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What are the factors that affect the service life of the ladle slide

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This article describes the factors that affect the service life of the ladle slide gate.

Key words: steel ladle; slide plate; service life

The ladle sliding nozzle refractory material consists of upper and lower nozzle bricks, upper and lower plate bricks, and joint mud. The fixed frame of the mechanism holds the upper slide brick in place. The sliding frame houses the lower plate brick and the drain brick, allowing mechanical operation to move them back and forth. This movement controls the flow amount by adjusting the overlap between the upper and lower holes. The tensioning elements of the mechanism press the upper and lower slide bricks tightly together. This pressure ensures no gaps form between the slides during movement, preventing steel leakage accidents.

The ladle slide gate plate repeatedly faces molten steel erosion, chemical erosion, and strong thermal shock. To ensure precise flow control, it must have high temperature resistance, high strength, and good corrosion resistance. It also needs excellent thermal shock resistance, oxidation resistance, and low creep. Specifically, it must meet the following criteria:

  1. It must have sufficient high-temperature strength to withstand molten steel’s static pressure.
  2. The sliding surface must be very smooth, with a flatness of no more than 0.05mm, ensuring tight contact during casting.
  3. It must resist erosion, corrosion, and maintain good thermal stability, withstanding rapid temperature changes and molten steel and slag erosion.

Factors Affecting the Service Life of Ladle Sliding Plate

Effect of thermal stress and external force

Before pouring molten steel, the temperature of the ladle slide gate plate brick is about 200-350°C; after pouring, the temperature of the casting hole of the slide gate plate rises rapidly to above 1500°C within a few seconds, and the slideboard is subjected to severe thermal shock. Under the action of thermal stress, cracks are inevitable. If it is used in multiple furnaces, it will inevitably undergo repeated thermal shocks, which will easily cause cracks and peeling off on the working surface of the sliding brick. According to Ringery’s thermoelastic theory, the initial thermal stress cracking coefficient R can be seen in formula (1). Once a crack is generated, it will continue to expand. The resistance coefficient RST of this crack stress follows Hasslman’s theory of fracture mechanics, see formula (2).

R=S(1-μ)/Eα(1)

RST=[γ(1-μ)/E0α2]1/2(2)

In the formula: S is the tensile strength; E is the elastic modulus; μ is Poisson’s ratio; E0 is the elastic modulus without cracks; α is the thermal expansion coefficient; γ is the fracture energy.

Equations (1) and (2) show that the greater the initial thermal stress cracking coefficient and resistance coefficient of cracking stress of the material, the smaller the thermal expansion coefficient and elastic modulus of the material, and the harder it is for cracks to generate or expand. The thermal stability is better.

The impact of high temperature molten steel and slag erosion, erosion and oxygen burning to clean casting holes

Molten steel and slag erosion during pouring expand the slide plate casting hole diameter. Melting loss and erosion also expand the casting hole. This causes refractory material loss at the slip mark. Pouring high manganese steel worsens the issue. Manganese in molten steel reacts with the slide plate refractory. See formula (3) and formula (4).

MnO+SiO2=MnO SiO2(3)

MnO+Al2O3=MnO·Al2O3(4)

According to the MnO-Al2O3-SiO2 phase diagram, MnO·SiO2 is a compound with a low melting point. However, no liquid phase is formed, but only a slight increase in the content of MnO in the working zone of the sliding plate, which changes the original structure of the corundum in the sliding plate. When pouring calcium-treated steel, SiO2 and Al2O3 in the slide plate are reduced by calcium in molten steel, and the reactions are shown in formula (5) and formula (6).

2[Ca]+SiO2=2CaO+Si(5)

3[Ca]+Al2O3=3CaO+2Al(6)

The generated CaO reacts with SiO2 and Al2O3 in refractory materials. According to the CaO-Al2O3-SiO2 phase diagram, the melting point of 2CaO·Al2O3·SiO2 is 1584°C. CaO·Al2O3 melts at 1600°C, while 3CaO·Al2O3 melts at 1539°C. CaO 2Al2O3 has a melting point of 1762°C, and 12CaO 7Al2O3 melts at a much lower temperature of 1392°C.

These low melting point compounds can turn into a liquid phase within the pouring temperature range. The resulting liquid phase continuously loses along with the steel flow. This enlarges the casting hole and damages the slide plate. Even without forming a liquid phase, these compounds increase the calcium content of the slide plate working belt. This changes the structure of the slide plate refractory material. It leads to a decline in the slide plate’s performance and affects its service life.

During the process of burning oxygen to clean the casting holes, the oxides of iron in molten steel are in direct contact with the nozzle, and diffuse to the inside through pores and cracks, and react with the corundum and mullite phases in the sliding bricks to form silicates with low melting points, see Formula (7) and formula (8).

2FeO+SiO2=2FeO SiO2(7)

FeO+Al2O3=FeO·Al2O3(8)

FeO·Al2O3 has a melting point of 1780°C and forms a spinel reaction layer around corundum particles. Fayalite (2FeO·SiO2) melts at 1205°C and remains liquid at steel pouring temperatures. It continuously flows away with the steel, causing the cast hole to expand and damaging the slide.

Effects of sliding resistance, oxidation and slag metal infiltration

When the ladle slide gate plate works, friction causes wear between the upper and lower boards. To prevent steel leakage, the contact surface must be very tight. A specific surface pressure of 0.5-1.0N/mm² is required. Molten steel and slag metal erosion increase friction in the slip mark area. This causes the slip mark to become rough. Adjusting the steel flow can generate turbulence, aggravating wear. This results in steel infiltration between the slide plates.

When the temperature exceeds 500°C, carbon oxidation reduces material strength. This roughens the surface and increases friction. In severe cases, steel breakout can occur.

LMM YOTAI established in 2007. Our production technology comes from Japanese Yotai. As an experienced and international player in the refractories industry. We have succeeded in expanding both the breadth of its product range and the depth of its services. From raw material selection, refractory portofio & optimization, installation & services & recycle of used refractories on site to further reduce client’s Opex & Capex in refractory consumption per ton steel output, meanwhile improve product quality of client.

Our Product have been supplied to world’s top steel manufacturer Arcelormittal, TATA Steel, EZZ steel etc. We do OEM for Concast and Danieli for a long time

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