A ceramic sealing head structure of a two-core armored heat tracing cable and a preparation method thereof

Abstract

The application discloses a ceramic sealing head structure of a two-core armored heat tracing cable and a preparation method thereof, and comprises a lead-out pipe, a sealing ceramic, a metal shell, a core wire separation ceramic and a fixing ceramic. The lead-out pipe is in sealing connection with the sealing ceramic, the sealing ceramic is internally provided with two groups of independent guide channels, two conductive core wires independently pass through the corresponding guide channels, the core wire separation ceramic is arranged in the metal shell, the fixing ceramic is arranged between the core wire separation ceramic and the armored metal sheath, and the lead-out pipe and the sealing ceramic, the sealing ceramic and the metal shell and the metal shell and the armored metal sheath are all in sealing connection through high-temperature brazing filler metal. Three continuous inorganic hard brazing nodes are used to build a full-inorganic sealing link with a closed head and tail, so that the defects of high-temperature failure, outgassing and thermal cycle debonding of organic sealing materials are eliminated. In addition, the three-dimensional staggered separation guide holes increase the space creeping distance between the double core wires in the limited axial space, and the insulation voltage level between the double core wires is improved.

Description

Technical Field

[0001] This invention relates to the field of armored heat tracing cable technology, specifically to a ceramic end cap structure for a two-core armored heat tracing cable and its preparation method. Background Technology

[0002] Armored heat tracing cables are special cables that convert electrical energy into heat energy to heat and insulate equipment such as pipes and containers. They can be used for heating and degassing graphite plates in vacuum environments. By heating at high temperatures, they promote the thermal release of hydrogen isotopes in the graphite plates, reduce fuel retention, and play a key role in tritium safety and nuclear fuel recycling.

[0003] In practical engineering applications, end caps must be installed at both ends of armored heat tracing cables. The end caps have two core functions: first, to seal the cable ends to prevent external moisture, corrosive gases, or other impurities from entering along the inner cavity of the cable, ensuring long-term stable insulation performance; second, to safely lead the two internal conductive core wires to the external circuit to achieve electrical connection.

[0004] However, existing end cap technology has the following technical shortcomings under high temperature, high pressure and special working conditions: (1) Poor temperature resistance: Some end caps are filled or bonded with organic sealing media such as epoxy resin and silicone rubber. These organic materials will soften, carbonize or oxidize and decompose under high temperature working environment, resulting in sealing failure. In vacuum or low pressure environment, organic materials will release gas, affecting the airtightness of the system. In addition, the thermal expansion coefficients between organic materials and metal sheaths are large, and interface cracking and debonding are prone to occur under temperature alternating cycle. (2) Poor thermal stress adaptability: Existing metal-ceramic heads do not have a thermal stress buffer structure. The thermal expansion coefficients of different materials are very different. After high and low temperature cycles, ceramic cracking and sealing failure are likely to occur. (3) Insufficient insulation and vibration protection structure: Existing end cap structures generally lack radial positioning of cable ends and internal ceramic components, relying only on a single-layer isolation structure. The creepage distance is short and the vibration resistance is weak. Long-term operation is prone to core wire displacement and insulation breakdown. Under vibration and impact loads, the internal core wire and ceramic components are prone to axial movement or radial displacement, affecting the sealing reliability and long-term stability of the end cap. Summary of the Invention

[0005] The purpose of this invention is to provide a ceramic end cap structure for a two-core armored heat tracing cable and its preparation method, so as to solve the problems of sealing failure, organic material venting, and insufficient insulation between the two cores of the existing end caps under complex working conditions such as high temperature, high pressure, and vibration.

[0006] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: a ceramic end cap structure for a two-core armored heat tracing cable, wherein the two-core armored heat tracing cable includes, from the inside to the outside, two conductive core wires, a core wire insulation layer and an armored metal sheath, and the ceramic end cap structure includes an outlet tube, sealing ceramic, metal shell, core wire separation ceramic and fixing ceramic. The conductive core wire passes through the lead tube, which is sealed to the sealing ceramic; and the sealing ceramic is located at one end of the metal shell, while the other end of the metal shell is sealed to the armored metal sheath. The sealing ceramic has two sets of independent guide channels inside, and the two conductive core wires pass out independently through the corresponding guide channels. The core wire separation ceramic is housed inside a metal casing, and its interior has separation guide holes for the two conductive core wires to pass through respectively. The separation guide holes make the distance between the two conductive core wires on the lead-out side greater than the distance on the cable side. The fixing ceramic is placed between the core wire separation ceramic and the armored metal sheath, and works with the core wire separation ceramic and the armored metal sheath to form a positioning support structure; Among them, the lead-out tube and the sealing ceramic, the sealing ceramic and the metal shell, and the metal shell and the armored metal sheath are all sealed and connected by high-temperature brazing filler metal. The three brazing connections together form a continuous inorganic hard seal link.

[0007] Furthermore, the guide channel consists of two sets of independent stepped holes, each set of stepped holes including a large hole section for inserting the lead-out tube and a small hole section for the corresponding conductive core wire to pass through.

[0008] Furthermore, the sealing ceramic is an alumina ceramic part formed by integral sintering. The outer circular surface and the inner wall of the large hole section of the sealing ceramic are respectively provided with metallization layers. The metallization layers include a molybdenum-manganese metallization layer and a nickel plating layer from the inside to the outside.

[0009] Furthermore, the two separation guide holes of the core wire separation ceramic are arranged in a three-dimensional staggered manner. The first separation guide hole is offset to one side in the horizontal direction and one side in the vertical direction, while the second separation guide hole is offset in the opposite direction. The hole spacing between the two separation guide holes gradually increases from the inlet end to the outlet end.

[0010] Furthermore, the inner wall of the central hole of the fixing ceramic forms a clearance fit with the end of the armored metal sheath, the outer cylindrical surface of the fixing ceramic is tightly fitted with the inner wall of the core wire separating ceramic, and the outer cylindrical surface of the core wire separating ceramic fits with the inner wall of the metal shell. The fixed ceramic, the core wire separation ceramic, and the metal shell are sequentially nested radially to form a three-level coaxial positioning vibration damping system.

[0011] Furthermore, the bottom surface of the core wire separating ceramic is provided with a positioning groove, and the lead-out end of the fixing ceramic is provided with a positioning protrusion that matches the positioning groove to form a plug-in positioning structure.

[0012] Furthermore, it also includes an insulating filler layer, which fills the inner cavity of the end of the armored metal sheath and is in a compacted state. The conductive core wire that passes through the lead tube is welded to the end of the lead tube to form a closed end.

[0013] This invention also provides a method for preparing a ceramic end cap structure for a two-core armored heat tracing cable, comprising the following steps: S1: Cable end pretreatment: Remove the insulation layer of the core wires and the armored metal sheath from the ends of the two-core armored heat tracing cable body to expose the two conductive core wires, and clean the cable ends. S2: Prefabricated sealing ceramic: The surface of the sealing ceramic to be brazed is metallized, the lead tube is inserted into the large hole section of the stepped hole of the sealing ceramic, and placed in a protective atmosphere furnace to complete the brazing and sealing of the lead tube and the sealing ceramic, forming the lead tube-sealing ceramic prefabricated component. S3: Insulation filling: Fill the inner cavity of the end of the armored metal sheath with insulating filler, and use tooling to compact the insulating filler until it is flush with the end face of the armored metal sheath. S4: Component assembly: The metal shell, fixing ceramic, core wire separation ceramic and lead tube-sealing ceramic prefabricated components are sequentially assembled on the end of the cable, so that the two conductive core wires pass through the corresponding separation guide hole and guide channel respectively; S5: Overall sealing: High-temperature brazing filler metal is placed between the sealing ceramic and the metal shell, and between the metal shell and the armored metal sheath. The overall assembly is placed in a vacuum furnace and vacuum brazing is completed according to the heating-heating-cooling process curve, so that a continuous inorganic hard seal link is formed between the lead tube and the sealing ceramic, between the sealing ceramic and the metal shell, and between the metal shell and the armored metal sheath. S6: Inspection and sealing: The insulation performance of the brazed end cap structure is tested. After passing the test, the conductive core wires at the lead-out end of the lead tube are sealed by argon arc welding to form a fully sealed system with closed ends.

[0014] Furthermore, the process curve in S6 includes at least one thermal stress relief and heat preservation section. The temperature of the thermal stress relief and heat preservation section is lower than the melting point of the high-temperature brazing filler metal. The heat preservation time is sufficient to make the internal temperature of the overall assembly component tend to be uniform. After the thermal stress caused by the difference in thermal expansion coefficients between the metal and ceramic is relieved, the temperature is then raised to the melting temperature of the brazing filler metal according to the set curve to complete the brazing, so as to prevent the ceramic parts from cracking due to thermal stress.

[0015] Furthermore, in S2, the metallization process involves sequentially preparing a molybdenum-manganese metallization layer and a nickel plating layer on the brazing surface of the sealing ceramic, with the protective atmosphere furnace being a hydrogen atmosphere furnace, and the insulating filler in S3 being magnesium oxide powder.

[0016] The present invention has the following beneficial effects: The ceramic end cap structure and its preparation method for a two-core armored heat tracing cable provided by the present invention are as follows: (1) By organically combining lead-out tubes, sealing ceramics, metal shells, core wire separation ceramics and fixing ceramics, a fully inorganic sealed link with closed ends is constructed with three continuous inorganic hard brazing nodes, which fundamentally eliminates the defects of organic sealing materials such as high temperature failure, gas release and thermal cycle debonding; secondly, the three-dimensional misaligned separation guide hole expands the spatial creepage distance between the two core wires from tens of micrometers on the cable side to several millimeters on the lead-out side in a limited axial space, which greatly improves the insulation withstand voltage level between the two core wires; and thirdly, the three-level coaxial sleeve radial positioning structure ensures the long-term structural stability of the end cap under vibration and shock environment. (2) The fixed ceramic, the core wire separation ceramic and the metal shell are sequentially arranged radially to form a three-level coaxial positioning structure, which realizes multi-level radial limiting of the cable end and internal ceramic components, effectively suppressing axial movement and radial displacement under vibration and shock environment, and ensuring the long-term mechanical stability of the end cap structure. (3) The overall brazing is carried out in a vacuum furnace. The heating process is equipped with a heat stress relief and heat preservation section to effectively balance the thermal stress between the metal parts and the ceramic parts, prevent the ceramic parts from cracking during the overall one-time brazing process, and improve the consistency and yield of batch manufacturing. Attached Figure Description

[0017] Figure 1 This is a schematic axial cross-sectional view of the entire invention; Figure 2 This is a schematic axial cross-sectional view of the sealing ceramic end face in this invention; Figure 3 This is a schematic axial cross-sectional view of the core wire separated ceramic in this invention; Figures 1 to 3 The reference numerals in the attached figures are respectively: 1-conductive core wire, 2-high temperature brazing filler metal, 3-armored metal sheath, 4-lead tube, 5-sealing ceramic, 6-metal shell, 7-core wire separation ceramic, 8-fixing ceramic, 9-guide channel, 10-separation guide hole, 11-large hole section, 12-small hole section, 13-insulating filling layer, 14-positioning groove. Detailed Implementation

[0018] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0019] like Figures 1 to 3 As shown, a ceramic end cap structure for a two-core armored heat tracing cable is disclosed. This ceramic end cap structure is used for end sealing and core wire lead-out of the two-core armored heat tracing cable body. The two-core armored heat tracing cable includes, from the inside out, two conductive core wires 1, a core wire insulation layer, and an armored metal sheath 3. At the cable end, the armored metal sheath 3 and the core wire insulation layer are stripped to a predetermined length, exposing the two conductive core wires 1 for insertion into the end cap assembly.

[0020] The ceramic head structure consists of, from the outside in, an axially arranged lead-out tube 4, a sealing ceramic 5, a metal shell 6, a core wire separation ceramic 7, and a fixing ceramic 8. All of the above components are made of inorganic materials, forming a completely inorganic sealing system that completely eliminates organic sealing media and can meet the requirements of harsh working conditions such as high temperature, high vacuum, and vibration.

[0021] From the cable end to the lead-out end, the axial arrangement sequence of each component in the metal housing 6 is as follows: the fixing ceramic 8 and the core wire separating ceramic 7 are located on the cable side of the inner cavity of the metal housing 6; the sealing ceramic 5 is set at the lead-out end of the metal housing 6, and the lead-out tube 4 is inserted into the sealing ceramic 5.

[0022] The metal outer shell 6 is an axially continuous sleeve structure with an overall stepped shape. One end (the lead-out side) has a first mating hole with a larger diameter, used to accommodate the sealing ceramic 5 and seal it to the outer surface of the sealing ceramic 5 using high-temperature brazing filler metal 2, forming a brazing joint. The other end (the cable side) has a second mating hole with a diameter matching the outer diameter of the armored metal sheath 3, used to fit into the armored metal sheath 3 and seal it to the outer surface using high-temperature brazing filler metal 2, forming a brazing joint. The metal outer shell 6 serves both structural connection and sealing load-bearing functions, and is the core metal load-bearing component in the continuous inorganic hard-seal link.

[0023] In a preferred embodiment of the invention, the metal shell 6 is made of oxygen-free copper (such as T2 copper). Oxygen-free copper has an extremely low oxygen content, making it less prone to internal oxidation during high-temperature brazing and not affecting the wetting and spreading of the brazing filler metal; at the same time, its good thermal conductivity is beneficial for the uniform temperature of the entire assembly during brazing, reducing thermal stress concentration. In other embodiments, the metal shell 6 may also be made of a nickel-based alloy (such as Incol Nickel 625) to meet higher corrosion resistance or strength requirements.

[0024] In this invention, the sealing ceramic 5 is an alumina ceramic part integrally sintered, and is cylindrical in shape, embedded in the first mating hole section of the metal shell 6. The sealing ceramic 5 has two sets of independent guide channels 9 inside, and the two conductive core wires 1 pass through the corresponding guide channels 9 independently to achieve electrical insulation isolation.

[0025] In a preferred embodiment of the present invention, the guide channel 9 comprises two sets of independent stepped holes. Each set of stepped holes includes a large hole section 11 for inserting the lead-out tube 4 and a small hole section 12 for passing through the corresponding conductive core wire 1. The large hole section 11 is located on the lead-out side, and the small hole section 12 is located on the cable side, and the two are coaxially connected. The diameter of the large hole section 11 is adapted to the outer diameter of the lead-out tube 4 (fitting gap 50-100μm), and is used for inserting and brazing the lead-out tube 4. The diameter of the small hole section 12 is adapted to the outer diameter of the corresponding conductive core wire 1, allowing the conductive core wire 1 to pass through the inner cavity of the large hole section 11 and enter the lead-out tube 4. The stepped hole structure design allows the lead-out tube 4 to be covered and clamped by the sealing ceramic 5 at the large hole section 11, significantly increasing the brazing interface area and improving the mechanical strength and sealing reliability of the brazing joint between the lead-out tube 4 and the sealing ceramic 5.

[0026] To ensure good wetting of the high-temperature brazing filler metal 2 on the surface of the sealing ceramic 5 and to form a metallographic seal, a metallization layer is provided on the outer circular surface of the sealing ceramic 5 and the inner wall of the large hole section 11 of the stepped hole. The metallization layer consists of a molybdenum-manganese metallization layer and a nickel plating layer from the inside out. The molybdenum-manganese metallization layer forms a metallographic bond with the ceramic substrate through a high-temperature sintering process, which is the basis for subsequent brazing filler metal wetting. The nickel plating layer covers the surface of the molybdenum-manganese layer, further improving the wettability of the brazing filler metal on the metallized surface and ensuring the tightness and airtightness of the brazed joint.

[0027] In a preferred embodiment of the present invention, the sealing ceramic 5 is made of 99% alumina ceramic. This material possesses high insulation, excellent thermal stability, high mechanical strength, and good matching with the thermal expansion coefficient of commonly used metal materials, making it a mainstream and mature material in the field of metal-ceramic sealing. In other embodiments, other high-performance ceramic materials such as 95% alumina or zirconium oxide can also be used.

[0028] In this invention, the lead tube 4 is a hollow tubular structure, the conductive core wire 1 passes through the lead tube 4, and the lead tube 4 is sealed to the sealing ceramic 5; and the sealing ceramic 5 is disposed at one end of the metal shell 6, and the other end of the metal shell 6 is sealed to the armored metal sheath 3.

[0029] The outer diameter of the lead-out tube 4 is matched with the diameter of the large hole section 11 of the stepped hole in the sealing ceramic 5, and the inner diameter is matched with the outer diameter of the conductive core wire 1, leaving an appropriate gap for the core wire to pass through. Two lead-out tubes 4 are respectively inserted into the large hole sections 11 of the two sets of stepped holes in the sealing ceramic 5, and are sealed together by high-temperature brazing filler metal 2, forming a brazing node in the continuous sealing link. The conductive core wire 1 passes through the small hole section 12 of the sealing ceramic 5 from the cable side, enters the inner cavity of the lead-out tube 4, and exits from the lead-out end of the lead-out tube 4. The lead-out tube 4 transfers the core wire exit point to the ductile metal tube end, protecting the sealing ceramic 5 from welding heat damage and making the sealing welding (argon arc welding) operation of the core wire exit end more reliable and convenient. Furthermore, the lead-out tube 4 increases the metal-ceramic interface area at the large hole section 11 of the stepped hole in the continuous sealing link, playing an important role in improving the overall sealing performance.

[0030] In a preferred embodiment of the invention, the lead-out tube 4 is made of pure nickel. The coefficient of thermal expansion of pure nickel is close to that of 99% alumina ceramic, which helps reduce residual thermal stress at the brazing joint. Pure nickel also has good ductility and brazing properties, and can form reliable brazed joints with both copper-based and nickel-based high-temperature brazing filler metals 2. In other embodiments, the lead-out tube 4 can also be made of a nickel-based alloy tube to meet higher requirements for high temperature resistance and corrosion resistance.

[0031] The core wire separating ceramic 7 is a sintered ceramic component, which is set inside the metal shell 6 and located on the cable side of the sealing ceramic 5. Its outer cylindrical surface fits into the inner wall of the metal shell 6. Inside, there is a separating guide hole 10 for the two conductive core wires 1 to pass through respectively. The separating guide hole 10 makes the distance between the two conductive core wires 1 on the lead-out side greater than the distance on the cable side.

[0032] The two separation guide holes 10 of the core wire separation ceramic 7 are arranged in a three-dimensional staggered manner. The separation guide holes 10 are oblique holes. The channel axis of the first separation guide hole 10 is offset to one side in the horizontal direction and one side in the vertical direction relative to the overall axis of the core wire separation ceramic 7. The channel axis of the second separation guide hole 10 is offset in the opposite direction in the horizontal and vertical directions. This three-dimensional spatial staggered arrangement of the two channels makes the two holes close to each other at the inlet end (cable side end face) (to match the original spacing of the core wires inside the cable), while the horizontal and vertical spacing between the two holes at the outlet end (lead-out side end face) is significantly increased. That is, the hole spacing between the two separation guide holes 10 gradually increases from the inlet end to the outlet end.

[0033] The principle behind the three-dimensional staggered oblique hole design is as follows: Inside the armored cable, two conductive cores 1 are arranged in parallel with a small spacing. If the two cores are directly led out to the sealing ceramic 5 with their original spacing, the creepage path between the two cores' exit points is extremely short, making it difficult to meet the insulation isolation requirements under high-voltage operating conditions. Guided by the three-dimensional staggered oblique holes, the core separation ceramic 7 gradually expands the spacing between the two cores from the cable side to the exit side within a limited axial dimension. This ensures that the two cores have a sufficiently large spatial spacing before reaching the sealing ceramic 5, effectively extending the creepage path between the two cores in the air and on the ceramic surface, significantly improving the insulation withstand voltage level between the two cores. Compared to a planar unidirectional offset channel design, the three-dimensional staggered arrangement can achieve a larger spatial spacing increment within the same axial length of the ceramic body, exhibiting significant structural advantages.

[0034] The bottom surface of the core wire separating ceramic 7 is provided with a positioning groove 14, and the lead-out end of the fixed ceramic 8 is provided with a positioning protrusion that cooperates with the positioning groove 14. The positioning groove 14 and the positioning protrusion of the fixed ceramic 8 are interlocked to form an insertion positioning structure, which is used to limit the relative rotation between the core wire separating ceramic 7 and the fixed ceramic 8 during assembly, and ensure that the orientation of the two separating guide holes 10 and the correspondence between the two conductive core wires 1 are accurately maintained during the assembly process, preventing core wire perforation errors due to assembly rotation deviation, and effectively improving assembly consistency and yield.

[0035] In a preferred embodiment of the present invention, the cross-sectional shape of the positioning groove 14 and the positioning protrusion can be a non-circular cross-sectional structure such as a rectangle (keyway type), D-shape, or polygon to achieve circumferential anti-rotation function. A rectangular cross-section is preferred, with the width of the rectangular groove matching the width of the positioning protrusion, and the fitting depth being 1–3 mm. This provides reliable circumferential positioning without excessively weakening the structural strength of the bottom of the core wire separation ceramic 7.

[0036] The fixing ceramic 8 is a sintered ceramic component, housed within the inner cavity of the metal outer shell 6. It is positioned between the core wire separating ceramic 7 and the armored metal sheath 3, forming a positioning and support structure in conjunction with both. The central hole of the fixing ceramic 8 is fitted onto the end of the armored metal sheath 3, with the inner wall of the central hole forming a clearance fit with the outer wall of the armored metal sheath 3, thus radially limiting the end of the armored metal sheath 3. The outer cylindrical surface of the fixing ceramic 8 is tightly fitted to the inner wall of the core wire separating ceramic 7, achieving coaxial positioning between them. The outer cylindrical surface of the core wire separating ceramic 7 mates with the inner wall of the metal outer shell 6.

[0037] The fixed ceramic 8, the core wire separating ceramic 7, and the metal shell 6 are sequentially arranged radially to form a three-stage coaxial positioning and vibration damping system: First stage: the center hole of the fixed ceramic 8 is fitted with the end of the armored metal sheath 3, achieving radial limitation of the cable end and realizing first-stage radial positioning; Second stage: the outer cylindrical surface of the fixed ceramic 8 fits against the inner wall of the core wire separating ceramic 7, achieving coaxial positioning between the fixed ceramic 8 and the core wire separating ceramic 7, realizing second-stage radial positioning; Third stage: the outer cylindrical surface of the core wire separating ceramic 7 mates with the inner wall of the metal shell 6, achieving coaxial positioning between the core wire separating ceramic 7 and the metal shell 6, realizing third-stage radial positioning. This three-stage radial positioning structure allows the radial load at the cable end to be transmitted step-by-step through the armored metal sheath 3 → fixed ceramic 8 → core wire separating ceramic 7 → metal shell 6, effectively suppressing the axial movement and radial offset of the internal conductive core wire 1 and ceramic components under vibration and impact conditions, ensuring the long-term stability of the end cap structure.

[0038] The inner cavity at the end of the armored metal sheath 3 is filled with an insulating filler layer 13. The insulating filler layer 13 is in a compacted state, and its top surface is flush with the end face of the armored metal sheath 3, forming a dense insulating filler. The conductive core wire 1 that passes through the lead-out tube 4 is welded to the end of the lead-out tube 4 to form a closed end. By setting the insulating filler layer 13, on the one hand, the exposed section of the conductive core wire 1 is insulated and protected to prevent short circuit between the two core wires before entering the fixing ceramic 8; on the other hand, the insulating filler layer 13 in the compacted state has a certain elastic buffering effect, which can absorb the energy of vibration and impact transmitted to the end of the cable, and play an auxiliary anti-vibration role.

[0039] In a preferred embodiment of the present invention, the insulating filler layer 13 is a magnesium oxide filler layer, that is, magnesium oxide powder is compacted and filled. Magnesium oxide powder has excellent electrical insulation, high temperature resistance and chemical stability, is compatible with the original inorganic insulating medium in the armored heat tracing cable body, and does not introduce any organic pollution, ensuring the completely inorganic characteristics of the overall structure.

[0040] In this invention, the lead-out tube 4 is sealed to the sealing ceramic 5, the sealing ceramic 5 is sealed to the metal shell 6, and the metal shell 6 is sealed to the armored metal sheath 3 using high-temperature brazing filler metal 2. These three brazing joints connect the above components into a single unit, forming a continuous inorganic hard-sealed link from the armored metal sheath 3 to the lead-out tube 4. The three brazing joints are now described in detail: Brazing node A (between lead-out tube 4 and sealing ceramic 5): Located within the large hole section 11 of the stepped hole in the sealing ceramic 5, the outer wall of the lead-out tube 4 and the metallized layer of the inner wall of the large hole section 11 are sealed by high-temperature brazing filler metal 2, achieving a metal-ceramic hard seal between the lead-out tube 4 (metal) and the sealing ceramic 5 (ceramic). The stepped hole structure allows the lead-out tube 4 to be covered by the sealing ceramic 5, effectively preventing the lead-out tube 4 from falling off due to the difference in thermal expansion coefficients between the metal and ceramic during temperature alternation.

[0041] Brazing node B (between sealing ceramic 5 and metal shell 6): The outer circular metallized layer of sealing ceramic 5 and the inner wall of the lead end of metal shell 6 are sealed together by high-temperature brazing filler metal 2, realizing ceramic-metal hard seal between sealing ceramic 5 (ceramic) and metal shell 6 (metal), ensuring that the high-temperature brazing filler metal fills the gap evenly under the drive of capillary force, forming a dense and non-porous sealed joint.

[0042] Brazing node C (between metal outer shell 6 and armored metal sheath 3): The inner wall of the cable end of metal outer shell 6 and the outer wall of armored metal sheath 3 are sealed together by high-temperature brazing filler metal, achieving a metal-to-metal hard seal between metal outer shell 6 and armored metal sheath 3. This metal-to-metal brazing method provides high connection strength and excellent sealing reliability.

[0043] Three brazing nodes A, B, and C form a complete sealed link from the outer wall of the armored metal sheath 3 to the outer wall of the lead-out tube 4, with a continuous and uninterrupted sealing path. Based on this, the conductive core wire 1, which exits the lead-out tube 4, is sealed and fixed to the end of the lead-out tube 4 by argon arc welding, sealing the threading gap between the conductive core wire 1 and the inner cavity of the lead-out tube 4. Together with the three continuous brazing sealing nodes mentioned above, this forms a fully sealed system that ensures comprehensive sealing protection for the internal conductive core wire 1, ceramic components, and the inner cavity of the cable.

[0044] In this invention, the high-temperature brazing filler metal is preferably an inorganic metal high-temperature hard brazing filler metal, such as copper-based brazing filler metal (solid-liquid phase temperature 700-950℃) or nickel-based brazing filler metal (solid-liquid phase temperature 970-1080℃), etc., whose operating temperature is much higher than that of organic sealing materials, and can meet the requirements of long-term sealing of the end cap under high-temperature conditions.

[0045] This invention also provides a method for preparing a ceramic end cap structure for a two-core armored heat tracing cable, comprising the following steps: S1: Cable end pretreatment: Remove the insulation layer of the core wires and the armored metal sheath 3 from the ends of the two-core armored heat tracing cable body to expose the two conductive core wires 1, and clean the cable ends, such as chemical degreasing and mechanical removal of oxide film, to ensure the bonding quality of subsequent brazing and welding operations.

[0046] S2: Pre-fabrication of sealing ceramic 5: The surface of the sealing ceramic 5 to be brazed is metallized. The specific operation of metallization is as follows: Molybdenum-manganese paste is evenly coated onto the surface to be brazed using screen printing or coating. It is then sintered in a hydrogen atmosphere furnace at 1300-1500℃ to form a molybdenum-manganese metallization layer that is metallurgically bonded to the ceramic substrate. Subsequently, a nickel plating layer is deposited on the surface of the molybdenum-manganese layer through electroplating or chemical plating to form a metallization layer. After the metallization is completed, the lead-out tube 4 is inserted into the stepped hole section 11 of the sealing ceramic 5. Brazing filler metal is placed at the mating gap, and the furnace is placed in a protective atmosphere furnace. Pre-brazing between the lead-out tube 4 and the sealing ceramic 5 is completed at an appropriate temperature (brazing node A), and the brazing seal between the lead-out tube 4 and the sealing ceramic 5 is completed, forming the lead-out tube-sealing ceramic prefabricated component. The pre-brazing is carried out in a hydrogen atmosphere. The reducing atmosphere of hydrogen can effectively remove the metallization layer and the oxide film on the surface of the lead-out tube 4, ensuring uniform wetting of the brazing filler metal.

[0047] S3: Insulation filling: Insulation filler is filled into the inner cavity of the end of the armored metal sheath 3. The insulation filler is compacted with tooling until it is flush with the end face of the armored metal sheath 3 to form an insulation filling layer 13. The compaction operation ensures that there are no loose gaps inside the insulation filling layer 13, thus ensuring the insulation protection effect between the two core wires.

[0048] S4: Component Assembly: The metal shell 6, fixing ceramic 8, core wire separating ceramic 7, and lead-out tube-sealing ceramic prefabricated assembly are sequentially assembled onto the cable end, so that the two conductive core wires 1 pass through the corresponding separating guide holes 10 and guide channels 9 respectively. The specific operation is as follows: First, the metal shell 6 is inserted from the lead-out side to the cable side, so that the cable end is fitted onto the outer wall of the armored metal sheath 3; then the fixing ceramic 8 is inserted, so that its center hole is fitted onto the end of the armored metal sheath 3; next, the core wire separating ceramic 7 is placed into the inner cavity of the metal shell 6, and the positioning protrusion of the fixing ceramic 8 is embedded into the positioning groove on the bottom surface of the core wire separating ceramic 7 to form a plug-in positioning, ensuring that the two separating guide holes 10 are accurately positioned; then the two conductive core wires 1 pass through the corresponding separating guide holes 10 respectively; finally, the lead-out tube-sealing ceramic prefabricated assembly is inserted, so that the two conductive core wires 1 pass through the corresponding lead-out tubes 4 and exit from the lead-out end, and the outer circular surface of the sealing ceramic 5 is aligned with the inner wall of the first mating hole section of the metal shell 6.

[0049] S5: Overall sealing: High-temperature brazing filler metal is placed between the sealing ceramic 5 and the metal shell 6 (brazing node B position) and between the metal shell 6 and the armored metal sheath 3 (brazing node C position), and the overall assembly is placed into a vacuum furnace. Vacuum brazing is completed according to the process curve of heating-heating-cooling, so that a continuous inorganic hard seal link is formed between the lead tube 4 and the sealing ceramic 5, between the sealing ceramic 5 and the metal shell 6, and between the metal shell 6 and the armored metal sheath 3. The process curve has at least one thermal stress relief and heat preservation section. The temperature of the thermal stress relief and heat preservation section is lower than the melting point of the high-temperature brazing filler metal. The heat preservation time is sufficient to make the internal temperature of the overall assembly component tend to be uniform. After the thermal stress caused by the difference in thermal expansion coefficient between the metal and the ceramic is relieved, the temperature is raised to the melting temperature of the brazing filler metal according to the set curve to complete the brazing, so as to prevent the ceramic parts from cracking due to thermal stress. Specifically: ① Heating stage: The temperature is increased from room temperature to the thermal stress relief and heat preservation temperature at an appropriate rate; ② Thermal stress relief and heat preservation stage: The temperature is maintained within a preset temperature range below the melting temperature of the brazing filler metal. The heat preservation time is usually 10 to 30 minutes, so that the internal temperature of the overall assembly component tends to be uniform, and the thermal stress caused by the difference in thermal expansion coefficients between the metal and ceramic parts is fully relieved, preventing the ceramic parts from cracking due to thermal shock during the subsequent heating and brazing process; ③ Brazing temperature stage: The temperature is continued to rise above the melting temperature of the brazing filler metal and maintained, so that the brazing filler metal is fully melted and fills the brazing gap under the action of capillary force, completing the sealing of brazing nodes B and C; ④ Cooling stage: The heating is turned off, and the furnace is slowly cooled to room temperature. The vacuum degree is maintained during the cooling process until the component temperature drops below 200°C before the gas is released. The use of a vacuum atmosphere eliminates the oxide film at the brazing interface, which is beneficial for the wetting and spreading of the brazing filler metal, resulting in a dense, non-porous brazed joint. By setting up a heat stress relief and heat preservation section, the engineering problem of cracking of ceramic parts due to the difference in thermal expansion coefficients during the overall one-time brazing of multi-segment metal-ceramic sealing structures is effectively solved, and the yield of mass production is greatly improved.

[0050] S6: Inspection and sealing: The insulation performance of the overall brazed head structure is tested. After the test is qualified, the conductive core wire 1 of the lead-out tube 4 is sealed by argon arc welding to form a fully sealed system with closed ends.

[0051] Additionally, it should be noted that components not described in detail in this article are existing technologies.

[0052] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A ceramic end cap structure for a two-core armored heat tracing cable, wherein the two-core armored heat tracing cable comprises, from the inside out, two conductive cores (1), a core insulation layer, and an armored metal sheath (3), characterized in that, It includes lead-out tube (4), sealing ceramic (5), metal shell (6), core wire separation ceramic (7) and fixing ceramic (8); The conductive core wire (1) passes through the lead tube (4), and the lead tube (4) is sealed to the sealing ceramic (5); and the sealing ceramic (5) is disposed at one end of the metal shell (6), and the other end of the metal shell (6) is sealed to the armored metal sheath (3). The sealing ceramic (5) has two sets of independent guide channels (9) inside, and the two conductive core wires (1) pass through the corresponding guide channels (9) independently. The core wire separation ceramic (7) is disposed inside the metal shell (6), and its interior is provided with separation guide holes (10) for the two conductive core wires (1) to pass through respectively. The separation guide holes (10) make the distance between the two conductive core wires (1) on the lead-out side greater than the distance on the cable side. The fixing ceramic (8) is disposed between the core wire separating ceramic (7) and the armored metal sheath (3), and cooperates with the core wire separating ceramic (7) and the armored metal sheath (3) to form a positioning support structure; Among them, the lead-out tube (4) and the sealing ceramic (5), the sealing ceramic (5) and the metal shell (6), and the metal shell (6) and the armored metal sheath (3) are all sealed and connected by high-temperature brazing filler metal (2), and the three brazing connections together form a continuous inorganic hard seal link.

2. The ceramic end cap structure of the two-core armored heat tracing cable according to claim 1, characterized in that, The guide channel (9) consists of two sets of independent stepped holes. Each set of stepped holes includes a large hole section (11) for inserting the lead tube (4) and a small hole section (12) for passing through the corresponding conductive core wire (1).

3. The ceramic end cap structure of the two-core armored heat tracing cable according to claim 2, characterized in that, The sealing ceramic (5) is an alumina ceramic part formed by integral sintering. The outer circular surface of the sealing ceramic (5) and the inner wall of the large hole section (11) are respectively provided with metallization layers. The metallization layers include a molybdenum-manganese metallization layer and a nickel plating layer from the inside to the outside.

4. The ceramic end cap structure of the two-core armored heat tracing cable according to claim 1, characterized in that, The two separation guide holes (10) of the core wire separation ceramic (7) are arranged in a three-dimensional staggered manner. The first separation guide hole (10) is offset to one side in the horizontal direction and one side in the vertical direction, and the second separation guide hole (10) is offset in the opposite direction. The hole spacing between the two separation guide holes (10) gradually increases from the inlet end to the outlet end.

5. The ceramic end cap structure of the two-core armored heat tracing cable according to claim 1, characterized in that, The inner wall of the center hole of the fixed ceramic (8) forms a clearance fit with the end of the armored metal sheath (3), the outer cylindrical surface of the fixed ceramic (8) is tightly fitted with the inner wall of the core wire separating ceramic (7), and the outer cylindrical surface of the core wire separating ceramic (7) is fitted with the inner wall of the metal shell (6). The fixed ceramic (8), the core wire separation ceramic (7), and the metal shell (6) are sequentially arranged radially to form a three-level coaxial positioning vibration damping system.

6. The ceramic end cap structure of the two-core armored heat tracing cable according to claim 1, characterized in that, The bottom surface of the core wire separating ceramic (7) is provided with a positioning groove (14), and the lead-out end of the fixing ceramic (8) is provided with a positioning protrusion that cooperates with the positioning groove (14) to form a plug-in positioning structure.

7. The ceramic end cap structure of the two-core armored heat tracing cable according to claim 1, characterized in that, It also includes an insulating filler layer (13), which fills the inner cavity of the end of the armored metal sheath (3) and is in a compacted state. The conductive core wire (1) that passes through the lead tube (4) is welded to the end of the lead tube (4) to form a closed end.

8. A method for preparing a ceramic end cap structure for a two-core armored heat tracing cable according to any one of claims 1 to 7, characterized in that, Includes the following steps: S1: Cable end pretreatment: Remove the core wire insulation layer and armored metal sheath (3) from the ends of the two-core armored heat tracing cable body to expose the two conductive core wires (1), and clean the cable ends. S2: Prefabrication of sealing ceramic (5): Metallize the surface of the sealing ceramic (5) to be brazed, insert the lead tube (4) into the large hole section (11) of the stepped hole of the sealing ceramic (5), and place it in a protective atmosphere furnace to complete the brazing and sealing of the lead tube (4) and the sealing ceramic (5) to form the lead tube-sealing ceramic prefabrication assembly. S3: Insulation filling: Insulation filler is filled into the inner cavity of the end of the armored metal sheath (3), and the insulation filler is compacted to be flush with the end face of the armored metal sheath (3) using tooling; S4: Component assembly: The metal shell (6), the fixing ceramic (8), the core wire separation ceramic (7) and the lead-out tube-sealing ceramic prefabricated assembly are sequentially assembled on the end of the cable so that the two conductive core wires (1) pass through the corresponding separation guide hole (10) and guide channel (9) respectively. S5: Overall sealing: High-temperature brazing filler metal (2) is placed between the sealing ceramic (5) and the metal shell (6), and between the metal shell (6) and the armored metal sheath (3). The overall assembly is placed in a vacuum furnace and vacuum brazing is completed according to the heating-heating-cooling process curve, so that a continuous inorganic hard seal link is formed between the lead tube (4) and the sealing ceramic (5), between the sealing ceramic (5) and the metal shell (6), and between the metal shell (6) and the armored metal sheath (3). S6: Inspection and sealing: The insulation performance of the overall brazed head structure is tested. After the test is qualified, the conductive core wire (1) of the lead-out tube (4) is sealed by argon arc welding to form a fully sealed system with closed ends.

9. The method for preparing the ceramic end cap structure of the two-core armored heat tracing cable according to claim 8, characterized in that, The process curve described in S6 has at least one thermal stress relief and heat preservation section. The temperature of the thermal stress relief and heat preservation section is lower than the melting point of the high-temperature brazing filler metal (2). The heat preservation time is sufficient to make the internal temperature of the overall assembly component tend to be uniform. After the thermal stress caused by the difference in thermal expansion coefficient between the metal and the ceramic is relieved, the temperature is raised to the melting temperature of the brazing filler metal according to the set curve to complete the brazing, so as to prevent the ceramic parts from cracking due to thermal stress.

10. The method for preparing the ceramic end cap structure of the two-core armored heat tracing cable according to claim 8, characterized in that, The metallization process described in S2 involves sequentially preparing a molybdenum-manganese metallization layer and a nickel plating layer on the brazing surface of the sealing ceramic (5). The protective atmosphere furnace is a hydrogen atmosphere furnace. The insulating filler described in S3 is magnesium oxide powder.

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