Isostatic Pressing Technology
1. Main equipment for isostatic pressing
The earliest isostatic press in the world was successfully developed by Sweden in 1939. It is still an exporter of isostatic presses. The isostatic press was first used in powder metallurgy (including cemented carbide) and ceramics industry, and was later adopted by the carbon and graphite material industry.
Isostatic pressing equipment is mainly composed of elastic molds, high pressure vessels, frames and hydraulic systems. Elastic molds are generally made of rubber or resin synthetic materials. The size and shape of material particles have a great influence on the life of elastic molds. Mold design is a key technical issue in hydroisostatic pressing. Elastic molds are closely related to the size and homogeneity of products. . Most of the high-pressure vessels are thick metal cylinders processed by machine tools after direct casting of high-strength alloy steel. The steel wire is wound to reinforce the cylinder, etc. The hydraulic system is composed of low-pressure pump, high-pressure pump, supercharger and various valves. At the beginning, the low-pressure pump with larger flow supplies oil, and after reaching a certain pressure, the high-pressure pump supplies oil, and the supercharger further increases the pressure in the high-pressure container. liquid pressure.
2. The operation process of the isostatic pressing process is as follows:
(1) Mold preparation The mold should be made of oil-resistant and heat-resistant materials. For example, a mold made of natural rubber can only be used once or twice immersed in transformer oil. Therefore, when transformer oil is used as the pressure medium, oil-resistant materials are generally selected. Neoprene can also be used to make molds from polyvinyl chloride plastic films.
(2) There are many kinds of raw materials for loading into the mold, such as uncalcined raw petroleum coke powder (binder may not be used), calcined petroleum coke powder mixed with asphalt, and the paste is used after grinding. Calcined petroleum coke is ground into powder and mixed with powdered asphalt. Different raw materials and proportions can be used to obtain different molding effects and different physical and mechanical properties. When charging, it should be vibrated at the same time to make the powdery raw materials preliminarily dense in the mold. After loading the material, shape the mold properly by hand, then plug the other end of the mold with a rubber plug or plastic plug, and tie it tightly with an iron wire to prevent the liquid medium from invading the mold. In order to fully discharge the gas in the powder when it is under pressure, When inserting an exhaust pipe into the powder in advance and connecting an external vacuum pump to produce some spherical products, the powder should be pre-pressed into a sphere by molding method, and then put into an isostatic molding mold of the corresponding size; then Place the mold filled with powder in a high-pressure container, and pressurize after sealing the inlet of the high-pressure container.
(3) Boost and depressurize to start the high-pressure pump, inject the liquid medium into the high-pressure container, and pay close attention to the boost and exhaust conditions. Generally, pressurization is carried out step by step. For example, first raise the pressure to 5MPa and keep it for a period of time. Let the gas in the mold be partially discharged. At this time, the volume of the powder under pressure shrinks, so the pressure in the high-pressure container drops slightly and then rises to about 20MPa again. After part of the gas is discharged, the volume of the powder shrinks again, and then the pressure is raised again to The required working pressure, and keep at the selected high pressure for 20-60 minutes and then reduce the pressure. When the pressure drops to normal pressure, open the inlet of the high-pressure container and take out the mold. You can also use the method of heating the high-pressure container to increase the pressure, because the liquid The heated volume expands, and the pressure automatically increases after heating, but there is a certain limit to this automatic pressure increase.
3. Jiangsu High Industry on the research and development and production of high-performance polyurethane isostatic pressing molds. Through in-depth cooperation with many isostatic pressing equipment manufacturers and in-depth study of the industry, the developed isostatic pressing polyurethane mold series products have the characteristics of long service life, high precision, small deformation, easy demoulding, etc., and are widely used in ceramics, etc. Static pressing mould, cemented carbide isostatic pressing mould, rare earth permanent magnet material isostatic pressing mould, graphite isostatic pressing mould, etc.
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