Note: Descriptions are shown in the official language in which they were submitted.
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The present invention relates to a method and to
apparatus for covering the core of an electric cable with a
foldable metal sheath, plated or unplated, and more particular-
ly, the invention relates to the manufacture of a cable in
which a metallic strip, plated inside and outside, or only on
the outside, with a thermoplastic material, is longitudinally
folded around the cable core as a tubular sheath with over-
lapped edges.
In the present description, the term "core" means
the part of the cable which serves for the transmission of
power or signals and, for example, may be a bundle of insulated
stranded conductors, or in general, pairs or quads or trefoils
forming telecommunication cables. The term "sheath" means the
outer covering of the core, for example a tape, a strip or in
the case of a telephone cable, a screen constituted by aluminum
plated with thermoplastic material on the opposite surfaces, or
only on the outer surface, and longitudinally folded into a
tubular shape around the core.
A possible solution for covering the cable core with
a metal sheath consists in passing the core and a metallic strip
through a shaping-die, i.e. a suitable device whose inner walls,
or equivalent and rigid guiding means, are shaped so as to give
to the flat strip a tubular configuration with overlapped edges
around the core. This solution has some drawbacks arising from
the formation of the cable core and of the shaping-die.
As a matter of fact, the core of an electric cable,
in particular for long lengths, assumes transverse, cross-
sectional sizes which can differ more or less from the desired
nominal value and this is for various reasons, for example, for
lack of precision of the relative apparatus used during the
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manufacture of the core, or because of variations in the stranding pitch
in the case of a core formed by a bundle of several stranded conductors.
These cross-sectional variations of the core cause adverse effects
during the passage of the core and sheath through the rigid shaping-dieJ
which is sized for a pre-determined nominal value of the cable diameter.
In the case in which the cross-section of the core exceeds the nominal value,
the metallic strip, constrained between the inner walls of the shaping-die
and the core, must be subjected to high traction forces with the risk of
possible stretching exceeding a tolerable amount. In the case in which
the cross-section of the core is less than the nominal one, the metallic
strip, shaped in accordance with a tubular configuration by the shaping-die
walls, does not tightly contact the core.
Consequently, these shaping-dies are not likely to guarantee a
covering of the core with a metal sheath which is at the same time, complete
and protective for the whole cable length and closely adhering around the
core.
As it can be seen, the known solution is not satisfactory, and
therefore, the present invention has, as one object, a process and the neces-
sary apparatus for continuously covering the core of an electric cable with
a tubular-shaped strip which is mainly constituted by a metallic material
placed longitudinally around the core with overlapped edges and which
closely adheres to the core and is devoid of the drawbacks set forth herein-
before.
According to one aspect of the present invention, there is provided
in a method for covering a relatively long and narrow core of an electric
cable with a wrinkle-free sheath of foldable metal in strip form, said
sheath tightly engaging the circumferential surface of said core throughout
its length and having edge portions of the strip in circumferentially
overlapping and interengaging relation and said strip being relatively long
and narrow and having a width greater than the circumference of said core,
in which method the core and the strip are advanced at the same rate from
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a first position at which the strip is partially folded around the core to
a second position at which the strip encircles and engages the core with
the edge portions in circumferentially overlapping and interengaging
relation and the strip is wrapped around the core by die means around said
strip and extending from said first position to said second position,
said die means having free longitudinal edges, being circumferentially
continuous between said longitudinal edges and being expandable by different
amounts along its length, the improvement comprising: engaging a centrally
disposed portion of the strip with said core at said first position while
leaving other portions of the strip, at opposite sides of the portion
thereof engaging the core, out of engagement with the core; partially folding
said strip around said core at said first position without overlapping the
edge portions of the strip; gradually and progressively wrapping said strip
around said core as the strip advances from said first position to said
second position to bring the edge portions into overlapping relation at
least by the time they reach said second position while maintaining the
portions at the edges of the strip in separated relation from said first
position to adjacent said second position and thereby forming a tube around
said core at least when the strip reaches said second position, said tube
completely encircling the core at the second position with said portions
at the edges of the strip overlapping and engaging each other, said wrap-
ping being carried out by: applying only elastic forces to said strip from
said first position to and including said second position by permitting
said die means to expand radially at said first position, at said second
position and at positions intermediate said first position and said second
position so that the die means cxpands corresponding to the size of the core
at said first position, said second position and at positions intermediate
said first and second positions; said forces being directed toward said
core and being applied to all portions of the strip at each circumferential
portion along the length thereof from said first position to and including
said second position so that~ in the circumferential direction, said other
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portions of the strip are simultaneously, progressively and substantially
equally curved toward the core intermediate said first position and said
second position and so that at least by the time said other portions reach
said second position said portions at the edges of the strip are overlapping
and interengaging; said elastic forces also having a magnitude such that
the strip is maintained in contact with the core where the strip engages
the core in spite of variations in the size of the circumference of the
core but permitting increases of the size of the circumference of the core
without causing lengthwise stretching of one part of the strip relative to
another part thereof sufficient to cause wrinkles in the strip; using a
stiff and resilient said die means which has a modulus of elasticity equi-
valent to that of metal, which is only partially around the strip and the
core at said first position and which encircles the strip and the core at
said second position to apply said elastic forces, said die means being
continuous from said first position to said second position and having a
normal inner cross-sectional dimension at the second position less than
the outer cross-sectional dimension of the strip on the core at the
second position so that the stiff and resilient means is expanded at the
second position by the strip and applying only elastic forces to said stiff
resilient die means at said second position; and flattening any wrinkles
which may form as the strip is wrapped around the core by pressing the
strip against the core by a portion of said die means.
In one aspect of the invention, the method is further characterized
by the extrusion of a plastic material around the sheath at a point spaced
from, and downstream of, the second position.
In particular, in the preferred embodiment, the method according to
the invention includes the covering of a core, constituted by a bundle of
insulated electric conductors stranded together as in a telephone cable,
with a metal sheath, said sheath being formed by an aluminum tape plated
inside and outside with a thermoplastic material, for example, polyethylene.
According to another aspect of the present invention there is pro-
~14~42~
vided apparatus for covering the core of an electric cable with a foldable,
thin metal sheath having overlapping edge portions, said apparatus compri-
sing: elastic tube forming means having an input end and an output end,
said tube forming means being a sheet having the shape of a partially formed
tube at the input end of the forming means and tapering to the shape of tube
with overlapping edge portions at the output end of the forming means and
said sheet being made of a material having a modulus of elasticity equi-
valent to that of metal and because of its elasticity, being expandable by
different amounts along its length between the input and output ends of the
forming means; advancing means for advancing a cable core and a sheath in
the form of a strip into the input end of said forming means and through
and out of said forming means with said strip intermediate the core and the
forming means for causing said strip to be folded around and into contact
with said core with overlapping and contacting edge portions at least by
the time the strip and the core leave the output end of said forming
means whereby all portions of the strip other than one overlapping portion
thereof are pressed against the core by the forming means and said forming
means is permitted to expand and contract with variations in the diameter
of the core; and said forming means being free to expand and contract from
the point where it engages the strip at its input end to the point at which
the forming means brings edge portions of strip into overlapping and con-
tacting relation.
Preferably, the sheet is formed by an elastically deformable metal-
lic material, for example, stainless steel.
The invention will now be described in detail with reference to the
accompanying drawings in which:
Figure 1 shows a transverse section of a preferred embodiment of a
completed cable;
Figure 2 is a diagrammatic plan of the apparatus for the manufacture
of the cable shown in Figure 1 with the extruder omitted;
Figure 3 shows, in a perspective view, the apparatus of Figure 2
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with the sheath forming around the core and with the extruder;
Figure 4 is an elevation view of the final gauging portion of the
apparatus shown in Figures 2 and 3;
Figure 5 is a cross-sectional view taken along the line 5-5
indicated in Figure 3;
Figure 6 is a cross-sectional view taken along the line 6-6
indicated in Figure 3.
The following description, at first explains one of the electric
cables to which the invention is particularly applicable (Figure 1) and
subsequently the related manufacturing apparatus (Figures 2-6).
The cable shown in Figure 1, when it is finished, is a telephone
cable mainly comprising a core 2 constituted by
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~14~4;~1
a bundle of insulated electric conductors 3 stranded together
in a known way, a sheath 4 formed by a metallic strip folded
longitudinally around the core and with overlapped edges 5 and
6, and an outer layer 7, which may be an insulating material,
extruded on the sheath 4. The metallic strip is an aluminum
tape plated with thermoplastic material on its surfaces to
permit, after the overlapping of edges 5 and 6, causing them to
adhere through a welding or heating operation. The sheath 4 has
the function of screening the core 2 from electric fields
outside the cable and also constitutes a further protective
element for the core 2.
It is to be understood that the components of the strip
forming the sheath 4 could be different from those described,
subject to the condition that taken singly, the components would
have the same behavior as the aluminum and as the thermoplastic
material, both with respect to the effects of the cited screening
or protective function and with respect to the adhesion of
edges 5 and 6. Obviously also, the cable 1 can comprise further
elements, known to those skilled in the art, and such further
elements have been omitted since they are not necessary for an
understanding of the invention.
The apparatus 8 (Figs~ 2 and 3) for manufacturing the
cable 1 of Fig. 1 comprises a shaping-die 9 for transforming
the flat aluminum tape into a tubular configuration with over-
lapped edges around the core 2, means 11 and 12 respectively for
guiding the tape towards the shaping-die 9 and for guiding and
centering the core 2, and an extruder 31 for covering the
sheath 4 with a protective layer.
The shaping-die 9 constitutes an important element of
the invention and, in the preferred embodiment, comprises
shaping parts made of an elastically deformable metallic
material, such as, for example, stainless steel.
11469LZ~
Upstream of the shaping-die 9, a die portion 13,
called a "pre-shaping-die portion", is arranged to receive and
to gradually shape the aluminum tape so that the edges 5 and 6
are divergent, or slightly convergent upward, when the sheath
material 4 enters into the first part 14 of the shaping-die.
Said shaping-die portion 9 comprises, starting from the inlet
part 14 and moving towards the outlet part 15, a first portion
having a first inner surface 16 with a curved bottom 17 and
lateral walls 18 and 19, with subsequent areas involved in the
passage of the core 2 and gradual folding of the tape, and
a second, further portion having a surface 20 substantially
obtained by the prolongation of the first portion. The first
and the second surfaces 16 and 20 are shaped, respectively, to
give a tubular shape to the sheath 4, and to cause the sheath 4
to closely adhere to the core 2 for its whole length.
The first surface 16, between the parts 14 and 21, is
constituted by a first length 22 between the sections 14 and 23
in which the lateral walls 18, 19 change from a divergent, or
slightly convergent configuration, to a definitely convergent
configuration at a second length 24, in which the walls 18 and
19 are circumferentially overlapped with opposite winding
senses so as to provide a funnel-shaped, tubular duct.
This geometric shape of the second length 24 of the
surface 16 of the shaping-die 9 is intentionally chosen and has
importance for the purposes of the invention. In fact, the
lateral walls 18 and 19, being overlapped but separated,
provide between them a space through which the upper edge 6 of
the tape 4, advancing along the shaping-die 9, passes while
simultaneously the lower edge 5 is guided, in the same length
24, below the wall 18 and above the core 2 tsee Fig. 6). In
other words, the overlapping of the lateral walls 18 and 19 of
114~
the shaping-die 9 permits the edges 5 and 6 of the already
tubular-shaped ~ape to be guided separately, and this action,
as will be clearer in the explanation of the working of the
apparatus, prepares and supports the evenness of the subsequent
direct overlapping of the edges 5 and 6 and consequently, also,
the definite sealing of the sheath 4.
The surface 20 is on an extension of the bottom and
of the wall 19 of the first surface and the second further
portion includes a second wall 19' with a lip overlapping and
overlying the wall 19 (see Fig. 4). In practice, this second
surface is equivalent to that which would be obtained by over-
lapping the lips of a metallic foil wound up according to a
tubular shape.
The surface 20 has a cross-section smaller than that
of the first surface 16 and is arranged to receive in its inside
the sheath 4 already formed according to a tubular shape around
the core 2 and to advance the lips 5 and 6 into contact.
Moreover, further elastic means 32 comprising a hinged
collar and a spring 25 is provided, as is clearly shown in
Fig. 4, in order to withstand the cross-sectional variations of
the channel bounded by the second surface 20 when the core 2 and
the sheath 4 pass therethrough. It will be apparent that this
shaping-die means 32 could be provided with a plurality of
springs arranged so as to withstand the sizing variations of
the core 2 rather than a single spring 25. The means 32 of the
shaping-die 9 constitutes the gauging device of the sheath 4
around the core 2.
Tape feeding means 11 is represented, for the sake of
simplicity, in Figs. 2 and 3 by a single transmission roller 26
and a core guiding means 12 consisting substantially of two
cylinders with vertical axes 27, 27' between which the core 2,
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unwinding towards the pre-shaping-die 13, is centered. Such
means 11 is located at the inlet of the pre-shaping-die portion
13.
Moreover, a pressure roller 28 is provided at the zone
of the pre-shaping-die portion 13 in order to press with its
periphery on the upper part of the core 2 during its rectilinear
advancing and to press the aluminum tape 4 on the curved bottom
of the pre-shaping-die portion 13 in such a way a longitudinal
stretching of the tape 4 central part is accomplished thereby
compensating for the stretching of the edges which happens in
the shaping-die 9.
An extruder 31 is further provided at the outlet of
the means 32 in order to cover the sheath 4 with a protective
layer. An extruder of the type suitable for electric cables
can be used for covering the sheath with polyethylene or other
thermoplastic material.
The method according to the invention is carried out
as described hereinafter utilizing the described apparatus.
In a first step, the aluminum tape 4 coming from the
transmission roller 26 (Fig. 2) is directed on the bottom of
the pre-shaping-die portion 13 of the shaping-die 9 and is
folded longitudinally around the cable core 2 which is
continuously mo~ed in the direction of its axis, starting from
the initial position between the centering cylinders of the
guiding means 12, then below and in contact with the pressure
roller 28 periphery and consequently through the shaping-die 9
and the extruder 31.
During the passage of the core 2 in the pre-shaping-
die portion 13, the aluminum tape is gradually shaped from the
original fl~t shape into a final shape in which the central part
30 of the tape is closely in contact with the lower part of thecore 2 and the edges 5 and 6 are both directed upwardly, as
1~4642~
clearly shown in Fig. 5.
Also, during this step, the pressure roller 28,
compressing the core 2 against the central part of the tape 4,
gives rise to a longitudinal stretching of said part compen-
sating, as already stated, for the stretching to which the
edges 5 and 6 are subjected in the subsequent shaping-die
stations. Therefore, the tape length remains substantially
equal throughout its width and easily avoids the occurrence of
wrinkles which is a desirable condition for an efficient
subsequent overlapping of the edges 5 and 6.
At the outlet of the pre~shaping-die portion 13,
the aluminum tape undergoes a subsequent forming around the
core 2, in the lengths 22 and 24 of the first surface 16 of the
shaping-die 9. During the passage along the first length 22,
the edges 5 and 6 of the tape, continuously advancing from the
left to the right side as viewed in Figs. 2 and 3, follow the
convergenc~ of the walls 18 and 19 getting nearer to each other
in the circumferential sense.
In the subsequent passage into the length 24, the
edges 5 and 6 still follow the convergency of the two walls 18
and 19 so as to overlap in the circumferential sense without
coming into contact the one with the other since they are
guided separately and at a distance (see Fig. 6). As a matter
of fact, as already stated, the upper edge 6 crosses the length
24 between the shaping-die walls 18 and 19 and the lower edge 5
crosses the same length between the wall 18 and the core 2.
Therefore, the edges 5 and 6, pressed separately on
opposite sides, respectively between the shaping-die walls and
between the shaping-die wall and core 2 (see Fig. 6), and
subjected contemporaneously to a traction action towards the
extruder 31, are stretched, obtaining in such a way a tubular
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shape devoid of wrinkles and any eventual irregularities
present in the tape surface.
Moreover, in the shaping-die length 24, owing to the
characteristic of the lateral walls 18 and 19 of elastically
deformable material, the sizing variations of each cross-section
of the core 2 are followed by the surface 16 of the shaping-die
and the consequent deformation of said surface gives rise to
elastic reactions whose effect is that of keeping the edges 5
and 6 of the tape tightened around the core 2.
Subsequent to the length 24, the core 2 and the sheath
4 pass through the channel of the second surface 20 of the
shaping-die. The passage of the tape 4 from the outlet part 21
of the length 24 to the means 32 takes place with the edges 5
and 6 directly in contact, since, while the shaping-die wall l9
continues up to the outlet 15 of the shaping-die 9, the wall 18 is
cut-away at the end of the length 24. Consequently, the lower
surface of the edge 6 no longer supported and guided by the wall
18 comes into contact with the lower edge 5, and both the edges
are compressed with high pressure by means of the action of the
spring 25 between the core 2 and the inner surface of the means
32. The pressure may be sufficient to seal the overlapping edges
together, or if necessary, heat may be applied to seal the over-
lapping edges together.
The edges 5 and 6 of the sheath 4, leaving the shaping-
die 9 are, in a further subsequent step, kept in contact by the
extrusion of polyethylene around the sheath 4.
The invention described with reference to the apparatus
shown in the figures can be applied, obtaining the same advantages,
to telephone cables of a different type, for example, to plug
cables in which the core is constituted by joining together the
various wires singly insulated and stranded together and gels
deriving from petroleum are inserted between screen and
~14~;~2~
conductors. In this case, the shaping-die 9 of the invention,
having elastically deformable walls, and owing to the already
explained principle, causes the adherence between the screen
and conductors to increase notably with respect to the known
rigid apparatus.
In particular, the described shaping-die 9 can be
applied to telephone cables having nominal size starting from
20 mm and also to cables having greater sizes obtaining the
same advantages.
In fact, it is possible to overlap more or less the
lateral walls 18 and l9 (see Figs. 2 and 3) of the shaping-die 9
and thus to realize a funnel shape corresponding to the cross-
section of the cable which is desired to cover with the tape.
The new shape of the walls is then fastened by the nut-screw
group 29 tFig. 4) and eventually, with the aid of a spring 25
with suitable elasticity characteristics.
Moreover, it is clear a~ the shaping-die 9 can be
constituted by a plurality of pieces instead of only one piece
without falling outside the scope of the invention. For example,
the means 32 could be detached from the upstream part of the
shaping-die 9, with the addition of further elastic means along
the walls of the shaping-die 9 itself. Also, the various parts
of the shaping-die 9 may be supported in an obvious manner.
Although preferred embodiments of the present
invention have been described and illustrated, it will oe
apparent to those skilled in the art that various modifications
may be made without departing from the principles of the
invention.
