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The injection forming technology of alumina ceramics


Alumina ceramic or ceramic, special ceramic, or high technology ceramics. It is the height of the selected raw materials, production in accordance with the special manufacturing process, can be precisely controlled chemical compositions and having excellent properties of ceramic. At present, the alumina ceramic mainly in the use ofhigh technology and cutting-edge industries, such as electronics, aerospace, nuclear reactor, MHD power generation, artificial bone and artificial joint. Alumina ceramic in the manufacturing process, should meet the following three requirements. The selection of raw materials to the high purity, fine particles as possible; strictcontrol of chemical composition. The manufacturing process to prevent contamination and the component itselfvolatile, to strictly control the sintering particle size, interface, porosity, to achieve the quality stable andreproducible; the precise shapes and dimensions. Alumina ceramic parts are generally not processed, used directly, especially ceramic electronic device requires a higher precision.

Alumina ceramic and the common ceramics are very different in composition and manufacturing process.Ordinary ceramic raw material preparation, blank forming and firing three steps; and the alumina ceramic mostly by powder sintering production. In the forming technique, because the ceramic hardness, difficult to cutprocessing, especially for complicated shape non type products, such as the turbocharger rotor of automobile engine, bones, teeth and other biological ceramic products, in the forming and sintering of later is finished, no longer processing. In order to meet this requirement, process for production of plastic parts injection people imitate polymer material forming industry, processing of alumina ceramic products, achieved satisfactory results.

Technology of ceramic injection molding, is adding thermoplastic resin, thermosetting resin in the ceramic powder,plasticizer and friction reducing agent, the ceramic powder become viscous body, and then heating the mixedslurry mixing from nozzle into the metal mold, cooling and solidifying into. Commonly used thermoplastic resinpolyethylene, polystyrene, polypropylene, adding 10-30%. This technique greatly improves the forming complex shape product accuracy and reliability.

Equipment, injection molding

Injection molding machine (or general plastic by injection device), clamping device, hydraulic device and electronic, power control device. According to the type of plasticizer internal structure of devices of different, can be divided into the plunger and the parallel propeller. In recent years, is generally believed that the latter has more.

Injection molding machine is electronic, power control device for the center, at the same time driven hydraulicdevice makes the plasticizing device, clamping device orderly work. The working procedure is: ceramic materialsby the funnel into, into the cylinder, the raw materials in the cylinder end send people at the same time, melting,mixing, the cavity injection nozzle to the mold cylinder end in blank. The control system of foreign advanced uses screen display mode (such as CRT, plasma, electroluminescence, liquid crystal using), and design graphicsconsole mode or a combination of the two composite console mode.

Mold materials commonly used Gao Jie, wear resistance, corrosion resistance high alloy steel. Die design should accord with the flow characteristics of ceramic polymer systems. In order to reduce the molding shrinkage, avoidthe die body air into shape, so die to control the export account. In the cyclic products, on the side of gate is easy to produce a weld line, so also should pay attention to the gate location. In order to make the injection conditionoptimization, and meticulous management of pressure sensor temperature management and mold need to rely on the mold, barrel in the. In addition, the mould should be cooling trough, can rely on cooling and heating,temperature regulator makes the mold temperature is kept constant, was effective in improving the moldingaccuracy. As the raw material to use large amounts of organic material, in order not to make the blank heat cracking, no residual carbon slag degreasing is a important project.

Two, technology

Ceramic injection molding principle and plastic injection molding is basically the same. Just a plastic inner mixed large ceramic powder. In order to improve the injection molding conditions, must be organic material selection and use of raw materials to match, and to the selected amount. In order to obtain compact and uniform injection molding, ceramic powder concentration is higher. But too high will make the forming performance variation. In order to improve the liquidity of mixing material, should reduce the dispersant viscosity of polymer system. As pretreatment is very important to improve the dispersion of ceramic powder, in order to enhance the liquidity of the polymer, the need to add the appropriate plasticizers and lubricants.

The size of ceramic raw materials for the general 1 ¦Ì m, adding adhesive (or additives), after full mixing, stirring. Process flow injection molding see below

In the mixing process, ceramic powder by adhesive wetting and cladding, all become complex uniform are injection molding. And need cooling, drying, crushing, was suitable for injection molding machine hopper feed particles.

In the following four aspects should be paid attention to and master the technical problems in the process of.

Mobility 1, raw materials

Injection molding ceramic particles used in general by the 80-90% (important than, the same below) adhesivepowder and 10 to 20%. The binder in the degreasing process removed, so add the amount to a minimum is appropriate, but should pay attention to if the adding amount of the shortage will affect the forming effect. In addition, the liquidity of the ceramic particles in the particle size is smaller, the more deviation from the spherical shape is worse. Therefore, using as much as possible simple method to test for liquidity.

2, the conditions of forming defects

Forming conditions and if not, will produce various defects