The principle of extrusion molding: the metal powder can be extruded at a certain temperature (usually in the range of 40-200 °C) after adding a certain amount of organic plasticizer to mix evenly. This method is called “cold extrusion method”. Or “plasticized powder extrusion”. It is generally extruded under normal temperature conditions. The ceramic powder used for extrusion molding must be mixed with water and plasticizer to prepare a billet before it can be used for extrusion molding. Vacuuming during the extrusion process is beneficial to the discharge of air in the blank, so that the green density of the shaped blank can be increased.
During the extrusion process of the ceramic material, the billet needs to overcome a certain resistance when it moves forward under the extrusion force.
When the billet is extruded to the extrusion nozzle, the flow rate of the billet is accelerated due to the significant reduction of the extrusion section. The portion of the billet that is free from the friction of the die wall in the center flows significantly faster than the portion near the die wall, which causes shear tension in the extruded part, which is called “additional internal stress”.
The existence of additional internal stress can easily cause delamination or cracking of the product. In order to reduce the additional internal stress, the roughness of the inner wall of the extrusion nozzle can be reduced to reduce the friction between the blank and the die wall. Therefore, a reasonable design of the angle of the extrusion nozzle can prevent the flow rate of the blank from changing too fast when entering the extrusion nozzle, thereby reducing its additional internal stress.
Features of extrusion molding: extrusion molding is suitable for forming tubular and cross-sectional parts, the length of the extruded parts is almost unlimited, and the extrusion shape can be controlled by changing the extrusion nozzle. Parts made by this method can have very thin walls, as listed in Tables 3-4. Honeycomb ceramic products, which have been widely used in recent years, are manufactured by extrusion molding.In addition, the extrusion molding method can also prepare thin sheets with a thickness of less than 1 mm, and then prepare parts of different shapes by cutting or punching methods.
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