Cable termination device

Abstract

The invention relates to a cable termination device (2) for a cable (1) of the type comprising at least one conductor wire (11) extending inside an outer sheath (10), a refractory insulator such as a mineral insulator (12) being disposed between the conductor wire(s) (11) and the outer sheath (10), said device comprising a metal insert (21) for fixing to the outer sheath (10) at the end of a cable (1), a metal insert (22) for fixing to a portion of the stripped end (11a) of the conductor wire(s) (11) of the cable, and a sleeve (20) extending between the two metal inserts (21, 22). The invention consists in that the sleeve (20) is made of a thermoplastic polymer material and is hermetically sealed by overmolding onto at least a portion of the metal inserts (21, 22). Figure 1.

Description

Title of the invention: Cable termination device

[0001] The present invention relates to a cable termination device for ensuring the sealing of the end of the cable and to a cable provided with such a device.

[0002] A shielded cable typically consists of one or more conductors surrounded by a layer of refractory insulation in the form of a compacted mineral powder (for example, magnesia (MgO), silica (SiO2), alumina (Al2O3)) with or without salt impregnation. The assembly is enclosed in at least one sealed sheath, generally made of metal. This sheath is conventionally made of stainless steel, metal alloys such as those known under the trade name Inconel, nickel, or high-temperature resistant refractory alloys, in order to withstand high temperatures during manufacturing and use.

[0003] The conductor wire(s) are made of a metal chosen according to the application requirements, for example, to obtain a specific resistivity. They are electrically insulated from the cable sheath by a mineral refractory insulator. To connect cables together, termination devices are used to ensure a watertight seal at the cable end, thus maintaining electrical insulation between the exposed end of the conductor wire and the outer metallic sheath.

[0004] Numerous termination devices are available on the market capable of meeting this need to create a watertight seal. Generally, the watertightness of cable terminations is achieved using a hermetic ceramic-metal bond, also called a ceramic / metal interface, or by depositing resin at the end of the cable.

[0005] Such a watertight passage therefore consists of a ceramic element comprising a passage in which a metallic insert is fixed in the form of an internal metallic tubular sheath into which the bare conductor wire of a cable can be inserted and secured. The passage further comprises a metallic tubular sleeve or sheath, one end of which is fixed to the outer periphery of the tubular ceramic element and the other end of which can be fixed to a metallic insert forming a connecting piece mounted on the end of a cable on its outer sheath.

[0006] Such ceramic / metal connections, once the cable end is stripped and inserted, ensure electrical insulation of the central conductor(s) from the outer sheath and guarantee moisture tightness. Depending on the cable's operating environment, this watertight ceramic / metal connection must be able to withstand operating temperatures up to +260°C peak, with a compact design. In particular, these connector or termination devices can be used for overheat detection cables intended for aeronautical market.

[0007] However, these ceramic / metal sealed passages have drawbacks, particularly their high cost. Furthermore, the metal inserts used are made of an iron / nickel alloy (ferronickel) to facilitate assembly with the ceramic, but this alloy presents a risk of oxidation over time, generating contact resistance which, if excessive, disrupts the function of overheat detectors by masking the alarms.

[0008] In order to overcome these drawbacks, the invention aims to provide a cable termination device of the type comprising at least one conductor wire extending inside an outer sheath, a refractory insulator such as a mineral insulator being disposed between the conductor wire(s) and the outer sheath, said device comprising: a metal insert designed to be fixed to the outer sheath at the end of a cable, a metal insert intended to be fixed on a part of the bare end of the cable conductor wire(s) and a sleeve extending between the two metal inserts, characterized in that the sleeve is made of a thermoplastic polymer material and assembled in a hermetic manner by overmolding on at least a part of the metal inserts.

[0009] Thus, advantageously, the invention proposes a termination device which allows assembly of the sleeve by overmolding which leads to a lighter structure, reduced bulk, simplified manufacturing because no longer requiring welding / brazing operations and therefore a lower cost.

[0010] Furthermore, in the device according to the invention, the seal between the inserts and the sleeve is ensured by the thermomechanical compression of the thermoplastic polymer material onto the metal inserts during overmolding. It is therefore no longer necessary to select metal inserts made of a specific material that promotes brazing.

[0011] Thus, the termination device according to the invention is mounted at the end of a cable whose conductor wire(s) have been stripped, that is to say that the outer sheath, for example metallic, as well as the mineral insulation surrounding the conductor wire(s) are removed to expose said conductor wire(s).

[0012] The metal inserts are cylindrical in shape, one in particular consisting of a ring of suitable dimensions to allow its engagement on the sheath, preferably metallic, outside the end of a cable, while the other metal insert is in the form of at least one metal tube whose dimensions are suitable to allow the engagement of a stripped conductor wire of the cable, the walls of the two metal inserts preferably being of a thickness less than The thickness of the sleeve wall. The plastic sleeve extends between the two metal inserts and ensures a seal between the cable end and the bare wire. When the cable has multiple conductors, the metal insert comprises several metal tubes, one for each conductor.

[0013] The seal between the sleeve and the metal inserts is ensured by the thermomechanical compression of the thermoplastic polymer material on the outer periphery of the cylindrical metal inserts.

[0014] In order to promote the sealing of the fixing of the thermoplastic polymer material on the metal inserts, the latter may include, provided in relief at their periphery, anchoring means for the thermoplastic polymer material such as at least one radially projecting collar, at least one rib, at least one groove, promoting the sealing fixing by thermomechanical compression of said thermoplastic polymer material on the metal inserts.

[0015] Advantageously, the device according to the invention ensures moisture tightness of the exposed end of the cable, electrical insulation between the conductor wire and the outer sheath of the cable, and offers a wider choice of materials for manufacturing the metallic inserts. Furthermore, it guarantees a watertight connection with another cable. Advantageously, these metallic inserts are made of nickel or stainless steel. These materials are highly resistant to corrosion, unlike the ferronickel bases used in ceramic-to-metal transitions, which oxidize over time and generate contact resistance that masks alarms.

[0016] Furthermore, the device according to the invention has a principal shape conferred by the shape of the sleeve overmolded onto the inserts. The device is thus similar in shape and dimensions to previous devices such as ceramic watertight passages. This shape is compact, with similar form and dimensions.

[0017] According to a preferred embodiment, the thermoplastic polymer material is selected from high-performance polymer materials and exhibits thermal resistance up to a temperature of 300°C. A termination device according to the invention is thus advantageously usable under critical temperature operating conditions.

[0018] In particular, a termination device according to the invention can be used in environments in which the conditions of use impose, for example, an operating temperature between -60°C and +150°C, continuously and with peaks up to 260°C, as is the case in the field of aeronautical application.

[0019] Preferably, the thermoplastic polymer material is a high-performance, thermostable, semi-crystalline polymer, in particular chosen from polyaryletherketones which have the following characteristics: - high mechanical properties in a temperature range from -100 °C to the glass transition temperature of said polymer between 132 °C and 187 °C; - a maximum operating temperature in continuous service without mechanical stress of 260°C; - excellent fire resistance; - good chemical resistance.

[0020] These materials can also be of the type reinforced / loaded with glass or carbon fibers.

[0021] Even more preferably, such a thermoplastic polymer material is polyetheretherketone known by the acronym PEEK (corresponding to the initials of its designation in English PolyEtherEtherKetone).

[0022] Advantageously, PEEK is a semi-crystalline, thermostable polymer material with low sensitivity to humidity. It is resistant to aggressive thermal, mechanical, and chemical environments. Furthermore, PEEK possesses excellent mechanical strength characteristics such as: - tensile strength (90 MPa or more) - high modulus of elasticity - high hardness - impact resistance - resistance to flaking.

[0023] It also exhibits high resistance to bending and compressive stresses, which advantageously allows it to be used in situations requiring high stability.

[0024] In a very advantageous way, PEEK also has a high shrinkage coefficient which makes it possible to guarantee the sealing between the parts of the device ensured by the thermomechanical compression of PEEK on the metal inserts.

[0025] PEEK is a heat-resistant thermoplastic polymer material that can be used at 260°C for 5000 hours without any change in its performance. PEEK has a long service life, even in the most demanding environments. It therefore exhibits the following properties: - Long-term thermal resistance: 260°C - Short-term thermal resistance: 300°C - Glass transition point: 150°C - Melting point: 341°C -HDT-A thermal deformation temperature: 162°C - Flame resistance: UL94 V-0

[0026] Once assembled, the molded sleeve can be protected by a nut placed on top which creates an additional thermal barrier and thus limits the impact of temperature.

[0027] The invention also relates to a method for manufacturing a termination device according to the invention, comprising the following steps: - Two metal inserts are mounted on a support that allows their spatial position to be fixed. - the support carrying the two metal inserts is positioned in a half-shell mold whose shape corresponds to the shape of a sleeve whose ends extend around part of the metal inserts, - a thermoplastic polymer material is injected under pressure into the mold at high temperature, the thermoplastic polymer material being injected onto a portion of the metal inserts to be overmolded there, the mold having been preheated, - the mold is cooled and removed

[0028] Preferably, the mold is opened once the cooling at the core of the injected part is sufficient.

[0029] During the injection of the thermoplastic polymer material, the flow of the polymer material must be symmetrical to the longitudinal axis of the sleeve being produced in order to avoid ovalization of said sleeve, which could lead to uneven shrinkage of the material and potentially create a risk of leakage. Furthermore, according to a preferred shape, the metal inserts then have a form that does not disrupt the flow of the polymer material.

[0030] Furthermore, the walls of the metal inserts are thinner than the thickness of the material deposited around said walls and therefore of the sleeve thus formed, which promotes compatible cooling at the metal-polymer interface. Preferably, the cylindrical metal inserts have a thin wall whose thickness is less than the wall thickness of the sleeve.

[0031] Once the termination device thus manufactured, for example with PEEK, is made, its helium tightness is checked with a test to verify its airtightness, the leakage criterion being less than 3.108 mbar.ls*. A termination device according to the invention made with PEEK can thus exhibit airtightness in use in the aeronautical field for a period of 60,000 flight hours.

[0032] The invention also relates to a cable of the type consisting of one or more metallic conductor wires and at least one hollow, cylindrical outer sheath, a powdered refractory insulator such as a mineral insulator being present between the conductor wire(s) and said outer sheath, characterized in that it comprises, at a bare end of said cable, a termination device according to the invention, consisting of a metallic insert fixed to the outer sheath of the cable, a metallic insert intended to be fixed to the bare end of the conductor wire(s) and a sleeve extending between the two metal inserts, made of a thermoplastic polymer material and sealed onto the metal inserts by overmolding.

[0033] The cable according to the invention may have an outer metal sheath and the metal insert is fixed by brazing or welding to said outer sheath.

[0034] Alternatively, the cable may have a non-metallic outer sheath, in which case a metallic interface piece is attached to this outer sheath, thus allowing the metallic insert of the termination device to be fixed by brazing or welding to said metallic interface piece of the cable (for example, for a cable with a PVC sheath, the latter is then fitted at the end with a metallic housing onto which the termination device is attached).

[0035] The invention will now be described in more detail with reference to the drawing in which the figures represent:

[0036] [Fig.1] a schematic longitudinal cross-sectional view of a cable equipped with a termination device according to the invention;

[0037] [Fig.2] a longitudinal cross-sectional view of a device according to the invention.

[0038] As can be seen in the figures, a mineral-insulated shielded cable 1 is consisting of one or more central metallic conductor wires 11 and at least one hollow, cylindrical and sealed outer metallic sheath 10, a powdered refractory insulator 12 such as mineral magnesia MgO, alumina Al2O3, silica SiO2 or any other suitable mineral insulator being introduced between the conductor wire(s) 11 and said outer sheath 10. It is possible to provide internal sheaths between the wire(s) and the outer sheath.

[0039] The outer sheath 10 is metallic, such as stainless steel, copper, nickel, nickel-chromium, a NiCr5Fe alloy known by the trade name Inconel 600, platinum, tantalum, or any other metallic material or alloy, particularly refractory metals or metal alloys resistant to high temperatures, especially those resistant to high temperatures exceeding 800°C and up to 1200°C during their manufacture and use. Thus, depending on the type of sheath and conductor, the heat treatments are generally between 800°C and 1200°C. For cables used as overheat detection cables, which contain eutectic salts that must not degrade, the temperature is limited to approximately 100°C above the detection threshold, i.e., generally between approximately 150°C and 300°C.

[0040] The metallic conducting wire(s) 11 are made, for example, of nickel-chromium, copper, iron, platinum, a metallic alloy consisting mainly of copper and nickel known by the trade name Constantan, or of thermoelectric wires. The material is chosen according to the requirements of the application to obtain a determined resistance or to provide a determined electromotive force.

[0041] The end of such a shielded cable is connected to a termination device for said cable, enabling it to be connected to another cable or device. For this purpose, the end of the cable 1 is stripped, i.e., the outer metal sheath 10 and the mineral insulation 12 surrounding the conductor 11 are removed to expose said conductor 11, the stripped end of which can then be connected to the conductor of another cable, for example.

[0042] In order to make this connection, a termination device 2 is installed at the end of the cable 1, comprising in particular a metal insert 21 fixed to the end of the cable 1 on the outer sheath 10. This metal insert 21 consists of a ring fixed by brazing B or welding to the outer metal sheath 10 of the cable 1.

[0043] The termination device 2 further comprises a metal insert 22 intended to be mounted on the bare end 1la of the metal wire 11. This metal insert 22 is in the form of a metal tube whose dimensions are suitable to allow the engagement of the conductor wire 11. The conductor wire 11 is fixed in the insert 22 by a weld S also at its end.

[0044] The termination device 2 further comprises a plastic material sleeve 20 extending between the two metal inserts 21 and 22, the attachment of said sleeve 20 to the metal inserts 21, 22 being watertight.

[0045] The sleeve 20 is thus made of a plastic material, such as a high-performance polymer material, which has long-term thermal resistance up to 260°C and short-term thermal resistance up to a temperature of 300°C and whose melting point is preferably above 300°C.

[0046] A material of this type can thus be used in environments in which the conditions of use impose an operating temperature between -60°C and +150°C, continuously with peaks up to 260°C.

[0047] Preferably, the material is polyetheretherketone known by the acronym PEEK, (corresponding to the English term polyetheretherketone) which is a thermostable semi-crystalline thermoplastic.

[0048] The termination device 2 must ensure electrical insulation between the central conductor wire 11 and the outer sheath 10 of the shielded cable 1, and exhibit high hermeticity, the leakage criterion being less than 3.108 mbar.ls-1 during a helium leak test.

[0049] The termination device according to the invention is made by overmolding the two metal inserts 21, 22, which are positioned on a support to fix their spatial position in which they are axially aligned. This assembly is then mounted in a half-shell mold whose shape corresponds to the sleeve 20. The PEEK is then injected under pressure into the mold at high temperature, typically around 370°C for PEEK, the mold itself being preheated to at least 170°C.

[0050] Once the PEEK injection has been completed, the mold is cooled and removed. The seal between the metal inserts 21, 22 and the sleeve 20 is ensured by the thermomechanical compression of the PEEK onto the metal inserts 21, 22, the outer periphery of which is most often smooth.

[0051] In the example presented, in order to promote the sealing of the fixing of the PEEK on the metal inserts 21, 22, the latter have at their periphery anchoring means such as radially projecting collars 21a, 22a promoting the sealing fixing by thermomechanical compression on the inserts 21, 22 of the PEEK which has a high shrinkage coefficient.

[0052] Once the PEEK injection has been completed, the mold is then cooled, opened and the device removed.

Claims

Demands

1. Termination device (2) for cable (1) of the type comprising at least one conductor wire (11) extending inside an outer sheath (10), a refractory insulator such as a mineral insulator (12) being disposed between the conductor wire(s) (11) and the outer sheath (10), said device comprising a metal insert (21) for fixing to the outer sheath (10) at the end of a cable (1), a metal insert (22) for fixing to a portion of the stripped end (1la) of the conductor wire(s) (11) of the cable and a sleeve (20) extending between the two metal inserts (21, 22), characterized in that the sleeve (20) is made of a thermoplastic polymer material and is hermetically sealed by overmolding onto at least a portion of the metal inserts (21, 22).

2. Device according to claim 1, characterized in that the metal inserts (21, 22) are cylindrical in shape, one (21) consisting of a ring is of suitable dimensions to allow its engagement on the outer sheath (10) at the end of a cable (1) while the other metal insert (22) is in the form of a metal tube whose dimensions are suitable to allow the engagement of a conductor wire (11) stripped from the cable (1), the walls of the two metal inserts (21, 22) preferably being of a thickness less than the thickness of the wall of the sleeve (20).

3. Device according to claim 1 or 2, characterized in that the metal inserts (21, 22) have raised features at their periphery providing anchoring means for the thermoplastic polymer material such as at least one radially projecting collar (21a, 22a), at least one rib, at least one groove (21b), promoting the tight fixing by thermomechanical compression of said thermoplastic polymer material on the metal inserts (21, 22).

4. Device according to any one of claims 1 to 3, characterized in that the metal inserts (21, 22) are made of nickel, or stainless steel.

5. Device according to any one of claims 1 to 4, characterized in that the thermoplastic polymer material is selected from high-performance polymer materials and exhibits thermal resistance up to a temperature of 300°C.

6. Device according to any one of claims 1 to 5, characterized in that the thermoplastic polymer material is a high-performance, thermostable, semi-crystalline polymer, preferably selected from polyaryl-therketones.

7. Device according to claim 6, characterized in that the thermoplastic polymer material is polyetheretherketone.

8. A method for manufacturing a termination device according to any one of claims 1 to 7, comprising the following steps: - two metal inserts (21, 22) are mounted on a support enabling their spatial position to be fixed, - the support carrying the two metal inserts (21, 22) is positioned in a half-shell mold whose shape corresponds to the shape of a sleeve whose ends extend around a part of the metal inserts (21, 22), - a thermoplastic polymer material is injected under pressure into the mold and at high temperature, the thermoplastic polymer material thus being injected onto a part of the metal inserts to be overmolded thereon, the mold having been preheated, - the mold is cooled and removed.

9. Shielded cable (1) of the type consisting of one or more metallic conductor wires (11) and at least one hollow outer sheath (10), cylindrical, a powdered refractory insulator such as a mineral insulator (12) being present between the conductor wire(s) (11) and said outer sheath (10), characterized in that it comprises at a bare end of said cable (1), a termination device according to any one of claims 1 to 7.

10. Cable (1) according to claim 9, characterized in that the outer sheath (10) is metallic and the metallic insert (21) of the termination device 2 is fixed by brazing or welding to said outer sheath (10).

11. Cable (1) according to claim 9, characterized in that the outer sheath (10) is non-metallic, a metallic interface piece is attached to said outer sheath (10), the metallic insert (21) of the termination device (2) being fixed by brazing or welding to said metallic interface piece.

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