Note: Descriptions are shown in the official language in which they were submitted.
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PARTIAL DISCHARGE RESISTANT ELECTRICAL CABLE AND METHOD
BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates to electrical cabling and, more particularly, to a
partial
discharge resistant electrical cable and a method for manufacturing the cable.
Description of Related Art
Generally, oilfield wireline operations concern the testing and measurement of
geologic formations proximate a well periodically prior to completion or after
the well has
been fully drilled. Electrical power requirements for tools used to test and
measure the
geologic formations have increased over time as the capabilities of the tools
have improved.
Accordingly, cables used to deliver electrical power to the tools are required
to handle greater
amounts of power.
As the electrical voltage applied to a cable exceeds a critical value,
generally known
as the inception voltage, a partial discharge of an electrical field within
the cable, produced
by the electrical voltage across the cable's conductor, may occur. Referring
to Figure 1,
conventional cables may contain voids 102 between a conductor 104 and an
insulating layer
106 surrounding the conductor 104. Partial discharge may occur within the
electrical cable
100 when air or other gases trapped within the voids 102 become ionized by the
electrical
field. Accordingly; it is generally desirable to at least minimize air or
other gases that may be
entrapped between the conductor and the insulation.
Generally, conventional wireline cables include stranded copper conductors
insulated
with fluoropolymers or polyolefins. It is desirable for the insulating
materials to be strong,
wear resistant, and capable of withstanding high temperatures, so that they
are able to tolerate
environments typically encountered during manufacturing and use. Such
polyolefin-type
polymers can generally be easily compression extruded in small thicknesses
onto stranded
copper conductors at economically viable speeds, producing insulated
conductors having
substantially no air or other gases entrapped between the conductor and the
insulation.
1
. . . , . .. . . ..., .. . .. . .. ..... ~ . .. . . .... ... . .. ....... .
.... . .... ..,. .i ... . . ...... . . . . . .. . . . .
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However, such fluoropolymers are generally very
difficult to compression extrude through small die orifices
to produce thin layers of insulation on conductors at
economically viable speeds. Secondary bonding forces (such
as Van der Waal's forces) within simple hydrocarbons, such
as polyolefin-type polymers, may generally be about
40 KJoules/mole, while such forces within fluoropolymers may
generally be about 4 KJoules/mole. Thus, fluoropolymers
generally achieve their strength and toughness by having
molecules with very high molecular weights that entangle
with neighboring molecules to compensate for the low
secondary bonding force. The high molecular weight of the
fluoropolymers leads to considerably higher viscosities at
their processing temperatures than other polymeric
insulation materials. Further, many fluoropolymers may
experience severe melt fracture, visible as excessive
surface roughness, when compression extruded in small
thicknesses due to their high molecular weights.
Accordingly, fluoropolymer insulation is typically
extruded through large die orifices and the material is
stretched, while in a melted state, to a desired thickness
and shaped onto the conductor. While this process may
produce cabling at economically viable speeds, air or other
gases are often trapped between the conductor and the
insulation.
The present invention is directed to overcoming,
or at least reducing, the effects of one or more of the
problems set forth above.
BRIEF SUMMARY OF THE INVENTION
According to one aspect of the present invention,
there is provided an electrical cable, comprising: a
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conductor comprising a plurality of strands defining
interstices therebetween; a first insulating layer
comprising a polymer that is disposed on the conductor such
that the first insulating layer substantially fills the
interstices, wherein the polymer of the first insulating
layer comprises a low molecular weight polymer; and a second
insulating layer comprising a high molecular weight polymer
that is disposed on the first insulating layer; wherein the
first insulating layer has a thickness within a range of
about 0.002 mm to about 0.500 mm.
According to another aspect of the present
invention, there is provided an electrical cable,
comprising: a conductor comprising a plurality of strands
defining interstices therebetween; a first insulating layer
comprising a polymer that is disposed on the conductor such
that the first insulating layer substantially fills the
interstices, the polymer of the first insulating layer
comprising a low molecular weight polymer; an adhesion layer
comprising a polymer that is disposed on the first
insulating layer; and a second insulating layer comprising a
polymer that is disposed on the adhesion layer, the polymer
of the second insulating layer comprising a high molecular
weight polymer; wherein the adhesion layer is miscible with
the polymer of the first insulating layer and the polymer of
the second insulating layer.
According to another aspect of the present
invention, there is provided an electrical cable,
comprising: a conductor comprising a plurality of strands
defining interstices therebetween; a first insulating layer
comprising a polymer that is disposed on the conductor such
that the first insulating layer substantially fills the
interstices, the polymer of the first insulating layer
comprising a low molecular weight polymer; a second
2a
. . _ .. . . . .. . .. .. , ..i . . ... .... .
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insulating layer comprising a polymer that is disposed on
the first insulating layer, the polymer of the second
insulating layer comprising a high molecular weight polymer;
and a lubricating layer comprising a low molecular weight
polymer that is disposed on the second insulating layer.
According to another aspect of the present
invention, there is provided an electrical cable,
comprising: a conductor comprising a plurality of strands
defining interstices therebetween; a first insulating layer
comprising a polymer that is disposed on the conductor such
that the first insulating layer substantially fills the
interstices, the polymer of the first insulating layer
comprising a low molecular weight polymer; an adhesion layer
comprising a polymer that is disposed on the first
insulating layer; a second insulating layer comprising a
polymer that is disposed on the adhesion layer, the polymer
of the second insulating layer comprising a high molecular
weight polymer; and a lubricating layer comprising a low
molecular weight polymer that is disposed on the second
insulating layer; wherein the adhesion layer is miscible
with the polymer of the first insulating layer and the
polymer of the second insulating layer.
According to another aspect of the present
invention, there is provided a method for producing an
electrical cable, comprising: providing a conductor
comprising a plurality of strands defining interstices
therebetween; applying a first insulating layer to the
conductor such that the interstices are substantially filled
by the first insulating layer, the first insulating layer
comprising a low molecular weight polymer; applying an
adhesion layer to the first insulating layer; and applying a
second insulating layer to the adhesion layer, the second
insulating layer comprising a high molecular weight polymer.
2b
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In one aspect of the present invention, an
electrical cable is provided. The electrical cable includes
a conductor comprising a plurality of strands defining
interstices therebetween and a first insulating layer
comprising a polymer that is disposed on the conductor such
that the first insulating layer substantially fills the
interstices.
In another aspect of the present invention, an
electrical cable is provided. The electrical cable includes
a conductor comprising a plurality of strands defining
interstices therebetween, a first insulating layer
comprising a polymer that is disposed on the conductor such
that the first insulating layer substantially fills the
interstices, and an adhesion layer comprising a polymer that
is disposed on the first insulating layer. The electrical
cable further comprises a second insulating layer comprising
a polymer that is disposed on the
2c
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adhesion layer, wherein the adhesion layer is miscible with the polymer of the
first insulating
layer and the polymer of the second insulating layer.
In yet another aspect of the present invention, an electrical cable is
provided. The
electrical cable includes a conductor comprising a plurality of strands
defining interstices
therebetween, a first insulating layer comprising a polymer that is disposed
on the conductor
such that the first insulating layer substantially fills the interstices, and
a second insulating
layer comprising a polymer that is disposed on the first insulating layer. The
electrical cable
further includes a lubricating layer comprising a low molecular weight polymer
that is
disposed on the second insulating layer.
In another aspect of the present invention, an electrical cable is provided.
The
electrical cable includes a conductor comprising a plurality of strands
defining interstices
therebetween, a first insulating layer comprising a polymer that is disposed
on the conductor
such that the first insulating layer substantially fills the interstices, and
an adhesion layer
comprising a polymer that is disposed on the first insulating layer. 'The
electrical cable
further includes a second insulating layer comprising a polymer that is
disposed on the
adhesion layer and a lubricating layer comprising a low molecular weight
polymer that is
disposed on the second insulating layer, wherein the adhesion layer is
miscible with the
polymer of the first insulating layer and the polymer of the second insulating
layer.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention may be understood by reference to the following description
taken in
conjunction with the accompanying drawings, in which the.leftmost significant
digit(s) in the
reference numerals denote(s) the first figure in which the respective
reference numerals
appear, and in which:
Figure 1 is a cross-sectional view of a conventional insulated electrical
conductor or
cable;
Figure 2 is a cross-sectional view of a first illustrative embodiment of an
insulated
electrical conductor or cable according to the present invention;
Figure 3 is a block diagram of a first illustrative embodiment of a method for
producing the insulated electrical conductor or cable of Figure 2;
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Figure 4 is a block diagram of a second illustrative embodiment of a method
for
producing the insulated electrical conductor or cable of Figure 2;
Figure 5 is a cross-sectional view of a second illustrative embodiment of an
insulated
electrical conductor or cable according to the present invention;
Figure 6 is a block diagram of a first illustrative embodiment of a method for
producing the insulated electrical conductor or cable of Figure 5;
Figure 7 is a block diagram of a second illustrative embodiment of a method
for
producing the insulated electrical conductor or cable of Figure 5;
Figure 8 is a cross-sectional view of a third illustrative embodiment of an
insulated
electrical conductor or cable according to the present invention;
Figure 9 is a block diagram of a first illustrative embodiment of a method for
producing the insulated electrical conductor or cable of Figure 8;
Figure 10 is a block diagrarn of a second illustrative embodiment of a method
for
producing the insulated electrical conductor or cable of Figure 8;
Figure 11 is a block diagram of a third illustrative embodiment of a method
for
producing the insulated electrical conductor or cable of Figure 8;
Figure 12 is a block diagram of a fourth illustrative embodiment of a method
for
producing the insulated electrical conductor or cable of Figure 8;
Figure 13 is a cross-sectional view of a fourth illustrative embodiment of an
insulated
electrical conductor or cable according to the present invention;
Figure 14 is a block diagram of a first illustrative embodiment of a method
for
producing the insulated electrical conductor or cable of Figure 13;
Figure 15 is a block diagram of a second illustrative embodiment of a method
for
producing the insulated electrical conductor or cable of Figure 13;
Figure 16 is a block diagram of a third illustrative embodiment of a method
for
producing the insulated electrical conductor or cable of Figure 13;
Figure 17 is a block diagram of a fourth illustrative embodiment of a method
for
producing the insulated electrical conductor or cable of Figure 13; and
Figure 18 is a block diagram of a pultrusion method for producing the
insulated
electrical conductor or cable of Figure 2.
While the invention is susceptible to various modifications and alternative
forms,
specific embodiments thereof have been shown by way of example in the drawings
and are
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herein described in detail. It should be understood, however, that the
description herein of
specific embodiments is not intended to limit the invention to the particular
forms disclosed,
but on the contrary, the intention is to cover all modifications, equivalents,
and alternatives
falling within the scope of the invention as defined by the appended claims.
DETAILED DESCRIPTION OF THE INVENTION
Illustrative embodiments of the invention are described below. In the interest
of
clarity, not all features of an actual implementation are described in this
specification. It will
of course be appreciated that in the development of any such actual
embodiment, numerous
implementation-specific decisions must be made to achieve the developer's
specific goals,
such as compliance with system-related and business-related constraints, which
will vary
from one implementation to another. Moreover, it will be appreciated that such
a
development effort might be complex and time-consuming but would nevertheless
be a
routine undertaking for those of ordinary skill in the art having the benefit
of this disclosure.
Figure 2 depicts, in cross-section, a first illustrative embodiment of an
insulated
electrical conductor or cable according to the present invention. In the
illustrated
embodiment, an electrical cable 200 includes a conductor 202 comprising a
plurality of
strands 202a, as shown in Figure 2. The electrical cable 200 further comprises
a first
insulating layer 204 disposed between the conductor 202 and a second
insulating layer 206.
The first insulating layer 204 substantially fills interstices 208 between
adjacent strands 202a
of the conductor 202. Each of the first insulating layer 204 and the second
insulating layer
206 electrically insulate the conductor 202.
In this first illustrative embodiment, the first insulating layer 204
comprises a low
molecular weight polymer having, for example, a melt index greater than about
15. Such low
molecular weight polymers may include injection moldable grade polymers. The
melt index
of a polymer is, in general, inversely proportional to its molecular weight
and is defined as
the amount, in grams, of the polymer that can be forced through a 2.0955 mm
diaineter
extrusion orifice when subjected to an extrusion force defined for the
particular material by
American Society for Testing Materials (ASTM) standards for ten minutes at a
temperature
also defined for the particular material by ASTM standards. Low molecular
weight polymers
typically have lower viscosities than higher molecular weight polymers, which
have lower
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melt indices. Thus, the lower viscosity of the low molecular weight polymer
allows the first
insulating layer 204 to flow into and substantially fill the interstices 208
(corresponding to the
voids 102 of Figure 1) between adjacent strands 202a of the conductor 202 as
the first
insulating layer 204 is formed onto the conductor 202. Accordingly, few if any
voids are
produced within the interstices 208 between the conductor 202 and the first
insulating layer
204. Thus, the likelihood of air or other gases becoming entrapped between the
conductor
202 and the first insulating layer 204 may be decreased.
While the present invention encompasses any low molecular weight polymer
deemed
suitable for the first insulating layer 204, in one embodiment, the first
insulating layer 204
comprises a low molecular weight fluoropolymer, e.g., MFA 940 AX (co-polymer
of
tetrafluoroethylene and perfluoromethyl vinyl ether with a melt index of 140
to 150)
manufactured by Ausimont U.S.A. of Thorofare, New Jersey, U.S.A. Such
fluoropolymers
are generally capable of withstanding higher temperatures encountered when the
cable 200 is
used in an oilfield wireline operation. In one embodiment, the first
insulating layer 204 has a
thickness tl within a range of about 0.002 mm to about 0.500 mm.
Low molecular weight polymers may generally lack the mechanical strength and
wear
resistance desired for electrical cables to be used in harsh environments,
such as in oilfield
wireline operations. Therefore, the second insulating layer 206 comprises a
high molecular
weight polymer that surrounds the first insulating layer 204 to provide a
strong, wear resistant
covering for the cable 200. Such high molecular weight polymers may include
fluoropolymers having melt indices of about 15 or less. While the present
invention
encompasses any high molecular weight polymer deemed suitable for the second
insulating
layer 206, in one embodiment, the second insulating layer 206 comprises a high
molecular
weight fluoropolymer, e.g., MFA 620 (co-polymer of tetrafluoroethylene and
perfluoromethyl vinyl ether with a melt index of 2 to 5) manufactured by
Ausimont U.S.A. of
Thorofare, New Jersey, U.S.A. Such fluoropolyrners are generally capable of
withstanding
higher temperatures and harsh physical conditions encountered when the cable
200 is used in
an oilfield wireline operation. In one embodiment, the second insulating layer
206 has a
thickness t2 within a range of about 0.13 mm to about 1.30 mm.
While the present invention is not so limited, in one embodiment, the first
insulating
layer 204 and the second insulating layer 206 are made from different species
of the same
polymer having different molecular weights. For example, the first insulating
layer 204 may
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be made from a low molecular weight fluoropolymer, while the second insulating
layer 206
may be made from the same, but higher molecular weight, fluoropolymer.
As discussed above, reducing the likelihood of air or other gases becoming
entrapped
between the conductor 202 and the first insulating layer 204 generally
decreases the
likelihood that partial discharge of the electrical field will occur. In one
embodiment, the
first insulating layer 204 may have a higher permittivity than that of the
second insulating
layer 206, thus further decreasing the likelihood of partial discharge of the
electrical field.
Generally, materials having higher permittivity values can store more energy
than materials
having relatively lower permittivity values. Thus, higher permittivity
materials are relatively
more capable of allowing an opposing electrical field to exist therein when
the cable 200 is in
use. Such opposing electrical fields may counteract at least a portion of the
electrical field
produced by the voltage across the conductor 202.
Further, the combination of the first insulating layer 204 and the second
insulating
layer 206 may result in tangential electrical fields being produced within the
insulating layers
204, 206 when the cable 200 is in use due to the higher permittivity, in a
relative sense, of the
first insulating layer 204 as compared to the second insulating layer 206.
Such tangential
electrical fields may also at least partially counteract the electrical field
generated by the
voltage across the conductor 202. In one embodiinent, the polymer comprising
the first
insulating layer 204 has a permittivity within a range of about 2.8 to about
8.0, while the
polymer comprising the second insulating layer 206 has a permittivity within a
range of about
1.8 to about 2.7.
Each of the first insulating layer 204 and the second insulating layer 206 may
be
applied to the conductor 202 by any means known to the art. For example, the
insulating
layers 204, 206 may be applied to the conductor by compression, semi-
compression, or
tubing extrusion methods, as are generally known in the art. In one
embodiment, depicted in
Figure 3, the conductor 202 is fed into a first extruder head 302 in a
direction indicated by the
arrow 304, wherein the low molecular weight polymer is extruded (e.g., by
compression,
semi-compression, or tubing extrusion methods) onto the conductor 202 to form
the first
insulating layer 204. Subsequently, the conductor 202, with the first
insulating layer 204
applied thereto, is fed into a second extruder head 306 in the direction
indicated by the arrow
304, wherein the high molecular weight polymer is formed on the first
insulating layer 204 by
a tubing process to form the second insulating layer 206, thus producing the
cable 200.
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Alternatively, in the illustrative embodiment shown in Figure 4, the conductor
202 is
fed into a two layer co-extruder head 402 in a direction indicated by the
arrow 404. In this
embodiment, the low molecular weight polymer is extruded (e.g., by
compression, semi-
compression, or tubing methods) onto the conductor 202 to form the first
insulating layer
204. The high molecular weight polymer is formed on the first insulating layer
204 by a
tubing process performed by the same two layer co-extruder head 402 to form
the second
insulating layer 206, thus producing the cable 200.
It may be desirable in certain situations to compression or semi-compression
extrude
the second insulating layer 206 onto the first insulating layer 204. However,
as discussed
above, the second insulating layer comprises a high molecular weight polymer.
Such
polymers include large molecules that result in the polymer having a greater
viscosity than
that of low molecular weight polymers. Generally, greater viscosity leads to
greater shear
stress between high molecular weight polymers and the extrusion die (not
shown) when
extruded than between low molecular weight polymers and the extrusion die.
This can lead
to severe melt fracture cracking of the surface of the polymer.
Thus, in a second illustrative embodiment, shown in Figure 5, an insulated
electrical
conductor or cable 500 is shown including a lubricating layer 502, comprising
a lubricating
polymer, such as a low molecular weight polymer, that has been added to an
outer surface
504 of the second insulating layer 206. Other than the lubricating layer 502,
the elements of
the cable 500 generally correspond to the elements of the cable 200 and are so
numbered.
The low molecular weight material comprising the lubricating layer 502
decreases the shear
stress (and thus melt fracture) between the second insulating layer 206 and
the extrusion die,
thereby allowing the second insulating layer 206 to be effectively compression
or semi-
compression extruded.
Still referring to Figure 5, the lubricating layer 502 may comprise the same
polymer
as the first insulating layer 204, as described above, or may comprise any
other desired low
molecular weight polymer. In one embodiment, the lubricating layer 502 has a
thickness t3
within a range of about 0.002 mm to about 0.050 mm.
The cable 500 may be produced as illustrated in Figure 6. The conductor 202 is
fed
into a three layer co-extruder head 602 in a direction indicated by arrow 604.
Each of the
first low molecular weight polymer and the high molecular weight polymer are
compression
or semi-compression extruded onto the conductor 202 by the three layer co-
extruder head 602
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to form each of the first insulating layer 204 and the second insulating layer
206, wherein a
low molecular weight polymer is applied to the high molecular weight polymer
just prior to
extrusion to form the lubricating layer 502. Thus, the insulating layers 204,
206 and the
lubricating layer 502 are co-extruded by the three layer co-extruder head 602.
Alternatively, as illustrated in Figure 7, the conductor 202 is fed into a
first extruder
head 702 in a direction indicated by arrow 704, wherein the first low
molecular weight
polymer is extruded (e.g., by compression, seini-compression, or tubing
extrusion methods)
onto the conductor 202 to form the first insulating layer 204. The conductor
202, with the
first insulating layer 204 applied thereto, is then fed into a two layer co-
extruder head 706,
wherein the high molecular weight polymer and the second low molecular weight
polymer
are then compression or semi-compression extruded onto the first insulating
layer 204 to
form the second insulating layer 206 and the lubricating layer 502,
respectively.
It may be generally desirable for the first insulating layer 204 and the
second
insulating layer 206, as illustrated in Figure 2, to bond to each other during
extrusion, so that
the insulating layers 204, 206 become integral. Some polymers that may be
chosen for the
insulating layers 204, 206, however, may be immiscible and, thus, fail to bond
together
sufficiently. Accordingly, a third illustrative embodiment of an electrical
cable according to
the present invention is depicted in Figure 8. The cable 800 includes an
adhesion layer 802
that is disposed between the first insulating layer 204 and the second
insulating layer 206.
Other elements of the cable 800 generally correspond to the cable 200 of
Figure 2 and are
numbered accordingly. The adhesion layer 802 comprises a polymer that is
miscible with
both the first insulating layer 204 and the second insulating layer 206. The
polymer making
up the adhesion layer 802 may vary widely, depending upon the polymers chosen
for the
insulating layers 204, 206.
For example, if the first insulating layer 204 comprises nylon and the second
insulating layer 206 comprises ethylene tetrafluoroethylene (ETFE), such as
regular Tefzel
2183 manufactured by E.I. du Pont de Nemours and Company (DuPont) of
Wilmington,
Delaware, U.S.A., it is unlikely that they will sufficiently bond together. In
this example, the
adhesion layer 802 may comprise modified Tefzel HT-2202, also manufactured by
DuPont,
which is miscible with both nylon and regular Tefzel. Thus, the insulating
layers 204, 206
may be bonded together via the adhesion layer 802. In one embodiment, the
adhesion layer
802 may have a thickness t4 within a range of about 1 to 2 mils.
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The cable 800 may be produced as illustrated in Figure 9. The conductor 202 is
fed
into a three layer co-extruder head 902 in a direction indicated by the arrow
904. The low
molecular weight polymer and the adhesion layer polymer are extruded (e.g., by
compression, semi-compression, or tubing extrusion methods) onto the conductor
202 to
form the first insulating layer 204 and the adhesion layer 802, respectively.
The high
molecular weight polymer is then formed on the adhesion layer 802 by a tubing
extrusion
process performed by the three layer co-extruder head 902 to form the second
insulating layer
206.
Alternatively, as shown in Figure 10, a two layer co-extruder head 1002 may co-
extrude the first insulating layer 204 and the adhesion layer 802 and a second
extruder head
1004 may apply the second insulating layer 206. In this illustrative
embodiment, the
conductor 202 is fed into the extruder 1002 in a direction indicated by arrow
1006, wherein
the low molecular weight polymer and the adhesion layer polymer are extruded
(e.g., by
compression, semi-compression, or tubing extrusion methods) onto the conductor
202 to
form the first insulating layer 204 and the adhesion layer 802, respectively.
The high
molecular weight polymer is then formed on the adhesion layer 802 by a tubing
extrusion
process performed by extruder head 1004 to form the second insulating layer
206.
The invention, however, is not so limited. Rather, as illustrated in Figure
11, an
extruder head 1102 may apply only the first insulating layer 204 and a two
layer co-extruder
head 1104 may co-extrude each of the adhesion layer 802 and the second
insulating layer
206. In this illustrative embodiment, the conductor 202 is fed into the
extruder head 1102 in
a direction indicated by arrow 1106, wherein the low molecular weight polymer
is extruded
(e.g., by compression, semi-compression, or tubing extrusion methods) onto the
conductor
202 to form the first insulating layer 204. The adhesion layer polymer is
extruded (e.g., by
compression, semi-compression, or tubing methods) onto the first insulating
layer 204 to
form the adhesion layer 802 and the high molecular weight polymer is formed on
the
adhesion layer 802 by a tubing extrusion process performed by two layer co-
extruder head
1104 to form the second insulating layer 206.
Each of the first insulation layer 204, the adhesion layer 802, and the second
insulating layer 206 may be applied by separate extruder heads 1202, 1204,
1206,
respectively, as illustrated in Figure 12. In this illustrative embodiment,
the conductor 202 is
fed into the first extruder head 1202 in a direction indicated by arrow 1208,
wherein the low
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molecular weight polymer is extruded (e.g., by compression,
semi-compression, or tubing extrusion methods) onto the
conductor 202 to form the first insulating layer 204. The
conductor 202, with the first insulating layer 204 applied
thereon, is then fed into the second extruder head 1204,
wherein the adhesion layer polymer is extruded (e.g., by
compression, semi-compression, or tubing extrusion methods)
onto the first insulating layer 204 to form the adhesion
layer 802. The conductor 202, with the first insulating
layer 204 and the adhesion layer 802 applied thereon, is
then fed into the third extruder head 1206, wherein the high
molecular weight polymer is formed onto the adhesion layer
802 by a tubing extrusion process performed by the third
extruder head 1206.
As indicated previously, it may be desirable in
certain situations to compression or semi-compression
extrude the second insulating layer 206, which comprises the
high molecular weight polymer. In a fourth illustrative
embodiment, shown in Figure 13, a cable 1300 is shown
including a lubricating layer 502, comprising a low
molecular weight polymer or other easily compression
extrudable polymer such as nylon, polyethylether-ketone
(PEEK), or polyphenylene sulfide (PPS), that has been added
to an outer surface 504 of the second insulating layer 206.
Other than the lubricating layer 502, the elements of the
cable 13000 generally correspond to the elements of the
cable 800 and are so numbered. As described in relation to
the second embodiment (depicted in Figure 5), the
lubricating layer 502 decreases the friction between the
second insulating layer 206 and the extrusion die (not
shown), thereby allowing the second insulating layer 206 to
be effectively compression extruded.
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The cable 1300 may be produced as illustrated in
Figure 14. The conductor 202 is fed into a four layer co-
extruder head 1402 in a direction indicated by the arrow
1404. The first low molecular weight polymer and the
adhesion layer polymer are co-extruded (e.g., by
compression, semi-compression, or tubing extrusion methods)
onto the conductor 202 to form the first insulating layer
204 and the adhesion layer 802, respectively. The high
molecular weight polymer and the second low molecular weight
polymer are also compression or semi-compression extruded
onto the adhesion layer 802 by the four layer co-extruder
head 1402 to form the second insulating layer 206 and the
lubricating layer 502, respectively. Thus, the insulating
layers 204, 206, the adhesion layer 802, and the lubricating
layer 502 are co-extruded by the four layer co-extruder head
1402. It should be noted that
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cable 1300 may be manufactured on a three layer co-extruder head if the
adhesion layer 802
is omitted.
Alternatively, as shown in Figure 15, a first two layer co-extruder head 1502
may co-
extrude the first insulating layer 204 and the adhesion layer 802 and a second
two layer co-
extruder head 1504 may co-extrude the second insulating layer 206 and the
lubricating layer
502. In this illustrative embodiment, the conductor 202 is fed into the two
layer co-extruder
head 1502 in a direction indicated by arrow 1506, wherein the first low
molecular weight
polymer and the adhesion layer polymer are extruded (e.g., by compression,
semi-
compression, or tubing extrusion methods) onto the conductor 202 to form the
first insulating
layer 204 and the adhesion layer 802, respectively. The high molecular weight
polymer and
the second low molecular weight polymer are then compression or semi-
compression
extruded onto the adhesion layer 802 by the second two layer co-extruder head
1504 to form
the second insulating layer 206 and the lubricating layer 502, respectively.
The invention, however, is not so limited. Rather, as illustrated in Figure
16, an
extruder head 1602 may apply only the first insulating layer 204 and a three
layer co-extruder
head 1604 may co-extrude each of the adhesion layer 802, the second insulating
layer 206,
and the lubricating layer 502. In this illustrative embodiment, the conductor
202 is fed into
the extruder head 1602 in a direction indicated by arrow 1606, wherein the
first low
molecular weight polymer is extruded (e.g., by compression, semi-compression,
or tubing
extrusion methods) onto the conductor 202 to form the first insulating layer
204. The
adhesion layer polymer, the high molecular weight polymer, and the second low
molecular
weight polymer are compression or semi-compression extruded onto the first
insulating layer
204 by the three layer co-extruder head 1604 to form the adhesion layer 802,
the second
insulating layer 206, and the lubricating layer 502, respectively.
Each of the first insulation layer 204, the adhesion layer 802, and the second
insulating layer 206 may be applied by separate extruder heads 1702, 1704,
1706,
respectively, as illustrated in Figure 17. In this illustrative einbodiment,
the conductor 202 is
fed into the first extruder head 1702 in a direction indicated by arrow 1708,
wherein the first
low molecular weight polymer is extruded (e.g., by compression, semi-
compression, or
tubing extrusion methods) onto the conductor 202 to form the first insulating
layer 204. The
conductor 202, with the first insulating layer 204 applied thereon, is then
fed into the second
extruder head 1704, wherein the adhesion layer polymer is extruded (e.g., by
compression,
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CA 02422989 2003-03-20
25.0199
semi-compression, or tubing extrusion methods) onto the first insulating layer
204 to form the
adhesion layer 802. The conductor 202, with the first insulating layer 204 and
the adhesion
layer 802 applied thereon, is then fed into the two layer co-extruder 1706,
wherein the high
molecular weight polymer and the second low molecular weight polymer are
compression or
semi-compression extruded onto the adhesion layer 802 to form the second
insulating layer
206 and the lubricating layer 502, respectively.
While extrusion has been presented herein as a means for applying the
insulating
layers 204, 206, the lubrication layer 502, and the adhesion layer 802 in
various
embodiments, the present invention is not so limited. Rather, any lneans known
to the art
may be used to apply the layers 204, 206, 502, 802. For example, a pultrusion
process may
be used to apply a high molecular weight polymer as the first insulating layer
204.
Pultrusion, as it relates to electrical cable insulation, is generally defined
as a process of
pulling a conductor through a polymer, such that the polymer clings to the
conductor. The
coated conductor is then pulled through a heated shaping die where the polymer
is softened
and formed into an insulating layer.
In one illustrative embodiment shown in Figure 18, the conductor 202 is fed,
in a
direction corresponding to arrow 1802, into an energy source 1804. The energy
source 1804
affects the conductor 202 such that particles of the first high molecular
weight polymer may
cling to the conductor 202. In one illustrative embodiment, the energy source
1804 is an
electrostatic energy source that applies an electrostatic charge to the
conductor 202 that
differs from such a charge on the high molecular weight polymer.
Alternatively, the energy
source 1804 is a thermal energy source (e.g., a heater or the like) that
applies heat to the
conductor 202.
As the conductor 202 is then fed through a container 1806 containing the
particles
(powder) of the first high molecular weight polymer, the polymer clings to the
conductor 202,
forming an unconsolidated coating 1808 of the high molecular weight polymer on
the
conductor 202. In one illustrative embodiment, the container 1806 contains a
fluidized bed of
the first high molecular weight polymer. The coated conductor 202 is heated to
make the
polymer particles melt before it is pulled through a heated pultrusion die
1810, which
compresses and consolidates the coating 1808 to form the first insulating
layer 204. The
combination of the heat and compression provided by the pultrusion die 1810
forces the high
molecular weight polymer into the interstices 208 (as shown in Figure 2)
between the strands
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CA 02422989 2003-03-20
25.0199
202a of the conductor 202. Thus, few if any voids are produced within the
interstices 208
and the likelihood of air or other gases becoming entrapped within the
interstices 208 is
decreased.
In this illustrative embodiment, the conductor 202, with the first insulating
layer 204
applied thereto, is fed into an extruder head 1812, wherein the second high
molecular weight
polymer is extruded onto the first insulating layer 204 to form the second
insulating layer
206. While the illustrative embodiment shown in Figure 18 depicts the
production of the
cable 200, the present invention is not so limited. Rather, the pultrusion
process shown in
Figure 18 may be applied to any embodiment of the present cable and may be
applied to any
embodiment of a method to produce such a cable. For example, the pultrusion
process may
be used to apply any of the insulating layers 204, 206 and the adhesion layer
802 and may be
used to form polymers into such layers irrespective of their molecular
weights. Further, such
a cable may have only one insulating layer (e.g., the first insulating layer
204) applied onto
the conductor 202. Such a pultrusion method may also be used to apply a thin
layer of high
molecular weight fluoropolymer or other polymers to metallic tubes or polymer
composite
rods.
The particular embodiments disclosed above are illustrative only, as the
invention
may be modified and practiced in different but equivalent manners apparent to
those skilled
in the art having the benefit of the teachings herein. Furthermore, no
limitations are intended
to the details of construction or design herein sliown, other than as
described in the claims
below. It is therefore evident that the particular embodiments disclosed above
may be altered
or modified and all such variations are considered within the scope of the
invention.
Accordingly, the protection sought herein is as set forth in the claims below.
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