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A non-return valve and a metal injection process for achieving high injection velocities when molding low volume articles

IP.com Disclosure Number: IPCOM000035558D
Publication Date: 2005-Jan-24
Document File: 4 page(s) / 501K

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The IP.com Prior Art Database

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EP0946319: PATENT [+4]

Abstract

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).

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A Non-Return Valve and a Metal Injection Process for Achieving High Injection Velocities when Molding Low Volume Articles

Abstract

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).

Background to Invention

In regards to molded articles (i.e. part) produced by means of metal semi-solid injection molding, the processes for their production are typically classified in terms of a thickness of the molded article produced thereby (i.e. thick or thin).  When contrasted, the processes themselves may be most readily distinguished in terms of the time required to fill the molding cavity (i.e. to avoid premature melt solidification). In particular, a thick walled part is typically produced with a process that includes the step of filling of the molding cavity within a relatively leisurely range of nominally 40-50ms.  However, when molding thin walled parts, the required fill times are much lower, nominally in the range of 10-20ms.  Consequently, the molding of the thin-walled parts are often attempted on larger units, having both a barrel of greater cross sectional area and higher injection velocity.

However, the process of molding thin walled parts with a very small volumetric fraction are also characterized by correspondingly short injection piston strokes. As such, accelerating and decelerating a screw (or piston) within such short distance not only places stress on the mechanical components, but also lowers the shot-to-s...