CA1057373A

CA1057373A - Cable splice

Info

Publication number: CA1057373A
Application number: CA138,599A
Authority: CA
Inventors: Duane D. Rodger
Original assignee: Raychem Corp
Current assignee: Raychem Corp
Priority date: 1971-03-31
Filing date: 1972-03-30
Publication date: 1979-06-26
Also published as: BE781546A; GB1475292A; IL39144A0; ZA722148B; BR7201898D0; NL7204265A; FR2132338A1; FR2132338B1; IT950996B; DE2215835A1

Abstract

Abstract A sleeve of polymeric material is disclosed, which is suitable for splicing mine cables. The sleeve has been radially expanded from an original heat-stable form to a form in which it is independently dimensionally heat-unstable and is capable of shrinking in the direction of its original form upon the application of heat alone. It has a tensile strength of at least about 1200 p.s.i. when measured in accordance with ASTM D 2671 using a jaw separation speed of 20 ? 2 inches per minute, a maximum stiffness of 10,000 p.s.i. when measured according to ASTM D 747 and a dielectric strength of at least 200 volts per mil determined in accordance with ASTM D 149 or a dielec-tric breakdown voltage of at least 6,000 volts when measured in accordance with ASTM 2671. At least part of the inner surface of the sleeve is provid-ed with an adhesive. Such sleeves allow the splicing of electrical cables without removing them from the mine, as was done hitherto, and also give a more rugged splice than hitherto. The splice is though, flexible and easily formed.
A repair kit may comprise at least one inner sleeve having the specified di-electric breakdown voltage and an outer sleeve having the specified dielectric strength. A splice is made by placing an inner sleeve over a broken conductor in which a joint has been made, heating it, placing around the covered joint an outer sleeve which is long enough to overlap the outer cable insulation and, finally, heating the outer sleeve.

Description

..: .
This invention relates to articles suitable for splicing mine cables and to methods of forming a splice.
Electrical cables are frequently used in the mining ~;i industry~ particularly in underground coal mines. These cables are subject to severe treatment which often causes breaks in the cable~ and these breaks require splicing.
~` Shuttle-car trailing cables are among the most troublesome from the stand-point of frequent splice requirements.
Breaks in the cable may be caused~ for example~ by shuttle-cars running over the cables or by excessive flexing under ~ tension during reeling and unreeling of cables.
; Various requirements have been laid down in connection with the making of splices in electrical cables used in the mining industry. Thus~ for example~ in the IJ~S.A.~ Title 1~ 30 USC~ Section 866(d) specifies thst only one temporary ; splice can be made in a trailing cable and that such a spliced trailing cable can be used only for a twenty-four hour period. Furthermore~ according to the provisions of 30 USC 866(e)~ permanent splices in trailing cables must be "(1) mechanically strong with adequate electrical conduc-tivity and flexibility~ (2) effectively insulated and - sealed so as to exclude moisture; and (3) vulcanized or otherwise treated with suitable materials to provide flame-resistant qualities ~nd good bonding to the outer jacket."
Permanent splices which have previously been employed by the mining industry have in general involved removal of cables from the mine. In a splicing method typical of those ^ used previously~ conductors are brazed together in the re-; pair shop and wrapped with a self-bonding elastomeric tape.
The ground wire usually is wrapped with a cotton-based tape

- 2 - ~

, .
.

~057373 " .: , ,':? and separated from the conductors with sheets of varnished cambric. The .~, . .~
~ insulated conductors are laced together and an elastomeric cover is then ,. ", ,.
moulded over them. Even with this cumbersome technique, the splices made are frequently unable to withstand repeated flexing under tension and thus , are generally not put back in service on shuttle-car trailing cables but are , ", ~2: used on other equipment on which the cable is not constantly reeled and unreeled. There has thus been a need in the mining industry for a tough, flexible and easily formed splice.
;. . .
The present invention provides an article comprising a sleeve of ~` 10 polymeric material which sleeve has been radially expa~ded from an original -heat-stable form to a form in which it is independently dimensionally heat-, unstable and is capable of shrinking in the direction of its original form ,i~., :.
upon the application of heat alone, the sleeve having a tensile strength of at least 1200 p.s.i. when measured in accordance with ASTM D 2671 using a , :
jaw s~paration speed of 20 ~? 2 inches per minute, a maximum stiffness of , 10,000 p.s.i. when measured according to ASTM D 747 and a dielectric strength ;, of at least 200 volts per mil determined in accordance with ASTM D 149, and at least part of the inner surface of the sleeve being provided with an !,, :
~i adhesive. Thé invention also provides an article as set forth above which ,~,,:i ~ ? 20 has a dielectric breakdown voltage of at least 6,000 volts when measured in ."~ I ~
accordance with ASTM D 2671.

The articles of thc invention may be used in the form of a repair q~ kit. Accordingly, the present invention also provides a repair kit which ~;, comprises an outer sleeve and at least one inner sleeve, the outer sleeve comprising the first-mentioned article of the invention and the or each inner sleeve comprising the second-mentioned article of the invention.
q-, The invention further provides a method of forming a splice in a cable comprising at least one insulated electrical conductor, which method comprises making a joint in the or each broken conductor, positioning around .. ' 30 the or each joint a heat-shrinkable inner sleeve as set forth above having , ~ - 3 -,.. .

?;. ~
':'1 ~;~
, i,, , '-- , ,, ,, _, .. .. .

~;

~.;' 1057373 .,;
;~ a layer of adhesive on the inner surface thereof, heating the or each sleeve ,~
,., to cause it to shrink into contact with the respective conductor, the adhes-' ive forming a bond between each sleeve and its respective conductor, posi-t:ioning an outer heat-shrinkable sleeve as set forth above having a layer of .: adhesive on the inner surface thereof around the covered joint, or all the ~ covered joints, the outer sleeve being of such a length that each end of it . overlaps the outer cable insulation and heating the outer sleeve so that it - shrinks into contact with the outer cable insulation, the adhesive forming a bond between the outer sleeve and the outer cable insulation, the result-.~ 10 ing splice having an insulation resistance after flexing for 10,000 cycles ....
} and immersion in water for 24 hours at 23 + 1C of at least 1,000 megohms . . .
when measured in accordance with ASTM D 257. The or each inner sleeve pre-'~:i ferably has an original inside diameter slightly less than the outer diameter of the cable conductor which it is to cover and an inside diametér in the , heat-unstable form greatér than the outside diameter of said conductor and the outer sleeve preferably has an original inside diameter slightly less than ,;~ the diameter of the outer insulation of the cable and an inside diameter in ., the heat-unstable form greater than the diameter of the outer insulation of the cable.
Also provided by the invention is a cable splice comprising a cable ~.; having an outer insulating jacket and at least one conductor, at least one .'~ of the conductors having been broken and physically joined, the or each .,~
. broken conductor being covered at the point where it was joined by a heat-. recoverable polymeric inner sleeve as set forth above which has been recov-ered around the conductor, a layer of adhesive bonding the or each sleeve to ~^ the respective conductor, the covered conductor, or all the covered conduc-! tors, being covered by a heat-recoverable polymeric outer sleeve as set forth above which covers the covered conductor~s) and overlaps the outer jacket of the cable, a layer of adhesive bonding the outer jacket to the inner ', ,!,~
~"t~
~- . . ' ' ~ ' ' ' ' ' ' . ' ' ' ~, ' ' ' '-~; 1057373,i ,....................................................................... .
. sleeve(s) and the cable jacket, the splice having an insulation resistance -after flexing for lO,OOO cycles and immersion in water for 24 hours at 23 + 1C of about at least 1,000 megohms when measured in accordance with ASTM D 257. The bond between the outer sleeve and the outer ... . .
,;, . .
,~'''''' ',' '` `.~ ' t; '`.:

', :
, ~, .
~7: .

.i~,"
,f !
,5,~, .
. ~ " .

~' .
~1 .
'~

, .
. . .
~ ' r~

~.' ' / ~.
?~i ~ .

- _ 5 _ i , `` 1057373 cable jacket preferably has a strength of about at least 20 pounds per inch of bond width when measured in accor- :
dance with ASTH D 1876 after 10,000 flex cycles of the bond.
""

.~
,.~:, ,~.;.;
Suprisingly, the present invention makes it possible to provide a cable splice which is strong, flexible~ abra-sion resistant and flame retarded and which meets the re-: ., quirements set out in 30 USC 866(e). Furthermore, the ..~i;
, present invention makes it possible to make a cable splice quickly and easily.
The articles of the present invention comprise heat-shrlnkable tubes or sleeves which may be made, for example, from a tough, flexible polyolefin base polymer. The sleeves have a coating on their inner surface of an adhesive which i~;, is capable of maintaining a strong bond between sleeves ;~"
after shrinking and a substrate (for example, a cable) and will remain flexible and have good dielectric properties.
The sleeves for use according to the present invention are made from polymers which are capable of having the ~' property of heat-recoverability imparted to them. Methods . :~.
r ~ for rendering such polymers~ and tubing made from such polymers, heat-recoverable are disclosed in U.S. Patent Nos. 3,086,242, 3,243,211 and 3,297,819.
,~` In general, it is more important that the inner sleeves which cover the conductor joints be flexible than ~ that they be tough; toughness is not such an important re-;I quirement because the inner sleeves are covered by the ~; outer sleeve which covers the entire joint. mus~ the -6_ .

- ~057373 , . .
inner sleeves may be formed fron a polymer which sacrifices . .
toughness for flexibility. The outer sleeve9 however~
should be fabricated from a polymer which is flexible~
tough and abrasion resistant.
~oth the inner ~nd outer sleeves can be formed with the desired mechanical properties if they are fabricated from crosslinked copolymers of ethylene ethylacrylate or ethylene-vinyl acetate and other copolymers of this type ,, .
well known to those skilled in the art. The crosslinking can be carried out either by irradiation or chemical means.
. .
The sleeves may be fabricated hy moulding~ extrusion or any --;,~, other desired fabrication method.
~ The materials used for the sleeves of the invention J ~ preferably contain a flame retardant. ~ny of the polymer ~ 15 flame retardants ~rell known to tbose skilled in the polymer ci art may be employedc Suitable flame retaraants for ethylene-ethylacrylate and ethylene-vinyl acetate copolymers are thoss dlsclosed in Belgian Patent NoO 7390630 h suitable composition for use in the invention com-, prises from 40~50~ for example about ~5~ of an ethylene vinyl acetate copolymer (eOg. alathon 3190) up to abou~
10% eOg. about 7~0 of an ethylene ethyl acrylate copolymer~
,s.i., 10-20~o e.g. about 15~o carbon black~ up to about 25~ flame ~i retardant e~gO about 18~ of a halogenated bis-imide as ~,.,j .
'J'.' 25 mentioned in the specification above~ up to 10~ e.g. about 6~ of antimony oxide~ the remainder being anti oxidants and chemical cross linking agents~ for example a per oxide.
~he inner surface of each of the heat-shrinkable sleeves used according to the invention is provided with a coating of adhesive. Preferably~ the adhesive is a hot-melt `" ~ J~Jc~q~k : `
,, ~ adhesive, that is~ an adhesive which displays its adhesive . . .
characteristics when it is heated to the molten state and than cooled. Curable adhesives~ for example~ epoxy ad-hssives~ may also be usedO In general~ any adhesive which will form a strong flexible bond between the sleeve and a ;-cable and which has good dielectric properties may be used.
Important characteristics of the adhesive material are the peel strength~ which indicates the strength of the bond be- -~
"
.-. tween the sleeve and the substrate over which it is shrunk~
and the extent of disbonding caused by flexing of the jointO
a~dc5 J4 p~trJ;~ r Particularly suitable hot melt adhesives are/poly-amide which produces very good results is a low molecular , ~
weight polyamide manufactured by General ;iills~ Inc. and ;~. deslgnated as TPX-327. This polyamide has the following "., ~
lg properties:
. Ring and Ball melting points 120 - lo&.
Fisher-Johns melting points 110 - 10 C.
;` Tensile yield strength: 280 to 400 pl~S.i.
Elongations 52~ ~
Dielectric constant at 50 ~Iz: 2.9 Dissipation factor 50 Hz: 0.0019 r~ Volume resistivity 206 x 10 6 ohm-cm In addition to the specific adhesive mentioned above~
it should be understood that any hot melt adhesive which possesses properties similar to those set forth above and which forms a strong flexible bond between the sleeve and i,~
the outer surface of a cable and has the desired properties - set forth hereinafter is suitable for use in the present invention. In general~ an adhesive may be saia to be suitable if it 'nas tensile ~ield strength of at least about . .

~ - 8 -,:

,. ... . ..

:1057373 :

- 280 p~s.i.~ a dielectric constant at 50 Hz of not more thani; about 2~9~ a dissipation factor at 50 Hz of not more than about 0c0019 and a volu~e resistivity of at least about 2~6 x 10l6 ohm~crn.
; 5 If the coated sleeves of the invention are to be used , ., ~
~ for forming a splice in a c~ble, one outer sleeve and as ."; ~ ~
many inner sleeves as there are individual conductors are normally usedO In forming the splice~ the outer sleeve is ,~` slipped over one portion of the c~ble and each of the inner sleeves is slipped over one portion of a respective con-ductor~ The individual conductors are then joined by mech-.. ~,,~' .
anical means~ for example by parallel beat rings~ parallel crimp connectors, butt crl~p cor~ectors~ or by welding.
The inner sleeves are positioned over the ~oints and the 1~ assembly ~s heated to shrink the inner sleeves firmly onto tl,e joints and~ if a hot-melt aahesive is used~ to activate the adhesiveO The inner sleeves are preferably of such a length that they overlap t~le conductor insulation at each end.
When the lnner sleeves have been installed~ the outer sleeve is positioned over the entire splice~ the outer :. !
f sleeve preferably being of such a length that it overlaps ~"
v the outer insulation of the cable at each end. The outer sleeve is then heated, whereupon it shrinks and is firmly ~l 25 bonded by the adhesive to the outer surface of the cable.
The heat used to shrink the heat-recoverable sleeves used in accordance ~ith the present invention may be sup-~, plied by any convenient source~ for example~ a torch, a hot ,, air heater~ or a catalytic heaterO Additionally~ or altern-atively~ a coating of exothermic material may be applied to _ 9 _ ;
:;

, the outer surface of the sleeves so that use may be made of ~; an exothermic reaction which generates enough heat to resultx in shrinking of the sleeves. Such a coating may be acti-vated by various means~ for example~ ignition by a flame or activation by addition of water. Exothermic coatings of ;
this type are disclosed in ~ritish Patent S~ecification No.
9~35~
, . .
If desired~ the outer surface of the heat-shrinkable sleeves may be covered witll a thermochromic paint or other - 10 thermochromic material which will change colour upon reach-ing a given temperature. The tenperature of colour change may be selected so that the change in colour will indicate ~; ~Jhen sufficient heat has been applied to the sleeve to en-sure complete shrinkage of the sleeve down over the part which it is to cover. The thermochromic coating may also be ~ , , ; selected so t7nat the temperature of colour change indicates when sufficient heat has been applied to c~use proper seal--~ ing by a hot melt adhesive. This is particularly desirable when the temperature required to activate the hot melt ad-hesive is highe~ than the temperature required to cause shrinking of the sleeve so that the ~ermochromic material indicates how much additional heat~ng, after shrinking~ is required to reach the temperature at w.llch the hot melt adhesive is activated.
The following is a s~ ary of tlle characteristics of the preferred sleeves alld splices of the invention. The properties of the complete assembly are of prime importance.
Inner and Outer Sleeves~
(a) The tensile strength~ measured in accordance i 30 with ASTiI D 2671 using l-inch bench marks, a l-inch initial .' .

, - .. ~. . . .. ' - - -~`i 1057373 ,, .;
;;~ jaw separation, and a jaw separation speed of 20 - 2 inches -~; per minute~ should be not less than 1~200 p s i. The ulti-mate elongation~ measured under the conditions glven for tensile strength~ is preferably not less than 250 percent.
(b) The stiffness, when measured in accordance with QSTM D 7~7~ should not exceed 105000 poS~iv (c) Tho dielectric breakdown voltage~ when tested in --;
i~ accordance with ~STlI D 2671~ should be not less than 6~000 volts for tl~e inner sleeve.
(d) The dielectric strength for the outer sleeve~
and preferably also for the inner sleeve~ when measured on moulded slabs in accordance with ~STi~ D 149~ should be at least 200 volts per mil.
J! ~e) The brittleness temperature~ when measured in accordance with ASTiI D 746~ is preferably not higher than -30 C. The choice of immersion fluid for the test is not important~
;:~
`~J~', (f) The heat resistance~ tested in accordance with AST~`I D 2671~ after conditioning for 168 hours at 175 ~ 5C~
$~, 20 preferably results in a retained ultimate elongation of not ~; less than 200 percent and, for the outer sleeve~ the re-tained tensils strength should preferably be not less than 1,000 p.s.i, , (g) The volume resistivity~ when tested in accor-dance with ~STM D 2671~ is preferably at least 1012 ohm-cm.
(h) The corrosive effect for both sleeves~ when measured in accordance with ASTi;I D 2671~ ~ppendix A 1O5O1~
is preferably such that the specimen causes copper removal of less than 5 percent when conditioned for 16 hours at 150 - 3 C. This test should include the adhesive coating.

':; .

:; ~
i:

. . .
(i) The flame retardancy for the inner sleeve~
tested in accordance witll AST-I D 2671~ is preferably such ,:, that the sleeve is self-extinguishing in 60 seconds lJith bu:rning or charring over less th~n 25 percent of the area.
- 5 (~) The flammability of the outer sleeve ? the sleeve~ ~hen tested in accordance with ~ST~I D 635 on speci-mens cut fro~ moulded slabs~ should preferably be jucl.ged to . be nonburning as described in Section 6(c) of ~STI`I D 635.
tk) The water absorpt~on for both sleeves ~s pre-ferably not more than 1.0 percent when determined in accor-dance with .~STkI D 2671 using a 2b,-hour iL7lmersion period at 23 - 1 C (l~STI~ D 2671 refers to AST~I D 570~ and procedure A
~i should be used) .
.i (1) The fluid resistance of the inner sleeve to `~ 15 water~ lubricating oils ancl non-lnflammable nydraulic fluids, 1!. ' tested in accordance with ASTI~I D 2671~ is preferably such .j .
that the tensila strength after immersion ~or 2~ hours at -23 + 1 C is at least 750 p.s.i. ~nd the dielectric break-.~ . .
down voltage~ after immersion for the same period~ is at . 20 least 5~000 volts.
;: (m) The fluid resistance of the outer sleeve to : water~ lubricating oils and non-inflammable hydraulic fluids -;~ should be determined on specimens i~nmersed for 24 hours at 23 + 1 C according to ASTM D b,12 using Die D. Rfter immer-;,.
25 sion the specimens should preferably have a tensile strength , of at least 750 p.s.i. and an ultimate elongation of not less th~n 200 percent.
Complete_S.~lic_ (a) The insulation resistance~ after imt~ersion for 30 ~b, hours at 23 - 1 C and while still immersed in accordance ``:

~ - 12 ,, ..;

~ ;
.
-: 1057373 ;~ with ASTlI D 257~ is preferably not less than 1~000 megohms.
A metal foil is used in A~TII D 257.
(b) P.epeated flex life is determined on a 4-foot length of specimen containing a splice~ The test is per-formed on a device that will cause the specimen to trav~rse a 4--inch diameter sheave while under tension. The length of travel is sufficient to allow the complete splice assem-bly to traverse the sheave in each direction. A suitable arrangement for performing the test includes an air-actuated reciprocal piston~ means for attaching the cable to the piston, a 4-inch diameter sheave~ a pulley and a 60~pound ... .
~ weight. The specimen makes a 90 turn around the sheave ; and the line attached to the specimen is placed over a pul-ley with a 60-pound weight on the end. Traversing is accomplish~d at 15 + 1 cycles per minute. After flexing for 10,000 cycles followed by immersion in water for 2~ hours at 23 - l&, the insulation resistance should not be less ~j than 1~000 megohms when measured by .~ST~I D 257 as in (a) ;l above.
I 20 (~) Bond strength to the c~ble jacket is measured i'~';l on two 12-~inch lengths of 2-conductor~ type G~ Flat~ Size 4 ~WG cable with an outer sleeve applied thereto. The con-" , ; ductors are removed by gripping each bare conductor and ., pulling them from the specimen. Mext each part is cut ln half longitudinally by making a band-saw cut on the major axis of the oval cross-section. From the flat portion of each of the four parts of the specimen~ a peel test speci-men using a 6 x -~ inch strip die is cut with a die on the ¦ inner surface of the cable jacket. One end of the specimen is heated and the sleeve separated from the cable jacket so ' :''.i.

j 1057373 that separate ends ~ay be clamped to the jaws o~ a tensile testing machine. ~Ihen the specimen is cooled to room temp~
; erature~ a T-peel test in accordance with ~STI;~ D 1876 ~7ith `
a constant head speed of 2 inches per minute is made. The splice perferably has a peel strength of not less than 20 pounds per inch of bond width.
(d) The bond strength to the cable after repeated .. .
; flexing is deter~ined on an outer sleeve centrally applied ,, , - to two 18-inch lengths of 2-conductor Type G~ Flat~ Size L~IG Cable hutted end to end~ The test is performed in accordance with the repeated flex life test except that in-sulation resistance and voltage breakdown measurernents are ! ., omitted. Ifter 10~000 flex cycles~ the bond strength test to cable jacket set forth above is determined. After 10~000 flex c~Jcle~ the average peel strength is preferably not less th~n 20 pounds per inch of bond width.
; (e) The voltage withstand~ on the same specimen ~s ,. ....................................................................... .
prepared for measuring insulation resistance (after flexing)~
; is preferably~ when ~easured in accordance with ~ST`~I D 149

3~000 volts for 5 minutes~ applled between each conductor and the remaining conductors and 3~000 volts for ~ minutes~ -,r applied between all conductors and the water.
(f) The flame resistance~ when ~easured on a com- -plete splice witll at least 6 inches of cable extending be-yond either end of the outer sleeve is deternined by placing the specimen in a forced ventilation type oven in a hori-~I zontal position with supporting members located so that contact Wit'il the outer sleeve is avoided. Specimens are placed in the oven for 30 minutes and heated at 218 - 5 C.
~ithin one minute after removing the specimen from the oven~
.. .

, .
. i .

i ~, 105~373 ,;,.:
~,, .. ..
~iy; a gas flame is applied directly under the centre of the ~: outer sleeve for 60 seconds . This splice is positioned so that the tip of the inner cone of a Tirrell burner flame ; touches the outer sleeve of the specimen. The splice of the present invention preferably has a burned area of less than 6 inches and burning preferably does not occur for more ~' than 60 seconds; there is preferably no dripping or burning particles during burning and after removal of the gas flame.
The invention will now be described, by way of example . , .
. 10 only~ with reference to the accompanying drawings, in which:
Figure 1 is a view of a heat shrinl~able sleeve suitable for use in covering a cable;
~igure 2 is a v~ew of a heat shrinkable sleeve suit-* l ~' able for covering Joined conductors;
Fig~res 3~ 4~ ~ and 6 illustrate various steps used in splicing a cable having three conductors using one sleeve of the kind show~ in Figure 1 and three sleeves of the kind shown in Figure 2. -Figure 1 illustrates a sleeve which may be used as an :; outer sleeve to cover an entire cable spliceO The sleeve~
which is generally indicated at 1, comprises a heat-~; recoverable, polymeric tube or sleeve 2 containing an inner coating 3 of a hot melt adhesive. The sleeve has been ex--. .
panded from an original heat stable form to an independ-ently dimensionally heat unstable form capable o~ moving in the direction of its original form upon the application of heat alone. Thus~ when the sleeve is placed over a cabla and heat is applied to it~ it shrinks to come into close ;~1 30 contact with a cable introduced into it. ~igure 2 shows ~,, ;
; 15 .
.~

: 1057373 :
; a sleeve 4 wh~ch may be used as an "inner" slee~e to cover the joint between individual conductors. The inner sleeve ~-~J

4 comprises a heat-recoverable polymeric tube 5 provided `
with an inner coating of a hot melt adhesive 6.
An outer sleeve l and one or more inner sleeves 4 may be used for splicing damaged cables. A damaged cable which has been prepared for splicing is shown in Figure 3. The damaged cable has an outer jacket 7 and three individual insulated conductors 8~ 9 and lO. ~lthough three conductors have been sho~m~ cables containing any number of conductors --can be spliced according to t-his invention. In forming the ~, :
splice~ the outer jacket 7 is first peeled away exposing the individual conductors 8~ 9 and 10; the insulation on the latter is then removed if necessary to expose the conducting material ll~ 12 and 13. At this point~ outer sleeve 1 is ; slipped over the cable and inner sleeves 4 are placed over .:, .
each of the conductors to be joined. The individual con-ductors are then mechanicall~ joined as shown in Figure 4 by a mechanical joining means 14. The mechanical joining e 20 means may be any suitable me~ns for joining electrical con-~ ductors. For example~ the mechanical joining means may com-'',.! prise parallel beat rings, parallel crimp connectors~ or butt crimp connectors. ~lternatively~ the conductors may be ;~ joined by welding or any other suitable method.
.,.~ .
;i 25 After the joints have been formed between the con-l ductors, an inner sleeve 4 is placed over each joint. The length of the sleeves 4 and the amount of exposed conducting l i~
; material is chosen so tnat the sleeves will extend beyond the area of exposed conducting material thus overlapping a portion of the insulation for each conductor 8~ 9 and lO.

;l - 16 -' . .... . . . . . .

.

~ 1057373 ~
The inner sleeves 4~ after ha~ing been placea over the joints, are heated so that they shrink~ thus coming into ~ contact with~ and forming a tight seal over~ the joints Y.~ (see Figure 5). ~t the same time~ the hot melt adhesive 6 ?
`~ 5 on the inner surface of each sleeve ~ forms a tough flex-~i ible bond between each sleeve ~ and the outer surface of the respective conductors. The hot melt adllesive also tends . to surround and insulate the ~oint between the conductor '',',',' materialsO
After the individual ~oints have ~een covered with i trle inner sleeves~ the outer sleeve 1 is positioned over ~: the spliceO The outer sleeve 1 is sufficiently long to cover the area of the ~oint and to overlap the outer jacket ., x 7 of the cable Oil both sides of tha ~oint. Heat is then 1~ applled to shrink sleeve 1 so that it comes lnto close con-; tact with the outer surface of the c.~ble (see Flgure 6).
The heat causes the hot melt adhesive to bond the outer ~. .
slesve 1 firmly to the outer surface of the c~ble ~acket 7 ~:1 to conductors 8~ 9 and 10 and to the outer surface of ~,.
;i 20 sleeves 49 tnus forming a tough~ flex-resistant covering and insulation for the spliceO

~i ' .:
. ., . ~

....
;'', :

,.. .
~ 17 ~

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An article comprising a sleeve of polymeric material which sleeve has been radially expanded from an original heat-stable form to a form in which it is independently dimensionally heat-unstable and is capable of shrinking in the direction of its original form upon the application of heat alone, the sleeve having a tensile strength of at least about 1200 p.s.i.
when measured in accordance with ASTM D 2671 using a jaw separation speed of 20 ? 2 inches per minute, a maximum stiffness of 10,000 p.s.i. when measured according to ASTM D 747 and a dielectric strength of at least 200 volts per mil determined in accordance with ASTM D 149, and at least part of the inner surface of the sleeve being provided with an adhesive.

2. An article as claimed in claim 1, wherein the material of the sleeve is such that, when tested in accordance with ASTM D 635 on specimens cut from moulded slabs, it is non-burning according to the definition given in Section 6 (c) of ASTM D 635.

3. An article as claimed in claim 1, wherein the resistance of the sleeve to water, lubricating oils and non-inflammable hydraulic fluids, det-ermined on specimens immersed for 24 hours at 23 ? 1°C according to ASTM D
412 using Die D, is such that, after immersion, the specimens have a tensile strength of at least 750 p.s.i. and an ultimate elongation of not less than 200 %.

4. An article as claimed in claim 1, wherein the sleeve has a heat res-istance such that, when tested in accordance with ASTM D 2671 after condition-ing for 168 hours at 175 ? 5°C, the retained tensile strength is not less than 1,000 p.s.i.

5. An article as claimed in claim 1, which has a dielectric breakdown voltage of at least 6,000 volts when measured in accordance with ASTM D 2671.

6. An article as claimed in claim 5, wherein, when tested in accordance with ASTM D 2671, the sleeve has a flame-retardancy such that it is self-extinguishing in 60 seconds with burning or charring over less than 25 % of the area.

7. An article as claimed in claim 5 or claim 6, wherein the resistance of the sleeve to water, lubricating oils and non-inflammable hydraulic fluids, tested in accordance with ASTM D 2671, is such that its tensile strength after immersion for 24 hours at 23 ? 1°C is at least 750 p.s.i., and its dielectric breakdown voltage, after immersion for 24 hours at 23 ? 1°C, is at least 5,000 volts.

8. An article as claimed in claim 1 or claim 5, wherein the sleeve has a heat resistance such that, when tested in accordance with ASTM D 2671 after conditioning for 168 hours at 175 ? 5°C, the retained ultimate elonga-tion is at least 200 %.

9. An article as claimed in claim 1 or claim 5, wherein the ultimate elongation of the sleeve, measured in accordance with ASTM D 2671 using a jaw separation speed of 20 ? 2 inches per minute is not less than 250 %.

10. An article as claimed in claim 1 or claim 5, wherein the brittleness temperature of the sleeve, measured in accordance with ASTM D 746, does not exceed -30°C.

11. An article as claimed in claim 1 or claim 5, which has a corrosive effect such that, when measured in accordance with ASTM D 2671, Appendix A

1.5.1, the specimen causes copper removal of less than 5 % when conditioned for 16 hours at 150 ? 3°C.

12. An article as claimed in claim 1 or claim 5, wherein the volume res-istivity of the sleeve is at least 1012 ohm-cm when tested in accordance with ASTM D 2671.

13. An article as claimed in claim 1 or claim 5, wherein the water absorp-tion of the sleeve is not more than 1.0 % when determined in accordance with ASTM D 2671 using a 24 hour immersion period at 23 ? 1 C.

14. An article as claimed in claim 1 or claim 5, wherein the polymeric material of the sleeve comprises an ethylene-ethylacrylate copolymer.

15. An article as claimed in claim 1 or claim 5, wherein the polymeric material of the sleeve comprises an ethylene-vinyl acetate copolymer.

16. An article as claimed in claim 1 or claim 5, wherein the sleeve includes a flame-retardant.

17. An article as claimed in claim 1 or claim 5, wherein the adhesive is a hot melt adhesive.

18. An article as claimed in claim 1 or claim 5, wherein the adhesive comprises a polyamide.

19. An article as claimed in claim 1 or claim 5, wherein the adhesive comprises a polyamide having a tensile yield strength of at least about 280 p.s.i., a dielectric constant at 50 Hz of not more than about 2.9, a dissi-pation factor at 50 Hz of not more than about 0.0019 and a volume resistivity of at least about 2.6 x 1016 ohm-cm.

20. A repair kit for electric cables which comprises an outer sleeve and at least one inner sleeve, the outer sleeve comprising an article as claimed in claim 1 and the or each inner sleeve comprising an article as claimed in claim 5.

21. A repair kit for cable splices comprising an outer sleeve and at least one inner sleeve, each of said sleeves comprising a tube comprising polymeric material which has been dimensionally changed from an original heat-stable form to an independently dimensionally heat-unstable form capable of moving in the direction of its original form upon the application of heat alone, the outer sleeve having an original inside diameter of slightly less than the outer diameter of the cable, an inside diameter in the heat-unstable form greater than the diameter of the outer jacket of the cable and the inner sleeve having an original inside diameter of slightly less than the outer diameter of the cable conductor it is to cover and an inside diameter in the heat-unstable form greater than the outside diameter of the conductor, the inner and outer sleeves having a tensile strength of about 1200 p.s.i.
measured in accordance with ASTM D 2671 using a jaw separation speed of 20 ? 2 inches per minute, a stiffness of not over about 10,000 p.s.i. when measured according to ASTM D 747, the outer sleeve having a dielectric strength of at least about 200 volts per mil determined in accordance with ASTM D 149 and the inner sleeve having a dielectric breakdown voltage of at least about 6,000 volts measured in accordance with ASTM D 2671, both the inner and the outer sleeves having a coating of adhesive on the inner surface.

22. A method of forming a splice in a cable comprising at least one insul-ated electrical conductor, which method comprises making a joint in the or each broken conductor, positioning around the or each joint a heat-shrinkable inner sleeve according to claim 5 having a layer of adhesive on the inner surface thereof, heating the or each sleeve to cause it to shrink into con-tact with the respective conductor, the adhesive forming a bond between each sleeve and its respective conductor, positioning an outer heat-shrinkable sleeve according to claim 1 having a layer of adhesive on the inner surface thereof around the covered joint, or all the covered joints, the outer sleeve being of such a length that each end of it overlaps the outer cable insula-tion, and heating the outer sleeve so that it shrinks into contact with the outer cable insulation, the adhesive forming a bond between the outer sleeve and the outer cable insulation, the resulting splice having an insulation resistance after flexing for 10,000 cycles and immersion in water for 24 hours at 23 ? 1°C of at least 1,000 megohms when measured in accordance with ASTM D 257.

23. A method as claimed in claim 22, wherein the strength of the bond between the outer sleeve and the outer cable insulation is at least 20 pounds per inch of bond width when measured in accordance with ASTM D 1876 (head speed of 2 inches per minute) after 10,000 flexing cycles.

24. A method as claimed in claim 22, wherein the or each inner sleeve has an original inside diameter slightly less than the outer diameter of the cable conductor which it is to cover and an inside diameter in the heat-unstable form greater than the outside diameter of said conductor and wherein the outer sleeve has an original inside diameter slightly less than the diameter of the outer insulation of the cable and an inside diameter in the heat-unstable form greater than the diameter of the outer insulation of the cable.

25. A method as claimed in claim 22, wherein the or each inner sleeve is of such a length that each end of it overlaps the conductor insulation.

26. A cable splice comprising a cable having an outer insulating jacket and at least one conductor, at least one of the conductors having been broken and physically joined, the or each broken conductor being covered at the point where it was joined by a heat-recoverable polymeric inner sleeve accord-ing to claim 5 which has been recovered around the conductor, a layer of adhesive bonding the or each sleeve to the respective conductor, the covered conductor, or all the covered conductors, being covered by a heat-recoverable polymeric outer sleeve according to claim 1 which covers the covered conduct-or(s) and overlaps the outer jacket of the cable, a layer of adhesive bonding the outer jacket to the inner sleeve(s) and the cable jacket, the splice having an insulation resistance after flexing for 10,000 cycles and immersion in water for 24 hours at 23 ? 1°C of about at least 1,000 megohms when meas-ured in accordance with ASTM D 257.

27. A cable splice as claimed in claim 26, wherein the bond between the outer sleeve and the outer cable jacket has a strength of about at least 20 pounds per inch of bond width when measured in accordance with ASTM D 1876 after 10,000 flex cycles of the bond.

28. A cable splice as claimed in claim 26, wherein the or each inner sleeve is of such a length that each end of it overlaps the conductor insula-tion.

29. A cable splice as claimed in claim 26, wherein each layer of adhes-ive comprises a hot melt adhesive.