Optical fiber composite flame-retardant medium voltage cable and preparation method thereof

Abstract

The present invention discloses an optical fiber composite flame-retardant medium voltage cable and a preparation method thereof. The cable includes an outer sheath, a plurality of conductor assemblies arranged at equal intervals inside the outer sheath, and an optical fiber assembly. The method includes the following steps: S1, preparation of ethylene propylene rubber material; S2, one-stage co-extrusion; S3, two-stage vulcanization; S4, two-stage co-extrusion. The present invention rationally selects the structure and components of the sheath layer in the conductor assembly and the optical fiber assembly, and finally forms a comprehensive cable suitable for use in medium voltage cables, which has good flame retardant and electromagnetic shielding effects, wherein the insulating thermal conductive carrier BN is compounded with the flame retardant additive TiO2 to achieve a comprehensive performance of high thermal conductivity + high flame retardancy, and the solid phase content of the coating as a conductor assembly is slightly higher than that of the coating as an optical fiber assembly. For medium voltage cables, good insulation and temperature resistance can be achieved without the use of mica tape.

Description

Technical Field

[0001] The present invention relates to the technical field of cable manufacturing, in particular to an optical fiber composite flame-retardant medium-voltage cable and a preparation method thereof. Background Art

[0002] Optical hybrid medium-voltage cables are specialized cables that combine optical fiber communications with power transmission, often used in scenarios requiring simultaneous transmission of power and data. Their core function is to combine medium-voltage power transmission with optical signal transmission within a single cable, enabling both power supply and information exchange. They are suitable for applications in power systems, industrial parks, urban infrastructure, and other fields.

[0003] The structure of this type of cable is divided into a power transmission layer and an optical communication layer. The power transmission layer typically consists of a conductor, insulation layer, shielding layer, and sheath. The conductor is made of copper or aluminum and is responsible for transmitting medium voltage currents from 6kV to 35kV. The insulation layer uses cross-linked polyethylene or ethylene propylene rubber to ensure safe power transmission. The shielding layer provides uniform electric field distribution. The outer sheath protects the internal structure from environmental corrosion. The optical communication layer contains the optical fiber unit, which is composed of multiple optical fiber bundles. The outer layer is wrapped in a loose tube to buffer mechanical stress. The outer layer is covered with water-blocking material and metal armor to prevent moisture penetration and physical damage.

[0004] When manufacturing and using these cables, electromagnetic interference resistance and flame retardancy are paramount considerations. Ethylene propylene rubber, with its excellent performance, can be used as the primary outer sheath material for fiber-optic composite medium-voltage cables. However, factors such as processing performance and cost have limited its widespread application. The invention patent with patent publication number CN106117825A discloses a preparation method of an EPDM insulated chloroprene rubber sheathed cable sheath material, comprising the following steps: mixing EPDM, chloroprene rubber, hydrogenated nitrile rubber, fluororubber, and styrene-butadiene rubber for 1-2 minutes; adding modified quicklime, coumarone resin, calcined clay, nano-titanium dioxide, bentonite, hollow microspheres, zirconium oxide, RF-90 resin, microcrystalline cellulose, thiuram disulfide, and hexamethylenetetramine, mixing evenly, and then discharging the mixture at a mixing temperature of 105-110°C; adding antioxidant RD, antioxidant H, antioxidant 4010NA, operating oil, pine tar, and dibutyl phthalate, mixing evenly, adding benzoyl peroxide and aluminum hydroxide for vulcanization at a vulcanization temperature of 158-163°C and a vulcanization time of 1-2 minutes, and cooling the mixture to obtain the EPDM insulated chloroprene rubber sheathed cable sheath material. However, this method does not make targeted optimization for the application of optical fiber composite medium voltage cables. Summary of the Invention

[0005] In view of the above problems, the present invention provides an optical fiber composite flame retardant medium voltage cable and a preparation method thereof.

[0006] The technical solution of the present invention is:

[0007] An optical fiber composite flame-retardant medium voltage cable comprises an outer sheath, a plurality of conductor components arranged circumferentially and at equal intervals inside the outer sheath, and an optical fiber component;

[0008] The conductor assembly includes, from the inside to the outside, a copper conductor, a PP shielding layer, a first EPDM insulation layer, and a conductor sheath;

[0009] The optical fiber assembly includes a plurality of optical fiber bundles arranged at equal intervals, a PBT sheath is provided on the outside of the optical fiber bundle, an optical fiber sheath is provided on the outside of the PBT sheath, and a second ethylene propylene rubber insulation layer is provided on the outside of each optical fiber sheath;

[0010] A filling layer is provided outside the conductor assembly and the optical fiber assembly, an armor layer is provided outside the filling layer, and an outer sheath is provided outside the armor layer.

[0011] Furthermore, the conductor sheath and the optical fiber sheath are both cross-linked polyethylene sheaths.

[0012] Description: Cross-linked polyethylene sheath is a commonly used material in cable sheaths. It has certain insulation, temperature resistance and corrosion resistance. It can play a good auxiliary insulation and flame retardant effect when used in conductor sheaths and optical fiber sheaths of medium voltage cables.

[0013] Furthermore, a filling medium is provided between the PBT sheath and the second EPDM rubber insulation layer. The filling medium is a fully dry filling medium, and the filling layer is a polypropylene filler.

[0014] Note: The overall strength of the cable is ensured by the internal filler of the optical fiber components and the PET points inside the cable.

[0015] Furthermore, the armor layer is a tinned copper wire braided armor tape, and the outer sheath is a PVC sheath.

[0016] Description: The overall mechanical strength of the cable is improved by setting the armor layer.

[0017] Furthermore, there are three conductor assemblies and six optical fiber bundles.

[0018] The present invention also provides a method for preparing an optical fiber composite flame-retardant medium voltage cable, comprising the following steps:

[0019] S1. Preparation of EPDM rubber material:

[0020] S1-1, mixing: take 100-120 parts of ethylene propylene rubber particles by mass, place them in an open mill for plasticating, and then perform thin-passing after plasticating. After thin-passing, add 1-2 parts of antioxidant, 0.5-0.7 parts of RF-90 resin and 0.3-0.5 parts of calcined clay in sequence, cut left and right several times, then add 110-130 parts of carbon black, 60-70 parts of paraffin oil, 3-4 parts of vulcanizing agent and 1-2 parts of co-vulcanizing agent in sequence, cut left and right several times, make triangle wrap several times and pass thin-pass again to obtain a mixed rubber;

[0021] S1-2, one-stage vulcanization: vulcanizing the rubber mix at 170-180° C. for 5-6 minutes to obtain an EPDM rubber material;

[0022] S2, one-stage co-extrusion:

[0023] S2-1, conductor assembly extrusion: extruding a PP shielding layer on the outside of the copper conductor, then extruding the EPDM rubber material on the outside of the PP shielding layer, and electrostatically coating the outside of the extruded EPDM rubber material to obtain a first EPDM rubber insulation layer;

[0024] S2-2, optical fiber assembly extrusion: extruding a PBT sheath on the outside of the optical fiber bundle, extruding an optical fiber sheath on the outside of the PBT sheath, then filling the outside of each optical fiber sheath with a medium and extruding the EPDM rubber material, and electrostatically coating the outside of the extruded EPDM rubber material to obtain a second EPDM rubber insulation layer;

[0025] S3, two-stage vulcanization: vulcanize the first EPDM rubber insulation layer of the conductor assembly and the second EPDM rubber insulation layer of the optical fiber assembly under steam conditions of 170-180°C and 0.5-1 MPa for 7-8 minutes;

[0026] S4, two-stage co-extrusion: then extrude a conductor sheath outside the first EPDM rubber insulation layer to obtain a conductor assembly, extrude a filling layer outside the several conductor assemblies and outside the second EPDM rubber insulation layer of the optical fiber assembly, and cover the filling layer with an armor layer, and then extrude an outer sheath outside the armor layer.

[0027] Furthermore, in S1, the roller spacing of the open mill during plasticating is 1 mm, and the roller spacing of the open mill is adjusted to 2 mm after plasticating, the number of left and right cuts is 3 times, the number of thin passes is 3 times, the number of triangle packages is 6 times, and the roller spacing of the open mill is adjusted to 4 mm when making triangle packages.

[0028] Note: By optimizing the specific parameters of the open mill, the rubber can be dispersed quickly, evenly and with high shear efficiency during mixing.

[0029] Furthermore, when the coating is applied in S2, the coating is prepared by:

[0030] Nano-TiO2 and nano-BN are placed in anhydrous ethanol and ultrasonically dispersed and mixed for 30 to 60 minutes to obtain a coating liquid, wherein the solid content of the coating liquid is 10 to 20%, and the particle sizes of the nano-TiO2 and nano-BN are 20 to 200 nm. In the first EPDM rubber insulating layer, the amount of nano-TiO2 added is 0.5 to 0.75 wt% of the EPDM rubber material, and the amount of nano-BN added is 0.75 to 1 wt% of the EPDM rubber material. In the second EPDM rubber insulating layer, the amount of nano-TiO2 added is 0.25 to 0.5 wt% of the EPDM rubber material, and the amount of nano-BN added is 0.5 to 1 wt% of the EPDM rubber material.

[0031] The spraying method is: fix the conductor component or optical fiber component on the roller, use the spray needle to spray the coating liquid onto the surface of the extruded EPDM rubber material, the spraying distance is 5 to 10 cm, apply a positive voltage of 10±1kV to the spray needle, apply a negative voltage of 10±1kV to the roller, and the spray needle advance speed is 3 to 6mm / min.

[0032] Description: By adding a coating on the surface of the EPDM rubber insulation layer, the flame retardant effect of the cable is further improved. The insulating thermal conductive carrier BN is compounded with the flame retardant additive TiO2 to achieve the combined performance of high thermal conductivity and high flame retardancy.

[0033] Furthermore, in the S4, the temperature of the die head during the entire two-stage co-extrusion process is 75°C to 80°C, the temperature of the front section of the body is 70°C to 75°C, and the temperature of the rear section of the body is 65°C to 70°C. The screw cooling method of the rubber extruder is water cooling.

[0034] Description: By optimizing the temperature control during the second stage extrusion, it is ensured that the conductor component, the optical fiber component and the filling layer are well bonded during the second stage extrusion of the cable.

[0035] The beneficial effects of the present invention are:

[0036] (1) The fiber-optic composite flame-retardant medium-voltage cable of the present invention is equipped with a conductor assembly and an optical fiber assembly. According to the application conditions of the medium-voltage cable, the structure and components of the sheath layer in the conductor assembly and the optical fiber assembly are reasonably selected, and finally a comprehensive cable suitable for use in medium-voltage cables is formed, which has good flame retardancy and electromagnetic shielding effects.

[0037] (2) In the preparation method of a fiber-optic composite flame-retardant medium-voltage cable of the present invention, the conductor component and the optical fiber component are prepared independently. The two components use an EPDM rubber insulation layer with a coating to improve their thermal conductivity and flame retardancy. At the same time, two-stage vulcanization is carried out simultaneously, and finally co-extrusion is formed. On the premise of having good flame retardancy and electromagnetic shielding effects, the mechanical strength is also greatly improved, especially when used in 8.7 / 15kV power systems, it can play a good practical use effect.

[0038] (3) In the preparation method of a fiber-optic composite flame-retardant medium-voltage cable of the present invention, the EPDM insulation layer of the conductor component and the optical fiber component are differentially adjusted so that the coatings of the two have differences in component content. The insulating thermal conductive carrier BN is compounded with the flame retardant additive TiO2 to achieve the comprehensive performance of high thermal conductivity + high flame retardancy. The solid phase content of the coating of the conductor component is slightly higher than that of the coating of the optical fiber component. For medium-voltage cables, good insulation and temperature resistance can be achieved without using mica tape. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a schematic diagram of the overall structure of an optical fiber composite flame-retardant medium-voltage cable of the present invention;

[0040] Figure 2 A schematic structural diagram of an optical fiber assembly in an optical fiber composite flame-retardant medium-voltage cable of the present invention;

[0041] Figure 3 Comparison chart of thermal conductivity of various cases in Experimental Example 1 of the present invention.

[0042] Among them, 1-conductor assembly, 11-copper conductor, 12-PP shielding layer, 13-first EPDM insulation layer, 14-conductor sheath, 2-optical fiber assembly, 21-optical fiber bundle, 22-PBT sheath, 23-optical fiber sheath, 24-second EPDM insulation layer, 25-filling medium, 3-outer sheath, 4-filling layer, 5-armor layer, DETAILED DESCRIPTION

[0043] Example 1

[0044] An optical fiber composite flame-retardant medium voltage cable, comprising an outer sheath 3, three conductor components 1 arranged circumferentially and at equal intervals inside the outer sheath 3, and an optical fiber component 2;

[0045] The conductor assembly 1 includes, from the inside to the outside, a copper conductor 11, a PP shielding layer 12, a first EPDM insulation layer 13, and a conductor sheath 14;

[0046] The optical fiber assembly 2 includes six optical fiber bundles 21 arranged at equal intervals. A PBT sheath 22 is provided on the outside of the optical fiber bundle 21. An optical fiber sheath 23 is provided on the outside of the PBT sheath 22. A second EPDM rubber insulation layer 24 is provided on the outside of each optical fiber sheath 23. A filling medium 25 is provided between the PBT sheath 22 and the second EPDM rubber insulation layer 24. The filling medium 25 is a fully dry filling medium 25. The conductor sheath 14 and the optical fiber sheath 23 are both cross-linked polyethylene sheaths.

[0047] A filling layer 4 is provided on the outside of the conductor assembly 1 and the optical fiber assembly 2. The filling layer 4 is a polypropylene filler. An armor layer 5 is provided outside the filling layer 4. An outer sheath 3 is provided outside the armor layer 5. The armor layer 5 is a tinned copper wire braided armor tape. The outer sheath 3 is a PVC sheath.

[0048] Example 2

[0049] This embodiment is a method for preparing an optical fiber composite flame-retardant medium-voltage cable of embodiment 1, comprising the following steps:

[0050] S1. Preparation of EPDM rubber material:

[0051] S1-1, mixing: by mass, take 110 parts of ethylene propylene rubber particles, place them in an open mill for mastication, and after mastication, perform thin passing 3 times. The roller spacing of the open mill during mastication is 1 mm. After mastication, the roller spacing of the open mill is adjusted to 2 mm. After thin passing, 1 part of antioxidant, 0.6 part of RF-90 resin and 0.4 part of calcined clay are added in sequence. After cutting with a knife 3 times, 120 parts of carbon black, 65 parts of paraffin oil, 4 parts of vulcanizing agent and 2 parts of co-vulcanizing agent are added in sequence. Cut with a knife 3 times and make triangle wraps 6 times and perform thin passing again 3 times. When making triangle wraps, the roller spacing of the open mill is adjusted to 4 mm to obtain a rubber mixture;

[0052] S1-2, one-stage vulcanization: vulcanize the rubber mix at 175°C for 5 minutes to obtain EPDM rubber;

[0053] S2, one-stage co-extrusion:

[0054] S2-1, extrusion of the conductor assembly 1: extruding a PP shielding layer 12 on the outside of the copper conductor 11, then extruding an EPDM rubber material on the outside of the PP shielding layer 12, and electrostatically coating the outside of the extruded EPDM rubber material to obtain a first EPDM rubber insulation layer 13;

[0055] S2-2, extrusion of optical fiber assembly 2: extruding a PBT jacket 22 on the outside of the optical fiber bundle 21, and extruding an optical fiber jacket 23 on the outside of the PBT jacket 22, then filling each optical fiber jacket 23 with a dielectric 25 and extruding an EPDM rubber material, and electrostatically coating the outside of the extruded EPDM rubber material to obtain a second EPDM rubber insulation layer 24;

[0056] When applying the coating, the coating is prepared by:

[0057] Nano-TiO2 and nano-BN are placed together in anhydrous ethanol and ultrasonically dispersed and mixed for 40 minutes to obtain a coating liquid. The solid content of the coating liquid is 15%, and the particle size of the nano-TiO2 and nano-BN is 100 nm. In the first EPDM rubber insulating layer 13, the amount of nano-TiO2 added is 0.6wt% of the EPDM rubber material, and the amount of nano-BN added is 0.8wt% of the EPDM rubber material. In the second EPDM rubber insulating layer 24, the amount of nano-TiO2 added is 0.4wt% of the EPDM rubber material, and the amount of nano-BN added is 0.7wt% of the EPDM rubber material.

[0058] The spraying method is as follows: the conductor component 1 or the optical fiber component 2 is fixed on the drum, and the coating liquid is sprayed onto the surface of the extruded EPDM rubber material using a spray needle. The spraying distance is 6 cm, a positive voltage of 10 kV is applied to the spray needle, a negative voltage of 10 kV is applied to the drum, and the spray needle advances at a speed of 5 mm / min.

[0059] S3, two-stage vulcanization: vulcanize the first EPDM rubber insulation layer 13 of the conductor assembly 1 and the second EPDM rubber insulation layer 24 of the optical fiber assembly 2 at 175° C. and 0.8 MPa steam conditions for 7 minutes;

[0060] S4, two-stage co-extrusion: Then, a conductor sheath 14 is extruded outside the first EPDM rubber insulation layer 13 to obtain a conductor assembly 1, and a filling layer 4 is extruded outside the several conductor assemblies 1 and the second EPDM rubber insulation layer 24 of the optical fiber assembly 2, and an armor layer 5 is coated outside the filling layer 4, and then an outer sheath 3 is extruded outside the armor layer 5. During the entire two-stage co-extrusion process, the head temperature is 77°C, the front section temperature of the fuselage is 72°C, and the rear section temperature of the fuselage is 68°C. The screw cooling method of the extruder is water cooling.

[0061] Example 3

[0062] This embodiment differs from embodiment 2 in that:

[0063] S1-1. Mixing: Take 100 parts of ethylene propylene rubber particles by mass, place them in an open mill for plasticating, and perform thin passing 3 times after plasticating. The roller spacing of the open mill during plasticating is 1 mm. After plasticating, adjust the roller spacing of the open mill to 2 mm. After thin passing and rolling, add 1 part of antioxidant, 0.5 part of RF-90 resin and 0.3 part of calcined clay in sequence. After cutting left and right 3 times, add 110 parts of carbon black, 60 parts of paraffin oil, 3 parts of vulcanizing agent and 1 part of co-vulcanizing agent in sequence. Cut left and right 3 times and make triangle wrap 6 times and thin pass again 3 times. When making triangle wrap, adjust the roller spacing of the open mill to 4 mm to obtain a mixed rubber.

[0064] Example 4

[0065] This embodiment differs from embodiment 2 in that:

[0066] S1-1. Mixing: 120 parts by mass of ethylene propylene rubber granules are taken and placed in an open mill for plasticating. After plasticating, thin-pass the mixture 3 times. The roller spacing of the open mill is 1 mm during plasticating. After plasticating, the roller spacing of the open mill is adjusted to 2 mm. After thin-passing and rolling, 2 parts of antioxidant, 0.7 parts of RF-90 resin and 0.5 parts of calcined clay are added in sequence. After cutting left and right 3 times, 130 parts of carbon black, 70 parts of paraffin oil, 4 parts of vulcanizing agent and 2 parts of co-vulcanizing agent are added in sequence. Cut left and right 3 times, make triangle wraps 6 times and thin-pass the mixture again 3 times. When making triangle wraps, the roller spacing of the open mill is adjusted to 4 mm to obtain a mixed rubber.

[0067] Example 5

[0068] This embodiment differs from embodiment 2 in that:

[0069] S1-2, one-stage vulcanization: vulcanize the rubber mix at 170°C for 6 minutes to obtain EPDM rubber.

[0070] Example 6

[0071] This embodiment differs from embodiment 2 in that:

[0072] S1-2, one-stage vulcanization: vulcanize the rubber mix at 180°C for 5 minutes to obtain EPDM rubber.

[0073] Example 7

[0074] This embodiment differs from embodiment 2 in that:

[0075] When applying the coating, the coating is prepared by:

[0076] Nano-TiO2 and nano-BN are placed together in anhydrous ethanol and ultrasonically dispersed and mixed for 30 minutes to obtain a coating liquid. The solid phase content in the coating liquid is 10%, and the particle size of nano-TiO2 and nano-BN is 20nm. In the first EPDM rubber insulating layer 13, the added amount of nano-TiO2 is 0.5wt% of the EPDM rubber material, and the added amount of nano-BN is 0.75wt% of the EPDM rubber material. In the second EPDM rubber insulating layer 24, the added amount of nano-TiO2 is 0.25wt% of the EPDM rubber material, and the added amount of nano-BN is 0.5wt% of the EPDM rubber material.

[0077] Example 8

[0078] This embodiment differs from embodiment 2 in that:

[0079] When applying the coating, the coating is prepared by:

[0080] Nano-TiO2 and nano-BN are placed together in anhydrous ethanol and ultrasonically dispersed and mixed for 60 minutes to obtain a coating liquid. The solid phase content in the coating liquid is 12%, and the particle size of nano-TiO2 and nano-BN is 50nm. In the first EPDM rubber insulating layer 13, the amount of nano-TiO2 added is 0.55wt% of the EPDM rubber material, and the amount of nano-BN added is 0.85wt% of the EPDM rubber material. In the second EPDM rubber insulating layer 24, the amount of nano-TiO2 added is 0.3wt% of the EPDM rubber material, and the amount of nano-BN added is 0.6wt% of the EPDM rubber material.

[0081] Example 9

[0082] This embodiment differs from embodiment 2 in that:

[0083] When applying the coating, the coating is prepared by:

[0084] Nano-TiO2 and nano-BN are placed together in anhydrous ethanol and ultrasonically dispersed and mixed for 60 minutes to obtain a coating liquid. The solid phase content in the coating liquid is 18%, and the particle size of nano-TiO2 and nano-BN is 150nm. In the first EPDM rubber insulating layer 13, the added amount of nano-TiO2 is 0.7wt% of the EPDM rubber material, and the added amount of nano-BN is 0.8wt% of the EPDM rubber material. In the second EPDM rubber insulating layer 24, the added amount of nano-TiO2 is 0.45wt% of the EPDM rubber material, and the added amount of nano-BN is 0.8wt% of the EPDM rubber material.

[0085] Example 10

[0086] This embodiment differs from embodiment 2 in that:

[0087] When applying the coating, the coating is prepared by:

[0088] Nano-TiO2 and nano-BN are placed together in anhydrous ethanol and ultrasonically dispersed and mixed for 60 minutes to obtain a coating liquid. The solid phase content in the coating liquid is 20%, and the particle size of nano-TiO2 and nano-BN is 200nm. In the first EPDM rubber insulating layer 13, the amount of nano-TiO2 added is 0.75wt% of the EPDM rubber material, and the amount of nano-BN added is 1wt% of the EPDM rubber material. In the second EPDM rubber insulating layer 24, the amount of nano-TiO2 added is 0.5wt% of the EPDM rubber material, and the amount of nano-BN added is 1wt% of the EPDM rubber material.

[0089] Example 11

[0090] This embodiment differs from embodiment 2 in that:

[0091] The coating spraying method is as follows: fix the conductor component 1 or the optical fiber component 2 on the roller, use the spray needle to spray the coating liquid onto the surface of the extruded EPDM rubber material, the spraying distance is 5 cm, a positive voltage of 9 kV is applied to the spray needle, a negative voltage of 9 kV is applied to the roller, and the spray needle advances at a speed of 3 mm / min.

[0092] Example 12

[0093] This embodiment differs from embodiment 2 in that:

[0094] The coating spraying method is as follows: fix the conductor component 1 or the optical fiber component 2 on the roller, use the spray needle to spray the coating liquid onto the surface of the extruded EPDM rubber material, the spraying distance is 10 cm, a positive voltage of 11 kV is applied to the spray needle, a negative voltage of 11 kV is applied to the roller, and the spray needle advances at a speed of 6 mm / min.

[0095] Example 13

[0096] This embodiment differs from embodiment 2 in that:

[0097] S3. Second stage vulcanization: vulcanize the first EPDM rubber insulation layer 13 of the conductor assembly 1 and the second EPDM rubber insulation layer 24 of the optical fiber assembly 2 at 170° C. and 0.5 MPa steam for 7 minutes.

[0098] Example 14

[0099] This embodiment differs from embodiment 2 in that:

[0100] S3. Second stage vulcanization: vulcanize the first EPDM rubber insulation layer 13 of the conductor assembly 1 and the second EPDM rubber insulation layer 24 of the optical fiber assembly 2 at 180° C. and 1 MPa steam conditions for 8 minutes.

[0101] Example 15

[0102] This embodiment differs from embodiment 2 in that:

[0103] S4, two-stage co-extrusion: Then, a conductor sheath 14 is extruded outside the first EPDM rubber insulation layer 13 to obtain a conductor assembly 1, and a filling layer 4 is extruded outside the several conductor assemblies 1 and the second EPDM rubber insulation layer 24 of the optical fiber assembly 2, and an armor layer 5 is coated outside the filling layer 4, and then an outer sheath 3 is extruded outside the armor layer 5. During the entire two-stage co-extrusion process, the head temperature is 75°C, the front section temperature of the fuselage is 70°C, and the rear section temperature of the fuselage is 65°C. The screw cooling method of the extruder is water cooling.

[0104] Example 16

[0105] This embodiment differs from embodiment 2 in that:

[0106] S4, two-stage co-extrusion: Then, a conductor sheath 14 is extruded outside the first EPDM rubber insulation layer 13 to obtain a conductor assembly 1, and a filling layer 4 is extruded outside the several conductor assemblies 1 and the second EPDM rubber insulation layer 24 of the optical fiber assembly 2, and an armor layer 5 is coated outside the filling layer 4, and then an outer sheath 3 is extruded outside the armor layer 5. During the entire two-stage co-extrusion process, the head temperature is 80°C, the temperature of the front section of the fuselage is 75°C, and the temperature of the rear section of the fuselage is 70°C. The screw cooling method of the extruder is water cooling.

[0107] Experimental Example 1

[0108] First, we investigate the thermal conductivity of the first EPDM rubber insulation layer 13 of the present invention separately, taking Examples 2 and 7 to 10 as examples, and comparing them with the EPDM rubber insulation layer without coating as Comparative Example 1. The results are as follows: Figure 3 shown.

[0109] It can be seen that there is a certain correlation between the thermal conductivity and the content of nano-TiO2 and nano-BN. As the mass fraction of the solid phase content increases, the thermal conductivity of the first EPDM rubber insulation layer 13 shows a trend of first increasing and then decreasing. This may be because when the mass fraction of the insulating thermal conductive carrier nano-BN is low, the contact area between nano-TiO2 and nano-BN is relatively small or even non-contact, and an effective heat conduction path cannot be formed, which makes the thermal conductivity of the first EPDM rubber insulation layer 13 increase slowly. As the mass fraction of the solid phase content increases, the nano-TiO2 and nano-BN on the surface of the first EPDM rubber insulation layer 13 begin to contact in large quantities to form a heat conduction network. Therefore, in Example 2, the thermal conductivity of the first EPDM rubber insulation layer 13 is the largest. At this time, if the mass fraction of the solid phase content continues to increase, the thermal conductivity decreases because the heat conduction network has become complete. Continuing to increase the solid phase content will only accumulate on the original heat conduction network and cannot form a new heat conduction channel. Therefore, continuing to increase the solid phase content will reduce the thermal conductivity and the thermal conductivity performance will decrease.

[0110] Example 2

[0111] Subsequently, we explored the various parameter indicators of the cable of the present invention and compared them with the required standard values ​​of the medium voltage cable. Among them, the mechanical properties were tested by a universal testing machine, the specimen was a standard dumbbell shape, the clamp spacing was 50mm, and the width of the middle narrow strip was 4mm; the breakdown performance test is an effective and direct method to identify the insulation strength of electrical insulation materials, which is of decisive significance for judging whether electrical insulation materials can be used; the experimental instrument uses a test system consisting of a high-voltage DC power supply, an AC power supply and an experimental transformer operating box to test the DC and AC breakdown field strengths of the cable; the test cable length is 5m, taking Examples 2 to 6 as examples (the parameter adjustments in Examples 2 to 6 are all adjusted within a reasonable range, only to increase the number of test groups, and will not affect the final performance parameters), and compared with Comparative Example 2, in Comparative Example 2, the first EPDM rubber insulation layer 13 and the second EPDM rubber insulation layer 24 in Example 2 of the present invention are replaced with mica tape, and the rest are the same. The results are shown in Table 1.

[0112] Table 1 Performance parameters of cables in various cases

[0113]

[0114]

[0115] It can be seen that the optical fiber composite flame-retardant medium voltage cable of the present invention successfully completed various tests, while in Comparative Example 2, the first EPDM rubber insulation layer 13 and the second EPDM rubber insulation layer 24 in Example 2 were replaced with mica tape, and the voltage test was not passed. This is because the optical fiber conductor has a small outer diameter and slow heat dissipation, and the heat is relatively concentrated. At high temperatures, the insulation resistance of the mica tape decreases, causing the optical fiber core to be punctured; at the same time, the mica tape insulated wrapped cable itself has a large water content, and its thermal weight loss is more than twice that of the first EPDM rubber insulation layer 13 and the second EPDM rubber insulation layer 24 of the present invention, resulting in a small insulation resistance value between the cores after production, which easily leads to failure to pass the tensile strength test.

[0116] In summary, the optical fiber composite flame-retardant medium-voltage cable of the present invention can be put into normal use, and has accumulated valuable experience for the design and production of cables with larger specifications and more complex structures in the future.

Claims

1. A method for preparing an optical fiber composite flame-retardant medium voltage cable, characterized in that: The cable comprises an outer sheath (3), a plurality of conductor components (1) arranged circumferentially and at equal intervals inside the outer sheath (3), and an optical fiber component (2); The conductor assembly (1) comprises, from the inside to the outside, a copper conductor (11), a PP shielding layer (12), a first ethylene propylene rubber insulation layer (13), and a conductor sheath (14); The optical fiber assembly (2) comprises a plurality of optical fiber bundles (21) arranged at equal intervals and surrounding each other, a PBT sheath (22) being provided on the outside of the optical fiber bundle (21), an optical fiber sheath (23) being provided on the outside of the PBT sheath (22), and a second ethylene propylene rubber insulation layer (24) being provided on the outside of each of the optical fiber sheaths (23); A filling layer (4) is provided outside the conductor assembly (1) and the optical fiber assembly (2), an armor layer (5) is provided outside the filling layer (4), and an outer sheath (3) is provided outside the armor layer (5); The preparation method comprises the following steps: S1. Preparation of EPDM rubber material: S1-1, mixing: take 100-120 parts of ethylene propylene rubber particles by mass, place them in an open mill for mastication, and then perform thin passing. After thin passing, add 1-2 parts of antioxidant, 0.5-0.7 parts of RF-90 resin and 0.3-0.5 parts of calcined clay in sequence after rolling. After cutting left and right several times, add 110-130 parts of carbon black, 60-70 parts of paraffin oil, 3-4 parts of vulcanizing agent and 1-2 parts of co-vulcanizing agent in sequence. Cut left and right several times and make triangle wrap several times and then thin pass again to obtain a rubber mixture; S1-2, one-stage vulcanization: vulcanizing the rubber mix at 170-180° C. for 5-6 minutes to obtain an EPDM rubber material; S2, one-stage co-extrusion: S2-1, extrusion of the conductor assembly (1): extruding a PP shielding layer (12) on the outside of the copper conductor (11), then extruding the EPDM rubber material on the outside of the PP shielding layer (12), and electrostatically coating the outside of the extruded EPDM rubber material to obtain a first EPDM rubber insulation layer (13); S2-2, extrusion of optical fiber assembly (2): extruding a PBT sheath (22) on the outside of the optical fiber bundle (21), extruding an optical fiber sheath (23) on the outside of the PBT sheath (22), then filling the outside of each optical fiber sheath (23) with a medium (25) and extruding the EPDM rubber material, and electrostatically coating the outside of the extruded EPDM rubber material to obtain a second EPDM rubber insulation layer (24); S3, two-stage vulcanization: vulcanizing the first EPDM rubber insulation layer (13) of the conductor assembly (1) and the second EPDM rubber insulation layer (24) of the optical fiber assembly (2) under steam conditions of 170-180°C and 0.5-1 MPa for 7-8 minutes; S4, two-stage co-extrusion: then, a conductor sheath (14) is extruded outside the first EPDM rubber insulation layer (13) to obtain a conductor assembly (1), a filling layer (4) is extruded outside the second EPDM rubber insulation layer (24) of the plurality of conductor assemblies (1) and the optical fiber assembly (2), and an armor layer (5) is coated outside the filling layer (4), and then an outer sheath (3) is extruded outside the armor layer (5).

2. The method for preparing a fiber-optic composite flame-retardant medium-voltage cable according to claim 1, characterized in that: The conductor sheath (14) and the optical fiber sheath (23) are both cross-linked polyethylene sheaths.

3. The method for preparing a fiber-optic composite flame-retardant medium-voltage cable according to claim 1, characterized in that: A filling medium (25) is provided between the PBT sheath (22) and the second EPDM rubber insulation layer (24); the filling medium (25) is a fully dry filling medium, and the filling layer (4) is a polypropylene filler.

4. The method for preparing a fiber-optic composite flame-retardant medium-voltage cable according to claim 1, characterized in that: The armor layer (5) is a tinned copper wire braided armor tape, and the outer sheath (3) is a PVC sheath.

5. The method for preparing a fiber-optic composite flame-retardant medium-voltage cable according to claim 1, characterized in that: There are three conductor assemblies (1) and six optical fiber bundles (21).

6. The method for preparing a fiber-optic composite flame-retardant medium-voltage cable according to claim 1, characterized in that: In the S1, the roller spacing of the open mill during plasticating is 1 mm. After plasticating, the roller spacing of the open mill is adjusted to 2 mm. The number of left and right cutters is 3 times, the number of thin passes is 3 times, and the number of triangle packages is 6 times. When making triangle packages, the roller spacing of the open mill is adjusted to 4 mm.

7. The method for preparing a fiber-optic composite flame-retardant medium-voltage cable according to claim 1, characterized in that: When the coating is applied in S2, the coating is prepared by: Nano-TiO2 and nano-BN are placed in anhydrous ethanol and ultrasonically dispersed for 30 to 60 minutes to obtain a coating liquid. The solid content of the coating liquid is 10 to 20%, and the particle size of nano-TiO2 and nano-BN is 20 to 200 nm. In the first EPDM rubber insulation layer (13), the amount of nano-TiO2 added is 0.5 to 0.75 wt% of the EPDM rubber material, and the amount of nano-BN added is 0.75 to 1 wt% of the EPDM rubber material. In the second EPDM rubber insulation layer (24), the amount of nano-TiO2 added is 0.25 to 0.5 wt% of the EPDM rubber material, and the amount of nano-BN added is 0.5 to 1 wt% of the EPDM rubber material. The spraying method is as follows: fixing the conductor component (1) or the optical fiber component (2) on a roller, spraying the coating liquid onto the surface of the extruded EPDM rubber material using a spray needle, the spraying distance is 5 to 10 cm, a positive voltage of 10±1 kV is applied to the spray needle, a negative voltage of 10±1 kV is applied to the roller, and the spray needle advances at a speed of 3 to 6 mm / min.

8. The method for preparing a fiber-optic composite flame-retardant medium-voltage cable according to claim 1, characterized in that: In the S4, the die head temperature during the entire two-stage co-extrusion process is 75°C to 80°C, the front section temperature of the body is 70°C to 75°C, and the rear section temperature of the body is 65°C to 70°C. The screw cooling method of the rubber extruder is water cooling.

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