The Extrusion Forming Method of Advanced Ceramics

Squeeze forming is a type of plastic forming method, which generally involves placing vacuum refined mud into an extruder and extruding it into a shaped billet under external force through an extrusion nozzle (also known as a die nozzle).

1 The process principle of extrusion molding

(1) Force analysis of extrusion process

After adding a certain amount of organic plasticizer to metal powder and mixing it evenly, it can be extruded at a certain temperature (usually within the range of 40-200 ℃). This method is called "cold extrusion method" or "plasticized powder extrusion method".

(2) Characteristics of extrusion molding

Extrusion molding is suitable for forming tubular and cross-sectional parts with consistent shapes. The length of extruded sections is almost unlimited, and the shape of the extrusion can be controlled by replacing the extrusion nozzle.

2. The process and application of extrusion molding

(1) The process of extrusion molding

The key process of extrusion molding is the preparation of clay.

In the production process of traditional ceramics, there is no need to add Plasticizer because the blank contains a certain amount of clay, which is inherently plastic. In the production process of advanced ceramics, except for a few varieties of billets containing a small amount of clay, almost all of them use chemical raw materials. These raw materials are barren and have no plasticity. Therefore, before extrusion molding, the blank needs to be plasticized. The Plasticizer used in actual production is generally composed of three substances, namely binder, plasticizer and solvent.

Solvent.

① Adhesives: Adhesives can be hydrophilic or hydrophobic. This requires a high bonding ability when dissolved or melted into a liquid state.

② Plasticizer: Plasticizers are generally used to dissolve organic binders and wet billet particles, forming a liquid interlayer between the particles, thereby improving the plasticity of the billet.

③ Solvent: Solvent can dissolve adhesives, plasticizers, etc., and can form a colloidal substance with the billet. The molecular structure of solvents is similar to them or has the same functional group.

(2) Application of extrusion molding

Extrusion molding is the process of evenly mixing powder, adhesives, lubricants, etc. with water, and then extruding the material out of a rigid mold to obtain tubular, columnar, plate-like, and porous columnar shapes.

3. Factors affecting extrusion molding

(1) Geometric dimensions of the extrusion nozzle

The extrusion nozzle is the most important component of the extrusion mold, which determines the compression ratio during the extrusion process and the shape and size of the workpiece.

(2) Pretreatment of billets

In order to improve the plasticity of the billet and increase the green density of the formed billet, it is necessary to pre-treat the billet. Ceramic billets need to undergo aging or vacuum refining processes before extrusion molding.

(3) Extrusion rate and extrusion temperature

The length of the green body extruded per unit time during extrusion molding is called the "extrusion rate".

(4) Performance of powder

Extrusion molding requires that the Granularity of the powder should be fine, and the shape should preferably be spherical.

4. Mechanical equipment for extrusion molding

The working principle of extrusion molding machinery is to place the plastic mud that has undergone vacuum refining into the cylinder of the extruder, and apply a considerable amount of extrusion pressure through a screw shaft or piston. The mud is then squeezed out of the nozzle mold to obtain a certain shape of the billet.

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