WO1996037925A1

WO1996037925A1 - Side-entry enclosure for electrical wiring joints

Info

Publication number: WO1996037925A1
Application number: PCT/GB1996/001063
Authority: WO
Inventors: Michael John Carpenter; Frank James Lowe; Alan George Ryder
Original assignee: Raychem Limited
Priority date: 1995-05-24
Filing date: 1996-05-03
Publication date: 1996-11-28
Also published as: GB9510542D0; AU5508996A; JPH11505954A; MX9709002A; EP0871990A1; ZA964199B; BR9609123A; CN1185235A

Abstract

Wraparound side-entry enclosure for joints in primary electrical wiring, especially for high-speed automotive installation, uses heat-shrinkable fabric with adhesive lining, which fabric is fastened around the wiring joint by fabric-piercing fasteners such as staples, rivets, or cable ties. The fabric either has a shrink ratio of less than 50 %, or has a higher shrink ratio and is wrapped loosely enough to limit residual unresolved shrinkage (after shrinking around the joint) to less than 50 %.

Description

Side-Entry Enclosure for Electrical Wiring Joints

This invention relates to a side-entry protective enclosure for a joint in primary electrical wiring.

It is known to protect such wiring joints by shrinking over them a piece of heat- shrinkable plastics tubing, preferably having an internal coating of heat-activatable adhesive. Such tubing must, however, be slipped over a free end of the wiring which may be inconvenient or impracticable.

It has been a long-standing problem to produce a commercially acceptable side- entry heat-shrinkable enclosure for primary wiring joints, which enclosure can be applied laterally to a mid-section of the wiring without cutting to produce free ends. Wrapping of heat-shrinkable plastics sheet around the joint has proved unsatisfactory due to lack of economically-feasible fastening means which can withstand the heat-shrinking forces. Adhesive fastenings tend to unwrap during shrinking, and it is not practicable to use on these relatively small-scale wiring joints the heavy-duty closure mechanisms which are available for large cable splice cases, as described for example in GB-A- 2134334.

The present invention provides a surprisingly simple side-entry primary wiring enclosure which may be adapted to provide both technically and economically acceptable results, even in mass-production wiring industries, for example automotive wiring assembly lines, where installation time and cost must be minimised.

The invention accordingly provides a side-entry protective enclosure for a joint in primary electrical wiring, comprising a heat-shrinkable fabric article wrapped around the joint and fastened around the joint by fabric-piercing fastening means, the fabric article either having a circumferential heat-shrink ratio in the direction encircling the joint of not more than 50% or being wrapped loosely enough so that its residual unresolved shrink ratio after shrinking closely around the wiring joint is not sufficient to damage the fabric article, preferably being not more than 50%; and the fabric article having a transverse heat-shrink ratio (in the direction transverse to the encircling direction) which is less than half (preferably less than one third, more preferably not more than 20%) of the circumferential heat-shrink ratio.

The heat-shrink ratio is the loss of length on S-irinking expressed as a percentage of the fully-shrunk length, which ratio is determined largely by the degree of stretch applied to the shrinkable fibres.

For the usual scale of primary wiring enclosures, it is preferred that the fabric article has a circumferential or residual heat-shrink ratio less than 40%, preferably not more than 33 % , more preferably not more than 25 % . It is usually also preferred that the fabric article has a circumferential heat-shrink ratio of at least 10%, preferably at least 20%. Circumferential heat-shrink ratios greater than 50% (eg 100% or 200%) may be used if the article is wrapped around the wiring joint loosely enough so that its residual unresolved shrink ratio after shrinking around the wiring joint is not more than 50%.

Simple-to-use fabric-penetrating fastening means, for example sewing, or preferably one or more staples or rivets, e.g. plastics rivets, have unexpectedly been found to fasten the fabric article around the wiring joint without tearing during subsequent heat-shrinking when the fabric article has the specified circumferential shrink ratios. For close wrapping, these ratios are preferably lower than the 40%-or-more shrink (recovery) ratios preferred for large scale fabric composites according to the aforementioned GB-A-2134334, which composites furthermore may require modification of the fabric edges to form closure elements or reinforcement to resist tearing by closure elements which penetrate the fabric. Plastics cable ties may be inserted through apertures formed (eg punched) in the fabric article and may be secured by known techniques to form an alternative fastening for the article. The fastening means of suitable form, rivets for example, may be pre-inserted in an edge region of the fabric article ready for onvenient fastening after the article has been wrapped around the wiring joint.

It will be understood that the relatively lower transverse shrinkage of the fabric article used in the present invention is preferable to control the amount of shrinkage of the enclosure along the enclosed wiring while permitting a useful degree of circumferential shrinkage. A maximum transverse shrink ratio of less than 25%, preferably less than 17%, more preferably not more than 10%, generally the lower the better, is accordingly envisaged.

With shrink ratios less than 50% the fabric article may be fastened closely around the joint, for example to grip the joint or wiring before the fabric article is shrunk. Such tight wrapping may be desirable in some circumstances, but in practice insertion of the fabric-piercing fastening means may advantageously be done with a degree of looseness or slack in the wrapping. This will usually facilitate the fastening operation and reduces any risk of the fastening means accidentally damaging the wire insulation. It is therefore preferred that the part of the fastening means which penetrates the fabric article is separated from the nearest part of the joint or wiring by a distance up to three times the average diameter (preferably not greater than twice the average diameter) of the largest diameter wire (including any insulation layer thereon) within the enclosure.

The fabric article may be made from heat-shrinkable fibres and other fibres as described generally in the aforementioned GB-A-2134334, but preferably with omission of the second plastics laminate and the metallised Mylar laminate described therein. For example the fabric could use a plain weave (1 over, 1 under) of shrinkable warp fibres of cross-linked high-density polyethylene of 0.2 - 0.3 mm diameter at 35.4 ends per centimetre (90 ends per inch) and weft fibres of glass 3 x 68g/km or 0.1 mm PET monofilaments (2 per pick) at 3.9 picks per centimetre (10 picks per inch). The weft fibres will be spaced apart so as not to interfere to an unacceptable extent with the shrinkage of the warp fibres. Alternative fabric designs are indicated on the following table.

FABRIC CONSTRUCTION

Warp Warp Diameter Weft Weft Diameter Weave Design

Ends/cm or picks or

(Ends/inch) Linear Density per cm Linear Density

& (picks &

Material per inch) Material

#1 15.7 HDPE 4.7 Ryton (trademark) 2/2

(40) fibrillated tape (12) PPS HOPSAK 200 g/km 0.2 mm

#2 27.6 PVDF 3.1 PET 2/2

(70) monofilament (8) monofilament BROKEN TWI 0.35 mm 0.1 mm

# 3 35.4 HDPE 3.5 E-Glassfibre PLAIN WEAV

Pref (90) monofilament (9) 2 x 68 g/km 0.25 mm

# 4 47.2 LLDPE 4.7 Hoechst Warp Interchan

(120) monofilament (12) Trevira

0.3 mm (Trade mark) 2 ply WEAVE Type 711 polyester multifil 110 g/km

Preferably, the fabric article includes adherent polymeric material, preferably an adherent polymeric film laminate (preferably a polyethylene film), which renders the fabric article substantially non-porous. For example, a low-density polyethylene film of about 0.2 mm thickness may be laminated by known lamination methods to one side of the woven fabric. After laminating, the film and fabric are preferably irradiated by the usual means (known per se), preferably to a dosage of at least 10, preferably at least 12, especially at least 14, megarads, to enhance the temperature performance and the bonding together of the laminated article. Suitable irradiation methods and equipment, for example electron beams, are well known. Doses over 20 Mrads are preferably not used, and little added advantage is gained by doses above 15 Mrads. The fabric article may be rendered resistant to transmission of liquids in the plane of the fabric sheet, usually known as making the article "planar tight" , by methods including those described in EP-A-0324630.

In many cases, it will be preferred that the enclosure also encloses a quantity of heat-activatable sealant material capable of flowing to seal the enclosure on heat shrinking of the fabric article around the joint. Such sealant material may be provided separately, but will advantageously be carried as an adherent layer on the inward-facing surface of the fabric article. Suitable sealant materials are well known, hot-melt adhesives such as ethylene/vinyl acetate copolymers or polyamides being preferred. The sealant melting point or softening point will be chosen to suit the temperatures experienced within the enclosure during heat shrinking of the fabric article. Preferred sealant materials are blends of polyamide and acrylic polymers. The sealant will preferably be selected to maintain the seal (formed on heat-shrinking of the fabric article in use) when the enclosure is exposed after shrinking to temperatures up to 125°C. For this purpose, it may be preferred that the sealant material is capable of curing after flowing to seal the enclosure so as to resist further flow at temperatures up to 125°C, and preferably at excursions up to 150°C.

Examples of adhesives which may be useful for the present purposes are described in WO-A-8707755 (RIG 10) and in co-pending International Application PCT/GB95/00731 (B247). Heat-curable adhesives, for example those described in GB- A-2104800 (RK149) and EP-A-0157478 (RK232), may also be useful. The disclosures of these four references are incorporated herein by reference.

The fastening of the fabric article around the wiring joint is preferably conducted so that opposite end regions of the said fabric article are fastened together by the said fastening means and each of the said end regions is arranged (preferably by folding near the respective ends) so that each piercing part of the fastening means pierces each end region at least twice. Such double-piercing arrangements enhance the resistance of the fastened regions to tearing during subsequent shrinking of the fabric. It has been found especially advantageous if one of the said end regions is folded and fastened so that its free end projects inwards from the fastening means towards the joint and the wiring. The inward-projecting end of the fabric tends to crumple during shrinking of the article to form a buffer between the joint and wires and the fastening means, thus helping to keep the fastening means clear of the joint and the wires. This is particularly advantageous when metallic fastening means such as staples are used. When both end regions of the fabric article are folded inwards, they can be brought together to form a butt joint with both of the free ends projecting inwards as aforesaid. However, it is preferred that one of the folded end regions is enclosed by the other to form an overlap joint with the said other end region leaving its free end on the outside of the enclosure and extending beyond the fastening means. The desired folding of the end regions may be effected in situ, after wrapping of the fabric member around the joint, by gripping the overlapping ends of the fabric so as to form a four-layered raised crease. Alternatively, the fabric article may be provided with pre-folded end regions, preferably with both end regions folded over toward the surface of the fabric member which will face inwards in use in the enclosure. The folded end regions will preferably not be bonded to the part of the fabric member adjacent to the fold, especially not if such bonding would interfere with the intended arrangement of the regions for fastening. Permanent or semi¬ permanent folds of the end regions at an angle of less than 180°, preferably between 90° and 180° to the remainder of the fabric member (when laid flat) are advantageous, and formation of such folds may be assisted by the weft fibres acting as folding lines across the shrinkable warp fibres.

Either the warp fibres or the weft fibres may be the main shrinkable fibres, to be wrapped in the circumferential sense for slirinking around the joint, with the less shrinkable other fibres (weft or warp, as the case may be) lying transversely to the main shrinkable fibres. In many cases, this will mean the less-shrinkable weft (or warp) fibres extend generally along the wires entering and leaving the enclosure.

In some preferred forms of enclosure, the wiring extends substantially straight through the enclosure and the fastening means pierces the fabric article at at least 2 (preferably at least 3, more preferably at least 4) points spaced along the wiring so as to fasten substantially the whole extent of the fabric member along the wiring. Apart from simple in-line joints having one wire entering and one wire leaving the enclosure, the enclosure may have one wire coming in joined to two or three wires going out, preferably with the wires lying substantially parallel to each other at least within the enclosure. Any branching of the wires in different directions will preferably occur outside the enclosure, but could occur within the enclosure, for example with suitable fastening means piercing the fabric between the "legs" of the branched wiring. The fastening means will often be arranged in a straight line substantially parallel with the wiring, but other arrangements are possible, for example to follow the outline of a diameter change from a single incoming wire to three or more outgoing wires in the joint.

A preferred form of fastening means for the present invention is one or more staples or rivets, (especially 10 mm x 10 mm x 10 mm staples of about 1 mm thickness), which will usually be made of metal (possibly with an electrically insulating coating), but may be made of plastics or other suitable insulating material.

For practical purposes, the size of the wiring joint will often be such that it can be enclosed by an enclosure in which the width of the fabric article (lying along the wiring) is within the range from 25 to 50 mm, preferably 30 to 40 mm. It will usually be preferable for the width of the fabric article to be sufficient to overlap the insulation of the wiring beyond the electrically conductive joint itself.

For efficiency in use, it is preferred that the substantially complete fastening of the fabric is effected by two staples substantially in lengthwise alignment with each other along the wiring, and preferably substantially evenly spaced from each other and from the extremities of the enclosure along the wiring.

The invention naturally includes the enclosure after it has been heat shrunk tightly around the joint. In addition," the invention includes a kit of parts for making the enclosure comprising a suitable fabric article and suitable fastening means, and preferably including means for applying the fastening means to fasten the fabric member.

It has very surprisingly been found that heat-shrunk enclosures according to this invention can pass a severe test in which the enclosure is placed under water and 0.5 bar air pressure is applied for 60 seconds through the tube of electrical insulation material carried by the wires, the enclosure passing this test only if no air bubbles come out of the enclosure.

Embodiments of the present invention will now be described by way of example, with reference to the accompanying drawings, wherein: -

Figures 1A, IB and 1C show schematically in end view alternative folding arrangements for the fabric article of an enclosure according to this invention;

Figures 2A and 2B show schematically in end view a preferred folding arrangement and one way of forming it for the enclosures according to this invention;

Figure 3 shows schematically in perspective a stage in the assembly of an enclosure according to this invention about wiring connections;

Figure 4 shows a further stage in the assembly of the enclosure of Fig. 3;

Figure 5 shows the fastening by staples of the fabric article of Figs. 3 and 4 around the wiring connection;

Figure 6 shows schematically the assembled enclosure of Fig. 5 after heat shrinking of the fabric article tightly around the wiring joint; Figure 7 shows a branched wiring joint with a staple fastener between the legs of the branch;

Figures 8A and 8B show schematically in cross-section a known form of plastics cable tie in open and closed positions; and

Figures 9A and 9B show schematically an assembled enclosure secured by means of cable ties like those of Figure 8.

Referring to Figure 1A, a fabric sheet 10 as hereinbefore described is shown wrapped around a wire 12 with insulation 14 entering a joint connector 16 of any suitable kind. The ends 17 and 18 of the fabric sheet have been folded outwards and are secured in a butt joint by a fastener 19 passing through a total of four layers of fabric, two layers in each of the folded end regions. Figure IB similarly shows one end 17 folded outwards and the other end 18 folded inwards and overlapping the folded end 17. Figure IC similarly shows both ends 17 and 18 folded inwards and stapled in a butt joint. The arrangements of Figures 1 A and IB have the disadvantage that the outwards- facing free ends of the fabric sheet to not form a buffer against the wire. The two inwards-facing free ends in Figure IC will tend to form a buffer as hereinbefore described, but the resulting butt joint may be more prone to leakage than an overlap joint.

A preferred overlap joint is similarly shown in Figure 2A, wherein both ends 27 and 28 are folded inwards as in Fig IC, but the end 28 overlaps the end 27, which forms the aforementioned buffer. Figure 2B shows one way of forming this preferred arrangement, by first wrapping the fabric sheet around the joint with ends 27 and 28 overlapping, then gathering the overlapping ends into a fold (broken lines) to form the arrangement of Fig 2A.

Figure 3 shows a preferred fabric sheet 30 with its ends 32 and 34 pre-folded inwards, which has been partly wrapped around a connector 36 foπning a joint between one incoming wire 37 and two outgoing wires 38 and 39. The form of the connector 36 is not critical. Soldered or wire-twisted joints may be acceptable, without any connector housing as such, and crimps or other connectors, with our without insulative coverings, may be used as appropriate.

Figure 4 shows the sheet of Figure 3 arranged to form an overlap around the joint similar to that described in Figure 2, and Figure 5 shows the enclosure after fastening with staples 50 through the overlapping folds of the fabric sheet, the woven fibres of which are suggested by lines 52 (the shrinkable warp fibres encircling the joint) and 54 (the glass weft fibres substantially parallel with the wires).

Figure 6 indicates the finished enclosure after shrinking of the fabric tightly around the joint and wires to form a desirably low profile, while keeping the staples 50 at a desirable distance from the wires and joint by virtue of the buffering end 34 of the fabric.

Figure 7 shows schematically a branched joint between a single wire 70 and a pair of branch wires 72, in which a staple 74 pierces the fabric article 73 between the diverging branch wires 72, in addition to the closure-fastening staples 76.

Figures 8 A and 8B show schematically a known type of plastics cable tie having a toothed strap 80 which can be wrapped around an object to be tied and inserted into the body portion 82 (see Fig. 8B), where a flexible detent 84 engages the teeth 86 to secure the end of the strap in the body, thus fastening the tie around the object in question. The projecting end 88 of the strap (Fig. 8B) may be trimmed off (see Fig. 9B)

Figures 9A and 9B show schematically cable ties 90 which have been inserted through holes 92 punched in a fabric article 94 according to this invention and secured to fasten the fabric article around a wiring joint. The projecting end of the tie strap (88, Fig. 8B) has been trimmed off for neatness.

Claims

1. A side-entry protective enclosure for a joint in primary electrical wiring, comprising a heat-shrinkable fabric article wrapped around the joint and fastened around the joint by fabric-piercing fastening means, the fabric article either having a circumferential heat-shrink ratio in the direction encircling the joint of not more than 50% or being wrapped loosely enough so that its residual unresolved shrink ratio after shrinking closely around the wiring joint is not sufficient to damage the fabric article, preferably being not more than 50%; and the fabric article having a transverse heat-shrink ratio (in the direction transverse to the encircling direction) which is less than half (preferably less than one third, more preferably not more than 20%) of the circumferential heat-shrink ratio.

2. An enclosure according to claim 1, wherein the part of the fastening means which penetrates the fabric article is separated from the nearest part of the joint or wiring by a distance up to three times the average diameter (preferably not greater than twice the average diameter) of the largest diameter wire (including any insulation layer thereon) within the enclosure.

3. An enclosure according to claim 1 or 2, wherein the fabric article includes adherent polymeric material, preferably an adherent polymeric film laminate (preferably a polyethylene film), which renders the fabric article substantially non- porous.

4. An enclosure according to claim 3, wherein the laminated fabric article has been irradiated with ionising radiation to a dosage of at least 10, preferably at least 12, more preferably at least 14, Megarads.

5. An enclosure according to any preceding claim, enclosing a quantity of heat- activatable sealant material capable of flowing to seal the enclosure on heat shrinking of the fabric article around the joint.

6. An enclosure according to claim 5, wherein the sealant material is carried as an adherent layer on the inward-facing surface of the fabric article.

7. An enclosure according to claim 5 or 6, wherein the sealant material is a hot-melt adhesive, preferably a blend of polyamide and acrylic polymers, capable of maintaining the seal formed on heat-shrinking of the fabric article in use when the enclosure is exposed after shrinking to temperatures up to 125°C, and preferably also when exposed to excursions to 150°C.

8. An enclosure according to claim 5, 6, or 7, wherein the sealant material is capable of curing after flowing to seal the enclosure so as to resist further flow at temperatures up to 125°C, and preferably also on excursions to 150°C.

9. An enclosure according to any preceding claim, wherein opposite end regions of the said fabric article are fastened together by the said fastening means and at least one of the said end regions is arranged (preferably by folding near the respective end) so that each piercing part of the fastening means pierces at least one of the end regions at least twice.

10. An enclosure according to claim 9, wherein one of the said end regions is folded and fastened so that its free end projects inwards from the fastening means towards the joint and the wiring.

11. An enclosure according to Claim 10, wherein the said one of the end regions is enclosed by the other end region having its free end on the outside of the enclosure and extending beyond the fastening means.

12. An enclosure according to any preceding claim, wherein the wiring extends substantially straight through the enclosure and the fastening means pierces the fabric at at least 2 (preferably at least 3, more preferably at least 4) points spaced along the wiring so as to fasten substantially the whole extent of the fabric member along the wiring.

13. An enclosure according to any preceding claim, wherein the fastening means is one or more staples or rivets.

14. An enclosure according to any preceding claim, wherein the width of the fabric article (lying along the wiring) is within the range from 25 to 60 mm, preferably 35 to 50 mm.

15. An enclosure according to any preceding claim, wherein the fabric article is fastened by two or three staples substantially in lengthwise alignment with each other along the wiring, and preferably substantially evenly spaced from each other and from the extremities of the enclosure along the wiring.

16. An enclosure according to any preceding claim, wherein the fabric article has a circumferential heat-shrink ratio of less than 40%, preferably not more than 33%, more preferably not more than 25 % .

17. An enclosure according to any of claims 1 to 15, wherein the fabric article has a circumferential heat-shrink ratio greater than 50%, preferably greater than 100%, more preferably 180 to 220%, and is wrapped loosely as specified in claim 1.

18. An enclosure according to any preceding claim, wherein the fabric article has a circumferential heat-shrink ratio of at least 10%, preferably at least 20%.

19. An enclosure according to any preceding claim, which has been heat shrunk tightly around the joint.

20. A fabric article suitable for making an enclosure according to any of the preceding claims, having one or both of its two opposed end regions folded over toward the surface of the fabric member which will face inwards in the enclosure.

21. A fabric article suitable for making an enclosure according to any of claims 1 to 19 having the said fastening means pre-installed in one region ready for fastening to another region of the fabric article.

22. A kit of parts for making an enclosure according to any of claims 1 to 19, comprising a suitable fabric article and suitable fastening means, and optionally including means for applying the fastening means to fasten the fabric member.

23. A method of forming an enclosure according to claim 19, comprising

(a) wrapping a length of the said fabric article around the said joint;

(b) fastening the fabric article around the joint by means of the said fabric- piercing fastening means; and

(c) heat-shrinking the fabric article tightly around the joint.