Patent Publication Number: US-6905109-B2

Title: Stiffening device for plastic fences

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention is directed to the field of plastic fencing. 
   2. Background Art 
   Plastic fencing has made severe inroads on traditional wooden fencing, and many miles of plastic fencing are installed each year. While there are numerous styles of fencing, one popular style consists of hollow posts which are sunk in the ground, with or without the aid of cement, or in the case of decks, mounted on special mounting bases. Spanning the gap between the posts are one or more horizontal rails. These rails may be unadorned, or vertical members may be attached to form solid fences, picket fences, etc. Numerous styles are possible. 
   Assembly of the fence requires the rails to be secured to the posts. For this purpose, metal brackets may be used, as disclosed in U.S. Pat. No. 5,938,184. However, this method of assembly is time consuming and results in an observable bracket which therefore fails to mimic a traditional wooden fence. Thus, more commonly, the posts are supplied with holes into which the rails pass. The holes may be manufactured into the post by the manufacturer or cut on the job site. A typical post/rail assembly is shown in  FIGS. 1 and 2 . In  FIG. 1 , a post and rail assembly is illustrated from the side. The post  1  in this case is a square post with walls  3  which may typically be about 0.25 inch thick. On faces  5  and  6 , are rectangular holes  7  for receiving a fence rail  9 . The rail end  10  protrudes some distance into the interior of the post. A section across  2 — 2  is shown in FIG.  2 . 
   A problem with post/rail systems such as those of  FIGS. 1 and 2  is that the fences exhibit a considerable amount of “wobble,” even when posts are set in concrete. The reason for this wobble has to do with a lack of rigidity due to the fact that the rails are free to move within their holes in the post, as shown in  FIG. 3 , the same structure as depicted in  FIG. 2 , but with a sidewards force imposed upon the structure. The rails, rather than being spaced 180° apart, now make an oblique angle with respect to each other. In long runs of fences, these problems are exacerbated. 
   In U.S. Pat. No. 5,702,090, rather than extend into the post through its sidewall, rails are captured by a recess, which also serves to hold a framing member for vertical slats. However, the recess is too shallow to cause any appreciable stiffening of the fence line. Moreover, this construction requires a more complex extruded post, one which also fails to mimic traditional wooden fencing, and requires greater accuracy during installation, as spacing is critical. 
   It would be desirable to provide a plastic fencing system which is economical, easy to install, and which has a much reduced tendency to wobble. Such a system would employ simple post/rail systems where the rails are inserted through holes in the post, while yet forming a robust assembly. 
   SUMMARY OF THE INVENTION 
   The inventor has surprisingly discovered that wobble in plastic fencing can be much reduced without undue complexity, by inserting over the penetrating rail ends, a stiffening member which grips the rail ends and itself is prevented from moving within the hollow post. The stiffening member is preferably a U-shaped channel which slips over the inwardly extending rail ends. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates one type of plastic fencing, from the side; 
       FIG. 2  is a top view of  FIG. 1  across  2 — 2 ; 
       FIG. 3  illustrates post/rail deflection in a fencing of  FIGS. 1 and 2 ; 
       FIGS. 4   a  and  4   b  illustrate two preferred embodiments of the subject invention stiffening devices; 
       FIG. 4   c  illustrates a device such as one of  FIGS. 4   a  or  4   b  being inserted into a hollow post, over rails extending into the post; 
       FIG. 5  illustrates a section across  5 — 5  of  FIG. 4   c;    
       FIG. 6  illustrates a further embodiment of a stiffening device of the present invention; 
       FIG. 7  illustrates a yet further embodiment of a stiffening device of the present invention; 
       FIG. 8  illustrates another embodiment of a stiffening device of the present invention; 
       FIG. 9  illustrates a dual channel device which may be used universally for straight T, or X fences; 
       FIGS. 10   a  and  10   b  illustrate a stiffening device which includes a decorative post cap; 
       FIGS. 11   a  and  11   b  illustrate multiple-way stiffening devices wherein channels at angles to each other serve as rail receiving elements and stabilizing elements; and 
       FIG. 12  illustrates a yet further embodiment of a subject invention stiffening device. 
       FIG. 13  illustrates a further embodiment of a subject invention stiffening device where rail gripping elements extend into hollow rail ends. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
   The stiffening devices of the present invention comprise a rail gripping means or element and a stabilizing means or element, as described in greater detail hereafter. 
   The rail gripping means or rail gripping element serves to grip, or “locate,” the end of a rail protruding into a post, most preferably two or more rail ends. It is more important that the ends of the rail be gripped as opposed to the portions of the rails just inside the post, as gripping the rail ends will have the greatest effect in reducing wobble. However, it is preferable that a substantial portion or all of the rail protruding into the post will be gripped, and in some designs, a portion of the rail just inside the post may be the sole portion of the rail gripped. The gripping means may constitute a plurality of narrow fingers which will slip over the rails, but is preferably an inverted U-section piece of metal or plastic, preferably plastic, as shown in  FIGS. 4   a  and  4   b . The rail gripping means or element may receive the rail ends with some degree of clearance, or may engage the rail in a spring-like or “interference fit” manner. The rail gripping means or element serves to locate the tail or rails in the desired location within the post. 
   The stiffening device also includes a stabilizing means or element. By “stabilizing” is meant reducing the number of degrees of freedom of movement of an assembly of one or more rail ends within a post, in combination with rail gripping means. The motion desired to be most eliminated is not vertical motion, but motion in a horizontal plane, particularly angular motion as shown in FIG.  3 . Such motion, for example, would ordinarily be produced by leaning against a fence or post, or by wind impinging upon the fence. 
   The stabilizing means will comprise a means for stably locating the rail gripping means within the post, such that angular or sidewards motion is reduced. In combination, the rail gripping means and stabilizing means substantially reduce wobbling. The stiffening devices may be applied over only the top rail, or may, when suitably configured, be applied over a second, lower rail, or a bottom rail. However, it is the topmost rail or rails for which wobbling is the greatest problem. As the stiffening device functional elements are contained solely within the post (with the exception of any embodiments employing a decorative cap), the traditional appearance of the fencing is maintained. 
   The stiffening devices will now be described in greater detail by referring to numerous embodiments, as depicted in  FIGS. 4-12 . 
   In  FIGS. 4   a  and  4   b , preferred embodiments are shown in perspective. In  FIG. 4   a , the stiffening device  13  comprises two pieces, a roughly square top piece  15  (in a hollow round post this top piece would preferably also be round) which serves as a stabilizing means, and a generally U-shaped channel  16  which serves as the rail gripping means. The two pieces, preferably of plastic, are affixed to each other in this embodiment, preferably by a screw or other fastener. The size of the interior of the channel  17  is selected so as to grip the rails, or to slip over the rails with only minimal clearance, since greater clearance will allow more wobble. In  FIG. 4   a , although a screw fastener is shown, the two pieces may be fusion bonded, adhesively bonded, or may, as shown in the stiffening device  14  of  FIG. 4   b , be molded or extruded as a single unit.  FIG. 4   c  illustrates placement of the stiffener  13  in the post/rail assembly, where the stiffener is merely inserted into the cavity in the post, with the rail gripping means  16  sliding over the inner portions  10  of the rails. A detail across  5 — 5  is shown in FIG.  5 . The roughly square top of the stiffening device is not free to rotate or to move appreciably sideways, and thus stabilizes the position of the rail gripping means. 
     FIG. 6  illustrates a less preferred stiffening device, where the rail gripping means comprises two pairs  17   a ,  17   b  of downwardly extending fingers, spaced inwardly from the sidewall of the post, so that inner portions of the rail ends may be gripped. 
     FIG. 7  illustrates an alternative embodiment of a stabilizing means, where a U-shaped channel  16  is located between two end-plates  20 , separated by a distance such that they may fit between the post walls. The U-shaped channel is shown extending only part way down the end plates, the latter having an open area  21  to facilitate locating over the rails. However, the channels may also extend further, or all the way down the end plates. 
   Further devices are illustrated in  FIG. 8 , where a U-shaped channel  16  is molded with two sidewards extending stabilizers  25 ,  26 . The stabilizer shown at  26  simply extends outward to contact or be in close proximity to the post interior wall. In devices of this type, having a stabilizer of the type  26  extending away from each side of the U-shaped channel  16 , the part of the channel most prone to sideways movement, i.e. in the center of the post, is constrained against movement by the stabilizing means abutting the post walls. A somewhat stiffer device even less prone to movement is a device of  FIG. 8  where two stabilizers  25  are employed, these stabilizers having an extension  27  which allows greater contact area with the post wall. 
   Yet further devices, of preferred construction, are shown in  FIGS. 9 and 10   a  and  10   b . In  FIG. 9 , two intersecting U-channels allow stabilizing not only linear fences, but fences where a “T” or “X” meeting of fence lines occur. These may be at right angles, or at other angles as well. In  FIG. 9 , two intersecting U-channels  28  and  29  are molded integral with a stabilizing plate  30  around a waist section of the device. The stabilizing plate may also be moved to the bottom (open end) of the U-shaped channels, towards the top, or may form a top plate as shown in  FIG. 4   b . An advantage of the device of  FIG. 9  is increased stiffness. A further advantage is the ease of inserting into the post, since the uppermost portions of the channels above the waist stabilizer element may be easily gripped. 
   The device of  FIG. 10   a  is similar to the device shown in  FIG. 9  but has been elongated and topped with a decorative cap  35 . The device of  FIG. 10   a  has two intersecting rail receiving channels  31 ,  32  extending downwards from the decorative cap  30 . The length of the channels is such that they abut or at least are in close proximity to the post interior walls, thus serving as both rail gripping means and stabilizing means. The same device is shown from the bottom in  FIG. 10   b . The channels  31 ,  32  are formed by angle sections  33  projecting away from the decorative cap. In use, the rails are placed in position in the post, and the combination device is pressed down into the post cavity, surrounding at least part of the rail or rails, until the bottom flange  34  of the device cap contacts the post. 
   A further preferred embodiment of a device of the subject invention is shown in  FIGS. 11   a  and  11   b . In the device of  FIG. 11   a , which may be used with one to four, preferably two to four rails, the intersecting channels  35 ,  36  extend to the inside walls of the post, and serve as both the rail gripping means and stabilizing means. Each channel is capable of gripping one or two rails entering the post from opposite sides, whereas for each channel, the channels at right angles serves to stabilize the other channel against rotation, twisting, etc. 
   A somewhat similar device is shown in  FIG. 11   b , however, one of the channels does not extend to the wall of the post, while the other does. In a linear fence, the short channels would be placed over the opposing rails, and the long U-channels would stabilize the device against twisting by contacting or being in close proximity to the interior wall of the hollow post. 
   From the above descriptions of numerous embodiments, which are illustrative and not limiting, the bounds of the invention are easily ascertained. The subject invention devices include at least one portion of the device which grips or receives at least one and preferably two rails, and a portion, which may be the same or a different portion from the first portion, which serves to minimize motion, flexion and/or rotation of the device in the post, particularly in a plane orthogonal to the longitudinal axis of the post. The structure of the device may range from a simple U-channel with thick sidewalls, whose open end abuts the wall of the post, to the more complex designs illustrated herein. The device is amenable for use in posts which are square, rectangular, polygonal, round, or are of other shapes. As a further aid in stiffening the fences, the stiffening devices may be adhered to the rails, for example by conventional PVC bonding compositions, in the case of PVC rails. However, in the latter case, disassembly of the fence to replace broken rails, etc. will be difficult. Hence, it is more desirable to secure the stiffening devices to the rails by fasteners such as rivets or screws, etc. A device which is manufactured with holes  37  for this purpose is shown in FIG.  11 . Holes may be manufactured into the remaining devices as well. Alternatively, holes may be drilled in the field, particularly with devices of preferred plastics constructions, where drilling is easy and rapid. 
   The devices may be made of metal, thermoplastic, or thermosetting resin, and may be filled and/or fiber reinforced. Preferred devices are injection molded of an injection moldable thermoplastic such as polyethylene, polypropylene, polyamide, polystyrene, polyacetal, polyvinyl chloride (“PVC”), thermoplastic polyurethane, etc. Preferably, the thermoplastics are unfilled, or are filled with conventional fillers, and may also contain short lengths of reinforcing fibers, e.g. fiberglass. The devices may also be made of thermoset materials such as sheet molding compound, epoxy resin, polyester resin, thermoset polyurethane, e.g. polyurethane RIM, and the like. Due to increased cost, metal devices are not preferred, although they are suitable. Preferably, the devices are of filled or unfilled thermoplastic, such as polyamide, polyolefin, or PVC, most preferably polypropylene or PVC. 
   The preferred rail gripping means or elements are simple channels, either produced separately, as shown in  FIG. 4   a , or molded integrally, as shown in  FIGS. 4   b ,  11 , etc. While the devices have often been described in terms of “U-channels,” channels of any section which suitably provide the rail receiving function are suitable, for example, but not by limitation, “C-channels,” “J-channels,” etc. Fingers or partitions, which are roughly equivalent to “short channels” may also be used, as illustrated by  FIG. 12 , which includes a decorative cap  30 , and two partitions  41  which extend to or proximate the interior of the sidewall of the hollow post. The stiffening device  40  is inserted into the post (not shown), recesses  42  in the partitions  36  slipping over the rails  10 . 
   Further embodiments are easily envisioned. For example, while the rail gripping elements have been shown as channels which fit over the rails, devices which grip the hollow rails from within are also within the scope of the invention. One such embodiment is shown in  FIG. 13 , where a vertical stabilizing element  45  is sized to fit between opposing hollow post walls, and is fitted with two extensions  46 , 47  which are sized to fit within post rail ends, e.g. extension  47  fitting within hollow post rail end  10 . The extensions may be solid, but are preferably of hollow construction to minimize material usage. The ends may be open as shown (U-shaped) or closed, and are preferably tapered at the ends  48 , 49  to facilitate entry into the ends of the rails. In this embodiment, the stiffening device is inserted prior to insertion of one or both rails. An analogous stiffening device where extensions penetrate into the rail ends may be configured for a “T” or “X” configuration ( 3  or  4  rails, or  2  rails at an angle), but dispensing with the stabilizing plate  45  and adding two extensions at an angle (e.g. a right angle) to extensions  46  and  47 , as for the external combination gripping and stabilizing device shown in  FIG. 11   a , but with the extensions sized to fit within rather than over the rails. One set of extensions serves as a stabilizer to the other set of extensions. 
   The depth which a channel or other locating or rail gripping means must have will be dependent upon other factors such as the post internal diameter and the nature of the stiffening device itself. For stiffening devices without a top plate (as shown in  FIGS. 4   a  and  4   b ); a waist plate (see  FIG. 9 ) or a bottom plate as described previously, it is desirable that the rail gripping elements be of considerable depth, e.g. preferably from about 0.15 to 1.0 or greater of the height of the rail, more preferably from about 0.20 to about 0.75 of the height of the rail. With more inherently stiff and stable stiffening devices, lesser depth will be required. Since fences are often installed on non-planar surfaces, e.g. hills, gulleys, rolling pasture, etc., some allowance may be made for rails which enter the post at an angle to the horizontal. A relatively deep channel or partition (as shown in  FIG. 12 ) can be made to accommodate substantial differences in rail angle in a vertical plane while still providing adequate rail location. 
   While the majority of fences are linear, or have projections at right angles, some fences must curve gradually or angle abruptly at other than 90° angles. Custom stiffening devices may be provided, or may be made in the shop or in the field, for example following the construction of  FIG. 4   a  but with two channel pieces at the correct angle to each other, secured to the top piece by fasteners and/or adhesive, etc. 
   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.