Plastic and nonmetallic article shaping or treating: processes – With step of making mold or mold shaping – per se
Reexamination Certificate
1999-11-19
2001-08-07
Kuhns, Allan R. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
With step of making mold or mold shaping, per se
C029S458000, C029S460000, C029S527500, C164S027000, C264S317000, C264S338000
Reexamination Certificate
active
06270710
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a process for manufacturing objects of synthetic resin.
In FR-PS 1 366 921 a process is disclosed for the manufacture of thermoplastic parts made by injection molding with at least one opening to a hollow cavity. For this purpose the molten thermoplastic material is injected into a mold which consists of strong material of good thermal conduction, and in which at least one core is provided which consists of a hard material and is resistant to collapse and deformation during injection molding, but begins to melt at a temperature that is between the deformation temperature and the resoftening temperature of the thermoplastic material. After injection molding the shaped object with the core is heated to a temperature between the deformation temperature and the softening temperature of the shaped object so that the core will melt out without melting the thermoplastic material, in order thus to remove the core from the casting. An alloy of bismuth and tin is named as the material for the remeltable cores. After melting out, the metal is usable again and is supplied again to the casting process.
Furthermore, DE-OS 26 28 390 discloses a method and an apparatus for producing one or more hollow sand cores for casting molds. These so-called shell cores are made by mixing thermosetting binding agent with sand. This sand is shaken in a heated core box and after the core surface has hardened the entire core box is rotated 180° and the excess sand that has not hardened is poured out. In this manner hollow cores are obtained which are more economical than solid cores due to the lesser amount of material and their quick preparation.
A disadvantage of the known state of the art is that, for one thing, a solid core requires the use of a large amount of material, but on the other hand the use of hollow cores, especially when metal is used as the core material, is complicated and at the same time there is no assurance that a uniform wall thickness will be maintained.
SUMMARY OF THE INVENTION
The invention is addressed to the problem of avoiding the aforementioned disadvantages and providing a process for manufacturing objects of synthetic resin which while using a small amount of material, will permit great accuracy of the cores and hence of the component being made.
This problem is solved by the invention as described and claimed hereinafter.
A process for manufacturing a hollow synthetic resin product is known from DE 41 21 441 in which half-shells or halves of a core are made of water-soluble resin. These halves, however, must additionally be sprayed with a water-resistant resin. After the hollow plastic product is made the non-water resistant resin is washed out, while the water-resistant resin remains in the synthetic resin product.
In contrast thereto, the advantage of the invention is that the partial shells of metal permit a seamless joining together and additional elements or additional spraying or wrapping are not necessary.
According to one embodiment of the invention the partial shells are pressed or squeezed together. It is also possible to affix the partial shells together via an undercut in the manner of a snap fastening. Of course, the metal of the partial shells can also be welded or cemented to each other.
If desired, the partial shells can be sprayed or coated with a lacquer or a hardenable liquid after assembly. The purpose of this layer is to improve the strength or the surface of the synthetic resin object after the core has been melted out of the synthetic resin object.
If the half shells or partial shells have a very large hollow interior cavity, it is possible to provide support by means of an internal structure. This structure is composed, of course, of the material of the cores and is removed from the hollow synthetic resin object when the cores are melted.
These and additional features of preferred embodiments of the invention will be found not only in the claims but also in the description and the drawings, and the individual features can each be realized individually or together in the form of subcombinations in embodiments of the invention and in other fields, and may constitute advantageous as well as independently patentable embodiments, for which protection is hereby claimed.
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Bartel Walther
Cedzich Wolfgang
Vaculik Robert
Veigel Richard
Crowell & Moring , L.L.P.
Filterwerk Mann & Hummel GmbH
Kuhns Allan R.
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