A continuous casting machine cable based on a polyimide composite and a method for producing the same

Abstract

The application relates to the technical field of continuous casting machine cables, in particular to a continuous casting machine cable based on a polyimide composite material and a preparation method thereof, which comprises a conductor layer, an insulation layer, a shielding layer and a sheath layer arranged in sequence from inside to outside. The BNNTs heat conduction network of the continuous casting machine cable based on the polyimide composite material and the preparation method thereof reduces the thermal resistance by 62%, so that the cable can work stably in a high-temperature environment above 250 DEG C for a long time, the short-term tolerance temperature can reach above 300 DEG C, and the high-temperature resistance is greatly improved; the double-layer shielding has a shielding effectiveness of 72.5 dB at a frequency point of 1 GHz; the resistance change rate of the shielding layer is less than 3% under high temperature, and the anti-interference property is greatly improved; the 45-degree braiding structure makes the bending life reach 600,000 times; the sheath wear resistance is greater than 500 times, and the mechanical property is higher.

Description

Technical Field

[0001] The present invention relates to the technical field of continuous casting machine cables, in particular to a continuous casting machine cable based on a polyimide composite material and a preparation method thereof. Background Art

[0002] In the continuous casting process, electromagnetic stirring technology improves the internal structure of the ingot by applying an alternating magnetic field, reducing defects such as segregation and shrinkage, and improving steel quality. One of the core components of the electromagnetic stirring system is the power supply cable, which is responsible for transmitting high-current, low-frequency electrical energy to the stirrer coil. The present invention significantly improves the overall performance of the cable by introducing polyimide composite materials as insulation and sheath materials, combining a multi-layer composite structure and an optimized preparation process, meeting the requirements of use in extreme environments.

[0003] Existing electromagnetic stirring cables for continuous casting machines mostly use silicone rubber or mineral insulated cables, which have the following defects:

[0004] 1. Insufficient temperature resistance: The cable needs to carry thousands of amperes of current. Traditional structures are prone to excessive temperature rise due to skin effect and eddy current loss. The long-term operating temperature of silicone rubber is ≤250°C, and it is prone to aging and cracking at high temperatures.

[0005] 2. Poor electromagnetic compatibility: High-frequency harmonics and strong magnetic field interference may affect the signal transmission of surrounding devices. Existing shielding designs cannot achieve both high anti-interference efficiency and flexibility.

[0006] 3. Low mechanical strength: The continuous casting site environment is harsh, and the cables are often subjected to vibration, bending, and metal slag splashing. Ordinary sheaths are prone to wear and tear, affecting long-term reliability;

[0007] 4. High maintenance cost: Mineral insulated cables have poor bending performance and are difficult to install and replace. Summary of the Invention

[0008] The technical problem to be solved by the present invention is that the existing electromagnetic stirring cables for continuous casting machines mostly use silicone rubber or mineral insulated cables, which have the defects of insufficient temperature resistance, poor electromagnetic compatibility, low mechanical strength and high maintenance cost.

[0009] The technical solution adopted by the present invention to solve the technical problem is: a continuous casting machine cable based on a polyimide composite material, comprising a conductor layer, an insulation layer, a shielding layer and a sheath layer arranged in sequence from the inside to the outside;

[0010] The conductor layer is a multi-strand silver-plated copper wire with a single wire diameter of 0.12-0.25 mm, a twist pitch ratio of 12-15, and an SZ twist direction;

[0011] The insulating layer is a polyimide-boron nitride nanotube composite material, wherein the boron nitride nanotube (BNNTs) content is 8-12wt%, the thickness of the insulating layer is 15% of the conductor diameter, and the breakdown strength is ≥35kV / mm;

[0012] The shielding layer includes an inner layer of nickel-plated aramid fiber braided mesh and an outer layer of vapor-deposited aluminum foil; the inner layer braided mesh has a coverage rate of ≥85%, a nickel layer thickness of 0.8-1.2 μm, and a braiding angle of 45±2°; the outer layer of vapor-deposited aluminum foil has a thickness of 50±5 μm and an overlap rate of ≥30%;

[0013] The sheath layer is a polyimide-polytetrafluoroethylene blend with a temperature resistance grade of 300°C.

[0014] The silver-plated layer of the conductor layer is formed by a pulse electroplating process, with a duty ratio of 1:5 and a silver crystal surface ratio of >80%.

[0015] The BNNTs in the insulating layer are modified with a silane coupling agent KH-550 and then dispersed in a polyimide precursor solution to form a three-dimensional thermal conductive network with a thermal conductivity coefficient of ≥1.2 W / m·K.

[0016] The insulating layer is added with 0.5-1 wt% of titanium dioxide.

[0017] The preparation method of the cable includes an insulation layer curing process: gradually heating to 80°C and keeping it for 2 hours → 200°C and keeping it for 3 hours → 300°C and keeping it for 1 hour, so that the crystallinity reaches 45-50%.

[0018] An electron beam irradiation cross-linking step is added after the sheath layer is extruded.

[0019] The sheath layer comprises a blend of polyimide and polytetrafluoroethylene in a mass ratio of 7:3, and is added with 2 wt % of silicon carbide micropowder and 0.5 wt % of polyetheretherketone.

[0020] The outer aluminum foil of the shielding layer is laser overlapped, with an overlap width of ≥3mm and a laser power of 50W.

[0021] The beneficial effects of the present invention are:

[0022] (1) The present invention relates to a continuous casting machine cable based on a polyimide composite material and a preparation method thereof. The BNNTs heat conduction network reduces thermal resistance by 62%, enabling the cable to operate stably for a long time in a high-temperature environment above 250°C, and the short-term temperature tolerance can reach above 300°C, greatly improving the high-temperature resistance.

[0023] (2) The double-layer shielding has a shielding effectiveness of 72.5dB at 1GHz; the shielding layer resistance change rate is less than 3% at high temperatures, and the anti-interference performance is greatly improved;

[0024] (3) The 45° braided structure makes the bending life reach 600,000 times; the sheath wear resistance is greater than 500 times, and the mechanical properties are higher. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The present invention will be further described below with reference to the accompanying drawings and examples.

[0026] Figure 1 It is a cross-sectional view of the present invention.

[0027] Figure 2 It is a structural schematic diagram of the reinforcing rib in the present invention.

[0028] Figure 3 It is a flow chart of the present invention. DETAILED DESCRIPTION

[0029] The present invention will now be described in further detail with reference to the accompanying drawings, which are simplified schematic diagrams that illustrate the basic structure of the present invention in a schematic manner.

[0030] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "connected" and "connection" should be understood in a broad sense. For example, they can refer to fixed connection, detachable connection, or integral connection; mechanical connection, electrical connection; direct connection, or indirect connection through an intermediary. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0031] Figure 1 The cable shown has a multi-layer composite construction consisting of the following layers (from inside to outside):

[0032] Conductor layer 1:

[0033] Silver-plated copper wire is used as the conductor, ensuring excellent conductivity and high-temperature resistance. The conductor adopts a 5-strand twisted structure with a single wire diameter between 0.12-0.25mm, which effectively balances the skin effect and flexibility, reducing capacitance loss. The SZ twisting direction (pitch ratio of 12-15) effectively suppresses eddy currents.

[0034] Insulation layer 2:

[0035] A polyimide-boron nitride nanotube composite (BNNT content 8-12wt%, breakdown strength ≥35kV / mm) is used as the insulation material. The BNNTs are modified with the silane coupling agent KH-550 and dispersed in a polyimide precursor solution (PMDA-ODA system). In-situ polymerization forms a three-dimensional thermally conductive network, increasing the thermal conductivity to 1.2 W / m·K, a 300% improvement over pure polyimide (PI). The insulation thickness is designed to be 15% of the conductor diameter, with a breakdown field strength ≥35kV / mm and a dielectric constant between 2.8 and 3.2 (0.5 lower than pure polyimide at 1MHz). A staged curing process (80°C / 2h + 200°C / 3h + 300°C / 1h) is used to prevent air bubbles.

[0036] Shield 3:

[0037] The cable utilizes a double-layer shielding structure, with an inner layer of nickel-plated aramid fiber braid (coverage ≥85%) and an outer layer of vapor-deposited aluminum foil (50μm thickness, overlap ≥30%). This dual-mechanism shielding mechanism combines magnetic and electrical shielding: the inner nickel plating (magnetic loss) and the outer aluminum foil (electrical reflection) work synergistically to effectively enhance the cable's shielding effectiveness. The nickel layer thickness of the nickel-plated aramid fiber is controlled between 0.8-1.2μm, achieving a balance between skin depth and flexibility (shielding effectiveness ≥70dB at a test frequency of 1MHz). A 45±2° braid angle optimizes axial tensile and radial compressive resistance (reducing the bending radius by 40% compared to a 90° braid). Elongation at break is increased to 25%, a 40% increase compared to conventional braiding. The outer vapor-deposited aluminum foil has an overlap width of ≥3mm and a thickness of 50±5μm.

[0038] Sheath layer 4:

[0039] The cable is constructed from a polyimide-polytetrafluoroethylene blend (PI:PTFE = 7:3, with 2% silicon carbide micropowder added to enhance wear resistance and 0.5% polyetheretherketone (PEEK) to increase interfacial compatibility). This sheath material is heat-resistant and can guarantee a continuous operating temperature of 300°C.

[0040] A filler 5 is provided inside the insulating layer 2 and outside the conductor layer 1 , and a wrapping tape 6 is provided between the insulating layer 2 and the filler 5 and between the shielding layer 3 and the sheath layer 4 .

[0041] like Figure 1 and Figure 2 As shown, a reinforcing rib 7 is provided between the five conductors, and an arc-shaped protrusion is provided on the outside of the reinforcing rib 7. The size of the arc-shaped protrusion is preset in advance according to the gap between the conductors, and is used to enhance the supporting force of the gap between the conductors. The arc-shaped protrusion on the outside of the reinforcing rib 7 is arranged in a spiral structure, which cooperates with the twisted structure between the conductors.

[0042] Cable specifications: 3×2.5mm²+2×1.0mm²;

[0043] like Figure 3 As shown, 1. Conductor stranding: 0.15mm silver-plated copper wire, pitch ratio 14;

[0044] 2. Insulation coating: BNNTs modified PI solution, thickness 0.25mm after curing;

[0045] 3. Shielding layer: Inner layer: 120 mesh nickel-plated aramid braid (tension 15cN), outer layer: 50μm aluminum foil laser overlap (power 50W);

[0046] 4. Sheath extrusion: screw temperature 290-310℃, die pressure 12MPa.

[0047] Process innovation

[0048] 1. The silver layer is achieved by pulse electroplating (duty cycle 1:5), the silver crystal orientation (111) plane accounts for more than 80%, and the high-frequency resistance is reduced by 12% compared with traditional DC plating (test frequency 10MHz);

[0049] 2. The insulation layer 2 is cured by gradient temperature rise: 80℃ / 2h (solvent evaporation) → 200℃ / 3h (imidization) → 300℃ / 1h (crystallization is controlled to 45-50%). This can effectively avoid the generation of bubbles and improve the performance of the insulation layer.

[0050] 3. Shielding braiding process: 45±2° braiding angle is adopted to optimize axial tensile and radial compressive performance. The bending fatigue life meets Nf=5×10^5×(D / d)^(-2.3), (D is the bending diameter and d is the cable outer diameter);

[0051] 4. Jacket extrusion process: Zone 1 (feeding section): 280°C → Zone 2 (compression section): 310°C → Zone 3 (metering section): 305°C → die 295°C. The jacket curing process is the same as the insulation curing process, but with the addition of a radiation cross-linking step to enhance interfacial bonding through electron beam irradiation. Die pressure: 12 ± 0.5 MPa (to ensure silicon carbide dispersion uniformity > 95%).

[0052] With the above-described preferred embodiments of the present invention as a guide, and with reference to the above description, relevant personnel are fully capable of making various changes and modifications without departing from the technical scope of this invention. The technical scope of this invention is not limited to the contents of the specification and must be determined according to the scope of the claims.

Claims

1. A continuous casting machine cable based on polyimide composite material, characterized in that: It comprises a conductor layer (1), an insulating layer (2), a shielding layer (3) and a sheath layer (4) which are arranged in sequence from the inside to the outside; The conductor layer (1) is a multi-strand silver-plated copper wire with a single wire diameter of 0.12-0.25 mm, a twist pitch ratio of 12-15, and an SZ twist direction; The silver-plated layer of the conductor layer (1) is formed by a pulse electroplating process, with a duty ratio of 1:5 and a silver crystal surface ratio of >80%; The insulating layer (2) is a polyimide-boron nitride nanotube composite material, wherein the boron nitride nanotube content is 8-12wt%, the thickness of the insulating layer is 15% of the conductor diameter, and the breakdown strength is ≥35kV / mm; The BNNTs in the insulating layer (2) are modified with a silane coupling agent KH-550 and then dispersed in a polyimide precursor solution to form a three-dimensional thermal conductive network with a thermal conductivity coefficient of ≥1.2 W / m·K; The insulating layer (2) is added with 0.5-1 wt% of titanium dioxide; Including the insulating layer (2) curing process: gradient heating to 80°C for 2 hours → 200°C for 3 hours → 300°C for 1 hour, so that the crystallinity reaches 45-50%; The shielding layer (3) comprises an inner layer of nickel-plated aramid fiber braided mesh and an outer layer of vapor-deposited aluminum foil; the coverage of the inner layer braided mesh is ≥85%, the nickel layer thickness is 0.8-1.2 μm, and the braiding angle is 45±2°; the outer layer of vapor-deposited aluminum foil has a thickness of 50±5 μm and an overlap rate of ≥30%; The outer aluminum foil of the shielding layer (3) is laser-stitched, with a width of ≥3 mm and a laser power of 50 W; The sheath layer (4) is a polyimide-polytetrafluoroethylene blend with a temperature resistance level of 300°C; After the sheath layer (4) is extruded, an electron beam irradiation cross-linking step is added; The sheath layer (4) comprises a blend of polyimide and polytetrafluoroethylene in a mass ratio of 7:3, and is added with 2 wt% silicon carbide micropowder and 0.5 wt% polyetheretherketone.

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