Barrier for spanning two supports and method of spanning

Abstract: The invention describes coated conductive elements of a type which are suitable for electric fencing applications and describes desirable characteristics of a coating. One described embodiment according to the invention comprises a coated conductive core; said coating, comprising at least one layer, being ultra-violet stable and flex-damage resistant as defined in the specification, the electric resistivity of said coating when measured radially exceeding 1300µΩ/cm, the coating being further characterised in that the product of its average thickness and dielectric strength is less than 8kV. Coatings may be applied,for example, to protect the core or to alter visibilty.

Description: TECHNICAL FIELD This invention relates to providing a coating for conductive elements. BACKGROUND ART Coatings for conductive elements are well known in situations where having an insulating coating does not affect the desired function of the element. In fact, in many situations it is preferable to provide an insulating protective coating such as a plastics material or a rubber about the conductive core. However, in the electric fencing and security fields, the opposite situation applies. The conductive elements used for electric fencing must be able to impart an electric shock to animals or intruders that touch the electric fence. Therefore, an insulating coating (as most coatings are) about the conductor can impair the effectiveness of the electric fence if it is applied in the normal manner. There are many instances, including in the electric fencing and security fields, where it is desirable to apply a coating about a conductive core though it is often desirable that the coating does not significantly inhibit the effectiveness of the element in performing its intended purpose. There are many reasons for providing a coating including, for example, providing protection to the naked core or for increasing the visibility of the element. While galvanic zinc coatings are often applied to steel for protection against corrosion, this is not always effective for other metals and alternative coatings may be desirable. Further, the grey colour of zinc coatings are not particularly visible and in some intended applications this can be a problem. This problem has been highlighted in at least one particular product for the farming sector. In 1980 the applicant introduced into the market a spring gate device comprising an electrifiable spring which was adapted to be suspended across a gateway and removed as required using an insulating handle. The concept has been very successful and was recognised as making a substantial contribution to safety on the farm by receiving a New Zealand Fieldays Rural Safety Award sponsored by the New Zealand Accident Compensation Commission (ACC). In giving the award the ACC recognised, that compared to plain wire gates, the spring gate had an advantage of increased visibility and as it was resilient in the event of a collision, it was less likely to cause injury. However, despite these improvements, the visibility of these electrifiable gates in field conditions has remained a problem and it has become evident that the grey of the galvanic coating can, under poor conditions of visibility such as low light or fog, actually camouflage the conductive element which would usually only be desirable for security applications. An attempted solution was to place coloured tape through the centre of the spring coil though while this improved visibility, problems of entanglement occurred when the spring was in a relaxed condition. Painting the spring was considered but initially dismissed due to problems of paint peel-off during the many extensions of a spring and also to an unsatisfactory level of conductivity loss. Consequently there has arisen a need to be able to apply a coating, for whatever reason, to a conductive element wherein the coating will not excessively impair the effectiveness of the element for applications such as, or similar to, electric fencing. Such coating are also partially known in relation to electric fence wires. For example, French Patent Nos. 2215676 and 2474276 both relate to electric fence wires (or cables) which comprise of a cable which includes a central conductive core and a sheath of semi-insulating material surrounding it, which operate to allow an electric shock to be transferred to animals that come in contact with the cable. French Patent No. 2215676 includes a sheath of insulating material which is rendered conductive by a charge of conductive particles (such as graphite, carbon or aluminium). The sheath comprises of a material such as rubber, plastic or PVC placed on the conductive material in the form of a plastic paint. The sheath in French Patent No. 2474276 comprises a thermo-plastic material which is covered with an electrically conductive powder. Although these coatings are partially suitable for electric fence wires, it has been found that these cables (and coatings) suffer from the significant problem that the cables are generally not particularly resilient, and lack any significant "springiness". This is a significant disadvantage when the cables are intended to be used as gates or barriers for spanning supports. For example, these cables are not capable of longitudinal extension to any significant degree, which prevents them from extending across barriers longer than the usual rest length of the cable. This is a significant disadvantage when used as gates. In addition, as no insulating portion is provided on either of the cables described in these specifications, it is difficult to handle this cable when the cable is connected to an electrically conductive source. The provision of an insulating area on the cable would be a considerable advantage in this type of invention. It is therefore an object of the present invention to address the foregoing problems or at least to provide the public with a useful 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 INVENTION According to a one aspect of the present invention there is provided a barrier for spanning two supports, the barrier comprising an expandable coiled length of a resilient and spring-like electrically conductive material, and at least one insulated handle portion, the electrically conductive material including a central conductive core and a coating, the coating being applied to the central core and enhancing the visibility of the electrically conductive material, the coating also allowing an electric shock to be delivered to animals coming in contact with the electrically conductive material when the material is electrically connected to an electric fence energiser, the barrier having a first end capable of being attached to a first of said support, the insulated handle portion enabling the second end of the barrier to be connected by a user to the second of said supports, the barrier in use capable of longitudinal extension in such a way so that the ends of the barrier can provide an electrical connection between each of said supports. According to a further aspect of the present invention there is provided a method of spanning two supports, the method including the steps of: a) attaching one end of a barrier to a first support, and b) expanding the barrier in such a way so that the second end of the barrier may come into contact with the second support, and c) attaching the barrier to the second support, the attachment of the barrier to both the first and second supports ensuring that electrical contact is made with both said supports, the barrier including resilient and spring-like electrically conductive material with a central conductive core and a coating applied thereto, the barrier further including an insulated handle portion to enable a user of the barrier to perform steps b) and c) above without risk of electric shock being impacted from contact with said barrier. According to a further aspect of the present invention there is provided a coated conductive element comprising a conductive core carrying a potential in excess of 1kV, and having a coating thereabouts, which coating has an electric resistivity when measured radially exceeding 1300 x 10⁻⁶Ω/cm, the coating being further characterised in that the product of its average thickness and dielectric strength is less than 8kV and also less than the potential carried by the core. According to a further aspect of the present invention there is provided an expandable elastic coil of a coated conductive element such as described above. According to yet a further aspect of the present invention there is provided a method of constructing a coated conducting element, said method comprising coating a conductive core with an ultra-violet stable and flex-damage resistant (as herein defined) coating, said applied coating having an electrical resistivity exceeding 1300 x 10⁻⁶Ω/cm measured radially therethrough and which is applied to the core such that the product of the average coating thickness and coating dielectric strength is less than 8kV. In its simplest form, a coated conductive element according to the present invention will comprise a conductive core with an applied coating. In many cases the coating will comprise a single applied layer, though multiple layers may also be applied. For the use of the elements in live fencing applications, it is important that the coating embodies some characteristics. Perhaps foremost among these is an ability to transfer a shock from the conductive core to an object coming into contact or very close proximity to the element. While many coatings can be readily applied which fulfil this requirement, and which may provide some protection to the conductive core (with respect to, for instance, corrosion), they do not address the problems of the prior art. On example of such a coating is a galvanised zinc coating though the dull grey colour has been previously mentioned to introduce visibility problems in farm applications. In the intended applications of the product, which is often in a rural environment, other considerations need to be made to the qualities of the coating. Visibility is one desirable attribute as is a resistance to flex-damage or abrasion likely to be encountered by the everyday use of the product. These desirable attributes will be discussed more fully throughout the course of this specification. There may also be some requirements imposed on the choice of the conductive core. It should be capable of satisfactorily carrying a potential (generally 1kV or higher for fencing applications) and current likely to be encountered in its intended use. 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 is not of a readily deformable substance or deformable embodiment of a substance. For instance, copper in such a form as would be commonly used in enamelled winding wire would not generally be suitable for use as a fence wire. If an animal brushed against the wire, it would tend to retain the shape imposed on it through the contact. Deformable materials would not generally be suitable for coiled stretchable embodiments of the present invention to be described later either. Consequently, it is desirable in many cases to use a conductive core of a material in such a configuration or state that it has a spring back exceeding 50° according to the test prescribed in Australian standard AS 1194.1 and according to the general conditions prescribed therein. For the purposes of experimentation, the equivalent of a filament having a 1.6-2.0 diameter core should be used for the test. More preferably, the spring back shall be higher and a value exceeding 300° would be even more preferable, especially for the stretchable embodiments of the invention. While the conductive core may take virtually any configuration, it is envisaged that in most embodiments of the present invention it will comprise a filament or filaments of an overall substantially circular cross-section. In some embodiments of the invention, such as for instance the expandable coil, the cross-section of the filament may be substantially that of a ribbon. Virtually any dimension may be used for the conductive core though again it is envisaged that in most applications that filament will have an average diameter of 2.5mm or less. In embodiments other than of circular cross-section, the cross-sectional area is envisaged to be in most cases that of a 2.5mm diameter circle or less. However this shall not limit use of the present invention to these particular values. For the present invention to be effective in fencing and security applications, it is important that the coating is still able to deliver an acceptable shock to an object coming into contact with same. Consequently, any coating which is applied should not totally insulate the conductive core. For the purposes of the present invention, the degree by which the coating insulates a core can be determined by calculating the product of the dielectric of the coating (preferably measured radially from the core outwards) and the coating thickness. It is preferable that the product of the coating's average thickness and its radial dielectric strength is less than 8kV as this still usually allows an acceptable shock to be delivered with a core having a potential of 10kV. This latter value is approximately the equivalent of the most powerful fence energiser units commercially available. However, it is preferable that the product of dielectric strength and thickness is 2kV or less and ideally 0.35kV or less. The dielectric strengths of many materials are known though a standard test or procedure for measuring dielectric strength may be followed. It is also desirable that the product of dielectric strength and coating thickness is less than the potential normally carried by the element during use. Thus if the core, for a typical application would normally carry a potential of 1-3kV, then it is desirable that the dielectric and thickness product is less than 1kV and even more preferably, such to ensure that an acceptable 'shock' is carried across the coating for its intended purpose. It is noted that materials may behave differently or unexpectedly once dielectric breakdown occurs and some initial experimentation may be desirable. Thus, some matching of the coating parameters to the intended application may be required. In most embodiments the applied coating shall be a non-conductor and possess a resistivity of 1300 x 10⁻⁶Ω/cm. For the purposes of determining the resistivity of a coating, and especially for multiple layer coatings, the resistivity shall be taken to be that through the coating i.e. radially with respect to the element, though it will normally be sufficient to consult a table specifying the resistivity of particular materials or to use a standard test to determine resistivity. Other advantages may possibly be realised through the use of the coating which as a whole is not a conductor. For instance, voltage will not generally be transmitted across the coating until such a time as the voltage differential is sufficient to result in dielectric breakdown of the coating. This may be desirable in some applications. As such a coating can conceivable protect the core against electrochemical reactions, some additional corrosion resistance may possibly be inferred to the element. Another desirable feature of a coating is resistance to flex-damage and resistance to UV (ultra-violet) damage. In many applications, an element according to the present invention will be coiled, rolled or stretched many times. The continual flexing and changing of shape can impose severe stress on an applied coating. For instance, to determine whether a coating has a suitable resistance to flex-damage, a flexibility test such as ASTMD522 may be used where a filament representing the element is wound about a conical mandrill. For a coated element of 2mm diameter (including coating) the results should pass 5mm or more ideally, 3mm. For a 4mm diameter element (including coating) test results should pass 10mm. Thus, preferably, the coated element should pass at least 2.5 times (or less) its diameter and ideally will pass 1.5 times (or less) its diameter. To determine ultra-violet stability, the procedure prescribed in ASTMG53-84 may be used. The equipment is a Q-UV ACCELERATED WEATHER TESTER by the "Q-Panel Company" of Ohio, U.S.A. The UV lamps are UVB-313/280. The cycle is 3hrs UV/65°C; 3hrs condensation/40°C. Total exposure time is 1008hrs (six weeks). There are no special conditions. At the end of this period the coated element may be subjected to a flex-damage test as prescribed above whereby it should pass at least 3.5 times its own diameter, more preferably 2.5 times its own diameter, and ideally 1.8 times is own diameter. To enhance visibility of a coated conductive element, it is desirable that a coating is pigmented or otherwise of a type which enhances its visibility. Typically a coating will be substantially opaque though may equally be substantially transparent or translucent if the visibility to the human eye is enhanced over a standard galvanised element of the same approximate dimensions. There are several manners in which a visibility may be enhanced. One manner is to employ a pigment so that the coating appears more visible to the eye, especially in low light levels. For instance, this may employ the use of the pigment so that the coating appears to be a colour falling within the group of white, yellow, orange (and various tones and hues thereof) and/or a fluorescent coating. Bands of these or other colours may also be employed. In security oriented applications it may be desirable to employ a coating or colour which camouflages the element instead. Alternatively, a reflective coating may be applied. Many reflective coatings are known, such as those used in many available reflective tapes. Many reflective finishes may be employed, including using the surface of the conductive core as a reflector and applying a protective coating to prevent tarnishing or damage through typical use. The core's surface may be etched or coated with reflective particles to increase its reflective properties. The outer coating, which is typically transparent, may also be coloured (while still substantially translucent/transparent) to further aid visibility - perhaps over a greater range of visibility conditions. As for in a pigmented embodiment, bands of different portions may be provided. Ideally, the reflectance of visibility enhancing coatings should be such that at least 40%, and preferably at least 50%, of incident white light (typically substantially normal to the coating surface and approximating normal sunlight in intensity) is reflected from the surface. The incident white light should be substantially within a visible spectrum and the reflected light need not be white. Where the reflected light is coloured, the minimum desired reflectance may be reduced to 30% and preferably 40%. There are many ways in which visibility can be enhanced. In some conditions and applications, certain colours or colour combinations may be more appropriate. Fluorescent finishes generally provide higher visibility though are prone to fade and lose their effectiveness in outdoor conditions. In low light levels a reflectorised finish may be preferable, especially where there may incident light such as a vehicle headlight (e.g. a farm-bike headlight on a farm gate). Varieties of different finishes may be applied so that a coated element may benefit from the attributes of several different finishes. For simplicity, it is envisaged that in most cases a coating will comprise an opaque pigment to provide the element with a substantially uniform colour. Experimental trials have shown white to be one of the more effective colours under normal farm conditions. Yellows and oranges may also be effective to lesser degrees and hues and tones in between may also be used. In some instances, such as for in snow, it may be desirable to provide a colour (e.g. yellow or orange) which contrasts with or stands out against the typical background. There are many other desirable qualities a coating may have, some of which may be employed in the present invention. One of these desirable properties is a resistance to abrasion during the normal conditions to be found in the application of the present invention. As a major intended use of the invention is on a farm, a test has been devised which approximates typical conditions to be encountered. The test is to be applied to an embodiment of the present invention which comprises a stretchable coil. For a closed coil comprising 2-2.5mm diameter element formed into a coil diameter of 50mm and an untensioned coil length of 500mm, the coil is fixed at one end and extended to 4m by pulling on its other end. The extended end of the coil is then released and the coil is allowed to fall on a bed of compacted dry clay or dirt free of particular matter such as gravel. The coil is allowed to retract to its untensioned length and the cycle is repeated 50 times where upon the coil is rotated about its axis by 90°. The process is then repeated until a total of 200 cycles have been achieved comprising 50 cycles on each of four different rotational points of the coil. At the end of the cycle the coil should be examined in a compressed state and at least 90% of the coating visible on the outer side of the coil should remain. More desirably 95% or more of the original coating should remain. For instances where it is not possible to achieve the 800% expansion of a coil, a comparable test whereby a coil is expanded to 75% of its maximum extension † should be undertaken. It is noted that while a coating which conforms to the abrasion test herein is often desirable, it may not be necessary for all applications of the present invention. It may also be desirable in some cases that the coating comprises other physical characteristics. As a guide-line to some desirable characteristics which may be inherent in any coating used in the present invention are: Hardness - a pass (no penetration) for 2000g according to the procedures of BS3900-E2; Impact resistance - equal to or exceeding 200"/lb 2.5mm pass according to the procedures of BS3900-E3; Adhesion - pass GTO (for 2mm cross-hatch) according to the procedures of BS3900-E6 or the equivalent thereof. In these examples it would be desirable that a coating equalled or exceeded results of these tests procedures. There are many other modifications which may be made to a coated element according to the present invention. For instance, the conductive element may not necessarily be fully coated with the coating material. For instance, the coating material may be applied to the conductive element in such a way that there are air gaps between the coating material on the conductor when seen at a microscopic level. Although the coating material itself may have a high dielectric strength, the dielectric strength of air is low, thus the overall 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 on its own. It is possible that the air gaps may be introduced as opened or closed cells in the applied coating. While many known coating techniques may be modified for use with the present invention, it has been found that one particularly suitable method of coating conductive elements in accordance with the attributes of present invention comprises using a technique of electrostatic powder coating. This method applies the coating material sufficiently thinly or sparsely on the conductive element such that the effectiveness of the element within an electric fence system is not compromised. A reasonable degree of control over coating parameters, such as thickness, can often be achieved by this technique. Suitable coating materials which have worked well in trials using electric static powder coating include epoxy and polyesters materials. PE Polyester series powder coatings by "WESTERN" of Glen Eden, Auckland, New Zealand have been found to be particularly suitable in tests. Coating thicknesses of approximately 50 microns have generally exhibited physical coating characteristics equal to or exceeding that previously outlined as desirable attributes. Further, this range of coatings also exhibits good weathering properties, good gloss retention and colour stability as well as corrosion resistance. These properties, characteristic of many epoxy and polyester materials make the most of the in particularly suitable for use as coatings and various embodiments of the present invention. While other methods of applying a coating, such as by dipping, spraying, or electro-plating, are envisaged each of these techniques may not always provide suitable control over coating the characteristics and parameters. Consequently, the suitability of each technique for a particular type of coating used in the present invention should be considered. The powder coating method also in many cases allows a suitably thin coating to be applied in order to satisfy requirements of dielectric strength and thickness requirements. Furthermore thin coatings are generally more resistant to flex-damage, especially for expandable coiled embodiments of the present invention. When applying a powder coating, or in fact most other coatings, to such an embodiment it is desirable to apply the coating to the article at near to full extension. This tends to make it less susceptible to flex-damage or cracking. Coating thicknesses of 20-150 microns are typically envisaged for most coatings though values outside of this range may also be used. The properties of different coating materials will influence coating thicknesses as well. BRIEF DESCRIPTION OF DRAWINGS Various aspects and embodiments of the present invention will now be described by way of example only. For some embodiments, reference shall be made to the drawings accompanying the provisional specification in which: Figure 1: illustrates a spring gate and adjacent fixtures, and Figure 2: is an expanded view of the encircled portion II of Figure 1. BEST MODES FOR CARRYING OUT THE INVENTION EXAMPLE 1 This example describes a coated element suitable for use as a fence wire or in other similar applications. The conductive core comprises a circular filament of steel, aluminium or a material generally used in the construction of electric fence wire. The spring back of a material should exceed 50° and preferably exceed 100°. To the core is applied a powder coating of a member of the WESTERN PE polyester series powder coatings at a thickness of 20-60 microns. Methods of application and any preliminary treatments of the core are according to the manufacturers specifications and technical data. Due to manufacturing tolerances and variations, it is recommended that tests are performed on any batch of coated elements to ensure that the product of coating dielectric strength and thickness do not exceed 8kV, or more preferably 2kV and ideally 0.35kV. Lower coating thicknesses may be applied to reduce the product of these parameters though a reduction in pigment coverage and visibility may eventuate. These losses may be acceptable for an improvement the electrical properties. EXAMPLE 2 In another embodiment of the present invention, a coated conductive element is used to form an expandable coil suitable for the applications such as (for example) a fence gate. In this embodiment, the core is of a spring material able to yield a coil spring with elastic memory. Ideally the spring back of a material used in such an embodiment shall equal or exceed 300° according to the spring back test previously defined. Furthermore, to be useful in this particular embodiment, it is desirable that the coil will be expandable by at least 300% (i.e. three times) its 'at rest' length and preferably by at least 600% (i.e. six times) its 'at rest' length. It should also have elastic memory such that a coil expanded to 600% of its 'at rest' length for a period of two hours will return to a length not exceeding 120% of its 'at rest' length within 180 seconds of its release. Furthermore it is also desirable that such an embodiment is expandable to a length of at least 800% of its 'at rest' length without irreversible deformation or substantial impairment to its elastic memory. A coating which is applied to the conductive core is substantially as described for Example 1 though preferably the coil will be expanded to at least 75% of its maximum operating length (while preserving its elastic memory) before a coating is applied. White or one of the other preferred colours is preferred in this described embodiment. Bands of other colours or finishes may be applied. For use, and with reference to the diagrams, one or more lengths of the electrically conductive coil spring 1 are suspended between two posts 2. Electrical connections including an under-gate cable 3 ensure continuity of supply of electric power from a supply source (not shown). The end 5 of the springs 1 are provided with an eyelet or hook 4 by which the springs are connected to an electrified wire 5 and insulated handles 6 also having eyelets or hooks for connection to electrified wires 7 of opposite post 2. The insulated handle provides a handpiece 8 and electrical continuity through the handle is achieved via a continuous shaft (not shown) which joins hook 4 up to the spring 1. Aspects of the present invention have been described by way of example only and it should be appreciated that modifications and additions thereto may be made without departing from the scope of the appended claims.

Claims: A barrier for spanning two supports, the barrier comprising an expandable coiled length of a resilient and spring-like electrically conductive material, and at least one insulated handle portion, the electrically conductive material including a central conductive core and a coating, the coating being applied to the central core and enhancing the visibility of the electrically conductive material, the coating also allowing an electric shock to be delivered to animals coming in contact with the electrically conductive material when the material is electrically connected to an electric fence energiser, the barrier having a first end capable of being attached to a first of said support, the insulated handle portion enabling the second end of the barrier to be connected by a user to the second of said supports, the barrier in use capable of longitudinal extension in such a way so that the ends of the barrier can provide an electrical connection between each of said supports. A barrier as claimed in claim 1 whereby the coating includes an opaque pigment to increase the visibility of the electrically conductive material. A barrier as claimed in either of claims 1 or 2 whereby the coating has a thickness of between 20 and 150 microns. A barrier as claimed in any of the above claims whereby the coating comprises a powder applied coating. A barrier as claimed in any of claims 1 to 4 whereby the coating comprises a polyester material. A barrier as claimed in any of claims 1 to 4 whereby the coating comprises an epoxy material. A barrier as claimed in any of the above claims whereby the insulated handle portion substantially surrounds at least part of the electrically conductive material. A barrier as claimed in any one of the above claims whereby the insulated handle portion includes a shaft through which the electrically conductive material may pass. A method of spanning two supports, the method including the steps of: a) attaching one end of a barrier to a first support, and b) expanding the barrier in such a way so that the second end of the barrier may come into contact with the second support, and c) attaching the barrier to the second support, the attachment of the barrier to both the first and second supports ensuring that electrical contact is made with both said supports, the barrier including resilient and spring-like electrically conductive material with a central conductive core and a coating applied thereto, the barrier further including an insulated handle portion to enable a user of the barrier to perform steps b) and c) above without risk of electric shock being impacted from contact with said barrier.

Inventors: GALLAGHER WILLIAM MURRAY, GALLAGHER, WILLIAM MURRAY
Applicants: GALLAGHER ELECTRONICS LTD, GALLAGHER ELECTRONICS LIMITED
Application year: 1991
Main classification: H01B5
IPC codes: H01B5