GB2220013A

GB2220013A - Plastics, extruded post

Info

Publication number: GB2220013A
Application number: GB8812723A
Authority: GB
Inventors: Robert Galletly
Original assignee: CALEDONIAN CABLES Ltd
Current assignee: CALEDONIAN CABLES Ltd
Priority date: 1988-05-27
Filing date: 1988-05-27
Publication date: 1989-12-28
Also published as: GB8812723D0; ES2016891A6

Abstract

An elongate plastics member such as a fence post of substantially square cross-section has a cavity 12 along its length. The body is strengthened by reinforcing wires 14 at the corners of the body. In the method of manufacture the post is made by extrusion and coolant is passed along the cavity to modify the rate of cooling of the body and the reinforcement is tensioned or so supported as to support the body during cooling. <IMAGE>

Description

ELONGATE MEMBER This invention relates to an elongate member such as a beam or a post, and to a method for its manufacture. More particularly this invention relates to an elongate post which is suitable for use in fencing and the like.

Fences are usually supported by means of a plurality of vertical posts which are securely attached to a foundation. Commonly these posts are partially driven into the ground in appropriate positions so as to provide support for the panels, wires, or other members of which the fence is comprised. An example of a fence which is contructed in this way is US Patent No: 4465263 (Robbins) which discloses a fence comprising plasticsheathed metal wires attached to wooden or concrete fence posts, the sheathed wires extending horlzontally between the spaced vertical posts.

Existing fence posts are usually made of a material such as wood, concrete or metal, which frequently matches that of the fence they support. Wooden posts require frequent maintenance to prevent rotting, and they can be of variable quality making them difficult to work with. Concrete posts are heavy and difficult to cut or drill, whole metal posts can also require regular painting to inhibit corrosion. These drawbacks, and others, make existing fence posts less effective than is desirable.

An object of this invention is to provide an improved elongate member, more particularly an improved fence post, which obviates or mitigates disadvantages of existing members.

According to an aspect of this invention there is provided an elongate member such as a fence post, of plastic material and including an internal longitudinally extending cavity.

Preferably the member further includes reinforcement such as one or more steel wires. Suitably the member has a square cross-section, and has a central cylindrical cavity. Advantageously there are four steel wires, one located adjacent each respective corner of the cross-section. Ideally the member is an extrusion, beneficially of hign-density polyethylene. To facilitate its use as a fence post, the member is preferably provided with a taper at one end and an endcap at the other end.

The member of this invention is particularly suitable for production by an extrusion-based process, being of a substantially constant cross-section.

However there are problems in extruding members having an appropriately thick cross-section, particularly distortion or sagging caused by the relatively slow cooling of the internal regions of the member after extrusion.

Therefore a further object of this invention is to provide an improved method of extrusion.

According to a further aspect of this inventIon there is provided a method of producing an elongate member, comprising the steps of extruding a materIal into an elongate bar having an internal cavity extending along its length, and passing a flow of coolant along the cavity to modify the rate of cooling of the bar.

Advantageously the method further includes the steps of cutting the bar into lengths to produce elongate members, providing a taper at one end of each member, and providing an end-cap for finishing the other end of each member. Beneficially, reinforcement such as steel wire is incorporated into the bar during extrusion. Preferably the reinforcement is tensioned or supported so as to support the extruded bar during cooling.

This invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is a plan view of a preferred embodiment of the invention; Figure 2 is a partial side view of the embodiment shown in Figure 1.

Referring to Figures 1 and 2, which show a preferred embodiment of the invention, a fence post 10 has a square cross-section which may have rounded corners as shown. Fence post 10 is substantially solid save for a cylindrical cavity 12, located at the centre of the cross-secrion, which extends along its entire length. Also extending along the length of fence post 10 are four steel wires 14, which are embedded on the diagonals of the cross-section, one adjacent each respective corner.

Cavity 12 reduces the amount of material required to form fence post 10, thereby saving cost and weight without serious detriment to its strength. Wires 14, which may be pre-tensioned, bonded or relatively loose within the fence post 10, enhance its strength.

Moreover, cavity 12 and wires 14 bring particular benefits to the production process, as will now be explained.

BeIng of a substantially constant cross-section, fence post 10 is particularly suitable for production by an extrusion-based process. However the thickness of the material being extruded can cause problems as it cools from the molten state during and after extrusion, the relatively slow cooling of the internal regions leading to distortion or sagging which deforms the desired shape. This problem can be lessened by incorporating wires 14 into the melt (the wires having a higher melting point than the material or which the post is made), and pulling them through the extrusion head in the appropriate positions for them to be surrounded by the material as It solidifies. By supporting or tensioning the wires, they help to support the extrusion as it cools and thus minimize distortion.Cavity 12 also acts to minrmfse distortion, to an extent by reducing the thickness of the material but mainly by providing a channel through which a flow of fluId, such as air or water, may be passed, so as to cool the internal regions of the extrusion at a sImIlar rate to th external regions. Suitably this cooling flow may be ducted into the cavity 12 through an opening in that part of the extruding die which defines the shape of the cavity.

Fence post 10 is preferably made of a rigid plastic material such as high-density polyethylene, or any material having favourable cost, strength, lightness, durability and suItabIlity for the chosen production process. Ideally it is integrally coloured to suit its application, thereby obviating the need for painting.

After extrusion, fence post 10 is advantageously cut into the desired lengths and provided with a tapered end to facilitate its being driven into the ground.

Alternatively it may be fitted into a support which is already anchored In this way. Suitably it is provided with a decorative end-cap which fits into cavity 12 and provides a neat, weatherproof finish for the top of the post.

Variations are possible, for instance wires 14 may be made of a variety of materials and may have a plain or braided configuration. Fence post 10 need not be square in cross-section but can have any suitable size and shape, as can cavity 12. There may be any number of cavities, and any number of wires, at any location within the fence post 10.

It will be clear to those skilled in the art that, although this invention has been described with reference to its application in fence posts, it is equally applicable to any elongate member.

This invention provides an elongate member which can be readily sawn and drilled, which is light in weight, robust, corrosion-resistant and easy to maintain. It can be driven into the ground with a hammer or the like, and provides a firm anchorage for nails, screws and other fixings. As such it is particularly suitable for use as a fence post for supporting fencing members comprising two or more wires ensheathed and connected by a plastic web, as manufactured by us and similar to the type disclosed in US 4465263.

Claims

1. An elongate member such as a fence post comprising an elongate body of plastics material and longitudinally extending cavity disposed within the elongate body.

2. An elongate member wherein the body further includes longitudinal reinforcement.

3. An elongate member according to Claim 1 or 2 wherein the body is substantially square in cross-section having a central cavity and four reinforcement wires, one located adjacent each corner of the body.

4. An elongate member according to any one of the preceding claims wherein the member is a fence post and includes a taper at one end of the body and an end cap at the other end of the body to close the longitudinally extending cavity.

5. A method of producing an elongate member, comprising the steps of extruding plastics material into an elongate bar having a longitudinally extending internal cavity, and passing a flow of coolant along the cavity to modify the rate of cooling of the bar.

6. A method according to Claim 5 comprising the further steps of cutting the bar into lengths to produce a plurality of elongate members, providing a taper at one end of each member, and providing an end-cap for the other end of each member.

7. A method according to Claim 5 or 6 comprising incorporating longitudinally extending reinforcement into the bar during extrusion.

8. A method according to Claim 7 wherein the reinforcement is tensioned or supported so as to support the extruded bar during cooling.

9. An elongate member substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

10. A method of producing an elongate member substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.