Ceramic forming is an essential part of the ceramic process, which helps special ceramics to obtain internally homogeneous and densely packed ceramic blanks before sintering. It can be said that the forming process largely determines the homogeneity of the blanks and the ability to prepare complex shaped parts, and has a direct impact on the reliability of the material and the cost of the final ceramic part.
Dry Press Molding
Dry compression molding, also known as molding, is one of the most commonly used molding methods. It is a powder that has been granulated with good fluidity and suitable particle gradation, loaded into a metal mold cavity, and pressed through an indenter, which is displaced in the mold cavity to transmit pressure, causing the powder particles in the mold cavity to rearrange and deform and be compacted to form a ceramic blank with a certain strength and shape.
The properties of the pelletizing powder, such as shape, size distribution and fluidity, have a great influence on the density of the ceramic blank, while the quality of the binder affects the properties of the pelletizing powder. In the dry pressing process, the binder mainly plays the role of bonding, increasing the pseudo-particle size and increasing the particle strength. If it is not added properly, it will be difficult to obtain a high-density blank during dry pressing.
The extrusion process is one of the most common processes used in the manufacture of cross-sectional ceramic products. The process allows extrusion of ceramic powder mixtures at low temperatures and pressures to produce long, equal-section wires, tubes or sheets. In addition to being widely used for the production of bricks, floor tiles, tubes, rods and long parts with equal cross-sections, extrusion can also be used for parts with very complex cross-sectional shapes, the most representative being honeycomb ceramics for automotive exhaust emissions.
The slurry used for ceramic extrusion is a mixture of solid powder and liquid. The basic requirements for the preparation of extrusion pastes are: to contain as little binder as possible to ensure minimal sintering shrinkage, to have good rheology to facilitate molding, and to ensure that the blank has the ability to maintain a certain shape after extrusion. Therefore, when selecting the binder, it is necessary to pay attention to its decomposition, water retention, wettability and shape retention to ensure that the softness, strength and wettability of the ceramic blank can meet the requirements.
Cast molding, first used in paper, paint and plastics, is a long-established molding technology that includes slurry preparation, ball milling, molding, drying, debinding and sintering. Compared with other molding processes, cast molding has the following: simple equipment process, continuous production, small defects in the product, uniform performance, high production efficiency, and is very suitable for the preparation of ceramic parts of large thin plates.
Binder as the only continuous phase in the cast strip, it has the greatest influence on the strength, plasticity, flexibility and smoothness of the cast strip. The binder used in the cast molding method, conformability must be good to ensure the molding accuracy of ceramic sheet, otherwise it is easy to occur sheet cracking, curling and other defects. Specific can be shown as: ① does not affect the solvent volatilization, no bubbles; ② can prevent particle settlement; ③ has a low glass transition temperature; ④ easy to burn off, no residue left; ⑤ will not be bonded to the substrate.
Ceramic Injection Molding Technology
Ceramic injection molding technology is a kind of rapid molding technology for precision ceramic materials, which is characterized by its suitability for preparing ceramic parts with small size, complex shape and high dimensional accuracy requirements, and is capable of automated continuous production. The production process includes the following main steps: mixing, injection, degreasing and sintering. Among them, the binder and degreasing processes are the core of the technology.
The binder for ceramic has two basic roles in the whole ceramic injection molding technology process: to mix uniformly with the ceramic powder, so that it has good fluidity at a certain temperature and injection pressure and can successfully complete the injection molding; in the degreasing stage, on the one hand, it can be quickly and smoothly removed from the ceramic injection sample by a certain degreasing process, and on the other hand, it must maintain the sample intact shape. In order to meet these basic requirements, the binder used in ceramic injection molding is generally a multi-component system. For water-based binders, the following components are generally included: water-soluble polymers, non-water-soluble polymers, surfactants, plasticizers and lubricants.
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