[0001] 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.
[0002] 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.
[0003] 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.
[0004] 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.
[0005] 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.
[0006] It is an object of the invention to provide an insulator whose insulating effect
in the long term is maintained with a greater reliability.
[0007] 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.
[0008] 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.
[0009] Special embodiments of the invention are laid down in the dependent claims.
[0010] 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.
[0011] 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.
[0012] 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.
[0013] 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.
[0014] 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.
[0015] 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.
[0016] 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.
[0017] 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.
[0018] 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.
[0019] 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.
[0020] 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.
[0021] 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.
[0022] 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.
[0023] 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.
[0024] 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.
[0025] 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.
[0026] 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.
[0027] 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.
1. 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).
2. 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).
3. An insulator according to claim 2, wherein the bushing (12) abuts at least locally
against said eye part (10).
4. 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).
5. An insulator according to claim 4, wherein an outer edge of the bushing (12) marks
the boundary.
6. 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).
7. 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.
8. 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.
9. An insulator according to any one of the preceding claims, wherein the insulating
body (4) and the bushing (12) are manufactured from plastic.
10. 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).
11. 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.
12. 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.
13. 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).
14. 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).