LNG ultra-low temperature cable and its production process

Abstract

The present invention relates to an LNG ultra-low temperature cable, which comprises a conductor, a wrapping tape, an insulating layer, a reinforcement layer and an outer sheath from the inside to the outside; the conductor is twisted in multiple layers, and the conductor comprises an inner layer, an outermost layer and an outermost layer from the inside to the outside, the twist pitch of the outermost layer is 18-20 times the outer diameter of the inner layer, and the twist pitch of the outermost layer is 15-16 times the outer diameter of the outermost layer; the outer diameter of the conductor is not greater than 12.4 mm. The present invention has the effect of not cracking and not being easy to break down when stretched at a low temperature of -276°C.

Description

Technical Field

[0001] The invention relates to the technical field of cables, in particular to LNG ultra-low temperature cables. Background Art

[0002] With the extensive use of clean energy LNG, ultra-low temperature cables used in large LNG carriers, LNG shore-based storage tanks, LNG distribution pump stations, etc. have achieved rapid development, which is also the largest application occasion of ultra-low temperature cables at present. The temperature range of common low temperature cables in ultra-low temperature medium environments (-100--270℃) such as Freon liquefied natural gas LNG, liquid nitrogen LN2, liquid helium LHe, liquid oxygen LO2, and liquid hydrogen LH2 is -40℃--60℃. When applied to -196℃, the insulation layer and sheath layer become hard, brittle, and even crack, which brings safety hazards. Summary of the invention

[0003] In view of the shortcomings of the prior art, one of the purposes of the present invention is to provide an LNG ultra-low temperature cable that is not easy to be punctured or cracked.

[0004] The above-mentioned object of the present invention is achieved through the following technical solutions:

[0005] The LNG ultra-low temperature cable comprises, from the inside to the outside, a conductor, a wrapping tape, an insulating layer, a reinforcement layer and an outer sheath; the conductor is twisted in multiple layers, and comprises, from the inside to the outside, an inner layer, an outermost layer and an outermost layer; the twisting pitch of the outermost layer is 18-20 times the outer diameter of the inner layer, and the twisting pitch of the outermost layer is 15-16 times the outer diameter of the outermost layer; the outer diameter of the conductor is not greater than 12.4 mm.

[0006] By adopting the above technical solution, the limitation of the pitch of each layer of the conductor can effectively control the outer diameter of the entire cable. The outer surface of the conductor will be relatively round and the single-filament gap will be small, ensuring that the external insulation layer and the outer sheath are extruded smoothly, and the internal stress is relatively small to avoid cracking.

[0007] In a preferred example, the present invention can be further configured as follows: the conductors are twisted in layers using a 1+6+12 structure, and the twisting direction of the outer layer is opposite to that of the inner layer and the outermost layer.

[0008] By adopting the above technical solution, the 1+6+12 structure has the characteristics of occupying less space, stable twisted connection, and easy use.

[0009] In a preferred example, the present invention can be further configured as follows: the pitch of the outer layer of the conductor is 100-130 mm, and the pitch of the outer layer is 130-160 mm.

[0010] By adopting the above technical solution, the pitch can ensure that the conductor has a short single-line moving distance and small friction during the bending process, and is easier to bend and more flexible during installation and use.

[0011] In a preferred example, the present invention can be further configured as follows: the wrapping tape is made of polytetrafluoroethylene, and the outer diameter of the wrapping is not greater than 13.4 mm.

[0012] By adopting the above technical solution, polytetrafluoroethylene has the characteristics of low relative density, low dielectric loss, small influence of temperature and signal frequency changes, stable dielectric constant, excellent temperature resistance and good weather resistance.

[0013] In a preferred example, the present invention can be further configured as follows: the thickness of the insulating layer at its thinnest point is between 2.40-2.45 mm, and the average thickness is between 2.6-3.0 mm; the outer diameter of the insulating core composed of the conductor, the wrapping tape and the insulating layer is not greater than 19.0 mm.

[0014] By adopting the above technical solution, the thickness of the insulation layer can ensure the anti-puncture performance of the cable, improve the safety performance of the cable and maintain the stability of the cable transmission.

[0015] In a preferred example, the present invention can be further configured as follows: the reinforcing layer (4) is woven from high-temperature resistant alkali-free glass fiber yarns, with a weaving density of not less than 97%, a weaving angle between 40-50°, and an outer diameter of not more than 19.6 mm; the thinnest point of the outer protective layer (5) is between 0.7-0.8 mm, the average thickness is between 0.75-1.25 mm, and the outer diameter is not more than 23.5 mm.

[0016] By adopting the above technical scheme, the reinforcement layer formed by weaving high-temperature resistant alkali-free glass fiber yarns can effectively improve the insulation layer and extend the service life of the cable when the insulation layer ages due to improper use or long-term low temperature, overload, etc. The outer sheath has the characteristics of super low temperature resistance, wear resistance, corrosion resistance, etc., thereby improving the service life of the product.

[0017] The technical solution for achieving the second object of the present invention is a production process for LNG ultra-low temperature cables.

[0018] The above-mentioned object of the present invention is achieved through the following technical solutions:

[0019] Step 1: The conductor is twisted by evenly dividing a plurality of tinned copper wires into 19 strands, and then twisting them in reverse according to a 1+6+12 structure to form the conductor;

[0020] Step 2: wrapping the conductor (1) with polytetrafluoroethylene to form the wrapping tape (2), and then drying the wrapping tape;

[0021] Step 3: Extrude FEP outside the wrapping tape (2) using an insulating extrusion die to form the insulating layer (3), and then place it in an oven for full drying. The insulating extrusion die has a die configuration stretch ratio K = (D1 2 -D2 2 ) / (D3 2 -D4 2 ), matching coefficient δ = (D1 / D3) / (D2 / D4), K value range (3-100), δ value range (1.01-1.3);

[0022] Step 4: Weaving alkali-free glass fiber yarns outside the insulating layer (3) to form the reinforcing layer (4), and performing a drying process;

[0023] Step 5: Extrude FEP outside the reinforcing layer (4) using an insulating extrusion die to form the outer sheath (5), and then place it in an oven for full drying. The insulating extrusion die has a die configuration stretch ratio (D1 2 -D2 2 ) / (D3 2 -D4 2 ), matching coefficient δ = (D1 / D3) / (D2 / D4), K value range (3-100), δ value range (1.01-1.3).

[0024] By adopting the above technical solution, the die configuration stretching ratio K=(D1 2 -D2 2 ) / (D3 2 -D4 2 ), matching coefficient δ = (D1 / D3) / (D2 / D4), K value range (3-100), δ value range (1.01-1.3), which can ensure that the cable passes the withstand voltage test of 21kV / 5min without breakdown and does not crack when stretched at -276℃ low temperature.

[0025] In a preferred example, the present invention can be further configured as follows: in the steps three and five, the FEP is selected to have a melt index of 7-9 g / 10 min, and the insulating layer (3) and the outer protective layer (5) are placed in an oven at 100-130° C. for 1-1.5 hours.

[0026] By adopting the above technical solution, the melt index of FEP is 7-9 g / 10 min, which has good fluidity while maintaining the viscosity of movement.

[0027] In a preferred example, the present invention can be further configured as follows: in the step 4, the outer insulating layer is woven with 4 strands of 40 / 4 alkali-free glass yarn per ingot to form a reinforcement layer, and the weaving density is not less than 97%.

[0028] By adopting the above technical solution, the alkali-free glass yarn is woven to form a reinforcement layer, which can effectively improve the temperature resistance level of the insulation layer. The density of the braided layer is not less than 97%. When the insulation layer of the cable is aged due to improper use or long-term overload, the service life of the cable can be greatly extended.

[0029] In summary, the present invention includes at least one of the following beneficial technical effects:

[0030] 1. The limitation of the pitch of each conductor layer in the present invention can effectively control the outer diameter, ensure the smooth extrusion of the insulation layer and the sheath, and avoid cracking;

[0031] 2. The mold configuration of the insulation extrusion mold in the present invention has a stretch ratio K = (D1 2 -D2 2 ) / (D3 2 -D4 2 ), the matching coefficient δ=(D1 / D3) / (D2 / D4), the K value range is between 3-100, and the δ value range is between 1.01-1.3, so as to ensure that the cable will not break down in the withstand voltage test of 21kV / 5min and will not crack in the low temperature stretching of -276℃. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below according to specific embodiments and in conjunction with the accompanying drawings, wherein

[0033] Figure 1 It is a schematic diagram of the structure of this embodiment.

[0034] The reference numerals in the accompanying drawings are:

[0035] 1. Conductor; 2. Tape; 3. Insulation layer; 4. Reinforcement layer; 5. Outer sheath. DETAILED DESCRIPTION

[0036] The present invention is further described in detail below in conjunction with the accompanying drawings.

[0037] Reference Figure 1, which is an LNG ultra-low temperature cable disclosed in the present invention, comprising a conductor 1, a wrapping tape 2, an insulating layer 3, a reinforcement layer 4 and an outer sheath 5. The conductor 1 uses 437 tinned copper wires with a wire diameter of 0.45 mm, which are evenly divided into 19 strands, each with 23 strands, and are layered and twisted in a structure of 1 strand + 6 strands + 12 strands, and are reversely twisted in a left-right-left manner from inside to outside, with the inner layer-outer layer-outermost layer being respectively twisted in reverse from inside to outside; the pitch of the inner layer is 100-130 mm, and the pitch of the outer layer is 130-160 mm. After twisting, the outer diameter of the conductor 1 is not greater than 12.4 mm. The thickness of the thinnest point of the insulating layer 3 is between 2.40-2.45mm, preferably 2.42mm in the present embodiment, and the average thickness is between 2.6-3.0mm, preferably 2.8mm in the present embodiment, ensuring the anti-puncture performance of the cable; the reinforcing layer 4 using alkali-free glass fiber yarn has a weaving density of not less than 97%, a weaving angle between 40-50°, preferably 45° in the present embodiment, and an outer diameter of not more than 19.5mm, which can effectively improve the fluoroplastic insulating layer 3 when the cable is improperly used or in a long-term low temperature, overload, etc., resulting in aging of the insulating layer, and can greatly extend the service life of the cable; the outer sheath 5 adopts a primary material FEP with a melt index of 7-9g / 10min, and the melt index is preferably 8g / 10min, which has the characteristics of ultra-low temperature resistance, wear resistance, corrosion resistance, etc. The thinnest point of the outer sheath 5 is between 0.7-0.8mm, preferably 0.75mm in the present embodiment, the average thickness is between 0.75-1.25mm, preferably 1.0mm in the present embodiment, and the outer diameter is not more than 23.5mm.

[0038] The cable has the characteristics of stable connection, not easy to break down or crack in ultra-low temperature environment, and long service life.

[0039] The production process of LNG ultra-low temperature cable includes the following steps:

[0040] Step 1: Conductor 1 is made of 437 tinned copper wires with a wire diameter of 0.45 mm, which are evenly divided into 19 strands, with 23 strands in each strand, and twisted in layers according to the structure of 1 strand + 6 strands + 12 strands. The inner layer, the outer layer, and the outermost layer are twisted in the left-right-left manner respectively; the pitch of the inner layer is 100-130 mm, and the pitch of the outer layer is 130-160 mm. After twisting, the outer diameter of the conductor 1 is not more than 12.4 mm, and the twisting pitch does not exceed 16 times the outer diameter of each layer of the conductor 1;

[0041] Step 2: Use polytetrafluoroethylene (PTFE) to wrap the conductor to form a tape, the outer diameter of the tape is no more than 13.4mm, and then dry it. The drying temperature is: 100-120℃; the drying time should be maintained for at least 24 hours after reaching the drying temperature; the dried wire core should be kept dry until the insulation is extruded;

[0042] Step 3: The material of the insulating layer 3 is selected from the primary material FEP with a melt index of 8g / 10min, which is placed in an oven at 100-130°C for 1-1.5h before extrusion and fully dried; the mold configuration stretch ratio K = (D1 2 -D2 2 ) / (D3 2 -D4 2 ), die matching coefficient δ=(D1 / D3) / (D2 / D4), K value range (3-100), δ value range (1.01-1.3), where D1 is the aperture of the die sleeve, D2 is the outer diameter of the die core, D3 is the outer diameter of the insulated wire core, and D4 is the outer diameter of the conductor 1. In this embodiment, a 65 extruder is used to produce the insulating layer 3, and the extruder body temperature is controlled from front to back in the range of 260℃-310℃, 350℃-380℃ and 360℃-380℃; the extrusion surface is uniform and smooth; the thinnest point of the insulating layer 3 is 2.42mm, and the average thickness is 2.8mm. The insulating layer produced in this way has super low temperature resistance and good electrical properties.

[0043] Step 4: Weave 4 strands of 40 / 4 alkali-free glass yarns outside the insulating layer 3 to form a reinforcing layer 4, with a weaving density of not less than 97%; and perform drying treatment; this can effectively improve the fluoroplastic insulating layer 3 when the insulating layer 3 is aged due to improper use or long-term low temperature, overload, etc., and can greatly extend the service life of the cable;

[0044] Step 5: Extrude the outer sheath 5 outside the reinforcement layer 4, and the mold configuration of the insulation extrusion mold has a stretch ratio K = (D1 2 -D2 2 ) / (D3 2 -D4 2 ), die matching coefficient δ=(D1 / D3) / (D2 / D4), K value range (3-100), δ value range (1.01-1.3). The outer sheath 5 has a thickness of 0.75mm at the thinnest point and an average thickness of 1.0mm; the outer diameter is not greater than 23.5mm.

[0045] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A production process for LNG ultra-low temperature cable, characterized in that: The LNG ultra-low temperature cable comprises, from the inside to the outside, a conductor (1), a wrapping tape (2), an insulating layer (3), a reinforcement layer (4) and an outer sheath (5); the production process of the LNG ultra-low temperature cable comprises the following steps: Step 1: twisting the conductor (1), dividing a plurality of tinned copper wires into 19 strands, and then twisting them in reverse according to a 1+6+12 structure to form the conductor (1); Step 2: wrapping the conductor (1) with polytetrafluoroethylene to form the wrapping tape (2), and then drying the wrapping tape; Step 3: Extruding FEP outside the wrapping tape (2) using an insulating extrusion die to form the insulating layer (3), and then placing the insulating layer in an oven for sufficient drying, wherein the insulating extrusion die has a die configuration stretch ratio K=(D12-D22) / (D32-D42), a die matching coefficient δ=(D1 / D3) / (D2 / D4), a K value range of 3-100, and a δ value range of 1.01-1.3; Step 4: Weaving alkali-free glass fiber yarns outside the insulating layer (3) to form the reinforcing layer (4), and performing a drying process; Step 5: Extruding FEP outside the reinforcing layer (4) using an insulating extrusion die to form the outer protective layer (5), and then placing the outer protective layer (5) in an oven for sufficient drying, wherein the insulating extrusion die has a die configuration stretch ratio K=(D12-D22) / (D32-D42), a die matching coefficient δ=(D1 / D3) / (D2 / D4), a K value range of 3-100, and a δ value range of 1.01-1.3; The conductor (1) is twisted in multiple layers, and comprises, from the inside to the outside, an inner layer, an outermost layer and an outermost layer, the twisting pitch of the outermost layer being 18-20 times the outer diameter of the inner layer, and the twisting pitch of the outermost layer being 15-16 times the outer diameter of the outermost layer; the outer diameter of the conductor (1) is not greater than 12.4 mm.

2. The production process of the LNG ultra-low temperature cable according to claim 1 is characterized in that: The pitch of the conductor (1) near the outer layer is 100-130 mm, and the pitch of the outer layer is 130-160 mm.

3. The production process of the LNG ultra-low temperature cable according to claim 1 is characterized in that: The outer diameter of the wrapping tape (2) is no greater than 13.4 mm.

4. The production process of the LNG ultra-low temperature cable according to claim 1, characterized in that: The thinnest point of the insulating layer (3) is between 2.40 and 2.45 mm, and the average thickness is between 2.6 and 3.0 mm; the outer diameter of the insulating wire core composed of the conductor (1), the wrapping tape (2) and the insulating layer (3) is not greater than 19.0 mm.

5. The production process of the LNG ultra-low temperature cable according to claim 1, characterized in that: The braiding angle of the high temperature resistant alkali-free glass fiber yarn of the reinforcing layer (4) is between 40-50 degrees, and the outer diameter is not greater than 19.6 mm; the thinnest point of the outer protective layer (5) is between 0.7-0.8 mm, the average thickness is between 0.75-1.25 mm, and the outer diameter is not greater than 23.5 mm.

6. The production process of LNG ultra-low temperature cable according to claim 1, characterized in that: In the steps 3 and 5, the FEP is selected to have a melting index of 7-9 g / 10 min, and the insulating layer (3) and the outer protective layer (5) are placed in an oven at 100-130° C. for 1-1.5 hours.

7. The production process of the LNG ultra-low temperature cable according to claim 1, characterized in that: In the step 4, the outer portion of the insulating layer (3) is woven with 4 strands of 40 / 4 alkali-free glass yarn per ingot to form a reinforcing layer (4), and the weaving density is not less than 97%.

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