A method for preparing a fusion joint of aluminum and aluminum alloy cables

Abstract

The present invention discloses a method for preparing a fusion joint of aluminum and aluminum alloy cables, wherein a high-frequency electric heater is used to heat and melt the main body material of the cable core to be fused; the cable joint to be fused is processed to expose the cable core, a fracture is opened at the end of the cable core, the outer core at the end of the cable core is removed, and the second core is arranged in a trumpet shape along the circumference; two cable cores to be fused are placed in a forming mold to obtain an initial fusion joint; secondary molding is performed: the initial fusion joint is first polished to remove excess edge material, and then hydraulic pliers are used to perform continuous pressure molding from the middle to both sides; the cable core is subjected to anti-oxidation treatment, and then the inner semi-conductive layer, the main insulating layer and the outer semi-conductive layer of the cable are restored in sequence. The fusion joints prepared by the present invention all meet the test standards, have good resistivity, use temperature and breakdown performance, effectively solve the defects in the prior art, and have good practicality.

Description

Technical Field

[0001] The invention belongs to the technical field of welding joints, and in particular relates to a method for preparing a welding joint of an aluminum or aluminum alloy cable. Background Art

[0002] On-site fusion joints are cable joints that fuse the high-voltage shield, insulation and outer shield of the cable according to the cable raw materials, main structure and specification requirements to form a consistent intrinsic characteristic, stress cone-free and air gap-free interface. The current aluminum / aluminum alloy cable joints are prone to heat creep during the fusion process, which makes the joint failure rate high and circuit failures prone to occur. Adaptive metal is used for fusion connection between the joints of the power transmission and distribution aluminum / aluminum alloy cable lines, and the two aluminum alloy conductor cores to be connected are placed in the adaptive metal liquid for cooling and solidification. However, the adaptive metal is different from the original cable core material, which is prone to different conductivity, and the size consistency of the naturally cooled and solidified connection part is poor. As the use time goes by, the resistance of the connection part is more or less increasing. The increase in resistance hinders the stable transmission of current and makes the joint part prone to overheating. The larger the current, the higher the temperature rises. In extreme cases, the heat causes electrical breakdown of the middle connector and the melting of the conductor crimping joint, which in turn causes power outages or fire accidents. Summary of the invention

[0003] The object of the present invention is to provide a method for preparing a fusion joint of aluminum and aluminum alloy cables, aiming to solve the above-mentioned problems.

[0004] The present invention is mainly achieved through the following technical solutions:

[0005] A method for preparing a fusion joint of an aluminum or aluminum alloy cable comprises the following steps:

[0006] Step S1: using a high-frequency electric heater to heat and melt the main body material of the cable core to be welded;

[0007] Step S2: treating the cable joint to be welded to expose the cable core, and dividing the cross section of the cable core into an outer core, a second core, a third core and a center core from the outside to the inside; opening a fracture at the end of the cable core, removing the outer core at the end of the cable core, and arranging the second core in a trumpet shape along the circumference;

[0008] Step S3: placing two cable cores to be welded in a molding mold, injecting the melt heated in step S1 into the molding mold, and cooling and solidifying to obtain an initial welded joint;

[0009] Step S4: secondary molding: the initial welded joint is firstly polished to remove the excess edge material, and then hydraulic pliers are used to continuously pressurize and mold from the middle to both sides;

[0010] Step S5: Perform anti-oxidation treatment on the cable core, and then restore the inner semi-conductive layer, main insulating layer and outer semi-conductive layer of the cable in sequence.

[0011] In order to better realize the present invention, further, in the step S1, during the smelting process, first start the high-frequency electric heater, and set the power to 90%-95%, add flux, and quickly melt the base material; when the temperature is raised to 690°C-730°C, add refining agent to form bubbles in the melt, float up to remove impurities, and form an oxide film on the top of the melt; then, adjust the power of the high-frequency electric heater to 60%-70%, and let it stand to keep warm; in step S3, inject the melt into the molding mold, and discard the oxide film.

[0012] In order to better realize the present invention, further, the flux comprises the following components:

[0013] KCl: 24.5 wt%-26 wt%;

[0014] NaCl: 13.5wt%-15wt%;

[0015] LiCl: 6.65wt%-7.5wt%;

[0016] NaF: 3.75wt%-4.5wt%;

[0017] Na3AlF6: 48.5wt%-51.5wt%.

[0018] In order to better realize the present invention, further, the refining agent includes the following components:

[0019] KCl: 35wt%-50wt%;

[0020] NaCl: 30wt%-40wt%;

[0021] CaF2: 5wt%-8wt%;

[0022] Na2B407*10H2O: 8wt%-15wt%;

[0023] Mg2N3: 5wt%-10wt%;

[0024] C2Cl6: 3wt%-6wt%;

[0025] Rare earth: 0.2wt%-0.5wt%.

[0026] In order to better implement the present invention, further, in step S2, the second layer of cable cores at the ends of the cable cores form an angle of 10°-45° with the third layer of cable cores.

[0027] In order to better implement the present invention, further, in step S2, the second layer of cable cores at the ends of the cable cores form an angle of 25° with the third layer of cable cores.

[0028] In order to better realize the present invention, further, in the step S3, the molding mold includes a first mold and a second mold, and one side of the first mold and the second mold are respectively provided with a connected injection groove, a joint molding groove and an introduction groove, and the two sides of the joint molding groove are respectively provided with an introduction groove connected; when the first mold is merged with the second mold, the adjacent injection grooves, joint molding grooves and introduction grooves are correspondingly spliced ​​into a connected injection cavity, a joint molding chamber and an introduction hole, and the joint molding chamber is provided with a vent hole connected to the outside, and the inner diameter of the joint molding chamber is larger than the inner diameter of the introduction hole by 5-8mm.

[0029] In order to better realize the present invention, further, in the step S3, one end of the cable core passes through the introduction hole and extends into the joint forming chamber, and the fracture of the cable core is located in the joint forming chamber, and the distance between adjacent cable cores is 3-5mm; the outer side of the cable core inside the introduction hole is wrapped with copper tape, and the copper tape is 25-30mm away from the fracture of the cable core.

[0030] In order to better implement the present invention, further, step S5 includes the following steps:

[0031] Step S51: wrapping the inner semiconducting layer and the main insulating layer in the fusion area of ​​the cable core in sequence; then, sleeve the cable hot-melt plastic tube, and wrap the polytetrafluoroethylene tape around the outer side of the cable hot-melt plastic tube;

[0032] Step S52: Wrap the glass fiber heating tape connected to the welding heater around the inner semi-conductive layer and the main insulating layer of the cable to be restored, and then wrap the outer layer of the glass fiber heating tape with glass fiber insulation cloth;

[0033] Step S53: Wrap the high-frequency heating coil of the high-frequency electric heater around the phase-separated portion of the cable to generate external heating.

[0034] The beneficial effects of the present invention are as follows:

[0035] (1) The present invention uses the main body material for welding, which improves the adaptability of the material; then the second layer of the core is arranged in a trumpet shape, which significantly increases the contact area of ​​the welding and reduces the bubble rate inside the core; and further increases the density of the welding point and discharges bubbles through secondary pressure molding, making the welding point more compact and reliable; finally, the cable to be restored and the cable phase separation part are respectively heated internally and externally by a welding heater and a high-frequency electric heater, and a temperature gradient is generated at the cable welding point and the phase separation part, which effectively improves the efficiency and quality of restoring the inner semi-conductive layer and the main insulation layer, and eliminates the generation of bubbles. In addition, since the polytetrafluoroethylene tape has good temperature resistance of 250-300℃, it will not stretch and soften when heated externally, and the external heating heat can be evenly distributed throughout the heating part, ensuring the quality of the welding part. Samples 1 and 6 prepared by the present invention meet the test standards, have good resistivity, use temperature and breakdown performance, effectively solve the defects in the prior art, and have good practicality.

[0036] (2) The present invention uses a high-frequency electric heater to melt the base material at 659°C-760°C. Within the temperature range of 659°C-793°C, the molten aluminum and molten aluminum alloy can more fully remove iron, silicon and magnesium impurities, discharge hydrogen, nitrogen and elemental aluminum vapor, and make the melt structure more stable.

[0037] (3) The present invention uses flux to quickly weld the oxide film on the surface of aluminum / aluminum alloy, and a crust is formed on the surface and falls off. The surface tension of the chloride salt is small, so it can quickly cover the oxide film, and quickly adsorb aluminum oxide through Na3AlF6. Under the synergistic effect of NaF, the melting point of the chloride salt is reduced, the coverage is accelerated, and the metal melt on the interface is corroded, so that the oxide film is mechanically detached and quickly melted, which effectively reduces the temperature and time of smelting. The present invention further uses a refining agent to float impurities, improves the purity of the melt, and quickly reacts on the surface of the melt to form an oxide film to protect the internal melt from oxidation, and finally removes the oxide film. In the refining agent, chloride salt is added and combined with the chloride salt in the flux to further cover the impurities in the melt, and bubbles are formed inside the melt. CaF2 increases the fluidity of the internal melt, reduces the surface tension between the flux and the aluminum liquid and the surface tension between the flux and the slag inclusions, and increases the adsorption of the flux on the slag inclusions, thereby accelerating the process of the flux adsorbing the slag inclusions and the effect of bubble flotation; by adding Mg2N3, a rapid reaction is achieved on the top of the melt to form an oxide film, which blocks the external oxygen from being integrated into the melt and protects the internal melt; secondly, through composite components such as fluoride salts, sodium borate salts and rare earths, it can fully diffuse from bottom to top without adsorption and agglomeration, and can quickly play a refining role, reducing the viscosity and temperature of the slag phase, improving the fluidity of the slag phase, and having a significant impurity removal and refinement effect.

[0038] (4) The forming mold of the present invention can be quickly assembled by a clamp and is easy to use; the joint forming chamber of the present invention is connected to the outside world, so that the aluminum / aluminum alloy melt can flow and exhaust fully, avoiding the situation where the liquid is not filled in place and bubble holes appear at the joint. Secondly, the present invention can protect the cable by wrapping the copper tape, and at the same time, the joint forming chamber can be connected to the outside world, and the exhaust can be fully exhausted, which reduces the doping amount of bubbles and has good practicality. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a structural schematic diagram of the forming mold;

[0040] Figure 2 It is a schematic diagram of the cross-sectional structure of the cable core;

[0041] Figure 3 It is a cross-sectional schematic diagram of the cable core in the forming mold;

[0042] Figure 4 A schematic diagram of heating;

[0043] Figure 5 Schematic diagram of the test structure of sample 1;

[0044] Figure 6 Schematic diagram of the test circuit of sample 1.

[0045] Among them: 1-injection groove, 2-joint forming groove, 3-introduction groove, 4-outer layer wire core, 5-second layer wire core, 6-third layer wire core, 7-center wire core, 8-copper belt, 9-fusion heating machine, 10-high frequency electric heater, 11-glass fiber heating belt, 12-high frequency heating coil. DETAILED DESCRIPTION

[0046] Embodiment 1:

[0047] A method for preparing a fusion joint of an aluminum or aluminum alloy cable comprises the following steps:

[0048] 1. Use the main material of the cable core that needs to be welded, use a high-frequency electric heater 10 to heat the material, and strictly control the temperature at 659℃-760℃.

[0049] The models of the main body material are: 6061, 6201, 8030. The high-frequency electric heater 10 is used to heat and melt the main body material, and the melting temperature is controlled at 659°C-760°C. As shown in Table 1, the mechanical properties of the main body material after melting treatment at this temperature are significantly improved. This is because within the temperature range of 659°C-793°C, the aluminum melt and the aluminum alloy melt can more fully remove iron, silicon and magnesium impurities, discharge hydrogen, nitrogen and elemental aluminum vapor, and make the melt structure more stable.

[0050] Table 1

[0051]

[0052] Specifically, during the heating process, high temperature resistant materials are used in combination with graphene crucibles to ensure heating efficiency. The heating equipment used includes a cooling circulating water pump, a high frequency electric heater 10, a composite asbestos insulation and high temperature resistant layer, a glass fiber insulation cover, a graphene crucible, and a high frequency heating coil 12. During the heating process, the high frequency electric heater 10 is connected to the high frequency heating coil 12 and the circulating water pump, and the power is turned on to start the equipment. Then the composite asbestos insulation and high temperature resistant layer is neatly coated on the graphene crucible, and placed in the middle of the high frequency heating coil 12, and aluminum / aluminum alloy materials are added to generate high frequency heating, and the glass fiber insulation cover is covered to melt the aluminum / aluminum alloy liquid. The process makes full use of heat energy, and there is no external release of heat energy. Human hands can directly touch the composite asbestos insulation and high temperature resistant layer coating the graphene crucible.

[0053] 2. When melting aluminum / aluminum alloy materials, add flux and refining agent.

[0054] Add 120g to 280g of cable core material into the graphene crucible, start the high-frequency electric heater 10, and set the power to 90%-95%. After heating for 2 minutes to 4 minutes, add aluminum / aluminum alloy flux. When the temperature of the aluminum / aluminum alloy melt rises to 690℃-730℃, add aluminum / aluminum alloy refining agent. After mixing for 1 minute to 3 minutes, adjust the power of the high-frequency electric heater 10 to 60%-70%, let the molten liquid stand for 3 minutes to 4 minutes, and then inject the molten liquid into the molding mold for welding.

[0055] Preferably, the composition and content of the aluminum / aluminum alloy flux are as follows:

[0056] KCl: 24.5 wt%-26 wt%;

[0057] NaCl: 13.5wt%-15wt%;

[0058] LiCl: 6.65wt%-7.5wt%;

[0059] NaF: 3.75wt%-4.5wt%;

[0060] Na3AlF6: 48.5wt%-51.5wt%.

[0061] Preferably, the components and contents of the aluminum / aluminum alloy refining agent are as follows:

[0062] KCl: 35wt%-50wt%;

[0063] NaCl: 30wt%-40wt%;

[0064] CaF2: 5wt%-8wt%;

[0065] Na2B407*10H2O: 8wt%-15wt%;

[0066] Mg2N3: 5wt%-10wt%;

[0067] C2Cl6: 3wt%-6wt%;

[0068] Rare earth: 0.2wt%-0.5wt%.

[0069] After adding the flux, the aluminum oxide on the surface of the bulk material can be quickly dissolved, forming a crust and falling off, thereby reducing the melting temperature and time of the bulk material. Then, the refining agent is used to react with aluminum / aluminum alloy to produce low-boiling point compounds that are insoluble in aluminum / aluminum alloy liquid, forming bubbles in the molten liquid, which play a role in degassing and removing impurities when floating, effectively improving the purity of aluminum / aluminum alloy and stabilizing the metal structure. An oxide film is formed on the surface of the aluminum / aluminum alloy melt to prevent the liquid injected into the mold from being oxidized. After injection, the graphene crucible is left with an oxide film produced by the reaction. As shown in Table 2, after adding the flux and refining agent, the melting temperature and smelting time are significantly reduced.

[0070] Table 2

[0071]

[0072] 3. Design of forming molds for aluminum / aluminum alloy cable cores and processing of cable cores.

[0073] The molding die is provided with an injection cavity and a joint molding chamber in communication with each other, and the two sides of the joint molding chamber are provided with introduction holes in communication with each other, and the joint molding chamber is provided with a vent hole communicating with the outside. One end of the cable core is passed through the introduction hole and extended into the joint molding chamber, and the molten metal is introduced into the injection cavity to flow into the joint molding chamber, so that an initial fusion joint is obtained between adjacent cables.

[0074] like Figure 2 As shown, the cross section of the cable core is divided into an outer core 4, a second core 5, a third core 6 and a center core 7 from the outside to the inside, and the outer core 4 at the end of the cable core is removed, and the second layer of cable cores is distributed in a bell-mouth shape. Specifically, on the original cable structure, take out a 80-100mm long cable core, mark the size of 15-25mm in the opposite direction of the insulation layer at the A and BC phase ports, remove the outermost cable core, as shown in FIG. Figure 3 As shown, use a tool to make the second layer cable core and the third layer cable core form a 25° angle.

[0075] The welding area of ​​the existing unprocessed cable core with the molten aluminum / aluminum alloy liquid in the joint forming chamber of the mold is the sum of the cross-sectional area of ​​the two cores + the surface area of ​​the two cable cores in the joint forming chamber. The present invention processes the cable core into a bell-mouth shape, and the welding area with the aluminum / aluminum alloy liquid in the joint forming chamber of the mold is the sum of the cross-sectional area of ​​the two cores + the outermost surface area of ​​the cable core in the joint forming chamber + the inner and outer surface area of ​​the second layer + the surface area of ​​the third layer. Compared with the prior art, the linear welding area of ​​the present invention is increased by 30-35%.

[0076] Preferably, if Figure 1 As shown, the molding mold includes a first mold and a second mold, and the first mold and the second mold are respectively provided with an injection groove 1, a joint molding groove 2 and an introduction groove 3, and the two sides of the joint molding groove 2 are provided with introduction grooves 3. When the first mold and the second mold are merged, the adjacent injection grooves 1, joint molding grooves 2 and introduction grooves 3 are correspondingly spliced ​​into a connected injection cavity, a joint molding chamber and an introduction hole. According to the parallel direction of the cable core, the molding mold is designed to be a symmetrical first mold and a second mold, and is combined into one with a four-hole clamp, and can be opened and closed quickly. Put the cable core into the introduction hole, reserve a 3-5mm gap in the middle of the two cores, close the mold, and fix the side clamp. Inject aluminum / aluminum alloy melt, cool for 1-3 minutes to form the joint, remove the side clamp and the four-hole clamp. Preferably, the size parameters of the molding mold are shown in Table 3. The present invention can ensure that the molten liquid flows fully and reduces the doping amount of bubbles through the setting of the joint molding chamber with a larger inner diameter and the vent hole, significantly improves the quality of cable joint welding, and has good practicality.

[0077] Specifically, Figure 3 As shown, the diameter of the introduction hole is the same as the diameter of the cable core, and a size of 25-30mm is measured from the cable core break toward the insulation layer, and the cable core is wrapped with a copper tape 8. The diameter after wrapping is 0.5-1mm larger than the diameter of the linear introduction hole of the mold; when the mold is closed, there is a gap of about 0.5mm in the mold. While the copper tape 8 protects the cable, it can ensure that the molten liquid flows fully and reduce the amount of bubble doping.

[0078] Since the cable core wrapped with the copper tape 8 is larger than the diameter of the lead-in hole, when the mold is closed, the cable is fixed in the lead-in hole by the side clamp, and no displacement occurs, so the cable core is not easily eccentric. The melting point of copper is 1083°C, and the melting point of aluminum / aluminum alloy is 659°C. When the copper tape 8 is placed in the lead-in hole, it is difficult to melt in contact with the aluminum / aluminum alloy melt, and it will not form a whole. By wrapping the copper tape 8 larger than the diameter of the lead-in hole, there is a gap of about 0.5mm at the joint of the mold, so that the aluminum / aluminum alloy melt in the joint forming chamber can flow fully and exhaust fully, avoiding the situation of insufficient liquid filling and bubble holes at the joint.

[0079] Table 3

[0080]

[0081] 4. After the welding joint of aluminum / aluminum alloy cable conductor core is formed, it is subjected to secondary molding.

[0082] After the joint is formed and exits the forming mold, a grinder is used to grind and remove the edge material. Then, a 15T hydraulic pliers is used to correspond to the steel die with the same cross section. At the joint forming place, continuous pressure is applied from the middle to both sides to increase the tightness, sealing effect, exclude air, and improve tensile strength. As shown in Table 4, the tensile strength of the cable is significantly improved after secondary molding.

[0083] Table 4

[0084]

[0085] 5. Perform anti-oxidation treatment on the cable core.

[0086] Apply composite conductive paste evenly on the cable core and joints to achieve the effect of anti-oxidation and reducing cable operating humidity.

[0087] 6. Use a high-frequency electric heater 10 and a welding heater 9 to restore the inner semi-conductive layer and the main insulating layer of the cable.

[0088] In step 1, the outer cable sheath, steel mirror, inner cable sheath, copper shielding layer, outer semi-conductive layer, main insulating layer and inner semi-conductive layer are stripped off in order according to the size. The cable breaks at both ends are connected and the cable conductors are welded together by welding. The specific steps to restore the inner semi-conductive layer and the main insulating layer include:

[0089] ① On the surface of the restored conductor joint, wrap the inner semi-conducting layer and the main insulating layer in turn according to the thickness size, and the wrapping thickness must be uniform and not eccentric. Put the cable hot-melt plastic tube on it, and wrap the polytetrafluoroethylene tape on it, such as Figure 4 As shown, the glass fiber heating belt 11 of the welding heater 9 is wrapped around the restored inner semi-conductive layer and the main insulating layer of the cable, and then the outer layer of the glass fiber heating belt 11 is coated with glass fiber insulation cloth.

[0090] ② If Figure 4 As shown, the high frequency heating coil 12 is wound around the phase separation portion of the cable.

[0091] ③ Start heating at the specified temperature, working frequency and time. The fusion-heated glass fiber heating belt 11 generates heat under the covering of the glass fiber insulation cloth, which basically does not dissipate, and heats the cable conductor and performs external heating. High-frequency heating is mainly based on the principle of magnetic induction. It converts alternating current into alternating current with a frequency of 15-200KHz or even higher, and then converts it into a magnetic field of the same frequency using an inductor coil tube, and then acts on the metal conductor in the magnetic field to generate internal heat.

[0092] When wrapping the polytetrafluoroethylene tape around the semi-conductive layer and the main insulation layer of the cable, the recovery part of the wrapping must be overlapped by 1 / 2, and the tape body does not need to be pulled hard in the natural state. Since the polytetrafluoroethylene tape has good temperature resistance of 250-300℃, it will not stretch and soften when heated externally, and the external heating heat can be evenly distributed throughout the heating part, ensuring the quality of the welding part.

[0093] The present invention adopts the main body material of the wire core for welding, thereby reducing the difference of the overall material of the cable; by adding a flux, the melting of the main body material is accelerated and the melting temperature is controlled at 659°C-760°C, iron, silicon and magnesium impurities are fully removed, hydrogen, nitrogen and elemental aluminum vapor are discharged, and the melt structure is more stable; by adding a refining agent, bubbles are formed in the liquid, and impurities float up to be removed; by setting the bell-mouth shape of the wire core, the welding contact area is increased, and the welding tightness is increased through secondary molding, thereby improving the reliability of the welding joint.

[0094] Table 5

[0095]

[0096] As shown in Table 5, samples 1 to 6 were prepared by the above method, where the test basis of sample 1 was GB / T9327-2008 Test methods and requirements for crimping and mechanical connection fittings for power cable conductors with rated voltages of 35 kV (Um=40.5 kV) and below. The welded structure of the prepared sample 1 is as follows: Figure 5 As shown in the figure, during the temperature rise test of sample 1, the ambient temperature is 26°C and the reference conductor temperature is 120.9°C. Figure 6 As shown, connect the samples in series into a loop, apply power with AC power, no wind and no sunshine, and allow natural air convection. When the reference conductor temperature stabilizes to 120°C, the temperature of the parts of the hardware that are made of the same material as the reference conductor is not higher than the reference conductor temperature. After the sample temperature stabilizes, record the corresponding parameters.

[0097] The test basis of Sample 2-Sample 5 is GB / T 12706.4-2020 Rated voltage 1kV (Um=1.2kV) to 35kV (Um=40.5kV) extruded insulation power cables and accessories Part 4: Test requirements for rated voltage 6kV (Um=7.2kV) to 35kV (Um=40.5kV) power cable accessories. The test circuit of Sample 2-Sample 5 includes a set of 26 / 35kV cross-linked aluminum alloy cable cold shrink outdoor terminal, a set of 26 / 35kV cross-linked aluminum alloy cable cold shrink straight joint, a set of 26 / 35kV cross-linked polyethylene insulated aluminum alloy power cable fusion straight joint (molding) (a set of test samples) and a three-core power cable with a length of 8 meters. The cable model specification is ZC-YJLHV23-26 / 353*400.

[0098] As shown in Table 6, it was found through testing that the aluminum alloy bare conductor welding connector prepared by the present invention meets the requirements of GB / T9327-2008 rated voltage 35kV (U m =40.5kV) and below for crimping and mechanical connection fittings for power cable conductors. The 26 / 35kV cross-linked polyethylene insulated aluminum alloy power cable fusion straight-through joint (injection molding), 26 / 35kV cross-linked aluminum alloy cable cold shrink indoor terminal, 26 / 35kV cross-linked aluminum alloy cable cold shrink outdoor terminal and 26 / 35kV cross-linked aluminum alloy cable cold shrink straight-through joint prepared by the present invention all comply with GB / T 12706.4-2020 rated voltage 1kV (U m =1.2kV) to 35kV (U m =40.5kV) extruded insulated power cables and accessories Part 4: Rated voltage 6kV (U m =7.2kV) to 35kV (U m =40.5kV) power cable accessories test requirements. It can be seen that the present invention has made significant progress and has a good promotion prospect in practice.

[0099] Table 6

[0100]

[0101] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any simple modification or equivalent change made to the above embodiment based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for preparing a fusion joint of aluminum and aluminum alloy cables, characterized in that: The following steps are involved: Step S1: using a high-frequency electric heater (10) to heat and melt the main body material of the cable core to be welded; during the melting process, firstly start the high-frequency electric heater (10) and set the power to 90%-95%, add a flux, and quickly melt the main body material; when the temperature rises to 690°C-730°C, add a refining agent to form bubbles in the melt, float up to remove impurities, and form an oxide film on the top of the melt; then, adjust the power of the high-frequency electric heater (10) to 60%-70%, and let it stand to keep warm; wherein the flux includes the following components: KCl: 24.5 wt%-26 wt%; NaCl: 13.5wt%-15wt%; LiCl: 6.65wt%-7.5wt%; NaF: 3.75wt%-4.5wt%; Na3AlF6: 48.5wt%-51.5wt%; the refining agent includes the following components: KCl: 35wt%-50wt%; NaCl: 30wt%-40wt%; CaF2: 5wt%-8wt%; Na2B407*10H2O: 8wt%-15wt%; Mg2N3: 5wt%-10wt%; C2Cl6: 3wt%-6wt%; Rare earth: 0.2wt%-0.5wt%; Step S2: treating the cable joint to be welded to expose the cable core, and dividing the cross section of the cable core into an outer core (4), a second core (5), a third core (6) and a center core (7) from the outside to the inside; opening a fracture at the end of the cable core, removing the outer core (4) at the end of the cable core, and arranging the second core (5) in a trumpet shape along the circumference; Step S3: placing two cable cores to be welded in a forming mold, injecting the melt heated in step S1 into the forming mold, discarding the oxide film, and cooling and solidifying to obtain an initial welded joint; Step S4: secondary molding: the initial welded joint is firstly polished to remove the excess edge material, and then hydraulic pliers are used to continuously pressurize and mold from the middle to both sides; Step S5: Perform anti-oxidation treatment on the cable core, and then restore the inner semi-conductive layer, main insulating layer and outer semi-conductive layer of the cable in sequence.

2. The method for preparing a fusion joint of an aluminum or aluminum alloy cable according to claim 1, characterized in that: In the step S2, the second layer of cable cores at the ends of the cable cores form an angle of 10°-45° with the third layer of cable cores.

3. The method for preparing a fusion joint of an aluminum or aluminum alloy cable according to claim 2, characterized in that: In step S2, the second layer of cable cores at the ends of the cable cores form an angle of 25° with the third layer of cable cores.

4. The method for preparing a fusion joint of an aluminum or aluminum alloy cable according to claim 1, characterized in that: In step S3, the molding mold comprises a first mold and a second mold, one side of the first mold and the second mold are respectively provided with a connected injection groove (1), a joint molding groove (2) and an introduction groove (3), and the two sides of the joint molding groove (2) are respectively provided with an introduction groove (3) connected to each other; when the first mold and the second mold are combined, the adjacent injection grooves (1), joint molding grooves (2) and introduction grooves (3) are correspondingly spliced ​​into a connected injection cavity, a joint molding chamber and an introduction hole, the joint molding chamber is provided with a vent hole connected to the outside, and the inner diameter of the joint molding chamber is larger than the inner diameter of the introduction hole by 5-8 mm.

5. The method for preparing a fusion joint of aluminum and aluminum alloy cables according to claim 4, characterized in that: In step S3, one end of the cable core passes through the introduction hole and extends into the joint forming chamber, and the fracture of the cable core is located in the joint forming chamber, and the distance between adjacent cable cores is 3-5 mm; the outer side of the cable core inside the introduction hole is wrapped with a copper tape (8), and the copper tape (8) is 25-30 mm away from the fracture of the cable core.

6. The method for preparing a fusion joint of aluminum and aluminum alloy cables according to claim 1, characterized in that: The step S5 comprises the following steps: Step S51: wrapping the inner semiconducting layer and the main insulating layer in the fusion area of ​​the cable core in sequence; then, sleeve the cable hot-melt plastic tube, and wrap the polytetrafluoroethylene tape around the outer side of the cable hot-melt plastic tube; Step S52: Wrapping a glass fiber heating tape (11) connected to the welding heater (9) around the inner semi-conductive layer and the main insulating layer of the cable to be restored, and then wrapping the outer layer of the glass fiber heating tape (11) with a glass fiber insulation cloth; Step S53: Winding the high-frequency heating coil (12) of the high-frequency electric heater (10) around the phase separation portion of the cable to generate external heating.

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