In the casting process, ceramic powders and dispersants are first added to a solvent. The mixture undergoes ball milling or ultrasonic oscillation to break up particle agglomerates and allow the solvent to wet the powder surface. Binders and plasticizers are then added, followed by a second ball milling step to obtain a stable and uniform slurry. The slurry is then cast on a casting machine to form a green body (tape). Subsequently, drying is carried out to evaporate the solvent, allowing the binder to form a network structure among the ceramic particles, resulting in a green tape. Product types include: ceramic plungers, ceramic pump cores, ceramic valve cores, ceramic pistons, ceramic bushings, ceramic suction cups, porous ceramics, etc. Materials used include: alumina, zirconia, silicon nitride, and silicon carbide. The green tape is then machined to obtain the desired specific shape. Finally, the finished product is obtained through debinding and sintering processes.
Through the unremitting efforts of researchers in materials science, new water-based tape casting methods have been developed based on the traditional tape casting process, such as gel tape casting, isostatic pressing tape casting, and UV-initiated polymerization casting.
1. Gel Tape Casting Process
Gel tape casting utilizes the principle of organic monomer polymerization. In this method, ceramic powders, dispersants, and plasticizers are added to a mixed solution of organic monomers and crosslinking agents to prepare a low-viscosity suspension with a high solid-phase volume fraction (greater than 50 vol%). After adding initiators and catalysts, the temperature is controlled to trigger monomer polymerization, increasing the suspension viscosity and causing in-situ solidification. This ultimately yields a green body with sufficient strength and suitability for machining.
The gel tape casting process not only significantly reduces the amount of organic substances in the slurry, but also increases the solid-phase volume fraction, thereby enhancing product density and strength. This is increasingly beneficial for building a resource-conserving and environment-friendly society.
2. Isostatic Pressing Tape Casting Process
The solid-phase volume fraction of slurries used in tape casting is relatively high, and the drying process is accompanied by solvent evaporation, which leaves pores in the green tape. As a result, green tapes obtained via tape casting generally have a relatively loose structure and lower density, making it difficult to directly obtain a dense green body through tape casting alone.
Although the green tape obtained by tape casting is not dense and has a loose structure, it possesses good ductility. Therefore, isostatic pressing can be used as a secondary forming process to increase the density of the green tape. However, isostatic pressing equipment is relatively expensive, which adds complexity to the process and increases production costs.
3. UV-Initiated Polymerization Casting Process
To address the shortcomings of the water-based tape casting process, researchers have adopted a UV-initiated in-situ polymerization mechanism. UV-photosensitive monomers and UV photoinitiators are added to the slurry to trigger UV-initiated in-situ polymerization, causing the slurry to solidify in place. Compared to the traditional tape casting process, the UV-initiated tape casting process can be completed simply by adding a UV light source to a standard casting machine, thereby eliminating the drying step, which is often the most critical factor leading to forming failures.
