What are the advantages of using unshaped refractory materials for ladle linings?

What are the advantages of using unshaped refractory materials for ladle linings?

Among refractory materials, unshaped refractories have been widely adopted due to their simple production process, low unit energy consumption, and strong adaptability. Steel ladle refractories account for approximately 35% of the total refractories consumed in steelmaking, holding a crucial position in the steelmaking system. Therefore, both domestic and international research on steel ladle lining materials, maintenance, and structure is highly valued to improve service life and reduce steelmaking costs and refractories consumption.

The increase in tapping temperature and the extended residence time of molten steel in the ladle have significantly changed the refractory materials used in steel ladles. Steel ladles were once primarily constructed with shaped refractories, but are now being replaced by unshaped refractories. The shift to unshaped ladles saves labor, enables automated construction and drying in the factory, and improves overall economic efficiency.

The main factor affecting the service life of a steel ladle is the damage to the refractory material. Causes include chemical corrosion and spalling and cracking due to thermomechanical stress. In addition, the material and dimensions of the refractory material, the masonry structure, the size of expansion joints, and refining conditions are all important factors affecting service life.

Monolithic Refractory Materials for Ladle Permanent Layer

The permanent layer of a ladle requires certain slag resistance, as well as good thermal shock resistance, low thermal conductivity, long service life, moderate strength, and high cost-effectiveness. High-alumina castables, medium-lightweight alumina spinel castables, high-purity calcium hexaaluminate castables, and calcium titanate castables have all been applied.

Monolithic Ladle Working Layer

The castable refractory for the ladle wall requires good resistance to slag penetration and structural spalling. The development of bauxite-grade alumina-magnesium (spinel) castables for small ladles has been rapid. Alumina-magnesium castables and precast alumina-magnesium bricks are widely used in large ladles. The method and amount of magnesium oxide addition, the amount of cement, and the amount of silica fume are key research areas for monolithic materials used in ladle wall construction. Alumina-magnesium castables and precast alumina-magnesium bricks each have their advantages and disadvantages under different working conditions.

The main forms of damage to the ladle bottom are cracking and spalling. The ladle bottom bears high pressure from molten steel, making it prone to sintering and slag penetration. Based on this characteristic, alumina-magnesium (spinel) castables with good resistance to slag erosion, slag penetration, and high-temperature volume stability are suitable for the ladle bottom.

Monolithic Refractory Materials for Ladle Slag

Magnesium-carbon bricks are commonly used in ladle slag lines, especially for refining slag lines. Slag line materials should possess excellent resistance to slag erosion, oxidation, thermal shock, and high-temperature strength. Currently, the various slag line castables developed for this purpose still cannot fully meet the requirements, and there is still much work to be done.

Optimization of Ladle Maintenance Mode

Japan’s refractory consumption for ladles is 1.1-1.5 kg/t.s, while China’s is 2-3 kg/t.s, a significant difference. Improving the service life of minor repairs and promoting wet spraying lining technology are key. Measures to improve service life include: the application of externally mounted permeable bricks, hot replacement of permeable cores, hot replacement of inlet nozzles, application of hot ladle bottom repair materials, and application of hot seat brick repair materials. The miniaturization of ladle wet spraying equipment and research on ladle wet spraying materials and accelerators are also important tasks.

Curing and Baking of Unshaped Materials

On-site curing and baking of castables are typically carried out at room temperature to 1100℃. During this process, the main process is dehydration of the castable. The dehydration behavior of the castable during heating is related to factors such as the bonding method, water addition, air permeability, curing conditions, and temperature.

Improving the explosion-proof performance of castables, optimizing baking curves, and developing automated ladle baking machines are also areas of future focus. Among these, high-speed, low-nitrogen, multi-stage baking machines offer better baking results and lower costs than second-generation regenerative baking machines.