A production method for reducing internal stress in a cable based on a continuous vulcanization process

Abstract

The application discloses a production method for reducing internal stress of a cable based on a continuous vulcanization process, comprising the following steps: S1, rubber mixture preparation, S2, extrusion coating, S3, three-stage continuous vulcanization, and S4, traction and winding; the semi-finished cable is sequentially treated through a microwave preheating area, a steam vulcanization area and a nitrogen slow cooling area by the three-stage continuous vulcanization, wherein the steam vulcanization area adopts a vulcanization pipe arranged in a catenary mode; the cable is uniformly heated inside and outside by microwave preheating, the mechanical stress is reduced by the specific curvature of the catenary vulcanization pipe, and the thermal stress is effectively reduced by adopting nitrogen gradient cooling, so that the internal residual stress of the cable product is significantly reduced, the eccentricity of the insulation layer and the crosslinking uniformity are improved, and the size stability and service life of the cable are improved.

Description

Technical Field

[0001] This invention relates to the field of cable manufacturing technology, specifically to a production method for reducing internal stress in cables based on a continuous vulcanization process. Background Technology

[0002] Continuous vulcanization is a key technology in the wire and cable manufacturing industry for improving the performance of rubber insulation and sheathing. Through vulcanization, the rubber molecular chains cross-link to form a three-dimensional network structure, significantly improving the cable's mechanical strength, heat resistance, insulation performance, and durability, ensuring long-term stable operation in complex applications such as power transmission and communication. This process integrates extrusion and vulcanization into a single continuous step, resulting in high production efficiency and material savings, and is widely used in the production of various rubber-sheathed cables.

[0003] In existing technologies, continuous vulcanization processes are mainly classified into horizontal, catenary, and vertical types based on the arrangement of the vulcanizing pipes. The vulcanizing medium typically uses saturated steam, superheated steam, or microwave energy. For example, the catenary arrangement utilizes the natural vertical curve of the pipe to guide the cable towards the center of the pipe under gravity, while the vertical arrangement aims to prevent the cable from becoming eccentric due to its own weight. Furthermore, some technologies employ guide wheels or adaptive mechanisms to position and pull the cable, reducing its contact and friction with the pipe wall. In recent years, continuous vulcanization methods using microwave preheating or electron beam irradiation have also emerged, aiming to improve heating efficiency and uniformity.

[0004] Despite technological advancements, a systematic solution remains elusive to the internal residual stress issues in cables caused by differences in thermal history and mechanical constraints during long-distance vulcanization. The poor thermal conductivity of rubber makes traditional outside-to-inside heating methods prone to causing asynchronous heating and vulcanization between the inner and outer layers, resulting in uneven cross-linking. These residual stresses are released during use due to thermal expansion and contraction, leading to microcracks or even full cracks in the protective layer, directly impacting the cable's lifespan and reliability. Therefore, effectively controlling and releasing internal stress in cables while ensuring efficient production has become a critical technological bottleneck that urgently needs to be overcome in this field. Summary of the Invention

[0005] The existing technology has the problem that it is difficult to simultaneously ensure the uniformity of cable vulcanization and control of mechanical stress during continuous vulcanization, resulting in inconsistent cross-linking degrees between the internal and external parts of the product and the easy generation of residual stress. To address the above technical problems, this invention provides a production method for reducing internal stress in cables based on a continuous vulcanization process.

[0006] The technical solution of this invention is: a production method for reducing internal stress in cables based on a continuous vulcanization process, comprising the following steps: S1, Preparation of rubber mixtures By mass percentage, 22-35% of silica, 2.8-5.6% of silane pretreatment solution, 1-2.5% of dicumyl peroxide, 0.6-1.2% of triallyl isocyanurate, 0.3-0.6% of antioxidant 1010, and the balance of ethylene-propylene-diene monomer rubber are added to an internal mixer and mixed at 50-70℃ for 15-25 minutes to obtain a compound. The compound is then transferred to an open mill for thin-pass treatment, with the roller temperature controlled at 45-55℃, the speed ratio between the two rollers at 1.2-1.5, the roller gap set at 0.8-1.2mm, and the number of thin-pass passes at 5-8. The compound after thin-pass treatment is then placed in a constant temperature and humidity environment for curing treatment, with an ambient temperature of 23-27℃, a relative humidity of 45-55%, and a curing time of 6-8 hours to obtain a cured compound. S2, Extrusion Coating The cured compound described in S1 is extruded through a cold-feed extruder at a feed section temperature of 30-40℃ and a die head temperature of 60-70℃, and then extruded onto the conductor, which serves as the core of the cable. After extrusion, the material passes through a three-stage stepped cooling water tank. The first stage water temperature is 40-45℃, and the cooling time is 20-30 seconds; the second stage water temperature is 25-30℃, and the cooling time is 30-40 seconds; the third stage water temperature is 15-20℃, and the cooling time is 20-30 seconds, forming a semi-finished cable. S3, Three-stage continuous vulcanization The semi-finished cable described in S2 is sequentially processed through a microwave preheating zone, a steam vulcanization zone, and a nitrogen slow cooling zone. The microwave preheating zone uses microwaves with a frequency of 2.4-2.5 GHz to preheat the semi-finished cable. The steam vulcanization zone uses a catenary-style vulcanization pipe and saturated steam for vulcanization. The nitrogen slow cooling zone uses nitrogen to perform gradient cooling on the semi-finished cable, resulting in a cooled cable. The entrance to the steam vulcanization zone is isolated by double steam curtains. The steam pressure of the steam curtains is 0.1-0.2 MPa, and the curtain spacing is 500-800 mm to prevent interference between the media in each zone. S4, Traction winding The cooled cable described in S3 is wound up under a constant tension of 100-200N, and then subjected to aging treatment to obtain the finished cable.

[0007] Note: This method has significant advantages in improving production efficiency. The combination of microwave preheating and steam vulcanization shortens the vulcanization time, while the optimization of the lead-out speed avoids defects such as bubbles or cracks, reducing the scrap rate. In addition, the use of nitrogen environment not only prevents oxidation and deterioration but also improves cooling safety, while constant tension winding ensures product consistency. These factors together contribute to cost savings and improved resource utilization efficiency.

[0008] Further, the silica mentioned in S1 is a precipitation product with a particle size of 20-50 nm; the preparation method of the silane pretreatment solution is as follows: γ-aminopropyltriethoxysilane and anhydrous ethanol are mixed at a mass ratio of 1:3-5 and stirred at 40-50°C for 30-45 minutes to obtain the silane pretreatment solution.

[0009] Explanation: Precipitated silica with a particle size of 20-50nm is selected because its primary particles are smaller and the secondary polymer particles are more evenly distributed, which can significantly improve its dispersibility and reinforcing effect in the rubber matrix, thereby reducing stress concentration caused by filler agglomeration. At the same time, γ-aminopropyltriethoxysilane, namely KH-550, is used as a coupling agent. The ethoxy group in its molecule reacts with the hydroxyl group on the surface of silica, and the amino group combines with the rubber molecular chain, which effectively enhances the interfacial adhesion between inorganic filler and organic rubber, further reducing the risk of interfacial debonding.

[0010] Furthermore, the cold feed extruder described in S2 has a screw length-to-diameter ratio of 12:1, a screw speed set to 30-50 rpm, and a corresponding extrusion rate that is stable at 1.5-2.0 kg / min.

[0011] Note: The screw length-to-diameter ratio of 12:1 combined with the speed setting of 30-50 rpm can enhance the shearing and mixing effect of the rubber compound during the extrusion process, ensuring uniform plasticization of the rubber compound and reducing residual air bubbles; a stable extrusion volume helps maintain the consistency of the coating thickness, avoiding uneven thickness or local internal stress caused by extrusion fluctuations from the source.

[0012] Furthermore, the microwave preheating zone described in S3 adopts a time-division power control strategy: during the preheating process with a total duration of 60-90 seconds, the power of 5-8kW is used for initial heating in the first third of the time period, the power is increased to 10-12kW in the middle third of the time period to accelerate the temperature rise, and the power is adjusted to the range of 12-15kW in the last third of the time period based on real-time temperature measurement feedback, so that the core temperature of the semi-finished battery is uniformly raised to 80-100℃.

[0013] Explanation: The time-sharing power control strategy uses a stepped, incremental microwave energy input to achieve a gradient temperature rise in the cable insulation layer from the inside out, effectively avoiding the accumulation of thermal stress caused by excessive temperature differences between the inside and outside of traditional heating methods. At the same time, the dynamic power adjustment based on real-time temperature feedback at the end stage ensures that the core temperature accurately reaches the set range, providing a uniform temperature field for subsequent steam vulcanization. This reduces the cross-linking degree differences and internal stress problems caused by uneven preheating from the source, enabling the cable core to rapidly and uniformly heat up to 80-100℃ within 60-90 seconds. This allows for simultaneous preheating of the inner and outer layers of rubber, reducing the thermal stress caused by temperature differences between the inside and outside of traditional heating methods, and laying the foundation for efficient cross-linking in the subsequent steam vulcanization stage.

[0014] Furthermore, the steam vulcanization zone described in S3 adopts a catenary-style vulcanization pipe, through which saturated steam with a pressure of 0.8-1.2MPa is introduced, the vulcanization temperature is 170-190℃, and the semi-finished cable passes through a 50-80 meter long pipe at a speed of 20-40 meters / minute, with the vulcanization time controlled at 2-4 minutes.

[0015] Note: The catenary-type vulcanizing pipe can accommodate the thermal expansion and deformation of the cable during the vulcanization process, reducing mechanical drag stress; introducing 0.8-1.2MPa saturated steam and controlling the vulcanization time to 2-4 minutes in a 50-80 meter pipe can ensure that the cross-linking reaction is sufficient and uniform, avoiding local performance differences caused by over-vulcanization or under-vulcanization.

[0016] Furthermore, the natural curvature radius of the vulcanizing pipe in the steam vulcanizing zone of S3 is 1.5-2 times the pipe length; the semi-finished cable is kept in the center of the vulcanizing pipe during the vulcanization process by a support set inside the vulcanizing pipe; the support includes a telescopic support member and a guide wheel connected to its end, the guide wheel slidingly engaging with the cable surface, and by adjusting the telescopic amount of the support member, it can accommodate cables of different specifications and fine-tune the cable position to ensure its centered position in the vulcanizing pipe.

[0017] Explanation: The vulcanizing pipe in the S3 stage steam vulcanization zone is designed with a natural curvature radius of 1.5-2 times the pipe length. The core benefit of this design is the creation of a sufficiently gentle catenary. This specific gentle curvature design allows the vulcanizing pipe to better accommodate the thermal expansion and deformation of the cable during high-temperature vulcanization, and utilizes the cable's own weight to allow it to naturally sag towards the pipe's centerline, thereby minimizing mechanical contact and friction between the cable and the pipe wall. This not only helps protect the cable's surface quality but also ensures that the cable is under uniform tension within the vulcanizing pipe, creating crucial conditions for achieving a uniform vulcanization effect and reducing additional stress caused by mechanical constraints. The support structure, through the cooperation of retractable supports and guide wheels, achieves dynamic adaptive centering of the cable within the vulcanizing pipe. The guide wheel makes rolling contact with the cable surface rather than being rigidly fixed, providing necessary support while minimizing frictional resistance. By finely adjusting the extension and contraction of the support in real time, cables of different specifications can be precisely controlled to always be on the central axis of the pipe, thereby ensuring uniform heating of the insulation layer in the circumferential direction, effectively eliminating cross-linking differences and mechanical stress concentration caused by eccentricity, and significantly improving cable concentricity and long-term service performance.

[0018] Furthermore, after passing through the steam vulcanization zone, the semi-finished cable described in S3 is subjected to mechanical vibration treatment using a low-frequency vibration device. The vibration amplitude is 0.1-0.3mm, and the treatment time is 30-60 seconds. The frequency of the vibration device is adjusted in real time according to the diameter of the semi-finished cable: when the diameter of the semi-finished cable is ≤20mm, the frequency of the vibration device is 15-20Hz; when the diameter of the semi-finished cable is 20-40mm, the frequency of the vibration device is 10-15Hz; and when the diameter of the semi-finished cable is >40mm, the vibration frequency is 8-12Hz.

[0019] Explanation: By combining a specific frequency adapted to the cable diameter with a micrometer-level amplitude, vibration energy is effectively transferred to the entire cross-section of the cable insulation layer, causing directional relaxation and rearrangement of the rubber molecular chains, thereby releasing the residual stress accumulated during vulcanization. This method specifically avoids the energy dissipation on the surface of large-diameter cables due to excessively high vibration frequencies or the incomplete stress elimination caused by insufficient frequencies in small-diameter cables. Through micro-amplitude oscillation, the rubber molecular chain segments are rearranged, releasing some of the curing shrinkage stress and reducing residual air bubbles, thereby improving the overall structural density of the cable. Nitrogen slow cooling is then applied, significantly improving the homogeneity of the cable structure and its long-term service stability.

[0020] Furthermore, the nitrogen slow cooling zone described in S3 is filled with nitrogen gas with a purity of ≥99.99%, which causes the temperature of the semi-finished cable to drop from the vulcanization temperature gradient to 40-50°C within 10-15 minutes at a rate of 5-10°C / minute.

[0021] Note: Using high-purity nitrogen and gradient cooling at a rate of 5-10℃ / min can inhibit the oxidative aging of rubber at high temperatures, while avoiding asynchronous surface hardening and core shrinkage caused by sudden cooling, thus reducing thermal stress cracks; adding 0.5-1% helium by volume can enhance the heat exchange efficiency of the nitrogen medium by utilizing its high thermal conductivity, and promote cooling uniformity.

[0022] Furthermore, the nitrogen slow cooling zone described in S3 is also filled with helium, which accounts for 0.5-1% of the volume of the nitrogen.

[0023] Note: Helium, as a monatomic gas, has a small molecular weight. When a small amount of helium is mixed with nitrogen, the resulting gas mixture can carry away heat from the cable surface more quickly and evenly, thereby effectively reducing the temperature gradient on the cable cross-section, avoiding thermal stress caused by asynchronous cooling and contraction of the inner and outer layers, and improving the dimensional stability and long-term reliability of the cable product.

[0024] Furthermore, the aging treatment described in S4 is carried out at a temperature of 40-50°C for 24-48 hours, with the relative humidity controlled at 40-60%.

[0025] Explanation: By maintaining a moderate temperature of 40-50℃, a sufficient time of 24-48 hours, and a controlled humidity of 40-60%, the molecular chains within the cable insulation layer gain enough energy and space for slow rearrangement and relaxation. This process effectively releases the thermal and structural stresses frozen during the vulcanization cooling process, while preventing polymer oxidative aging caused by excessively high temperatures or prolonged periods. After this treatment, the cable's dimensional stability, mechanical properties, and long-term electrical performance are significantly improved.

[0026] The beneficial effects of this invention are: This invention significantly reduces internal stress and improves product quality in cables by optimizing the rubber formulation and introducing a three-stage continuous vulcanization process. Specifically, the synergistic effect of silica and silane coupling agent in the rubber mixture enhances filler dispersibility, while the ratio of dicumyl peroxide to triallyl isocyanurate ensures uniform crosslinking, reducing stress concentration caused by uneven vulcanization at the source. Simultaneously, the three-stage vulcanization process uses microwave preheating to ensure a uniform temperature rise inside the cable, preventing premature surface curing. The catenary arrangement in the steam vulcanization zone, combined with saturated steam, ensures thermal stability and crosslinking efficiency. The nitrogen slow cooling zone suppresses deformation stress caused by rapid cooling and shrinkage of rubber molecular chains through gradient cooling. Finally, constant tension winding further avoids the introduction of external mechanical stress, thus achieving overall synergistic control of internal and external stresses, resulting in cables with higher dimensional stability and longer service life. Attached Figure Description

[0027] Figure 1 This is a line graph comparing the eccentricity performance of sample cables in Examples 1-18 and Comparative Examples 1-3 of the present invention; Figure 2 These are line graphs comparing the residual stress performance of samples from Examples 1-18 and Comparative Examples 1-3 of the present invention. Figure 3 This is a line graph comparing the insulation strength performance of samples from Examples 1-18 and Comparative Examples 1-3 of the present invention. Detailed Implementation

[0028] To further illustrate the methods and effects of this invention, the technical solution of this invention will be clearly and completely described below in conjunction with experiments.

[0029] Example 1: A production method for reducing internal stress in cables based on a continuous vulcanization process includes the following steps: S1, Preparation of rubber mixtures By weight percentage, 30% of silica, 3.5% of silane pretreatment solution, 2% of dicumyl peroxide, 0.9% of triallyl isocyanurate, 0.5% of antioxidant 1010, and the balance of ethylene-propylene-diene monomer rubber are added to an internal mixer and mixed at 60°C for 20 minutes to obtain a compound. The compound is then transferred to an open mill for thin-pass processing, with the roller temperature controlled at 50°C, the speed ratio between the two rollers at 1.35, and the roller gap set... The particle size is 1 mm, and the number of thin passes is 7. The compounded rubber after thin pass treatment is placed in a constant temperature and humidity environment for curing treatment. The ambient temperature is 25℃, the relative humidity is 50%, and the curing time is 7 hours to obtain a cured compounded rubber. The silica is a precipitation product with a particle size of 35-38 nm. The silane pretreatment solution is prepared by mixing γ-aminopropyltriethoxysilane and anhydrous ethanol at a mass ratio of 1:4 and stirring at 45℃ for 38 minutes to obtain the silane pretreatment solution. S2, Extrusion Coating The cured compound described in S1 is extruded through a cold-feed extruder at a feed section temperature of 35°C and a die head temperature of 65°C, and then extruded onto the conductor, which serves as the core of the cable. After extrusion, the material passes through a three-stage stepped cooling water tank. The first stage water temperature is 42°C, and the cooling time is 25 seconds; the second stage water temperature is 28°C, and the cooling time is 35 seconds; the third stage water temperature is 18°C, and the cooling time is 25 seconds, forming a semi-finished cable. The cold-feed extruder has a screw length-to-diameter ratio of 12:1, a screw speed set to 40 rpm, and a corresponding extrusion rate that is stable at 1.8 kg / min. S3, Three-stage continuous vulcanization The semi-finished cable described in S2 is sequentially processed through a microwave preheating zone, a steam vulcanization zone, and a nitrogen slow cooling zone. The microwave preheating zone uses microwaves at a frequency of 2.45 GHz to preheat the semi-finished cable. The steam vulcanization zone uses a catenary-style vulcanization pipe and saturated steam for vulcanization. The nitrogen slow cooling zone uses nitrogen to perform gradient cooling on the semi-finished cable, resulting in a cooled cable. The entrance to the steam vulcanization zone is isolated by double steam curtains with a steam pressure of 0.15 MPa and a curtain spacing of 700 mm. The microwave preheating zone employs a time-sharing power control strategy: during a total duration of 75 seconds... During the preheating process, the power is initially 6.5kW for the first third of the time period, increased to 11kW for the middle third of the time period to accelerate the temperature rise, and adjusted to 13.5kW for the last third of the time period based on real-time temperature feedback, so that the core temperature of the semi-finished cable rises uniformly to 90℃. The steam vulcanization zone uses a catenary-style vulcanization pipe, through which saturated steam at a pressure of 1MPa is introduced, and the vulcanization temperature is 180℃. The semi-finished cable passes through a 70-meter-long pipe at a speed of 30 meters / minute, and the vulcanization time is controlled within 3 minutes. The natural bending radius of the vulcanization pipe in the steam vulcanization zone is 1.8 times the length of the pipe. The nitrogen slow cooling zone is filled with nitrogen gas with a purity of ≥99.99%, which causes the temperature of the semi-finished cable to drop from the vulcanization temperature gradient to 45°C within 12 minutes at a rate of 8°C / minute. S4, Traction winding The cooled cable described in S3 is wound up under a constant tension of 150N and then subjected to aging treatment to obtain the finished cable. The aging treatment temperature is 45℃, the treatment time is 32 hours, and the relative humidity is controlled at 50%.

[0030] Example 2: This example is basically the same as Example 1, except that the semi-finished cable described in S3 is subjected to mechanical vibration treatment by a low-frequency vibration device after passing through the steam vulcanization zone. The amplitude of the vibration is 0.1 mm and the treatment time is 45 seconds. The diameter of the semi-finished cable is 35 mm and the frequency of the vibration device is 13 Hz.

[0031] Example 3: This example is basically the same as Example 1, except that the semi-finished cable described in S3 is subjected to mechanical vibration treatment by a low-frequency vibration device after passing through the steam vulcanization zone. The amplitude of the vibration is 0.2mm and the treatment time is 30 seconds. The diameter of the semi-finished cable is 18mm and the frequency of the vibration device is 15Hz.

[0032] Example 4: This example is basically the same as Example 1, except that the semi-finished cable described in S3 is subjected to mechanical vibration treatment by a low-frequency vibration device after passing through the steam vulcanization zone. The amplitude of the vibration is 0.3mm and the treatment time is 60 seconds. The diameter of the semi-finished cable is 43mm and the frequency of the vibration device is 12Hz.

[0033] Example 5: This example is basically the same as Example 1, except that the nitrogen slow cooling zone in S3 is also filled with helium, which accounts for 0.5% of the volume of the nitrogen.

[0034] Example 6: This example is basically the same as Example 1, except that the nitrogen slow cooling zone in S3 is also filled with helium, which accounts for 1% of the volume of the nitrogen.

[0035] Example 7: This example is basically the same as Example 1, except that the nitrogen slow cooling zone in S3 is also filled with helium, which accounts for 0.8% of the volume of the nitrogen.

[0036] Example 8: This example is basically the same as Example 1, except that the semi-finished cable is kept in the center of the vulcanizing tube during the vulcanization process by a bracket set inside the vulcanizing tube; the bracket includes a commercially available telescopic support and a guide wheel connected to its end, the guide wheel slidingly engaging with the cable surface, and by adjusting the telescopic amount of the support, it can accommodate cables of different specifications and fine-tune the cable position to ensure its centering position in the vulcanizing tube.

[0037] Example 9: This example is basically the same as Example 1, except that the screw length-to-diameter ratio of the cold feed extruder described in S2 is 12:1, the screw speed is set to 30 rpm, and the corresponding extrusion rate is stable at 1.5 kg / min.

[0038] Example 10: This example is basically the same as Example 1, except that the screw length-to-diameter ratio of the cold feed extruder described in S2 is 12:1, the screw speed is set to 50 rpm, and the corresponding extrusion rate is stable at 2.0 kg / min.

[0039] Example 11: This example is basically the same as Example 1, except that the microwave preheating zone in S3 adopts a time-division power control strategy: during the preheating process with a total duration of 60 seconds, the power of 5kW is used for initial heating in the first third of the time period, the power is increased to 10kW in the middle third of the time period to accelerate the temperature rise, and the power is adjusted to the range of 12kW in the last third of the time period based on real-time temperature measurement feedback, so that the core temperature of the semi-finished battery rises uniformly to 80℃.

[0040] Example 12: This example is basically the same as Example 1, except that the microwave preheating zone in S3 adopts a time-division power control strategy: during the preheating process with a total duration of 90 seconds, the power of 8kW is used for initial heating in the first third of the time period, the power is increased to 12kW in the middle third of the time period to accelerate the temperature rise, and the power is adjusted to the range of 15kW in the last third of the time period based on real-time temperature measurement feedback, so that the core temperature of the semi-finished battery is uniformly raised to 100℃.

[0041] Example 13: This example is basically the same as Example 1, except that the steam vulcanization zone in S3 adopts a chain-type vulcanization pipe, and saturated steam with a pressure of 0.8MPa is introduced. The vulcanization temperature is 170℃, and the semi-finished cable passes through a 50-meter-long pipe at a speed of 20 meters / minute. The vulcanization time is controlled within 2 minutes.

[0042] Example 14: This example is basically the same as Example 1, except that the steam vulcanization zone in S3 uses a catenary-style vulcanization pipe, saturated steam with a pressure of 1.2 MPa is introduced, the vulcanization temperature is 190°C, the semi-finished cable passes through an 80-meter-long pipe at a speed of 40 meters / minute, and the vulcanization time is controlled within 4 minutes.

[0043] Example 15: This example is basically the same as Example 1, except that the natural bending radius of the vulcanizing pipe in the steam vulcanizing zone described in S3 is 1.5 times the pipe length.

[0044] Example 16: This example is basically the same as Example 1, except that the natural bending radius of the vulcanizing pipe in the steam vulcanizing zone described in S3 is twice the length of the pipe.

[0045] Example 17: This example is basically the same as Example 1, except that S1 and the preparation of the rubber mixture are different. By weight percentage, 22% silica, 2.8% silane pretreatment solution, 1% dicumyl peroxide, 0.6% triallyl isocyanurate, 0.3% antioxidant 1010, and the balance ethylene-propylene-diene monomer rubber are added to an internal mixer and mixed at 50°C for 15 minutes to obtain a compound. The compound is then transferred to an open mill for thin-pass processing, with the roller temperature controlled at 45°C, the speed ratio between the two rollers at 1.2, and the roller gap set to... The particle size was 0.8 mm, and the number of thin passes was 5. The compounded rubber after thin pass treatment was placed in a constant temperature and humidity environment for curing treatment. The ambient temperature was 23℃, the relative humidity was 45%, and the curing time was 6 hours to obtain a cured compounded rubber. The silica was a precipitation product with a particle size of 20-25 nm. The silane pretreatment solution was prepared by mixing γ-aminopropyltriethoxysilane and anhydrous ethanol at a mass ratio of 1:3 and stirring at 40℃ for 30 minutes to obtain the silane pretreatment solution. S2. Extrusion Coating: The cured compound described in S1 is extruded and coated onto the conductor, which serves as the core of the cable, through a cold-feed extruder at a feed section temperature of 30°C and a die head temperature of 60°C. After extrusion, the material passes through a three-stage stepped cooling water tank. The first stage water temperature is 40°C, and the cooling time is 20 seconds; the second stage water temperature is 25°C, and the cooling time is 30 seconds; the third stage water temperature is 15°C, and the cooling time is 20 seconds, forming a semi-finished cable. The microwave preheating zone in S3 uses microwaves with a frequency of 2.4 GHz to preheat the semi-finished cable; the entrance of the steam vulcanization zone is isolated by double steam curtains, the steam pressure of the steam curtains is 0.1 MPa, and the curtain spacing is 500 mm; the nitrogen slow cooling zone is filled with nitrogen gas with a purity of ≥99.99%, which reduces the temperature of the semi-finished cable from the vulcanization temperature gradient to 40°C within 10 minutes at a rate of 5°C / minute; the cooled cable in S3 is wound up under a constant tension of 100 N, and then subjected to aging treatment to obtain the finished cable; the aging treatment in S4 is carried out at a treatment temperature of 40°C for 24 hours, with the relative humidity controlled at 40%.

[0046] Example 18: This example is basically the same as Example 1, except that S1, the preparation of the rubber mixture... By weight percentage, 35% of silica, 5.6% of silane pretreatment solution, 2.5% of dicumyl peroxide, 1.2% of triallyl isocyanurate, 0.6% of antioxidant 1010, and the balance of ethylene-propylene-diene monomer rubber are added to an internal mixer and mixed at 70°C for 25 minutes to obtain a compound. The compound is then transferred to an open mill for thin-pass processing, with the roller temperature controlled at 55°C, the speed ratio between the two rollers at 1.5, and the roller gap set... The particle size is 1.2 mm, and the number of thin passes is 8. The compounded rubber after thin pass treatment is placed in a constant temperature and humidity environment for curing treatment. The ambient temperature is 27℃, the relative humidity is 55%, and the curing time is 8 hours to obtain a cured compounded rubber. The silica is a precipitation product with a particle size of 45-50 nm. The silane pretreatment solution is prepared by mixing γ-aminopropyltriethoxysilane and anhydrous ethanol at a mass ratio of 1:5 and stirring at 50℃ for 45 minutes to obtain the silane pretreatment solution. S2. Extrusion Coating: The cured compound described in S1 is extruded and coated onto the conductor, which serves as the core of the cable, through a cold-feed extruder at a feed section temperature of 40°C and a die head temperature of 70°C. After extrusion, the cable passes through a three-stage stepped cooling water tank. The first stage water temperature is 45°C, and the cooling time is 30 seconds; the second stage water temperature is 30°C, and the cooling time is 40 seconds; the third stage water temperature is 20°C, and the cooling time is 30 seconds, forming a semi-finished cable. The microwave preheating zone described in S3 uses microwaves with a frequency of 2.5GHz to preheat the semi-finished cable. The entrance to the steam vulcanization zone is isolated by a double steam curtain with a steam pressure of 0.2MPa and a curtain spacing of 800mm. The nitrogen slow cooling zone described in S3 is filled with nitrogen gas with a purity of ≥99.99%, which causes the temperature of the semi-finished cable to drop from the vulcanization temperature gradient to 50°C within 15 minutes at a rate of 10°C / minute. The cooled cable described in S3 is wound up under a constant tension of 200N, and then subjected to aging treatment to obtain the finished cable; the aging treatment described in S4 is performed at a temperature of 50℃ for 48 hours, with the relative humidity controlled at 60%.

[0047] Comparative Example 1: The difference between this comparative example and Example 1 is that there is no nitrogen slow cooling step in S3.

[0048] Comparative Example 2: The difference between this comparative example and Example 1 is that there is no microwave preheating step in S3.

[0049] Comparative Example 3: The difference between this comparative example and Example 1 is that there is no horizontal vulcanizing tube step in S3.

[0050] To investigate the cable performance of the above embodiments and control examples, the main materials were determined according to the experimental formula, and samples were obtained for testing. The testing of the finished cables was mainly based on national standards GB / T 5013 and GB / T 12706 and international standard IEC60811. Conductivity was verified by conductor DC resistance testing, insulation thickness and eccentricity measurements were used to ensure structural uniformity, power frequency withstand voltage tests were used to evaluate insulation strength, and residual stress was detected using ultrasonic non-destructive testing. All operations were performed in a temperature-controlled environment using calibrated high-voltage testing instruments to ensure the reliability of the results. The results are as follows: Figure 1-3 As shown, the specific investigation is as follows: 1. Investigate the impact of mechanical vibration post-treatment on the performance of cable samples: like Figure 1-3As shown, Example 3, using vibration parameters of 15Hz frequency and 0.2mm amplitude, achieved a cable residual stress as low as 9.5MPa and an insulation strength as high as 29.8 kV / mm, making it the best performing example in this group and even among all the schemes. Example 4, using intermediate parameters of 12Hz and 0.3mm, achieved a residual stress of 10.1MPa, outperforming Example 2, which used 13Hz and 0.1mm parameters, with a residual stress of 10.8MPa. This demonstrates that moderate vibration energy effectively promotes molecular chain relaxation and stress release; excessively high frequencies or amplitudes, exceeding the material's tolerance, will weaken the gain.

[0051] 2. Investigate the synergistic effect of cooling medium and formulation on the performance of cable samples: like Figure 1-3 As shown, in Example 7, the addition of 0.8% helium resulted in the best residual stress control, at 10.8 MPa. In Example 6, the addition of 1% helium resulted in the highest insulation strength, reaching 29.2 kV / mm. In Example 5, the addition of 0.5% helium had a relatively weaker effect. This reflects that there is an optimal ratio of helium to improve cooling uniformity, and more is not necessarily better. In contrast, Control Example 1, which completely eliminated gradient cooling, performed the worst, with a residual stress as high as 16.8 MPa, highlighting the fundamental role of controlled cooling.

[0052] 3. Investigate the impact of vulcanization tube structure and cable attitude control on the performance of cable samples: like Figure 1-3 As shown, among the natural curvature radius parameters of the catenary vulcanizing pipe, Example 16 uses a radius of 2, with an eccentricity of 4.6%, which is superior to Example 15, which uses a radius of 1.5 and has an eccentricity of 4.7%. Example 8 reduces the eccentricity to a minimum of 3.8% by actively controlling the cable alignment with the support, resulting in a significant performance improvement. Examples 15 and 16 are not as effective as Example 8 in stress control, indicating that the combination of curvature reduction and active control is more effective. In contrast, Control Example 3, which uses a horizontal vulcanizing pipe, lacks an effective alignment mechanism, resulting in an eccentricity as high as 7.5%, and exhibits the worst performance.

[0053] 4. Explore the impact of balancing comprehensive process parameters on the performance of cable samples: like Figure 1-3As shown, Example 18 achieved an insulation strength of 29.1 kV / mm, while Example 14, using high-pressure, high-temperature vulcanization, had slightly lower performance. Examples 9 and 11, due to their lower screw speeds and microwave power, exhibited higher residual stresses of 12.5 and 12.8 MPa, respectively, while Example 13, using lower vulcanization strength, had the highest residual stress at 13.0 MPa. This demonstrates the strong coupling between the upstream and downstream processes of the production line; deficiencies in the upstream process directly affect the final quality of the downstream vulcanization. Control Example 2, which omitted microwave preheating, had the worst performance compared to all examples, further proving the irreplaceable role of the microwave preheating process in achieving uniform vulcanization and reducing thermal stress at its source.

Claims

1. A production method for reducing internal stress in cables based on a continuous vulcanization process, characterized in that, Includes the following steps: S1, Preparation of rubber mixtures By mass percentage, 22-35% of silica, 2.8-5.6% of silane pretreatment solution, 1-2.5% of dicumyl peroxide, 0.6-1.2% of triallyl isocyanurate, 0.3-0.6% of antioxidant 1010, and the balance of ethylene-propylene-diene monomer rubber are added to an internal mixer and mixed at 50-70℃ for 15-25 minutes to obtain a compound. The compound is then transferred to an open mill for thin-pass treatment, with the roller temperature controlled at 45-55℃, the speed ratio between the two rollers at 1.2-1.5, the roller gap set at 0.8-1.2mm, and the number of thin-pass passes at 5-8. The compound after thin-pass treatment is then placed in a constant temperature and humidity environment for curing treatment, with an ambient temperature of 23-27℃, a relative humidity of 45-55%, and a curing time of 6-8 hours to obtain a cured compound. S2, Extrusion Coating The cured compound described in S1 is extruded through a cold-feed extruder at a feed section temperature of 30-40℃ and a die head temperature of 60-70℃, and then extruded onto the conductor, which serves as the core of the cable. After extrusion, the material passes through a three-stage stepped cooling water tank. The first stage water temperature is 40-45℃, and the cooling time is 20-30 seconds; the second stage water temperature is 25-30℃, and the cooling time is 30-40 seconds; the third stage water temperature is 15-20℃, and the cooling time is 20-30 seconds, forming a semi-finished cable. S3, Three-stage continuous vulcanization The semi-finished cable described in S2 is processed sequentially through a microwave preheating zone, a steam vulcanization zone, and a nitrogen slow cooling zone. The microwave preheating zone uses microwaves with a frequency of 2.4-2.5 GHz to preheat the semi-finished cable. The steam vulcanization zone uses a catenary-style vulcanization pipe and saturated steam for vulcanization. The nitrogen slow cooling zone uses nitrogen to perform gradient cooling on the semi-finished cable, resulting in a cooled cable. The entrance to the steam vulcanization zone is isolated by a double steam curtain with a steam pressure of 0.1-0.2 MPa and a curtain spacing of 500-800 mm. S4, Traction winding The cooled cable described in S3 is wound up under a constant tension of 100-200N, and then subjected to aging treatment to obtain the finished cable.

2. The production method for reducing internal stress in cables based on a continuous vulcanization process according to claim 1, characterized in that, The silica mentioned in S1 is a product produced by precipitation, with a particle size of 20-50 nm; the preparation method of the silane pretreatment solution is as follows: γ-aminopropyltriethoxysilane and anhydrous ethanol are mixed at a mass ratio of 1:3-5, and stirred at 40-50℃ for 30-45 minutes to obtain the silane pretreatment solution.

3. The production method for reducing internal stress in cables based on a continuous vulcanization process according to claim 1, characterized in that, The cold-feed extruder described in S2 has a screw length-to-diameter ratio of 12:1, a screw speed set to 30-50 rpm, and a corresponding extrusion rate that is stable at 1.5-2.0 kg / min.

4. The production method for reducing internal stress in cables based on a continuous vulcanization process according to claim 1, characterized in that, The microwave preheating zone described in S3 adopts a time-division power control strategy: during the preheating process with a total duration of 60-90 seconds, the power of 5-8kW is used for initial heating in the first third of the time period, the power is increased to 10-12kW in the middle third of the time period to accelerate the temperature rise, and the power is adjusted to the range of 12-15kW in the last third of the time period based on real-time temperature measurement feedback, so that the core temperature of the semi-finished battery can be raised to 80-100℃ evenly.

5. A production method for reducing internal stress in cables based on a continuous vulcanization process according to claim 1, characterized in that, The steam vulcanization zone described in S3 uses a catenary-style vulcanization pipe, through which saturated steam at a pressure of 0.8-1.2 MPa is introduced, and the vulcanization temperature is 170-190℃. The semi-finished cable passes through a 50-80 meter long pipe at a speed of 20-40 meters / minute, and the vulcanization time is controlled within 2-4 minutes.

6. A production method for reducing internal stress in cables based on a continuous vulcanization process according to claim 5, characterized in that, The natural bending radius of the vulcanizing pipe in the steam vulcanizing zone of S3 is 1.5-2 times the pipe length; the semi-finished cable is kept in the center of the vulcanizing pipe during the vulcanizing process by a support set inside the vulcanizing pipe; the support includes a retractable support and a guide wheel connected to its end, the guide wheel being slidably engaged with the cable surface.

7. A production method for reducing internal stress in cables based on a continuous vulcanization process according to claim 1, characterized in that, After passing through the steam vulcanization zone, the semi-finished cable described in S3 is subjected to mechanical vibration treatment using a low-frequency vibration device. The vibration amplitude is 0.1-0.3mm, and the treatment time is 30-60 seconds. The frequency of the vibration device is adjusted in real time according to the diameter of the semi-finished cable: when the diameter of the semi-finished cable is ≤20mm, the frequency of the vibration device is 15-20Hz; when the diameter of the semi-finished cable is 20-40mm, the frequency of the vibration device is 10-15Hz; and when the diameter of the semi-finished cable is >40mm, the vibration frequency is 8-12Hz.

8. A production method for reducing internal stress in cables based on a continuous vulcanization process according to claim 1, characterized in that, The nitrogen slow cooling zone described in S3 is filled with nitrogen gas with a purity of ≥99.99%, which causes the temperature of the semi-finished cable to drop from the vulcanization temperature gradient to 40-50℃ within 10-15 minutes at a rate of 5-10℃ / minute.

9. A production method for reducing internal stress in cables based on a continuous vulcanization process according to claim 8, characterized in that, The nitrogen slow cooling zone described in S3 is also filled with helium, which accounts for 0.5-1% of the volume of the nitrogen.

10. A production method for reducing internal stress in cables based on a continuous vulcanization process according to claim 1, characterized in that, The aging treatment described in S4 is carried out at a temperature of 40-50℃ for 24-48 hours, with the relative humidity controlled at 40-60%.

Images