A high temperature fire-resistant mineral insulated cable

Abstract

The invention relates to a high-temperature fire-resistant mineral insulated cable, and belongs to the technical field of cables. The mineral insulated cable at least comprises: a wire core, a metal sheath sleeved on the outer side of the wire core, and a composite mineral layer filled between the wire core and the metal sheath, wherein the components of the composite mineral layer are: 100 parts of low-dielectric modified magnesium oxide, 6.2-7.5 parts of a binder, 2.4-3.2 parts of a lubricant, and 5.5-6.5 parts of a filler; the low-dielectric modified magnesium oxide takes magnesium oxide as a core, and forms a composite oxide layer on the surface that is mainly silicon oxide and doped with boron, zirconium, and yttrium oxides; the composite oxide coating layer plays a role of partition, effectively reducing the dielectric constant of magnesium oxide and the dielectric loss in a high-frequency environment; the low-dielectric modified magnesium oxide is used as the main material of the cable mineral layer, which can maintain the heat and fire resistance of magnesium oxide, and at the same time greatly reduce the attenuation value of the cable, so that the mineral insulated cable can be suitable for some high-frequency transmissions.

Description

Technical Field

[0001] The invention belongs to the technical field of cables, and in particular relates to a high-temperature fire-resistant mineral insulated cable. Background Art

[0002] Mineral insulated cable is a special type of cable. It is mostly made of copper sheath wrapped around the copper conductor core wire, and magnesium oxide powder is used as inorganic insulating material to isolate the conductor and the sheath. It has extremely high temperature resistance and fire resistance, and is suitable for power transmission and control systems in extreme environments. It is especially widely used in high-end industries such as aerospace, nuclear industry, etc.

[0003] However, magnesium oxide mineral cables are greatly limited in high-frequency transmission. This is because magnesium oxide, as an insulating material, has good insulation properties at low frequencies, but its dielectric loss will increase at high frequencies, which means that during high-frequency transmission, more energy will be converted into heat energy, resulting in signal attenuation. Based on this technical defect, the present application performs surface modification on magnesium oxide, aiming to provide a mineral insulated cable that can meet certain high-frequency working conditions. Summary of the invention

[0004] In order to solve the technical problems mentioned in the background technology, the object of the present invention is to provide a high temperature fire-resistant mineral insulated cable.

[0005] The purpose of the present invention can be achieved through the following technical solutions:

[0006] A high-temperature fire-resistant mineral insulated cable comprises at least: a wire core, a metal sheath sleeved on the outside of the wire core, and a composite mineral layer filled between the wire core and the metal sheath; wherein the components of the composite mineral layer are: 100 parts of low-dielectric modified magnesium oxide, 6.2-7.5 parts of a binder, 2.4-3.2 parts of a lubricant, and 5.5-6.5 parts of a filler.

[0007] Low dielectric modified magnesium oxide is prepared by the following method:

[0008] Step A1: premix γ-aminopropyltriethoxysilane, triethylamine and anhydrous tetrahydrofuran under a dry nitrogen atmosphere, heat to 40-50° C., stir at 90-120 rpm, slowly add methyl chloroacetate and react for 2-3 hours, then continue to heat to 65-70° C. and reflux for 1.5-2 hours to obtain a promoter;

[0009] Furthermore, the feed ratio of γ-aminopropyltriethoxysilane, methyl chloroacetate, triethylamine and anhydrous tetrahydrofuran is 10mmol:28-33mmol:1-1.5mL:10-18mL, and the methyl chloroacetate and γ-aminopropyltriethoxysilane are substituted with active amino groups.

[0010] Step A2: premix ethyl orthosilicate, accelerator, triethyl borate and ethanol aqueous solution, add magnesium oxide powder and mix for 1.2-1.5h, then add zirconium nitrate and yttrium nitrate aqueous solution, adjust the pH value to 8-9 with ammonia water, control the temperature in a water bath to 55-70°C and stand for 24h, take the bottom precipitate and dry it to obtain a composite precursor;

[0011] Furthermore, the feed ratio of magnesium oxide powder, tetraethyl orthosilicate, promoter, triethyl borate, zirconium nitrate, yttrium nitrate and ethanol aqueous solution is 50g:2.2-3.5g:0.6-0.9g:1.1-1.5g:0.5-0.7g:0.1-0.2g:130-170mL. In the ethanol aqueous solution, triethyl borate, tetraethyl orthosilicate and promoter are co-hydrolyzed to form a gel state and attached to the surface of magnesium oxide powder, and then zirconium and yttrium ions added later are captured to form a complex on the surface of magnesium oxide.

[0012] Furthermore, the average particle size of the magnesium oxide powder is not higher than 10 μm, which is conducive to filling and compaction.

[0013] Step A3: The composite precursor is first placed in a muffle furnace for oxidation roasting, and then placed in a vacuum sintering furnace for vacuum sintering, and then broken up after cooling to obtain low dielectric modified magnesium oxide.

[0014] Furthermore, the oxidation roasting temperature is 480-550° C., and the roasting time is 1.5-2 hours, so as to remove low-boiling substances and organic substances in the composite precursor and form an oxide adhesion layer.

[0015] Furthermore, the vacuum sintering temperature is 950-1020° C. and the sintering time is 1-1.3 h, so that the oxide attachment layer is sintered densely and maintains good structural stability.

[0016] Furthermore, the binder is calcium silicate powder, which, as an inorganic binder, has a porous surface and a large specific surface area, and produces a good bonding effect with other particle surfaces through mechanical anchoring.

[0017] Furthermore, the lubricant is graphite powder, which is conducive to smooth filling and compaction of the powder.

[0018] Furthermore, the filler is silica fume, which has a micro-nano particle size and is filled into the gaps between other particles, thereby facilitating the formation of a dense protective layer.

[0019] Beneficial effects of the present invention:

[0020] The invention discloses a low-dielectric modified magnesium oxide suitable for a mineral insulated cable. The magnesium oxide micropowder is used as a core, and a promoter having an ethoxysilane structure is obtained by a substitution reaction of an active amino group of methyl chloroacetate and gamma-aminopropyltriethoxysilane. In an alcohol-water environment, triethyl borate, ethyl orthosilicate and the promoter are co-hydrolyzed to form a gel state and attached to the surface of the magnesium oxide micropowder. The gel captures added zirconium and yttrium ions by adsorption. In addition, a methyl diacetate structure containing tertiary amine in the promoter forms a complex to fix zirconium and yttrium ions. After high-temperature calcination, a composite oxide layer mainly composed of silicon oxide and doped with boron, zirconium and yttrium oxides is formed on the surface of the magnesium oxide. The composite oxide coating layer serves as a partition, effectively reducing the dielectric constant of the magnesium oxide and the dielectric loss in a high-frequency environment. The low-dielectric modified magnesium oxide is used as the main material of the cable mineral layer, so that the heat and fire resistance of the magnesium oxide can be maintained, and the attenuation value of the cable can be greatly reduced, so that the mineral insulated cable can be suitable for some high-frequency transmissions. DETAILED DESCRIPTION

[0021] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0022] Example 1, preparation of high temperature fire-resistant mineral insulated cable, the specific implementation process is as follows:

[0023] (1) Preparation of low dielectric modified magnesium oxide

[0024] Step A1: premix γ-aminopropyltriethoxysilane, triethylamine and anhydrous tetrahydrofuran under a dry nitrogen atmosphere, heat to 50°C, stir at 120rpm, slowly add methyl chloroacetate to react for 2h, then continue to heat to 70°C and reflux for 1.5h, wherein the feed ratio of γ-aminopropyltriethoxysilane, methyl chloroacetate, triethylamine and anhydrous tetrahydrofuran is 10mmol:33mmol:1.5mL:18mL. After the reaction is completed, remove excess methyl chloroacetate and tetrahydrofuran by vacuum rotary evaporation to obtain a promoter.

[0025] Step A2: prepare a 60% volume fraction ethanol aqueous solution, add tetraethyl orthosilicate, accelerator and triethyl borate to premix, add magnesium oxide powder and stir and mix at 120rpm for 1.2h, take zirconium nitrate and yttrium nitrate hydrate to prepare a saturated aqueous solution, add it to the mixed solution and mix well, adjust the pH value to 8 with ammonia water, control the temperature at 70℃ in a water bath and let it stand for 24h, wherein the feed ratio of magnesium oxide powder, tetraethyl orthosilicate, accelerator, triethyl borate, zirconium nitrate, yttrium nitrate and ethanol aqueous solution is 50g:3.5g:0.6g:1.5g:0.7g:0.1g:170mL, take the bottom precipitate and dry it after the reaction to obtain a composite precursor.

[0026] Step A3: Place the composite precursor in a muffle furnace, set the temperature to 550°C, and calcine for 1.5 hours, perform oxidation calcination on the composite precursor, and then transfer it to a vacuum sintering furnace, set the temperature to 1020°C, and calcine for 1 hour, perform vacuum sintering on the oxidation calcination product, and break it up after cooling to obtain low dielectric modified magnesium oxide.

[0027] (2) Preparation of mineral insulated cables

[0028] Step S1: taking raw materials according to weight parts, 100 parts of low dielectric modified magnesium oxide, which is prepared in this embodiment; 7.5 parts of binder, which is calcium silicate powder; 2.4 parts of lubricant, which is graphite powder; 6.5 parts of filler, which is silica fume; adding each raw material into a high-speed mixer and mixing at 1200 rpm for 10 minutes to obtain a mineral powder batch;

[0029] Step S2: Take a copper wire with a diameter of 2.3 mm as the wire core and a copper tube with an inner diameter of 5.5 mm as the metal sheath, laminate a mineral powder compound on the surface of the wire core to form a composite mineral layer, and then stretch and compact it three times on a cold drawing machine after the metal sheath is covered, so as to obtain a mineral insulated cable.

[0030] Example 2, preparing a high temperature fire-resistant mineral insulated cable, the specific implementation process is as follows:

[0031] (1) Preparation of low dielectric modified magnesium oxide

[0032] Step A1: premix γ-aminopropyltriethoxysilane, triethylamine and anhydrous tetrahydrofuran under a dry nitrogen atmosphere, heat to 40°C, stir at 90 rpm, slowly add methyl chloroacetate to react for 3 hours, then continue to heat to 65°C and reflux for 2 hours, wherein the feed ratio of γ-aminopropyltriethoxysilane, methyl chloroacetate, triethylamine and anhydrous tetrahydrofuran is 10 mmol: 28 mmol: 1 mL: 10 mL. After the reaction is completed, remove excess methyl chloroacetate and tetrahydrofuran by vacuum rotary evaporation to obtain a promoter.

[0033] Step A2: prepare a 60% volume fraction ethanol aqueous solution, add tetraethyl orthosilicate, accelerator and triethyl borate to premix, add magnesium oxide powder and stir and mix at 120rpm for 1.5h, take zirconium nitrate and yttrium nitrate hydrate to prepare a saturated aqueous solution, add it to the mixed solution and mix well, adjust the pH value to 9 with ammonia water, control the temperature at 55°C in a water bath and let it stand for 24h, wherein the feed ratio of magnesium oxide powder, tetraethyl orthosilicate, accelerator, triethyl borate, zirconium nitrate, yttrium nitrate and ethanol aqueous solution is 50g:2.2g:0.9g:1.1g:0.5g:0.2g:130mL, take the bottom precipitate and dry it after the reaction to obtain a composite precursor.

[0034] Step A3: Place the composite precursor in a muffle furnace, set the temperature to 480°C, and calcine for 2 hours to perform oxidation calcination on the composite precursor. Then transfer it to a vacuum sintering furnace, set the temperature to 950°C, and calcine for 1.3 hours to perform vacuum sintering on the oxidation calcination product. After cooling, break it up to obtain low dielectric modified magnesium oxide.

[0035] (2) Preparation of mineral insulated cables

[0036] Step S1: taking raw materials according to weight parts, 100 parts of low dielectric modified magnesium oxide, which is prepared in this embodiment; 6.2 parts of binder, which is calcium silicate powder; 3.2 parts of lubricant, which is graphite powder; 5.5 parts of filler, which is silica fume; adding each raw material into a high-speed mixer and mixing at 1200 rpm for 10 minutes to obtain a mineral powder batch;

[0037] Step S2: Take a copper wire with a diameter of 2.3 mm as the wire core and a copper tube with an inner diameter of 5.5 mm as the metal sheath, laminate a mineral powder compound on the surface of the wire core to form a composite mineral layer, and then stretch and compact it three times on a cold drawing machine after the metal sheath is covered, so as to obtain a mineral insulated cable.

[0038] Example 3, preparation of high temperature fire-resistant mineral insulated cable, the specific implementation process is as follows:

[0039] (1) Preparation of low dielectric modified magnesium oxide

[0040] Step A1: premix γ-aminopropyltriethoxysilane, triethylamine and anhydrous tetrahydrofuran under a dry nitrogen atmosphere, heat to 45°C, stir at 120 rpm, slowly add methyl chloroacetate and react for 2.5 hours, then continue to heat to 68°C and reflux for 1.8 hours, wherein the feed ratio of γ-aminopropyltriethoxysilane, methyl chloroacetate, triethylamine and anhydrous tetrahydrofuran is 10 mmol: 30 mmol: 1.3 mL: 15 mL. After the reaction is completed, remove excess methyl chloroacetate and tetrahydrofuran by vacuum rotary evaporation to obtain a promoter.

[0041] Step A2: prepare a 60% volume fraction ethanol aqueous solution, add tetraethyl orthosilicate, accelerator and triethyl borate to premix, add magnesium oxide powder and stir and mix at 120rpm for 1.5h, take zirconium nitrate and yttrium nitrate hydrate to prepare a saturated aqueous solution, add it to the mixed solution and mix well, adjust the pH value to 9 with ammonia water, control the temperature at 60℃ in a water bath and let it stand for 24h, wherein the feed ratio of magnesium oxide powder, tetraethyl orthosilicate, accelerator, triethyl borate, zirconium nitrate, yttrium nitrate and ethanol aqueous solution is 50g:2.8g:0.7g:1.3g:0.6g:0.15g:150mL, take the bottom precipitate and dry it after the reaction to obtain a composite precursor.

[0042] Step A3: Place the composite precursor in a muffle furnace, set the temperature to 520°C, and calcine for 1.8 hours, perform oxidation calcination on the composite precursor, and then transfer it to a vacuum sintering furnace, set the temperature to 980°C, and calcine for 1.2 hours. Perform vacuum sintering on the oxidation calcination product, and break it up after cooling to obtain low dielectric modified magnesium oxide.

[0043] (2) Preparation of mineral insulated cables

[0044] Step S1: taking raw materials according to weight parts, 100 parts of low dielectric modified magnesium oxide, which is prepared in this embodiment; 6.5 parts of binder, which is calcium silicate powder; 2.8 parts of lubricant, which is graphite powder; 6 parts of filler, which is silica fume; adding each raw material into a high-speed mixer and mixing at 1200 rpm for 10 minutes to obtain a mineral powder batch;

[0045] Step S2: Take a copper wire with a diameter of 2.3 mm as the wire core and a copper tube with an inner diameter of 5.5 mm as the metal sheath, laminate a mineral powder compound on the surface of the wire core to form a composite mineral layer, and then stretch and compact it three times on a cold drawing machine after the metal sheath is covered, so as to obtain a mineral insulated cable.

[0046] Example 4, preparation of high temperature fire-resistant mineral insulated cable, the specific implementation process is as follows:

[0047] (1) Preparation of low dielectric modified magnesium oxide

[0048] Step A1: premix γ-aminopropyltriethoxysilane, triethylamine and anhydrous tetrahydrofuran under a dry nitrogen atmosphere, heat to 50°C, stir at 120rpm, slowly add methyl chloroacetate to react for 2.2h, then continue to heat to 65°C and reflux for 1.7h, wherein the feed ratio of γ-aminopropyltriethoxysilane, methyl chloroacetate, triethylamine and anhydrous tetrahydrofuran is 10mmol:30mmol:1.2mL:15mL. After the reaction is completed, remove excess methyl chloroacetate and tetrahydrofuran by vacuum rotary evaporation to obtain a promoter.

[0049] Step A2: prepare a 60% volume fraction ethanol aqueous solution, add tetraethyl orthosilicate, accelerator and triethyl borate to premix, add magnesium oxide powder and stir and mix at 120rpm for 1.5h, take zirconium nitrate and yttrium nitrate hydrate to prepare a saturated aqueous solution, add it to the mixed solution and mix well, adjust the pH value to 8 with ammonia water, control the temperature at 65°C in a water bath and let it stand for 24h, wherein the feed ratio of magnesium oxide powder, tetraethyl orthosilicate, accelerator, triethyl borate, zirconium nitrate, yttrium nitrate and ethanol aqueous solution is 50g:3g:0.8g:1.4g:0.6g:0.18g:160mL, take the bottom precipitate and dry it after the reaction to obtain a composite precursor.

[0050] Step A3: Place the composite precursor in a muffle furnace, set the temperature to 500°C, and calcine for 1.7 hours to perform oxidation calcination on the composite precursor. Then transfer it to a vacuum sintering furnace, set the temperature to 1000°C, and calcine for 1.2 hours to perform vacuum sintering on the oxidation calcination product. After cooling, break it up to obtain low dielectric modified magnesium oxide.

[0051] (2) Preparation of mineral insulated cables

[0052] Step S1: taking raw materials according to weight parts, 100 parts of low dielectric modified magnesium oxide, which is prepared in this embodiment; 7 parts of binder, which is calcium silicate powder; 3 parts of lubricant, which is graphite powder; 6 parts of filler, which is silica fume; adding each raw material into a high-speed mixer and mixing at 1200 rpm for 10 minutes to obtain a mineral powder batch;

[0053] Step S2: Take a copper wire with a diameter of 2.3 mm as the wire core and a copper tube with an inner diameter of 5.5 mm as the metal sheath, laminate a mineral powder compound on the surface of the wire core to form a composite mineral layer, and then stretch and compact it three times on a cold drawing machine after the metal sheath is covered, so as to obtain a mineral insulated cable.

[0054] Comparative Example 1, referring to Example 4, the low dielectric modified magnesium oxide was replaced with the same amount of magnesium oxide powder, and the rest of the implementation process was exactly the same.

[0055] Comparative Example 2, referring to Example 4, the low-dielectric modified magnesium oxide was replaced with 50 parts of magnesium oxide powder and 50 parts of SIC-L3A type low-dielectric ceramic powder, and the rest of the implementation process was exactly the same.

[0056] The mineral insulated cable prepared as above was subjected to a fire resistance test in accordance with GB / T 13033.1-2007. The test conditions were: 750°C fire and 180 min continuous power supply. 100 m was cut from the cable prepared as above, and the attenuation value of the cable was tested in accordance with IEC 61196-1-113:2018. The specific test results are shown in Table 1:

[0057] Table 1

[0058]

[0059] It can be seen from the test results in Table 1 that the mineral insulated cable prepared in the embodiment has stable heat and fire resistance, can meet most heat and fire resistance requirements, and the attenuation value of the cable is low, so that the mineral insulated cable can be suitable for some high-frequency transmission.

[0060] The mineral powder prepared as above was pressed into a 2 mm sheet, and the dielectric properties of the sheet were tested using a dielectric impedance spectrometer. The specific test results are shown in Table 2:

[0061] Table 2

[0062]

[0063] It can be seen from the test results in Table 2 that the dielectric constant of the composite mineral layer of the cable of the embodiment is lower, and the dielectric loss is lower at 10-20 MHz.

[0064] In the description of the specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0065] The above contents are merely examples and explanations of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described or replace them in a similar manner. As long as they do not deviate from the invention or exceed the scope defined by the claims, they shall all fall within the protection scope of the present invention.

Claims

1. A high temperature fire-resistant mineral insulated cable, comprising at least: A wire core, a metal sheath sleeved outside the wire core, and a composite mineral layer filled between the wire core and the metal sheath, wherein the composite mineral layer comprises: 100 parts of low-dielectric modified magnesium oxide, 6.2-7.5 parts of a binder, 2.4-3.2 parts of a lubricant, and 5.5-6.5 parts of a filler; The low dielectric modified magnesium oxide is prepared by the following method: Step A1: premix γ-aminopropyltriethoxysilane, triethylamine and anhydrous tetrahydrofuran under a dry nitrogen atmosphere, heat to 40-50° C., stir and slowly add methyl chloroacetate to react for 2-3 hours, then continue to heat to 65-70° C. and reflux for 1.5-2 hours to obtain a promoter; Step A2: premix ethyl orthosilicate, accelerator, triethyl borate and ethanol aqueous solution, add magnesium oxide powder and mix for 1.2-1.5h, then add zirconium nitrate and yttrium nitrate aqueous solution, adjust the pH value to 8-9 with ammonia water, control the temperature in a water bath to 55-70°C and stand for 24h, take the bottom precipitate and dry it to obtain a composite precursor; Step A3: The composite precursor is first placed in a muffle furnace for oxidation roasting, and then placed in a vacuum sintering furnace for vacuum sintering, and then broken up after cooling to obtain low dielectric modified magnesium oxide.

2. A high temperature fire-resistant mineral insulated cable according to claim 1, characterized in that: The feed ratio of γ-aminopropyltriethoxysilane, methyl chloroacetate, triethylamine and anhydrous tetrahydrofuran is 10 mmol: 28-33 mmol: 1-1.5 mL: 10-18 mL.

3. A high temperature fire-resistant mineral insulated cable according to claim 2, characterized in that: The feed ratio of magnesium oxide powder, tetraethyl orthosilicate, accelerator, triethyl borate, zirconium nitrate, yttrium nitrate and ethanol aqueous solution is 50g: 2.2-3.5g: 0.6-0.9g: 1.1-1.5g: 0.5-0.7g: 0.1-0.2g: 130-170mL.

4. A high temperature fire-resistant mineral insulated cable according to claim 3, characterized in that: The average particle size of the magnesium oxide powder is not higher than 10 μm.

5. A high temperature fire-resistant mineral insulated cable according to claim 4, characterized in that: The oxidation roasting temperature is 480-550°C, and the roasting time is 1.5-2h; the vacuum sintering temperature is 950-1020°C, and the roasting time is 1-1.3h.

6. A high temperature fire-resistant mineral insulated cable according to claim 1, characterized in that: The binder is calcium silicate powder.

7. A high temperature fire-resistant mineral insulated cable according to claim 1, characterized in that: The lubricant is graphite powder.

8. A high temperature fire-resistant mineral insulated cable according to claim 1, characterized in that: The filler is silica fume.

Images