Swage-forming of container threads

Abstract

A method of making a plastic container having a threaded wide-mouth finish includes providing a preform having at least an exterior surface of molded polyester construction. The preform is placed in a mold cavity having a first portion for forming a container body, a second portion adjacent to the first portion for forming a cylindrical finish wall without threads, and a third portion adjacent to the second portion for forming a trim dome or moil. The preform is expanded within the mold cavity to form a one-piece intermediate product that includes a body, a cylindrical wide-mouth finish wall and a moil. After removing the intermediate product from the cavity, the moil is severed from the end of the finish wall. At least one thread is then formed on the finish wall by engaging the finish wall with at least one thread-forming tool, which may be heated to facilitate the forming operation.

Description

[0001] The present invention is directed to wide-mouth containers, and more particularly to a method of forming threads on a container finish of polyester construction, particularly PET. BACKGROUND AND SUMMARY OF THE INVENTION [0002] In the manufacture of plastic containers, such as monolayer or multilayer PET containers, it is conventional to mold a container preform having a body and a finish with one or more external threads. The finish typically is molded to its final geometry in the preform, while the body of the preform is subsequently blow molded to the desired geometry of the container body. Although this manufacturing technique is satisfactory for fabrication of containers with narrow-neck finish diameters, the throughput of the process is greatly reduced when employed for fabricating preforms and containers of larger finish diameters. For example, a preform mold cavity block that has ninety-six mold cavities for preforms with a 28 mm finish diameter would typically accommo...

AI Technical Summary

Benefits of technology

The present invention provides a method and apparatus for making plastic containers with a wide-mouth finish and internal or external threads. The method involves molding a preform and then expanding it in a mold to form a one-piece intermediate container product with a body, a cylindrical finish wall without threads, and a trim moil. The moil is then severed from the finish wall and at least one internal or external thread is formed on the finish wall by engaging it with a thread-forming tool. The apparatus includes a mold and a tool for forming the threads. The technical effect of this invention is that it allows for improved quality and definition of the container threads, which would be difficult to achieve using conventional blow molding techniques.

Problems solved by technology

Although this manufacturing technique is satisfactory for fabrication of containers with narrow-neck finish diameters, the throughput of the process is greatly reduced when employed for fabricating preforms and containers of larger finish diameters.

A problem with this technique is that the external threads on the container finish are blow molded, and are not as sharply defined and detailed as desired.

Furthermore, this thread definition and are not as sharply defined and detailed as desired.

Furthermore, this thread definition problem is exacerbated in the case of containers having at least an external surface of polyester construction, such as PET, because the polyester material can strain harden as it expands during blow molding, making it more difficult to force the finish material into the thread-forming portions of the blow mold.

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