Plastic and nonmetallic article shaping or treating: processes – Mechanical shaping or molding to form or reform shaped article – Shaping against forming surface
Reexamination Certificate
1998-10-13
2001-01-23
Heitbrink, Jill L. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Mechanical shaping or molding to form or reform shaped article
Shaping against forming surface
C264S328100, C264S334000, C425S556000
Reexamination Certificate
active
06177041
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a new and improved apparatus and method for forming a plastic cap of the type used with five gallon water bottles. More particularly the invention relates to the mold for forming such a cap and the method whereby the cap is fabricated.
2. Description of Related Art
Caps resembling the cap illustrated in the drawings and hereinafter described have been molded on injection molding equipment for many years. The particular cap referred to is similar to part of the disclosure in U.S. Pat. No. 5,232,125. By reason of the molding apparatus and method of the present invention, the cap may be made much more rapidly and with less use of material.
SUMMARY OF THE INVENTION
The cap shown in some of the drawings and hereinafter described is of a particular style known as “non-spill”. The well of the cap is closed with a plug and the cap is applied to a bottle such as a five gallon bottle used for spring water and the like. It will be understood that the present invention may be used in the fabrication of other caps wherein there is a top and a skirt depending from the periphery thereof.
The molds hereafter described may be installed in conventional plastic injection molding machines. The molds and the method of forming the cap make possible the use of thinner walls throughout the cap resulting in reduction in the weight of material. In addition, the cycle time for operation of the molding machine is substantially reduced. Reduction in cycle time and reduction in weight are great economic advantages. By way of example, the weight of a cap in accordance with the present invention may be reduced from approximately 13 grams to approximately 8 grams and the cycle time may be reduced from about 15 seconds to about 8 seconds by practice of the present invention.
One of the features of the invention is that the cap is ejected from the mold by pushing upward against the bottom edge of the cap skirt, whereas previously a push pin has pushed against the top of the cap. A push pin method of ejection requires the top wall thickness be much greater then actually necessary for cap function. Otherwise unacceptable top “doming” on ejection will result. A further disadvantage of using a push pin to push up against the underside of the top of the cap is that the top tends to be deformed upward resulting in the upper portion of the skirt being stressed to pull inwardly against the mold, thereby increasing the force necessary to eject the cap and thereby requiring thicker walls. In accordance with the present invention, by pushing upward on the bottom edge of the skirt, the stress on the cap top is considerably less and inward distortion of the skirt of the cap is avoided. This makes possible the thinning of the wall thickness of the cap skirt. Increased wall thickness results in substantial material requirements for prior art closures.
Another feature of the present invention is that in practical effect the core around which the cap is molded does not employ parts which slide relative to each other. In previous mold constructions, the interior of the skirt is defined by a core which is hollow and within the hollow is a push pin which slides relative to the core during a portion of the cycle of operation. Since in accordance with the present invention the parts do not move relative to each other, cooling of the mold is much improved and heat transfer through relatively moving surfaces is avoided.
Still another advantage of the invention is the fact that the parting line between the cavity portion of the mold and the core part of the mold coincides with the bottom edge of the cap skirt. Such a construction makes it possible to include ribbing or design material on the outside of the lower portion of the skirt.
Another feature of the invention is that the stripper ring which originally is in contact with the core and the core have mating upwardly inwardly tapering surfaces. Accordingly when the stripper ring moves upward relative to the core there is no potential for galling which might inhibit movement of the parts. One of the problems with molds heretofore used to fabricate caps of the type used with the present invention is that the parts of the mold tend to gall inasmuch as there are three separate parts in the “lower” part of the mold, all of which must move relative to each other. Further, because the parts slide relative to each other, heat transfer between the mating surfaces is poor because there must be sufficient clearance between the parts to permit such movement. These problems are solved in accordance with the present invention.
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patent: 5609894 (1997-03-01), Rathbun
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Rosato, Donald V. et al., Injection Molding Handbook, second edition, pp. 312-313, 1995.
Flehr Hohbach Test Albritton & Herbert LLP
Heitbrink Jill L.
Portola Packaging, Inc.
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