Plastic article or earthenware shaping or treating: apparatus – With upstream screen or perforated plate for straining,...
Utility Patent
1999-03-18
2001-01-02
Heitbrink, Tim (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
With upstream screen or perforated plate for straining,...
C264S039000, C425S198000, C425S199000
Utility Patent
active
06168411
ABSTRACT:
BACKGROUND
Generally, polymer injection molding machines include an elongate barrel with a bore extending therethrough. A powered elongate screw is housed within the bore of the barrel. Rotation of the screw within the bore plasticizes and melts polymer pellets fed into the bore from a hopper. In an injection stroke, forward translation of the screw relative to the bore forces a shot of accumulated molten polymer from the bore for injection into a mold.
In some instances, a filter assembly is positioned at the end of the barrel for filtering contaminants from the molten polymer as the polymer is forced in a shot from the bore by the forward translation of the screw. The filter assembly can include a mechanism which removes contaminated filter elements from the polymer flow path and then repositions clean filter elements back into the flow path. A drawback of such a filter assembly is that filtering the molten polymer during the injection stroke of the screw results in a very high flow rate of polymer through the filter assembly which increases resistance to the injection stroke as well as the time required to perform the injection stroke. In addition, the filter elements usually require handling by the machine operator, which, depending upon the design of the filter assembly, can be unwieldly. Previous attempts to position a purgable filter within the barrel to filter polymer prior to the injection stroke in order to avoid these problems require special channels formed within the barrel for purging contaminants from the filter. Such channels can be difficult to manufacture.
SUMMARY OF THE INVENTION
The present invention includes a filtration apparatus for an injection molding machine where the injection molding machine includes a screw housed within a bore for generating molten polymer. The filtration apparatus filters molten polymer prior to but not during the injection stroke of the screw and does not require any changing of filter elements or special channels in the barrel, thereby avoiding the problems discussed above.
In the preferred filtration apparatus, a tip member extends axially from the screw within the bore. The tip member has radially extending upstream and downstream flanges positioned axially apart from each other. A filter encircles the tip member and is capable of filtering contaminants from the molten polymer. An annular ring member encircles the tip member and is slidably positioned within the bore between the upstream and downstream flanges. The ring member is capable of slidably engaging the downstream flange of the tip member for directing the molten polymer through the filter. The filtered molten polymer accumulates within the bore. The ring member is also capable of slidably engaging the upstream flange for preventing back flow of the molten polymer past the upstream flange when forcing a shot of accumulated molten polymer from the bore with forward translation of the screw. An end stop is positioned relative to the bore and is capable of engaging and preventing movement of the ring member past the end stop while allowing the downstream flange of the tip member to be translated forwardly therepast to simultaneously space the upstream and downstream flanges apart from the ring member. This directs the molten polymer past the upstream surfaces of the filter rather than through the filter for purging contaminants filtered from the molten polymer.
In preferred embodiments, the tip member is mounted to the screw and the end stop is an annular surface of an end cap which forms a shoulder when positioned against the bore. In some of the preferred embodiments, the filter includes a series of holes extending within the tip member. The holes in one embodiment extend radially inwardly into the tip member to a central bore in an area between the flanges. In another embodiment, the holes extend axially through the downstream flange. In yet another embodiment, the filter includes a filter screen.
In other preferred embodiments, the ring member includes an inner radial wall and opposing upstream and downstream walls which substantially enclose an annular region. A series of holes extend through the radial wall of the ring member to form the filter. The downstream wall of the ring member includes axial openings for allowing the molten polymer to pass from the annular region through the downstream wall.
The present invention also provides an injection molding machine including a bore and a screw positioned within the bore for plasticizing polymer into polymer melt. The screw is translatable between forward and rearward positions to allow polymer melt to flow and accumulate forward of the screw and to allow injection of the melt with a forward stroke of the screw. A filter is included for filtering polymer melt as the melt flows forward of the screw. A normally closed bypass path for directing polymer melt past the filter is opened during a contaminant purge by forward flow of polymer melt while the screw is in a forward position in which polymer melt is delivered by the screw past the filter and out of the bore.
In preferred embodiments, the screw includes a screw tip having a forward flange and a rearward flange. An axially translatable ring is positioned about the screw tip for controlling the bypass path. The ring is moved forward against the forward flange by forward flow of polymer melt during normal operation to close the bypass path. A restraint formed by a shoulder in the bore restrains the ring from abutting the forward flange to open the bypass path when the screw is moved in the forward position while the screw causes polymer melt to flow forward. The ring abuts the rearward flange to prevent backflow along the screw and through the filter during an injection stroke.
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Dynisco Extrusion, Inc.
Hamilton Brook Smith & Reynolds PC
Heitbrink Tim
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