Applications of Cold Isostatic Pressing
Alumina ceramic balls are currently made primarily through isostatic pressing, which has the advantages of low wear and stable product quality. Current applications of cold isostatic pressing technology include daily-use ceramics, architectural ceramics, and special ceramics. Disks, dishes, alumina grinding balls, alumina chemical filler balls, refractory bricks, ceramic sticks, spark plugs, high-frequency porcelain sleeves, composite ceramics, and so on are examples.
Cold isostatic pressing is used to compact graphite, refractories, electrical insulators, and advanced ceramics. The technology is being used in more and more areas, such as pressing sputtering targets and coating engine valve parts to reduce cylinder wear. It is also being used in telecommunications, electronics, aerospace, and the automotive industry, among others.
Detailed Introduction of Ceramic Cold Isostatic Pressing
The pressure that is applied to the powder during cold isostatic pressing comes from a liquid medium, such as water, oil, or a glycol mixture. The powder is put into a mold with a fixed shape to keep liquid from seeping through. Cold isostatic pressing can achieve about 100% of theoretical density for metals, whereas ceramic powders, which are more challenging to compress, can reach about 95% of theoretical density.
In order to produce a green body with adequate strength, the cold isostatic pressing process can apply higher pressure to ceramic or metal powder, up to 100-600MPa at room temperature or slightly higher temperature (93°C). The voids in the powder become smaller or even disappear under the extremely high pressure. Metal powders deform under high pressure because of their ductility, but ceramic powders can be slightly broken up and made denser under pressure, producing green parts that can be handled, machined, and sintered.
Cold isostatic pressing typically occurs at room temperature with pressures between 100 and 600 MPa. A heat exchanger can increase the temperature to about 93°C if higher temperatures are necessary. However, because the temperature of water rises when compressed, it increases by about 4°C for every 100MPa, the risk of boiling at higher temperatures emerges accordingly.
Gas gets trapped between the particles when metal or ceramic powders are compacted. The entrained air will naturally be released following the cold isostatic pressing procedure because metal compacts are extremely strong and ductile, and the pressure builds up with the externally applied pressure during processing.
However, because ceramic green compacts are more brittle, they are more likely to break where air cannot escape if the pressure is released too quickly and without control. By fine-tuning the pressure relief system, which is crucial at lower pressures, the above issue can be prevented by releasing the applied pressure gradually. The trapped air contributes to the internal stress when the externally applied pressure is equivalent to the gas pressure contained within the structure.
Special precautions must be taken in many metal alloy systems to prevent the presence of harmful phases. Rapid cooling to a corresponding safe area is usually necessary to prevent the emergence of dangerous phases; in the absence of rapid cooling, the arisen mixed phase will negatively affect the material's properties, grain growth, and oxides, carbides and nitride formation at grain boundaries.
Due to the fact that ceramics are more brittle and less ductile than metals, controlling the cooling rate and cooling profile is as important or even more important than controlling the cooling rate. Because ceramic components are fragile, there must be enough time for the ceramic powder to crack and restack during the cold isostatic pressing process in order to keep the porosity below 40%.
A gas cooling rate exceeding 3000°C/min is called uniform rapid cooling. Throughout the cooling process, a stable pressure must be controlled and maintained. After the material has been cooled, the temperature can be raised once more to perform a heat treatment on it and achieve the optimal amount of grain growth before the final part is cooled. The best grain size can be achieved and the likelihood of cracking and spalling can be decreased by maintaining pressure throughout the whole cycle.
In this manner, heat treatment becomes very effective in softening, annealing, and even tempering, which ultimately results in the production of better-quality material while simultaneously lowering costs and reducing repeated work as a result of reduced scrap rates. In addition, the heat treatment of the components can be done in the same furnace, which eliminates the need for separate steps of heat treatment such as heating and quenching. This results in a reduction in both the overall capital and operating costs.
Advantages of Cold Isostatic Pressing
(1) Increase the degree to which the product can be consolidated;
(2) Improve the product's mechanical properties;
(3) The data in the production link is relatively centralized, which allows for production to be controlled in a more secure manner;
(4) A low degree of corrosivity;
(5) Highly efficient while maintaining a low cost.