the fast erosion of refractory materials, the arc lining life is low and the steelmaking efficiency is affected. This kind of steel to the ladle scour seriously, also affected the life of ladle; The disadvantage of this steel production is that the molten steel dissipates and is oxidized. Seriously affect the quality of steel; Then it is difficult to leave steel slag out of steel. Because the steel slag can be left out to make better use of the heat to reduce the power consumption, no slag into the ladle, can reduce the erosion of slag on refractories, so groove steel is not conducive to reduce the loss of refractories and reduce power consumption.

In order to overcome these shortcomings, the technology of eccentric hearth ejection was developed in the late 1970s, and the technology of eccentric eaf ejection ejection was used in China in the 1980s. Eccentric furnace bottom steel has the following characteristics :(1) water cooling wall area can be increased, refractory consumption and cost reduction; (2) It can produce steel quickly without diffusing flow, reduce air oxidation, and improve the quality of steel; (3) It is easy to leave steel without slag, which reduces heat loss and erosion of refractories. This can reduce power consumption and improve lining life.

When the gate is closed, fill the outlet with filler from the upper side, and then the charge can be loaded to make steel. When the gate is opened, packing and molten steel are left at the outlet. The gate is a mechanical structure, and the filler is generally magnesium, silicon and olivary refractory. Tail brick is magnesium, corundum - silicon carbide - carbon and magnesium carbon refractory. Sleeve bricks are made of magnesia and magnesia carbonaceous refractory materials. Block brick is oil - impregnated and then combined with magnesia brick. The gap between sleeve brick and seat brick is commonly filled with magnesium seam material. In the process of use, it is mainly the damage of the tail brick and sleeve brick, their life marks the life of the outlet or the replacement times of the outlet.

 

2. Loss mechanism of refractory for steel outlet

Thermal shock peeling and molten steel scouring are the main factors for firing magnesia sleeve brick and tail brick. For MGO-C sleeve brick and seat brick, thermal shock peeling is not the main factor, but the carbon oxidation in mGO-C sleeve brick and seat brick forms a relatively loose decarbonization layer. The molten steel then washes away the decarbonized layer. For some reason, such as power supply is low, not refining furnace and some equipment parts out of order, delayed operation, to stay in the electric arc furnace steel for a long time, or steel temperature is higher, or packing performance is bad, in these cases can make packing sintering, sometimes in the infiltration of molten steel tapping hole packing, solidification and the tapping hole packing welded together, open the tapping hole gate, tapping hole is blocked and is not made of steel. In this case, the oxygen pipe must be used to boil the oxygen out of the steel mouth. This will result in local high temperature and overheating, resulting in thermal shock peeling and mechanical abrasion of the magnesia sleeve brick, resulting in high-temperature chemical corrosion and mechanical wear of the magnesia carbon sleeve brick. This local damage is serious. High quality alkaline fillers should be selected with low output temperature and short time to make steel.

The erosion process of channel steel is such that, because it is exposed to the outside of the furnace, it is subjected to greater resistance to thermal shock and oxidation. Because the slag is produced when the steel is produced, the erosion of the steel trough by slag is more serious. In other words, in the process of steelmaking, the steel outlet tank is oxidized by the air to form a loose decarbonization layer, and at the same time, it is also subjected to the abrupt cooling of cold air, which causes the thermal stress inside the steel outlet tank, and cracks occur in severe cases. In the process of steel production, the molten steel is scour by molten steel and molten slag is corroded, and the heat of molten steel also causes the thermal stress inside the steel trough, and cracks and spalling occur in severe cases.

 

3. Refractory for steel outlet

The steel trough has brick masonry, rammed or poured on site into prefabricated parts. In terms of materials, there are magnesium carbon, aluminum carbon ramming materials, aluminum carbide carbon, asphalt magnesia brick, high aluminum brick and high aluminum castable. In the service effect, the life of carbon - containing refractories is longer. If the properties of magnesium charcoal bricks are better, the life of more than 150 times is quite possible. For the foreign situation, the special report data is less, but we know from the relevant information that Europe USES magnesia ramming material, Magnesia chrome ramming material, bituminous oil-impregnated magnesia brick, Al2O3-O3-SIC prefabricated parts, and in the part of the steel outlet more provide bitumen impregnated magnesia brick or magnesia carbon brick. From this point of view, the steel tank with carbon - containing material had better. Because it is easy to repair, Al2O3-SiC-C quality castable will get a good effect.

Eccentric furnace bottom outlet originally used general magnesia brick masonry, but also with a steel pipe in the middle of pouring, sometimes with a thickness of 25mm thin-wall ceramic pipe or with 2~3 pieces of electric fusion brick composition. However, it is usually after every 50-70 furnaces, a steel tube is placed in the center and a new outlet is made around it with a high MgO content of ramming or pouring material. This material has a low service life and is difficult to maintain. With the development of refractory technology, magnesia carbon brick is commonly used in pipe brick, and steel outlet seat brick is used in addition to pipe brick. This service life is generally in 140~250 times. When the pipe brick wear out, can quickly install the new sleeve brick, and in the surrounding gap filling seam material. The joint material is usually magnesium ramming or pouring material. There are chemical bonds and there are bituminous bonds. Under normal circumstances, the outlet block brick is not easy to break, the main materials used are asphalt magnesia brick and fired magnesia brick and magnesia carbon brick.

It should be pointed out here that the tail brick is subject to strong thermal shock and oxidation, so some steel mills choose aluminum carbide bricks with better thermal shock resistance. In order to improve the service life of tail brick, more attention should be paid to the improvement of antioxidant property.

In order to improve the service life of the steel outlet, maintenance and repair of the steel outlet should be carried out. The repair method is as follows: when the erosion diameter of the outlet is large enough, a magnesium carbon brick pipe (better than steel pipe) or steel pipe is inserted in the middle of the outlet, and then a hot boiling castable is placed to fill the gap between the insert pipe and the remaining brick surface of the outlet. It takes about 1h to repair the steel outlet, and the service life can be up to 30~60 furnaces (magnesium carbon tube) or 5~15 furnaces (steel tube). The castable material is composed of magnesium chrome containing water and magnesium charcoal containing magnesium.