1. Raw material quality
Chemical composition: The alumina content must meet the requirements of the corresponding refractory grade. Generally speaking, the higher the alumina content in the high-aluminum material, the better the refractory performance of the refractory material. For example, for some high-grade high-aluminum refractory bricks, the alumina content may need to reach 70% or even higher. The content of impurity elements must be strictly controlled because these impurities will reduce the high-temperature performance of the refractory material. For example, too much alkali metal oxides (potassium oxide, sodium oxide) may form a low-melting point liquid phase at high temperatures, causing the refractory material to soften and deform prematurely. It is also necessary to pay attention to the content and proportion of other main components such as silicon dioxide in the raw materials. The appropriate silicon-aluminum ratio has an important influence on the phase composition and performance of the material.
Particle size and particle grading: The particle size of the high-aluminum material must meet the production process and the performance requirements of the final product, and there must be a reasonable coarse and fine combination. If the particles are too coarse, the density of the green body after molding may be poor, affecting the strength and refractory performance; if the particles are too fine, the green body may have poor air permeability and cracking and other defects may occur during the drying and firing process. Through scientific particle grading, such as the use of continuous grading, small particles can fill the gaps between large particles, which helps to improve the packing density of the green body and thus improve the overall performance of the finished refractory material.
2. Molding process requirements
Binder selection: Select a suitable binder according to the specific type of high-aluminum refractory material and the use conditions. Common ones include clay binders and phosphate binders. Clay binders are relatively low in cost and can give the green body a certain plasticity and bonding strength, which is conducive to molding; phosphate binders can make the product have better high-temperature strength and other properties, which are suitable for some occasions with demanding high-temperature performance requirements. The amount of binder added must be precisely controlled. If the amount added is too little, the green body will be insufficient in strength after molding and it is easy to loosen; if the amount added is too much, too many impurities may be introduced, or the high-temperature performance of the product may be affected. For example, some binders decompose at high temperatures to produce too much gas, causing problems such as loose product structure.
Molding pressure control: Different high-aluminum refractory products should be subjected to appropriate molding pressure according to their shape, size and use requirements. For example, when making high-aluminum refractory bricks, appropriate pressure can compact the blank, improve its density and strength, and ensure the dimensional accuracy and appearance quality of the brick. If the pressure is too low, the density of the blank is not enough, and the finished product is prone to quality problems such as corner loss and edge loss; while if the pressure is too high, the mold may be damaged, and for some blanks with special structures or brittle materials, internal cracks and other defects are prone to occur.
3. Firing process requirements
The reasonable firing temperature should be determined based on the characteristics of high-aluminum refractory bricks materials and the performance indicators of the target refractory materials. Generally speaking, as the firing temperature increases, the mineral phases in the high-aluminum refractory can be better sintered, which helps to improve the strength and refractoriness and other properties. However, too high a temperature may lead to overburning, such as deformation and cracking of the product, and may also cause undesirable conditions such as decomposition of some mineral phases, affecting product quality; if the temperature is too low, the blank is not sintered sufficiently, and the performance indicators such as density and strength cannot meet the requirements.
The heating rate and holding time during the firing process also need to be strictly implemented in accordance with the process regulations to ensure that the products are heated evenly and have stable and reliable performance.
