United States Patent [19J
`Clouet et al.
`
`I lllll llllllll Ill lllll lllll lllll lllll lllll 111111111111111111111111111111111
`US005922155A
`[11] Patent Number:
`[45] Date of Patent:
`
`5,922,155
`Jul. 13, 1999
`
`[54] METHOD AND DEVICE FOR
`MANUFACTURING AN INSULATIVE
`MATERIAL CELLULAR INSULATOR
`AROUND A CONDUCTOR AND COAXIAL
`CABLE PROVIDED WITH AN INSULATOR
`OF THIS KIND
`
`[75]
`
`Inventors: Pascal Clouet, Gregy sur Yerres;
`Jean-Jacques Maisseu, Reims;
`Francois Vaille, Corbeil Essonnes;
`Alain Vernanchet, Draveil, all of
`France
`
`[56]
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`3,771,934 11/1973 Delves-Broughton .................. 425/135
`
`FOREIGN PATENT DOCUMENTS
`
`539772
`2133453
`
`7/1955 Belgium .
`1/1973 Germany .
`
`Primary Examiner-Francis J. Lorin
`Attorney, Agent, or Firm-Sughrue, Mion, Zinn, Macpeak
`& Seas, PLLC
`
`[73] Assignee: Filotex, Draveil, France
`
`[57]
`
`ABSTRACT
`
`[21] Appl. No.: 08/844,878
`
`[22] Filed:
`
`Apr. 22, 1997
`
`Related U.S. Application Data
`
`[30]
`
`Foreign Application Priority Data
`
`Apr. 23, 1996
`
`[FR]
`
`France ................................... 96 05101
`
`Int. Cl.6
`..................................................... B29C 63/20
`[51]
`[52] U.S. Cl. ......................................... 156/51; 156/244.12
`[58] Field of Search ................................. 156/244.12, 51,
`156/244.11; 264/171.1, 171.12, 171.26,
`172.1, 171.14, 172.15, 177.1, 177.12, 177.14,
`177.16; 425/113
`
`A method of manufacturing an insulative material cellular
`insulator around a conductor, the insulator having a longi(cid:173)
`tudinal passage in which the conductor is housed and closed
`cells extending longitudinally and separated from each other
`by radial walls, includes the following operations: the insu(cid:173)
`lative material in the viscous state is extruded to impart the
`required shape to it to form the cells, the insulative material
`shaped in this way is applied to the conductor, and the
`insulative material is cooled to obtain the insulator. The
`insulative material is applied to the conductor at a distance
`from the exit of the shaping device such that the material is
`drawn down sufficiently for the walls of the cells not to be
`thinned without pressurizing the cells.
`
`6 Claims, 2 Drawing Sheets
`
`5
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`

`

`U.S. Patent
`
`Jul. 13, 1999
`
`Sheet 1 of 2
`
`5,922,155
`
`FIG .1
`
`5
`
`---
`
`FIG.2
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`3
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`37
`
`y 2
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`U.S. Patent
`
`Jul. 13, 1999
`
`Sheet 2 of 2
`
`5,922,155
`
`FIG. 3
`
`51
`
`FIG .4
`
`FIG .5
`
`FIG .6
`
`52 11
`
`2
`
`40 11
`
`3 911
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`38 11
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`Page 3 of 7 (PGR2021-00078)
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`

`

`1
`METHOD AND DEVICE FOR
`MANUFACTURING AN INSULATIVE
`MATERIAL CELLULAR INSULATOR
`AROUND A CONDUCTOR AND COAXIAL
`CABLE PROVIDED WITH AN INSULATOR
`OF THIS KIND
`
`5,922,155
`
`2
`Finally, this method cannot be used to manufacture
`coaxial cables with cellular insulation having a low dielec(cid:173)
`tric constant and a small diameter intermediate insulator.
`A first aim of the present invention is therefore to develop
`a method of manufacturing a cellular insulator around a
`conductor which enables pressurization of the cells to be
`dispensed with.
`Another aim of the present invention is to develop a
`method of this kind that is free of the risk of cracking of the
`10 shaped insulator.
`
`SUMMARY OF THE INVENTION
`
`BACKGROUND OF THE INVENTION
`1. Field of the Invention
`The present invention concerns a method and a device for
`manufacturing an insulative material cellular insulator
`around a conductor. It applies more particularly, but not in
`any limiting way, to the manufacture of dielectric interme(cid:173)
`diate insulators of coaxial cables.
`2. Description of the Prior Art
`Coaxial cables usually include a solid or stranded central
`conductor surrounded by an intermediate insulator made of
`an insulative dielectric material in turn surrounded by an
`outer conductor protected by a protective outer sheath. The
`dielectric intermediate insulator must have specific dielec- 20
`tric properties in order to obtain the attenuation character(cid:173)
`istics required of the cable, in particular at high frequencies.
`To be more precise, this insulator is generally required to
`have a dielectric constant less than about 1.8 and as close as
`possible to 1. The closer the dielectric constant to 1, the 25
`higher the frequencies at which the cable can be used.
`The insulative materials conventionally used in cable(cid:173)
`making do not have dielectric constants of this order when
`they are used in solid form. Their dielectric constants are
`generally close to 2. This applies to polyethylene and to
`polytetrafiuoroethylene (PTFE) in particular. The use of
`these materials to form cellular insulators to reduce the
`dielectric constant is known in itself.
`Cellular insulators are those into which a plurality of
`bubbles filled with air or with a gas having a dielectric
`constant close to 1 are introduced during the application
`(generally by extrusion) of the insulative material to form an
`insulator, and usually by means of a chemical reaction. The
`present invention is not concerned with this type of insulator.
`Cellular insulators, with which the present invention is
`concerned, have cells extending longitudinally (in a straight
`line or in a helix) along the cable and separated from each
`other by radial walls, the cells being obtained by shaping the
`insulative material used, which in this case is solid, using an
`extrusion device having the appropriate openings and pas(cid:173)
`sages for this purpose. The cells are entirely closed, with the
`result that the intermediate insulator is cylindrical or polygo(cid:173)
`nal and its cross-section resembles a spoked wheel.
`One method of manufacturing a cylindrical cellular inter(cid:173)
`mediate insulator in which the cells are entirely closed is
`described in U.S. Pat. No. 3,771,934. It involves extruding
`the insulative material, in the viscous state of course, impart(cid:173)
`ing the required shape to it by shaping means to form the
`cells, applying the material formed in this way to the central
`conductor, and finally cooling this insulative material to
`obtain the insulator.
`In this method, the material shaped by extrusion is applied
`to the central conductor immediately on leaving the shaping
`means. Accordingly, to prevent thinning of the very thin top
`walls of the cells (those adapted to come into contact with
`the outer conductor of the cable) it is necessary to pressurize
`the cells during manufacture. This complicates manufacture.
`Moreover, the shaped material passes suddenly from the
`guide to the conductor, which causes it to undergo a large
`variation in diameter which can cause longitudinal cracks in
`the shaped insulator.
`
`30
`
`15
`
`To this end, the present invention consists in a method of
`manufacturing an insulative material cellular insulator
`around a conductor, the insulator having a longitudinal
`passage in which the conductor is housed and closed cells
`extending longitudinally and separated from each other by
`radial walls, the method comprising the following opera-
`tions:
`the insulative material in the viscous state is extruded to
`impart the required shape to it by means of shaping
`means to form the cells,
`the insulative material shaped in this way is applied to the
`conductor, and
`the insulative material is cooled to obtain the insulator,
`and in which method the insulative material is applied to the
`conductor at a distance from the exit of the shaping means
`such that the material is drawn down sufficiently for the
`walls of the cells not to be thinned without pressurizing the
`cells.
`Using the method of the invention, given that the shaped
`material is not applied to the conductor immediately after it
`leaves the shaping means, the drawing down of the material
`35 is sufficient to prevent the walls of the cells thinning and it
`is therefore no longer necessary to pressurize the cells. The
`method of the invention is therefore much simpler to use
`than the prior art method.
`Furthermore, because of the drawing down, no cracking
`40 of the manufactured insulator can occur.
`The method of the invention can be used to manufacture
`the intermediate insulator of a coaxial cable with a small
`diameter (less than 5 mm) intermediate insulator having a
`low dielectric constant (less than 1. 7), which has not previ-
`45 ously been possible.
`The device for implementing the method described in
`U.S. Pat. No. 3,771,934 includes a guide in which there is an
`interior longitudinal channel through which the central con(cid:173)
`ductor of the cable passes and a die coaxial with the guide,
`50 surrounding the latter and defining with the exterior surface
`of the guide a passage for the insulative material in the
`viscous state, the shape of the insulator being obtained by
`openings formed in the guide itself, so that the shape of the
`cross-section of the intermediate insulator obtained is sub-
`55 stantially identical to that of the openings in the guide
`associated with that of the passage defined between the die
`and the guide.
`This arrangement cannot be used to manufacture coaxial
`cables with a small diameter intermediate insulator, typically
`60 less than 5 mm, used in the medical field in particular. To
`manufacture the intermediate insulator of such cables by the
`method described in the previous patent, in which the shape
`of the intermediate insulator obtained is a "photograph" with
`no "reduction" of the empty parts of the guide, to obtain an
`65 insulator having the required dimensions immediately on
`leaving the device it would be necessary to use a very small
`guide. A high ratio is required in the cross-section of the
`
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`5,922,155
`
`4
`The method and the device of the invention have enabled
`a cable of this kind to be made for the first time.
`Other features and advantages of the present invention
`will emerge from the following description of a method and
`of a device in accordance with the invention given by way
`of illustrative and non-limiting example.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`In the accompanying figures:
`FIG. l is a partially cut away perspective view of a coaxial
`cable with a cellular intermediate insulator made in accor(cid:173)
`dance with the invention.
`FIG. 2 shows a diagrammatic side view of a device of the
`15 invention.
`FIG. 3 is a cross-section of FIG. 1 showing only the inner
`conductor and the intermediate insulator.
`FIG. 4 is a cross-section of FIG. 2 at the level of the guide
`and of the die producing the intermediate insulator shown in
`20 FIG. 3.
`FIG. 5 is a cross-section of FIG. 1 showing only the inner
`conductor and a variant of the intermediate insulator.
`FIG. 6 is a cross-section of FIG. 2 at the level of the guide
`and of a variant of the die for producing the intermediate
`insulator shown in FIG. 5.
`
`25
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`
`30
`
`3
`insulator between the total surface area of the parts devoid
`of material and the total surface area which is typically
`greater than 40, i.e. a low dielectric constant, typically less
`than 1.7. It is not possible to form in a guide this small
`openings capable of producing a ratio of this magnitude, as
`this would lead to the guide having insufficient mechanical
`strength to be used to manufacture the intermediate insula(cid:173)
`tor.
`Another aim of the present invention is therefore to
`provide a device for implementing the above method 10
`enabling manufacture of cables having both a small diameter
`intermediate insulator and a low dielectric constant.
`To this end the present invention proposes a device for
`implementing the method of the invention comprising:
`a guide having an interior longitudinal channel through
`which said conductor passes,
`a die coaxial with and around the guide, defining with the
`exterior surface of the guide a passage for the insulative
`material in the viscous state,
`and including at least one opening communicating with said
`passage and into which said material in the viscous state can
`be introduced, the position around said passage and the
`shape of said opening(s) being such that on leaving said die
`said material incorporates said cells.
`The combination of the following two features:
`use of a device in which the openings are formed in the
`die and not in the guide, and
`drawing down of the material before its application to the
`conductor,
`produces intermediate insulators having dimensions as small
`as required and in particular dimensions compatible with
`applications in the medical field.
`In one particularly advantageous embodiment of the
`device of the invention the die includes a plurality of
`identical openings disposed symmetrically about its longi(cid:173)
`tudinal axis, the cross-section of each of the openings having
`substantially the shape of a T the horizontal bar of which is
`curved about the longitudinal axis, the curved horizontal
`bars of the various Ts all forming parts of a common cylinder 40
`and lines extending their vertical bars intersecting on the
`longitudinal axis.
`With a device of this kind, given that the shaped insulative
`material is drawn down before it is applied to the conductor,
`it is subject to a pressure at the exit from the die which tends 45
`to bring the horizontal bars of the Ts into contact with each
`other to produce the required insulator.
`With the device and the method of the invention, depend(cid:173)
`ing on the draw down rate applied, it is possible to manu(cid:173)
`facture intermediate insulators having either a shape that is 50
`substantially identical, ignoring a coefficient of geometrical
`similarity, to that of the die (if the latter includes T-shaped
`openings, the shape of the insulator is identical to that of the
`die after closing up of the horizontal bars of the Ts), or
`somewhat different.
`Finally, the present invention concerns a coaxial cable,
`preferably made by the method of the invention, comprising,
`coaxially disposed from the interior towards the exterior:
`a central conductor,
`an insulative dielectric material intermediate insulator 60
`including a longitudinal passage in which the conduc-
`tor is housed and closed cells extending longitudinally
`and separated from each other by radial walls,
`an outer conductor, and
`an outer protective sheath,
`wherein the outside diameter of the intermediate insulator is
`less than 5 mm and its dielectric constant is less than 1.7.
`
`Components common to all the figures carry the same
`reference numbers.
`A coaxial cable 10 that can be made in accordance with
`the invention is shown in FIG. 1. It includes, disposed
`coaxially from the interior towards the exterior about a
`35 longitudinal axis X:
`a copper inner electrical conductor 4, for example a
`plurality of stranded conductor wires,
`a dielectric insulative material, for example ethylene and
`propylene fluoride (EPF) intermediate insulator 5 hav(cid:173)
`ing a cylindrical tubular part 51 in contact with the
`conductor 4, a plurality of cells 52 extending longitu(cid:173)
`dinally and in a straight line along the axis X and
`separated from each other by radial walls 53, and a
`cylindrical tubular part 54 surrounding the radial walls
`53 so that the cross-section of the intermediate insulator
`5 resembles a spoked wheel,
`a braided or woven outer conductor 6 which bears on the
`cylindrical tubular part 54 of the insulator 5,
`a protective outer sheath 7.
`Typical dimensions are given below for two coaxial
`cables of the type described hereinabove.
`A coaxial cable for use in the medical field, i.e. of small
`size, has the following dimensions:
`diameter of the inner conductor 4: 0.12 mm,
`outside diameter of the intermediate insulator 5: 0.51 mm,
`outer conductor 6 made up of woven strands 0.03 mm in
`diameter with 98% overlap,
`outside diameter of the outer sheath 7: 0.55 mm.
`A coaxial cable for use in telecommunications, i.e. of
`medium size, has the following dimensions:
`diameter of the inner conductor 4: 0.25 mm,
`outside diameter of the intermediate insulator 5: 1.20 mm,
`outer conductor 6 made up of braided strands 0.10 mm in
`diameter with 66% overlap,
`outside diameter of the outer sheath 7: 2 mm.
`
`55
`
`65
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`5,922,155
`
`5
`FIG. 2 shows an extrusion device 1 of the invention for
`manufacturing the intermediate insulator 5 of the cable 10
`from FIG. 1. This device includes a guide 2 and a die 3.
`The guide 2 has a cylindrical interior channel 20 around
`the longitudinal axis Y of the guide. The channel 20 provides
`a passage for the conductor 4. The guide 2 has a substantially
`cylindrical part 21 extended by a frustoconical part 22 the
`smaller diameter base of which has a diameter equal to that
`of the cylindrical part 21.
`The die 3 surrounds and is coaxial with the guide 2. Its 10
`outside surface is cylindrical and its inside surface 30 has a
`cylindrical part 31 extended by a frustoconical part 32. The
`inside surface 30 of the die 3 defines with the guide 2 a
`cylindrical passage 34 for the insulative material 35 that is
`to constitute the intermediate insulator 5. This insulative
`material 35 comes from the crosshead (not shown) of the
`extrusion device, located downstream of the die-guide
`assembly.
`Openings (not shown in FIG. 2) communicating with the
`passage 34 are formed in the cylindrical part 31 of the die 3 20
`to confer upon the insulative material 35 the shape required
`for the insulator 5 to have a transverse cross-section resem(cid:173)
`bling a spoked wheel. These openings could equally well be
`in the guide 2, but as explained below it is preferable for
`them to be in the die 3.
`To manufacture the insulative intermediate insulator 5
`around the conductor 4, the latter is caused to move in the
`channel 20 in the direction indicated by the arrow Fin FIG.
`2, i.e. in the sense of reducing diameters of the frustoconical
`parts 21 and 31 of the guide 2 and of the die 3, respectively.
`Simultaneously, the insulative material 35 in the viscous
`state is introduced under pressure so that it fills the passage
`34 and the openings in the die 3.
`In accordance with the invention, the material shaped in
`this way does not come into contact with the conductor 4 35
`immediately at the exit 37 from the die 3 (in the direction of
`the arrow F), but at a non-null distance from this exit 37, so
`that it is drawn down before it is applied to the conductor 4.
`It is this drawing down which prevents the walls 53 and 54
`of the cells 52 thinning when the material of which they are 40
`constituted is still viscous, without any pressurization of the
`cells 52 being needed, as in the prior art.
`The distance between the exit 37 from the die 3 and the
`area of contact between the shaped insulator and the con(cid:173)
`ductor 4 depends on the required draw down ratio. For a
`given draw down ratio, it is set by the speed of movement
`of the conductor 4. For example, it can vary between twice
`and 20 times the inside diameter of the die 3.
`In accordance with the invention, the distance between
`the exit 37 of the die 3 and the point of application to the 50
`conductor 4 of the insulator being formed must be such that
`the draw down ratio is at least equal to 25.
`It will be remembered that the draw down ratio (DDR) is
`given by the following formula:
`
`55
`
`6
`than and geometrically similar to that of the empty parts
`defined by the openings through which the material passes
`in the viscous state. In this way, when the openings are in the
`die, which necessarily has a larger surface area than the
`guide, by choosing an appropriate draw down ratio it is
`possible to obtain an intermediate insulator having very
`small dimensions and a low dielectric constant by adjusting
`the size of the openings so that the cells have a large
`cross-section.
`FIG. 4 shows in cross-section the guide 2 and a die 3' of
`the invention. The four openings 38' of the die 3' extend
`longitudinally through its cylindrical part 31 and commu(cid:173)
`nicate with the passage 34. Each of the openings 38' is
`substantially T-shaped with the horizontal bar 39' curved
`15 about the axis Y. They all form part of a common cylinder
`with the same axis Y. The vertical bars 40' of the Ts
`communicate with the passage 34 and lines extending them
`intersect on the axis Y.
`The diameter at the top of the curved horizontal parts 39'
`is 8 mm and their diameter at the base is 6.4 mm, with the
`result that they have a thickness of 0.8 mm.
`The die 3' produces the intermediate insulator 5' shown in
`FIG. 3 when the draw down ratio is 235. FIG. 3 shows that
`the parts of the insulator 5' originating in the horizontal bars
`25 of the Ts 39' have come into contact with each other to form
`the substantially cylindrical exterior tubular part 54' of the
`insulator 5'. This figure also shows that the cross-section of
`the insulator 5' is practically identical to that of the empty
`parts (openings 38' and passage 34) of the die 3', apart from
`30 the fact that the horizontal bars of the Ts have come into
`contact with each other. This occurs if the draw down ratio
`is high, in practise greater than 150. In this case, the volume
`of air present in the insulator 5' can be precisely controlled
`since the insulator is geometrically similar to the empty parts
`of the die 3'. This type of die, used with a high draw down
`ratio, can be used to produce coaxial cables of small size,
`usable in particular in the medical field.
`Accordingly, an intermediate insulator with small dimen(cid:173)
`sions (outside diameter: 0.51 mm) having a low dielectric
`constant (1.57) can be produced.
`FIG. 6 shows the cross-section of the guide 2 and of
`another die 3" of the invention. The five openings 38" of the
`die 3" extend longitudinally through its cylindrical part 31
`and communicate with the passage 34. Each of the openings
`45 38" is substantially T-shape with the horizontal bar 39"
`curved around the axis Y. They all form parts of a common
`cylinder with the same axis Y. The vertical bars 40" of the
`Ts communicate with the passage 34 and lines extending
`them intersect on the axis Y.
`The diameter at the top of the curved horizontal parts 39"
`is 7 mm and their diameter at the base is 4.37 mm, with the
`result that they have a thickness of 1.315 mm, i.e. they are
`much thicker than the curved horizontal parts 39' of the
`openings 38' in the die from FIG. 3.
`The die 3" can be used to produce the intermediate
`insulator 5" shown in FIG. 5 if the draw down ratio is 32.
`FIG. 5 shows not only that the parts of the insulator 5"
`originating in the horizontal bars of the Ts 39" have come
`into contact with each other, but also that they interpenetrate
`60 to form the outside substantially cylindrical tubular part 54"
`of the insulator 5". This figure also shows that the cross(cid:173)
`section of the insulator 5" is somewhat different than that of
`the empty parts (openings 38" and passage 34) of the die 3".
`This occurs when the draw down ratio is lower, in practise
`in the order of 50. In this case, the volume of air in the
`insulator 5" is controlled less precisely, since the insulator is
`no longer geometrically similar to the empty parts of the die
`
`D}-Db
`DDR=--(cid:173)
`D}-D~
`
`where DF is the outside diameter of the openings in the die
`3, DG is the outside diameter of the cylindrical part 21 of the
`guide 2, D1 is the outside diameter of the insulator 5 and D g
`is the outside diameter of the tubular part 51 of the insulator
`5.
`
`Given that the shaped insulative material is drawn down 65
`before it is applied to the conductor 4, the cross-section of
`the intermediate insulator obtained is necessarily smaller
`
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`5,922,155
`
`8
`
`There is claimed:
`1. A method of manufacturing an insulative material
`cellular insulator around a conductor, said insulator having
`a longitudinal passage in which said conductor is housed and
`closed cells extending longitudinally and separated from
`each other by radial walls, said method comprising the
`following steps:
`
`extruding said insulative material in the viscous state to
`impart the required shape to it by means of shaping
`means to form said cells,
`applying said insulative material thus shaped to said
`conductor, and
`cooling said insulative material to obtain said insulator,
`wherein said applying step is performed at a distance from
`the exit of the shaping means such that said material is
`drawn down sufficiently for the walls of the cells not to be
`thinned without pressurizing said cells.
`2. The method claimed in claim 1 wherein said distance
`20 is such that the draw down ratio of said material is at least
`equal to 25.
`3. The method claimed in claim 1 wherein said insulative
`material is a thermoplastics material.
`4. The method claimed in claim 3 wherein said insulative
`material is ethylene and propylene fluoride.
`5. A device for implementing the method claimed in claim
`1 comprising:
`a guide having an interior longitudinal channel through
`which said conductor passes,
`a die coaxial with and around said guide, defining with the
`exterior surface of said guide said cell for passage of
`said insulative material in the viscous state,
`35 and including at least one opening communicating with said
`passage and into which said material in the viscous state can
`be introduced, the position around said passage and the
`shape of said opening(s) being such that on leaving said die
`said material incorporates said cells.
`6. The device claimed in claim 5 wherein said die includes
`a plurality of identical openings disposed symmetrically
`about its longitudinal axis, the cross-section of each of said
`openings having substantially the shape of a T the horizontal
`bar of which is curved about said longitudinal axis, the
`45 curved horizontal bars of the various Ts all forming parts of
`a common cylinder and lines extending their vertical bars
`intersecting on said longitudinal axis.
`
`7
`3". This type of die, used with a lower draw down ratio, is
`intended rather for the manufacture of intermediate insula(cid:173)
`tors having medium dimensions, for coaxial cables used in
`telecommunications.
`Accordingly an intermediate insulator having an outside
`diameter of 1.2 mm and a low dielectric constant (1.56) can
`be obtained.
`The coaxial cables obtained by the method and the device
`of the present invention have electrical specifications that
`satisfy the requirements of the intended applications. Their 10
`impedance is around 75 Q.
`Their intermediate insulators can be stripped as easily as
`from solid insulation. The external cylindrical shape of the
`intermediate insulators is sufficient to enable the outer
`conductor to be cut quickly and precisely. Moreover, these 15
`insulators are homogeneous and free of cracks.
`The cables obtained are resistant to crushing and to
`bending stresses.
`Finally, the method of the invention enables the use of the
`same type of device as those used to extrude solid insulators,
`apart from the machining of the die.
`Of course, the present invention is not limited to the
`embodiments just described.
`Firstly, it can be used not only to manufacture cellular
`insulators of coaxial cables, but also to manufacture cellular
`insulators in all types of cable requiring this type of
`insulator, for example twisted pair or twisted quad cables.
`Moreover, the material used to manufacture the insulator
`can be any type of material that can be extruded, and in
`particular a thermoplastics material, capable of withstanding 30
`draw down ratios of the magnitude of those required to put
`the invention into effect. This can be EPF or ethylene
`tetrafiuoroethylene (ETFE), polyvinylidine difiuoride
`(PVDF) or perfiuoroalkoxy (PFA)® (registered trade mark
`of Du Pont de Nemours).
`The cells can be filled with air or any other gas for
`reducing the dielectric constant of the insulator. In this case
`the extrusion is carried out in an atmosphere of the gas filling
`the cells.
`Moreover, by rotating the die about its longitudinal axis it 40
`is possible to obtain helical cells enabling the cable to
`withstand bending stresses better.
`The openings in the die can have any geometry enabling
`the required insulator shape to be obtained. In particular, the
`die can have an opening having a shape identical to the
`cross-section of the insulator to be manufactured.
`Finally, any means as described can be replaced by
`equivalent means without departing from the scope of the
`present invention.
`
`25
`
`* * * * *
`
`Page 7 of 7 (PGR2021-00078)
`G&H DIVERSIFIED MANUFACTURING, LP v. DYNAENERGETICS EUROPE GMBH
`
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