Polypropylene insulated cable capable of preventing insulation shrinkage and conductor preparation process thereof

Abstract

The invention discloses a polypropylene insulated cable capable of preventing insulation shrinkage and a conductor preparation process thereof, and relates to the field of cable manufacturing. A plurality of insulated wire cores of the cable are twisted together, and a metal shield is wrapped outside the insulated wire cores; the twisted insulating wire cores are wrapped in an isolation sleeve, and a filling rope is filled between the isolation sleeve and the insulating wire cores. A wrapping tape is arranged on the lining of the isolation sleeve; an armor layer and an outer sheath layer are sequentially arranged outside the isolating layer in a sleeving manner; the insulating wire core comprises a conductor, an inner screen material, an insulating material and an outer screen material, a groove is formed in the outer layer of the conductor, and the inner screen material is embedded in the groove; the process comprises the steps of conductor manufacturing, wire twisting and extrusion of an insulating layer. According to the application, the stranding gap of the insulating wire cores is reduced through the filling rope and the wrapping tape, the adhesive force of the inner screen material is enhanced by using the conductor groove structure, the stranding pitch and extrusion parameters are optimized by combining a special conductor preparation process, the shrinkage of the insulating layer is effectively inhibited, and the operation safety of the cable is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of cable manufacturing, in particular to a polypropylene insulated cable for preventing insulation shrinkage and a conductor preparation process thereof. BACKGROUND

[0002] Currently, cross-linked polyethylene is commonly used as an insulation material for medium and high voltage cables. During the high-temperature and high-pressure cross-linking production process or subsequent wire core standing process, a large amount of by-products are generated, which leads to the shrinkage of the insulation layer. This shrinkage can expose the conductor end, and during the operation process after the cable terminal is installed, insulation shrinkage may cause end breakdown or even explosion accidents, which poses a serious safety hazard. At the same time, in order to meet the demand for cost reduction, the existing conductors are generally produced in a full-type wire structure, and there is almost no gap between the single strands of the stranded conductor. This smooth and round conductor surface characteristic can exacerbate the shrinkage of the insulation material. In particular, during the operation of the cable, due to temperature changes and mechanical stress, the adhesion between the insulation layer and the conductor will be further weakened, exacerbating the insulation shrinkage problem. In addition, the production process of traditional cross-linked polyethylene material is complex, the energy consumption is high, and the by-products generated during the cross-linking process can affect the long-term performance of the cable. These problems seriously restrict the reliability and service life of medium and high voltage cables. SUMMARY

[0003] In order to avoid the problem of insulation shrinkage caused by the smooth surface of the cable conductor, the present application provides a polypropylene insulated cable for preventing insulation shrinkage and a conductor preparation process thereof.

[0004] In a first aspect, the present application provides a polypropylene insulated cable for preventing insulation shrinkage, which adopts the following technical solution:

[0005] A polypropylene insulated cable for preventing insulation shrinkage, comprising a plurality of insulated cores twisted together, and a metal shield wrapped outside the insulated cores; the twisted insulated cores are wrapped in an isolation sleeve, and a filling rope is filled between the isolation sleeve and the insulated cores; a tape is lined in the isolation sleeve; a armor layer and an outer sheath layer are sequentially wrapped outside the isolation layer.

[0006] The insulated core comprises a conductor, an inner shielding material, an insulation material, and an outer shielding material, and a groove is provided on the outer layer of the conductor, and the inner shielding material is embedded in the groove.

[0007] In a second aspect, the present application further provides a preparation process of a conductor in a polypropylene insulated cable for preventing insulation shrinkage, which adopts the following technical solution:

[0008] A preparation process of a conductor in a polypropylene insulated cable for preventing insulation shrinkage, comprising the following steps:

[0009] S1, conductor monofilament manufacturing, the outermost layer of the conductor monofilament adopts a special type of wire, and the two sides of the large arc surface of the conventional T-shaped wire are rounded;

[0010] S2, stranding: using a frame stranding machine to first strand each inner layer monofilament;

[0011] S3, extrusion of the insulation layer: the insulation layer adopts thermoplastic high-performance polypropylene elastomer insulation material and polypropylene inner and outer shielding material and CVV semi-catenary production line.

[0012] Optionally, in step S1, the metal round rod is drawn through a plurality of passes of a drawing equipment to a type line wire of a required outer layer or inner layer single wire size and shape.

[0013] Optionally, in step S3, the frame stranding machine is used to first strand each inner layer monofilament, and the pitch is controlled at 30-40 times to improve the conductivity of the conductor, and then the outer layer monofilament is stranded and the pitch is controlled at 13-16 times to improve the shrinkage resistance of the conductor surface to the insulation layer; due to the larger pitch of the inner layer, the length of the sizing area of the stranding and combining die is lengthened to prevent the inner layer from loosening and producing a snake-shaped conductor.

[0014] Optionally, in step S4, since the melting temperature of PP polypropylene is about 100 degrees higher than that of XLPE cross-linked polyethylene, the heating tile of the extruder is increased to 12KW; three-layer co-extrusion is used during extrusion, and the insulation extrusion temperature is 130-210℃, and the shielding material is controlled at 130-200℃;

[0015] After extrusion, since cross-linking is not required, the first four cross-linking pipes are not heated but are connected to 0.5Mp pressure nitrogen for air cooling and shaping, and the water cooling liquid level of the cross-linking pipes is pumped to the fifth section for early cooling to prevent the insulation from being eccentric.

[0016] In summary, the present application has the following beneficial technical effects:

[0017] The present application utilizes the conductor groove structure to enhance the adhesion of the inner shielding material, optimizes the stranding pitch and extrusion parameters in combination with a special conductor preparation process, effectively suppresses the insulation shrinkage, and improves the operation safety of the cable. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 is the overall structure diagram of a polypropylene insulation cable for preventing insulation shrinkage according to the present application;

[0019] Figure 2 is Figure 1 the effect diagram of the outermost layer conductor of the insulation core in

[0020] Figure 3Figure 2 is a schematic view of the lengthening of the sizing zone in step S3 in the present application.

[0021] Reference signs:

[0022] 1, conductor; 2, inner shielding material; 3, insulation material; 4, outer shielding material; 5, metal shield; 6, filling rope; 7, wrapping tape; 8, isolation sleeve; 9, armor layer; 10, outer sheath layer. DETAILED DESCRIPTION

[0023] The following will be described in detail below in combination with the accompanying Figures 1-3 The present application will be further described in detail.

[0024] The embodiments of the present application disclose a polypropylene insulation cable for preventing insulation shrinkage and a preparation process thereof;

[0025] In the prior art, the insulation material of a medium-high voltage cable is usually cross-linked polyethylene material, and the insulation is extruded and then cross-linked at high temperature and high pressure for production. By-products generated in the production process can cause insulation shrinkage, which in turn causes the conductor 1 end to protrude. If insulation shrinkage occurs during the operation of the cable after installation of the terminal, the end can be punctured and exploded. In addition, the smooth and round characteristics of the surface of the full-type conductor 1 can easily cause the insulation layer wrapped on the surface of the conductor 1 to have a serious shrinkage reaction.

[0026] In order to solve the above problems, in view of the defect that the smooth surface of the conductor 1 causes insufficient adhesion of the insulation layer, it is considered to enhance the interfacial bonding force by changing the structure of the conductor 1. In order to solve the safety hazard caused by insulation shrinkage, a buffer layer is arranged in the cable structure to absorb the shrinkage stress. Based on the research on the bonding force between the conductor 1 and the insulation layer, it is found that the specific structure arranged on the surface of the conductor 1 can effectively improve the interfacial friction coefficient.

[0027] Therefore, the present application proposes a cable including a plurality of insulated cores twisted together, and a metal shield 5 wrapped outside the insulated cores. The twisted insulated cores are wrapped in an isolation sleeve 8, and the isolation sleeve 8 and the insulated cores are filled with a filling rope 6. The isolation sleeve 8 is lined with a wrapping tape 7. An armor layer 9 and an outer sheath layer 10 are sequentially arranged outside the isolation layer. The insulated core includes a conductor 1, an inner shielding material 2, an insulation material 3, and an outer shielding material 4. The conductor 1 is provided with a groove on the outer layer, and the inner shielding material 2 is embedded in the groove.

[0028] The metal shield 5 refers to a conductive layer wrapped outside the insulating core, which can be realized by winding copper or aluminum alloy strips, and is used for uniform electric field distribution. The filling rope 6 refers to a filling material located between the isolation sleeve 8 and the insulating core, which can be realized by polypropylene fiber rope, and is used to eliminate the twisting gap of the core. The wrapping tape 7 refers to a wrapping layer lined on the inner side of the isolation sleeve 8, which can be realized by non-woven fabric or polyester tape, and is used to buffer mechanical stress. The groove is a recess structure arranged on the outer surface of the conductor 1, which can be formed by wire drawing die, and is used to increase the contact area between the inner shielding material 2 and the conductor 1.

[0029] Specifically, a plurality of insulating cores are twisted to form a compact structure, and the metal shield 5 layer is wrapped outside the core to improve the electric field distribution. The filling rope 6 between the isolation sleeve 8 and the core eliminates the twisting gap, and the wrapping tape 7 layer buffers the interaction force between the isolation sleeve 8 and the core. The groove structure on the surface of the conductor 1 makes the inner shielding material 2 form mechanical interlocking, and enhances the interface bonding strength. The armor layer 9 and the outer sheath layer 10 are successively wrapped outside the isolation sleeve 8 to form a multi-layer protection structure.

[0030] Through the above technical solution, the relative displacement between the insulating layer and the conductor 1 is effectively inhibited, and the risk of end breakdown caused by insulation shrinkage is reduced. The groove structure of the conductor 1 enhances the bonding strength of the inner shielding material 2 and the conductor 1, and the filling rope 6 and the wrapping tape 7 layer synergistically absorb the shrinkage stress, and the multi-layer protection structure improves the overall mechanical strength of the cable.

[0031] The application further provides a preparation process of the conductor 1 of the polypropylene insulated cable for preventing insulation shrinkage, which comprises the following steps:

[0032] S1, single wire manufacturing of the conductor 1, the outermost single wire of the conductor 1 adopts a special type wire, and the two arc surfaces of a conventional T-shaped wire are rounded; the inner layer single wire of the conductor 1 still adopts a common T-shaped wire;

[0033] S2, the inner layer of each single wire is twisted by using a frame stranding machine;

[0034] S3, the insulating layer adopts a thermoplastic high-performance polypropylene elastomer insulating material 3 and a polypropylene inner and outer shielding material, and a CVV semi-suspension type production line is used for extrusion.

[0035] Among them, special-shaped wires refer to irregular structures formed by adjusting the edge shape of T-shaped wires. Specifically, this can be achieved by multi-pass drawing of metal rods. This structure increases the contact area between the outer layer of conductor 1 and the insulation layer. Rounding treatment refers to the rounded transition processing on both sides of the large arc surface of the T-shaped wire. Specifically, this can be achieved by mechanical grinding or die forming. This treatment creates uniform depressions on the surface of the stranded conductor and enhances the overall surface roughness of conductor 1. The frame-type stranding machine refers to stranding equipment with a multi-axis rotating structure. Specifically, it can be implemented using a device with a wire separating disc and a tension control system. This equipment ensures the uniformity of the inner layer monofilament stranding. The thermoplastic high-performance polypropylene elastomer insulation material 3 refers to a thermoplastic composite based on polypropylene. Specifically, it can be prepared by adding an anti-shrinkage modifier. This material maintains shape stability without cross-linking after high-temperature extrusion. The CVV semi-overhead line production line refers to extrusion equipment with a vertical overhang section. Specifically, it can be implemented using a combination of a segmented temperature-controlled extruder and cooling pipes. This production line can prevent the insulation layer from eccentric deformation due to gravity.

[0036] Specifically, the outer monofilaments are rounded to form an irregular surface profile, which, after stranding, creates a conductor outer layer with a concave-convex structure, thereby increasing the mechanical interlocking with the insulation layer. The inner monofilaments are conventionally T-shaped stranded, with the stranding density controlled by a frame-type stranding machine to maintain conductivity. The insulation layer is made of polypropylene-based material, which, during extrusion on a CVV semi-carrier production line, utilizes a segmented cooling process to eliminate material shrinkage stress while avoiding byproducts generated by high-temperature cross-linking.

[0037] Compared to existing technologies, the current conductor 1 uses a full-wire structure, resulting in an overly smooth surface. This solution, however, creates a rough surface by rounding the corners of the outer monofilament, and combines this with differentiated stranding processes for the inner and outer layers, effectively enhancing the conductor 1's constraint on the insulation layer. Furthermore, existing technologies rely on cross-linked polyethylene materials requiring high-temperature cross-linking. This solution uses polypropylene elastomer materials combined with a non-cross-linking process, fundamentally avoiding insulation shrinkage problems caused by cross-linking byproducts.

[0038] Through the above technical solution, this application solves the problem of insulation layer shrinkage caused by the smooth surface of the full-type conductor 1. By optimizing the structure of conductor 1, the deformation of the insulation material is suppressed. At the same time, the characteristics of polypropylene material are used to eliminate cross-linking process defects, thereby reducing the risk of cable end breakdown and improving operational safety.

[0039] This application further proposes that in step S1, the metal round rod is drawn thin to the required outer or inner single wire size and shape by multiple drawing dies of the wire drawing equipment.

[0040] Among them, multi-pass drawing die refers to a device that uses multiple dies with different apertures to draw a metal rod in stages. Specifically, it can be achieved using a die set with progressive apertures. Through staged drawing, the diameter and shape of the metal rod are gradually adjusted to the target size, avoiding stress concentration inside the material caused by a single large deformation. The profile wire refers to a single wire with a specific cross-sectional shape, which can be achieved through the cavity design of the die. For example, the outer layer of single wire uses a special profile wire with rounded corners, while the inner layer of single wire uses a conventional T-shaped wire. The cross-section of the single wire is controlled by the die shape to adapt to the structural requirements after conductor 1 is stranded.

[0041] Specifically, the metal rod is first fed into a wire drawing machine and processed step-by-step through multiple drawing dies. Each pass corresponds to a die, with the die aperture decreasing successively, causing the diameter of the metal rod to gradually shrink. Simultaneously, the cross-sectional shape of the single wire is controlled by the die cavity. The outer and inner monofilaments are processed through different dies. The outer monofilament is formed into a smooth profile using a rounded-corner die, while the inner monofilament is formed into a conventional profile using a T-die. Through staged drawing, the crystal structure of the metal material is uniformly adjusted, reducing residual stress during processing and thus preventing deformation or breakage of the monofilaments due to stress release during subsequent stranding.

[0042] Through the above technical solution, this application solves the problem of insulation shrinkage caused by the excessively smooth surface of the existing full-wire conductor 1. By using staged drawing and die cavity design, the outer monofilament surface forms a rounded corner structure, increasing the frictional resistance between the conductor 1 and the insulation layer, thereby suppressing insulation shrinkage; the inner monofilament maintains a conventional T-shaped structure, ensuring the overall tightness of the conductor 1 stranding. In addition, the multi-pass drawing process reduces the internal stress of the monofilament, avoiding the loosening of the conductor 1 due to stress release after stranding, further ensuring the long-term stability of the cable.

[0043] This application further proposes that in step S3, a frame stranding machine is used to first strand each single wire of the inner layer, with the pitch controlled at 30-40 times to improve the conductivity of conductor 1, and then the single wire of the outer layer is stranded with the pitch controlled at 13-16 times to improve the shrinkage resistance of the conductor 1 surface to the insulation layer; since the inner layer pitch is large, in order to prevent the inner layer from loosening, the sizing area of ​​the stranded wire die is lengthened.

[0044] Among them, the frame-type stranding machine refers to a stranding device with a multi-axis rotating structure. This is achieved by configuring multiple stranding shafts and tension adjustment devices, and its function is to control the stranding tightness of the conductor 1 monofilaments in layers. A pitch control of 30-40 times refers to the ratio of the axial distance of the monofilament spiraling upwards during stranding to the diameter of conductor 1. This can be achieved by adjusting the transmission ratio of the stranding gears. This range balances the tightness of the conductor 1 structure with its conductivity. An outer layer monofilament pitch control of 13-16 times refers to using a smaller spiral spacing during outer layer stranding. This can be achieved by shortening the transmission stroke of the stranding gears. This design increases the surface roughness of conductor 1 to suppress insulation shrinkage. The lengthened sizing zone of the parallel die refers to increasing the forming channel length of the metal die after stranding. This can be achieved by replacing the die with one featuring an extended guide section. Its function is to prevent the inner layer stranding structure from loosening by extending the constraint path of the monofilaments.

[0045] Specifically, when the inner layer monofilaments are stranded with a large pitch, the electrical energy can be transmitted over a shorter distance per unit conductor length within conductor 1, thereby reducing resistance loss and improving conductivity. When the outer layer monofilaments are stranded with a small pitch, a dense spiral pattern forms on the surface of conductor 1. When the insulation layer is applied, the mechanical interlocking effect of the pattern effectively hinders the axial shrinkage of the insulation material under thermal stress. To prevent the inner layer from loosening due to the large pitch stranding, the extended sizing zone of the parallel die applies continuous pressure to the stranded monofilaments, ensuring their stable alignment before cooling and setting.

[0046] Through the above technical solution, this application effectively solves the problem of insulation shrinkage caused by the excessive smoothness of the surface of the full-type conductor 1. The irregular surface formed by the outer stranding increases the bonding force between the insulation layer and the conductor 1. At the same time, the inner stranding structure avoids the risk of loosening caused by excessive pitch while ensuring conductivity, thereby improving the insulation stability of the cable during operation.

[0047] This application further proposes that in step S4, since the melting temperature of PP polypropylene is about 100 degrees higher than that of XLPE cross-linked polyethylene, the heating element of the extruder is increased to 12KW; three-layer co-extrusion is used during extrusion, the insulation extrusion temperature is 130-210℃, and the shielding material is controlled at 130-200℃; after extrusion, since cross-linking is not required, the first four cross-linking pipes are not heated but are air-cooled and shaped by passing 0.5MPa of pressurized nitrogen, while the water-cooled liquid level of the cross-linking pipes is pumped to the fifth section for pre-cooling to prevent the insulation from becoming eccentric.

[0048] The melting temperature of PP (polypropylene) refers to the temperature range required for the material to transform from a solid to a molten state. This can be achieved by adjusting the extruder's heating power; for example, increasing the heating element power to 12KW can meet the high-temperature processing requirements of polypropylene. Three-layer co-extrusion refers to the simultaneous molding of conductor 1, inner shield material 2, insulation material 3, and outer shield material 4 through three independent extrusion channels. This can be achieved through zoned temperature control; for example, the insulation extrusion temperature can be controlled within the 130-210℃ range to match the melting characteristics of polypropylene. Pressurized nitrogen air cooling and shaping refers to accelerating the cooling and solidification of the molten material by injecting pressurized inert gas into the unheated cross-linking pipe. Specifically, a nitrogen pressure of 0.5Mp combined with contact with the inner wall of the pipe can achieve uniform heat dissipation. Pre-cooling refers to moving the cooling initiation position of the water cooling system forward. This can be achieved by adjusting the coolant level pump position to the 5th cross-linking pipe section to suppress material deformation caused by temperature differences.

[0049] Specifically, during the insulation layer extrusion process, because the melting temperature of polypropylene is significantly higher than that of traditional cross-linked polyethylene, the extruder heating power is increased to maintain material fluidity. The three-layer co-extrusion process independently controls the extrusion temperatures of the insulation material 3 and the shielding material, allowing the polypropylene material to complete melt shaping within the range of 130-210℃. When the extruded insulation layer enters the cross-linking pipeline, the first four sections of the pipeline remain unheated and are purged with pressurized nitrogen gas, utilizing gas flow to remove heat and achieve initial shaping. Simultaneously, the cooling liquid level of the water cooling system is advanced to the fifth section of the pipeline, rapidly reducing the material temperature and minimizing insulation layer eccentricity caused by differences in local cooling rates.

[0050] Through the above technical solution, this application effectively suppresses the shrinkage and deformation of the polypropylene insulation layer during the cooling process, avoiding the risk of conductor 1 exposure due to material eccentricity. By matching the temperature control and cooling strategy with the characteristics of polypropylene material, stable molding of the insulation layer is achieved without chemical cross-linking, solving the problem of end breakdown caused by insulation shrinkage in traditional processes.

[0051] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A polypropylene insulated cable that prevents insulation shrinkage, characterized in that: It includes multiple insulated wire cores twisted together, with the insulated wire cores wrapped with a metal shield; the twisted insulated wire cores are wrapped in an isolation sleeve, and there is also a filler rope between the isolation sleeve and the insulated wire cores; the isolation sleeve is lined with wrapping tape; an armor layer and an outer sheath layer are successively wrapped around the isolation layer; The insulated wire core includes a conductor, an inner shield material, an insulating material, and an outer shield material. Grooves are provided on the outer layer of the conductor, and the inner shield material is embedded in the grooves.

2. A process for preparing a conductor in a polypropylene insulated cable to prevent insulation shrinkage, used to produce the conductor in the polypropylene insulated cable to prevent insulation shrinkage as described in claim 1; characterized in that... Includes the following steps: S1. Conductor monofilament manufacturing: The outermost monofilament of the conductor uses a special type of wire, with the large arc surface of the conventional T-shaped wire rounded on both sides; the inner monofilament of the conductor still uses the common T-shaped wire. S2, stranded wire: Each single wire in the inner layer is first stranded using a frame stranding machine; S3. Extrusion of the insulation layer: The insulation layer uses thermoplastic high-performance polypropylene elastomer insulation material and polypropylene inner and outer shielding material and CVV semi-overhead conveyor production line.

3. The process for preparing the conductor in a polypropylene insulated cable to prevent insulation shrinkage according to claim 2: In step S1, the metal round rod is drawn thin to the required outer or inner single wire size and shape by passing through a multi-pass drawing die of a wire drawing device.

4. The process for preparing the conductor in a polypropylene insulated cable to prevent insulation shrinkage according to claim 3, characterized in that: In step S3, a frame stranding machine is used to first strand each single wire in the inner layer, with the pitch ratio controlled at 30-40 times to improve the conductivity of the conductor. Then, the single wires in the outer layer are stranded, with the pitch ratio controlled at 13-16 times to improve the resistance of the conductor surface to the shrinkage of the insulation layer. Since the pitch of the inner layer is large, in order to prevent the inner layer from loosening, the sizing area of ​​the stranded wire die is lengthened.

5. The process for preparing the conductor in a polypropylene insulated cable to prevent insulation shrinkage according to claim 4, characterized in that: In step S4, since the melting temperature of PP polypropylene is about 100 degrees higher than that of XLPE cross-linked polyethylene, the heating element of the extruder is increased to 12KW; three-layer co-extrusion is used during extrusion, the insulation extrusion temperature is 130-210℃, and the shielding material is controlled at 130-200℃. After extrusion, since no cross-linking is required, the first four cross-linking pipes are not heated but are air-cooled and shaped by passing 0.5 MPa of pressurized nitrogen. At the same time, the water-cooled liquid level of the cross-linking pipes is pumped to the fifth section for pre-cooling to prevent insulation from becoming eccentric.

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