DE69118354T2 - Electric fence door stretched between two posts and method for tensioning electric fence wire between two door posts - Google Patents

Description

FIELD OF THE INVENTION

The invention relates to the provision of a coating for conductive elements.

KNOWN TECHNICAL STATUS

Coatings for conductive elements are known for situations where the presence of an insulating coating does not affect the intended function of the element. In fact, in many situations it is advantageous to provide an insulating protective coating of, for example, a plastic material or rubber around a conductive core. However, in electric fencing and in the field of security, the opposite is true. The conductive elements used for electric fencing must be able to give an electric shock to animals or intruders who touch the electric fence. Therefore, an insulating coating (as most coatings are) around a conductor can affect the effectiveness of the electric fence when applied in the usual way.

There are many areas, including electric fencing and the security field, where it is desirable to provide a coating around a conductive core, although it is often also desirable that the coating not significantly affect the effectiveness of the element in performing its intended purpose. There are many reasons for providing a coating, for example to protect the bare core or to improve the visibility of the element. While electroplated zinc coatings have often been applied to steel to protect it from corrosion, this is not always effective on other metals and it may be desirable to work with other coatings. In addition, the grey colour of a zinc coating is not particularly visible and this can be a problem in certain intended applications.

This problem was clearly visible in at least one specific product in the agricultural field. In 1980, the applicant brought to market a spring gate device which had an electrically operated spring which could be stretched across a gate passage and removed when required using an insulating handle. The concept was very successful and was recognised as a significant contribution to rural safety by being awarded a New Zealand Fieldays Rural Safety Award by the New Zealand Accident Compensation Commission (ACC). In awarding the prize, the ACC recognised that the spring gate has the advantage of being more visible than a simple gate and, being resilient, presents a reduced risk of injury in the event of a collision. However, despite these improvements, the visibility of these electrically operated gates in field conditions has remained a problem and it has become apparent that in poor visibility conditions, such as twilight or fog, the grey of the electroplated coating can effectively obscure the conductive element, which is generally only desirable in safety applications.

One attempted solution was to run a coloured band through the centre of the spring coil, but although this improved visibility, problems now arose with the spring catching when relaxed. Painting the spring in colour was also considered, but was initially rejected due to difficulties in the paint flaking off as the spring was frequently tensioned, and also because an unreasonable amount of loss of conductivity occurred.

Consequently, the need arose to be able to apply a coating to a conductive element for whatever reason, whereby the coating must not unduly impair the effectiveness of the element for applications such as electric fences or similar.

Such coatings are also partly known in connection with electric fence wires.

For example, F-PS 2215676 and 2474276 both relate to electric fence wires (or wire ropes) comprising a wire rope including a central conductive core and a sheath of semi-insulating material surrounding it, thereby making it possible to transmit an electric shock to animals that come into contact with the wire rope. F-PS 2215676 includes a sheath of insulating material that is made conductive by a charge of conductive particles (such as graphite, carbon or aluminum). The sheath comprises a material such as rubber, plastic or PVC applied to the conductive material in the form of a synthetic resin coating. The sheath in F-PS 2474276 comprises a thermoplastic material covered with an electrically conductive powder.

Although these covers are particularly suitable for electric fence wires, it has been found that these wire ropes (and the covers) have a serious problem in that the wire ropes are not particularly elastic and lack any significant "springback". This is particularly disadvantageous when the wire ropes are to be used as gates or barriers to be stretched between supports. For example, it is not possible to stretch these wire ropes to any significant degree in the longitudinal direction, making it impossible to stretch them transversely to barriers longer than the usual length of the wire rope at rest. This is a significant disadvantage when these wire ropes are used as gates.

In addition, since none of the wire ropes described in these specifications provide an insulating section, it is difficult to handle this wire rope when connected to an electrically conductive source. The provision of an insulating section on the wire rope would be a significant advantage in this type of invention.

It is therefore an object of the present invention to solve the above-mentioned problems or at least to offer the public a viable choice.

Further objects and advantages of the present invention will become apparent from the following description, which is given by way of example only.

DISCLOSURE OF THE INVENTION

According to one aspect of the present invention there is provided a barrier for stretching between two posts, the barrier comprising an expandable, coiled section of a resilient and spring-like electrically conductive material and at least one insulated hand portion, the electrically conductive material including a central conductive core and a coating, the coating being applied to the central core and improving the visibility of the electrically conductive material, and the coating also enabling animals which come into contact with the electrically conductive material to be given an electric shock when the material is electrically connected to a power source for the electric fence, the barrier having a first end which can be attached to a first of the posts, the insulated hand portion enabling the second end of the barrier to be connected by a user to the second of the posts, the barrier being so positioned in the can be stretched longitudinally so that the ends of the barrier can establish an electrical connection between the individual supports.

According to a further aspect of the present invention, a method of clamping between two supports is provided, the method including the following steps:

a) securing one end of a barrier to a first support and

b) stretching the barrier in a manner that allows the second end of the barrier to be brought into contact with the second support, and

c) securing the barrier to the second support, wherein securing the barrier to both the first and second supports ensures that electrical contact is made between the two supports, the barrier including a resilient and spring-like electrically conductive material having a central conductive core and a coating applied therearound, the barrier further including an insulated hand portion to enable a user of the barrier to carry out the above steps b) and c) without the risk of receiving an electric shock due to contact with the barrier.

According to a further aspect of the present invention there is provided a coated conductive element comprising a conductive core carrying a potential of more than 1 kV and provided with a coating, said coating having a specific electrical resistance measured radially exceeding 1300 x 10-6 Ωcm, said coating being further characterized in that the product of its average thickness and dielectric strength is less than 8 kV and also less than the potential carried by the core.

According to another aspect of the present invention, there is provided an expandable elastic coil of a coated conductive member as described above.

According to a further aspect of the present invention there is provided a method of providing a coated conductive element, said method comprising coating a conductive core with a UV stable and bend damage resistant (as defined herein) coating, said applied coating having a resistivity measured radially therethrough 1300 x 10⊃min;⊃6; Ωcm, and which is applied to the core such that the product of the average thickness of the coating and the dielectric strength of the coating is less than 8 kV.

In its simplest form, the coated conductive element of the present invention comprises a conductive core with a coating applied thereto. In many cases, the coating will comprise a single applied layer, although multiple layers may be applied.

For the use of the elements in live fencing, it is important that the coating incorporate certain properties. Perhaps the most important of these is the ability to transmit a shock from the conductive core to an object that comes into contact with the element or into very close proximity to the element. While a wide range of coatings can easily be used that meet this requirement and also provide some protection for the conductive core (for example against corrosion), they do not solve the problems of the current state of the art. An example of such a coating is a galvanic zinc coating, although, as already mentioned, the dull grey colour has caused problems with visibility in agricultural applications.

For the intended applications of the product, which are often in rural areas, other considerations must be taken into account in relation to the qualities of the coating. Visibility is a desirable property, as is resistance to bending damage or abrasion likely to occur during day-to-day use of the product. These desirable properties are discussed in more detail later in this specification.

There may also be certain requirements which are important in the choice of the conductive core. It should be able to carry satisfactorily a potential (generally 1 kV or more in fencing applications) and the current likely to be encountered in the intended application. Many conductive materials may be chosen for the core, but in most cases it will generally be a metal such as steel, aluminium and in some cases copper. Various alloys of these and other metals may also be used. However, it is desirable that the conductive core not comprised of a readily deformable substance or a deformable form of substance. For example, copper in the form commonly used in enamelled winding wire would generally not be suitable for use as a fencing wire. If an animal were to brush against the wire, the wire would tend to retain the shape induced by the contact. Deformable materials would generally not be suitable for the coiled, stretchable embodiments of the present invention to be described later. Consequently, in many cases it is desirable to employ a material configured or in a condition such that it has a springback of 50º under the test prescribed in Australian Standard AS1194.1 and under the general conditions specified therein. For experimental purposes, the equivalent of a fine wire having a core diameter of 1.6 to 2.0 should be used for the test. Even better is if the springback is higher, and a value of more than 300º would be particularly advantageous, especially in the stretchable embodiments of the invention.

While the conductive core may be of virtually any configuration, it is envisaged that in most embodiments of the present invention it will comprise a fine wire or wires having a substantially circular cross-section as a whole. In some embodiments of the invention, such as the expandable spiral, the cross-section of the fine wire may be substantially that of a ribbon. Virtually any desired dimensions for the conductive core may be used, although again it is envisaged that in most applications the fine wire will have an average diameter of 2.5 mm or less. In the embodiments having a cross-section other than circular, it is envisaged that the cross-sectional area will in most cases be equal to that of a circle of 2.5 mm diameter or smaller. This is not intended, however, to limit the application of the present invention to these specific values.

In order for the present invention to be effective in fencing and security applications, it is important that the coating remain capable of delivering an adequate shock to an object that comes into contact with it. Consequently, any coating applied should not completely insulate the conductive core. For the purposes of the present invention, the degree to which the coating insulates a core insulated, can be determined from calculating the product of the dielectric strength of the coating (preferably measured radially outwards from the core) and the thickness of the coating. It is advantageous if the product of the average thickness of the coating and its radial dielectric strength is less than 8 kV, as at this value it is generally still possible to deliver an appropriate shock when the core is at a potential of 10 kV. This latter value is approximately the equivalent of the most powerful fencing energy sources available on the market. However, it is better if the product of dielectric strength and thickness is 2 kV or less, and ideally 0.35 kV or less. The dielectric strength of many materials is known, but a standard test or procedure for measuring dielectric strength can be used.

It is also desirable that the product of the dielectric strength and thickness of the coating be less than the potential normally carried by the element during use. Thus, if the core in a typical application would normally carry a potential of 1 to 3 kV, then it is desirable that the product of the dielectric strength and thickness be less than 1 kV, and better still be of a value which ensures that an adequate "shock" is transmitted through the coating for the intended purpose. It should be noted that materials behave differently or in unexpected ways once dielectric breakdown occurs, so it may be desirable to carry out some initial experimentation. It may therefore be necessary to match the parameters of the coating to the intended application.

In most embodiments, the coating applied will be a non-conductor and will have a resistivity of 1300 x 10-6 Ωcm. For the purposes of determining the resistivity of a coating, and particularly of a multi-layer coating, the value is considered to be the resistivity occurring through the coating, i.e. in the radial direction relative to the element, although it will normally be sufficient to consult a table giving the resistivity of particular materials or to carry out a standard resistivity test. Other advantages may possibly arise from using a coating which is not a conductor as a whole. For example, voltage will generally not be induced through the coating until the voltage differential is sufficient to cause dielectric breakdown of the coating. This may be desirable in some applications. As such, a coating can protect the core from electrochemical reactions while still potentially providing some additional corrosion resistance to the element.

Another desirable feature of the coating is resistance to bending damage and resistance to UV (ultraviolet) damage. In many applications, an element according to the present invention is repeatedly wound, rolled or stretched. The constant bending and changing of shape can result in severe stress on the applied coating. For example, a flexibility test such as ASTMD522, in which a fine wire representing the element is wound around a tapered mandrel, can be used to determine if a coating has adequate resistance to bending damage. For a coated element of 2 mm diameter (including coating), the result should be 5 mm or, more preferably, 3 mm. For an element of 4 mm diameter (including coating), the result should be 10 mm. Thus, the coated element should preferably be at least 2.5 times (or less) its diameter and ideally 1.5 times (or less) its diameter.

To determine UV stability, the procedure prescribed in ASTMGS3-84 can be used. A Q-UV accelerated weathering tester from the Q-Panel Company of Ohio, USA is used. UV lamps UVB-313/280 are used. The cycle is 3 hours UV/65º C, 3 hours condensation/40º C. The total exposure time is 1008 hours (six weeks). No special conditions are applied. At the end of this period, the coated element can be subjected to a bending damage test as prescribed above, reaching at least 3.5 times its own diameter, preferably 2.5 times its own diameter and ideally 1.8 times its own diameter.

To improve the visibility of the coated conductive element, it is desirable to use a pigmented coating or otherwise of a type that increases visibility. Typically, a coating is substantially opaque, although it may equally well be substantially transparent or translucent if thereby increasing visibility to the human eye over that of a standard galvanic cell of the same approximate dimensions. There are several ways to improve visibility. One method is to use a pigment so that the coating is more visible to the eye, especially in dim light. This may, for example, involve using the pigment in a way that gives the coating a colour belonging to the group of white, yellow, orange (and various shades and tints thereof) and/or a fluorescent coating. It may also be possible to use stripes of these or other colours. On the other hand, in applications where security is a priority, it may be desirable to use a coating or colour that camouflages the element.

Alternatively, a reflective coating may be used. Many reflective coatings are known, such as those present in many of the reflective tapes available. A variety of reflective surface treatments may be used, including those that use the surface of the conductive core as a reflector and application of a protective coating to prevent haze or damage in the typical application. The surface of the core may be etched or coated with reflective particles to enhance its reflective properties. The outer coating, which is typically transparent, may also be colored (while at the same time being substantially translucent/clear) to further aid visibility - perhaps over a wider range of viewing conditions. In the context of a pigmented embodiment, stripes of different sections may be provided.

Ideally, the reflectivity of visibility-enhancing coatings should be such that at least 40% and preferably at least 50% of incident white light (typically substantially perpendicular to the surface of the coating and of approximately the intensity of normal sunlight) is reflected from the surface. The incident white light should be substantially in the visible spectrum and the reflected light need not be white. If the reflected light is colored, the desired minimum reflectivity can be reduced to 30% and preferably 40%.

There are many ways to improve visibility. In some conditions and applications, certain colours and colour combinations may be indicated. Fluorescent finishes generally provide greater visibility, although they are prone to fading and losing effectiveness in outdoor applications. In low light conditions, a reflective finish may be advantageous, particularly where the incident light comes from, for example, the headlights of a vehicle (e.g. the headlight of an agricultural vehicle at a farm gate). Variations of the different finishes can be used so that the coated element can benefit from the advantages of several different finishes. For simplicity, it is intended that the coating in most cases will comprise an opaque pigment to give the element a substantially uniform colour. Experiments have shown that white is one of the most effective colours under normal agricultural conditions. To a lesser extent, yellow and orange may also be effective, and the intermediate tones and shades may also be used. In certain circumstances, such as snow, it may be desirable to provide a colour (such as yellow or orange) that contrasts with or stands out against the typical background.

There are many desirable properties that a coating can have, some of which can be utilized in the present invention. One of these desirable properties is resistance to abrasion under the normal conditions encountered in the practice of the present invention. Since one of the main intended uses of the invention is agriculture, a test has been devised which approximates the typical conditions encountered. The test is intended to be applied to an embodiment of the present invention which comprises a stretchable spiral. For a closed spiral comprising a 2 to 2.5 mm diameter member wound into a 50 mm diameter spiral and having an unstretched spiral length of 500 mm, the spiral is secured at one end and stretched to 4 m by pulling on the other end. The stretched end of the spiral is then released and the spiral is allowed to fall onto a bed of compacted, dry clay or dirt free of particulate material such as gravel. The spiral allowed to contract to its unstressed length and the cycle is repeated 50 times, after which the coil is rotated 90º on its axis. The process is then repeated until a total of 200 cycles have been completed, 50 cycles at each of the four different rotation points of the coil. At the end of the cycle, the coil should be examined in the compressed state and at least 90% of the coating should remain visible on the outside of the coil. Better still, 95% or more of the original coating should be present.

In examples where it is not possible to achieve 800% elongation of a coil, a comparable test should be performed in which the coil is stretched to 75% of its maximum elongation* (*i.e., the maximum elongation at which no irreversible deformation or damage to its elastic memory occurs). It should be noted that a coating conforming to the abrasion test described here, while often desirable, may not be required for all applications of the present invention.

In some cases it may also be desirable for the coating to have other physical properties. The following is a guideline for some of the desirable properties that may be inherent in any coating used in the present invention:

HARDNESS : one pass (no penetration) at 2000 g according to the methods of BS3900-E2;

IMPACT STRENGTH : equal to or greater than 200"/pound 2.5mm passage according to the procedures of BS3900-E3;

ADHESION : Pass GTO (for 2mm cross cut) according to the procedures of BS3900-E6 or its equivalent.

In these examples, the aim is for a coating to meet or exceed the results of these test procedures.

There are numerous other modifications that can be made to a coated element according to the present invention. For example, the conductive element need not necessarily be completely coated with the coating material. For example, the coating material can be applied to the conductive element in such a way that air gaps remain between the coating material and the conductor when viewed under a microscope. While the coating material itself has a very high dielectric strength, the dielectric strength of air is low, so that the total effect or "nominal" dielectric strength of the coating material as a whole on the conductor is less than the actual dielectric strength of the coating material alone. It is possible to introduce the air gaps as open or closed cells in the applied coating.

While many known coating techniques can be modified for use with the present invention, it has been found that one technique particularly suitable for coating conductive elements in accordance with the properties of the present invention involves the use of an electrostatic powder coating technique. In this technique, the coating material is applied to the conductive element sufficiently thinly or sparingly so that the effectiveness of the element within an electric fence system is not impaired. This technique can often provide a reasonable degree of control of coating parameters such as thickness. Suitable coating materials which have been found to be effective in trials using electrostatic powder coating include epoxy and polyester materials. Powder coatings from the PE polyester range from Western of Glen Eden, Auckland, New Zealand, have been found to be particularly suitable in trials. With a coating thickness of about 50 µm, physical properties of the coating that met or exceeded those listed above as desirable properties were generally achieved. In addition, this range of coatings also exhibited good weathering properties, good gloss retention and color stability, and corrosion resistance. These properties, which are characteristic of many epoxy and polyester materials, make most of them particularly suitable for use as a coating and for various embodiments of the present invention.

Although other methods of applying a coating are also contemplated, such as dipping, spraying or electroplating, each of these methods does not always provide sufficient control over the coating properties and parameters. Consequently, the suitability of each of these methods for a particular type of coating used in the present invention should be considered.

The powder coating process also allows, in many cases, a sufficiently thin coating to be applied to meet dielectric strength and strength requirements. In addition, thin coatings are generally more resistant to bending damage, particularly in the stretchable spiral embodiments of the present invention. When a powder coating, or indeed most of the other coatings, are applied to such an embodiment, it is desirable to apply the coating to the article while it is at nearly full stretch. This makes the article less susceptible to bending damage or cracking. Typically, most coatings will be applied in the range of 20 to 150 microns, although values outside this range can be used. The properties of the various coating materials also affect the coating thickness.

BRIEF DESCRIPTION OF THE DRAWINGS

The various aspects and embodiments of the present invention will now be described by way of example only. For some embodiments, reference is made to the drawings accompanying the preliminary specification, in which

Fig. 1 shows a spring gate and the adjacent brackets and

Fig. 2 is an exploded view of the circled section II of Fig. 1.

PREFERRED MODES FOR CARRYING OUT THE INVENTION EXAMPLE 1

This example describes a coated element suitable for use as fencing wire or in other similar applications. The conductive core comprises a round fine wire made of steel, aluminum or a material commonly used in the manufacture of electric fencing wire. The springback of the material should exceed 50º and preferably be more than 100º.

A powder coating made of an element from the PE polyester series of WESTERN powder coatings is applied to the core with a thickness of 20 to 60 µm. The application procedures and any pre-treatment of the core must be carried out in accordance with the manufacturer's specifications and technical data. Due to manufacturing tolerances and -variations, it is recommended that tests be carried out on each batch of coated elements to ensure that the product of dielectric strength and coating thickness does not exceed 8 kV or, better still, 2 kV or, ideally, 0.35 kV. Lower coating thicknesses can be used to reduce the product of these parameters, but this may ultimately result in a reduction in pigment coverage and visibility. These losses may be acceptable for the purpose of improving electrical properties.

EXAMPLE 2

In another embodiment of the present invention, a coated conductive element is used to make an expandable coil suitable for (for example) such applications as a fence gate. In this embodiment, the core is made of a spring material capable of providing a coil spring with elastic memory. Ideally, the springback of the material used in such an embodiment should be equal to or greater than 300° in the springback test defined above. In addition, it is desirable that the coil be able to be stretched by at least 300% (i.e., three times) of its "at rest" length, and preferably by at least 600% (i.e., six times) of its "at rest" length to be useful in this particular embodiment. It should also have such an elastic memory that a coil which has been stretched to 600% of its "rest position" length for a period of two hours returns to a length not exceeding 120% of the "rest position" length within 180 seconds of release. In addition, it is also desirable that such an embodiment can be stretched to a length of at least 800% of the "rest position" length without irreversible deformation or significant impairment of the elastic memory occurring.

A coating is applied to the conductive core substantially as described in Example 1, with the coil preferably being stretched to at least 75% of its maximum operational length (while retaining elastic memory) before the coating is applied. In the embodiment described here, white or another of the preferred colors is preferred. Stripes of other colors or finishes may be used.

In use, referring to the diagrams, one or more sections of electrically conductive coil spring 1 are stretched between two posts 2. Electrical connections, including a cable 3 running under the gate, ensure continuity of the supply of electrical energy from a power source (not shown). The end 5 of the springs 1 is provided with an eyelet or hook 4 by means of which the springs are connected to a live wire 5 and insulated handles 6, which also have eyelets or hooks for connection to the live wires 7 of the opposite post 2. The insulated handle provides a handle 8 and electrical continuity through the handle is achieved via a through shaft (not shown) connecting the hook 4 to the spring 1.

The aspects of the present invention have been described by way of example only, and it will be apparent that modifications and additions are possible thereto without departing from the scope of the appended claims.

Claims (9)

1. A barrier for stretching between two posts, the barrier comprising an expandable coiled portion of a resilient and spring-like electrically conductive material and at least one insulated hand portion, the electrically conductive material comprising a central conductive core and a coating, the coating being applied to the central core and improving the visibility of the electrically conductive material, and the coating also enabling animals coming into contact with the electrically conductive material to be given an electric shock when the material is electrically connected to an electric fence power source, the barrier having a first end that can be attached to a first of the posts, the insulated hand portion enabling a user to connect the second end of the barrier to the second of the posts, the barrier being able to be stretched lengthwise in use such that the ends of the barrier can make an electrical connection between the two posts. 2. A barrier according to claim 1, wherein the coating includes an opaque pigment to improve the visibility of the electrically conductive material. 3. A barrier according to any one of claims 1 or 2, wherein the coating has a thickness of between 20 and 150 µm. 4. A barrier according to any preceding claim, wherein the coating comprises a powder coated coating. 5. A barrier according to any one of claims 1 to 4, wherein the coating comprises a polyester material. 6. A barrier according to any one of claims 1 to 4, wherein the coating comprises an epoxy material. 7. A barrier according to any preceding claim, wherein the insulated hand portion substantially encloses at least a portion of the electrically conductive material. 8. A barrier according to any preceding claim, wherein the insulated hand portion includes a shaft through which the electrically conductive material can be passed. 9. Method for spanning two columns, which includes the following steps: a) securing one end of a barrier to a first support, and b) stretching the barrier in a manner that allows the second end of the barrier to be brought into contact with the second support, and c) securing the barrier to the second support, wherein securing the barrier to both the first and second supports ensures that electrical contact is made between the two supports, the barrier including a resilient and spring-like electrically conductive material having a central conductive core and a coating applied therearound, the barrier further including an insulated hand portion to enable a user of the barrier to carry out the above steps b) and c) without the risk of receiving an electric shock from contact with the barrier.