How to choose a binder for different ceramic molding methods|Chemical Study

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How to choose a binder for different ceramic molding methods

Ceramic molding is an essential part of ceramic technology, which can help special ceramics to obtain a uniform and dense ceramic body before sintering. It can be said that the molding process largely determines the uniformity of the green body and the ability to manufacture complex moldings, directly affecting the reliability of the material and the cost of the final ceramic parts.

For special ceramics with different applications, manufacturers often use different molding processes. Whether dry pressing, extrusion molding or strip casting, their effectiveness is strongly related to the choice of binder.

1. Press dry

Dry pressing also called casting, is one of the most commonly used casting methods. It is to place the powder with good granulation, fluidity and proper particle distribution in the metal mold cavity, apply pressure through the printhead, the printhead moves into the mold cavity, transfer the pressure, rearrange and deform the powder particles in the mold cavity and then compacted into a ceramic rod of a certain strength and shape.

Among them, the properties of granulated powder, such as shape, size distribution and fluidity, will greatly affect the compaction of the ceramic body, while the quality of the binder will affect the properties of granulated powder. During the dry pressing, the binder mainly plays the role of adhesion, increasing the size of false particles and increasing the strength of particles. If not added properly, it will be difficult to achieve a high density green body during dry compaction.

When choosing the binder for dry forming, the following factors must be taken into account: thermal decomposition, crushing, strength, demoulding and powder type. To ensure that the above points meet the requirements, it is better to choose a water binder without ash residue, which is safer and more environmentally friendly.

2. Extrusion molding

Extrusion process is one of the most widely used processes in the production of ceramic products with constant cross section. The process can extrude the low-temperature, low-pressure ceramic powder mixture to obtain long wires, pipes or sheets of equal cross-section. The process is widely used in the production of bricks, floor tiles, pipes, rods and long components with constant cross section. The components with very complex cross-section can also be extruded. The most representative is honeycomb ceramic used in car exhaust fumes.

The slurry used for ceramic extrusion is a mixture of solid powder and liquid. The basic requirements for the preparation of extrusion slurry are as follows: containing as little binder as possible to ensure the minimum shrinkage of sintering, with good rheological properties to facilitate formation, while at the same time being able to form a certain shape of the billet after extrusion must be insured. Therefore, when choosing the binder, attention should be paid to the degradability, water retention, wettability and dimensional stability, to ensure that the softness, strength and wettability of the ceramic body can meet the requirements.

At present, more attention has been paid to inorganic binders, such as water-based binders, because of their lower GM quota, GM fire loss quota; and low carbon residue. However, water-based slurry is susceptible to phase separation in the solid and liquid states, leading to the situation that the extruder is blocked due to the increasing extrusion pressure. Therefore, it is necessary to improve the stability of the slurry to improve this situation.

3. Casting tape
Tap casting is a type of casting technology with a long history, which is first used in the field of papermaking, paint and plastics. It mainly includes the processes of slurry preparation, ball milling, mixing, pouring, drying, rubber discharge and sintering. In comparison with other molding processes, tape casting has the following advantages: simple equipment process, continuous production, small product defects, uniform performance, high production efficiency, which is very suitable for the preparation of large-scale thin plate ceramic parts.
As the only continuous phase in tire casting, the binder has the greatest influence on the strength, plasticity, flexibility and smoothness of tire casting. According to manager Zhang, the binder used in the casting process must have good dimensional stability to ensure the molding accuracy of ceramic plates, otherwise the plate is prone to cracking, curling and other defects. In particular, it can be represented as follows: ① it does not affect the volatilization of solvents and does not cause bubbles; Deeltjes particles can settle; ③ it has a lower glass transition temperature; ④ it is easy to burn off and there is no residue behind; ⑤ it does not adhere to the substrate.

4. Ceramic injection molding technology

Ceramic injection molding technology is a rapid prototyping technology for precision ceramic materials, which is characterized by: it is suitable for the preparation of small volume ceramic parts, complex shape and high dimensional accuracy requirements, and can realize automatic and continuous production. The technology manufacturing process includes the following main steps: mixing, injecting, degreasing and sintering. Bonding and degreasing technology are at the heart of the technology.

In the whole ceramic injection molding process, the binder has two basic functions: evenly mixing with ceramic powder, which gives it good fluidity under a certain temperature and injection pressure, and can successfully finish the injection molding; in the degreasing phase, on the one hand, it can be quickly and smoothly removed from the ceramic injection sample by means of a certain degreasing process, on the other hand, it can maintain the completion of the sample. Good shape. To meet the above 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 polymer, water-insoluble polymer, surfactant, plasticizer and lubricant.

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