METHOD OF BLOCKING A CABLE OR BUNDLE OF CONDUCTORS

Abstract: Induction heating of wires in a harness or wiring bundle generates heat to cause fusible blocking material to flow and block the spaces within the harness and to shrink a plastics sleeve around the blocked region. Either the blocking material or the sleeve (but not both) may also be inductively heatable.

Description: METHOD OF BLOCKING A CABLE OR BTIND E OF CONDUCTORS This invention relates to a method of blocking a cable or bundle of conductors. Blocking to prevent fluids from flowing along a cable or wire bundle is known, for example from US-A-4972042 (RK310), wherein a body of hot-melt adhesive is placed in contact with the (usually insulated) conductors and a heat-shrinkable sleeve is shrunk around the portion of the cable or bundle carrying the adhesive. The heat applied to shrink the sleeve, usually by means of a hot air gun or a flame torch, causes the adhesive to melt and flow between and around the conductors, assisted by the shrinking action of the sleeve, thus blocking the cable or bundle. These known blocking procedures are subject to the limitations that the adhesive must be able to melt and flow at relatively low temperatures, often less than 100°C, which can be achieved inside the sleeve without overheating and damaging it. This can undesirably limit the temperatures which can be tolerated by the blocked cable or bundle in subsequent service. An alternative cable blocking system is described in WO-A-94/24837 (MP1474), wherein particles of ferromagnetic material are incorporated in hot melt blocking adhesive, the particles being shaped to couple inductively with an alternating magnetic field to which the cable carrying the adhesive is subjected. The resulting inductive heating of the specially-shaped ferromagnetic particles causes the adhesive to melt and flow to block the cable. A heat-shrinkable sleeve is also provided with the ferromagnetic particles to heat it to its shrinkage temperature on exposure to the magnetic field. This system alleviates the aforementioned limitations of external heating. The present invention also avoids external heating while ingeniously reducing or eliminating the need for the specially-shaped ferromagnetic particles, which may be expensive or otherwise undesirable to use in some circumstances. The invention accordingly provides, in its broadest aspect, a method of blocking a cable or bundle of conductors, comprising (a) applying to a portion of the cable or bundle to be blocked a body of heat-flowable blocking material; (b) optionally applying around at least the portion of the cable or bundle to be blocked a cover; wherein the blocking material and the cover (when present) are (i) substantially electrically non-conductive and substantially non-magnetic (substantially non-inductively-heatable), or (ii) one of them is inductively-heatable and the other is substantially non-inductively-heatable, with the proviso that the blocking material is inductively-heatable if the conductors are not; and (c) subjecting the cable or bundle to an alternating magnetic field which couples inductively (i) with the said conductors and/or (ii) with the inductively-heatable blocking material, thereby inductively heating the conductors and/or the inductively-heatable blocking material to a temperature which causes the blocking material to flow and block the cable or bundle. In one more specific aspect, the invention provides a method of blocking a cable or bundle of metallic conductors, comprising (a) applying to a portion of the cable or bundle to be blocked a body of heat-flowable blocking material which body is substantially electrically non-conductive and substantially non-magnetic, and (b) subjecting the cable or bundle to an alternating magnetic field which couples inductively with the said conductors, thereby inductively heating the conductors to a temperature which causes the blocking material to flow and block the cable or bundle. The invention is based on the surprising discovery that sufficient heat can be inductively generated in the conductors, in the substantial absence of induction-heatable additives in the blocking material, to melt and flow the blocking material to achieve a satisfactory block. The invention has the advantage of being equally applicable when a cover is provided around at least the portion of the cable or bundle to be blocked. Such a cover may be an article which is elastomeric and is arranged to compress the said portion on the cable or bundle at least before and during the flowing of the blocking material. It is even more surprising that the cover may be a heat-shrinkable article which is caused to shrink around the said portion of the cable or bundle. This novel use of heat generated by the conductors inside the cable or bundle advantageously enables blocking materials of higher melting or softening temperatures to be used without damage to the heat-shrinkable cover. Alternatively, the heat-shrinkable article might carry induction- heatable additives within itself or in an internal lining of an adhesive or other material, so that only the blocking material relies on the heat generated in the conductor. The melting or softening point of the blocking material, and the threshold shrinkage temperature of the heat-shrinkable cover, if present, will normally be selected to suit temperatures which can be generated by the induction heating of the conductors without damage to any electrical insulation materials carried by the conductors. For example car harness with up to 100 wires made of PNC-insulated wires of diameters 0.25 to 6 mm 2 with a temperature rating of 105 °C (T2 Rating) can be blocked within 3 minutes using an adhesive with a softening temperature of 85 °C and a flow temperature of 110°C with a heat-shrinkable sleeve of recovery temperature below 100°C, and using an induction generator operating at a frequency between 0.2 and 1 Mhz with 2.5 kW power. Lower-temperature-rated (i.e. Tl =70°C) PNC requires the use of hot-melt adhesives with softening points of 50 - 60°C and flow temperatures of 80 - 90°C with heat-shrinkable tubing of recovery temperatures less than 90°C. As an alternative blocking adhesive for wire with low insulation softening points in the range of 50 - 60°C, the melt adhesive can be replaced with a mastic material such as polyisobutylene. During installation the heat from the wires softens the mastic and increases its flow. Under these circumstances either a heat-shrink sleeve or a rubber sleeve can be used to consolidate the block. This invention is especially applicable to conductors composed of fine metal filaments whose geometry lends itself to inductive coupling with the applied magnetic field, for example copper wire consisting of many individual strands typically 75 to 150 micro-metres in diameter. These are roved together to make the wire and typically from 7 to 50 strands can be used depending on the final cross sectional area of the wire. The normal material is copper and it may be plated with either nickel, tin or silver. However, other conductor materials can be used such as nickel or aluminium. Any suitable blocking material may be used which will flow at the temperatures generated by the conductors and will solidify sufficiently to block the cable in subsequent service. Preferred hot melt adhesives are those described in the aforementioned US-A- 4972042, the disclosure of which is incorporated herein by reference. The heat-shrinkable cover will preferably be as described in US-A-4972042 or in WO-A-94/24837, the disclosure of which is incorporated herein by reference. When an elastomeric cover is used, this may be made of, for example, EPDM rubber, polychloroprene rubber, polyester rubber, or natural rubber. The size and shape of the cover are not critical, provided that it squeezes the assembly sufficiently to confine the following blocking material in position to form an adequate block in the cable or bundle. Specific examples of this aspect of the present invention will now be described in more detail by way of further illustration. EXAMPLE 1 A wire bundle consisting of 60 1.5mm 2 copper conductors of 100 micron diameter strands with a 0.5mm jacket of PNC insulation rated to T2 (105°C) was blocked using Rayblock 85 Polyamide hot melt adhesive applied in the form of 4, 5 channel comb profiles. The wires were fitted into each channel of the comb with a maximum of three wires per channel. The outer heat shrink tubing was a 40mm length of TAT-125 heat shrink tubing 25mm in diameter. A 250kHz induction heater was used to generate a field within a 5 turn 50mm diameter helical coil. The coil was operated at 150 amps giving a filed strength of 750 ampere turns and the cable harness was blocked in 60 seconds, the maximum temperature reached in the bundle was 130°C. EXAMPLE 2 A bundle consisting of 100 wires was sealed as above but using 6 Rayblock 85 adhesive combs with 6 chanels and the heat shrink tubing was a 50mm length of TAT- 125 tubing 75mm in diameter. The sealing time was 45 seconds. EXAMPLE 3 A bundle as described in Example 1 except that a 40mm sleeve of 15mm diameter chloroprene rubber of 60IRHD hardness was used instead of the heat shrink sleeving. Under the same conditions as that example the sample was blocked in 45 seconds. EXAMPLE 4 A bundle as described in Example 1 was blocked using a poly iso butylene mastic (3M's EMB-45R) with a chloroprene rubber sleeve as described in Example 3. The sample was heated in the induction heater for 60 seconds during which time the mastic flowed from under the elastomeric tubing and completed the sealing process. EXAMPLE 5 A bundle as described by Example one except the insulation on the wire was Raychem Type 62 polyester wire with a temperature rating of T3 (125°) was used with polyamide adhesive combs Rayblock 105. The heat shrink sleeve was Raychem ATUM 24/8 (Trade Mark) and the bundle was heated for 90 seconds to seal with a maximum temperature of 160°C being recorded in the bundle. A further alternative aspect of the present invention, wherein the blocking material is inductively-heatable and the cover is substantially non-inductively-heatable, provides a method of blocking a cable or bundle of conductors, comprising (a) applying to a portion of the cable or bundle to be blocked (i) a body of inductively-heatable heat-flowable blocking material and (ii) a substantially non-inductively-heatable cover around at least the portion of the cable or bundle to be blocked, and (b) subjecting the said portion of the cable or bundle to an alternating magnetic field which couples inductively with the said blocking material, thereby inductively heating the blocking material to a temperature which causes it to flow and block the cable or bundle. In this alternative method, the conductors may be inductively-heatable as before, or may be substantially non-inductively-heatable, for example optional fibres. When the substantially non-inductively heatable cover is heat-shrinkable, it will preferably shrink at temperatures which it encounters as a result of the inductive heating and/or the resultant flowing of the blocking material. When the cover is elastomeric, it will preferably be arranged to compress the portion of the cable or bundle to be blocked at least before and during the flowing of the blocking material. Suitable inductively-heatable blocking materials for this method may for example be selected from the materials described in WO-A-9424837 (MP1474). For non- inductively-heatable blocking materials in all aspects of the present invention, it may be desirable in some cases to use materials which are curable so that their viscosity increases after flowing and blocking the cable or bundle, thus reinforcing the blocking effect and reducing the risk of the block becoming ineffective due to later temperature variations. Preferred curable blocking materials may be selected from those comprising interleaved sheets containing respectively the spearate reactive components of a curing system, which are described in WO-A-9527764 (B247), the disclosure of which is incorporated herein by reference.

Claims: Claims: 1. A method of blocking a cable or bundle of conductors, comprising (a) applying to a portion of the cable or bundle to be blocked a body of heat-flowable blocking material; (b) optionally applying around at least the portion of the cable or bundle to be blocked a cover; wherein the blocking material and the cover (when present) are (i) substantially electrically non-conductive and substantially non-magnetic (substantially non- inductively-heatable), or (ii) one of them is inductively-heatable and the other is substantially non-inductively-heatable, with the proviso that the blocking material is inductively-heatable if the conductors are not; and (c) subjecting the cable or bundle to an alternating magnetic field which couples inductively (I) with the said conductors and/or (H) with the inductively-heatable blocking material, thereby inductively heating the conductors and/or the blocking material to a temperature which causes the blocking material to flow and block the cable or bundle. 2. A method according to claim 1, wherein the conductors are metallic, comprising (a) applying to a portion of the cable or bundle to be blocked a body of heat- flowable blocking material which body is substantially electrically non-conductive and substantially non-magnetic, and (b) subjecting the cable or bundle to an alternating magnetic field which couples inductively with the said conductors, thereby inductively heating the conductors to a temperature which causes the blocking material to flow and block the cable or bundle. 3. A method according to claim 1, comprising (a) applying to a portion of the cable or bundle to be blocked (i) a body of inductively-heatable heat-flowable blocking material and (ii) a substantially non- inductively-heatable cover around at least the portion of the cable or bundle to be blocked, and (b) subjecting the said portion of the cable or bundle to an alternating magnetic field which couples inductively with the said blocking material, thereby inductively heating the blocking material to a temperature which causes it to flow and block the cable or bundle. 4. A method according to claim 1 or 2, wherein a cover (preferably substantially electrically non-conductive and substantially non-magnetic) is provided around at least the portion of the cable or bundle to be blocked. 5. A method according to claim 3 or 4, wherein the cover is a heat-shrinkable article which is caused to shrink around the said portion of the cable or bundle. 6. A method according to claim 5, wherein the heat-shrinkable article shrinks at temperatures which it encounters as a result of (i) the inductive heating of the conductors and/or the blocking material, and/or (ii) the resulting flowing of the blocking material. 7. A method according to claim 3 or 4, wherein the cover is elastomeric and is arranged to compress the said portion of the cable or bundle at least before and during the flowing of the blocking material. 8. A method according to any preceding claim, wherein the said conductors are inductively-heatable and are inductively heated by the said magnetic field. 9. A method according to claim 1, 3, or any claim when dependent thereon, wherein at least some of the said conductors are substantially non-inductively-heatable. 10. A method according to claim 9, wherein the substantially non-inductively-heatable conductors are optical fibres.

Inventors: CROFTS DAVID, CROFTS, DAVID
Applicants: CROFTS DAVID, RAYCHEM LTD, CROFTS, DAVID, RAYCHEM LIMITED
Application year: 1996
Main classification: H01B13
IPC codes: H01B13