A non-return valve and a metal injection process for achieving high injection velocities when molding low volume articles
Publication Date: 2005-Jan-24
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The present invention teaches a non-return valve and a metal injection molding process for achieving high injection velocities, to assist in complete mold filling, when injection molding low volumetric molded articles. In an embodiment of the invention, a typical ring type non-return valve is configured to have a significantly longer valve stroke (i.e. >5mm, more particularly between 10-20mm), whereby the increased stroke delays the closing of the valve and thus, defers the pressurization of a melt prior to injection. This delay allows the screw to reach an optimal speed prior to injection, such that the melt can be injected at a higher velocity to attain a desired fill time of a molding process. In accordance with an alternative embodiment of the invention, an injection molding process is provided that includes an additional step of screw pullback prior to injection (after recovery), whereby a space is provided for the screw to accelerate in order to attain an optimal velocity prior to melt pressurization. The foregoing process may be implemented with a typical non-return valve (i.e. stroke of 5mm).