Note: Descriptions are shown in the official language in which they were submitted.
This invention relates to heat recoverable articles,
especially to heat shrinkable articles that may be po~itioned
around a cable pipe, or connector at a joint or splice and
then cau~ed to heat recover in place to encap~ulate the
joint or ~plice.
There are many application~ where it i9 de3irable to
provide a sealing, insulating or protective encapsulating or
enclosing member for elongate objec~s for example cable~ or
pipes. Such encapsulation is particulal-ly important where
pipes or cables are joined or spliced, particularly when a
joint involving a plurality of pipes or cables i5 involved.
In many instances, the ends of elongate objects (hereinafter
the term cables will be used, although the invention i9, of
course, useful for enclosing or encapsulating pipes ducts,
conduits and the like elongate substrate especia:Lly junctions
between them) are not conveniently accessible to allow a
tubular sealing member to be placed thereover. To overcome
this shortcoming, closure members suitable for wrapping around
the elongate objectQ have been developed. See for example,
20 U.S. Patent Nos. 3 379 218 issued 23rd April, 1968, to Conde,
3,455,336 issued 15th`July, 1969, to Ellis or 3,770 556 issued
6th November, 1973, to Evans et al. These so-called "wrap-
around" closures can be installed around an elongate member
without access to a free end thereof. There is nevertheless
a significant need for a closure, hereina~ter referred to as
a "splice case" suitable for encloqing electrical cable joint~
or splices which provides effective environmental protection,
in particular, for a qplice i`nvolving more than two
incoming cable ends and/or splice~ ~
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between dif~erent si~e~ of cable~ but which may be applied without
acce~ to a free end of the cableO '!
~ he present invention i~ dlrected to a he~t-reooverable,
splice case which can, in VariOuB embodiment~, ~ocommodate a
pluralit~ of cable~ o~ dif~ering SiZC6, i.e. outside dlameter~
whlch can be removed and in ~ome embod:Lments reapplled to a
splice and which doe~ not require acoe~3~ to a *ree end o~ the
cable. The present design i~ not refe:rre~ to as a "wrap
around" sinoe it encapsulate~ a splice in a. somewh~t; dif~erent
~ashion ~rom the a~or~ment~oned "wrap~around" closuxes~ In
alternative embodiments the s~lice case of the present
: invention utilizes elther a "clam shell" or ~eparate ba~e
plate and cover member design~
In one em~odimcnt the present invention contemplate~ a
; 15 splice ca6e which will recover and encapsulate a cable or other
~ splice when ~ubjected to an external heat source, for example
: a propane toroh or hot air blower.
Many applications ~or splice case~ in~ol~e on ~ite u~eg
where~the sp~ice i6 rel~tively inacce~sible or i~ in a
potentially ha~ardous environment, and great care mu~t be
taken in installing the splice case.
For e~ample, in the oonnexion o~ overhead telephone cables,
or ~n mine~ and other location~ that may co~tain flammable gase~,
the use of an open ~lame torch for reco~ery i~ o~ten not onl~
dangerouæ, but ~ometimes prohibited~ Under such cixcumstanc~
a wrap-around clo6ure, i.e. spl~ce ca~e, that doe~ not require
the applica~ion o~ e~ternal heat, particularly a ~lame, would
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be ~articularly advantageous.
In a preierred embodiment, thera~ore, the a~lice ca~e of
the nresent invention has a built-i~ heatlng me~n~ eO the
splice ca~e contains an integral electrical reei~t~nce heating
element which, when connected to an appropriate external
; electric power 6uppl~, i6 capable of genQrating ~ufficient heat
to cause the ~plice case to reoover and encap~ulate the ~plice.
~his heat recoverable splice caee doe~ not require an out~ide
heating source, but instead may be caused to recover 6imply
by connecting it to an electric power cour~e, whether battery
or mains, e.g. a 12 or 24 volt battery9 or a 115 vo~t or other
appropriate A.C. supply, and which, when connected to such
a power source, will recover and may also activate an adhesive
or sealant on its inner eur~ace.
In *ormulating the materials which provide the integral
heating element ~or u~e in the splice cases o~ this in~ention9
arrangements and compositions ~hich provide uni~orm heating
are important. In ad~ition, for applicatlons w~ere the heating
element mu~t cau~e heat activation o~ an adhesive or sealantg
aæ well a~ heat reco~er~ o~ the article, relatively high
temperatureæ o~ the oraer of 120C to 200C mu~t be obtained,
but carefully controlled. I~ temperatures above that nace~sary
for heat reco~ery o~ the splice ca~e and adhesive activatio~
are reached5 then per~anent damage to the seal~ng article, i.e.
the splice case, and/or to the part to be sealed, e ~ gO the :~
substrate cable, ma~y result, such damage Ireauently not being
apparent by visual ins~eotion OI the recovered splice case and
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immediately adjoining areas of the cable.
Thermostats and/or other heat control devices may be
employed to control the temperature of the recovering and
recovered article. But for many applications, thi~ defeats the
object of using a ~elf-containing, i.e., self~heating, closure
sy~tem, in that expensive, sen~itive and,/or bulky external
temperature control devices must be employed in what are
sometimes virtually inacce~sible places. Moreover, the tempera-
ture sen3ed by th4 control device i3 only that of its immediate
10 environment, while other area~ of ~he ca~e may be at considerably
lower or higher temperatures.
In recent years a new approach for electrical heating
appliances ha~ been the use of self-regulating heating systems
which utilize plastic materials exhibiting positive temperature
coefficient of electrical resistance characteristics (herein-
after referred to as PTC characteristics or materials~. Such
materials generally comprise crystalline thermopla~tics with
a conductive particulate filler.
The distinguishing characteristic of these PTC materials
is that upon reaching a certain temp~rature a rapid rise in
resistance occurs. The temperature at which the resistance
increases sharply is often designated the switching temperature
(Tg) since the current at that point tends to switch off,
thereby preventing permanent damage through further temperature
increase to the heating article itself or any article being heated
thereby.
Although a number of th~ories have been propounded for
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the sharp rise in resi~tance of the PTC material usually at
about its crystalline melting point, it i9 generally believed
that such behaviour i9 rela~ed to the diffarenc0 in thermal
expan~ion of the conductive filler and 1:he t~ermoplastic
matrix material at the melting point. For a more detailed
discussion of a number of alternative mechanismq to explain
the PrC phenomenon, see "~lass Transition Temperatures a~ a
Guide to the Selection of Polymers Suitable for PTC Materials"
J. Meyerq Polymer Engineering in 5cience November 1973,
13, no. 6.
Most ~elf-regulating heating devices utilizing a PTC
material contemplate steep R = f(T) curves at about Tg so that
above this temperature the device will in effect completely
shut off while, below this temperature, relatively constant
wattage output at a given voltage is achieved. At low tempera-
; tures, the resistance i~ at a relatively low and constant level
and the current i~ relatively high for any given voltage. The
energy generated iq di~sipated in the form of heat, thereby
warming up the material. The resistance ~ays at the relatively
low level until Ts, where a rapid increase in resistance occurs.With the increase in resistance, there is a decrease in power,
thereby limiting the amount of heat generated and for extremely
steep R = f(T) curves, heating is in effect stopped. Upon a
lowering of the temperature, the resistance drops in turn
increasing the power output.
In general, when a voltage is applied across a PTC heating
element, the energy dis~cipated causes rapid heating of the PTC
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element up to its switching temperature, after which little
additional temperature rise will occur because c~f the steep
increa~e in re~istance. Because of the steep resistance rise,
the heating element will theoretically ;reac~ a steady state at
about the switching temperature, thereb~r self-regulating the
heat output without re30rt to fu~es or thermostat~.
Thermoplastic PTC materials conternplated b~ the prior
art are highly crystalline and exhibit 21 Tg at about the
crystalline melting point. However, most such materials in
fact show a ~Icurl over" effect, i.e. the resistance drops again
at temperatureq much above the melting point. This decrease in
resistance above the melting point i~ generally undesirable,
especially in case~ where the PTC material is itself heat
recoverable, or is used in intimate proximity to a heat recover-
able material to effect recovery thereof, since under suchcircumstances it i8 preferred to heat the heat shrinkable
material as rapidly as possible up to its melting point (i.e.
by means of hig~ power den~ities) and thereafter keep ~he heater
temperature very slightly above the melting point of the
thermoplastic constituent(~) of the heater in order to facilitate
- rapid and effective shrinkage of the heat recoverable article.
However, heat recoverable articles such as are comprehended by
the instant invention are intended in use to encapsulate and
environmentally seal splices between, for example, telephone cables,
by shrinking down onto and bonding securely, u~ually by the use
of an adhesive, to the cable jacket, which generally comprises
a low melting, partly crystalline, thermoplastic composition,
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for example, a carbon black loaded ethylen0vinyl acetate poly~er.
Such cable jackets are almost always uncros~linked and
therefore, will flow and distort readily if the heater cause~
them to reach too high a temperature (i.e. over their melting
points) during the time at such temperat:ure needed to activate
an adhesive. Even more seriou~ re~ults would occur with a
heater which does not very positively "~Ihut off" if, through
omission, the power supply were not disconnected from the heat
shrinkable article. Under such circumstances, it i~ conceivable
that the PTC heater could remain energized for periods far
in exces~ of that needed to complete the encapsulation process
which may take only, for example, ten minutes. The above
considerations are even more important if, as often happen~, the
individual conductors within telephone cables are each insulated
with similar thermoplastic compositions. Any di~tortion of
such conductor jackets is unacceptable, as it causes that
section of the cable to become nonfunctional. Thus, ~he heater
for the splice ca~e preferably undergoes a steep and exten~ive
increase in resi,stance above the Ts of the heater element and
continues to rise as the temperature of the heater is increased
above the melting point of the thermoplastic constituent, rather
than "curling over" i.e. declining more or less steeply as occurs
with most, if not all, prior art heaters. It is believed that
the "curl over" phenomenon and its problems have not previously
been generally recognized.
Furthermore, it has heretofore been generally believed
that conductive polymeric materials exhibiting PTC characteristics
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did not have s-lfficient hea-ting capacity to cause recovery of
relatively thick sections of heat recoverable mat~rials as
contemplated for the splice case of this invention, nor the
capacity to activate the high temperature adhesives also con-
templated by this invention. .
The shortcomings of the prior art: PTC material forarticles such as the splice case of the present invention can
be to a large extent overcome by the use of the compositions
disclosed in our co-pending Canadian Application No. 236,~56
filed September 26, 1975, and by utilizing constructions of the
type disclosed in our co-pending Canadian Application No.236,506
filed September 26, 1975. However, it should be noted that,
although prior art PTC materials are not preferred, they are
suitable for use in the splice case of the present invention
under many circumstances.
During use and operation of telephone cables, especia-
lly when the individual conductors are wrapped with a paper-
based dielectric, it is re~uired that moisture be excluded
since, if the moisture content of the wire insulation increases
beyond a certain relatively low critical level, the electrical
characteristics of the wire are unacceptably impaired. For
this reason it is customary when cables are spliced to place in
the assembly just prior to closure, a small paper bag of
desiccant (usually silica gel) in an amount sufficient to main-
tain the interior humidity of the splice at a very low level
over the lifetime of the splice, whatever the outside humidity.
In a typical instance, about 50 gram of silica gel might be
used.
_ 9 _
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As might be expected, the desiccant is frequently forgotten
or, even if not, the bags (which are customarily qealed for
storage) are ~ometimes left in an unsealed condit:ion for
extended period~ of time before emplacement or, ln the
extreme, even dropped into water or wet mud and emplaced
nonetheless. A preferred embodiment of this invention offers
an alleviation of this problem.
Excess humidity leads to an unacceptable drop in the
level of paper-insulated cable performance. At 30/O relative
humidity (R.H.) and at 15 C the insulation resistance of paper
insulated strands of the type often used in telephone cables
decreases to an unacceptable level of about 0.5 giga ohm per
kilometer. ~elow 30~0 R.H., performance is acceptable. We
have found that the humidity inside the splice case need not
be maintained at as low a value as po~sible but should simply
be maintained below 30~O whenever possible, Unexpected and
surprising benefits are derived from encapsulating the
..
desiccant in a container whose water vapour transmission
characteristics have been carefully matched to those of the
splice case it9elf so that the relative humidity inside the
said splice case may in all normally encountered circumstances
be maintained at less than 30/O whatever the relative humidity
outside, as the following exposition demonstrates.
For 100% R.H. outside an~ 0~0 R.H. inside if a typical
splice case of the instant invention has a moisture vapour
transmission (MVT) of 100 ~g/hr at 15C, the container for the
desiccant must have a MVT vloo ~g/hr at 3~/O RoH~ or ~333 ~g/hr
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at 100% R~H. Thus if the desiccant container has a MVT of
500 ~g/hr the requirement i9 satisfied.
Assume the container holds about 100 g. of desiccant
such as silica gel which i9 capable of absorbing about 50 g
water. Under shelf storage conditions at 10~/o R.H. with no
othex protective covering the desiccant thus contained will
lose half its absorptive capacity in about six years. ~hus, a
container of this type permanently affix~ed inside the splice
case will suffer no appreciable diminution in effectiveness even
if the splice case is removed from its protective wrapping
during storage and periods of many months elapse before it is
used.
An especially useful feature of certain of the qelf-
heating splice cases of the present invention i9 their potential
re-enterability. The case may be re-entered ~y merely electri-
cally connecting the installed splice case to an electrical power
source, waiting a few minutes to soften the adhesive, removing
the electrical contacts and the side and end clip members (if
they have been left on) and s~parating the upper and lower
splice case halves. If desired, after necessary changes to
the individual splices or replacement of any component, the
whole splice case may be reassembled as be~ore and a short
period of reconnexion to an electrical power source will
result in a reforming of the adhesive bonds to yield an assembly
of unimpaired structural integrity. This ease of re-enter-
ability means that if not all the ca~le folds are required at
the initial installation a plug or plugs may be used, sized
to maintain the redundant folds in an expanded condition
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during initial installation. On subsequent re-entry additional
cables can be added at any time and any newly added components
sealed as effectively as any of the original component~.
Re-entry of the non-self heating splice cases can also be
S effected by use of an external heat source to melt the adhesive.
It is an object of this invention to provide a heat
recoverable closure system which is isuitable for encapsulating
a plurality of cables of various si2es.
It is a further object of this invention to provide a
heat recoverable closure assembly which may be inserted over
or wrapped around cables and which may have the self-heating
; capacity to seal such cables without resort to outside heating
sources.
It is another object of this invention to provide a
self-heating closure system which i9 capable of self-regulating
and not overheating to cause permanent damage to the article
encapsulated, nor on the other hand shut off at a less than
the design temperature.
The present invention provides a closure article
comprising first and second members adapted to be brought
together to form a generally tubular structure having a central
cavity portion the first member being heat recoverable and
the second member optionally being non-heat-recoverable and
means for maintaining said members together during heat recovery
of szid first member the structure so formed being adapted
at at least one end thereof to heat recover around and seal
a plurality of cables inserted therein.
Advantageously the article also comprises at least
between a pair of the plurality of cables inserted in one end
- 12 ~
1 G~351~7
means for maintaining together opposed portions c)f the end.
Preferably, the means fox maintaining together the
opposed portions comprise a clip or clamp~
Further, the invention also provides a method oE
encapsulating a junction between a plurality of elongate
substrates which comprises po~itioning an article, at least
a part of which is heat-recoverable, about the junction with
at least one pair of the substrates extending from one end
of the article applying over two opposed portions of the
said end of the article between at least the pair of substrates
means for maintaining the opposed portions together during
recovery and heating the article to cause it to recover about
and encapsulating the junction.
Preferably the means for maintaining the opposed
portions together i8 a clamp or clip.
~ Advantageously the heat recoverable portions of the
article comprise a polymeric material dimen~ionally changed
from a heat stable configuràtion or form to a diwensionally
heat unstable one capable of recovering to or toward the
stable form on the application of heat.
Preferably at least a part of the material also forws
heating means and advantageously this part also orm~ the
dimensionally heat unstable portion of the article.
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The portlons of the surface of the article which
will face the sub~trate to be covered and those portions
which will contact each other when the article is
po~itioned over the substrate advantageously have a
coating of heat-activatable sealant or adhesive thereon,
which preferably is activated at about the recovery
temperature of the article. m e portions which engage
each other are preferably provided with means to hold
them in engagement during recovery. The central portion
of the article may be provided with a heat
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~table insert, which will define a cavity for surrounding the
splice, while the end portions are shaped to re,cover indivi-
dually around each of the cables, etc,. w~ich ~oin at the
splice.
Advantageously, the heating mean~3 is sel~-regulating
and comprises
a first layer of conductive polymeric material having
a positive temperature coefficient of resistance, and in
surface-to-surface contact with at least one face of the layer,
a 3econd layer of conductive polymeric material having
a substantially constant resistance at lea~t up to the recovery
temperature of the article to give a substantially constant
wattage at a given voltage, and at least a pair of electrodes
so positioned that current passing between them will pass
through at least a portion of the constant wattage material
and from one face to the other of the first layer.
Preferably, there is a constant wattage layer in
face-to-face contact with the first layer and the electrodes
are each in contac~ with a constant wattage layer.
The article preferably contains an insulating layer,
which may al 30 be heat recoverable.
In some instances, the article constructed in accordance
with the invention can be recovered by an external heating
means, and in those cases, of course, the conductive layers
and the electrodes may be omitted.
The inven~ion also provides a method of covering a
junction, b~ recovering an article constructed in accordance
with the invention, and a junction covered thereby, esp~cially
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a cable splice.
The optional self-contained heating means advantageously
compri3es a polymer having dispersed thexein an electrically
conductive filler to render it capable of conducting current
S at a ~iven voltage (e g. 12 or 24 volts from a battery) while
having sufficient resistance at its operating temperature 90
that its heat output is capable of causing a relatively thick
section of heat recoverable materials, on the order of some
millimetres thickness, to heat to its recovery temperature
and recover about the splice to be encapsulated. In
addition, the heating means is advantageou~ly capable of
giving sufficient heat output to activate a high temperature
thermoplastic or thermosetting adhesive or sealant.
When a PTC material is in the form of a structure having
two comparatively large dimensions and one comparatively small
dimension, e.g. a layer such as a sheet, passage of current
along the small dimension is preferred for more uniform heat-
ing. When the current flow is along the plane of the PTC layer
localized heating along certain conductive paths may result
causing non-uniform heat output. T~is in turn can cause an
even greater problem, rendering the entire heating device use-
less for a majority of its heating cycle. If localized heating
causes the material to reach Ts along a line transverse to the
current path, it will prevent the flow of current across the
25 path, in effect causing the heating device to shut down until
the temperature of the thus -formed "hot-line" drops below Ts.
In other words, the "hot-line" across the layer between end
electrodes e~fectively shuts down the heating device even though
. . : . . : ~
only a small surface area of the layer has achieved Ts~ This
renders the heater so inefficient that it appears to exhibit a
very low heating capacity. The hot-lining problem can be
minimized by positioning the PTC material between the electrodes
in a way that minimize the length of the conductive paths
across which hot-lining can occur. For maximum efficiency with
minimum current path, the length to thickness ratio of the layer
should be minimized. This is achieved, for example, with a
sheet in which the electrodes sandwich the PTC material.
However, because of the short current path, and limited surface
required for some application, inadequate heating for such a
configuration may occur at lower power inputs. To remedy this,
a material giving a constant wattage or Joule heat output, at a
given voltage, i.e. a material not having PTC characteristics,
is advantageously laminated with the PTC layer so that the
laminate exhibits good heating effectiveness yet is self-regu-
lating, without hot-lining~ A more thorough discussion of the
advantages of applying a current through the layer, as opposed
to along its length, and fabricating a layered composite, is
disclosed in the above-mentioned Canadian Application No.
236,506.
~ or a more detailed discussion of suitable PTC
compositions which are preferably employed as layers for use in
the present invention, especially for relatively high tempera-
ture applications, the reader is referred to the above-mentioned
Canadian Application No. 236,456.
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35~l~7
Such compositions comprise blends of thermoplastic and
elastomeric matexials havlng conductive materials di~persed
therein. As pointed out in the specification, such blend~
exhibit a steep rise in resistance at about the melting point
of the thermoplastic component, the resistance continuing to
ri~e with temperature thereafter. Because of the increased
safety margin given by the further increases of resistance above
the melting point such heaters can be designed to control
("3witch off") at temperatures above the theoretical Ts and
have resistances well in excess of that at T~ but yet avoid
the ri~k of thermal runaway and/or burn out which occurs w~en
prior art PTC compositions are used in such desi~ns. Such
heaters, especially when the increase in resistance with
temperature above Ts is very steep, are very "demand insensitive"
tha~ is the operating temperature of the PTC material varies
very little with thermal load. ~hey can also be designed to
generate very high powers up to Ts when electrically connected
to a power source. Because of their excellent temperature
control, they can be employecl to activate adhesive~ and cause
heat recoverable devices such as the present invention to
recover around substrates such as thermoplastic telephone
cable jackets with reduced risk of melting or deforming the
substrate even if left connected for considerable periods of
time.
It should be noted that a variety of closure means,
including an adhesive as discussed above for the splice case '
can be employed. ~he closure'means should be such as to with-
stand the heat re~overy forces at the temperature of recovery~
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for examples of which see U.S. Patents No~. 3,379,218 and
3,455,336
The devices and methods of splice encapsulation provided
fox in the instant invention differ substantially from and
thereby overcome to some extent or otherwise avoid some of
the deficiencies which characterize prior art devices and
methods. For example, in one of the preferred embodi]ments
of the invention, the heat recoverable f~lds when positioned
around the substrate, e.g., the cable, enfold the substrate
in such a manner that the opposing heat recoverable surface
do not come in contact with one another but butt up against
opposing surfaces of, for example, long fingers forming
ridges on the mating surfaces of the non-heat recoverable ba~e
member. The forming of closure or splice case from a combina-
tion of a heat shrinkable and heat stable member as in certainpreferred embodiments so that the areas of the members which
abut to define the cavity containing the cable splice are
not themselves heat shrinkable is another significant departure
from the prior art as will be apparent from the following
more detailed discussion.
It has been long realized that when a heat-recoverable
member is folded or wrapped around a substrate and shrunk down
to region in which the heat recoverable member is brought to-
gether and secured with a closure member consitutes an area-of
weakness both mechanically and in its resistance to the environ-
ment, for example, to penetration of watar. In the abovementioned
Ellis patent are described ways to solve this problem by the use
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of a design with an overlapping 1ap und0r the abutting edges
of the heat recoverable member and secured to th~ overlying
layer by an adhesive to provide a long leakage path.
However, this solution fails if the substrate does not
provide a firm foundation against which. the heat recoverable
enclosure can press the flap so as to cau~e the adhesive to
flow and wet the faying surfaces. When to this factor i9
added the difficulty of constructing a multiple entry ~plice
case having overlapping heat recoverable regions it can be
seen that an article constructed in accordance with the
Ellis patent, while extremely useful in most instanceq,
does not solve all the problems which the instant invention
solves~
.~ ~0
These problems are solved in :
a surprisingly simple and highly effective manner by the preferred
approach of the present invention. The optional provision of
an intervening ridge or finger on the non-heat recoverable base
member in combination with the clips and flanges on the heat
xecoverable member, which flanges can be used preci~ely because
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385~:7
the heat recoverable member in the~e re~ions contains non-heat
recoverable ~eg~ent~ ~acilitates obtain.ing thi~ highly de~ir~ble
re6ult.
~he invention will now be described in greater detail
by way o~ example only, with re~erence to the acoompanyin~
drawing~, ~n which:
~igure t i8 a per~pective view o~ a ~ir~t embodiment
o~ a heat recoverable article~ i.e. a s~lioe
case, con~tructed in accord~nce with the
~n~ention, in whlch ha~ been positione~d and
joined a plurality o~ cables of VQXioU8 dimensione;
~igure 2 18 an end view of the article o~ ~igure 1 prior
to expan~ion to its heat unstable, i.e. heat
. recoverable form;
Flgure 3 i~ an end view o~ th~ article after expan~ion to
- it~ heat un~table form;
Figure 4 i8 an end view o~ the article aiter it has been
ca~ed to heat recov~r about cables;
~i~ure 5 iB t~ken along line 5-5 of ~igure 3 ~howlng ln
more detail the layered con~truction o~ the article;
~i~ure 6 i~ a perspective view o~ the article prior to
cable in~ertion;
~igure 7 is a perspective view of an alternative con- :
*iguration embodiment of an article constructed
in accordance with the invention.
It should be noted that, with the e~ception of ~`igure 5,
and the schematic electric circuit in ~igure 6~ Figures 1 to 7
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are illustrated of a splice case whether or not it incorporates
self-heating means. Figure 5 show~ a layered construction
which exemplifies an embodiment wherein th0 splice case
incorporates ~elf-heating mean~. Figures 8 to 11 show the
structure of a second preferred embodiment of a ~plice ca9e
constructed in accordance with the invention.
Figure 8 which follows Figure 9 i~ a cross section
~hrough one end of the s~plice case,
Figure 9 is a perspective view of one end cut away to
show the details of the structure,
Figure lO is a perspective view of the splice ca~e
from below the non-heat recoverable base member,
Figure 11 isa longitudinal section through the splice
case showing details of the internal cavity,
Figure~ 12 to l9 show details of the preferred method
of construction of a third preferred form of splice case
con~tructed in accordance with the invention.
Figure 12 illustrates the formation of the preferred
braid electrodes;
Figure 13 shows the positioning of electrode~ over and
attachment to the bus bars
Figure 14 shows various layers ~cut away to facilitate
understanding) of the blank for the heat
recoverable member positioned in a jig
prior to lamination,
Figure 15 Yhows the blank being formed into the basic
shape for the heat recoverable member,
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Figure 16 show~ the heat recoverable mem~er in it~
heat stable configuration after being cross-
linked,
Figure 17 shows the con~truction of the reinforciny
flanges for the ends and sides of the heat
recoverable member,
Figure 18 shows the flange~ keing applied to the heat
recoverable member positioned in a jig prior
to expan~ion,
Figure 19 shows the heat recoverable member at the end
of the expansion step,
Figure 20 which follows Figure 21 shows the upper
lower members of the splice case in perspective
to show additional details of the interior,
Figure 21 shows the espec1ally preferred embodiment
after installation around a cable 3plice.
Referring now to the drawings, Figure 1 shows a heat
recoverable closure apparatus constructed in accordance with
this invention, adapted for receiving a plurality of cables
and having an enlarged central section for accommodating a
splice between the cables. Such a configuration i~ particularly
suited for low voltage telephone cables wherein a plurality of
cables are to be joined quickly and efficiently at minimum cost.
The apparatuq shown in Figure 1 may be entirely made of
a heat recoverable material, preferably having layered therein
- a ~elf-heating composition, as shown in Figure 5, which will be
discu~sed in more detail hereafter~ -Alternatively, only that
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portion of each end of the splice case comprising the folds,
i.e. that portion of the ~plice case b~tween the ends thereof
and da~hed lines 18, can be made heat recoverab~e with the
center portion being non-heat recoverable. The layar or
layers of heat recoverable material are cros~linked as, for
example, by irradiation ~o as to render then heat recoverable.
A heat recoverable part comprising a layer 10 is positioned
in its stable, unexpanded state with folds 11 as shown in
Figure 2. The unexpanded folds can, of course, take on any
configuration, including the general configuration of the
cable provided that a sufficient excess of material for
expansion i9 allowed. The folds are expanded by known tech-
niques to a dimension greater than the diameter of the cables
to be sealed, as shown in Figure 3. The material is sufficiently
resilient and flexible that the cable may be snapped into
the opening of the fold. As best seen in Figures 3 and 4,
the openings may be of varying dimensions depending upon the
size of the cable which is to be inserted, although lt should
be kept in mind that one size opening is recoverable over to
seal a wide range of ~able sizes. The heat recoverable part
10 is mated with a bottom part of the splice case 12 which
is not heat recoverable although as shown, for example, ln
Figure 7, it may be heat recoverable in some embodiments.
~he bottom part 12 may serve as a permanent mounting for the
cable splice giving rigidi~y to the system. Alternatively,
the parts 10 and 12 may have a cooperating hinge at one edge
14 (Figure 4) with a closure means at the opposite edge 6.
Alternatively, where parts 10 and 12 are formed from the same
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material, they may be integral at the edge 14, utilizing a
clo~ure at ~he edge 6, or the parts 10 and 12 may be separate
parts separated at both edge~ 14 and 6 in which ca3e the heat
shrinkabls part 10 is merely lifted from the part 12 for
in~ertion of the cables. If desired, the parts 10 and 12
may have reinforcing strip~ emk~dded thlerein along the ~ong
axis thereof, preferably adjac~nt the edges 14 and 6. Such
strips can also serve as bus bars.
In sealing cable splices in accordance with the process
of the invention, the parts 10 and 12 are separated and cables
20, 22 and 24 are placed therein. Referring more specifically
to Figures 2, 3 and 6, where the parts 20 and 12 are neither
integral nor hinged, a clamping device, for example, hinged
clamps 52 and 54 are utilized, such clamps being tightened by
means of a bolt 56 and a wingnut 58. The clamps may serve to
maintain the parts 10 and 12 together during expansion (Figure
2) as well as during insertion of the cables and reco~ery
thereover (Figure 4). Although such clamps could form a
:;, .
; permanent part of the installation, they are preferably removed
after installation and an adhesive such as, for example, that
described in U.S. Patent 3,770,556 is used to seal the edges
permanently.
Also, at the ends, proper spacing between cables is most
suitably assured by a clamping device. As best seen in Figure 6
this may be a plate separator 62 having openings therein to
accommodate the folds 11 (Figure 2), such plate tightly sealing
the parts 10 and 12 by clamps 64 and 66 during the expansion
and sealing operaiions. ~
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To add ~trength and further to protect the system, and
where necessary to provide moisture vapour transmission protection
or radio frequency shielding, the cable splice it~elf can
optionally be encapsulated within a rigid can with the case,
having an outline defined by dashed lines 18 and 18a located
beneath the central portion of the heat recoverable member
generally designated 26 in Figure 1. Where the central portion
26 is heat recoverable, it will conform to the shape of the can
which can suitably be fabricated of any rigid material, including
10 metal or moulding plastic. The end openings 19 21 and 23 are
adapted to receive individual cables of varying dimensions. The
other end of the heat recoverable member will generally contain
openings of similar dimensions to accommodate the cables to be
joined, although all of the openings may be confined to one side.
Where a rigid can is employed for covering the splice,
sealing at the central portion by the heat recoverable member
may not be necessary. Therefore, as heretofore indicated, the
heat recoverable portion of the article of this invention can be
limited to the end portions s~ that it will seal the individual
incoming cables up to the can. In this case, the central portion
26 can be of non-recoverable material or if recoverable, need
not be caused to recover. Alternatively, the material need not
extend across the can so that the can is allowed to remain
exposed, or only an insulation layer, for example the layers 30
or 31 of Figure 5, need extend across the can with remaining
layers being confined to the ends.
Referring now more specifically to Fi~ure 5 the heat
- 26 -
~ ' '. ' '
recoverable closure preferably comprises a self-heating
laminate having electrodes embedded therein, the electrodes
being connectable to an appropriate power source. A suitable
laminate is more fully described in the above-mentioned Canadian
Application No. 236,506. Briefly the laminate consists of an
outer insulating layer 30, which is heat recoverable. A layer
34 comprises a polymer or polymer blend, for e~ample a blend of
a highly crystalline polyolefin and ethylene-propylene rubber,
having dispersed therein conductive carbon black. The :Layer 3~
preferably exhibits positive temperature coefficient of resist-
ance properties to control the heating. The layer 34 is
preferably interleaved between layers 32 and 36 which may also
be polymer blends having carbon black dispersed therein, these
layers preferably yielding constant wattage outputs at a given
voltage over a wide temperature range and not exhibiting
significant positive temperature coefficient of resistance
properties. An inner insulating layer 31 may also be provided.
The layers 31, 32, 34 and 36 are preferably also heat recover-
able. The inner layer can advantageously contain an adhesive
coating (not shown) on its free surface for bonding and sealing
to the cable. ,
Embedded in the constant wattage layers 32 and 36 are
electrode grids 38 and 40, which are capable of being connected
to a suitable power source for example a battery as schematic-
ally shown in Figure 6. This configuration causes the current
to pass through the PTC layer 34 from electrode 38 to electrode
40. A preferred type of electrode design and con Eiguration is
more fully described below.
--27--
,: ~
Re~erring now more especially to Figure 7, an alterna-
tive configuration of the present invention i8 shown. Such a
configuration may be formed and expanded out of a single sheet
; of material, generally having the layered configuration of
Figure 5. ~fter inserting the cables as previously described
through openings 44, 46 and 48 the apparatus is closed by
bringing together the opposite edge 50 of the sheet by a suit-
able closure means 51. Such apparatus may, of course, be made
to confirm to various cable diameters and shapes as shown. It
can be "clam shell" design having a closure means at 50 and
self-hinging at 47.
An especially preferred embodiment of the invention is
illustrated in cross-section in Figure 8. It comprises upper
and lower members 96 and 80. The upper member 96 comprises an
outer splice case shell 67 affixed firmly to a heater which
consists of outer and inner layers of constant wattage material
68 and 70 and a core layer of PTC material 69. To the inside
surface of the inner constant wattage layer 70 is affixed an
adhesive layer 71. The heater PTC core 69 preferably construct-
ed as described in the above-mentioned Canadian ~pplication No.
236,456 is combined with constant wattage outer layers 68 and
70 of compositions whose thermoplastic polymer ingredients, if
any, have a lower melting point than that of the thermoplastic
polymer component of the PTC composition. The constant wattage ~;
layers, if comprising thermoplastic polymers, may be made heat
recoverable and preferably an additional outer shell 68 com-
prising a layer of a heat recoverable polymer composition
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having a recovery temperature less than the melting point of
the thermoplastic component of the PTC compositi.on i~ al~o
provided. An additional layer 71 of a hot melt adhe3ive or
mastic may al~o be provided, t~e hot me:Lt, if used, having a
melting point similar to that of the heat recoverable member
and an activation temperature le88 than the melting point
of the thermoplastic component of the PTC composition. Such
an embodiment has been found to be particularly advantageouæ
where the substrate is heat 3en~itive "L e. where if warmed
above its melting point it will deform or flow.
As shown in greater detail in Figure 9, embedded in the
constant wattage layerq are flexible and complaint electrodes
72 whiah may be advantageously formed from braided wires. Each
heat shrinkable end fold contains six electrodes 72, three being
connected together for connexion to one terminal and three to
another, opposed to each other in pairs and running transverse
to the longitudinal axis of the case. Electrodes of the first
polarity are connected (as by welding, soldering, or glueing
with a conductive adhe~i~e at tha area~ of intersection)
to bus electrode3 73 and 73a, and of the second polarity to
bus electrodes 74 and 74a, running the length of each side
of the caseO T~e electrodes 73, 73a, 74 and 74a may be
constructed from wire braid or thin metallic strip, optionally
perforated. To the mid portion of electrode 73 on one side and
to the mid portion of electrode 74a on the other side are
affixed tabs 75 and 76 adapted for easy connexion to an
electrical power source. On the top of the primary heat
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shrinkable layar (see al~o Figure 8~ along each side and
between the heat recoverable end fold structure~3 are
attached ~by ~lueing or otherwise adhering) rei~lforcing
flanges 77, 78 and 79, fabricated from any suitably rigid
material. E~pecially ~uitable materials include metals, and
engineering thermoplastics, for example, po}ycarbonates,
acrylonitrile butadiene styrene or SAN resins and filled
polymers for example polyamides or polyolefins. Especially
pre~erred i8 a gla~ filled polyamide (nylon). I~e lower
memb~r 80, which i8 not heat recoverable, preferably has
external ribs 81 for increased rigidity and, optionaLly,
internal ridge3 82 corresponding to and adapted to be mated
with the open sides of khe heat recoverable folds as also
shown in Figure 10. The splice case may be a~sembled by
bringing the upper and lower members together and securing
with spring dip8 83, 84 and 85 suitably constructed of
j similar materials to flanges 77, 78 and 79.
Turning now to Figure 11 there i8 shown a section along
the longitudinal axis ~ t~e case. A central c~vity 86 ser~es
to contain the individual spliced wires from the cables.
Optionally and advantageously, there is present a small con-
tainer 95 ~filled with a desiccant) whose walls permit water
to diffuse through at a rate in excess of the diffusion rate
into the splice case internal cavity, as previously explained
i~ greater detail. A valve may be provided to afford access
to cavity 86 enabling pressure te~ting of the installed
splice case.
The preferred method o~ fabrication of à splice case will
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be illustrated, with particular reference to the embodiment
of Figures B to 11, with re~erence to Figure~ 12 to 21~
The electrode material, pr~ferably a metallic brald,
which may be, for example, formed rom sixteen carriers each
of fOur ~trands of 38 AWG (about 0.010 cm diameter) tinned
copper ~ire braided at as high a braid angle as possible
(to achieve a high degree of compliability~ i8 formed around
a thin conductive or nonconductive thermoplastic tube.
Excellent result~ have been obtained wi~h a braid angle o
75 around a 6.25 mm outside diameter 0.25 mm wall tubing of
the ~ame compositio~ a~ the constant wattage materi~l. The
b~aided tube i~ then heated to or above the softening tempera-
ture of the thermopla~tic tube and flattened, care being taken
to pre~ent stretching of the braidO These steps are ~hown
in Figure 12.
The next stage in the process i8 the construction of the
electrode/bus system compri~ing the steps of affixing the
tab 75 to the side electrode 73a, followed by attachment of
the end electrode~ 72. Suitable affixing method~ include
spot welding ~oldering and glueing. When the electrode
comprises wire braid around a conductive core of the ~ame
material as the constant wattage layer it has been found that
excellent results are obtained by hot bonding using the con-
ductive thermoplastic core to bond the electrodes together.
25 Attachment o~ the electrodes to one another to form the basic ~ :
configuration is facilitated by the use of a jig as shown in
Figure 14. The material used for the end electrode~ in
addition to the flattened braid referred to hereinabo~e, may
include knitted or woven or plated metal wire~, conductive
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fibres or metal plated polymer fibres or polymeric fibres
containing conductive particles which have been so treated as
to render them highly conductive in the fibre direction.
It i~ preferred in all these embodiments that the
S resultant electrode be highly exten3ible and compliant so as
not to offer any appreciable resistance to expansion or
recovery of the heat recoverable portions of the splice case
as occurs during manufacture and installation in service of
the Qplice ca3e.
Similar materials may be used for the side or bus
electrodes. As theAe electrodes are not required to undergo
any significant deformation during manufacture and installation
they may additionally be formed out of such relatively non-
extensible and noncompliant materials as ~lat metal or other-
wise highly conductive strips, preferably perforated and single
or multiple stranded wires.
The con~truction of the blank for the splice case is 4hown
in Figures 13 and 14. The various heater layers prepared by,
for ex~mple, extrusion, coextrusion or hot calendering, are
conveniently assembled in a jig frame. In the particular
embodiment illustrated, a skin layer 67 is placed in the frame
and successively a constant wattage~layer 68a the first set of
electrodes 73/73a (with the tab 75 pointing to the right as
shown in the drawing), another constant wattage layer 68b, the
PTC control layer 69 another constant wat-tage layer 70a, the
second set of electrodes 74/74a (with the tab 76 pointing to the
left), and a final constant wattage layer 70b laid over. The
whole structure is sandwiched between polytetrafluoroethylene
~ - 32 -
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protective layers 97 and laminated together by heating under
pres~ure. A jig is used to hold the variou~ la~er~ and the
electrodes in fixed relation to one another during lamination,
the minimum pre~sure being applied. After lamination and removal
of the polytetrafluoroethylene layers, the assembled splice
case blank i~ preferably sandwiched between foam rub~er sheets
100 and annealed for example at about 185C for a ~ufficient
period of time with minimum applied pressure to allow the
constituent layers to relax thoroughly~ Depending on the materials
involved annealing periods of as little as two minute~ to over
one hour are suitable, five minuteq to fifteen minut~e~ being
preferred. The blank i~ removed while still at the annealing
temperatures and conformed over a male mould as in Figure 15
using pressure as indicated by the arrows so as to form the
unexpanded splice case configuration 87 shown in Figure 16.
In this operation, a~ previously, care should be taken to ensure
~hat the heater is not stretched during the forming operation.
If desired a plurality of ridges, preferably wedge shaped, may
be present on the upper surface of flanges 77 78 and 79 which
ridges serve to direct the compressive forces exerted by clamps
83 and 8g.
The b~sic splice case 87 is then irradiated with ionizing
radiation using techniques well known to those skilled in the
art to ensure uniform irradiation. Suitable ionizing radiations
include gam~a rays, X-rays and accelerated elections. The
dose required should be sufficient to ensure integrity of the
configuration above the crystalline melting point of any of its
polymeric constituents but not sufficiently`high as adversely
- 33 -
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to effect the elongation behaviour during the expansion operation
to form it into the heat recoverable configuration. A ~uitable
irradiation dose range has been found to be 2 to ~0 megarads,
5 to 20 megarads being preferred.
The blank which following irradiakion may be considered
to be in a "heat stable" configuration is then formed into the
"heat recoverable" configuration 88 in the sequance of operations
shown in Figures 17 to 19. After a preheat sufficient to warm
the article 87 to about the melting point of its crystalline
polymeric constituents the formed blanks are inserted into a
jig 89 as shown in Figure 18. The reinforcing flanges 77 78
and 79 which have their contacting surfaces coated with an
adhesive 90 as shown in Figure 17 are placed on the sides and
ends of the formed blank 87. The end flanges 78 (and the
corresponding flange at the other end of the splice case~ is
made with a long "break off" tab 91 having locating holes 92 for
mounting in the jig 89 as shown in Figures 17 and 18. All the
flanges have turned down lips 98 at their outer edges to serve
to contain and protect the edges of the heater from mechanical
damage. The side flanges 77 and 79 have a small shroud 99 in
the middle outside edge surrounding the electrode tabs 75 ann
76 and sized to accept a standard "quick disconnect" connector
6.3 x 0.8 mm ~uch as are supplied by the Arc-Less Company.
Pressure is applied to the side and end flanges and the
eplice case folds and central cavity formed by suitable expansion
means. Such expansion techniques are well known to the prior art
and include mandrel expansion and pneumatic or vacuum forming.
- 34 _
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In this operation care should be taken to prevent longitudinal
compression of the folds when a mandrel is used. Suitable means
for minimizing such compres~ion include provision of a radially
expansible or circumferentially segmented ~leeve member between
the mandrel and the fold which serves to decouple the longi-
tudinal insertion forces exerted by the mandrel from the folds.
Alternatively pneumatic or hydraulic expansion of an elastomeric
tube longitudinally constrained may be used. The central
splice case cavity is preferably formed pneumatically. The
expanded blank is then cooled while under constraint as in
Figure 19, removed from the jig and an adhesive layer 93 affixed
to the surfaces that will butt on to the lower member and on
to the interior surfaces of the folds. An adhesive layer can
also be affixed to the abut-ting surface of member 80. At this
stage if desired, a container 95 filled with a desiccant may
be fixed to the inner wall of the central cavity 94 as shown
in Figure 20 which is a view of the completed upper heat recover-
able member 96 where the relation of the folds and central
ca~ity can be seen. Alternatively, the desiccant can be
affixed to the base plate as shown in Figure 11.
In use after completion of the splices and incorporation
into the splice case the complete splice case is assembled as
above described ~y bringing the upper and lower members 96
and 80 together and securing with the side clips 83 and 85
25 and end clips 84a and 84b. The heater is then electrically -~
connected to a power source.
Because of the disposition of the electrodes in the splice
- 35 -
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case upper member and the relative resi~tance~ of the constant
wattage and PTC layers on connexion to a power source for
example, a 12 or 24 volt lead acld battery, heating to cause
; reaovery and/or activation of the adhesive occur~ predominantly
at the folds and in the flange regions~ Thus, the central cavity
does not develop enough power to warm to,a significant extent.
As has been mentioned hereinabove t:he compositions used
in the heater layers may be chosen so a~ to provide extremely
quick heating of the splice case. For example, using the
10 preferred PTC compositions of the type hereinabove re~erenced,
it has heen found that the heater in the fold area typically
heats to 115 - 120C in less than one minute. On reaching such
temperature the fold regions start to recover. In about two
minutes the fold regions have shrunk around the substrate, e.g.
cable and after a further eight to thirteen minutes the
adhesive layers have been thoroughly activated and have wet
and sealed to the cable jacket and to the non-heat recoverable
base member. Thus, in a typical instànce the heater is
appropriately connected to a power source for from about ten
to fifteen minutes during which time the assembly may be safely
left unattended, ailowing the assembler to proceed with other
operation~. Those skilled in the art will realize that the
period of time the heater is under power will vary according
to the temperature demands of the adhesive, the thermal
load and other factors. Surprisingly it has been found that
the period of time required is relatively insensitive to
the ambient temperature. It is believed that this may
be due to the extremely sharp PTC cut off made possible
- 36 -
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by the particular advantageous design combination of the
instan~ invention.
After an appropriate period of ti~e the electrical power
~ource i8 removed and the splice ca~e allowQd to cool to
5 ambient temperatureq. At this time the ~ide and end clip~
may be removed or left in place to provide additional mechani-
cal protection if desired.
A particularly advantageous result of the combination of
elements in the instant invention is that because the heater
is capable of maintaining it~qelf in a particularly limited
range of temperatures whatever the environmental thermal load,'
even if this temperature range is very clo~e to the melting
points of commonly used thermoplastic cable jacketing or
individual wire insulating materials, the ~plice case may be
left electrically connected to a power source for periods
(e.g. of several hours) after the joint has been made and
damage to the telephone wire~ or cables may be avoided.
In order to facilitate re-en~ry, the article may be
provided with restraining means to inhibit the complete recovery
of the recoverable member when the installed member is re-heated
,to soften it and any adhesi~e. The restraining means may
comprise rigid, e.g., metal, tongues which will underlie the
portions which are to surround the cable. Ref~rring to Fig. 9,'
a tongue having the same width as the flat portion 78'between
the cable entrie~ is positioned on the surface of the flat
portion, with a portion extending axially outwardly therefrom.
Similar tongues may be positioned on the outer flat surfaces
77 and 79, and all the axially extending portions joined
together by appropriately shaped connecting links to form an
integral restraining means. '~his means may be left in positio,n
during use~ if desired.
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