Threaded lid injection mold release

Details Threaded lid injection mold release Threaded lid injection mold release

1998-06-01

2001-06-05

Pyon, Harold (Department: 1722)

Plastic and nonmetallic article shaping or treating: processes

Mechanical shaping or molding to form or reform shaped article

Shaping against forming surface

C264S334000, C249S059000, C425S418000, C425S451400, C425S577000

Reexamination Certificate

active

06241931

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates plastic injection molding, and in particular, to injection molding large container lids having threads for attaching the lids to a container.
BACKGROUND OF THE ART
Large containers, for example, in the 10 to 20 liter (2.5 to 5.0 gallon) size, have been produced in the past where the lids screw onto the containers. Such lids have been produced by injection molding them in molds that have an annular thread-forming ring. When the lid has been molded and the mold opened, the lid is removed from the mold by rotating the annular ring, effectively to unscrew the mold from the lid. A difficulty with this method of molding these lids, however, is that the thread-forming annular ring has to be sealed in the mold during the molding process. In the past, this has been done by using large diameter O-rings. The problem is that such O-rings deteriorate or wear out very quickly due to the rotation of the annular ring against the O-rings.
The present invention overcomes these problems by eliminating these large O-rings. The thread-forming annular ring is made stationary in the mold and a rotatable mold center section spins the lid after it is molded to unscrew the lid from the mold.
SUMMARY OF THE INVENTION
According to one aspect of the invention, there is provided, a threaded lid injection mold comprising a cavity mold portion defining the outer shape of an injection molded lid and core mold portion defining the inner shape of the injection molded lid. The cavity and core mold portions mate to define the shape of the lid and include means for injecting plastic into the mold to form the lid and means for separating the mold portions to permit removal of the molded lid. The core mold portion includes a stationary thread forming annular ring and a co-axial rotatable center section located inside the annular ring. The center section includes axially disposed engagement surfaces for turning the molded lid upon rotation of the center section after a lid has been molded and the mold portions have been separated. Also, drive means are provided for rotating the center section.
According to another aspect of the invention there is provided a method of injection molding a threaded lid comprising the steps of providing a mold having mating cavity and core mold portions to define the shape of the lid. One of the cavity and core portions includes a stationary thread-forming annular ring. The mold portions are closed and plastic is injected therein to form the lid. The mold portions are opened and the molded lid is spun to unscrew and release it from the thread-forming annular ring. The molded lid is spun by providing a mold center section axially located inside the annular ring. The center section includes axially disposed engagement surfaces for engagement with a lid injection molded in the mold. The lid is spun by spinning the center section.


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Weast, Robert C., ed. CRC Handbook of Chemistry and Physics 58th edition, CRC Press Inc. pp. B-10, 11; B-54,55.

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