GB2275127A

GB2275127A - Electric cable

Info

Publication number: GB2275127A
Application number: GB9302264A
Authority: GB
Inventors: Peter Hill Ming Wong
Original assignee: RICH CITY Ltd
Current assignee: RICH CITY Ltd
Priority date: 1993-02-05
Filing date: 1993-02-05
Publication date: 1994-08-17
Also published as: GB9302264D0

Abstract

An electric cable (10) suitable for use as speaker cable comprises at least two electrically-conductive cores (11) having insulation (12) moulded under a practically air-free condition around the cores (11), the insulation (12) being provided with a hollow passage (13) co-extending with and between said cores (11). Three cores (16, fig 4) may be disposed around the passage (18). The separation of the cores by the passage inhibits electrical interference and mechanical vibration. The insulation may be transparent or translucent PVC and is extruded (figure 2) around the cores (11) in an annular space (31), the space being evacuated at (28). A tube (27) open to the air provides the passage (13). <IMAGE>

Description

ELECTRIC CABLE The present invention relates to an electric cable.

According to the invention, there is provided an electric cable which comprises at least two electrically-conductive cores and insulation moulded under a practically air-free condition around the cores, wherein the insulation is provided with a hollow passage co-extending with and between said at least two cores.

It is preferred that the hollow passage has a circular cross-section.

Preferably, the insulation is of a transparent or translucent material.

It is preferable for the insulation to have an external profile resembling the shape of the combined cross-section of the cores and hollow passage, thereby forming two relatively thin flexible webs connecting in a co-extending manner the individual insulations of the respective cores.

In a preferred embodiment, the cores are arranged on opposite sides of the hollow passage.

The electric cable may comprise more than two said cores, in which each pair of adjacent cores are lying on opposite sides of the corresponding hollow passage provided therebetween.

In another preferred embodiment, the electric cable may comprise three said cores which are arranged equi-angularly around the hollow passage.

The electric cable is suitable, but not necessarily, for use as a speaker cable.

The invention will now be more particularly described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a cross-sectional end view of an embodiment of an electric cable in accordance with the invention; Figure 2 is a cross-sectional side view of moulding apparatus for use in manufacturing the electric cable of Figure 1; Figure 3 is an end view of a die provided at the forward end of the moulding apparatus of Figure 2; and Figure 4 is a cross-sectional end view of another embodiment of an electric cable in accordance with the invention.

Referring firstly to Figure 1 of the drawings, there is shown an electric cable 10 embodying the invention, which electric cable is provided by a pair of electricallyconductive, individually stranded cores 11 and PVC insulation 12 moulded around the two cores 11. A hollow passage 13 having a circular cross-section is formed in the insulation 12, co-extending with and between the two cores 11. In this construction, the cores 11 are provided on opposite sides of the hollow passage 13 and their separation is thus extended by the presence of the hollow passage 13. The extended separation assists to reduce undesirable electro-magnetic interference between signals transmitted through the respective cores 11.

The external profile of the insulation 12 is designed to follow closely around or resemble the shape of the combined cross-section of the cores 11 and hollow passage 13. This results in the formation of two relatively thin flexible webs 14 connecting in a co-extending manner the individual insulations of the respective cores 11.

The air in the hollow passage 13 serves as a good damping medium against mechanical vibration. The flexibility of the thin bridging webs 14 also reduces the vibrational interference across the cores 11. These characteristics against cross-core vibrational interference render the cable 10 particularly suitable for use as a speaker cable, compared with conventional flat twin-core speaker cables.

The manufacture of the cable 10 will now be described with reference to Figures 2 and 3 showing suitable moulding apparatus 20 which comprises a barrel 21 having a conical entrance 22 through which molten PVC is supplied under pressure into the barrel 21. The barrel 21 is provided at its forward end with a die 23 (as best shown in Figure 3) which has a converging opening 24. A co-axially extending tubular chamber 25 is located within the barrel 21, which has a conical forward end 26 extending into the converging opening 24 of the die 23 to define an annular outlet for the molten PVC. The chamber 25 is provided with a co-axial tube 27 extending through the chamber 25 and the die 23.

The internal annular space, designated by reference numeral 31, between the chamber 25 and the tube 27 is closed and in operation maintained at practically vacuum by means of a vacuum pump (not shown) connected to an evacuation point 28 provided near the rear end of the chamber 25 outside the barrel 21.

The rear end of the chamber 25 is closed by an end plate 29 which has a central opening 30 for the tube 27 and two side openings (not shown) for a pair of said cable cores 11 to enter the chamber 25. The cable cores 11 pass through the internal annular space 31, parallel to the tube 27 and on opposite sides thereof, and exit through the forward end 26 of the chamber 25 and the opening 24 of the die 23.

In operation, molten PVC is supplied under pressure through the entrance 22 into the barrel 21 of the moulding apparatus 20 and subsequently exits through the die 23 while the cable cores 11 are drawn through the chamber 25 at an appropriate speed. The molten PVC completely fills the forward part of the barrel 21 including the die 23, whilst the cable cores 11 are drawn out of the chamber 25 and exiting the chamber forward end 26 under a practically air-free condition. This results in the molten PVC being moulded onto the cable cores 11 immediately upon exiting the die 23 in a practically air-free condition which ensures that the molten PVC adheres directly onto the cable cores 11 in the absence of air, thereby avoiding oxidation of the cable cores 11 which are protected by the insulation 12.

The insulation 12 is preferably transparent or translucent such that the cable cores 11 can be seen protected air-free within the insulation 12.

The tube 27 serves to act as a former for the molten PVC to bear on upon exiting the chamber forward end 26, thereby enabling formation of the passage 13 in the insulation 12.

The tube 27 is preferably open at both ends to ensure that there is always sufficient air pressure within the passage 13 at where the insulation 12 leaves the forward end of the tube 27, otherwise the passage 13 may be formed improperly, either contracted or collapsed.

Figure 4 shows another electric cable 15 embodying the invention, which electric cable 15 has three separate stranded cores 16 protected by moulded insulation 17. The cores 16 are arranged in an equi-angular manner around a central co-extending hollow passage 18. As the external profile of the insulation 17 is likewise designed to resemble the shape of the combined cross-section of the cores 16 and hollow passage 18, three relatively thin flexible webs 19 are formed each connecting in a co- extending manner the individual insulations of two adjacent cores 16.

It is envisaged that three or more cable cores may also be arranged in a flat manner with a hollow passage in the insulation between each pair of adjacent cores.

It is to be appreciated that the provision of the hollow passage not only extends the cable core separation but is also insulation material saving.

The invention has been given by way of example only, and various other modifications of and/or alterations to the described embodiments may be made by persons skilled in the art without departing from the scope of the invention as specified in the appended claims.

Claims

1. An electric cable comprising at least two electrically-conductive cores and insulation moulded under a practically air-free condition around the cores, wherein the insulation is provided with a hollow passage coextending with and between said at least two cores.

2. An electric cable as claimed in claim 1, wherein the hollow passage has a circular cross-section.

3. An electric cable as claimed in claim 1 or claim 2, wherein the insulation is of a transparent or translucent material.

4. An electric cable as claimed in any one of claims 1 to 3, wherein the insulation has an external profile resembling the shape of the combined cross-section of the cores and hollow passage, thereby forming two relatively thin flexible webs connecting in a co-extending manner the individual insulations of the respective cores.

5. An electric cable as claimed in any one of claims 1 to 4, wherein the cores are arranged on opposite sides of the hollow passage.

6. An electric cable as claimed in any one of claims 1 to 5, comprising more than two said cores, in which each pair of adjacent cores are lying on opposite sides of the corresponding hollow passage provided therebetween.

7. An electric cable as claimed in any one of the claims 1 to 4, comprising three said cores which are arranged equi-angularly around the hollow passage.

8. An electric cable as claimed in any one of the preceding claims, being a speaker cable.

9. An electric cable substantially as hereinbefore described with reference to Figures 1 to 3 or Figure 4 of the accompanying drawings.