Low-smoke halogen-free small-wall-thickness power cable for railway passenger car and processing technology of low-smoke halogen-free small-wall-thickness power cable

Abstract

The invention relates to the technical field of wires and cables, in particular to a low-smoke halogen-free small-wall-thickness power cable for a railway passenger car and a processing technology of the low-smoke halogen-free small-wall-thickness power cable. The cable comprises a wire core conductor, a nano flame-retardant polyolefin insulating layer, a glass fiber tape wrapping layer, an aramid fiber braid layer, an aluminum foil mylar shielding layer, a low-smoke halogen-free flame-retardant polyolefin outer sheath and a wear-resistant anti-skid coating from inside to outside, wherein the aramid fiber braid layer is coated with a silane coupling agent. And the wire core conductor adopts a high-purity oxygen-free copper wire with a specific twisting standard. And the insulating layer is excellent in electrical performance, flame-retardant and low-smoke. The structures of all the layers cooperatively provide mechanical protection and electromagnetic shielding functions. The processing technology starts from core conductor manufacturing, parameters of each step are strictly controlled, key steps are supplemented with raw material processing, monitoring regulation and control and special mold and cooling design, it is ensured that the cable meets the power transmission requirement of the railway passenger car, safe and efficient operation is achieved under complex working conditions, and stability of a passenger car electrical system is guaranteed.

Description

Technical Field

[0001] The present invention relates to the technical field of electric wires and cables, and in particular to a low-smoke, halogen-free, small-size, thick-walled power cable for railway passenger cars and a processing technology thereof. Background Art

[0002] With the rapid development of railway transportation, the safety and reliability of railway passenger cars have become the core concern. Among the many systems of passenger cars, the power transmission system plays a vital role, and the performance of power cables, as the key carrier of power transmission, is directly related to the stability and safety of passenger car operation. Traditional railway passenger car power cables have gradually exposed many disadvantages in practical applications. Due to the poor materials or structural design of some cables, a large amount of thick smoke and toxic hydrogen halide gas will be released when a fire occurs. These thick smoke will quickly fill the carriage, seriously obstructing the passengers' vision and making evacuation difficult. The hydrogen halide gas will cause strong irritation and damage to the human respiratory tract and eyes, greatly threatening the lives of passengers.

[0003] The smoke produced by the burning of cables used in some old passenger cars caused the visible distance in the car to be drastically reduced to almost zero in a short period of time, and it was difficult for passengers to find a safe exit in the chaos. The internal space of railway passenger cars is extremely limited and the wiring is intricate, which places extremely strict requirements on the size of cables. Some conventional cables are too large and face many difficulties during the installation process, which not only consumes a lot of manpower and time, but may also damage the cables or peripheral equipment due to forced installation. Moreover, when the passenger car is running, the cable needs to frequently withstand mechanical stress such as vibration, bending, and stretching. If the mechanical properties of the cable are insufficient, such as insufficient tensile strength or poor flexibility, it is easy to cause problems such as insulation cracking and conductor breakage during long-term operation, which will cause electrical failures and affect the normal operation of the passenger car. With the increasing complexity and precision of the electrical system of railway passenger cars, the requirements for the electromagnetic environment are also getting higher and higher. Some cables that do not have effective shielding measures are easily affected by external electromagnetic interference, resulting in distortion or interruption of signal transmission, causing misoperation or failure of the control system and communication system of the passenger car, and even endangering driving safety in serious cases. For example, on roads with strong electromagnetic interference, errors occurred in the control signals transmitted by some unshielded cables, causing the bus's braking system to temporarily fail, a dangerous situation. Summary of the invention

[0004] In order to meet the high requirements of railway passenger cars for power transmission and improve the safety, reliability and operation efficiency of railway passenger cars, the present invention proposes the following technical solutions: A low-smoke, halogen-free, small-size, thick-walled power cable for railway passenger cars, characterized in that it comprises a core conductor, on the outside of which are sequentially provided a nano flame-retardant polyolefin insulation layer, a glass fiber tape wrapping layer, an aramid fiber braided layer, an aluminum foil Mylar shielding layer, a low-smoke, halogen-free, flame-retardant polyolefin outer sheath, and a wear-resistant and non-slip coating on the surface of the outer sheath, and the outside of the aramid fiber braided layer is coated with a silane coupling agent.

[0005] Preferably, the core conductor is formed by twisting multiple strands of high-purity oxygen-free copper wires, the diameter of the copper wires ranges from 0.2 to 0.3 mm, and the seven-category copper conductor standard is adopted. The twisting pitch is between 10 and 18 times the diameter of the copper wire, and its resistivity at 20°C does not exceed 0.017241Ω・mm² / m, and the minimum bending radius is not greater than 6 to 8 times the outer diameter of the cable.

[0006] Preferably, the aluminum foil Mylar shielding layer is composited with aluminum foil having a thickness of 0.05-0.1 mm and polyester film, and its shielding effectiveness is not less than 60 dB in the frequency range of 30 MHz-1 GHz.

[0007] Preferably, the nano flame retardant polyolefin insulation layer has a thickness of 0.9-1.3 mm and a volume resistivity of not less than 10 at 20°C. 5 Ω・m, can withstand the electrical insulation requirements of rated voltage 750V or 1500V and above, and the smoke density level released during combustion shall not exceed 60 according to IEC61034 standard, and the hydrogen halide release shall not exceed 5mg / g according to IEC60754 standard.

[0008] Preferably, the wrapping overlap rate of the glass fiber tape wrapping layer is not less than 25%, and the thickness is 0.2-0.3 mm; the weaving density of the aramid fiber braided layer is 85%-90%, and the thickness is not more than 0.4 mm.

[0009] Preferably, the thickness of the low-smoke halogen-free flame-retardant polyolefin outer sheath is 1.8-2.8mm, its tensile strength is not less than 15MPa, and its elongation at break is not less than 350%. When the flame is burning, it is tested in accordance with the IEC60332-1 standard, and the self-extinguishing time does not exceed 8s, and the burning length does not exceed 50mm; when the bundled burning test is carried out in accordance with the IEC60332-3 standard, the flame spread height does not exceed 2.5m, and there is no molten dripping to cause secondary combustion; the wear-resistant and anti-slip coating has a thickness of 0.1-0.2mm, and the coating material is a mixture of polyurethane and silicon carbide micropowder, and its surface friction coefficient is not less than 0.6.

[0010] A processing technology of a low-smoke, halogen-free, small-size, thick-walled power cable for railway passenger cars, characterized in that it comprises the following steps: S1: The core conductor is made of multiple strands of high-purity oxygen-free copper wire, twisted according to the seven-category copper conductor standard, and the copper wire diameter, twisting pitch and other parameters are controlled. The resistivity at 20°C does not exceed 0.017241Ω・mm² / m, and the minimum bending radius is not more than 6-8 times the outer diameter of the cable; S2: Extrude the nano flame-retardant polyolefin insulation layer outside the wire core conductor through precision extrusion process, control the extruder temperature at 180-220℃, the screw speed at 30-60 rpm, and the pulling speed at 5-15 m / min, so that the insulation layer thickness reaches 0.9-1.3 mm; S3: A constant tension wrapping machine is used to wrap the glass fiber tape wrapping layer outside the nano flame retardant polyolefin insulation layer, with a wrapping overlap rate of not less than 25% and a thickness of 0.2-0.3mm; S4: An aramid fiber braided layer is made by weaving technology outside the glass fiber tape wrapping layer, with a weaving density of 85%-90% and a thickness of no more than 0.4mm, and a silane coupling agent treatment layer is coated on the outer surface of the aramid fiber braided layer; S5: The aluminum foil Mylar shielding layer is wrapped outside the aramid fiber braided layer. The aluminum foil Mylar shielding layer is made of aluminum foil with a thickness of 0.05-0.1mm and polyester film. S6: A low-smoke, halogen-free, flame-retardant polyolefin outer sheath is made by extrusion process outside the aluminum foil Mylar shielding layer, and the extrusion temperature is controlled at 190-230°C, the screw speed is 25-50 revolutions per minute, and the pulling speed is 4-12 meters per minute, so that the outer sheath thickness reaches 1.8-2.8mm; S7: A wear-resistant and anti-skid coating is applied on the surface of the outer sheath, the coating thickness is 0.1-0.2mm, and the coating material is a mixture of polyurethane and silicon carbide powder, so that its surface friction coefficient is not less than 0.6.

[0011] Preferably, in step S2, before extruding the nano flame retardant polyolefin insulation layer, the raw material is dried to make its water content less than 0.1%, and during the extrusion process, the thickness accuracy of the insulation layer is controlled within ±0.05mm through an online thickness monitoring and automatic adjustment device.

[0012] Preferably, in step S4, during the aramid fiber weaving process, the tension of the weaving machine is monitored and adjusted in real time to ensure weaving uniformity, and the humidity of the weaving environment is controlled to maintain its relative humidity at 40%-60%.

[0013] Preferably, in step S6, the low-smoke halogen-free flame-retardant polyolefin outer sheath extrusion die adopts a special flow channel design to make the outer surface of the sheath smooth without defects such as flow marks and bubbles, and adopts a segmented cooling method after extrusion, first air cooling to initially shape the sheath, and then water cooling to improve the crystallinity and mechanical properties of the sheath.

[0014] The beneficial effects of the present invention are: 1. The present invention is formed by twisting multiple strands of high-purity oxygen-free copper wires of specific specifications. While ensuring good flexibility to adapt to the complex wiring environment of railway passenger cars, it has excellent electrical conductivity, effectively reduces energy loss during power transmission, and ensures that electric energy is efficiently and stably transmitted to various electrical equipment in the passenger car, such as traction motors, lighting systems, etc., to ensure the normal operation of the passenger car electrical system.

[0015] 2. The nano flame-retardant polyolefin insulation layer of the present invention has a suitable thickness and excellent electrical insulation performance, which can effectively prevent current leakage and breakdown, provide reliable electrical isolation protection for the safe operation of the cable, and maintain stable insulation performance even under long-term operation and complex working conditions, thereby reducing the probability of electrical failures.

[0016] 3. When the present invention is burned, the smoke density level released by the nano flame retardant polyolefin insulation layer, the low-smoke halogen-free flame retardant polyolefin outer sheath and other materials is low and the amount of hydrogen halide released is extremely small, which greatly reduces the threat of thick smoke and toxic gases to the life safety of passengers when a fire occurs, creates more favorable environmental conditions for the evacuation of passengers in emergency situations, and also meets environmental protection requirements and reduces pollution to the environment.

[0017] 4. The low-smoke halogen-free flame-retardant polyolefin outer sheath of the present invention has an excellent flame-retardant effect. Whether it is a single cable combustion test according to the IEC60332-1 standard or a bundle combustion test according to the IEC 60332-3 standard, it can effectively prevent the rapid spread of flames, control the fire hazard to the minimum range, protect the overall structure and equipment integrity of the bus, and reduce the losses caused by the fire.

[0018] 5. The specific twisting standard of the present invention enables the core conductor to have good conductivity while having sufficient flexibility and tensile strength, and can withstand mechanical stresses such as vibration, bending, stretching, etc. during the operation of railway passenger cars, and is not prone to breakage or damage, thereby ensuring the continuity and stability of power transmission.

[0019] 6. The glass fiber tape wrapping layer of the present invention provides a certain mechanical buffer and wear resistance for the cable, and the aramid fiber braided layer further enhances the tensile strength and overall mechanical stability of the cable. The two work synergistically to effectively protect the internal core conductor and insulation layer, enabling it to work normally in a complex and harsh mechanical environment, thereby extending the service life of the cable.

[0020] 7. In the various processing steps of the present invention, such as the precise control of parameters such as the copper wire diameter and the twisting pitch when the core conductor is twisted, the strict setting of the extruder temperature, screw speed, and pulling speed when the nano flame-retardant polyolefin insulation layer is extruded, and the temperature, speed, and pulling speed control when the outer sheath is extruded, all help to ensure the uniformity, consistency, and performance stability of each layer of the cable structure, and improve the reliability and stability of product quality.

[0021] 8. The raw material drying treatment before extrusion of the nano flame-retardant polyolefin insulation layer and the online thickness monitoring and automatic adjustment device during the extrusion process of the present invention can effectively avoid the degradation of insulation performance caused by the moisture of the raw materials and ensure the thickness accuracy of the insulation layer, thereby improving the quality of the insulation layer; the real-time monitoring and adjustment of the tension during the weaving of the aramid fiber and the humidity control can ensure the weaving uniformity and quality stability; the special flow channel design and segmented cooling method of the low-smoke halogen-free flame-retardant polyolefin outer sheath extrusion die can make the outer surface of the sheath smooth and defect-free and improve the crystallinity and mechanical properties. These process measures combinedly improve the production quality and performance level of the entire cable, reduce the defective rate, and improve production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a process diagram of a low-smoke, halogen-free, small-size, thick-walled power cable for railway passenger cars according to the present invention.

[0023] Figure 2 The present invention is a schematic structural diagram of a low-smoke, halogen-free, small-size, thick-walled power cable for railway passenger cars.

[0024] In the figure: 1. Core conductor; 2. Nano flame-retardant polyolefin insulation layer; 3. Glass fiber tape wrapping layer; 4. Aramid fiber braided layer; 5. Aluminum foil Mylar shielding layer; 6. Low-smoke halogen-free flame-retardant polyolefin outer sheath; 7. Wear-resistant and anti-slip coating. DETAILED DESCRIPTION

[0025] A low-smoke, halogen-free, small-size, thick-walled power cable for railway passenger cars, characterized in that it comprises a core conductor 1, which is formed by twisting multiple strands of high-purity oxygen-free copper wires, the diameter of the copper wires is in the range of 0.2-0.3mm, and the seven-category copper conductor standard is adopted. The twisting pitch is between 10-18 times the copper wire diameter, and the resistivity at 20°C does not exceed 0.017241Ω・mm² / m, and the minimum bending radius is not greater than 6-8 times the outer diameter of the cable.

[0026] The core conductor 1 is provided with a nano flame retardant polyolefin insulation layer 2, a glass fiber tape wrapping layer 3, an aramid fiber braided layer 4, an aluminum foil Mylar shielding layer 5, a low-smoke halogen-free flame retardant polyolefin outer sheath 6 and a wear-resistant and anti-skid coating 7 on the surface of the outer sheath in sequence.

[0027] The aluminum foil Mylar shielding layer 5 is made of aluminum foil with a thickness of 0.05-0.1mm and polyester film, and its shielding effectiveness is not less than 60dB in the frequency range of 30MHz-1GHz. The nano flame retardant polyolefin insulation layer 2 has a thickness of 0.9-1.3mm and a volume resistivity of not less than 10¹ at 20°C. 5 Ω・m, can withstand the electrical insulation requirements of rated voltage 750V or 1500V and above, and the smoke density level released during combustion shall not exceed 60 according to IEC61034 standard, and the hydrogen halide release shall not exceed 5mg / g according to IEC60754 standard. The wrapping overlap rate of the glass fiber tape wrapping layer 3 shall not be less than 25%, and the thickness shall be 0.2-0.3mm. The weaving density of the aramid fiber braided layer 4 is 85%-90%, the thickness is not more than 0.4mm, and the aramid fiber braided layer 4 is coated with silane coupling agent. The thickness of the low-smoke halogen-free flame-retardant polyolefin outer sheath 6 is 1.8-2.8mm, its tensile strength is not less than 15MPa, and its elongation at break is not less than 350%. When the flame is burning, it is tested in accordance with the IEC60332-1 standard, and the self-extinguishing time does not exceed 8s, and the burning length does not exceed 50mm; when the bundled burning test is carried out in accordance with the IEC60332-3 standard, the flame spread height does not exceed 2.5m, and there is no molten dripping to cause secondary combustion; the thickness of the wear-resistant and anti-slip coating 7 is 0.1-0.2mm, and the coating material is a mixture of polyurethane and silicon carbide micropowder, and its surface friction coefficient is not less than 0.6.

[0028] A processing technology of a low-smoke, halogen-free, small-size, thick-walled power cable for railway passenger cars, characterized in that it comprises the following steps: S1: The core conductor 1 is made of multiple strands of high-purity oxygen-free copper wire, twisted according to the standard of Category 7 copper conductors, and the copper wire diameter, twisting pitch and other parameters are controlled. The resistivity at 20°C does not exceed 0.017241Ω・mm² / m, and the minimum bending radius is not more than 6-8 times the outer diameter of the cable; S2: Extruding a nano flame retardant polyolefin insulation layer 2 outside the wire core conductor 1 through a precision extrusion process, controlling the extruder temperature at 180-220°C, the screw speed at 30-60 rpm, and the pulling speed at 5-15 m / min, so that the insulation layer thickness reaches 0.9-1.3 mm, wherein before extruding the nano flame retardant polyolefin insulation layer 2, the raw material is dried to make its water content less than 0.1%, and during the extrusion process, the online thickness monitoring and automatic adjustment device is used to control the insulation layer thickness accuracy within ±0.05 mm; S3: A glass fiber tape wrapping layer 3 is wrapped outside the nano flame retardant polyolefin insulation layer 2 by a constant tension wrapping machine, with an overlap rate of not less than 25% and a thickness of 0.2-0.3 mm; S4: an aramid fiber braided layer 4 is manufactured by a braiding process outside the glass fiber tape wrapping layer 3, the braiding density is 85%-90%, the thickness is not more than 0.4 mm, and a silane coupling agent treatment layer is coated on the outer surface of the aramid fiber braided layer 4. During the aramid fiber braiding process, the tension of the braiding machine is monitored and adjusted in real time to ensure the braiding uniformity, and the humidity of the braiding environment is controlled to keep the relative humidity at 40%-60%; S5: an aluminum foil Mylar shielding layer 5 is wrapped outside the aramid fiber braided layer 4, and the aluminum foil Mylar shielding layer 5 is made of aluminum foil with a thickness of 0.05-0.1 mm and a polyester film; S6: A low-smoke, halogen-free, flame-retardant polyolefin outer sheath 6 is made by extrusion process outside the aluminum foil Mylar shielding layer 5, and the extrusion temperature is controlled at 190-230°C, the screw speed is 25-50 revolutions per minute, and the traction speed is 4-12 meters per minute, so that the thickness of the outer sheath reaches 1.8-2.8mm. Among them, the extrusion die of the low-smoke, halogen-free, flame-retardant polyolefin outer sheath 6 adopts a special flow channel design to make the outer surface of the sheath smooth without defects such as flow marks and bubbles, and adopts a segmented cooling method after extrusion, first air cooling to initially shape the sheath, and then water cooling to improve the crystallinity and mechanical properties of the sheath; S7: A wear-resistant and anti-skid coating 7 is applied on the surface of the outer sheath. The coating thickness is 0.1-0.2 mm. The coating material is a mixture of polyurethane and silicon carbide powder, so that the surface friction coefficient is not less than 0.6.

Claims

1. A low-smoke, halogen-free, small-size, thick-walled power cable for railway passenger cars, characterized in that: The invention comprises a core conductor (1), wherein the core conductor (1) is provided with a nano flame-retardant polyolefin insulation layer (2), a glass fiber tape wrapping layer (3), an aramid fiber braided layer (4), an aluminum foil Mylar shielding layer (5), a low-smoke halogen-free flame-retardant polyolefin outer sheath (6), and a wear-resistant and anti-skid coating (7) on the surface of the outer sheath in sequence, and the aramid fiber braided layer (4) is coated with a silane coupling agent.

2. The low-smoke, halogen-free, small-size, thick-walled power cable for railway passenger cars according to claim 1, characterized in that: The core conductor (1) is formed by twisting a plurality of high-purity oxygen-free copper wires, the diameter of the copper wires is in the range of 0.2-0.3 mm, and the Category 7 copper conductor standard is adopted. The twisting pitch is between 10 and 18 times the diameter of the copper wires, and the resistivity thereof at 20°C does not exceed 0.017241 Ω・mm² / m, and the minimum bending radius is not greater than 6 to 8 times the outer diameter of the cable.

3. The low-smoke, halogen-free, small-size, thick-walled power cable for railway passenger cars according to claim 1, characterized in that: The aluminum foil Mylar shielding layer (5) is made of a composite of aluminum foil with a thickness of 0.05-0.1 mm and polyester film, and its shielding effectiveness is not less than 60 dB in the frequency range of 30 MHz-1 GHz.

4. The low-smoke, halogen-free, small-size, thick-walled power cable for railway passenger cars according to claim 1, characterized in that: The nano flame retardant polyolefin insulation layer (2) has a thickness of 0.9-1.3 mm and a volume resistivity of not less than 10 at 20°C. 5 Ω・m, can withstand the electrical insulation requirements of rated voltage 750V or 1500V and above, and the smoke density level released during combustion shall not exceed 60 according to IEC61034 standard, and the hydrogen halide release shall not exceed 5mg / g according to IEC60754 standard.

5. The low-smoke, halogen-free, small-size, thick-walled power cable for railway passenger cars according to claim 1, characterized in that: The glass fiber tape wrapping layer (3) has a wrapping overlap rate of not less than 25% and a thickness of 0.2-0.3 mm; the aramid fiber braiding layer (4) has a braiding density of 85%-90% and a thickness of not more than 0.4 mm.

6. The low-smoke, halogen-free, small-size, thick-walled power cable for railway passenger cars according to claim 1, characterized in that: The low-smoke halogen-free flame-retardant polyolefin outer sheath (6) has a thickness of 1.8-2.8 mm, a tensile strength of not less than 15 MPa, an elongation at break of not less than 350%, and a self-extinguishing time of not more than 8 seconds and a burning length of not more than 50 mm when tested in accordance with the IEC60332-1 standard during flame combustion; when a bundle combustion test is conducted in accordance with the IEC60332-3 standard, the flame spread height does not exceed 2.5 m, and there is no molten dripping to cause secondary combustion; the wear-resistant and anti-skid coating (7) has a thickness of 0.1-0.2 mm, and the coating material is a mixture of polyurethane and silicon carbide micropowder, and the surface friction coefficient is not less than 0.

6.

7. A processing technology for low-smoke, halogen-free, small-size, thick-walled power cables for railway passenger cars, characterized in that: The following steps are involved: S1: The core conductor (1) is made of multiple strands of high-purity oxygen-free copper wire, twisted in accordance with the Category 7 copper conductor standard, with controlled parameters such as copper wire diameter and twisting pitch. The resistivity at 20°C does not exceed 0.017241Ω・mm² / m, and the minimum bending radius is not greater than 6-8 times the outer diameter of the cable; S2: Extruding a nano flame-retardant polyolefin insulation layer (2) outside the wire core conductor (1) by a precision extrusion process, controlling the extruder temperature at 180-220° C., the screw speed at 30-60 rpm, and the pulling speed at 5-15 m / min, so that the insulation layer thickness reaches 0.9-1.3 mm; S3: A glass fiber tape wrapping layer (3) is wrapped around the nano flame retardant polyolefin insulation layer (2) using a constant tension wrapping machine, with an overlap rate of not less than 25% and a thickness of 0.2-0.3 mm; S4: using a weaving process to produce an aramid fiber braided layer (4) outside the glass fiber tape wrapping layer (3), wherein the weaving density is 85%-90% and the thickness is not greater than 0.4 mm, and a silane coupling agent treatment layer is coated on the outer surface of the aramid fiber braided layer (4); S5: an aluminum foil Mylar shielding layer (5) is wrapped outside the aramid fiber braided layer (4), wherein the aluminum foil Mylar shielding layer (5) is made of a composite of aluminum foil with a thickness of 0.05-0.1 mm and polyester film; S6: A low-smoke, halogen-free, flame-retardant polyolefin outer sheath (6) is produced by extrusion process outside the aluminum foil Mylar shielding layer (5), the extrusion temperature is controlled at 190-230° C., the screw speed is 25-50 revolutions per minute, and the pulling speed is 4-12 meters per minute, so that the thickness of the outer sheath reaches 1.8-2.8 mm; S7: A wear-resistant and anti-skid coating (7) is applied to the surface of the outer sheath. The coating thickness is 0.1-0.2 mm. The coating material is a mixture of polyurethane and silicon carbide powder. The surface friction coefficient is not less than 0.

6.

8. The processing technology of the low-smoke, halogen-free, small-size, thick-walled power cable for railway passenger cars according to claim 7 is characterized in that: In step S2, before the nano flame retardant polyolefin insulation layer (2) is extruded, the raw material is dried to make its water content less than 0.1%, and during the extrusion process, an online thickness monitoring and automatic adjustment device is used to control the thickness accuracy of the insulation layer within ±0.05 mm.

9. The processing technology of a low-smoke, halogen-free, small-size, thick-walled power cable for railway passenger cars according to claim 7, characterized in that: In step S4, during the aramid fiber weaving process, the tension of the weaving machine is monitored and adjusted in real time to ensure weaving uniformity, and the humidity of the weaving environment is controlled to keep its relative humidity at 40%-60%.

10. The processing technology of a low-smoke, halogen-free, small-size, thick-walled power cable for railway passenger cars according to claim 7, characterized in that: In step S6, the low-smoke halogen-free flame-retardant polyolefin outer sheath (6) is extruded with a special flow channel design to make the outer surface of the sheath smooth without defects such as flow marks and bubbles, and after extrusion, a segmented cooling method is adopted, first air cooling is used to initially shape the sheath, and then water cooling is used to improve the crystallinity and mechanical properties of the sheath.

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