[vc_row][vc_column][vc_column_text]Before talking about the reasons for the damage of the ladle slide, we first have a general understanding of the sliding mechanism of the ladle. The structure diagram of the nozzle and the sliding plate is as follows:
The ladle sliding nozzle is composed of a sliding mechanism, an upper nozzle, a sliding plate, and a lower nozzle. The skateboard is divided into upper skateboard and lower skateboard. The shape of the skateboard depends on the required shape of the mechanism. The upper and lower skateboards can be used mutually if they have the same external dimensions, but they cannot be mutually used because of different sizes. The upper slide is fixed and the lower slide is movable. There are two types of movement: linear reciprocating and rotary.
The linear reciprocating sliding nozzle mechanism usually consists of a reference plate, a fixed frame, a movable frame, and a sliding box. The lower sliding plate is installed in the sliding box, compressed by a spring, and the gap between the upper and lower sliding plates is controlled. The sliding plate usually uses hydraulic cylinders and electric push rods to reciprocate to control the flow of steel flow.
Thermomechanical erosion
The first thing the skateboard produces during use is thermomechanical corrosion. The temperature of the skateboard before use is very low. During pouring, the inner hole of the skateboard suddenly comes into contact with high-temperature molten steel (1600℃) and suffers a strong thermal shock (temperature change is about 1400℃) ), therefore, a tensile stress exceeding the strength of the sliding plate is generated outside the casting hole, resulting in the formation of radial micro-cracks centered on the casting hole.
The appearance of cracks is conducive to the diffusion, accumulation and penetration of foreign impurities, and accelerates chemical attack. At the same time, the chemical corrosion reaction promotes the formation and expansion of cracks, and this cycle will gradually expand and damage the casting holes of the sliding plate. In addition, the scouring of high-temperature molten steel will damage the refractory material at the friction part of the steel, and cause peeling and block loss.
Thermochemical attack
Thermal chemical erosion is another major cause of skateboard damage. Refractory materials for skateboards come into contact with high-temperature molten steel and slag during use, and a series of chemical reactions occur, causing chemical corrosion. According to the different chemical damage mechanisms of different steel grades to the skateboard, and then according to different use conditions, choose the skateboard of the corresponding material, which can increase the service life of the skateboard and reduce the cost of refractory materials. The chemical mechanism of Al₂O₃-C and ZrO₂-Al₂O₃-C slide damage:
(1) Carbon oxidation. There are two main ways to oxidize graphite and carbon: one is that the oxygen in molten steel, especially high-oxygen steel, oxidizes carbon to form pores, and then iron penetrates into the pores and makes the surface of the sliding plate adhere to the molten steel; the other is oxygen in the air to oxidize carbon After the low-melting material is formed, the low-melting material continues to corrode and penetrate along the pores.
(2) Decomposition of mullite. After use, mullite decomposes to varying degrees, transforming into columnar and crystalline corundum crystals, forming a porous structure, destroying the original dense eutectic structure composed of mullite and clinoperite, making the structure Porosity, deterioration of the structure, greatly reduced strength and corrosion resistance, accelerated the damage of the skateboard.
(3) (Mn) and (Fe) erosion of the sliding plate. The SiO₂ in the skateboard reacts with FeO and MnO in the steel and slag to form the low-melting mineral phase 2FeO·SiO₂ (1205℃) and MnO·SiO₂ (1291℃).
(4) (Ca) Damage to the skateboard. Al₂O3·SiO₂ reacts with CaO in steel and molten slag to form low melting point 2CaO·Al₂O₃·SiO₂ (1327℃) and 12CaO·7Al₂O₃ (1392℃).
The influence of operating factors on the skateboard
There are three main aspects of damage to the skateboard caused by operating factors.
- One is the unreasonable installation of the skateboard.
When the sliding plate is installed on the sliding mechanism, if there is warping or loose clamping, a great external stress will be generated during use, which will eventually cause the overall damage of the sliding plate.
- The second is the unreasonable pouring flow control in production.
If the flow control is unreasonable during the pouring process (for example, the operation range is too large, the movement is too frequent, etc.), it is easy to cause the sliding, erosion, and steel clamping of the sliding surface. In particular, the damage caused by human factors to the skateboard is the biggest when it is manual.
- Third, the oxygen burning operation is unreasonable.
When the ladle does not flow down during the pouring process, the ladle nozzle must be burned with oxygen. At this time, if the oxygen burning operation is unreasonable, serious oxygen burning will occur. The improper operations mainly include
①The skateboard does not blow oxygen completely to the eyes, causing oxygen to directly impact the working surface of the skateboard;
②When the drainage sand is not completely discharged, it is difficult to boil. At this time, oxygen blowing will easily cause the oxygen blowing time to be too long;
③The oxygen tube is not parallel to the abortion , Causing oxygen flow to flush the side wall of the slide hole, forming a reaming.
④When the ladle turnover time is unreasonable, it will cause the overall temperature of the ladle to drop, which will cause thermal shock when it is used again;
⑤Improper proportion of the fire mud used in the skateboard, uneven mixing, or impurities inside.
The skateboard is repeatedly exposed to high-temperature molten steel during use, and the use conditions are harsh. Therefore, the skateboard is required to have the following properties to ensure that there is no leakage of molten steel between the skateboards during the casting process. Its structure and performance should generally meet:
(1) The sliding surface is smooth and flat. .
(2) High mechanical strength.
(3) Strong corrosion resistance to molten steel and molten slag.
(4) It is not easy to adhere to molten steel. Many scholars and steel mills have come to some measures to improve the longevity of skateboards through practice, and this article also shares some. The first is the material of the skateboard. Generally, corundum, mullite, and oblique zircon are used as the main crystal phase and carbonaceous materials are used as the binder. The advantages of this type of material are high thermal conductivity, low thermal expansion coefficient, and resistance to Strong thermal shock.
During the installation of the skateboard, pay attention to clean up the upper and lower nozzles. The inside of the skateboard frame and the door of the mechanism need to be cleaned without residue. If the skateboard is deformed or cracked, it cannot be used.
It is strictly forbidden to blow oxygen from inside to outside to clean the ladle when changing the nozzle. The oxygen cleaning speed should be fast, and the slide plate needs to be replaced if abnormal conditions are found.
The advantages and disadvantages of several commonly used skateboards of different materials
- High aluminum skateboard
Disadvantages: (1) Poor corrosion resistance, serious erosion of sliding surface and nozzle.
(2) Poor thermal shock stability and easy to crack during use.
- Aluminum carbon skateboard
The aluminum-carbon skateboard has experienced non-burned aluminum-carbon and fired aluminum-carbon. In order to improve the corrosion resistance and thermal shock stability of the non-burning carbon slide plate, synthetic mullite, andalusite and silicon carbide materials are added to the pellets, and corundum and silicon carbide are added to the matrix.
The aluminum-carbon skateboard has experienced non-burned aluminum-carbon and fired aluminum-carbon. In order to improve the corrosion resistance and thermal shock stability of the non-burning carbon slide plate, synthetic mullite, andalusite and silicon carbide materials are added to the pellets, and corundum and silicon carbide are added to the matrix.
- Aluminum zirconium carbon skateboard
The aluminum-zirconium-carbon slide is developed on the basis of firing aluminum-carbon slide. The skateboard of this material uses low expansion rate Al2O3-SiO2-ZrO2 raw materials, made of oblique zircon, mullite, corundum, etc. as the main crystal phase, a refractory material characterized by carbon bonding, aluminum-carbon skateboard It has quite good performance and applicability, but the cracking and sliding surface wear in repeated use are the key to restricting the improvement of its life.
Carbon-bonded aluminum-carbon and aluminum-zirconium-carbon slides are currently commonly used slide materials in domestic and foreign steel mills, but these two slides have poor calcium corrosion resistance when casting calcium-treated steel, and are not suitable for calcium-treated steel, Al/ Casting of Si-killed steel and other steel grades.
- Magnesia carbon and spinel carbon skateboard
Magnesium sliding plates were first used in Europe. Because magnesium oxide has good resistance to mechanical stress and chemical corrosion, it meets the requirements of cast calcium-treated steel and high-oxygen steel to a certain extent. However, the coefficient of thermal expansion of the magnesium oxide slide plate is large, and it is prone to thermal spalling when casting steel, and the thermal shock resistance needs to be improved.
Spinel carbon slide is a refractory material that uses magnesium-aluminum spinel as the main crystal phase and is characterized by the combination of ceramic and carbon. The thermal expansion coefficient and elastic modulus of the magnesium aluminum spinel material are both smaller than that of magnesium oxide, and the thermal shock resistance is stronger than that of magnesium oxide. But the spinel material and the calcium in the steel have a slow chemical reaction, resulting in low-melting substances that affect its service life.
- Zirconia Slide
The zirconia slide plate made by hot pressing has the characteristics of high high temperature strength, low apparent porosity, small pore diameter, etc., and good resistance to molten steel corrosion when used on a tundish.
Zirconia material has good high temperature performance, but due to its cost and other reasons, the industry generally uses zirconia zirconia ring embedded around the casting hole of aluminum-carbon slide plate to make composite slide plate.[/vc_column_text][/vc_column][/vc_row]
