Plastic and nonmetallic article shaping or treating: processes – With step of cleaning – polishing – or preconditioning...
Reexamination Certificate
1999-02-26
2001-07-03
Heitbrink, Jill L. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
With step of cleaning, polishing, or preconditioning...
C264S328600, C264S328190, C425S225000, C425S558000
Reexamination Certificate
active
06254813
ABSTRACT:
BACKGROUND OF THE INVENTION
In the manufacture of plastic objects comprising several raw materials, the essential factor is to mix the materials as well as possible before injection into the mold. This ensures that the two different raw materials form an homogeneous injection molding material.
A generic method is known from the DE-GM 74 14 436. Multi-component plastics, i.e., polyurethanes, are processed by conducting individual components to a mixing chamber via feed lines. At the same time, a mixing chamber is energized. As a result, the mixed plastic also begins to exit from the exit opening of the mixing chamber into the mold cavity.
SUMMARY OF THE INVENTION
Problems with these known techniques, however, arise when two or more reactive materials (e.g. epoxy resins and plastic) are processed. After injection molding the plastic parts, the reactive mixture tends to clog and plug the injection molding apparatus.
According to the present invention an apparatus and method are disclosed that avoids this plugging-effect that plagues conventional systems, even when processing these reactive mixtures.
In general according to one aspect, the invention features a method in which before, during, and/or after the plastic objects have been injection molded, a portion of the first plastic component, the second material, and/or a mixture of the two components is conveyed to at least one storage element with a variable volume. This element adjoins the flow path of the material melt. After completion of the injection molding process of the plastic objects and/or before the material is injected for the next plastic object to be produced, the plastic or the material stored in a storage element with a variable volume is conveyed to the flow path of the melt of the plastic or material. This process frees the melt flow path of a mixture of the two plastic components and/or obtains a desired material mixture for producing the next plastic object.
According to specific embodiments of the invention, before, during, and/or after the injection molding process, preferably non-reactive raw material of one of the processcomponents is thus brought into the storage elements with a variable volume. Then, after the injection molding process has been completed, the material stored therein is again expelled from the storage elements. This process flushes the injection molding apparatus, effectively cleaning it. The material stored in the storage elements can also be used, before the production of the next plastic object, to create clearly defined new mixing conditions for the mixture of at least two components, with which the next object is produced.
Further, the thorough mixing of at least two materials in the mixing element is effected by a mixing motion caused by a mechanical drive, usually an electric or hydraulic drive.
In general according to another aspect, the inventive features an apparatus for injection molding plastic objects comprising at least two different materials. The apparatus comprises a first transport element for transporting a first plastic component and at least a second transport element for transporting a second material, preferably a second plastic component. A mixing element receives the first plastic component and at least one further material. A melt flow path extends from the first transport element and the second transport element to the mold cavity such that the materials enter the cavity of an injection molding tool via the mixing element. At least one storage element with a variable volume is additionally provided. The storage element adjoins the melt flow path of the plastic, the material, or the mixture. The storage element receives the plastic or the material before, during, or after the injection molding process of the plastic objects, and releases the plastic or the material at a later time.
The invention preferably includes tempering elements, which can influence the solidification of the plastic material. The elements are preferably located in the region of the storage element with a variable volume.
Furthermore, to manage the process accurately, the storage element with a variable volume is capable of exactly metering the takeup and/or delivery of plastic or material. The storage element with a variable volume can be disposed in the region of the flow path of the first plastic component, in the region of the flow path of the second material, and/or in the region of the flow path of the mixture of the two components in the region of the entry opening into the mold. In one implementation, the storage element with a variable volume comprises of a piston-cylinder system.
Indeed, the mold could be flushed even without the inventive method and the associated apparatus, by extruding only one component. However, this would have the disadvantage that the volume to be injected could not be measured exactly and would be poorly reproducible, due to the low counterpressure. Furthermore, the injected material would uncontrollably escape into the open. The invention prevents all of this in an advantageous manner.
The above and other features of the invention including various novel details of construction and combinations of parts, and other advantages, will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular method and device embodying the invention are shown by way of illustration and not as a limitation of the invention. The principles and features of this invention may be employed in various and numerous embodiments without departing from the scope of the invention.
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Berger S., et al., “Spüelen mit einer Komponente,”Kunststoffe, Bd. 86, Nr. 2, 1., pp. 186, 188, 190 (Feb. 1996).
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Eckardt Helmut
Ehritt Jurgen
Hill Karl-Heinz
Battenfeld GmbH
Hamilton Brook Smith & Reynolds P.C.
Heitbrink Jill L.
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