1E-grade K1-type flooding-resistant cable assembly

Abstract

The invention discloses a 1E-level K1-type flooding-resistant cable assembly, belongs to the field of cables, and solves the problem that an existing cable assembly cannot effectively resist abnormal working conditions under the 1E-level K1-type safety level in an integrated small reactor. According to the technical scheme, the cable assembly mainly comprises a cable main body and a connector; the connector comprises a shell, a metal clamping sleeve and a tail cover, the shell is provided with a plugging end and a tail end, a cavity is formed between the plugging end and the tail end and is filled with inorganic powder, the tail cover is detachably connected with the tail end, the metal clamping sleeve is arranged on the peripheral side of the cable body in a sleeving mode and located between the tail cover and the tail end of the shell, and the metal clamping sleeve is connected with the tail end of the shell. The metal clamping sleeve is inserted between the tail end and the cable main body along with the connection of the tail cover and the tail end so as to seal an assembly gap between the tail end and the cable main body, and the tail cover and the cable main body are in sealed connection through laser welding. The sealing device has better sealing performance and shock resistance.

Description

TECHNICAL FIELD

[0001] The application discloses a 1E-grade K1-type water-flood-resistant cable assembly and belongs to the technical field of cables. BACKGROUND

[0002] In the accident condition of the nuclear power plant heat supply reactor safety shell, the temperature is as high as 354.4 DEG C, the maximum design pressure is 7Mpa, and the maximum irradiation dose is 107 Gray gamma. In the design reference accident condition, the cable assembly also needs to resist the immersion of the solution for 4 months, and if the connector assembly cannot meet the sealing requirement in the accident condition, the instrument signal in the safety shell will fail, and then a safety accident of the nuclear power plant will occur, and even nuclear leakage.

[0003] However, the existing cable assembly cannot effectively solve the problem of abnormal condition resistance under the 1E-grade K1-type safety level in the integrated small reactor, and in the nuclear environment of the integrated small reactor, the cable assembly needs to be used below the water level in the nuclear reactor under the conditions of high temperature, high pressure, high irradiation and vibration, and meet the working requirements of the long-term high temperature and water-flooded immersion environment in the safety shell of the nuclear power plant heat supply reactor. SUMMARY

[0004] The application aims to solve the problem that the existing cable assembly cannot effectively solve the problem of abnormal condition resistance under the 1E-grade K1-type safety level in the integrated small reactor, and provides a 1E-grade K1-type water-flood-resistant cable assembly, which has better sealing performance and shock resistance.

[0005] To solve the above technical problems, the application adopts the following technical scheme:

[0006] A 1E-grade K1-type water-flood-resistant cable assembly comprises:

[0007] A cable main body;

[0008] A connector comprising a shell, a metal sleeve and a tail cover, the shell has a plug-in end and a tail end, the plug-in end and the tail end have a cavity therebetween, the cavity is filled with inorganic powder, the tail cover is detachably connected with the tail end, the cable main body passes through the tail cover and the tail end and extends into the shell and is electrically connected with the plug-in end;

[0009] The metal sleeve is sleeved on the outer circumferential side of the cable main body and is located between the tail cover and the tail end of the shell, the metal sleeve is inserted between the tail end and the cable main body with the connection of the tail cover and the tail end, so as to seal the assembly gap between the tail end and the cable main body, and the tail cover and the cable main body are sealingly connected through laser welding.

[0010] The application has the following beneficial effects:

[0011] The tail cover is detachably connected with the tail end of the shell, the metal sleeve is sleeved on the outer circumferential side of the cable main body and is between the tail cover and the tail end, the metal sleeve is gradually inserted between the cable main body and the tail end along with the connection of the tail cover and the tail end, the metal sleeve is pressed between the tail end and the cable main body by external force during the installation of the tail cover, the metal sleeve can seal the assembly gap between the tail end and the cable main body, and the sealing between the tail end and the cable main body is realized, so that the sealing difficulty between the tail cover and the shell is reduced; in addition, the tail cover and the cable main body are sealed and connected by laser welding, the tail cover and the cable main body can be fixed, the tail cover can stably apply force to the metal sleeve, the possibility of loosening between the metal sleeve and the tail end is reduced, the sealing life between the tail end and the cable main body can be significantly improved, compared with the traditional sealing ring, the metal sleeve has higher high-temperature resistance, in addition, the metal sleeve and the tail cover are tightly combined through the deformation of the metal, and have better sealing performance and water flooding resistance, and are more suitable for extreme abnormal working conditions of a nuclear reactor; secondly, the laser welding has higher high-temperature resistance, reduces the risk of melting at the welding position, and makes the fixation of the tail cover and the cable more firm and reliable, and provides stable support for the combination of the sleeve and the tail end; furthermore, the shell cavity is filled with inorganic powder, the inorganic powder can withstand higher temperature and has better temperature resistance, can also absorb vibration, reduces the impact force on the cable main body in the shell, and improves the anti-vibration performance of the cable.

[0012] Preferably, the metal sleeve is provided with a first insertion end, the outer diameter of the first insertion end gradually decreases as it approaches the insertion end, the tail end is provided with a first insertion slot for the first insertion end, and the structure of the first insertion slot matches that of the first insertion end. According to the above technical scheme, the first insertion end of the metal sleeve is conical, the structure of the first insertion slot of the tail end corresponds to that of the first insertion end, and the metal sleeve is gradually inserted into the first insertion slot under the thrust of the tail cover. The conical structure can make the insertion of the metal sleeve more smooth, and as the insertion depth increases, the force between the metal sleeve and the tail end will also gradually increase, which can play a wedging effect, thereby realizing the tight fixation of the metal sleeve and the tail end and reducing the possibility of loosening of the sleeve. In addition, the first insertion end adopts an inclined surface structure, which can increase the contact area between the first insertion end and the first insertion slot, increase the sealing area between the metal sleeve and the shell, and improve the sealing performance.

[0013] Preferably, the tail cover and the tail end are connected by a thread, and the end of the metal ferrule away from the first insertion end is provided with an abutment end. The inner side of the tail cover is provided with an abutment surface. The connection between the tail cover and the tail end is achieved by pushing the metal ferrule into the space between the tail end and the cable body through the abutment surface. Using the aforementioned technical solution, the threaded connection reduces the difficulty of connecting the tail cover and the tail end of the outer shell. Furthermore, the threaded connection has a self-locking property. As the tail cover is tightened, the force between the tail cover and the metal ferrule increases continuously. The self-locking property of the threaded connection reduces the possibility of the tail cover automatically retracting, ensuring that the tail cover and the outer shell are properly connected. Simultaneously, the tail cover provides stable support for the metal ferrule. Secondly, the abutment surface and the abutment end between the tail cover and the metal ferrule reduce the possibility of the metal ferrule deflecting during insertion, ensuring a tight fit between the first insertion end and the first slot.

[0014] Preferably, the metal sleeve comprises a split first component and a second component. The first insertion end is located on the outer periphery of the first component. The second component has a second insertion end near the end of the first component and an abutment end facing away from the first component. The outer diameter of the second insertion end gradually decreases along the insertion direction of the metal sleeve. The first component has a second slot for the second insertion end to be inserted. By adopting the aforementioned technical solution, the metal sleeve is divided into a first component and a second component, and the first component and the second component are respectively provided with a second slot and a second insertion end. The first component and the second component also have a wedging effect through the second slot and the second insertion end, which can further reduce the external force required between the metal sleeve insertion end and the cable body, and can significantly reduce the assembly difficulty of the tail cover.

[0015] Preferably, the end of the tail cover furthest from the outer casing is provided with a guide ring. The guide ring extends along the length of the cable body, and the end of the guide ring furthest from the outer casing is sealed to the surface of the cable body by laser welding. Using the aforementioned technical solution, the guide ring can guide the tail cover during installation, allowing it to move along the correct path and preventing misalignment at the connection between the tail cover and the tail end, thus making the connection between the tail cover and the tail end more precise and reliable.

[0016] Preferably, the outer shell further includes a sleeve, the cavity is disposed inside the sleeve, the plug end is inserted into the sleeve and forms a seal at one end of the sleeve, and the plug end and the sleeve are sealed together by laser welding.

[0017] Preferably, the plug-in terminal is provided with a contact element, and the core wires within the cable body are electrically connected to the contact element through crimping and laser welding. Using the aforementioned technical solution, the core wires and contact elements are first crimped using crimping pliers, and then connected using laser welding. This makes the connection between the core wires and contact elements more secure. Furthermore, laser welding has high high-temperature resistance, reducing the risk of the welded area between the core wires and contact elements melting under high-temperature conditions, making the cable suitable for the extreme operating environments of nuclear reactors.

[0018] Preferably, the cable body comprises, from the inside out, a core wire, an insulation layer, a shielding layer, another insulation layer, and a metal sheath layer.

[0019] Preferably, the insulating layer is made of silicon dioxide; the shielding layer is made of copper; the shielding layer is located between the two insulating layers; and the metal sheath layer is made of stainless steel. Using the aforementioned technical solution, silicon dioxide insulators possess excellent flame-retardant, high-temperature resistant, low-smoke, and halogen-free properties, and have extremely high resistivity and a stable molecular structure, making it difficult for charges to flow on their surface, thus maintaining excellent insulation performance even at high temperatures.

[0020] Other features and advantages of the present invention will be disclosed in detail in the following detailed description and accompanying drawings. Attached Figure Description

[0021] The invention will be further described below with reference to the accompanying drawings:

[0022] Fig. 1 This is a cross-sectional view of the Class 1E K1 water-resistant cable assembly of the present invention;

[0023] Fig. 2 This is a cross-sectional view of the metal ferrule in the Class 1E K1 water-resistant cable assembly of the present invention;

[0024] Fig. 3 This is a cross-sectional view of the cable body in the Class 1E K1 water-resistant cable assembly of the present invention.

[0025] Reference numerals: 1. Cable body; 11. Core wire; 12. Insulation layer; 13. Shielding layer; 14. Metal sheath layer; 2. Outer shell; 21. Plug end; 211. Contact element; 212. Pin; 22. Tail end; 221. First slot; 23. Sleeve; 231. Cavity; 3. Tail cover; 31. Guide ring; 4. Metal ferrule; 41. First component; 411. First plug end; 412. Second slot; 42. Second component; 421. Abutment part; 422. Second plug end. Detailed Implementation

[0026] The technical solutions of the embodiments of the present invention will be explained and described below with reference to the accompanying drawings. However, the following embodiments are only preferred embodiments of the present invention and not all of them. Other embodiments obtained by those skilled in the art based on the embodiments in the implementation methods without creative effort are all within the protection scope of the present invention.

[0027] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0028] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0029] like Figs. 1 to 3 As shown in the figure, this embodiment demonstrates a Class 1E K1 water-resistant cable assembly, including a cable body 1 and a connector. The connector includes a housing 2, a metal sleeve 4, and a tail cover 3. The housing 2 includes a sleeve 23, a plug end 21, and a tail end 22. The plug end 21 and the tail end 22 are located at the two ends of the sleeve 23, respectively. The sleeve 23 has a cavity 231 inside, which is located between the plug end 21 and the tail end 22. The tail cover 3 is detachably connected to the tail end 22, and both the tail cover 3 and the tail end 22 are provided with through holes for the cable body 1 to pass through. After passing through the tail cover 3 and the tail end 22, the cable body 1 extends into the cavity 231 and is electrically connected to the plug end 21.

[0030] In this embodiment, the metal sleeve 4 is fitted onto the outer periphery of the cable body 1, and the metal sleeve 4 is located between the tail cover 3 and the tail end 22 of the outer shell 2. During the connection process between the tail cover 3 and the tail end 22 of the outer shell 2, the gap between the tail cover 3 and the tail end 22 gradually decreases. At this time, the tail cover 3 will push the metal sleeve 4 to be inserted between the tail end 22 and the cable body 1 to seal the assembly gap between the tail end 22 and the cable body 1. After the tail cover 3 and the tail end 22 are connected in place, the end of the tail cover 3 away from the sleeve 23 is sealed to the cable body 1 by laser welding.

[0031] In this embodiment, the tail cover 3 and the tail end 22 of the outer shell 2 are detachably connected. The metal ferrule 4 is fitted onto the outer periphery of the cable body 1 and positioned between the tail cover 3 and the tail end 22. As the tail cover 3 and the tail end 22 are connected, the metal ferrule 4 is gradually inserted between the cable body 1 and the tail end 22. The external force used during the installation of the tail cover 3 presses the metal ferrule 4 into the space between the tail end 22 and the cable body 1, allowing the metal ferrule 4 to seal the assembly gap between the tail end 22 and the cable body 1, thereby achieving a seal between the tail end 22 and the cable body 1 and reducing the difficulty of sealing between the tail cover 3 and the outer shell 2. Furthermore, the tail cover 3 and the cable body 1 are sealed together using laser welding, which can fix the tail cover 3 and the cable body 1, allowing the tail cover 3 to stably apply force to the metal ferrule 4, reducing the possibility of loosening between the metal ferrule 4 and the tail end 22, and significantly improving the sealing performance of the tail end 22. The sealing life between the ferrule 2 and the cable body 1 is improved. Compared with traditional sealing rings, the metal ferrule 4 has higher high-temperature resistance. In addition, the metal ferrule 4 and the tail cover 3 are tightly bonded by the deformation between the metals, and the leakage rate can reach 1×10-9 Pa•m3 / s. It can work under an ambient pressure of 10MPa and has better sealing performance, making it more suitable for the extreme abnormal conditions of nuclear reactors. Secondly, laser welding has higher high-temperature resistance, reducing the risk of melting at the welding position, making the fixation of the tail cover 3 and the cable more firm and reliable, and providing stable support for the combination of the ferrule and the tail end 22. Furthermore, the cavity 231 of the outer shell 2 is filled with inorganic powder. Inorganic powder can withstand higher temperatures and has better temperature resistance. At the same time, it can also absorb vibration, reduce the impact force on the cable body 1 inside the outer shell 2, and thus improve the shock resistance of the cable.

[0032] Specifically, such as Fig. 1 and Fig. 2As shown, in this embodiment, the metal sleeve 4 has a first insertion end and a contact end. The contact end is located at the end of the metal sleeve 4 facing the tail cover 3, and the first insertion end is located at the end of the metal sleeve 4 facing the outer shell 2. The outer diameter of the first insertion end gradually decreases as it approaches the contact end 21. The tail end 22 has a first slot 221 for the first insertion end to be inserted. The structure of the first slot 221 matches the structure of the first insertion end. The first insertion end of the metal sleeve 4 is tapered, and the structure of the first slot 221 at the tail end 22 corresponds to that of the first insertion end. The tail cover 3 pushes... Under the action of force, the metal sleeve 4 is gradually inserted into the first slot 221. The conical structure makes the insertion of the metal sleeve 4 smoother. As the insertion depth increases, the force between the metal sleeve 4 and the tail end 22 also gradually increases, which can play a wedge-tightening role, thereby achieving a tight fixation between the metal sleeve 4 and the tail end 22 and reducing the possibility of the sleeve loosening. In addition, the first insertion end 411 adopts a beveled structure, which can increase the contact area between the first insertion end 411 and the first slot 221, increase the sealing area between the metal sleeve 4 and the outer shell 2, and improve the sealing performance.

[0033] Specifically, in this embodiment, the tail cover 3 and the tail end 22 of the outer shell 2 are threadedly connected. The outer surface of the tail end 22 is provided with external threads. The tail cover 3 includes a connecting sleeve with internal threads. The inner diameter of the connecting sleeve is larger than the outer diameter of the metal ferrule 4, and the axial length of the connecting sleeve is larger than the axial length of the metal ferrule 4. When the tail cover 3 and the tail end 22 are initially connected, the metal ferrule 4 has not yet been compressed. In addition, the inner side of the tail cover 3 is provided with an abutting surface opposite to the abutting end of the metal ferrule 4. As the tail cover 3 is tightened, the distance between the tail cover 3 and the tail end 22 continuously decreases. At this time, the tail cover 3 pushes the metal ferrule 4 towards the tail end 22 through the abutting surface and the abutting end, so that the first insertion end 411 is inserted into the first slot. Within 221, the assembly gap between the tail end 22 and the cable body 1 is sealed. The use of threaded connection can reduce the connection difficulty between the tail cover 3 and the tail end 22 of the outer shell 2. In addition, the threaded connection has a self-locking performance. As the tail cover 3 is tightened, the force between the tail cover 3 and the metal ferrule 4 will continue to increase. The self-locking performance of the threaded connection can reduce the possibility of the tail cover 3 automatically retracting, so that the tail cover 3 and the outer shell 2 can be connected in place. At the same time, the tail cover 3 can also provide stable support for the metal ferrule 4. Secondly, the tail cover 3 and the metal ferrule 4 abut against each other through the abutting surface and the abutting end, which can reduce the possibility of the metal ferrule 4 being deflected during the insertion process, and ensure that the first insertion end 411 and the first slot can form a tight fit.

[0034] Specifically, in this embodiment, the metal sleeve 4 includes a first component 41 and a second component 42. The first component 41 and the second component 42 are separate structures. The first insertion end is located on the outer periphery of the first component 41. The end of the second component 42 near the first component 41 is provided with a second insertion end, and the end facing away from the first component 41 is the abutment end. The outer diameter of the second insertion end gradually decreases along the insertion direction of the metal sleeve 4. The first component 41 is provided with a second slot 412 for the second insertion end to be inserted, dividing the metal sleeve 4 into the first component 41 and the second component 42. The first component 41 and the second component 42 are respectively provided with a second slot 412 and a second insertion end 422. The first component 41 and the second component 42 also play a wedge-tightening role through the second slot 412 and the second insertion end 422, which can further reduce the external force required between the metal sleeve 4 insertion tail end 22 and the cable body 1, and can significantly reduce the assembly difficulty of the tail cover 3.

[0035] It is understandable that the metal sleeve 4 described in other embodiments is also a one-piece structure.

[0036] Specifically, in this embodiment, the end of the tail cover 3 away from the outer shell 2 is provided with a guide ring. The guide ring extends along the length of the cable body 1. After the tail cover 3 is connected to the tail end 22, the end of the guide ring away from the outer shell 2 is sealed to the surface of the cable body 1 by laser welding. After welding, mirror polishing is performed to remove laser welding marks, which can hide assembly marks and make the connection between the connector and the cable body 1 more integrated. In addition, the guide ring can play a guiding role during the installation of the tail cover 3, so that the tail cover 3 can move along the correct path and prevent the connection between the tail cover 3 and the tail end 22 from being skewed, making the connection between the tail cover 3 and the tail end 22 more accurate and reliable.

[0037] Specifically, in this embodiment, the tail end 22 and the sleeve 23 are an integral structure, while the plug end 21 and the sleeve 23 are separate structures. The plug end 21 is connected to the sleeve 23 by plugging. After the plug end 21 and the sleeve 23 are plugged in, laser welding is used to achieve a sealed connection between the plug end 21 and the sleeve 23, thereby sealing the end of the sleeve 23. The laser-welded connector can work under an ambient pressure of 8MPa, and after processing, there are only slight welding marks, which can improve the overall appearance of the connector. In addition, the traditional soldering process can only withstand a temperature of about 350°C, while the temperature of the accident conditions in a nuclear reactor is as high as 354.4°C. Therefore, the soldering process cannot withstand the highest temperature of the accident conditions, resulting in the risk of the solder melting. The high temperature that laser welding can withstand exceeds the highest temperature of the accident conditions in a nuclear reactor, thus significantly reducing the risk of solder melting and giving the connector a longer service life.

[0038] Specifically, in this embodiment, the plug-in end 21 is provided with a contact 211. The core wire 11 in the cable body 1 is electrically connected to the contact 211 by crimping and laser welding. The core wire 11 and the contact 211 are first crimped with crimping pliers and then connected by laser welding. This makes the connection between the core wire 11 and the contact 211 more secure. At the same time, the use of laser welding has high high temperature resistance, which can reduce the risk of the weld position between the core wire 11 and the contact 211 melting in high temperature conditions, making the cable suitable for the extreme operating environment of nuclear reactors.

[0039] Specifically, such as Fig. 3 As shown, in this embodiment, the cable body 1, from the inside out, includes a core wire 11, an insulation layer 12, a shielding layer 13, an insulation layer 12, and a metal sheath layer 14. The insulation layer 12 is made of silicon dioxide; the shielding layer 13 is made of copper; the shielding layer 13 is located between the two insulation layers 12; and the metal sheath layer 14 is made of stainless steel. Using the aforementioned technical solution, silicon dioxide insulators possess excellent flame retardant, high temperature resistance, low smoke, and halogen-free properties. Furthermore, they have extremely high resistivity, a stable molecular structure, and make it difficult for charges to flow on their surface, thus maintaining excellent insulation performance even at high temperatures.

[0040] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that the present invention includes, but is not limited to, the contents described in the accompanying drawings and the specific embodiments above. Any modifications that do not depart from the functional and structural principles of the present invention will be included within the scope of the claims.

Claims

1. A Class K1 water-resistant cable assembly of grade 1E, characterized in that, include: Cable body; A connector comprising a housing, a metal ferrule, and a tail cover, the housing having a plug end and a tail end, a cavity between the plug end and the tail end being filled with inorganic powder, the tail cover being detachably connected to the tail end, and a cable body extending through the tail cover and the tail end into the housing and electrically connected to the plug end. The metal ferrule is fitted onto the outer periphery of the cable body and is located between the tail cover and the tail end of the outer shell. The metal ferrule is inserted between the tail end and the cable body as the tail cover is connected to the tail end, so as to seal the assembly gap between the tail end and the cable body. The tail cover and the cable body are sealed together by laser welding.

2. The Class 1E K1 water-resistant cable assembly according to claim 1, characterized in that, The metal sleeve is provided with a first insertion end, the outer diameter of which gradually decreases as it approaches the insertion end, and the tail end is provided with a first slot for the first insertion end to be inserted into, the structure of which matches the first insertion end.

3. A Class 1E K1 water-resistant cable assembly according to claim 2, characterized in that, The tail cover and the tail end are connected by a thread. The end of the metal ferrule away from the first insertion end is provided with an abutment end. The inner side of the tail cover is provided with an abutment surface. The tail cover and the tail end are connected by pushing the metal ferrule into the space between the tail end and the cable body through the abutment surface.

4. A Class 1E K1 water-resistant cable assembly according to claim 3, characterized in that, The metal sleeve includes a first component and a second component that are separate. The first insertion end is located on the outer periphery of the first component. The second component has a second insertion end at the end near the first component and an abutment end at the end opposite to the first component. The outer diameter of the second insertion end gradually decreases along the insertion direction of the metal sleeve. The first component has a second slot for the second insertion end to be inserted.

5. A Class 1E K1 water-resistant cable assembly according to claim 1, characterized in that, The end of the tail cover away from the outer shell is provided with a guide ring. The guide ring extends along the length of the cable body. The end of the guide ring away from the outer shell is sealed to the surface of the cable body by laser welding.

6. A Class 1E K1 water-resistant cable assembly according to claim 1, characterized in that, The outer shell also includes a sleeve, the cavity is disposed inside the sleeve, the plug end is inserted into the sleeve and forms a seal at one end of the sleeve, and the plug end and the sleeve are sealed together by laser welding.

7. A Class 1E K1 water-resistant cable assembly according to claim 1, characterized in that, The plug-in terminal is provided with a contact element, and the core wires in the cable body are electrically connected to the contact element by crimping and laser welding.

8. A Class 1E K1 water-resistant cable assembly according to claim 1, characterized in that, The cable body, from the inside out, includes a core wire, an insulation layer, a shielding layer, an insulation layer, and a metal sheath layer.

9. A Class 1E K1 water-resistant cable assembly according to claim 8, characterized in that, The insulating layer is made of silicon dioxide; the shielding layer is made of copper; the shielding layer is located between the two insulating layers; and the metal sheath layer is made of stainless steel.

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