Tungsten Copper Power Injection Molding — Key Technologies(2/2)

Water atomization can refine the powder, has higher efficiency, be suitable for mass production, which can be widely used in many fields. However, a powder of irregular shape and size, so that it is easy to form an oxide film on the powder surface, thus affecting the performance of the MIM parts; the powder by aerosol method is spherical, the degree of oxidation of the surface of the powder compared to the formation of low-water atomizing method, but also a lower collection efficiency; From the point of view of the characteristics of the powder, the powder purity carbonyl prepared higher, fine-grained, but the process method subject to certain constraints, and now has only used in pure nickel and pure iron.

2. Adhesive: Except sintering process, the adhesive involved in all steps, and any injection molding process defect can not be obtained from the process to remedy or eliminate, so it played a key role in the tungsten-copper powder injection molding. Overall, the main function of the binder is to increase liquidity and to maintain the shape of the powder product, a powder can be well filled with a complicated shape under the effect of the injection pressure of the cavity. From the base of the sub-species, the adhesive can be divided into oil-based, polymer-based, paraffin-based, thermosetting adhesive gel adhesive, etc. PIM ideal binder should have a viscosity and moderate fluctuations, has a certain rigidity and strength, small weight After cooling, the metal powder has good adhesion and capillary force, the contact angle is small, high chemical stability, non-toxic safety, low thermal expansion coefficient, can be used repeatedly, and so on.

3. Degreasing and sintering process: Degreasing process is in fact warming or incubation stage of gradual removal of the adhesive, so the selection of the binder also determines the process for degreasing. The degreasing time should be shortened as far as possible and ensure that the chemical composites of blank within the permitted range. Degreasing methods can be broadly divided into hot degreasing and solvent degreasing, degreasing hot atmosphere can be divided into hot fat, vacuum thermal degreasing, degreasing and oxidation siphon degreasing, solvent degreasing can be divided into the condensed vapor degreasing and supercritical degreasing. The last process is sintering, which rely on heat treatment and promotes the grains flow and improve the bonding strength of the product sintering temperature, atmosphere, heating and cooling speed and other parameters have a certain influence on the accuracy and performance of the final product.

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