Aiming at the damage mechanism of the ladle slide, the influence of operating factors on the slide and the advantages and disadvantages of several commonly used slide materials are analyzed.
Key words: ladle slide; damage mechanism; advantages and disadvantages
Before talking about the cause of damage to the ladle slide, let’s have a general understanding of the ladle’s sliding mechanism. The structural diagram of the nozzle and the slide plate is as follows:
The ladle sliding nozzle is composed of a sliding mechanism, an upper nozzle, a slide plate and a lower nozzle. Skateboards are divided into upper skateboards and lower skateboards. The shape of the skateboards depends on the shape required by the mechanism. The upper and lower skateboards can be used interchangeably if they have the same dimensions, but they cannot be used interchangeably if they are different in size. The upper slide is fixed and the lower slide is movable. There are two forms 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 sliding plate is installed in the sliding box, which is compressed by a spring, and the gap between the upper and lower sliding plates is controlled. The sliding plate is usually moved reciprocatingly with hydraulic cylinders and electric push rods to control the flow of the steel stream.
Damage mechanism of skateboard
Thermomechanical damage
During the use of the skateboard, the first thing that occurs is thermomechanical corrosion. The temperature of the skateboard before use is very low. When pouring, the inner hole of the skateboard suddenly comes into contact with high-temperature molten steel (1600°C) and suffers a strong thermal shock (the temperature changes at about 1400°C. ), so a tensile stress exceeding the strength of the slide plate is generated outside the casting hole, resulting in the formation of radial microcracks centered on the casting hole.
The appearance of cracks is conducive to the diffusion, accumulation and penetration of foreign impurities, and accelerates chemical erosion. At the same time, the chemical erosion reaction promotes the formation and expansion of cracks, and this cycle gradually expands and destroys the casting holes of the slide plate. Moreover, the scouring of high-temperature molten steel will damage the refractory material at the friction part with the steel, and cause peeling and block loss.
Thermochemical attack
Thermochemical attack is another major cause of skateboard damage. The refractory materials used for sliding plates are exposed to high temperature molten steel and slag during use, and a series of chemical reactions occur, resulting in chemical erosion. According to the different chemical damage mechanisms of different steel types to the skateboard, and then according to different service conditions, select 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) Oxidation of carbon. There are two main ways to oxidize graphite and carbon: one is that 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 slide plate adhere to molten steel; the other is that oxygen in the air oxidizes carbon Element and molten steel, after the low melting material is formed, the low melting material continues to erode and infiltrate along the pores.
(2) Decomposition of mullite. After use, mullite decomposes to varying degrees and transforms into columnar and crystalline corundum crystals, forming a porous structure, destroying the original dense eutectic structure composed of mullite and plagioclase, making the structure Porosity, tissue deterioration, greatly reduced strength and corrosion resistance, accelerated the damage of the skateboard.
(3) Corrosion of (Mn) and (Fe) on the slide plate. SiO₂ in the slide reacts with FeO and MnO in steel and slag to form low melting point mineral phases 2FeO·SiO₂(1205℃), MnO·SiO₂(1291℃).
(4) (Ca) Damage to the slide. Al₂O3·SiO₂ reacts with CaO in steel and slag to form low-melting 2CaO·Al₂O₃·SiO₂ (1327°C) and 12CaO·7Al₂O₃ (1392°C).
Influence of operational factors on skateboards
There are three main aspects of the damage factors of the operating factors to the skateboard.
One is that the installation of the skateboard is unreasonable. When the skateboard is installed on the sliding mechanism, if there is warping or loose clamping, a large external stress will be generated during use, which will eventually lead to the overall destruction of the skateboard.
The second is that the pouring control flow during production is unreasonable. 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 plate working surface. Especially when manual, the damage caused by human factors to the skateboard is the greatest.
The third is that the operation of burning oxygen is unreasonable. When the ladle is not flowing down during the pouring process, it is necessary to burn oxygen at the nozzle of the ladle. At this time, if the oxygen burning operation is unreasonable, serious oxygen burning erosion will occur. The improper operation in the middle mainly includes ① blowing oxygen when the skateboard is not completely facing the eye, causing the oxygen to directly impact the working surface of the skateboard; ② it is difficult to boil when the drainage sand is not completely flowed out, and blowing oxygen at this time will easily cause the oxygen blowing time to be too long; ③The oxygen pipe is not parallel to the abortion, causing the oxygen flow to scour the side wall of the slide hole, forming a reaming hole, etc. ④ When the turnover time of the ladle is unreasonable, the overall temperature of the ladle will drop, which will cause thermal shock when it is reused;
Skateboards are repeatedly exposed to high-temperature molten steel during use, and the conditions of use are harsh. Therefore, the skateboard is required to have the following properties to ensure that there is no leakage of molten steel between the slides during the casting process. Its structure and performance must generally meet:
(1) The sliding surface is smooth and has good flatness.
(2) High mechanical strength.
(3) Strong corrosion resistance of molten steel and slag.
(4) It is not easy to adhere to molten steel.
Many scholars and steel mills have come up with 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 baddeleyite are used as the main crystal phase, and carbonaceous materials are used as the binder. The advantages of this type of material are large thermal conductivity, small thermal expansion coefficient, and durability. Strong thermal shock resistance.
During the installation process of the skateboard, it is also necessary to clean up the upper and lower nozzles. The inside of the skateboard frame and the mechanism door need to be cleaned without residue. If the skateboard is deformed, cracked or other uneven, it cannot be used.
It is strictly forbidden to clean the ladle by blowing oxygen from the inside to the outside when changing the nozzle. Oxygen cleaning speed should be fast, if any abnormality is found, the slide plate needs to be replaced.
Advantages and disadvantages of several commonly used skateboard
High Aluminum Skateboard
Disadvantages: (1) Poor erosion resistance, severe erosion of sliding surface and gate. (2) The thermal shock stability is poor, and cracks are easy to occur during use.
Aluminum carbon skateboard
Aluminum-carbon skateboards have experienced non-burning aluminum-carbon and fired aluminum-carbon. In order to improve the corrosion resistance and thermal shock stability of the non-fired aluminum 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.
However, the skateboards made of this material gradually have problems such as low thermal strength, severe sliding surface wear and poor crack resistance during use. The disadvantage of firing aluminum-carbon bricks is that they have low thermal shock resistance, cannot be used continuously for many times, and carbon is easily oxidized during use, and their corrosion resistance is low.
Aluminum zirconium carbon skateboard
Aluminum-zirconium carbon slides are developed on the basis of fired aluminum-carbon slides. The sliding plate of this material uses Al2O3-SiO2-ZrO2 series raw materials with low expansion rate, and is made of baddeleyite, mullite, corundum, etc. as the main crystal phase, and the refractory material characterized by carbon bonding, aluminum carbon sliding plate 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 the slide materials commonly used by steel mills at home and abroad, 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 types.
Magnesia carbon and spinel carbon slides
Magnesium slides were first used in Europe, because magnesium oxide has good mechanical stress resistance and chemical corrosion resistance, which meets the requirements of cast calcium-treated steel and high-oxygen steel to a certain extent. However, the thermal expansion coefficient of the magnesium oxide sliding plate is large, and it is prone to thermal spalling when pouring steel, so it needs to be improved in terms of thermal shock resistance.
Spinel carbon sliding plate is a refractory material that uses magnesium-aluminum spinel as the main crystal phase and is characterized by the combination of ceramics and carbon. The thermal expansion coefficient and elastic modulus of magnesium aluminum spinel materials are smaller than that of magnesium oxide, and their thermal shock resistance is stronger than that of magnesium oxide. However, the slow chemical reaction between the spinel material and the calcium in the steel produces low-melting material which affects its service life.
Zirconia sliding plate
The zirconia sliding plate formed by hot pressing has the characteristics of high high temperature strength, low apparent porosity, small pore diameter, etc., and has good corrosion resistance to molten steel when used on the tundish.
Zirconia material has good high-temperature performance, but due to its cost and other reasons, the industry generally adopts zirconia-zirconia rings embedded around the casting holes of aluminum-carbon slides to make composite slides.
