EP1566818A1

EP1566818A1 - Insulator for a fence and method for the manufacture thereof

Info

Publication number: EP1566818A1
Application number: EP05075371A
Authority: EP
Inventors: Lambertus Jan Pezij
Original assignee: Handelsonderneming Veldman en Dijkstra BV
Current assignee: Handelsonderneming Veldman en Dijkstra BV
Priority date: 2004-02-20
Filing date: 2005-02-15
Publication date: 2005-08-24
Anticipated expiration: 2025-02-15
Also published as: NL1025536C2; EP1566818B1

Abstract

An insulator for holding fencing material (3) with an electrical conductor in position. An insulating body (4) from electrically insulating material is provided with a passage (5) through the insulating body for receiving a portion located in the passage of the fencing material extending through the passage (5). The passage (5) extends in an axial passage direction (7) between opposite end surfaces (8) of the insulating body (4). A bushing (12) from electrically insulating material extends around at least a part of the circumference (6) of the passage (5). The bushing, or a change in color or hue obtained in a different manner marks a boundary around the passage. A method for manufacturing such an insulator is also described.

Description

The invention relates to an insulator according to the introductory portions of claims 1 and 10 and to a fence provided with such insulators and to a method for the manufacture of such an insulator.
An insulator as indicated hereinabove for holding fencing material such as wire, rope or tape in position relative to a supporting structure is known from practice.
Insulators are important parts of an electric fence. Poor electric insulation of the conductors of the fence may entail voltage loss in that a leakage current towards the ground is formed and that, at such a current intensity, the fence device (the electrical voltage source for applying a voltage across conductors of the fencing material) cannot keep the voltage at a sufficiently high level. Such leakage currents also lead to energy loss which, in practice, is particularly disadvantageous when a battery is used as a power supply.
A first cause of leakage currents is that the insulating body wears down through abrasion so that the metal reinforcing structure of the insulator material is exposed and comes into contact with a conductor of the fencing material. As this phenomenon occurs in the passage of the insulating body, it is difficult to detect without electric circuit testing of the conductors of the fencing material or extensive visual inspection of the insulator.
Another cause of the formation of leakage currents is that, due to an incorrect positioning in the insulating body, the metal reinforcing structure is exposed adjacent the passage, or is at least so close to the surface that it is already exposed with very little wear. This may have been caused with, for instance, a metal reinforcing structure with an eye extending around at least a part of the circumference of the passage, in that, with respect to the intended position in a plane transverse to the central axis of the passage, the metal reinforcing structure is rotated about the central axis of the stem of the metal reinforcing structure. An incorrect position of the reinforcing structure - which can also occur with metal reinforcing structures without an eye - is that the stem, in the direction of the central axis thereof, is located too far towards the passage. Depending on the design of the metal reinforcing structure, an otherwise incorrect positioning of the metal reinforcing structure can also harm the intended electrical insulation thereof with respect to the conductor or conductors of the fencing material.
It is an object of the invention to provide an insulator whose insulating effect in the long term is maintained with a greater reliability.
According to the invention, this object is achieved by providing an insulator according to claim 1. According to a different embodiment of the invention, a ring insulator according to claim 10 is provided. The invention can also be embodied in a method according to claim 12, with which, with great reliability, insulators with a long lasting, highly insulating effect are obtained.
As the bushing from electrical insulating material extends around at least a part of the circumference of the passage, it is reliably ensured that the thickness of the insulating material in the area where, in operative condition, the insulating material insulates the conductors of the fence from the metal of the reinforcing structure, has the intended thickness. The bushing which, during manufacture, is placed over a core part of the mold, effects in a simple manner the intended positioning of the metal reinforcing structure in the mold prior to and during injection of the insulating material of the insulating body and functions as spacer which guarantees that the metal reinforcement structure is held at a sufficient distance from the passage. The marking, which marks a boundary which extends radially at a distance outside the circumference of the passage and around at least a part of the circumference of the passage, simplifies, as wear-indicator, observing the degree of wear of the insulating body at the inside of the passage in relation to the position of the metal reinforcing structure and in relation to the minimum thickness of the insulation body that still ensures a sufficiently reliable positioning of the fencing material.
Special embodiments of the invention are laid down in the dependent claims.
In the following, the invention is further illustrated and elucidated in and by an exemplary embodiment with reference to the drawing. In the drawing:
Fig. 1 shows a perspective view of an example of an insulator according to the invention;
Fig. 2 shows a cutaway perspective view of the insulator according to Fig. 1;
Fig. 3 shows a top plan view in longitudinal cross section through a center plane of an end part of the insulator according to Figs. 1 and 2;
Fig. 4 shows a cutaway perspective view of parts of the ring insulator according to Figs. 1- 3; and
Fig. 5 shows a perspective view of a bushing of the ring insulator according to Figs. 1 - 4.
The Figures show an example of an insulator 1 for holding in position relative to a supporting structure 2 - somewhat schematically represented as a part of a post in Fig. 1 - fencing material 3 such as wire, rope or tape provided with at least one electrical conductor over which an electric voltage can be applied for deterring animals touching the fence.
According to the VDE electric fence equipment regulations, the voltage should at least be 2000 Volts at 500 Ohm (approximately the resistance of an animal touching the conductor). The discharge energy is then limited so no injuries are inflicted on animals touching a conductor of the fence. The electrical conductor should be insulated well with respect to the earth, because leakage currents lead to voltage loss so that the deterring effect may drop below the required level. Moreover, leakage currents form energy loss which is disadvantageous particularly when a battery is used as a power supply, because then, the battery empties quicker. That is why the fencing material of which the conductors form part is held in position by means of insulators. For fencing a meadow a large number of insulators are required. It is therefore of great importance that the insulators are of simple construction and can be manufactured at low costs.
The insulator 1 according to the exemplary embodiment of the invention shown here is provided with an insulating body 4 from electrically insulating material with a passage 5 having a circumference 6 for receiving a portion located in the passage of fencing material 3 extending through the passage. The passage 5 extends in an axial passage direction (arrow 7 in Fig. 1) between opposite end surfaces 8 of the insulating body 4.
The insulator 1 is further provided with a metal reinforcing structure 9, provided according to this example with an eye part 10 extending around the passage 5 over at least a part of the circumference 6 of the passage 5. With the insulator 1 according to this example, the metal reinforcing structure 9 also forms a screw 11 (see Fig. 2) for screwing the insulator 1 into a post or the like. However, the insulator 1, and in particular the metal reinforcing structure thereof can also be designed to be fastened in a different manner, for instance by means of screws reaching through holes in the insulator and, optionally, the metal reinforcing structure.
A bushing 12 from electrically insulating material extends through the eye part 10 and around a part of the circumference 6 of the passage 5.
The bushing 12 from electrically insulating material which extends around at least a part of the circumference 6 of the passage 5 ensures in a reliable manner that in the area where, in operative condition, the insulating material insulates the conductors 3 of the fence from the metal of the reinforcing structure 9, the insulating material has the intended thickness. The bushing 12 which, during manufacture, is placed over a core part of the mold ensures in a simple manner that prior to and during injection of the insulating material of the insulating body 4, the metal reinforcing structure 9 in the mold is kept at a sufficient distance from the passage 5.
A passage 13 forms an interruption of the insulating body 4, the bushing 12 included, and extends via an opening in the eye part 10 between the passage 5 and the surroundings. Through the passage 13, fencing material 13 can be brought into the passage 5 with a movement in a direction at an angle relative to the passage direction 7. It is therefore not necessary to thread the fencing material through the passage 5 in the passage direction 7. As the passage 13 runs obliquely relative to the passage direction 7, fencing material 3, which has been tensioned in the passage direction 7, cannot escape from the passage 5.
For a reliable seal between the bushing 12 and the rest of the material of the insulating body 4, and in particular the prevention of slits through which leakage currents can run when moisture accumulates therein, the bushing 12 is preferably manufactured from plastic, like the rest of the insulating body, and preferably from a similar kind of plastic. The bushing 12 is further provided with anchorages 15 - 19. As a number of the anchorages 15 - 17 grip the metal reinforcing structure 9 on both sides, they also contribute to a mutual positioning of the metal reinforcing structure 9 and the bushing 12 in axial direction 7 of the passage 5 before the rest of the material of the insulating body 4 is injected around these parts 9, 12. By providing the anchorages 16 - 17 as snap fingers engaging the reinforcing structure 9, furthermore, a reliable mutual fastening between the reinforcing structure 9 and the bushing 12 is realized prior to injection. It is also possible, for that matter, to design the anchorages on only one side of the reinforcing structure 9 as snap fingers. The anchorages on the other side of the reinforcing structure 9 can then, for instance, be designed to be substantially form-retaining.
Furthermore, two of the anchorages 18, 19 extend as far as the circumference in axial view of the insulating body and are designed as flat flanges. As a result, the wall thickness of the material which must solidify after it has been injected around the reinforcement structure 9 and the bushing 12 is limited and after injection around the reinforcing structure 9 and the bushing 12 has taken place, the cooling of the material in the center area of the insulating body 4 is accelerated. All this contributes to the reduction of the cycle time during injection molding. As the flanges 18, 19 themselves are thin-walled, they do not contribute to the increase of the cycle time.
The bushing 12 abuts locally against the eye part 10. This offers the advantage that prior to the formation of the insulating body 4, the bushing is held accurately in position with respect to the eye part 10 of the reinforcing structure 9.
The end surfaces 8 of the insulating body 4 exhibit a marking 14, marking a boundary which extends radially at a distance outside the circumference 6 of the passage 5 and around at least a part of the circumference 6 of the passage 5. An outer edge of the bushing 14 marks this boundary. The eye part 10 has an inside circumference located in radial direction at a distance outside this boundary. As a result, the bushing 12 still has sufficient insulating action when it has worn down to the outer edges located at the location of the end surfaces 8. With the insulator 1 according to this example, this is realized in that the bushing is provided with projections 20 distributed over the part of the outer circumference which is placed in the eye 10 of the metal reinforcing structure.
The marking 14 forms a wear-indicator by means of which it can easily and clearly be seen whether the insulating body 4 has worn down in the area of the passage 5 to such an extent that a reliable insulation of the conductor 3 with regard to the reinforcing structure 9 is no longer ensured.
As the transition from the bushing 12 to surrounding material of the insulating body 4, which preferably has a highly deviating and, preferably, contrasting color relative to the bushing 12, forms this marking, a marking is provided which, also with long-term exposure to influences from the surroundings, remains present in a reliable manner, also when the insulator is manufactured from material such as polyolefin plastic to which printing and stickers adhere poorly, and it is not necessary to provide a special printing or change in form for forming the marking 13.
However, it is also possible to provide a marking which is arranged in a different manner. Further, if the insulator is not provided with a metal reinforcing structure extending around at least a part of the circumference, the wear-indicator formed by the marking can also serve to indicate whether the insulating body is still sufficiently thick for holding the fencing material in a reliable manner in the passage through the insulating body.
When manufacturing an insulator 1 according to the example shown, preferably, the metal reinforcing structure 9 is placed in a mold. Prior to injecting, together with the metal reinforcing structure 9, the bushing 12 from electrically insulating material is placed in the mold too. Then, the mold is closed and plastic is injected around a part 10 of the metal reinforcing structure 9. After the plastic has solidified into a sufficiently solid form, the metal reinforcing structure 9, around whose eye part 10 the plastic insulating body 4 is provided, is taken from the mold. Prior to and during injection, the bushing 12 serves as spacer which ensures that the eye part 10 of the metal reinforcing structure 9 is located at a sufficient distance from the core part of the mold defining the location of the inner surface of the passage 5.
Preferably, when the metal reinforcing structure 9 is placed in the mold, the bushing 12 is fixed with respect to the metal reinforcing structure 9, for instance by clamping. This enables the bushing 12 and the metal reinforcing structure 9 to be placed into the mold in one operation, which, in turn, is advantageous for shortening the cycle time of the injection molding.
Further, the bushing 12 prevents the metal reinforcing structure 9 from being moved prior to and during injection around the reinforcing structure 9. With the insulator according to this example, the bushing 12 substantially prevents the reinforcing structure 9 from being tilted around the central axis of the screw 11, and positioning errors and movements in axial direction of the screw 11.

Claims

Insulator for holding in position relative to a supporting structure a flexible fencing material (3) such as wire, rope or tape comprising at least one electrical conductor, comprising:

an insulating body (4) from electrically insulating material with a passage (5) having a circumference (6) for receiving a portion located in the passage of fencing material (3) extending through the passage (5), while the passage (5) extends in an axial passage direction (7) between opposite end surfaces (8) of the insulating body (4),

a metal reinforcing structure (9),

characterized in that the insulating body (4) comprises a bushing (12) from electrically insulating material extending at least around a part of the circumference (6) of the passage (5).
An insulator according to claim 1, wherein the metal reinforcing structure (9) has an eye part (10) extending around at least a part of the circumference (6) of the passage (5) around the passage (5) while the bushing (12) is located within the eye part (10).
An insulator according to claim 2, wherein the bushing (12) abuts at least locally against said eye part (10).
An insulator according to any one of the preceding claims, wherein at least one of the end surfaces (8) of the insulating body (4) exhibits a marking, which marks a boundary which extends radially at a distance outside the circumference (6) of the passage (5) and around at least a part of the circumference (6) of the passage (5).
An insulator according to claim 4, wherein an outer edge of the bushing (12) marks the boundary.
An insulator according to claim 5, wherein the bushing (12) has at least a different texture, colour or hue than a surrounding part of the insulating body (4).
An insulator according to claim 5 or 6, wherein the outer edge of the bushing (12) is located in radial direction at a distance inwards relative to the metal reinforcing structure.
An insulator according to claim 2 or 3 and according to any one of claims 4 - 7, wherein the eye part (10) has an inside circumference (6) which coincides in radial direction with the boundary or is located outside this boundary.
An insulator according to any one of the preceding claims, wherein the insulating body (4) and the bushing (12) are manufactured from plastic.
An insulator for holding in position relative to a supporting structure flexible fencing material (3) such as wire, rope or tape comprising at least one electrical conductor, comprising an insulating body (4) from electrically insulating material with a passage (5) having a circumference (6) for receiving a portion located in the passage of fencing material (3) extending through the passage (5), while the passage (5) extends in axial passage direction (7) between opposite end surfaces (8) of the insulating body (4),
characterized in that at least one of the end surfaces (8) of the insulating body (4) exhibits a marking formed by a transition in at least hue or color, which marking marks a boundary which extends radially at a distance outside the circumference (6) of the passage (5) and around at least a part of the circumference (6) of the passage (5).
A fence comprising at least one supporting structure, insulators (1) according to any one of the preceding claims borne by the supporting structure, and fencing material (3) such as wire, rope or tape comprising at least one electrical conductor, running through the passages (5) of the insulators.
A method for manufacturing an electrical insulator, comprising placing a metal reinforcing structure (9) into a mold, closing the mold, injecting plastic around at least a part (10) of the metal reinforcing structure (9), having plastic injected into the mold solidify into a solid form and taking the metal reinforcing structure (9), around said part (10) of which a plastic insulating body (4) is provided, from the mold, characterized in that prior to injection, a bushing (12) from electrically insulating material is placed in the mold too.
A method according to claim 12, wherein prior to and during placement of the metal reinforcing structure (9) in the mold, the bushing (12) is fixed with respect to the metal reinforcing structure (9).
A method according to claim 12 or 13, wherein the metal reinforcing structure has an eye part (10) and wherein the bushing (12) is placed such that the eye part (10) extends around at least a part of the circumference of the bushing (12).