WO2002014627A2

WO2002014627A2 - Plastic fence post assembly and method of manufacture

Info

Publication number: WO2002014627A2
Application number: PCT/US2001/041489
Authority: WO
Inventors: Carl I. Schwartz; Christopher J. Waites; Richard C. Kruyer
Original assignee: Plastics Research Corporation
Priority date: 2000-08-14
Filing date: 2001-07-31
Publication date: 2002-02-21
Also published as: AU2001285386A1; WO2002014627A3

Abstract

A fence post (10) and forming is disclosed wherein a pair of substantially similar elongate channels (16a & 16b) are injection molded oriented relative to one another in a clam shell manner and joined together forming a rigid elongate structure with a continuous outer periphery (40) and an enclosed interior.

Description

PLASTIC EENCE POST ASSEMBLY AND METHOD OF MANUFACTURE

TECHNICAL FIELD

The present invention relates to plastic fence posts and methods for manufacturing thereof.

BACKGROUND ART

Fence posts were traditionally formed of wood. While attractive, wood fence posts are susceptible to rot and require frequent painting or staining. As a result of these problems wooden fence posts gradually gave way to steel tubular posts which are inexpensive, very strong and if galvanized will last many years without any maintenance.

There have been various efforts over the 20 years to make fence posts out of plastic in order to have the weatherability characteristics of galvanized steel with the appearance of traditional wood posts. Plastic fence posts, however, have failed to become widely accepted due to trade offs between cost, strength, appearance and manufacturability. Plastic fence posts are typically a unitary construction formed using an extrusion process. The problem with extruded fence posts is that they lack detail as a result of their inherently uniform cross-sectional area. In order to strengthen extruded plastic posts, extruded posts have been filled with a variety of materials from concrete, as used in the U.S. Patent No. 5,255,899 (Von Grozney) to rigid plastic foam, as shown in U.S. Patent No. 5,078,367 (Simpson, et al.) and various density materials falling there between, such as post consumer waste recycled plastic. DISCLOSURE OF INVENTION

Accordingly the present invention is directed to a plastic fence post and a method of manufacture wherein is post made of a pair of substantially similar elongate channel members formed of plastic. Each channel member has two spaced apart elongate edge surfaces and an outer periphery. The channel members are oriented relative one another in opposed clamshell configuration and the elongate edges are securely joined to form a rigid elongate structure with an axial cross section defining the closed interior and a continuous outer peripheral surface. Preferably the channel members are formed utilizing an injection molding process whereupon the channel members are properly oriented and joined preferably using a welding process. The preferred construction of the invention includes integrally forming at least the two ribs on each of the elongate channel members which are jointed together to increase post structure. Preferably, adjacent ribs at one end of the post define a pair of axially spaced apart apertures to facilitate telescopically mounting the post on a relatively small diameter steel anchor post.

BRIEF DESCRIPTION OF DRAWINGS

FIGURE 1 is a partial cut-away side elevation of a plastic fence post of the present invention mounted upon a steel anchor post held in the ground on a concrete footing;

FIGURE 2 is a cross-sectional side elevational view of an alternative embodiment of the present invention mounted directly in the ground without use of an anchor post;

FIGURE 3 is an exploded perspective of two elongate channel members prior to joining;

FIGURE 4 is an end side elevational schematic illustration of two elongate channel members being joined together in a welding fixture; FIGURE 5 is an end view of the elongate channel member utilized in Figures 1-4; and

FIGURE 6 is an end view of an alternative embodiment of the elongate channel member used to fabricate a round post.

BESTMODE FOR CARRYING OUT THE INVENTION

A fence post assembly 10 is illustrated in Figure 1 installed in the ground upon a tubular steel anchor post 12 securely retained in a concrete footing 14. Plastic fence post assembly 10 is made up of a pair of elongate channel member 16a and 16b. Best illustrated in Figure 3 which are joined together to form an elongate structure having a longitudinally extending central axis. Preferably, the upper end of plastic fence post 10 is provided with a cap 18 formed of molded plastic. The cap 18 is both decorative and functional, it serves to close out the end of the elongate fence post preventing foreign objects from entering and protects the end of the post from damage.

In order to facilitate telescopically mounting the plastic post assembly

10 upon steel anchor post 20, the plastic post is provided with a pair of spaced apart rib assemblies 20 and 22 at the lower end of the fence post as illustrated in Figure 1. The upper end of the post not shown in Figure 1 but visible in Figure 3 includes a second pair of rib assemblies 24 and 26. Each of the rib assemblies 20, 22, 24 and 26 are made up of rib pairs 20a and 20b, 22a and 22b, 24a and 24b, and 26a and 26b. Each of the rib portions are integrally formed on one of a corresponding pair of elongate channel members 16a or 16b. In the preferred embodiment each of the rib members is provided with a semicircular opening 28 concentric with central axis of the elongate structure of the fence post which when joined with its complimentary rib member defines the circular opening for telescopically receiving an anchor post 12. The orientation of the anchor post 12 and the rib assembly 20 and 22 is best illustrated in Figure 1 cross-section. Plastic post assembly 10 will telescopically slide over anchor post 12 with the bottom free and the post assembly 10 sitting upon the concrete footing 14. Alternatively in situations where a concrete footing is unnecessary a long steel anchor post can be driven directly into the ground using conventional slide hammer or the like and the plastic post assembly 10 is simply mounted on the anchor post without a footing.

In many fence applications, anchor posts are only necessary periodically at high and low points, such as fence corners, end points, and gate openings. Posts simply located in a long straight section of fence may be simply mounted directly in the ground as plastic post assembly 30 is in Figure 2. Post assembly 30 differs from plastic fence post assembly 10 in that fence post assembly 30 is filled with a rigid plastic foam 32. Rigid plastic foam 32 gives a fence post a more wood like feel and eliminates the hollow sound which occurs in a hollow plastic post. Ideally the rigid plastic foam will not be provided in the region 34 in which an anchor post would be inserted if so desired.

An elongate channel member 16a and 16b are each formed of molded plastic preferably elongate channel members are injection molded thermal plastic such as polypropylene or the like such as high density polyethylene having a 0 to 20% foam content. Of course other plastic materials could be utilized. Alternatively, elongate channel members could be molded of a plastic bulk molding compound, however, injection molding using a thermal plastic such as polypropylene is preferred.

Elongate channel members 16a and 16b have a pair of spaced apart elongate edge surfaces 36 and 38 denoted by the a and b suffix. Corresponding a and b parts make up the pair of channels forming a single post. Each of the elongate channel members 16a and 16b is further provided with a convex outer peripheral surface 40 in a concave inner surface 42. A pair of substantially similar elongate channel members are oriented elongate edge to the elongate edge in a clamshell manner is illustrated in Figures 3 and 4. The edges are joined together forming a rigid elongate structure having an axial cross-section defining a closed interior and a continuous outer periphery. Spaced apart elongate edges 36 and 38 are joined to their corresponding edges of the mating part using any one of a number of conventional joint processes. Preferably, the edges are joined by welding. In the case of the preferred plastic post assembly 10 made of polypropylene, welding can be achieved using a vibration welding fixture shown in Figure 4 or using a hot plate welder. During the joining process, rib members 20a - 26a are joined to the complimentary rib members 20b - 26b, further adding to the structural rigidity of the elongate structure.

In the preferred embodiment illustrated each elongate channel member has a right triangle end view shape causing the resulting post to have a rectangular cross-section. In the preferred embodiment, the finished post is a square. It should be appreciated that a wide variety of post shapes can be achieved utilizing the present invention such as a round post utilizing elongate channel member 50 illustrated in Figure 6 or a hexangular_. or octagon shape post using a correspondingly shaped elongate channel member.

By using an injection molding process, a post having a very decorative design can be achieved. In the post assemblies 10 and 30, illustrated Figures 1 - 5 have a simulated millwork detail 44 formed in each of the exterior side surfaces. Additionally, a detent 46 can be molded in place in order to retain cap 18. The elongate channel member embodiment 50 shown in Figure 6 having a generally semicircular outer peripheral with simulated millwork flutes 52 formed therein.

A post made in accordance with the present invention can be highly decorative, strong and lightweight, and formed of relatively low cost material.

Plastic can be used which can withstand many years of use and hostile environments with the post being exposed to sun, water, and hot and cold temperature extremes experienced in the residential communities throughout the world.

While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention.

Claims

WHAT IS CLAIMED IS:

1. A fence post comprising: a pair of substantially similar elongate channel members formed of molded plastic, each having a pair of spaced apart elongate edge surfaces and a convex outer peripheral surface; wherein the channel members are oriented relative to one another in a clam shell manner with their respective opposed elongate edge surfaces securely joined together forming a rigid elongate structure with an axial cross-section having an enclosed interior and a continuous outer peripheral surface.

2. The fence post of claim 1 wherein each elongate channel member is provided with at least two transverse ribs which are aligned with and joined to the corresponding ribs on the opposed elongate channel member.

3. The fence post of claim 2 wherein the opposed ribs which are joined together extend generally peφendicular to a central axis of the elongate structure and collectively define a pair of axially spaced apart apertures which are substantially smaller in cross-section than the enclosed interior of the elongate structure .^"

4. The fence post of claim 1 wherein the plastic material is polypropylene.

5. The fence post of claim 1 wherein the plastic material is polypropylene foam having a density of 0 to 20% .

6. The fence post of claim 1 wherein the pair of substantially similar elongate channel members are formed of an injection molded thermal plastic material.

7. The fence post of claim 1 wherein the pair of substantially similar elongate channel members are joined to one another by a vibration weld.

8. The fence post of claim 1 wherein the outer peripheral surface of the cross-section defines a rectangle.

9. The fence post of claim 8 wherein the outer peripheral surface of the fence post is generally square.

10. A fence post comprising a pair of substantially similar elongate channel members formed of injection molded plastic each having a pair of spaced apart edge surfaces, an outer convex peripheral surface, an inner concave peripheral surface and at least two ribs at least partially spanning the inner concave peripheral surfaces; wherein the channel members are oriented relative to one another in an opposed clam shell manner with the respective opposed elongate edge surfaces and rib surfaces securely joined together forming a rigid elongate structure with an axial cross-section having an enclosed interior and a continuous outer peripheral surface.

11. A method of forming a fence post comprising: injection molding a pair of plastic substantially similar elongate channel members each having a pair of spaced apart elongate edge surfaces and a convex outer peripheral surface; orienting the channel members in an opposed clam shell manner with their respective elongate edge surfaces aligned about a common central axis; and joining the opposed elongate edge surfaces of the elongate channel members together forming a rigid elongate channel members together forming a rigid elongate structure with a cross-section having an enclosed interior and a continuous outer peripheral surface.

12. The method of claim 1 lwherein the step of injection molding further comprises forming at least two axially spaced apart ribs on each of the elongate channel members which are subsequently joined together.

13. The method of claim 11 wherein the step of joining further comprises welding.

14. The method of claim 11 wherein the step of joining further comprises vibration welding.

15. The method of claim 11 wherein the step of joining further comprises hot plate welding.

16. The method of claim 11 further comprising installing an end cap on one end of the post.