Note: Descriptions are shown in the official language in which they were submitted.
The invention relates to heat shrinkable coverings. Heat shrink-
able coverings, for example of polymeric materials, are used to
seal or to protect pipe weld joints, telephone cables, electrical
splices, pipelines and the like from adverse environmental con-
ditions such as corrosion and moisture.
Heat shrinkable tubular sleeves are known. These can provide an
excellent seal and protection around articles to which they are
applied. One limitation of their use is, however, that they can
not be applied to continuous pipelines or the like, which have no
accessible exposed end over which the tubular sleeve can be
fitted. Further, the known tubular sleeves are usually formed by
extrusion and there are practical limits on the diameters of
tubes that can be extruded, at least with the conventional extru-
sion equipment.
50-called "wrap-around sleeves" are also known. These are heat-
shrinkable sheets which are adapted to be wrapped around the
article to be sealed or protected and then to have the edges of
the ~heet joined together to form a sleeve. Some forms of wrap-
around sleeve employ mechanical fastenin~ devices to connect the
edges of the sheet together. The mechanical connection is
intended to prevent the edges of the shee~ from separating when
the sheet is shrunk down. Prior devices of which the applicant
is aware have, however, been difficult or inconvenient to connect
together, have provided a connection which tends to be weakened
or destroyed on heating, and have tended to leave elements of the
fastening devices protruding from the comple~ed shrunk-down
sleeve, which can present risk of the protruding elements
engaging with or snagging on adjacent conduits or cables and
cutting into relatively soft~ e.g. plastic, protective cov2rings
of the latter, thus leading to the possibility of ingress of
moisture, corrosion, leaks and short circuits.
The present invention provides a heat shrinkable covering adapted
to be wrapped around an article, comprising a flexible sheet that
is heat shrinkable in a longitudinal direction and has two long-
itudinally spaced transversely extending parallel zones adapted
~ 2~
to be brought into superimposed overlapping relationship when the
sheet is applied to the article, a heat-resistant stiffening mem-
ber offering differential rigidity connected along each zone and
providing relatively more rigid resistance to longitudinal defor-
mation of the zone in the plane of the sheet and providing rela-
tively less resistance to deformation of the zone in directions
perpendicular to the plane of the sheet, one of said stiffening
membe~s, of one zone adapted to form the overlap portion, being
formed with a series of transversely spaced holes through it, and
the other sti~fening member, of the zone adapted to form the
underlap portion, having connected to it a series of stud members
securable through said holes, respectively, each stud member
comprising arm portions which are malleable and can be spread
apart and flattened onto the upper surface of the overlap portion
to couple said one stiffening member and its overlap portion
relative to the other stiffening member and its underlap portion,
the coupled stiffening members resisting deformation forces
tendin~ to separate the overlapped zones longitudinally while
permittin~ the zones to be deformed together inwardly toward a
pro~ile of the article underlying the zones when the sheet is
wrapped around the article and is heat shrunk.
The superimposed zones of the sheet can be engaged with one
another relatively easily in a corlfined space, e.g. in a pit dug
out to expose an underground pipe or other conduit. The spread-
able and flattenable arm portions serve to retain the super~
imposed portions securely together during and subsequent to the
shrinking-down operation, and the flattened arm portions avoid or
reduce risk of engagement or snagging of the shrunk-down sleeve
on ad~acent conduits and reduce risk of cutting into or other
interference with the protective coverings o~ adjacent conduits.
In one highly preferred form, the arm portions o~ the stud member
form, adjacent the upper end, a laterally resiliently compress-
ible head portion which is of increased lateral dimension and
which snap fits through holes ~ormed through the sheet adjacent
the holes in the stiffening member of the overlap portion. In
many cases, the covering is relatively stiff and tends to spring
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~2~ 7
upwardly in the course of applying the overlap portion over the
underlap. The snap fitting arrangement greatly facilitates in
positioning the portions and locating them in the desired super-
imposed relationship until they have been more securely coupled
together by flattening the arm portions.
The stiffening members can readily be made of metal, a heat
resistant polymer, a polymer composite, e.g. fibre reinforced
plastic, or some other material that will withstand the heat to
which they are subjected during the heat-shrinking operation, so
that the strength and integrity of the covering are not impaired
by the heatinq.
The covering is well adapted to be manufactured employing sheet
material which is provided with its heat shrink property by an
operation in which a continuous length of ~he sheet material is
subjected to stretching in its longitudinal direction. In order
to provide coverings of increased width, the sheet may, if
desired, be a length severed from an extruded or other continuous
sheet material stretched in its transverse direction thus impart-
ing a heat shrink property in a direction extending transversely
of the original continuous sheet material.
Further advantages of the arrangement of the present invention
will become apparent from the following detailed description,
given by way of example only, with reference to the accom~anying
drawings, in which:
Figure 1 shows a perspective view of one form of covering in
accordance with the invention;
Figure 2 shows an end view o the covering of Figure 1;
Figure 2A is a fragmentary perspective view showiny a modified
form of stud;
Figures 3 and 4 show successive stages in the sequence of
applying the covering to an article to be wrapped;
Figure 5 which appears on the same sheet as Figures 1 and 2 shows
a side view, partly in section, of the ~overing applied to a pipe
joint;
Figure 6 shows a perspective view of a presently preferred form
of covering in accordance with the invention;
Figure 7 is a fragmentary perspective view of a preferred form of
stud and its connection to a stiffening member;
Figure 8 shows a longitudinal section through the covering of
Figure 6;
Figures 9 and 10 show successive stages in the sequence of
applying the covering to an article to be wrapped;
Figure 11 which appears on the same sheet as Figures 6 to 8 shows
a side view partly in section of the covering of Figure 6 applied
to a pipe joint; and
Figure 12 shows a longitudinal section through a further
preferred form of covering in accordance with the invention,
shown partially exploded.
Referring to the drawings, wherein like reference numerals indi-
cate like parts, these show a heat recoverable sheet 1. In a
typical example, the sheet 1 is a flexible crosslinked polymeric
material which has been subjected to an expansion procedure along
one axis in such manner that it retains a memory of its original
shape~ On heating to a certain ~emperature or ~emperature range,
the sheet shrinks down to its original configuration. In the
present case, the sheet has been expanded in such manner that~ on
being heated, it shrinks down along its longitudinal direction,
indicated by the double-ended arrows in Figures 1 and 6.
Examples of polymeric or other materials that may be employed in
the fabrication of heat recoverable sheets, the procedures
employed in the fabri~ation of the sheet, and the procedures
~2~27
employed in imparting to the sheet a heat-recoverable property,
are all well known to those skilled in the art, and need not be
discussed in detail herein. It may, however, be noted that the
sheet 1 as shown may be a piece severed from a continuous length
of heat-recoverable sheet. As will be appreciated by those
skilled in the art, the sheet 1 illustrated may be very readily
formed by extruding a continuous sheet to the re~uired width, and
subjecting it to a stretching operation along its longitudinal
axis. Such stretching o~eration may be employed using high
speed, highly efficient machineryO This machinery may, for
example, comprise rolls around which the continuous sheet is led,
some of these rolls being run at differential speeds in order to
stretch the sheet longitudinally between them. If desired, how-
ever, an extruded sheet may, however, be subjected to a stretch-
ing operation in which the sheet is stretched transversely, e.g.
by employing tentering apparatus.
Further with reference to Figures 1 and 6, transversely extending
zones at opposite ends of the sheet 1 are stiffened with trans-
versely extending stiffening members 2 and 3 which are connected
to these transversely extending parallel zones so as to afford
desired longitudinal rigidity characteristics to these zones. In
the examples illustrated, the stiffening members 2 and 3 are in
strip form and, as best seen in the end view in Figures 2 and 8,
have an elongated, rectangular cross-section, with the elongated
axis of the cross-section disposed parallel to the plane cf the
adjacent end zone o~ the sheet 1. The strips 2 and 3 are o~ a
bendable~ heat-resistant material, whose property of stiffness
sufficient to resist separation of the juxtaposed zones is
retained at the temperatures attained during heat shrinking of
the sheet. As will be appreciated, owing to the geometry of the
cross-sections o~ the strips, they can more readily be bent about
bending lines extending transversely of the strips, but they
function somewhat like a cantilever support and resist
deformatioo in directions parallel to their planes.
In the examples shown in Figures 1, 2, 2a, and 6 to ~, the
stiffening strips 2 and 3 are connected to the end zones by being
encapsulated within respective pockets forrned by folding over an
end portion 4 or 5 of the sheet and connecting it to the
underside of the sheet 1, e.g. by fusing or welding or adhesively
bonding, at 7 and 8. The end portion 4 or 5 may be first wrapped
somewhat loosely around the strip 2 or 3 and, after the
connection 7 or B has been effected, the pocket thus formed is
shrunk down by heating the portions 4 and S and the adjacent
upper portions of the sheet 1 in order to shrink this down thus
tightly encapsulating the strips 2 and 3 as shown in Figure 2.
Each stiffening strip 2 and 3 is formed with a series of through
holes 9 spaced apart at points along its length. In fabricating
the covering of Figures 1 to 5, after the strips 2 and 3 have
been tightly encapsulated within the pockets formed by the folded
over portions 4 and 5, holes 10 may be formed through the adja-
cent portions of the sheet 1 and through the folded over portions
4 and 5 in registry with the holes 9 in the strips 2 and 3.
Fastener studs are inserted through the holes 9 through the strip
3. In the example shown in Figures 1 to 5, each stud 11 com-
prises a pair of blade-like arm portions connected together on a
common foot portion 12. The foot portion 12 is of somewhat wider
diameter so that it will not pass through the holes 9 in the
strip 3 to which the studs 11 are applied. These studs 11 may be
similar to conventional paper fastenersO
Adjacent one end, the sheet 1 is provided with an underflap 13
connected to the side of the sheet 1 which will be the underside
in i~s wrap-around application. In the preferred form, the
underflap 13 is of the same material as the main sheet 1~ but is
dimensionally heat-stable, i~e. it has not been subjected to a
stretching operation in the same manner as the main sheet 1, and,
when heated, will not alter its dimensions.
Preferably, the underflap 13 is fused to the material of the main
sheet along its rear edge at 14 as seen in Figures 2 and 8.
-- 6 --
~2~
The underside of the sheet 1, i.e. ~he side which forms the
innermost surface when the sheet is wrapped around an article and
preferably also of the underflap 13, is provided with a func-
tional coating 15, the nature of which may vary according to the
application to which the heat shrinkable covering is to be put.
The coating may be, for example, a sealant, an adhesive material,
a mastic, a grease, or a two-component curable composition.
These functional coating materials are all well known to those
skilled in the art, and need not be discussed in detail herein.
It may be noted, however, that many of these materials may need
to be applied to the sheet 1 in a hot, fluid condition. Where,
as in the preferred form, the sheet 1 is fabricated employing a
continuous, longitudinal stretching operation, the application of
these hot coating compositions is much facilitated, as it is
relatively easy to maintain tension on the stretched sheet
material while applying the hot coating composition to it, thus
avoiding or reducing any tendency for the sheet to commence to
shrink down as it is heated by contact with the hot csating com~
position. Such premature shrinkage would, of course, be undesir-
able, as it would detract from the desired heat shrinkable pro-
perties of the sheet. Areas of the sheet 1 which are to be left
free from the functional coatiny may be masked with a suitable
paper during the application of the coatin~. The masking is done
at the appropriate spacings, and the bare areas, free from the
functional coating, left after removal of the paper masking~ may,
for example, be used for encapsulating the strips 2 and 3.
In one preferred form the faces of the sheet 1 at one or both
ends adjacent the stifening members ~ and 3 are provided with a
hold-down adhesive to at least temporarily bond the faces
together. In the example illustrated in Figures 1 to 5, a strip
of an adhesive which can form a bond when the ends are pressed
together, e.g. a pressure-sensitive adhesive, is provided on both
faces. Such strip of adhesive is indicated at 16 on the face
adjacent the studs 11 in Figures 2 and 3, and the corresponding
strip on the underside of the sheet is indicated at 17 in Figure
2. Figure 9 shows a pressure-sensitive adhesive layer 16a
forming a hold-down layer adjacent the uppPr face of the underlap
120~a.~27
portion of the covering. In another preferred form (not shown),
the functional coating 15 extends over the lower face of the end
portion 4, to form a seal when stiffening member 2 is placed over
stiffening member 3.
In use of the covering member of Figures 1 to 5, as indicated in
Figures 3 and 4, the sheet 1 is wrapped around an article, e.g. a
pipe 18 to be covered, and the studs 11 are passed through the
respective holes 9 and 10 in the opposite edge of the sheet 1 and
in the stiffening member 2~ The blade-like arm portions of the
studs 11 are then spread apart, and flattened onto the exterior
of the overlap portion, as indicated in Figure 4. Finger
pressure is applied to the overlapped ends of the sheet in order
to force the contacting faces of the superimposed portions into
tight engagement. The adhesive coatings 16 and 17 assist in
retaining these contacting faces in tight engagement while the
blades of the studs 11 are being spread apart. Frequently, the
covering illustrated will be applied to the wrapping of pipes or
other articles having relatively large transitions and pronoun-
cedly varying profiles. In such case, it will usually be desir-
able to press firmly with the fingers onto the regions of thestrip members 2 and 3, in order to bend these inwardly to conform
to the profile of the article to be wrapped in the region
directly underlying the strips 2 and 3. The thus formed wrap-
around sleeve is then shrunk down by heating it, e.g by playing
a blowtorch over its external surface, or applying some other
source of heat, to raise the sheet material to a temperature
sufficient to result in its longitudinal retraction or shrinking,
thereby closing the sleeve tightly down over the article to be
covered. Figures 5 and 11 r for example~ illustrate the shrinking
of wrap-around sleeves 1 indicated in broken lines down to their
shrunk condition indicated in solid linest wherein the sleeve is
applied over a bell and spigot joint formed between a pipe 19 and
a pipe 18 having a bell portion 20.
In a typical application, the covering will be employed to form a
seal around the article, e.g. the bell and spigot joint illus-
trated, and, in such case, the functional coating may comprise a
- 8 -
~2~
sealant or mastic which may be less flowable at ambient
temperature and which may be rendered more readily flowable on
heat application. The stretched sheet 1 may have a relatively
high expansion ratio, which may, for example, range from about
1:1.15 to 1:15, more typically about 1:2 to 1:5~ and, for many
applications, desirably in the range about 1:~ to about 1:3. As
a result of the heat-shrinkage, high hoop stresses will be
generated within the sleeve, thus forcing the sheet material 1
into tight embracement around the article, and forcing any
functional coating, such as a sealant, mastic or the like to flow
into and fill up any surface irregularities or voids in the
exterior of the article, thus forming a tight covering and seal
around the article.
It will be noted that with the above described arrangement, the
upper surface of the flap 13 forms a tight seal with the under-
side of the superimposed portion of the sheet 1. The flap 13
also serves to cushion the studs 11 and form a barrier between
these and the article to be wrapped, thus reducing any risk of
the inwardly-directed resultant of the hoop stresses tending to
urge portions of the studs, e.g. the enlarged foot portion 12,
inwardly to penetrate any underlying functional coating. Where,
as will be usual, the studs 11 are of metal or some other
relatively good thermal or electrical conductor, the underflap 13
insulates the studs 11 from any underlying functional coating,
e.g. the coating 15, and reduces any risk of undesirable contact
with the surface of the article being covered, sealed; or
protected.
With the arrangement shown, the stiffening members 2 and 3 are
provided with coupling means such as the studs 11 and holes 9 for
coupling the stiffening members 2 and 3 together at a number of
discrete, transversely spaced apart coupling points. This
provides means whereby the stifenng members can be conveniently
coupled together and located relative to one another in a manner
which will withstand the forces tending to separate the
stiffening members 2 and 3 under the action of the hoop stresses
generated in the sheet 1 during the heat shrinking operation.
- ~æ~
A form of resilient metal stud 11a as illustrated in Figure 2 may
be employed in place of the blade-like stud members 11. At their
widest portion, the two arm portions of the studs 11a are spaced
apart by a distance greater than the diameters of the holes 10
through the sheet 1 adjacent the strip member 2 at the opposite
end, so that the studs 11a snap-fit through the holes 10 when the
strips 2 and 3 are superimposed and urged toward one another.
Preferably, the diameters of the holes 10 in the sheet 1 adjacent
the strip 2 are slightly smaller than the holes 9 through the
latter. The arm portions of the studs 11a at their widest
portion may be slightly smaller than the width of the holes 9,
although it is also possible to have the holes 9 of smaller
diameter than the widest portion of the studs 11a so that these
snap fit through the holes 9. After the strips have been located
relative to one another in superimposed relationship, the resil-
ient metal studs 1la may be permanently deformed or flattened
downwardly, e.g. by a hammer blow, to conform them to the
exterior surface of the sheet 1~ so that no part protrudes above
the surface of the sheet. The lower end of each stud 11a may be
located within or below the underside of the strip member 3 e.g.
by an enlarged foot portion not visible in Figure 2a similar to
the foot portion 12 on the stud members 11 shown in Figure 2.
Various other types of spreadable and flattenable fasteners can
be used to connect the members 2 and 3, e.g. other ~ypes of snap
asteners such as dome snap fasteners, similar to the snap
fasteners used on clothing articles. The fastening should be
sufficiently rigid to resist the deformation forces tending to
separate members 2 and 3 and should be heat resistant.
In the presently preferred form, a stud 11b formed of resilient
metal is employed as illustrated in Figures 6 to 12. This has
arm portions 21 forming adjacent the upper end of the stud an
approximately diamond shape enlarged head which is laterally
resiliently compressible in the direction tending to close the
sides of the diamond, a lower body portion of reduced width, and
laterally extending foot portions 22 of increased width. The
stud is a one-piece structure, with the arm portions 21 being
integrally joined at the apex of the diamond.
The studs 11b are assembled to the stiffening member 3 by passing
their heads through the holes 9. The foot portions 22 engage the
adjacent under surface of the stiffening member 3. In the
example shown in Figures 6 to 8, the studs 11b, assembled to the
stiffening member 3, are passed through the holes 10 pre-cut in
the sheet 1 before the portion 5 is folded over and connected to
the underside of the sheet 1.
As best seen in Figure 7, each arm portion 21 of the stud 11b is
of strip material of an elongated generally rectangular cross-
section. Desirably, each arm portion 21 is disposed so that thelonger dimension of said cross-section extends parallel to the
longitudinal direction of the sheet 1, i.e. parallel to the axis
along which the sheet shrinks in use.
In the example shown in Figure 12, the end of the sheet 1
adjacent the strip 3 is not folded over. The flap 13 is applied
over the strip 3 having the studs 1lb assembled to it, with ~he
studs 11b passed through the holes 10 in the sheet 1. The strip
3 is located and secured relative to the flap 13 by a double-
sided adhesive tape 31. The flap 13 is connected to the sheet 1
along the zones 32 and 33 by welding or adhesively bonding, thus
encapsulating the strip 3. Further, the strip 2 is located and
secured relative to the sheet 1 and the folded over portion 4 by
two double sided adhesive tapes 34 and 35 before the portion 4 is
connected to the sheet along the zone 7.
In use, as illustrated in Figures 9 and 10 the enlarged heads of
~he studs 1lb snap fit through the holes 10 in the sheet 1
adjacent the stiffening member 2 of the overlap portion and pass
through the holes 9 formed through the strip 2. As before, the
holes 10 in the sheet may be of slightly smaller diameter than
the holes 9 in the strip 2. Once the stud 11b is snap fitted
through the hole 10, the overlap portion is retained quite firmly
adjacent the underlap portion in the position shown in Figure 10,
thus avoiding difficulties in positioning the overlapped portions
relative to one another owing to the tendency of the usually
. ,. ~,
~20~
relatively stiff material of the sheet 1 to cause the overlap
portion to spring upwardly and outwardly away from the underlap
portion.
Before heat shrinking the covering member, the studs 11b are
subjected to pressure sufficient to permanently deform them to a
spread and flattened condition, eOg. with a blow from a hammer 23
as shown in Figure 10. Alternatively, the studs 11b may be
flattened using a special tool, e.g. a tool similar to a pair of
pliers having a slot extending longitudinally inwardly from the
1~ tip of one of jaws of the pliers, to receive the relatively
narrow body portion of the stud, while the other jaw, in the open
position of the jaws, extends above the diamond shape head of the
stud 1lb and is manipulated to press the head and the upper part
of the body portion into the spread and flattened conditionc
As will be noted from Figures 8 and 12, in the preferred form,
the stiffening member 3 together with the foot portions 22 of the
studs 1lb is enwrapped in the pocket formed by the folded over
portion 5 of the sheet 1 or by the flap 13, and the lower portion
of the stud 1lb does not extend through the portion 5 or flap
13. Desirably also, as best seen in Figure 6, the ends of the
strips 2 and 3 are spaced inwardly from the longitudinal edges 24
and 25 of the sheet 1, and the edges of the folded over portions
4 and 5, or, in the example of Figure 12, the end edges of the
flap 13, are connected to the underside of the sheet 1, e.g. by
fusing or welding or adhesive bonding so that the strips 2 and 3
are encapsulated and are not exposed at their endss where, in the
case in which they are of metal, they would be liable to come
into contact with other metal elements or with the surface of a
metal pipe or other conduit around which covering is wrapped and
lead to the possibility of a differential metal cell being set
up, with resultant corrosion.
A covering of material which is dimensionally stable on heating
may be provided on the upper face of sheet 1 adjacent the end
which forms the overlap portion. As shown in Figures 6 to 12,
this covering may be in the form of a strip 26 and has the holes
fl - 12 -
,^,~, ,
~12~3$f..~
10 formed through it corresponding in position to the holes 9 in
the stiffening member 2. Usually, the strip 26 will be of the
same material, e.g. a crosslinked polymeric material, as the
sheet 1, but has not been subjected to a stretching operation.
The strip 26 is connected to the upper side of the sheet 1 at
least around the periphery of the holes, and more usually is
connected over the whole area of the strip by welding or fusing,
or by adhesive bonding, and serves to preserve the integrity of
holes 10 50 that on heating these do not tend to elongate or pull
away longitudinally from the underlying holes 9 in the stiffener
` member 2, which might lead to portions of the stiffener member 2
adjacent the holes 9 being exposed in the shrunk-down covering.
In some cases, the functional coating 15 does not cover the whole
width of the sheet 1 but as best seen in Figure 6, has its
longitudinal edges 27 and 28 spaced inwardly from the edges 24
and 25 of the sheet, leaving exposed longitudinal margins 29 and
30 of the sheet 1. This reduces any tendency for the functional
coating 15 to spread laterally or ooze out beyond the ends of the
covering when the sheet 1 is shrunk down onto an article, e.g.
the bell and spigot pipe joint illustrated in Figure 11, and the
functional coating tends confined between the margins 29 and 30
which are drawn into tight sealing contact with the articled
e.g. the surfaces of the pipes 18 and 19l particularly in the
case in which the functional coating is melted or made more
readily flowable during the heating of the sheet in the
shrinking-down operation.
The function of the stiffening members 2 and 3 is to support the
edges of the sheet intermediate the coupling points, e.gO the
studs 11, 11a or 11b and the holes 10, and to provide relatively
more rigid resistance to longitudinal deformation of the edges of
~he sheet such as would tend to result in the superimposed edges
separating from one another under the hoop stresses generated in
the sheet when it is shrunk down. At the same time, the stiffen-
ing members 2 and 3 are relatively more flexible with respect to
being bent downwardly toward the underlying profile of the arti-
cle to be wrapped, e.g. the bell and spigot joint illustrated in
- 13 -
Figures 5 and 11. In the example illustrated, this is achieved
with strip members 2 and 3 that are of an elongated, rectangular
cross-section, as seen in Figures 2 and 8, so that they are rela-
tively resistant to bending or other deformation in directions
parallel to the plane of the sheet 1. Owing to the relatively
thinner cross-sec-tion in the direction perpendicular to the sheet
1, the strip members are, however, relatively more readily bend-
able to permit them to deEorm downwardly perpendicular to the
plane of the sheet 1. The stiffening members 2 and 3 may be, for
example, metal strips which are relatively more easily plastical-
ly deformable by bending them out of the plane of the sheet 1.
The use of stainless steel or other relatively inert metal as the
material of the strip 2 and 3 may be preferred~ particularly
where in service the wrapped article will be exposed to a moist
or other corrosion-inducing environment. Merely by way of
example it may be mentioned that the strips may be of stainless
steel about 4 to about 20 ml in thic~ness and about 1/2 to about
1 inch in width. Plastic strips may also be employable, e.g.
fibre reinforced plastic strips.
Instead of employing a stiffening member which is a one-piece
integral strip, composite stiffening members may be employed.
For example, the strip may be composed of a series of hinge
elements each articulated to its neighbour along a pivot axis
extending parallel to the longitudinal stretching axis of the
sheet indicated by the double-ended arrow in Figures 1 and 6.
Such articulated strip may be formed so as to be highly flexible
with respect to bending out of the plane of the shee~ 1~ The
resultant forces of the circumferential hoop stress generated on
heat shrinking may themselves be sufficient to flex the strips
and conform them closely to the profile of the article to be
wrapped, without requiring any separate step of forcefully
bending the stiffening members down into conformity with the
profile of the article before commencing the heating operation.
Other variants may be employed. The stiffening members 2 and 3
may be connected on the end zones of the sheet 1 by bonding them
firmly thereto, e.g. by applying the stiffening member to one
~ 14 -
æ~
face of the sheet 1~ applying a discrete strip of the flexible
sheet material over the stiffening member, and bonding or fusing
this to the main sheet at its marginal edges on either side of
the stiffening member. Further, the sheet material may be
extruded with the meta~ strips or other stiffening members 2 and
3 embedded within the opposite edge portions of the extrusion.
This arrangement requires the extruded sheet to be subsequently
stretched transversely with respect to its original direction of
extrusion in order to impart to it the desired heat-shrink
1n property, and would require that the stud elements 11, 11a or 1lb
be inserted from the underside of the sheet 1 into holes formed
through the stiffening member 3 and the adjacent portions of the
sheet 1, along the lines of the arrangement shown in Figure 2.
In order to provide a smoother surface on the sleeve and protect
the coupling members such as the studs 11, 11a or 1lb, small
adhesive-coated patches of the sheet material may be applied over
the ends of the coupling members, e.g. over the flattened down
ends of the studs 11, 1 la or 1lb before or after the heating
operation~
- 15 -
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, . ~,
