The present invention relates to a cutting element insertable into a data-transmission cable over a conductor such that it is translatable along and rotatable about a longitudinal axis of the conductor to cut away spaced partitions of a polymer dielectric through which the conductor extends. Cutting of the spaced partitions releases the conductor and allows subsequent extraction and recovery of the conductor from the polymer dielectric. Data, digital or coaxial transmission cables for transmitting data and digital signals into homes have been used for many years and are usually buried underground, often beneath pavements and the front gardens of the homes to which data is being supplied. There are various different cables commonly in use, but a typical cable generally comprises a conductor formed from a single wire or a bundle of strands made of copper or other electrically conductive material.

The conductor is surrounded by a dielectric, which may be a relatively hard plastic or similar polymer material that insulates, protects and provides support for the conductor. A sheath made of PVC or similar material may extend over the dielectric and a copper or other metallic shield may line the sheath. This cable configuration provides good overall mechanical, weather, chemical and electrical protection.

Developments in technology, together with demand for better and faster data transfer, have recently necessitated the use of optical fibres for data transmission purposes, as optical fibre is capable of transmitting much larger quantities of data at high speed relative to traditional copper and other traditional metal conductors. Where optical fibre is required, the standard approach is to disconnect the existing cable and to lay an entirely new cable containing the optical fibre, with the old disconnected cable being left in the ground. It will be appreciated that this approach necessitates the digging of a trench in order to lay the new cable, which is disruptive, time consuming and expensive. It also results in valuable metals forming the conductor being left unused in the ground.

Extraction of the conductor allows it to be recycled. It may also enable part of an existing data transmission cable, such as the outer sheath and part of the insulating dielectric, to be re-used once the conductor has been extracted, by inserting optical fibres therethrough. Alternatively, those parts of the data transmission cable remaining in the ground may be decommissioned.

The present applicant has previously developed apparatuses and methods for the extraction of the core from a data-transmission cable.

For example, in EP3055910B1, the present applicant has described an apparatus and method for removing a cable conductor from a cable sheath of a particular cable type in which the conductor is surrounded by an insulator formed by a relatively soft polymer filler material. With this type of cable, by supplying a voltage along the conductor sufficient heat can be generated to reduce the viscosity of the soft polymer material to a point at which the friction between the conductor and the sheath is low enough to enable the conductor to be extracted from its sheath by pulling it from one end. In another example described in EP3095164B1, the apparatus comprises a pump to generate hydraulic pressure against one end of the core and insulator. A pulling mechanism is also configured to simultaneously exert a pulling force on the opposite end of the core an insulator. The combination of hydraulic pressure applied to one end of the core and insulator, and a pulling force being applied to the opposite end of the core and insulator, will displace the core and insulator relative to its outer sheath, thereby allowing extraction of the core and insulator with the outer sheath remaining in-situ.

The above-described techniques have proven to be effective in the removal of the conductor from certain cable types having a soft polymer dielectric insulator. However, displacing the conductor from the sheath using the hydraulic action of the fluid or by applying a voltage cannot be used in all cases when the cable has an insulating dielectric material formed from a harder polymer which may be physically bonded into or to the shield or sheath. In this case an alternative method must be used.

As illustrated in Figure 1, there is a particular cable type 1 in which the dielectric 4 is formed from a relatively hard tubular polymer. The conductor 6 extends along a tubular passage 7 within the dielectric 4 and is centralised within the passage 7 by a series of evenly spaced dividing walls or partitions 5 along its length. Each partition 5 has a central opening 8 through which the conductor 6 extends. As shown in Figure 1, the outer surface of the dielectric 4 may have ridges in the vicinity of each partition 5 which assists in binding the dielectric 4 to an outer sheath 2. A metallic, i.e. copper, shield 3 is disposed between the outer sheath 2 and the dielectric 4.

To date, it has proven difficult to successfully extract the dielectric 4, with partitions 5, and the conductor 6 from cables 1 of the above-described type to enable the remaining part of the cable to be reused and/or the conductor to be reclaimed and recycled.

An apparatus and method for preparing a data-transmission cable of the type that comprises a metallic conductor, to enable the conductor to be replaced with optical fibre and in which the conductor is centralised within a tubular passage of a polymer dielectric by a series of spaced integrally formed partitions, is described in the Applicants own earlier PCT patent application PCT/GB2021/051857. This application describes a cutter that is insertable into the tubular passage of the cable over a conductor. The cutter includes a cutting element that cuts away the spaced partitions of the dielectric as the cutter rotates and translates along the conductor within the tubular passage. Cutting of the spaced partitions releases the conductor thereby enabling it to be extracted.

The present invention seeks to provide a cutting element which has improved performance over previously known cutting elements, and which is resistant to clogging, blockage and melting of the dielectric as cutting ensues. Melting of the dielectric and/or damage to the outer sheath results in the conductor being more difficult to extract and/or rendering the remaining cable sheath damaged and unusable should the intention be to insert fibre optic strands into the original cable sheath.

According to the invention, there is provided a cutting element insertable into a data- transmission cable over a conductor such that it is translatable along and rotatable about a longitudinal axis of the conductor to cut away spaced partitions of a polymer dielectric through which the conductor extends to release the conductor and allow subsequent extraction of the conductor from the polymer dieletric, the cutting element comprising a body portion and a plurality of spaced cutting teeth each of which extend in an axial direction from the body portion such that the cutting teeth engage and cut said spaced partitions as the cutting element is translated along, and is rotated about, the conductor. The cutting element may comprise a passage extending through the body portion to receive a conductor, when in use, such that the axis of the conductor is coaxial with an axis of the passage. The cutting teeth, of which there may be two, three, or more, may extend in an axial direction, i.e. the cutting direction or direction of translation of the cutting element during cutting, from a periphery of the passage.

In a preferred embodiment, there are three cutting teeth, each tooth being circumferentially spaced from its adjacent cutting tooth about the longitudinal axis.

The cutting teeth may each have an inner surface that will face a conductor when the conductor is extending through the passage. The inner face of each cutting tooth may be axially aligned with the longitudinal axis. Alternatively, the inner face maybe angled relative to the longitudinal axis.

The inner face of each cutting tooth may be curved in an angular direction about the axis so that it more closely matches the curvature of a conductor extending through the cutting element.

If the inner face is curved, then the radius of curvature of the inner face of each cutting tooth maybe the same as the radius of curvature of the passage. In certain embodiments, the cutting element may comprise a ridge on the inner face of each cutting tooth that protrudes from said inner face towards the axis.

Each cutting tooth may have an outer surface that tapers in a direction away from the body portion and towards the axis. This effectively makes each cutting tooth wedge shaped.

A leading end of each cutting tooth may comprises a primary cutting edge. The primary cutting edge can be linear. If so, the primary cutting edge may extend at a tangent to a circle centred on the longitudinal axis.

The primary cutting edge may have a radius of curvature that extends about the axis. A secondary cutting edge may extend between the primary cutting edge and the body. The secondary cutting edge extends in a generally axial direction. The body portion may taper in an axial direction opposite to the direction that the cutting teeth extend from the body portion, i.e. in a direction opposite to the direction in which the cutting element is translated during cutting.

The cutting element may have recessed regions formed in tapering body portion. These may be located between each tooth that extends in the opposite direction from the body portion.

The cutting element may have a cylindrical portion extending from the tapering body portio. The cylindrical portion may have a fitting at its remote end for attachment of the cutting element to an elongate, cylindrical drive member for rotating the cutting element about its longitudinal axis and about the conductor, and for translating the cutting element in an axial direction along the conductor.

It is envisaged that the cutting element may be a unitary component, i.e. the body portion, the cutting teeth and the cylindrical portion may be integrally formed from the same, preferably metal, material. However, the teeth could be permanently or removably attached to the body portion and/ or the cylindrical portion could be permanently or removably attached to the body portion. Embodiments of the invention will now be described, by way of example only, with reference to Figures 2 to 4 of the accompanying drawings, in which:

FIGURE 1 is a diagrammatic perspective view of a portion of a known cable having a dielectric with spaced partitions supporting the conductor along its length;

FIGURE 2 is a perspective view from the leading end of a cutting element according to an embodiment of the invention;

FIGURE 3 is a side elevation of the cutting element shown in Figure 2

FIGURE 4 is a leading end view of the cutting element shown in Figures 2 and 3, and FIGURE 5 is a perspective image of an actual cutting element according to an embodiment of the invention. With reference to Figures 2 to 5, there is shown a number of views of a cutting element 8 according to an embodiment of the invention. Figure 2 is a perspective view taken from a leading end of the cutting element 8, which is the end which is inserted into a data-transmission cable 1 over a conductor 6 and which cuts the spaced partitions 5 of the cable 1. The cutting element 8 has a body portion 9 with a cylindrical passage or opening 10 defining a longitudinal axis A- A. Circumferentially spaced cutting teeth 11 (three in the illustrated embodiment, but more cutting teeth 11 or two cutting teeth 11 is also envisaged) extend from a periphery of the passage 10 in a first axial direction away from the body portion 9. The teeth 11 are spaced from each other in an angular direction about the longitudinal axis A-A of the cutting element 8. The body portion 9 and the cutting teeth 11 may be integrally formed as a unitary component.

A cutting element 8 is selected for a particular cable 1 so that the passage 10 extending through the body portion 9 is at least slightly larger than the diameter of the conductor 6 so that the cutting element 8 can easily translate and rotate relative to the conductor

6 without resistance and so that the axis of the conductor will remain substantially coaxial with an axis A-A of the passage 10.

Each cutting tooth 11 has an inner surface 12 that extends in an axial direction to face a conductor 6 extending through the passage 10. The inner face 12 may be arcuate so as to mimic the curvature of the conductor 6 and the curvature of the cylindrical passage 10 through the body portion 9, i.e. the radius of curvature of the passage 10 and the radius of curvature of the inner surface 12 of each tooth 11 maybe similar or identical. In some embodiments, each tooth 11 may incorporate a ridge 13 or shoulder that protrudes from the inner surface 12 towards the axis A-A. If each ridge 13 is arcuate, then they may have a radius of curvature which is less than the radius of curvature of the inner surface 12 of the teeth 11. The ridge 13 may be formed at, or close to, the remote end of each tooth 11 which forms a primary cutting element 14, which may be an integrally formed blade or sharpened edge. As the ridge 13 protrudes towards the axis A-A and brings the tooth 11 closer to the conductor 6 extending through the cutting element 8, the primary cutting element 14 is closer to the conductor 6 and cuts the spaced partitions close to the conductor 6, thereby making the conductor 6 easier to extract once all the spaced partitions 5 have been cut. The primary cutting element 14 at the remote end of each tooth 11 may be arcuate so that it conforms to the curved outer surface of the conductor 6. However, the primary cutting element 14 may also be straight. If the primary cutting element 14 is straight it may extend at a tangent to a circle centred on the longitudinal axis A-A of the cutting element 14. Although it is envisaged that the primary cutting elements 14 will extend perpendicular to the longitudinal axis A-A, it is also possible for each primary cutting element 14 to extend at another angle to the longitudinal axis A-A, so that initial engagement with a spaced partition 5 will be with a tip of each of the primary cutting elements 14, the rest of the primary cutting elements 14 engaging the partition 5 as the cutting element 8 is translated over the conductor 6.

Each cutting tooth 11 also has an outer surface 15. The outer surface 15 of each cutting tooth 11 may taper in a direction away from the body portion 9 towards the primary cutting element 14 and towards the axis A-A.

Each cutting tooth 11 comprises a secondary cutting edge 16 that extends between the primary cutting edge 14 and the body portion 9. The secondary cutting edge 16 may extend parallel to the longitudinal axis A-A, or may extend at a relatively small angle to the longitudinal axis A-A. The secondary cutting edge 16 of each tooth 11 cuts the partition 5 after the primary cutting element 14 has cut and passed through the partition 5. The secondary cutting edge 16 may be an integrally formed blade or sharpened edge.

The body portion 9 may taper in an axial direction opposite to the direction that the cutting teeth 11 extend from the body portion 9, and so that the body portion 9, together with the cutting teeth 11, form a generally diamond-like shape. The tapering of the body portion 9 in the opposite direction to the teeth 11 provides space behind the body portion 9 for the passage of cut material to travel back behind the cutting element 8. The tapering part 17 of the body portion 9 may have recessed or dished regions 18 formed in its surface. These regions 18 may be circumferentially spaced around the body portion 9 so that they are positioned between the teeth 11 extending from the body portion 9 in the opposite direction. The recessed regions 18 help to promote the passage of cut material rearwardly over the body portion 9. The point at which the body portion 9 and cutting teeth 11 meet is where the cutting element 8 has its maximum diameter. This diameter is at least slightly less than the internal diameter of the cable i into which the cutting element 8 is to be inserted so the cutting element 8 is able to freely translate along the conductor 6 and rotate about the conductor 6. The cutting element 8 further includes a cylindrical portion 19 extending from the tapering body portion 17. The cylindrical portion 19 may have a threaded end or other type of fitting 20 for connection to tubular drive transmission members that translate the cutting element 8 along the cable 1 over the conductor 6. It is envisaged that the speed of rotation of the drill is likely to be in the region of 200 to 600 RPM, depending on the specifications of the data-transmission cable. It is also anticipated that the drill bit will be translated along the cable at a pace of 0.3 and 1.0m per minute, although this will also depend on the cable specification, as well as the straightness of the cable.

Many modifications and variations of the invention falling within the terms of the following claims will be apparent to those skilled in the art and the foregoing description should be regarded as a description of the preferred embodiments of the invention only.