Alumina Forming Process And Key Technical Points

Alumina (Al₂O₃), an important industrial ceramic material, is widely used in electronics, machinery, chemicals, and aerospace due to its high hardness, excellent wear resistance, high temperature resistance, and chemical stability. The performance of alumina products depends not only on their chemical composition but also on their forming process. A suitable forming process ensures that the alumina green body has uniform density, good strength, and the necessary densification for subsequent sintering.

Currently, the main alumina forming processes include dry pressing, isostatic pressing, slip casting, extrusion, and hot die casting. Dry pressing is one of the most common methods, suitable for components with simple shapes and high dimensional precision. This process involves mixing alumina powder with a small amount of binder and then applying pressure (typically tens to hundreds of MPa) in a mold to form the product. Dry pressing has the advantages of high production efficiency and simple equipment, but the density distribution of the green body can be uneven, especially for complex-shaped components.

Isostatic pressing is suitable for applications requiring high green body density uniformity, such as precision ceramic bearings and high-voltage electrodes. This process involves placing alumina powder into an elastic mold and exposing it to a high-pressure fluid (such as water or oil). Densification is achieved through uniform pressure (typically 100-300 MPa) in all directions. Isostatic pressing produces a green body with high strength and uniform density distribution, but it requires significant equipment investment and production costs.

For complex shapes or thin-walled components, slip casting and hot die casting offer advantages. Slip casting utilizes the fluidity of the alumina slurry, allowing the slurry to gradually solidify through water absorption within the plaster mold. This makes it suitable for large, thin-walled ceramic parts. Hot die casting, on the other hand, uses heat to melt a paraffin-based binder, allowing the alumina powder to fill the mold under pressure. This makes it suitable for small, complex, and precision components.

In addition, during the alumina molding process, the choice of binder, particle size distribution, and control of molding pressure all have a significant impact on the final product's performance. Subsequent drying and sintering processes are also critical to ensure the green body achieves the desired density and mechanical properties after sintering.

In summary, the choice of alumina molding process requires a comprehensive consideration of factors such as product shape, dimensional accuracy, production efficiency, and cost. With the development of ceramic materials science, advanced molding technologies such as injection molding and 3D printing have gradually been applied to the production of alumina products, further expanding its application areas.