Boot and method of insulating and waterproofing electrical wire ends

Abstract: A boot 23a for insulating the bare end of an insulated electrical wire include a neck 25 to hold a wire or wires 21a centrally in the boot. The boot is filled with a solidifiable liquid substance 24, such as epoxy resin, to encapsulate the wire or wires after insertion. The boot may be transparent and include depth markings 26,27 to determine the minimum insertion depth of the wire or wires 21a, and the minimum level of substance 24.

Description: This invention relates to a boot for insulating and waterproofing the bare ends of electrical wires. The invention also concerns a method of insulating and waterproofing the ends of electrical wires. Insulated electrical wire usually comprises a conductive core and a sheath of insulating material. The bare ends of wires are insulated in the appliance to which they are attached, or by a separate insulator. Separate insulators can be expensive. In manufacture of a wiring harness it may be necessary to join several wires. This may be accomplished by using connector devices but a more reliable connection can be made by joining the conductive cores by soldering or welding, and applying an insulating boot. In conditions where moisture or corrosion is likely it is important that the boot is sealed. Bared ends of insulated wires may be capped by a boot containing fluid substance which is solidified after the boot is fitted. Such an arrangement is disclosed for example in US 3550765, and encapsulates the bare wire ends. However this kind of boot may be unreliable in wet or corrosive conditions if the insulated wires lie against the wall of the boot, thus preventing the fluid substance encircling the wires. US 3597528 discloses a cover to centralize wires in the boot, but this additional component increases cost and assembly time. Problems may also arise with this kind of boot if the bare wire is not sufficiently inserted in the fluid substance, thus leading to insufficient depth of insulation. Further problems arise if the depth of insertion in the boot is correct but the amount of fluid substance is insufficient, or if external pressure results in insufficient encapsulation of the bared wire end. US-A-3768941 discloses an insulating cover of heat shrink tubing for a rigid conductive sleeve attached to an electrical wire. The cover includes a constriction near one end to prevent the escape of a water repellent dielectric paste placed between the sleeve and the cover. US-A-4350841 discloses a rigid transparent connector for an electric wire, the transparent wall permitting the wire to be viewed to check for folded back wire strands. The present invention seeks to overcome these problems and provide a boot which is inexpensive and reliable. According to one aspect of the invention there provided is in combination, an insulated wire and a flexible boot for waterproofing and insulating a bare end of said insulated wire, the boot having a solidifiable fluid substance therein, and into which the bare end of the wire is inserted, the boot comprising an elongate tubular sheath closed at one end and having an opening at the other end, the boot having a neck intermediate said ends, and defining a narrowed internal diameter on either side of which the internal diameter of the boot is substantially greater than that of the neck, and the neck being sized to receive said wire, wherein said neck maintains said wire centrally in the boot, characterized in that said fluid substance surrounds said wire above and below said neck, so that, when solidified, said end is encapsulated, with the proviso that said combination does not include an internal sleeve between said insulated wire and boot. The neck of such a boot restricts movement of the insulated wire and ensures that the wire is maintained centrally in the boot intermediate the ends thereof. This in turn ensures that the wire is encapsulated both above and below the neck. Preferably the boot is of flexible plastics material. The neck may be defined in any suitable manner, for example by an inward depression or a plurality of inward depressions, or by outward bulges on either side of the neck. In the case of forming a neck by deformation of the side wall of the boot, it may be possible to form the neck either before or after insertion of the insulated wire. The fluid substance is solidifiable, and may be for example an epoxy resin curable by heat or the like after insertion of the insulated wire therein. More than one wire can be encapsulated at once, and a plurality of wires may be joined by e.g. soldering or welding prior to encapsulation. Preferably the boot is made of transparent material, and include depth marks thereon to indicate the desired depth of insertion of the wire and the desired depth of fluid substance. Such marks ensure that an adequate depth of encapsulation and depth of the curable substance can be provided in all cases, and checked by external examination. Quality control and reliability are thus improved. The depth marks are preferably on either side of said neck and may be constituted by outward bulges of the boot. The invention ensures that the likelihood of a gap between the insulated wire and the curable substance is unlikely because of the increased depth of substance around the insulated wire. In another aspect the invention comprises a method of encapsulating the bare end of an insulated wire, the method comprising the steps of a) forming a tubular boot having a closed end and an open end; b) filling said boot with a solidifiable fluid substance; c) inserting said wire into said boot; d) crimping said boot to define a neck intermediate the ends thereof such that said substance encapsulates said wire above and below said neck; and e) causing said substance to solidify. Where the boot is transparent and has depth marks, the method may further include the steps of b2) filling said boot to the outermost depth mark; and c2) inserting the wire so that the bare end is inward of the inwardmost depth mark; d2) crimping said boot intermediate the depth marks. In an alternative method the crimping step may be prior to insertion of the wire. In another alternative method the solidifiable fluid substance may be filled after insertion of the wires, or after the crimping step. Other features of the invention will be apparent from the following description of preferred embodiments shown by way of example only in relation to a wire harness and in the accompanying drawings in which Fig. 1 illustrates a correctly applied prior art insulation boot. Fig. 2 illustrates an incorrectly applied prior art insulation boot. Fig. 3 illustrates another incorrectly applied prior art insulation boot. Fig. 4 is a cross section of Fig. 2 on line 4-4. Fig. 5 illustrates a first embodiment of the invention. Fig. 6 is a cross-section on line 6-6 of Fig. 5; Fig. 7 is a cross-section through an alternative boot which corresponds to Fig. 6; Fig. 8 is a longitudinal section through another boot according to the invention; Fig. 9 is a cross-section on line 9-9 of Fig. 8; Fig. 10 is a longitudinal cross-section through yet another boot according to the invention. Figs. 1-3 are transverse cross sections through prior art insulation boots containing an encapsulation substance such as a biphenyl polychloride. In Fig. 1 a plurality of insulated electrical wires 11a have exposed bare ends 12 which are electrically connected, for example by soldering or welding. A boot 13 of suitable flexible plastics material, such as polyethylene, contains a curable liquid substance 14, such as epoxy resin. Insulated wires 11a are inserted into the boot 13, and the resin is cured, for example by the application of heat so that the curable substance 14 becomes solid, and the insulated wires are encapsulated. Such a boot, when correctly applied, has good resistance to current leakage and moisture ingress. Fig. 2 illustrates an incorrectly applied boot in which the insulated wires 11b lie against the sidewall of the boot 13. In this case the wires 11b cannot be encapsulated fully because there is too little curable substance between the insulated wires 11b and the boot 13; there is a possibility of moisture ingress between the insulated wires 11b and the boot, and consequent corrosion. Furthermore external pressure may cause a gap to occur or a small gap to enlarge. Fig. 4 is a cross-section through the boot of Fig. 2 from above and shows a typical moisture channel 15. Fig. 3 illustrates another incorrectly applied boot. In this case the insulated wires 11c are inserted to an insufficient depth and the bare ends are too close to the top of the boot with the possibility that moisture may be able to pass between the substance 13 and the boot 14 to the bare ends 12. Here also external pressure may cause a gap to occur between the boot 14 and the insulated wires 11c. In the case of the boots of Figs. 2-4, moisture and corrosion can lead to a poor electrical connection, current leakage, and thus unreliability. Fig. 5 illustrates a first embodiment of the invention. Insulated wires 21a are joined electrically at their bare ends 22 by soldering, welding or the like. A flexible boot 23a contains a curable liquid substance 24, also as previously described. The boot 23 has a neck 25 defining a narrow internal diameter on either side of which the internal diameter of the boot is much greater. The wires are inserted into the boot and a retained centrally by the neck 25 as illustrated. The portion above and below the neck permits the substance 24 to surround and fully encapsulate the wires, and thus avoid the prior art problem illustrated in Fig. 2. As illustrated the boot 23a also has outward bulges 26,27 on either side of the neck. These bulges are optional, but provide convenient depth markings which are useful if the boot is made of transparent material. The lower bulge 26 can indicate to an operator the minimum depth of insertion of the wires 21a, whilst the upper bulge 27 can indicate the minimum depth of substance 24. In this way the prior art problem illustrated in Fig. 3 can be avoided. Depth markings can be provided on a transparent boot in any convenient manner, for example by an external printed line or horizontal rib or recess. The neck 25 may be formed before or after insertion of the wires 21a and substance 24. The latter may be preferable in the case where the substance is rather viscous. The neck may comprise an inward deflection of the wall of the boot around the entire circumference thereof as illustrated in Fig. 6, or may be constituted by several separate indentations 26 of the boot 23b, as illustrated in Fig. 7, which are sufficient to maintain the wires 21b in the centre of the boot. A boot could be moulded with suitable internal projections or ribs such as those illustrated in Figs. 8-10. Figs 8 and 9 illustrate a plurality of internal ribs 28 integrally moulded in the boot 23c and sufficient in number to maintain the wires 21c centrally in the boot. Fig. 10 illustrates alternative spokes 29 moulded integrally in the wall of the boot 23d and which maintain the wires 21d centrally. Other embodiments of the invention are practicable within the scope of the claims defined herewith.

Claims: In combination, an insulated wire (21A) and a flexible boot (23A) for waterproofing and insulating a bare end of said insulated wire (21A), the boot (23A) having a solidifiable fluid substance (24) therein, and into which the bare end of the wire is inserted, the boot (23A) comprising an elongate tubular sheath closed at one end and having an opening at the other end, the boot having a neck (25) intermediate said ends, and defining a narrowed internal diameter on either side of which the internal diameter of the boot is substantially greater than that of the neck (25), and the neck being sized to receive said wire, wherein said neck (25) maintains said wire (21A) centrally in the boot (23A), characterized in that said fluid substance surrounds said wire above and below said neck, so that, when solidified, said end is encapsulated, with the proviso that said combination does not include an internal sleeve between said insulated wire and boot. The combination according to claim 1 wherein the boot is transparent. The combination according to claim 2 wherein the boot includes a wire depth mark thereon whereby the depth of insertion of said wire can be ascertained. The combination according to claim 2 or claim 3 wherein the boot includes a fluid depth mark thereon whereby the depth of said fluid substance can be ascertained. The combination according to claim 3 or claim 4 wherein said wire depth mark and fluid depth mark are constituted by outward bulges of the boot. The combination according to any preceding claim wherein said neck is defined by an inward depression of the side wall of the sheath. The combination according to any of claims 1-5 wherein said neck is defined by a plurality of circumferentially spaced inward depressions of the side wall of the sheath. The combination according to any of claims 1-5 wherein said neck is defined by outward bulges in the side wall of the sheath. The combination according to any of claims 1-5 wherein said neck is defined by internal projections of the sheath. A method of encapsulating the bare end of an insulated wire, the method comprising the steps of a) forming a tubular boot having a closed end and an open end b) filling said boot with a solidifiable fluid substance c) inserting said wire into said boot d) crimping said boot to define a neck intermediate the ends thereof such that said substance encapsulates said wire above and below said neck; and e) causing said substance to solidify. A method according to claim 10 and including the steps of a2) forming said boot of transparent material. a3) placing a first depth mark adjacent said closed end. a4) placing a second depth mark adjacent said open end. b2) filling said boot with said substance to said first depth mark. c2) inserting said wire so that the bare end is inward of said second depth mark. d2) crimping said boot intermediate said depth marks.

Inventors: SUGIYAMA MASASHI, UCHIYAMA KENICHI, SUGIYAMA, MASASHI, UCHIYAMA, KENICHI, Sugiyama, Masashi c/o Sumitomo Wir. Syst., Ltd,, Uchiyama, Kenichi c/o Sumitomo Wir. Syst.,Ltd,
Applicants: SUMITOMO WIRING SYSTEMS, SUMITOMO WIRING SYSTEMS, LTD.
Application year: 1996
Main classification: H01R4
IPC codes: H01R4