Mineral insulated cable and preparation method thereof

Abstract

The invention discloses a mineral insulated cable and a preparation method thereof, and belongs to the technical field of mineral insulated cables. A mineral insulated cable comprises a conductive core, an insulating layer and an embossed copper protective layer. The insulating layer is the magnetic particles coated with the silicon dioxide layer, has high insulativity, can replace magnesium oxide, has better low water absorption than magnesium oxide, and is beneficial to long-term stable power supply. After being magnetized, the magnetic particles wrapped with the silicon dioxide layers have permanent magnetism, can keep magnetism in a high-temperature environment for a long time, and can ensure that the insulating property is not reduced after the insulating layer is bent; the technical defects that a conventional magnesium oxide insulating layer needs to adopt a binder and the bending insulating property is reduced are overcome; and the cable is easy to bend and convenient to construct.

Description

Technical Field

[0001] This invention relates to the field of mineral-insulated cable technology, specifically to a mineral-insulated cable and its preparation method. Background Technology

[0002] Mineral-insulated cables (MI cables) are widely used in high-risk fields such as construction, chemical industry, and energy due to their excellent properties such as high temperature resistance, fire resistance, explosion resistance, and corrosion resistance. However, in actual production, installation, and application, they still face several technical challenges. These challenges mainly focus on four dimensions: material property limitations, manufacturing process bottlenecks, installation and construction difficulties, and long-term reliability maintenance. Specific technical issues and details are as follows: the moisture absorption and stability of the insulation layer.

[0003] Magnesium oxide (MgO), a mainstream insulating material, has extremely strong hygroscopic properties. Even after being exposed to air for several hours, it will absorb moisture and form magnesium hydroxide (Mg(OH)2), causing a sharp drop in insulation resistance (from 10). 14 Ω·cm decreased to 10 6 (below Ω·cm), which may cause leakage risk.

[0004] Mechanical brittleness: Although copper sheaths have good ductility, they are prone to fatigue cracks under long-term bending conditions; steel sheaths (used for mechanical impact resistance) have high hardness and poor ductility, and are prone to irreversible deformation after bending, leading to insulation layer compression damage.

[0005] Mineral-insulated cables can have their internal insulation layer damaged when bent, leading to a decrease in insulation performance and increasing the risk of leakage.

[0006] The thermal expansion of the conductor and the insulation layer is mismatched. The coefficient of thermal expansion of the conductor (copper) is 16.5 × 10⁻⁶. -6 / ℃) is much higher than that of the magnesium oxide insulation layer (6.5×10 -6 / ℃)——When a cable operates in a high-temperature environment (such as above 200℃) for a long time, the conductor elongates much more than the insulation layer due to heat, which will cause gaps between the two. This not only reduces the heat conduction efficiency (affecting the current carrying capacity), but may also cause local bulging or cracking of the sheath due to the expansion of air in the gap due to heat.

[0007] Therefore, in view of the above-mentioned technical problems, there is an urgent need in this field to develop a mineral-insulated cable that is fire-resistant, bend-resistant, easy to bend, has low water absorption, and high insulation. Summary of the Invention

[0008] In order to overcome the shortcomings of the existing technology, the present invention aims to provide a mineral-insulated cable and its preparation method, which has significant technical effects such as fire resistance, bending resistance, easy bending, low water absorption and high insulation.

[0009] This invention is achieved through the following technical solution: a mineral-insulated cable, comprising, from the inside out: a conductive core, an insulating layer, and an embossed copper protective layer. The insulating layer consists of magnetic particles coated with a silica layer, with a particle size ranging from 300nm to 500nm, preferably 300nm to 400nm. The magnetic particles are Fe3O4 nanoparticles, with a particle size ranging from 150nm to 300nm, preferably 200nm to 300nm. The magnetic particles coated with the silica layer are magnetized.

[0010] In one specific embodiment, the mineral-insulated cable may also have a plastic protective layer overlaid on the embossed copper protective layer.

[0011] In one specific embodiment, the method for preparing the magnetic particles (Fe3O4@SiO2) coated with a silicon dioxide layer is as follows:

[0012] Step S1: Preparation of Fe3O4 nanoparticles

[0013] Deionized water was used as the solvent. The mixture was evacuated and purged with nitrogen to maintain the nitrogen atmosphere. FeCl2, FeCl3, and oleic acid were added, and the mixture was stirred at 200-1000 rpm for 10-20 min. The temperature was then raised to 50-80℃, and sodium hydroxide solution was added. The mixture was stirred continuously at 500-800 rpm for 10-30 min until the reaction was stopped. The mixture was then magnetically separated, and the resulting precipitate was washed repeatedly with ultrapure water 1-3 times and dried under vacuum to obtain Fe3O4 nanoparticles.

[0014] Step S2: Preparation of SiO2 coating layer

[0015] Fe3O4 was added to 60%-80% ethanol, ultrasonically mixed, and then 25% ammonia was added. Tetraethyl orthosilicate was added, and the mixture was stirred at 20-40℃ for 5-12 hours. After separation, the mixture was washed successively with anhydrous ethanol and deionized water, vacuum dried at 40℃, calcined in a muffle furnace at 400-700℃, and magnetized to obtain magnetic Fe3O4@SiO2 nanoparticles coated with a silicon dioxide layer.

[0016] In one specific embodiment, the molar ratio of FeCl2 to FeCl3 in step S1 is 1:(1.75-2).

[0017] In one specific embodiment, the molar ratio of FeCl2 to sodium hydroxide is 1:(7.5-8.5).

[0018] In one specific embodiment, the ethanol concentration in step S2 is preferably 75%.

[0019] In one specific embodiment, the amount of tetraethyl orthosilicate used is 20-40 times the mass of the Fe3O4 nanoparticles.

[0020] In one specific embodiment, the volume ratio of 25% ammonia water to Fe3O4 nanoparticles is (0.5-3):1 (mL / g).

[0021] In one specific embodiment, the muffle furnace calcination temperature is preferably 500°C.

[0022] In one specific embodiment, the embossed copper protective layer has one of the following: a ring pattern or a spiral pattern, preferably a ring pattern.

[0023] In one specific embodiment, the magnetization treatment specifically involves adding the calcined nanoparticles to anhydrous ethanol, ultrasonically dispersing them uniformly, and maintaining them under a magnetic field strength of 1-2T for 5-30 minutes.

[0024] On the other hand, the present invention provides a method for preparing a mineral-insulated cable, as follows:

[0025] Step S1: Dry the magnetic particles (i.e., insulating material) coated with silicon dioxide under vacuum in a constant temperature oven at 50-100℃.

[0026] Step S2: Clean and remove dirt from the copper tube and conductive core material. Place the required wire core material into the copper tube on the assembly table and fix one end of the copper tube.

[0027] Step S3: Fill the gaps formed by the copper tube and the conductive core material with insulating material.

[0028] Step S4: After the insulation material is filled, the insulation layer of the insulated cable is further compacted by micro-vibration with a vibrating hammer. After multiple vertical rolling processes to reduce the diameter to close to the design specifications, the cable is annealed for the first time at 420℃-550℃. After further horizontal reduction to meet the design specifications and pressing annular patterns, the cable is annealed for the second time at 420℃-550℃. A protective gas (nitrogen or other inert gas) is used to protect the copper tube and copper sheath to make the surface bright.

[0029] Beneficial effects

[0030] This invention provides a mineral-insulated cable and its preparation method, comprising: a conductive core, an insulation layer, and an embossed copper protective layer. The cable has significant fire resistance, bending resistance, easy bending, low water absorption, and high insulation.

[0031] The magnetic particles coated with a silica layer prepared in this invention possess high insulation properties, can replace magnesium oxide, and exhibit better low water absorption than magnesium oxide, which is beneficial for long-term stable power supply. After magnetization, the silica-coated magnetic particles acquire permanent magnetism and can maintain their magnetism for a long time in high-temperature environments (the Curie temperature of iron(III) oxide is approximately 585°C). This ensures that even after bending, the magnetic attraction between the silica-coated magnetic particles remains tightly and evenly distributed around the conductive core, providing excellent insulation. Furthermore, it avoids the technical drawbacks of conventional magnesium oxide insulation layers, which require adhesives and suffer from reduced insulation performance upon bending. The embossed copper protective layer has an embossed pattern, and the silica-coated magnetic particles are not adhered with adhesives, exhibiting relative free flow, easy bending, and convenient construction. Attached Figure Description

[0032] Figure 1 This is a TEM image of the magnetic particles 1 coated with a silicon dioxide layer in Example 1.

[0033] Figure 2 This is a TEM image of the comparative magnetic particle 1 in Comparative Example 1. Detailed Implementation

[0034] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. The described embodiments are only some preferred embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] Unless otherwise specified, the experimental methods used in the embodiments are conventional or common methods in the art, and the materials and reagents used are commercially available unless otherwise specified.

[0036] The raw materials used in the examples and comparative examples are described below:

[0037] Magnesium oxide particles (particle size 2μm, purity 99.99%): purchased from Guangdong Wengjiang Chemical Reagent Co., Ltd.

[0038] FeCl2: Purchased from Wuhan Jiyesheng Chemical Co., Ltd.;

[0039] FeCl3: Purchased from Wuhan Jiyesheng Chemical Co., Ltd.;

[0040] Ethyl orthosilicate: purchased from Shanghai Zhuorui Chemical Co., Ltd.

[0041] Unless otherwise specified, all components and raw materials used in the embodiments and comparative examples of this invention are commercially available, and the same type of components and raw materials are used in each parallel experiment.

[0042] Preparation of magnetic particles (Fe3O4@SiO2) coated with silica layer (1):

[0043] Step S1: Preparation of Fe3O4 nanoparticles

[0044] 50 L of deionized water was injected into the reaction vessel, evacuated, and purged with nitrogen to maintain a nitrogen atmosphere. 25 mol FeCl, 9.5 mol FeCl, and 1000 ml oleic acid were added, and the mixture was stirred at 600 rpm for 15 min. The temperature was raised to 70 °C, and 20 L of sodium hydroxide solution (containing 38 mol sodium hydroxide) was added. The reaction was stopped after stirring continuously at 600 rpm for 20 min. The mixture was magnetically separated, and the resulting precipitate was washed three times with ultrapure water and dried under vacuum to obtain Fe3O4 nanoparticles.

[0045] Step S2: Preparation of SiO2 coating layer

[0046] Fe3O4 was added to 10 L of 75% ethanol, and the mixture was sonicated at 40 W for 15 min. Then, 1.5 L of 25% ammonia water was added, followed by tetraethyl orthosilicate. The mixture was stirred at 30 °C and reacted for 8 h. The mixture was then separated and washed successively with anhydrous ethanol and deionized water. The nanoparticles were dried under vacuum at 40 °C, calcined in a muffle furnace at 500 °C for 1 h, and then magnetized (the calcined nanoparticles were added to anhydrous ethanol, sonicated at 40 W, and kept under a magnetic field of 1.5 T for 10 min) to obtain Fe3O4@SiO2 nanoparticles coated with a silica layer (magnetic particles coated with silica layer 1).

[0047] In step S2, the mass ratio of Fe3O4 nanoparticles to tetraethyl orthosilicate is 1:30.

[0048] Table 1. Ingredients (parts by weight) of magnetic particles coated with silica layer

[0049]

[0050] Particle size was measured using a Malvern particle size analyzer (Zetasizer Ultra).

[0051]

[0052]

[0053] Example 1

[0054] A method for preparing a mineral-insulated cable is as follows:

[0055] Step S1: Dry the magnetic particles 1 (i.e., insulating material) coated with silicon dioxide in a vacuum oven at 50-100℃ for 2 hours.

[0056] Step S2: Clean the copper tube and conductive core material with a detergent to remove dirt. Place the required wire core material into the copper tube on the assembly table and fix one end of the copper tube.

[0057] Step S3: Fill the gaps formed by the copper tube and the conductive core material with insulating material (magnetic particles 1 wrapped with silicon dioxide layer).

[0058] Step S4: After the insulation material is filled, the insulation layer of the insulated cable is further compacted by micro-vibration with a vibrating hammer. After multiple vertical rolling processes to reduce the diameter to close to the design specifications, the cable is annealed for the first time at 450℃. After further horizontal reduction to meet the design specifications and pressing annular patterns, the cable is annealed for the second time at 450℃. A protective gas (nitrogen) is used to protect the copper tube and copper sheath to make the surface bright.

[0059] Example 2

[0060] A method for preparing a mineral-insulated cable is as follows:

[0061] Step S1: Dry the magnetic particles 2 (i.e., insulating material) coated with silicon dioxide in a vacuum oven at 50-100℃ for 2 hours.

[0062] Step S2: Clean the copper tube and conductive core material with a detergent to remove dirt. Place the required wire core material into the copper tube on the assembly table and fix one end of the copper tube.

[0063] Step S3: Fill the gaps formed by the copper tube and the conductive core material with insulating material (i.e., magnetic particles 2 wrapped with silicon dioxide).

[0064] Step S4: After the insulation material is filled, the insulation layer of the insulated cable is further compacted by micro-vibration with a vibrating hammer. After multiple vertical rolling processes to reduce the diameter to close to the design specifications, the cable is annealed for the first time at 450℃. After further horizontal reduction to meet the design specifications and pressing annular patterns, the cable is annealed for the second time at 450℃. A protective gas (nitrogen) is used to protect the copper tube and copper sheath to make the surface bright.

[0065] Example 3

[0066] A method for preparing a mineral-insulated cable is as follows:

[0067] Step S1: Dry the magnetic particles 3 (i.e., insulating material) coated with silicon dioxide in a vacuum oven at 50-100℃ for 2 hours.

[0068] Step S2: Clean the copper tube and conductive core material with a detergent to remove dirt. Place the required wire core material into the copper tube on the assembly table and fix one end of the copper tube.

[0069] Step S3: Fill the gaps formed by the copper tube and the conductive core material with insulating material (i.e., magnetic particles 3 wrapped with silicon dioxide layer).

[0070] Step S4: After the insulation material is filled, the insulation layer of the insulated cable is further compacted by micro-vibration with a vibrating hammer. After multiple vertical rolling processes to reduce the diameter to close to the design specifications, the cable is annealed for the first time at 450℃. After further horizontal reduction to meet the design specifications and pressing annular patterns, the cable is annealed for the second time at 450℃. A protective gas (nitrogen) is used to protect the copper tube and copper sheath to make the surface bright.

[0071] Comparative Example 1

[0072] A method for preparing a mineral-insulated cable is as follows:

[0073] Step S1: Dry the comparative magnetic particles 1 (i.e., the insulating layer material) in a vacuum oven at 50-100℃ for 2 hours.

[0074] Step S2: Clean the copper tube and conductive core material with a detergent to remove dirt. Place the required wire core material into the copper tube on the assembly table and fix one end of the copper tube.

[0075] Step S3: Fill the gaps formed by the copper tube and the conductive core material with insulating material (i.e., comparative magnetic particles 1).

[0076] Step S4: After the insulation material is filled, the insulation layer of the insulated cable is further compacted by micro-vibration with a vibrating hammer. After multiple vertical rolling processes to reduce the diameter to close to the design specifications, the cable is annealed for the first time at 450℃. After further horizontal reduction to meet the design specifications and pressing annular patterns, the cable is annealed for the second time at 450℃. A protective gas (nitrogen) is used to protect the copper tube and copper sheath to make the surface bright.

[0077] Comparative Example 2

[0078] A method for preparing a mineral-insulated cable is as follows:

[0079] Step S1: Dry the comparative magnetic particles 2 (i.e., the insulating layer material) in a vacuum oven at 50-100℃ for 2 hours.

[0080] Step S2: Clean the copper tube and conductive core material with a detergent to remove dirt. Place the required wire core material into the copper tube on the assembly table and fix one end of the copper tube.

[0081] Step S3: Fill the gaps formed by the copper tube and the conductive core material with insulating material (i.e., contrast magnetic particles 2).

[0082] Step S4: After the insulation material is filled, the insulation layer of the insulated cable is further compacted by micro-vibration with a vibrating hammer. After multiple vertical rolling processes to reduce the diameter to close to the design specifications, the cable is annealed for the first time at 450℃. After further horizontal reduction to meet the design specifications and pressing annular patterns, the cable is annealed for the second time at 450℃. A protective gas (nitrogen) is used to protect the copper tube and copper sheath to make the surface bright.

[0083] Comparative Example 3

[0084] A method for preparing a mineral-insulated cable is as follows:

[0085] Step S1: Dry the control particles 3 (i.e., the insulating layer material) in a vacuum oven at 50-100℃ for 2 hours.

[0086] Step S2: Clean the copper tube and conductive core material with a detergent to remove dirt. Place the required wire core material into the copper tube on the assembly table and fix one end of the copper tube.

[0087] Step S3: Fill the gaps formed by the copper tube and the conductive core material with insulating material (i.e., comparative particles 3).

[0088] Step S4: After the insulation material is filled, the insulation layer of the insulated cable is further compacted by micro-vibration with a vibrating hammer. After multiple vertical rolling processes to reduce the diameter to close to the design specifications, the cable is annealed for the first time at 450℃. After further horizontal reduction to meet the design specifications and pressing annular patterns, the cable is annealed for the second time at 450℃. A protective gas (nitrogen) is used to protect the copper tube and copper sheath to make the surface bright.

[0089] Table 2 Comparison of Insulating Layers in Examples and Comparative Examples

[0090]

[0091]

[0092] Performance verification

[0093] 1) Fire resistance test

[0094] The fire resistance test was conducted in accordance with GB / T13033.1-2007. The test conditions were: flame supply at 750℃ and continuous power supply for 180 minutes.

[0095] 2) Bending resistance and fire resistance test

[0096] The fire resistance test was conducted in accordance with GB / T13033.1-2007. The test conditions were: 750℃ flame supply and 180min continuous power supply; at three points on the same cable, the pipe bend was 90° and then straightened, and 50 bends were performed within 10min at each point, with the last bend not straightened.

[0097] 3) Determination of water absorption rate (%) and volume resistivity (Ω·cm)

[0098] The water absorption rate was measured using an MTSY-4 digital display ceramic water absorption rate tester; (Refer to...)

[0099] GB / T13033.1-2007 Determination of volume resistivity.

[0100] Table 3 Performance Test Record Sheet

[0101]

[0102]

[0103] Table 3 shows that the mineral-insulated cables prepared in Examples 1-3 exhibit significant fire resistance, bending resistance, low water absorption, and high insulation. 1) Comparative Example 1 failed the fire resistance test, exhibiting poor fire resistance and electrical breakdown, thus affecting normal power supply. This is related to the use of comparative magnetic particles 1. The mass ratio of Fe3O4 nanoparticles to tetraethyl orthosilicate used in the preparation of comparative magnetic particles 1 was 1:15. The amount of tetraethyl orthosilicate used was less than that in Example 1, and the prepared silica layer could not form a complete and sealed encapsulation of the Fe3O4 nanoparticles, resulting in poor insulation performance. This is consistent with the experimentally measured volume resistivity (5.62 × 10⁻⁶). 5 Low consistency () Figure 2 1) In Comparative Example 1, the TEM image of the comparative magnetic particle 1 shows that the silica layer is thin and uneven. 2) In Comparative Example 2, electrical breakdown occurred during the bending and fire resistance test, affecting normal power supply. This is because after multiple bends, the insulating material (comparative magnetic particle 2) at the bend was unevenly distributed, leading to insulation layer fracture. The comparative magnetic particle 2 was not magnetized and did not possess permanent magnet properties, so it could not attract each other evenly at the bend, thus causing insulation layer fracture. 3) Electrical breakdown occurred during the bending and fire resistance test, affecting normal power supply, because the magnesium oxide particle insulation layer fractured.

[0104] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A mineral-insulated cable, characterized in that, From the inside out, it includes: a conductive core, an insulating layer, and an embossed copper protective layer; the insulating layer consists of magnetic particles coated with a silicon dioxide layer, with a particle size range of 327nm-392nm; the magnetic particles are Fe3O4 nanoparticles with a particle size range of 237nm-249nm; the magnetic particles coated with a silicon dioxide layer are magnetized.

2. The mineral-insulated cable according to claim 1, characterized in that, It also includes a plastic protective layer covering the embossed copper protective layer.

3. The mineral-insulated cable according to claim 1, characterized in that, The method for preparing the magnetic particles coated with a silicon dioxide layer is as follows: Step S1: Preparation of Fe3O4 nanoparticles Deionized water was used as the solvent. The mixture was evacuated and purged with nitrogen to maintain the nitrogen atmosphere. FeCl2, FeCl3, and oleic acid were added, and the mixture was stirred at 200-1000 rpm for 10-20 min. The temperature was then raised to 50-80℃, and sodium hydroxide solution was added. The mixture was stirred at 500-800 rpm for 10-30 min to stop the reaction. The mixture was then magnetically separated, and the resulting precipitate was washed repeatedly with ultrapure water 1-3 times and dried under vacuum to obtain Fe3O4 nanoparticles. Step S2: Preparation of SiO2 coating layer Fe3O4 was added to 60%-80% ethanol, ultrasonically mixed, and then 25% ammonia was added. Tetraethyl orthosilicate was added, and the mixture was stirred at 20-40℃ for 5-12 hours. After separation, the mixture was washed successively with anhydrous ethanol and deionized water, vacuum dried at 40℃, calcined in a muffle furnace at 400-700℃, and magnetized to obtain magnetic particles coated with a silica layer.

4. The mineral-insulated cable according to claim 3, characterized in that, In step S1, the molar ratio of FeCl2 to FeCl3 is 1:(1.75-2).

5. The mineral-insulated cable according to claim 3, characterized in that, The molar ratio of FeCl2 to sodium hydroxide is 1:(7.5-8.5).

6. The mineral-insulated cable according to claim 3, characterized in that, In step S2, the ethanol concentration is 75%.

7. The mineral-insulated cable according to claim 3, characterized in that, In step S2, the amount of tetraethyl orthosilicate used is 20-40 times the mass of Fe3O4 nanoparticles.

8. The mineral-insulated cable according to claim 1, characterized in that, The magnetization process specifically involves adding the calcined nanoparticles to anhydrous ethanol, ultrasonically dispersing them evenly, and maintaining them under a magnetic field strength of 1-2T for 5-30 minutes.

9. The mineral-insulated cable according to claim 1, characterized in that, The embossed copper protective layer has one of the following: a ring pattern or a spiral pattern.

10. The method for preparing the mineral-insulated cable according to any one of claims 1-9, characterized in that, The steps include the following: Step S1: Dry the magnetic particles coated with a silicon dioxide layer in a vacuum oven at 50-100℃. Step S2: Clean and remove dirt from copper tubes and conductive core materials. Place the required wire core material into the copper tube on the assembly table and fix one end of the copper tube. Step S3: Fill the gaps formed by the copper tube and the conductive core material with insulating material; Step S4: After the insulation material is filled, the insulation layer of the insulated cable is further compacted by micro-vibration with a vibrating hammer. After multiple vertical rolling processes to reduce the diameter to close to the design specifications, the cable is annealed for the first time at 420℃-550℃. After further horizontal reduction to meet the design specifications and pressing annular patterns, the cable is annealed for the second time at 420℃-550℃. The copper tube and copper sheath are protected with protective gas to make the surface bright.

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