Plastic and nonmetallic article shaping or treating: processes – Mechanical shaping or molding to form or reform shaped article – To produce composite – plural part or multilayered article
Reexamination Certificate
2000-01-24
2002-04-30
Heitbrink, Jill L. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Mechanical shaping or molding to form or reform shaped article
To produce composite, plural part or multilayered article
C264S255000, C264S308000, C264S328800
Reexamination Certificate
active
06379600
ABSTRACT:
The invention relates to the manufacture of continuous length troughs and more particularly to an improved drainage trough assembly and method of injection molding continuous length ribbed plastic drainage troughs of the type used in the handling of fluid run off in ground level applications.
BACKGROUND OF THE INVENTION
Drainage troughs, are in common use for collecting and distributing ground level run-off of fluids, such as storm water, waste fluid spills, and various cleaning and drainage applications. Generally such troughs are installed at or formed just below ground level in a paved area and the arrangement comprises a screen, grate or the like which covers the trough to enable vehicles, pedestrians and/or large objects to pass thereover without falling into the trough, while allowing fluids to pass through.
Pre-manufactured troughs have been generally available, formed from a rigid metal or plastic, typically by extruding or casting same to a desired length or various standard lengths. To protect against crushing, such troughs are generally sturdily manufactured and thus are difficult to cut into variations from standard lengths. In recent years, there has been a desire to manufacture and use extruded plastic troughs in place of metal troughs for both corrosion resistance and ease of handling, however the wall thickness required to produce a suitably crush resistant plastic trough is significant and thus material costs are expensive. To reduce costs, a plastic trough of lesser wall thickness has been proposed which is formed with a plurality of circumferential supporting ribs. The support ribs enable support of a weight supporting grate and provide suitable resistance against crushing the form of the trough, but the presence of the ribs generally are problematic to the convenient manufacture of the trough by extrusion. Thus, the manufacture of troughs by injection molding is not particularly desirable in that multiple distinct molds are generally necessary to enable the manufacture of the various standard sizes and lengths for general availability, and variations from such standards generally require the creation of additional expensive molds.
U.S. Pat. No. 3,992,503 discloses a method of manufacturing continuous ribbed pipes from thermoplastic materials, wherein a section of pipe is formed by injection molding, the section is allowed to set in the mold, the set pipe casting is ejected from the mold, an end of the set pipe casting is reset into an open end of the same mold, and further molten thermoplastic material is injected into the mold. The molten thermoplastic material engages against the end of the reset pipe casting, and is said to fuse with the thermoplastic material at the end of the reset pipe, with repetition of the operation resulting in the formation of a continuous molded pipe of welded sections. Provisions are made in the patent for a heating wire located at the open end of the mold to surround the reset end of the pipe and soften it to enable welding of the sections, and/or for the pipe to comprise a stepped diameter at the ends to facilitate softening of the thermoset resin to form a weld among the sections.
The disclosure of U.S. Pat. No. 3,992,503, makes it apparent that the final product being manufactured merely comprises a continuous length of thermoplastic pipe formed from a plurality of sections which have been welded together using conventional welding means, and thus having the inherent seam weakness of thermoplastic welds.
It is an object of the present invention to provide a method of manufacturing injection molded, continuous length troughs having suitable ribbed supports integral therewith.
It is a further object of the present invention to provide a method of injection mold manufacturing of troughs, which enables a homogeneous continuity of thermoplastic material throughout its length.
It is another object of the present invention to provide a novel injection mold formed drainage trough, having integrally molded raised ribs and support attachment elements.
It is still another object of the present invention to provide a novel drainage trough system enabled for rapid and convenient installation in diverse environments.
These and other objects of the invention will become apparent from the following recitation of the invention.
SUMMARY OF THE INVENTION
The present invention comprises a method of manufacturing a continuous length trough, comprising spaced, raised integral ribs, from thermoplastic resin material, comprising the steps of: (a) providing an injection mold cavity arranged between mating male and female molds, said cavity being shaped to form an elongate section of a trough having spaced, outwardly raised ribs, said cavity being open at a first end and closed at the opposite end, said opposite end of said cavity being configured to form a plurality of spaced extensions arranged along an end of a formed trough section; (b) providing means for removably covering the open first end of said mold cavity; (c) providing means for cooling a molten thermoplastic resin comprised in said cavity; (d) covering said first end of said mold cavity and injecting a molten thermoplastic resin, at an elevated temperature, into said cavity between said male and female molds; (e) cooling said molten thermoplastic resin to a pre-determined resin setting temperature; (f) uncovering said first end and removing a molded resin-set trough section from the female and male molds; (g) inserting the opposite end of said resin-set trough section, comprising the spaced extensions, into the open end of the mold cavity sufficient to close the open end of said mold cavity; (h) injecting molten thermoplastic resin into the mold cavity, at an elevated temperature sufficient to melt said spaced extensions of said first resin-set trough section and form a continuing section of trough, homogeneous with said first trough section; (i) cooling the molten thermoplastic resin to a pre-established setting temperature; (j) removing the molded second trough section from the female and male molds; and repeating steps (g) through (j) in successive order until a trough of a desired length is formed.
In a preferred embodiment, the elongate mold cavity in an injection molding process is formed by the confluence of three or more components. Thus, in a particularly preferred arrangement an elongate male mold, having an exterior surface configured to form the generally trough shaped configuration of an interior surface of a molded trough, is juxtaposed between two or more generally opposing female molds with the cooperative engagement of the three or more components forming the cavity to be injection filled, and the formed product is released from the mold cavity by disengagement of the three or more components. In a preferred operating arrangement between three components, a female mold is fixed in position and the male and another female mold are arranged to move toward and away from the female mold. Thus, in a preferred molding cycle, the female mold is arranged in a generally stable position, while a male and female molds are arranged in generally opposing relationship to the female mold and are enabled to be moved from a first position spaced from the stable female mold to a second position surrounding the male mold and defining the mold cavity. When moved to the second position, the female molds generally engage each other and the male mold, forming a sealed mold cavity surrounding about the length of the elongate male mold. The mold cavity is then injected with a suitable plastic composition; the injected plastic composition is allowed to cool to at least initiate setting thereof, with or without cooling assist; and upon the plastic composition reaching a suitable setting point, the male and movable female mold are withdrawn from the second position toward the first position.
Such arrangement of male and female molds enables the convenient formation of diverse integrally molded structures on the exterior surface of the molded trough, such as raised ribs and/or other protruding in
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