Note: Descriptions are shown in the official language in which they were submitted.
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METHOD AND APPARATUS FOR FORMING
A SHIELDED ELECTRIC CABLE
Background of the Invention
The present invention relates to a method and apparatus for forming
shielded electric cables for transmission of signals through the cables, and
more particularly relates to an improved method and apparatus for rapidly,
economically, and uniformly manufacturing such cables.
It is common practice to provide a shielded cable for transmitting
signals. A shielded cable usually includes a core of one or more insulated
conductors enclosed within at least one conducting layer. The shielding of the
conducting layer resists signal leakage from the core and eliminates or
reduces
the interfering effects of extraneous electrical fields.
One type of shielded electric cable used consists of a center conductor
having a foam dielectric extending therearound to form a core. A first shield
is
provided by a tape wrapped around the core. The tape comprises an
elongated metallic ribbon. It is also possible to provide a second metallic
shield formed from copper or aluminum braid around the metallic tape. An
outer cover or jacket of non-metallic material is then extruded around the
second metallic shield. Shielded electric cables of the foregoing type are
usually provided for use with standard electric connectors, so the cables have
a standard diameter selected to accommodate the connectors. Braided
shields, because of the spaces between the wire braids, have the
disadvantage of providing less than 100% coverage and thus less than 100%
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shielding of the core. Additionally, the braided shields ~:re difficult to cut
and
attach to standard electrical connectors, thus increasing i stallation time
and
costs.
Other shielded electric cable designs have been prop~~sed, including
those disclosed in U.S. Patent Nos. 5,321,202, 5,414,213, and 5,521,331, to
overcome the deficiencies of such braided cables. In some of the shielded
electric cable designs disclosed in these patents, a core including an
insulated
conductor is provided, along with a first shielding member formed rrom an
elongated ribbon of insulating material and a pair of elongated metal foil
strips
arranged in a parallel relationship with the ribbon. The strips are bonded to
opposite sides of the ribbon. The first shielding member is applied
longitudinally to the core and wrapped circumferentially around the core in a
generally parallel relationship forming two concentric substantially closed
shielding layers. A layer of insulating material surrounds the first shielding
member, and a second shielding member surrounds the insulating layer, the
second shielding member being capable of being formed of non-braided
metallic material of various kinds. The shielded electric cable is provided
with
an outer jacket of nonconductive material over the second shielding member.
The above patents also describe various methods for making such
shielded, nonbraided electric cable, the methods varying depending in some
cases on the form of the component parts of the cable. As disclosed in U.S.
Patent Nos. 5,321,202, 5,414,213 and 5,521,331, it may be desirable to have
at least some bonding between layers of such shielded electric cable to
minimize or prevent migration of moisture between surfaces of the layers. To
provide bonding between such layers in a triaxial cable, the above three
patents disclose using a tape with an adhesive backing for the first shielding
member to bond the first shielding member to the core. The latter two of the
above three patents also disclose using either: a) a heat-activated adhesive
added to the insulating layer, activated upon the extrusion of the outer
jacket
over the second shielding member, or b) a coating of adhesive on mating
surfaces to bond the layer of insulating material to both shielding members.
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The latter two of the above three patents also disclose that the outer jacket
may be bonded to the second shielding member.
The shielded electric cable and the manufacturing methods disclosed in
the above patents work well for their intended purposes. However, once
capital investment has been made in facilities and equipment for manufacturing
shielded electric cable, a slow line speed at which the cable can be
manufactured (measured in feet of cable manufactured per second or minute)
can negatively impact the efficiency of manufacturing the shielded electric
cable.
For example, braided shielding layers cannot be applied to electric
cables at a rate faster than about 10 feet per minute. However, even if
upbraided shielding layers are used thereby allowing faster line speed,
various
imperfections can be introduced due to difficulty in assembling component
parts of cable at the greater line speed. Further, if a manufacturing line is
set
up to manufacture shielded electric cable at such a higher rate of speed, any
imperfection induced will cause a correspondingly larger production of
defective cable that must be discarded. Thus, there is a need for a rapid,
efficient, and uniform method of manufacturing shielded electric cable.
Summary of the Invention
In accordance with the invention, a method is provided for forming a
shielded electric cable from a core including a center conductor and a first
insulating layer surrounding the center conductor, the method comprising the
steps of applying a first electrically shielding tape lengthwise along and
circumferentially around the core, and activating a first heat-activated
adhesive
no later than immediately after the applying the first tape step to bond the
first
tape around the first insulating layer to form a first shielding member.
The first activating step may comprise heating at least one of the core,
the first tape, and the first heat-activated adhesive prior to, during, or
immediately after the applying the first tape step.
The method may include the step of applying the first heat-activated
adhesive to the core or first tape prior to or after the first activating
step, and
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may also include the step of providing a core having the first heat-activated
adhesive within the first insulating layer prior to the first activating step,
or of
providing the first tape including the first heat-activated adhesive prior to
the
first activating step.
The method may further comprise the steps of applying a second
insulating layer surrounding the first shielding member, and activating a
second
heat-activated adhesive to bond the second insulating layer to the first
shielding member. if so, the second activating step may comprise heating at
least one of the first shielding member, the second insulating layer and the
second heat-activated adhesive prior to the applying the second insulating
layer step.
The method may also further comprise the steps of applying a second
insulating layer surrounding the first shielding member, applying a second
electrically shielding tape lengthwise along and circumferentially around the
second insulating layer, and activating a third heat-activated adhesive no
later
than immediately after the applying the second tape step to bond the second
tape around the second insulating Payer to form a second shielding member.
The third activating step may comprise heating at least one of the
second tape, the second insulating layer, and the third heat-activated
adhesive
prior to, during, or after the applying the second tape step.
The method may further comprise the step of applying the third heat-
activated adhesive to the second tape or the second insulating layer prior to
or
after the third activating step, and may also include the step of providing
the
second tape including the third heat-activated adhesive prior to the third
activating step, or the step of providing the second insulating layer
including
the third heat-activated adhesive.
The first activating step preferably includes heating the exterior of the
core to about 65-125~C, and more preferably includes heating the exterior of
the core to about 80-1007C.
The third activating step preferably includes heating the second
insulating layer to about 65-135~C, and more preferably includes heating the
second insulating layer to about 80-100CC.
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Preferably, the applying the first tape step includes applying the first
and/or second tape at a speed of at least about 50 feet per minute, and more
preferably at a speed of at least about 200 feet per minute.
Preferably, the steps of applying the first and second tapes include
5 tensioning the tapes to about 10 pounds or less, and more preferably, 1
pound
or less.
In accordance with another aspect of the invention, an apparatus is
provided for forming a shielded electric cable from a core including a center
conductor and a first insulating layer surrounding the center conductor, the
apparatus comprising a first tape applying assembly for applying a first
electrically shielding tape lengthwise along and circumferentially around the
core, and a first heating assembly located no further downstream than
immediately downstream of the first tape applying assembly for activating a
first heat-activated adhesive to bond the first tape around the first
insulating
layer to form a first shielding member.
The first heating assembly may comprise a heating station located
upstream from the first tape applying assembly for heating at least one of the
core, the first tape, and the first heat-activated adhesive, a heated tape die
forming a part of the first tape applying assembly, or a heating station
located
immediately downstream of the first tape applying assembly.
The apparatus may further comprise an insulation assembly
downstream of the first tape assembly for applying a second insulating layer
to
the first shielding member, a second tape applying assembly downstream of
the insulation assembly for applying a second electrically shielding tape
lengthwise along and circumferentially around the second insulating layer, and
a second heating assembly located no further downstream than immediately
downstream of the second tape applying assembly for activating a second
heat-activated adhesive to bond the second tape to the second insulating layer
to form a second shielding member.
Preferably, the apparatus further comprises a cooling assembly located
between the insulation assembly and the second heating assembly.
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The second heating assembly preferably includes a heating station
located upstream from the second tape applying assembly for heating at least
one of the second insulating layer, the second tape, and the second heat-
activated adhesive, a heated tape die forming a part of the second tape
applying assembly, or a heating station located immediately downstream from
the second tape assembly.
Preferably, the first and/or second tape applying assemblies include a
tape folding tool and a tape die.
Accordingly, the invention has the advantages of providing a method
and related apparatus allowing a rapid, efficient, and uniform manufacture of
shielded electric cable of various designs. Additional advantages of the
invention will be set forth in part in the following description, or may be
obvious
from the description, or may be learned from practice of the invention.
Brief Description of the Drawings
Fig. 1 is a perspective view of one embodiment of a shielded electric
cable manufactured in accordance with the present invention, having a portion
thereof partially removed for illustration of the construction of the cable;
Fig. 2 is a longitudinal sectional view of the shielded electric cable taken
along line II-I I in Fig. 1;
Fig. 3 is a perspective view of another embodiment of a shielded electric
cable manufactured in accordance with the present invention, having a portion
thereof partially removed for illustration of the construction of the cable;
Fig. 4 is a longitudinal sectional view of the shielded electric cable taken
along lines IV-IV in Fig. 3;
Fig. 5 is a flow chart diagrammatically showing manufacturing steps and
pieces of apparatus according to the present invention useful to manufacture
either of the shielded electric cables shown in Figs. 1 through 4, or other
shielded electric cables;
Fig. 6A is a schematic representation of the cable core supply and tape
supply indicated in Fig. 5;
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Fig 6B is a schematic representation of the tape lubricant supply
indicated in Fig. 5;
Fig 6C is a schematic representation of one heating station indicated in
Fig. 5, the heating station being representative of the others indicated in
Fig. 5;
Fig 6D is a schematic representation of one tape applying station
indicated in Fig. 5, the tape applying station being representative of the
other
indicated in Fig. 5;
Fig 6E is a schematic representation of one extruding station indicated
in Fig. 5, the extruding station being representative of the others indicated
in
Fig ~; and
Fig 6F is a schematic representation of one cooling station indicated in
Fig. 5, ;he cooling station being representative of the others indicated in
Fig. 5.
Description of the Preferred Embodiments
Ftefer~~nce will now be made in detail to the presently preferred
embodiments of the invention, one or more examples of which are illustrated in
the drawings. Each example is provided by way of explanation of the
invention, and not meant as a limitation of the invention. For example,
features
illustrated or described as part of one embodiment can be used on another
embodiment to yield yet another embodiment. It is intended that the present
invention include such modifications and variations.
Figs. 1-4 show two examples of shielded electric cables that can be
manufactured according to the present inventive method and apparatus. It
should be understood, however, that other variations in design of cables
resulting from the inventive method and apparatus are possible within the
scope of the invention, depending on the specific properties of the desired
cable and the corresponding method steps and apparatus portions selected.
As broadly depicted, Figs. 1 and 2 show a shielded electrical cable 10
including a number of layers. Cable 10 is a coaxial cable, as will be
described
below. Figs. 3 and 4 show a triaxial s~oielded electrical cable 10a having a
number of elements in common with coaxial cable 10. Common elements
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between cables 10 and 10a are given common reference numerals for ready '
identification.
Cable 10 includes a center conductor 12 and an insulating layer 14
surrounding the center conductor. Together, center conductor 12 and
insulating layer 14 comprise a core 16 of cable 10. A first shielding member
18
surrounds core 16, and a jacket 20 surrounds first shielding member 18.
Center conductor 12 may be made of any suitable conductor material.
Typically, copper clad steel is used, but other metals or other materials
could
be used as center conductor 12 within the scope of the invention. Insulating
layer 14 preferably comprises a foam dielectric material such as a
thermoplastic foamable polymer. For example, polyolefins such as
polyethylene and polypropylene, and fluoropolymers, such as fluorinated
ethylene propylene polymer or perfluroro alkoxy copolymer, or various mixtures
thereof, may be used. First insulating layer 14 may be extruded onto center
conductor 12 to thereby create core 16, as is commonly known.
First shielding member 18 preferably comprises an electrically shielding
tape suitable for forming an electrical shield around core 16. As shown in Fin
2, first shielding member 18 comprises a single-layer tape made of a metallic
material and extending lengthwise along and circumferentially around core 16.
First shielding member 18 may comprise a tape made of an elongated
aluminum foil strip, or may be made of copper or other metallic material
suitable for providing shielding of core 16. Alternatively, first shielding
member
18 may comprise a multi-part tape. Such tapes often include at least three
layers: a central strip of insulating material and a pair of outer strips of
metallic
material. Such tape, when wrapped around core 16, provides two concentric,
substantially closed shielding members, each being formed by one of the
respective metallic strips. Use of such tape in such application is described
for
example in U.S. Patent No. 5,321,202, the description of which is incorporated
by reference herein. One commercially-available multilayer tape is APA tape,
available from Facile Technologies of Patterson, NJ
It should be understood that first shielding member 18 may have other
constructions within the scope of the invention. Applicants have merely
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discussed two examples of potential materials for use as first shielding
member
18 herein in connection with Figs. 1 and 2 to provide some background for the
inventive method and apparatus discussed below.
Similarly, the joint along the edges of shielding member 18 has been
depicted as an overlap joint. However, other types of joints are possible
within
the scope of the invention. For example, a butt joint, a Z-fold, or a shorting
fold
such as a single fold, double interlocking fold, etc. may also be employed
within the scope of the invention.
Jacket 20 is formed of a non-conductive material. Preferably, jacket 20
is made of an extruded polyethylene, polyvinyl chloride, or some other
suitable
non-conductive material. The material chosen for jacket 20 should be selected
so as to be suitable for the intended application of cable 10. For example,
depending on whether the cable is to be used indoors or outdoors, above
ground or underground, etc., the jacket material may be selected from various
suitable materials.
Cable 1 Oa, shown in Figs. 3 and 4 is substantially similar to cable 10
shown in Figs. 1 and 2, except that cable 10a is a triaxial cable. Thus, cable
10a includes center core 16, first shielding member 18, and jacket 20, all as
described above regarding cable 10. Additionally, cable 10a includes a second
insulating layer 22 and a second shielding member 24.
Second insulating layer 22 may be constructed of any of the materials or
mixtures thereof mentioned above regarding first insulating layer 14. Second
insulating layer 22 may be made of the same material as first insulating layer
14, or may be made of a different material for certain applications.
Similarly, second shielding member 24 may be made of any of the
materials discussed above as suitable for first shielding member 18, and
second shielding member 24 may be of the same or different construction as
first shielding member 18. it is also possible, within the broadest scope of
the
invention, for second shielding member to comprise a braided metallic shield,
as described above, or some structure other than a tape. Use of such a
braided metallic shield or other structure for the second shielding member
would provide certain benefits of the invention regarding the claimed method
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and apparatus. However, it is preferable that second shielding member 24
comprise some sort of tape more rapidly applicable to cable 10a than is a
metallic braid in order to enjoy the full scope of the invention.
Cable design options other than coaxial or triaxial cables are also
5 possible within the scope of the invention, such as those commonly called
messenger cable, siamese cable, etc.
Fig. 5 is a flow chart outlining the claimed methods for forming shielded
electric cable using the claimed apparatus according to the present invention.
Options are set forth on Fig. 5 for manufacturing a coaxial cable such as
cable
10 10 or a triaxial cable such as cable 10a. It should be understood that
further
modifications are possible to the methods outlined in Fig. 5 for making
variations of such cables within the scope of the invention.
As shown in Fig. 5, the method for forming a shielded electric cable from
a core begins with a core supply, identified as reference numeral 30. As
mentioned above, such core 16 is typically made by extruding an insulating
layer 14 over a center conductor 12. Core supply 30 is (schematically) also
shown in Fig. 6A.
As also indicated in Figs. 5 and 6A, a tape supply or tape feed 32 is
provided for supplying a first electrically shielding tape 18a to be used to
form
first shielding member 18. As schematically indicated in Fig. 6A, tape supply
32 may include a reel 34 from which a supply of tape 18a is paid out through
tensioning rollers 36. Tape 18a is preferably tensioned at 10 pounds or less,
and more preferably at 1 pound or less. Such tension levels reduce the
possibility of damage to tape 18a that could negatively impact the ability of
shielding member 18 to provide uniform shielding. Other guide and drive
rollers may be provided if desired, along with control and feedback systems
(not shown).
As shown in Figs. 5 and 6B, an optional lubricant application station 38
may be provided including rollers 40 for guiding the tape 18a used to form
first
shielding member 18 across a lubricant wick 42 or other lubricant applying
element. Lubricant is used to reduce friction on tape 18a as it passes to and
through the tape applying assembly, as will be described below, to thereby
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maintain uniformity along cable 10 and increase line speed. The lubricant may
be dehydrogenated mineral oil or other similar substances.
As stated, lubricant station 38 is optional. If desired, a lubricant may be
placed on one or both sides of tape 18a during its manufacture, thereby
eliminating the need for station 38. Also, no lubricant need be used, although
such would reduce the speed of manufacture and increase wear on component
parts and tape 18a itself, possibly also impairing shielding of shielding
member
18.
In accordance with the invention, a heating assembly is used in a first
activating step to activate a heat-activated adhesive to bond the first tape
around the first insulating layer to form the first shielding member. This
first
activating step occurs no later than immediately after the step of applying
the
first tape. The term "immediately after" is defined below.
One embodiment of the heating assembly is a heating station 44, which
is schematically indicated in Fig. 6C and may embody several forms and have
several locations. Preferably, heating station 44 comprises an elongated
enclosed housing 46 including an inlet 48 and outlet 50 through which an
element or portion of cable 10 such as core 16 passes. A number of heating
elements 52 are located within housing 46 and may take a number of forms.
For example, heating elements 52 may comprise electrical, ceramic, gas, or
any other type of heating element in accordance with the invention. Options
for
placing heat-activated adhesive in position to form a bond between core 16
and first shielding member 18 are discussed below.
Heating station 44 may be optionally located upstream of the tape
applying assembly, with either first tape 18a or core 16 passing through it.
Thus, either first tape 18a or core 16 would be heated and the first heat-
activated adhesive be activated, prior to the first tape being applied to the
core.
Alternately, two such heating stations could be provided, one each for heating
first tape 18a and core 16 prior to application of the tape to the core. Also,
heating station 44 may be located immediately downstream of the tape
applying assembly, thereby heating all of first tape 18a (first shielding
member
18), core 16, and the first adhesive simultaneously. "Immediately downstream"
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means downstream of the tape applying station and upstream of any other
cable manufacturing assemblies for adding to or modifying layers or other
portions of the cable being manufactured. Immediately downstream therefore
means prior to a downstream extruder, if used, so that a downstream heating
station 44 provides heat apart from that provided by a downstream extruder.
An immediately downstream heating station 44 beneficially can provide
controlled heating at desired temperatures, durations, etc., that a downstream
extruder likely cannot. Thus, any extruder downstream of the first tape
applying station does not comprise part of the first heating assembly for
activating the first heat-activated adhesive to bond first tape 18a around
first
insulating layer 14 to form first shielding member 18.
A second embodiment of the heating assembly is a heated portion of
the tape applying assembly. That heated portion will be described below in
conjunction with the description of one embodiment of tape applying assembly,
namely tape applying station 54. In this embodiment, the heat-activated
adhesive that bonds first shielding member 18 to core 16 is activated during
the application of first tape 18a to core 16. Thus, first tape 18a, core 16,
and
the adhesive are all heated to some extent simultaneously.
A third embodiment of the heating assembly is a heated supply of heat-
activated adhesive. Thus, adhesive supplying station 68, as described below,
could also be heated, thereby providing activated heat-activated adhesive to
either core 16 or first tape 18a prior to application of the tape to the core.
The heat-activated adhesive that bonds first shielding member 18 to
core 16 thus may be activated either prior to, during, or immediately after
first
tape 18a is applied to core 16 within the scope of the present invention.
As shown in Figs. 5 and 6D, the tape applying assembly is provided
downstream of core supply 30 and tape supply 32. At the tape applying
assembly, core 16 is joined with first tape 18a to form a coaxial (non-
jacketed)
cable portion. As indicated in Fig. 5, whether it is intended to create a
coaxial
cable such as cable 10, a triaxial cable such as cable 10a, or some other type
of cable based on either of these types, all methods and apparatus for
manufacturing cable according to the present invention begin with and include
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at least the core supply 30, the tape supply 32, a heating assembly of some
sort, and the tape applying assembly.
One preferred form of the tape applying assembly comprises tape
applying station 54, which preferably includes a tape folding tool 58 held by
holders 60, as indicated in Fig. 6D. Tape folding tool 58 is preferably a thin
piece of metal or some other material that at the upstream end 58a has a flat
configuration that is continuously bent along the downstream direction to a
circular configuration at the other end 58b. Tape folding tool 58 may have
various other shapes according to the invention, and may be modified or
augmented, for example, if a joint or fold other than the overlap joint shown
in
Figs. 1 and 3 is used. For example, a series of blocks (not shown) having
openings of progressively smaller size could be substituted for folding tool
58.
Holders 60 are shown schematically in Fig. 6D and may be adjustable in
various directions to accommodate differently sized tools 58, cores 16, first
tapes 18a, etc. As shown in Fig. 6D, if adhesive is applied to or supplied
with
first tape 18a, first tape 18a should be oriented so that such adhesive 18b is
on
the side of the tape facing insulating layer 14 prior to entry into tool 58.
Any
lubricant on first tape 18a should be on the opposite side facing the folding
tool
58.
Tape applying station 54 also preferably includes a tape die 62 including
an orifice 64 disposed through a removable portion 66, through which the core
16 and first tape 18a pass to squeeze the first tape tightly onto the core to
thereby seal them together via the heat-activated adhesive when activated.
Also, orifice 64 can be precisely machined to ensure that core 16 and first
shield member 18, which comprises first tape 18a, is precisely sized. If
desired, orifice 64 may narrow slightly in diameter in the downstream
direction
to provide a smooth flow through tape die 62. Tool 58 and portion 66 may be
replaceable with corresponding parts of different sizes for manufacture of
different sizes of cable.
As mentioned above, a portion of the tape applying assembly is
preferably heated to provide additional activation of the heat-activated
adhesive during the application of the first tape to the core. Accordingly,
tape
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die 62 of heating station 54, may be heated, for example, by an electrical
resistance heater (not shown). If so, heated tape die 62 would be considered
at least a part of the heating assembly. Alternately, heated tape die 62 alone
could comprise all of the heating assembly, avoiding the necessity of
employing any other heating station 44, either upstream or downstream of tape
applying station 54. However, for most applications, it is preferable for the
heating assembly to include both an upstream heating station 44 for heating
core 16 and heated tape die 62.
As indicated in Fig. 5, tape applying station 54 may further include a
temperature sensor 56 for monitoring the temperature of core 16 just prior to
the folding of first tape 18a to ensure that the heat-activated adhesive is
being
properly activated by the heat within core 16. Such temperature sensor 56 is
used where core 16 passes through an upstream heating station 44. Any
commonly available temperature-sensing device may be employed as
temperature sensor 56, such as an infrared sensor, etc.
Point 70 in Fig. 5 denotes the point at which the methods and apparatus
outlined for forming coaxial cable and triaxial cable depart. If coaxial cable
such as shielded electric cable 7 0 is desired, the joined core 16 and
shielding
member 18 go directly along path 72 to a jacket applying station such as an
extruder 76. If a triaxial cable such as shielded electric cable 10a is
desired,
the joined core 16 and shielding member 18 follow path 74 to additional
intermediate stations prior to jacket applying extruder 76. It should be kept
in
mind that paths 72 and 74 are used only for schematic reference in Fig. 5, and
are not intended to indicate that separate, optional feed paths are required
for
the practice of the inventive method and apparatus. As a practical matter, one
could set up triaxial cable path 74 as a production line in a manufacturing
facility and simply remove certain elements from the line to alter the end
product to manufacture coaxial cable or other types of cable. The present
invention thus provides ready adjustability in manufacturing and ready change
out of manufacturing capability so that one production line can be easily
altered
to manufacture a number of different cable products.
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As shown in Figs. 5 and 6E, extruder 76 is disposed downstream of tape
applying station 54 for applying an outer jacket 20 over the manufactured
cable. If following path 72, extruder 76 applies outer jacket 20 over
shielding
member 18 to form coaxial cable 10, shown in Figs. 1 and 2. Extruder 76 may
5 be any commonly available extruder capable of extruding jacket 20 over
shielding member 18. A heat-activated adhesive may also be used to bond
shielding member 18 to jacket 20. Such adhesive may either be placed on
shielding member 18 or extruded with jacket 20.
As indicated in Figs. 5 and 6F, a cooling assembly such as a cooling
10 station 78 is disposed downstream of extruder 76 for cooling and setting
the
extrudate from extruder 76 into jacket 20. As shown, cooling station 78
includes an elongated tray 80 having an inlet 82 and an outlet 84. Tray 80 is
filled with water 86 that may be circulated into and out of the tray to remove
heat transferred from the cable passing though the tray. If desired, a
cleaning
15 station (not shown) may be disposed at ar near outlet 84 to remove any
impurities or other extraneous materials from the finished cable. The cleaning
station may clean the cable, for example, by wiping or passing it through an
air
current, or both, or by some other means. Alternately, the cooling assembly
could employ an airflow such as chilled or room temperature air, or a liquid
spray to cool the extrudate. The distance between the cooling assembly and
the extruder should be selected so that any heat-activated adhesive employed
may be sufficiently activated to bond shielding member 18 to jacket 10 before
cooling occurs.
A take up assembly of some sort (not shown) may be provided to wind
the manufactured cable onto replaceable spools after leaving the cooling
assembly.
There are several options for selecting the type and placement of the
heat-activated adhesive according to the present invention, all of which
impact
the point at which the heat-activated adhesive is activated. For example, the
heat-activated adhesive may be formed on one or both sides of first tape 18a.
Also, the heat-activated adhesive may be part of the extrudate used to form
insulating layer 14 and/or jacket 20. The heat-activated adhesive could also
be
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16
applied to any of first tape 18a, core 16, or shielding member 18 during
manufacture, and could be so applied, for example, by wicking, wiping,
electrostatic deposition, using a hot-melt adhesive such as by liquid adhesive
bath, or any other method within the scope of the invention. Thus, optional
adhesive applying station 68 is indicated in Fig. 5 as providing adhesive to
either of core 16 or tape 18a, either in an activated condition or an
unactivated
condition for later activation.
The adhesive selected should be a heat-activated adhesive that is
activated at a temperature substantially lower than the melting temperature of
insulating layer 14. Also, the adhesive selected should be chosen according to
its ability to bind the relevant portions of the cable, and this factor may be
determinative of the method of application.
If the heating assembly includes an upstream heating station 44 for
heating core 16, the heating station should not heat core 16 to the extent
that
insulating layer 14 begins to melt, degrade, or deform. Similarly, if the
heating
assembly includes a heating station 44 for heating first tape 18a, the heating
station should not damage the tape. It is thus preferable that such heating
stations 44 be placed upstream of and relatively close to tape applying
station
54 to minimize or at least reduce cooling between heating station 44 and tape
applying station 54, to thereby allow economically efficient activation of
heat-
activated adhesive. If a downstream heating station is used, similar concerns
also arise regarding first shielding member 18 and core 16.
The temperature of heating elements 52, the ambient atmospheric
temperature within housing 46, the length of housing 46, and the size of inlet
48 and outlet 50 should all be selected, in conjunction with desired line
speed,
to bring the heat-activated adhesive to the desired temperature to effectively
activate it. The thermal properties of center conductor 12, insulating layer
14,
first tape 18a and the thermally-activated adhesive are all also relevant to
the
design of heating stations) 44.
!f the heating assembly applies heat to core 16 through tape die 62,
factors such as the temperature, dimensions, conductivity, etc. of tape die 62
may also affect activation of the adhesive. Further, the dimensions, spacing,
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17
and operating parameters of extruder 76, as well as those of cooling station
78,
may also affect the activation of the adhesive. Thus, all of the above factors
may cause certain adhesives to be better for certain applications or may
require adjustment in order to manufacture certain types of cable.
If a triaxial cable 10a is desired, optional path 74 may be chosen, as
shown in Fig. 5. Fig. 5 indicates a preferable arrangement in which extruder
76a, cooling station 78a, and heating station 44a are disposed downstream of
tape applying station 54. Extruder 76a may be any commonly-available
extruder suitable for extruding second insulating member 22 around shielding
member 18, and may be of the same type, or may be of a different type, as
extruder 76. Similarly, cooling station 78a may be similar to or different
than
cooling station 78, and heating station 44a may be similar to or different
than
heating station 44. Also, adhesive station 68a may be similar or different
than
adhesive station 68. The placement, dimensions, and operating parameters of
cooling station 78a, heating station 44a, and adhesive station 68a should be
chosen according to the temperature of the extrudate used to form second
insulating layer 22, the speed of the manufacturing line, the type and
placement of adhesive, etc., and thus may differ from their upstream
counterparts.
As indicated in Fig. 5, a second tape applying station 54a and a second
tape supply 32a may also be used, along with an, optional lubricant station
38a,
to attach second shielding member 24 to create a triaxial cable. Tape applying
station 54a may be essentially similar to tape applying station 54, although
the
dimensions of the tape folding tool and the orifice in the tape die will
necessarily be slightly larger than in station 54 in order to accommodate the
increasing diameter of the manufactured cable.
To make triaxial cable, extruder 76a forms second insulating layer 22
around first shielding member 18, and cooling station 78a cools second
insulating layer 22 in place. A heating assembly of some sort, as described
above, may be employed in a second activating step to activate a second heat-
activated adhesive to bond second insulating layer 22 to first shielding
member
18. The activation may be accomplished by heating at least one of first
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18
shielding member 18, second insulating layer 22, and the second adhesive
prior to extrusion. The second adhesive also may be applied to first shielding
member 18. Preferably, the second adhesive is mixed with the extrudate used
to form second insulating layer 22, and the adhesive is thus extruded into
place
and activated simultaneously.
Second shielding member 24 is then applied to form a triaxial cable.
Preferably, second shielding member 24 is bonded to second insulating layer
22 via a third heat-activated adhesive, and this bonding may be carried out in
any of the ways set forth above regarding first shielding member 18 and first
insulating layer 14. Preferably, a heating station 44 upstream of second tape
applying station 54a applies heat to second insulating layer 22 to activate a
heat-activated adhesive that is extruded along with that layer. In this case,
the
second and third heat-activated adhesives may actually be the same material.
Also, preferably, a second heated tape die (not shown) also activates the
third
heat-activated adhesive. However applied, the third heat-activated adhesive
should be activated no later than immediately downstream of the second tape
applying assembly.
Once second shielding member 24 is in place, jacket 20 is preferably
placed on cable 1 Oa by .extruder 76. If desired, jacket 20 may be bonded to
second shielding member 24 by a fourth heat-activated adhesive that may be
applied to second shielding member 24 prior to extruder 76 or extruded along
with jacket 20.
The present invention thus provides improved methods and apparatus
for manufacturing various forms of cable. If desired, bonding between many or
all layers and members may be achieved.
The following are examples of cables made according to the claimed
method and apparatus by applicants corresponding to cables 10 and 10a
discussed above indicating how and where bonding is achieved between
layers.
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19
Example 1
Part Material O.D. (inches)
Center Conductor copper clad steel 0.064
First Insulating Layer foam polyethylene 0.280
Adhesive ethylene acrylic acid--
(on
tape)
First Shielding Member aluminum/ 0.287
polypropylene/
aluminum tape
Adhesive ethylene acrylic acid--
(within
second insulating
layer
extrudate)
Second Insulating Layer thermoplastic material0.314
Adhesive ethylene acrylic acid--
(within
second insulating
layer
extrudate)
Second Shielding Member aluminum/ 0.321
polyester/aluminum
tape
Adhesive ethylene acrylic acid--
(within
jacket extrudate)
Jacket low density polyethylene0.400
The above example was manufactured with a line speed of 303 feet per
minute using an upstream heating station maintained at a temperature of
800°C measured via an internal thermocouple to heat the core. At the
first
tape applying station, the exterior of the core was 95°C, measured via
an intra-
red sensor. The tape die at the first station was heated to 88°C
measured via
a thermocouple. The first extrudate for the second insulating layer was a mix
of thermoplastics and ethylene acrylic acid, and was extruded at about
400°C.
A cooling station followed the first extruder. A second heating station
maintained at 750°C measured via an internal thermocouple heated the
second insulating layer to 88°C measured via an infrared sensor on the
second
tape applying station. The second tape die was heated to 88°C measured
via
a thermocouple. A second extruder extruded the jacket, which was a mix of
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low-density polyethylene and ethylene acrylic acid at about 465°C. A
second
cooling station followed.
Example 2
Part Material O.D. finches)
Center Conductor copper clad steel .040
First Insulating Layerfoam polyethylene 0.180
Adhesive ethylene acrylic --
acid (on
tape)
First Shielding Memberaluminuml 0.187
polypropylene/
aluminum tape
Adhesive ethylene acrylic --
acid
(within second insulating
layer extrudate)
Second Insulating thermoplastic material0.216
Layer
Adhesive ethylene acrylic --
acid
(within second insulating
layer extrudate)
Second Shielding Memberaluminum/ 0.221
polyester/aluminum
tape
Adhesive ethylene acrylic --
acid
(within jacket extrudate)
Jacket low density polyethylene0.280
5
The above example was manufactured with a line speed of 197 feet per
minute using an upstream heating station maintained at a temperature of
700°C measured via an internal thermocouple to heat the core. At the
first
tape applying station, the exterior of the core was 95°C, measured via
infrared
10 sensor. The tape die at the first station was heated to 88°C,
measured via
thermocouple. The first extrudate for the second insulating layer was a mix of
thermoplastics and ethylene acrylic acid, and was extruded at about
400°C. A
cooling station followed the first extruder. A second heating station
maintained
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21
at 595°C measured via an internal thermocouple heated the second
insulating
layer to 100°C measured via an infrared sensor on the second tape
assembly.
The second tape die was heated to 88°C measured via a
thermocouple. A
second extruder extruded the jacket, which was a mix of low-density
polyethylene and ethylene acrylic acid about 400°C. A second cooling
station
followed.
It should be understood all of the apparatus shown in Figs. 6A through
6F are commonly available apparatus that could be assembled by one of
ordinary skill in the art or purchased from commercial providers. Applicants
have claimed an inventive apparatus and related methods herein that relate to
the arrangement of such apparatus and the usage of such apparatus in such
methods. The representations of the apparatus shown in Figs. 6A through 6F
are thus intended to be no more than representations, and are thus not
considered to be limiting as to the form or design of the claimed apparatus or
method. Further, as described above, various optional changes are possible to
the inventive methods and apparatus within the scope of the invention. It is
intended that these optional changes and additions to the inventive methods
and apparatus be included within the claimed invention and its equivalents.
It should also be apparent that control systems, feedback systems, and
drive systems can be applied to or added to the above described method and
apparatus by one skilled in the art to allow for precision operation of a
manufacturing line according to the disclosed method and apparatus. Detailed
descriptions of such systems have not been included herein as it is within the
ordinary skill in the art to use such systems in concert with the present
invention.
Thus, it will generally be apparent to those skilled in the art that various
modifications and variations can be made in the present invention without
departing from the scope and spirit of the invention. It is intended that the
present invention include such modifications and variations as come within the
scope of the appended claims and their equivalents.
