An enameled flat wire and a method for manufacturing the same

Abstract

This invention relates to a method for preparing enameled flat wire, comprising the following steps: S1, continuously extruding a soft oxygen-free copper rod to obtain a round wire blank; S2, rolling the round wire blank with four rollers to obtain a rolled flat blank; S3, stretching the rolled flat blank through multiple passes to obtain a first flat wire core; S4, sequentially ultrasonically cleaning and annealing the first flat wire core to obtain a second flat wire core; S5, sequentially coating and curing each layer of enamel on the second flat wire core to obtain the enameled flat wire. The preparation method of this invention, through continuous extrusion, four-roll rolling, and multiple stretching, while controlling relevant parameters, reduces the fillet radius of the flat wire blank, increasing the cross-sectional area of ​​a single conductor by 3.5-6.5%. The cross-sectional area ratio of a single conductor is increased by 5-15%, and the current carrying capacity is increased by 5-15%.

Description

Technical Field

[0001] This invention relates to the field of enameled flat wire technology, and more particularly to an enameled flat wire and its preparation method. Background Technology

[0002] The core driving component of new energy vehicles is the drive motor, which needs to meet the power requirements of various operating conditions within a limited space. Therefore, achieving motor lightweighting and reducing vehicle energy loss are key issues that need to be addressed. Enamelled flat wire is currently an important conductive material for the windings of high-power, high-torque miniaturized new energy vehicle motors. To meet the higher power density requirements of new energy vehicle drive motors, the slot dimensions are often designed to be closer to the external dimensions of the enamelled wire to improve slot fill factor, increase conductor cross-sectional area, and increase motor current carrying capacity. The external dimensions of the enamelled wire are determined by the thickest part of the enamel film, while the insulation performance is determined by the thinnest part of the enamel film. To improve motor power density, on the one hand, the radius of the flat wire conductor fillet is reduced, increasing the conductor cross-section and conductor area to improve current carrying capacity; on the other hand, the insulation performance of each enamel layer is improved, and the consistency of enamel film thickness is controlled, thereby reducing the external dimensions of the enamelled wire and improving the slot fill factor.

[0003] Currently, it is difficult to produce flat conductors with a corner radius of less than 0.5mm using the processing methods for flat conductors. Furthermore, the wear resistance of existing enameled flat wires can only withstand 5000 cycles of reciprocating scratches, which cannot meet the requirements of motor manufacturers for high slot fill factor and high wear resistance.

[0004] Therefore, there is an urgent need for an enameled flat wire and its preparation method. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by providing an enameled flat wire and its preparation method.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] The first aspect of the present invention is to provide a method for preparing enameled flat wire, the steps of which include:

[0008] S1. Soft oxygen-free copper rods are continuously extruded to obtain round wire blanks;

[0009] S2. The round wire blank is rolled by four rolls to obtain a rolled flat blank;

[0010] Four-roll rolling involves rolling the copper wire blank simultaneously onto the same cross-section using rolls in both horizontal and vertical directions. In contrast, traditional rolling uses two rolls to roll the blank on one side in the horizontal and vertical directions respectively. During single-side rolling, the non-stressed surface of the copper wire blank will exhibit a semi-circular arc change, making it impossible to reduce the radius of the rounded corners and resulting in poor dimensional accuracy of the copper wire blank. However, since the copper wire blank is rolled on all four sides simultaneously in four-roll rolling, there is no semi-circular arc change, allowing for the production of smaller rounded corners. The dimensional accuracy of the copper wire blank can be controlled within ±0.01mm, enabling better dimensional correction in subsequent flat drawing processes. The minimum rounded corner radius can reach 0.24mm.

[0011] S3. The rolled flat billet is stretched multiple times to obtain the first flat wire core material;

[0012] Tension is the result of metal flowing simultaneously in the radial, axial and circumferential directions; in the cross-sectional direction, the distance the material plastically flows in the length and width directions of a narrow rectangle is different, and the magnitude of the resistance is also different.

[0013] S4. The first flat wire core material is subjected to ultrasonic cleaning and annealing in sequence to obtain the second flat wire core material.

[0014] Annealing can remove residual stress, as well as residual emulsion and oil.

[0015] S5. The second flat wire core material is coated and each layer of paint is cured sequentially to obtain the enameled flat wire.

[0016] After the enamel coating on the flat wire passes through the coating mold, the enamel flows from the four rounded corners to the straight section in the cross-sectional direction of the flat wire due to the interaction of intermolecular attraction, gravity, and resistance. In the longitudinal direction, i.e., the direction of the flat wire's movement, the enamel flows from the straight section to both sides. After coating and baking, the enamel film is thinner at the rounded corners and in the middle of the straight section, and thicker at both ends of the straight section, resulting in uneven enamel film. The thinnest point is the weak point of the enameled wire insulation, while the thickest point determines the outer dimensions of the enameled wire and affects its spatial proportion. To achieve the best insulation performance and the highest conductor cross-sectional area ratio, the enameled wire must be as small as possible and the enamel film as thick as possible. By designing the straight section of the coating mold to be arc-shaped, the amount of enamel coating in the middle of the straight section of the flat wire cross-section is increased.

[0017] The extrusion speed of the continuous extrusion is 80m / min-150m / min;

[0018] The speed of the four-high rolling mill used in the four-high rolling process is 80 r / min-150 r / min, and the roll gap of the four-high rolling mill is 0.2 mm-0.5 mm.

[0019] If the gap between the rolls is too small, the machining amount will be too large, which may cause the rolls to bite and the thread to break; if the gap between the rolls is too large, the machining amount will be too small, the dimensional accuracy cannot be guaranteed, and the radius of the rounded corners cannot be made smaller.

[0020] The stretching speed for the multiple stretching passes is 6 m / min - 30 m / min;

[0021] The annealing temperature is 400℃-650℃, and the speed is 6m / min-30m / min;

[0022] The curing zone temperature of the oven used for sequentially coating and curing each paint layer is 350℃-700℃, the rotation speed of the circulating fan in the oven is 1000r / min-4000r / min, the rotation speed of the exhaust fan in the oven is 1000r / min-4000r / min, and the linear velocity in sequentially coating and curing each paint layer is 6m / min-30m / min.

[0023] Preferably, the deformation during the four-roll rolling process is 0.5mm-1.5mm.

[0024] Preferably, the cone angle of the last stretching die used in the multi-pass stretching is 16°-20° in both the compression zone and the exit zone;

[0025] If the cone angles of the mold compression zone and the exit zone are too small, the friction at the cone angles will be too large, and the surface of the blank's R-corner will easily become rough, affecting the surface forming quality. After painting, particles will appear, and the insulation performance will decrease. If the cone angles of the mold compression zone and the exit zone are too large, the blank's radius R-corner deformation time will be too short, and the radius R-corner will easily become too large, failing to reach the design dimensions. The blank surface will easily stick to oil stains, affecting the insulation performance and conductor occupancy rate.

[0026] Preferably, the radius of the rounded corner of the first flat wire core is 0.24mm-0.5mm.

[0027] Preferably, the cone angle of the coating mold used for sequentially coating and curing each layer of paint in the coating area is 6°-14°;

[0028] Controlling the taper of the coating area ensures that even after some of the paint is lost due to gravity and resistance, the paint film applied to the straight sections and rounded corners of the flat wire cross-section can maintain the same thickness, achieving the highest insulation performance and the highest conductor cross-sectional area ratio. If the taper angle of the coating area is too small, the amount of paint applied to the rounded corners will be less due to increased coating resistance. If the taper angle is too large, too much paint will seep in, causing particles to form at the rounded corners, resulting in decreased insulation.

[0029] Preferably, the height of the four sides of the coating mold used for sequentially coating and curing each layer of paint is 2.5μm-10μm in the cross-section of the coating area and the sizing area;

[0030] If the height of the arc on the four sides of the cross-section of the coating area and the sizing area is less than 2.5μm, the varnish film in the middle of the coating is too thin, the two ends bulge, the shape of the enameled wire becomes larger and the insulation performance decreases; if it is greater than 10μm, the varnish film in the middle of the coating bulges, the shape of the enameled wire becomes larger, and the cross-sectional area of ​​the enameled wire is affected.

[0031] Preferably, the steps further include:

[0032] After coating and curing each layer of enamel on the second flat wire core material, the material is then cooled, lubricated, and wound up to obtain the enameled flat wire.

[0033] A second aspect of the present invention is to provide an enameled flat wire prepared by the preparation method described above, wherein the conductor volume ratio of the enameled flat wire is not less than 78%, and the wear resistance of the enameled flat wire is not less than 22,500 cycles.

[0034] The present invention adopts the above technical solution and has the following technical effects compared with the prior art:

[0035] The preparation method of this invention, through continuous extrusion, four-roll rolling, and multi-pass stretching, while controlling relevant parameters, reduces the fillet radius of the flat wire blank, and increases the cross-sectional area of ​​a single conductor by 3.5% to 6.5%. The cross-sectional area ratio of a single conductor is increased by 5% to 15%, and the current carrying capacity is increased by 5% to 15%.

[0036] The preparation method of the present invention also controls the amount of paint in the cross-sectional area of ​​the coating mold by adjusting the paint mix and coating process. Under the premise of the same insulation performance (BDV, PDIV), the cross-sectional area occupied by a single enameled wire is reduced by 4.5% to 6.5%, and the number of scratch resistance (wear resistance) is increased by more than 480%. This can reduce the gap between the motor slot and the enameled wire and further improve the slot fill factor. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the enameled flat wire in this invention;

[0038] The reference numerals in the figures include:

[0039] Conductor 1; Coating 2. Detailed Implementation

[0040] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some 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.

[0041] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0042] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but this is not intended to limit the scope of the invention.

[0043] Example 1

[0044] This embodiment provides an enameled flat wire and its preparation method, the preparation steps of which include:

[0045] S1, will The soft oxygen-free copper rod is obtained by continuous extrusion. Circular wire blank;

[0046] The extrusion speed is 80 m / min;

[0047] S2, the above The round wire rod is passed through a four-roll mill to obtain a rolled flat billet of 2.65mm × 3.35mm;

[0048] The four-roll mill has a rotational speed of 100 r / min and a roll gap of 0.25 mm.

[0049] S3. The 2.65mm×3.35mm rolled flat billet is stretched multiple times through a stretching die to obtain a first flat wire core material with a diameter of 1.950mm×2.651mm and a corner radius of 0.27mm.

[0050] The stretching speed is 12.5 m / min, the cone angle of the last stretching die in the compression zone and the exit zone is 18°, and the stretching dies are set to 2.45 mm × 3.15 mm, 2.20 mm × 2.90 mm and 1.95 mm × 2.651 mm respectively.

[0051] S4. The first flat wire core material is subjected to ultrasonic cleaning and annealing in sequence to obtain the second flat wire core material.

[0052] The annealing temperature was 540℃ and the annealing rate was 12.5m / min.

[0053] S5. The second flat wire core material is coated and each layer of paint is cured sequentially to obtain the first enameled flat wire.

[0054] The curing zone temperature of the oven is 490℃, the speed of the circulating fan is 2500r / min, the speed of the exhaust fan is 2250r / min, the linear speed is 12.5m / min, the cone angle of the painting mold in the painting zone is 10°, and the arc height of the four sides of the painting mold in the cross-section of the painting zone and the sizing zone is 5.5μm.

[0055] S6. The first enameled flat wire is cooled, lubricated, and wound up sequentially to obtain the enameled flat wire.

[0056] Example 2

[0057] This embodiment provides another type of enameled flat wire. The difference in the preparation method is that the radius of the rounded corner of the first flat wire core is 0.24 mm, the cone angle of the last stretching die in the compression zone and the exit zone is 16°, the cone angle of the coating die in the coating zone is 8°, and the arc height of the four sides of the coating die in the coating zone and the sizing zone is 8 μm.

[0058] Example 3

[0059] This embodiment provides another type of enameled flat wire. The difference in the preparation method is that the radius of the rounded corner of the first flat wire core is 0.30 mm, the cone angle of the last stretching die in the compression zone and the exit zone is 20°, the cone angle of the coating die in the coating zone is 12°, and the arc height of the four sides of the coating die in the coating zone and the sizing zone is 2.5 μm.

[0060] Comparative Example 1

[0061] This comparative example provides another type of enameled flat wire and its preparation method, the preparation steps of which include:

[0062] S1, will The soft oxygen-free copper rod is obtained by continuous extrusion. Circular wire blank;

[0063] The extrusion speed is 80 m / min;

[0064] S2, the above The round wire rod is rolled into a flat billet of 2.65mm × 3.7mm by a two-roll mill;

[0065] The rotational speed of the twin-roll mill is 100 r / min;

[0066] S3. The 2.65mm×3.7mm rolled flat billet is stretched multiple times through a stretching die to obtain a first flat wire core material with a diameter of 1.950mm×2.650mm and a corner radius of 0.50mm.

[0067] The stretching speed is 12.5 m / min, the cone angle of the last stretching die in the compression zone and the exit zone is 16°, and the stretching dies are set to 2.45 mm × 3.15 mm, 2.20 mm × 2.90 mm and 1.95 mm × 2.650 mm respectively.

[0068] S4. The first flat wire core material is subjected to ultrasonic cleaning and annealing in sequence to obtain the second flat wire core material.

[0069] The annealing temperature was 540℃ and the annealing rate was 12.5m / min.

[0070] S5. The second flat wire core material is coated and each layer of paint is cured sequentially to obtain the first enameled flat wire.

[0071] The curing zone temperature of the oven is 490℃, the speed of the circulating fan is 2500r / min, the speed of the exhaust fan is 2250r / min, the linear speed is 12.5m / min, the cone angle of the painting mold in the painting zone is 12°, and all four sides of the cross-section of the painting mold are straight segments.

[0072] S6. The first enameled flat wire is cooled, lubricated, and wound up sequentially to obtain the enameled flat wire.

[0073] Comparative Example 2

[0074] This embodiment provides another type of enameled flat wire and its preparation method, the preparation steps of which include:

[0075] S1, will The soft oxygen-free copper rod is obtained through a large drawing machine. Circular wire blank;

[0076] The wire pulling speed is 15m / s;

[0077] S2, the above The round wire blank is drawn multiple times by a wire drawing machine to obtain the first flat wire core material with a diameter of 1.950mm × 2.650mm and a corner radius of 0.65mm;

[0078] The wire drawing speed is 12.5 m / min, and the cone angle of the last drawing die in the compression zone and the exit zone is 18°. The drawing dies are set to 3.30 mm × 3.65 mm, 2.85 mm × 3.40 mm, 2.45 mm × 3.18 mm, 2.20 mm × 2.91 mm and 1.950 mm × 2.649 mm respectively.

[0079] S3. The first flat wire core material is subjected to ultrasonic cleaning and annealing in sequence to obtain the second flat wire core material.

[0080] The annealing temperature was 540℃ and the annealing rate was 12.5m / min.

[0081] S4. The second flat wire core material is coated and each layer of paint is cured sequentially to obtain the first enameled flat wire.

[0082] The curing zone temperature of the oven is 490℃, the speed of the circulating fan is 2500r / min, the speed of the exhaust fan is 2250r / min, the linear speed is 12.5m / min, the cone angle of the painting mold in the painting zone is 10°, and all four sides of the cross-section of the painting mold are straight segments.

[0083] S5. The first enameled flat wire is cooled, lubricated, and wound up sequentially to obtain the enameled flat wire.

[0084] The coating layers applied and cured sequentially in Examples 1-3 and Comparative Examples 1-2 are as follows:

[0085]

[0086]

[0087] Polyimide paint is generally prepared by heating and condensing polyimide resin, N,N-dimethylformamide, xylene, fluorinated inorganic compounds, wax paste, and nano-sized alumina particles and other fillers in N-methylpyrrolidone or other strongly polar solvents.

[0088] Detection Examples

[0089] Conductor fillet radius: According to GB / T 4074.2-2008 Winding Wire Test Methods Part 2: Dimensional Measurement, three flat wire samples are cast in resin, the flat wire samples embedded in the resin are cut along the direction perpendicular to the flat wire axis, the cross section is ground and polished, and the conductor fillet radius is checked under Keyence metallographic microscope at 500x magnification.

[0090] Dimensions of enameled flat wire: According to GB / T 4074.2-2008 Winding wire test method part 2: Dimension measurement, the dimensions of the wide side and narrow side are measured three times at three positions more than 200mm apart on a straightened sample, and the average value of the three positions of the wide side and narrow side is calculated.

[0091] Coating thickness: According to GB / T 4074.2-2008 Winding wire test method Part 2: Dimensional measurement, three flat wire samples were cast in resin, the flat wire samples embedded in the resin were cut along the direction perpendicular to the flat wire axis, the cross section was ground and polished, and the coating thickness was checked under Keyence metallographic microscope at 500x magnification.

[0092] Breakdown voltage: According to GB / T 4074.5-2008 Winding wire test method part 5: electrical properties, remove the varnish film from one end of a 350mm straight sample, bend the wide side of a 25mm diameter round bar 180° into a U shape, place the sample in a container of 2mm metal beads, immerse the sample to a depth of 90mm, apply an AC test voltage from zero between the conductor and the metal beads, increase the voltage at a constant rate of 500V / s until breakdown, record five breakdown voltage values, and calculate the average value.

[0093] Corona resistance: According to GB / T 4074.21-2008 Winding wire test method: high frequency pulse voltage resistance performance, two 250mm straight specimens are used. The varnish film is removed from one end of each specimen to serve as the test electrode. Each specimen is made into a shape with a 150mm straight section in the middle and the two ends open with the same width using an appropriate tooling model. The straight sections of the two specimens are back to back and cut together with high temperature resistant tape. The specimens are placed in a 155℃ hot high frequency corona resistance tester. A high frequency pulse voltage of VP-P 4000V with a frequency of 20KHZ and a rise time of 100ns is applied between the two conductors of the specimen. Five breakdown time values ​​are recorded and the average value is calculated.

[0094] Hydrolysis resistance: According to GB / T 4074.4-2008 Winding Wire Test Methods Part 4: Chemical Properties, remove the varnish film from one end of each of the five 350mm straightened specimens. Bend the wide side of each specimen 180° into a U-shape on a 25mm diameter round bar. Remove the varnish film from one end of each of the ten 250mm straightened specimens to serve as test electrodes. Using appropriate tooling, shape each specimen into a 150mm straight section in the middle with both ends open at the same width. Bind the straight sections of two specimens back to back with high-temperature resistant tape to form five pairs of arrows. Place the five U-shaped specimens and the five pairs of arrows into a pressure vessel containing 0.4% ATF oil. Seal the pressure vessel and heat it to 150℃ for 1000 hours. Cool it to room temperature and test the breakdown voltage of the U-shaped specimens and the PDIV of the five pairs of arrows. Record the five breakdown voltage and PDIV values ​​and calculate the average breakdown voltage and PDIV retention rate.

[0095] PDIV: According to GB7354-2003 Partial Discharge Measurement, two straightened 250mm test specimens are used. The varnish film is removed from one end of each specimen to serve as the test electrode. Each specimen is made into a straight section of 150mm in the middle and open at both ends with the same width using an appropriate tooling model. The straight sections of the two specimens are tied back to back with high-temperature resistant tape to form a pair. A 50Hz AC test voltage is applied between the two conductors from zero and increased at a constant rate of 25V / s until discharge. Five PDIV values ​​are recorded and the average value is calculated.

[0096] Scratch resistance test: According to GB / T 4074.3-2008 Winding Wire Test Methods Part 4: Mechanical Properties, a 350mm sample with a maximum straightness of 1% was wiped clean and placed in a reciprocating scratch resistance tester. A steel needle with a diameter of 0.23mm was applied to the sample. A DC voltage of 6.5V was applied between the conductor and the steel needle, and a short-circuit current of 5mA was applied. A 500g weight was applied to the steel needle. The number of reciprocating cycles after three short circuits was recorded, and the average value was calculated.

[0097] The cross-sectional area of ​​a single conductor is increased, calculated based on the cross-sectional area of ​​the single conductor in Comparative Example 2.

[0098] The cross-sectional area occupied by a single enameled wire = maximum narrow side dimension of the enameled wire × maximum wide side dimension of the enameled wire

[0099] The reduction rate of the space occupied by a single enameled wire cross-section is calculated based on the space occupied by the single enameled wire cross-section in Comparative Example 2.

[0100] Single conductor cross-sectional area ratio = Cross-sectional area of ​​single conductor ÷ Space occupied by single enameled wire cross-section

[0101] The increase in the cross-sectional area ratio of a single conductor is calculated based on the cross-sectional area ratio of a single conductor in Comparative Example 2.

[0102] The specific test results are as follows:

[0103]

[0104]

[0105] In summary, the preparation method of the present invention, through continuous extrusion, four-roll rolling, and multi-pass stretching, while controlling relevant parameters, reduces the fillet radius of the flat wire blank and increases the cross-sectional area of ​​a single conductor by 3.5% to 6.5%. The cross-sectional area ratio of a single conductor is increased by 5% to 15%, and the current carrying capacity is increased by 5% to 15%.

[0106] The preparation method of the present invention also controls the amount of paint in the cross-sectional area of ​​the coating mold by adjusting the paint mix and coating process. Under the premise of the same insulation performance (BDV, PDIV), the cross-sectional area occupied by a single enameled wire is reduced by 4.5% to 6.5%, and the number of scratch resistance (wear resistance) is increased by more than 480%. This can reduce the gap between the motor slot and the enameled wire and further improve the slot fill factor.

[0107] The above description is merely a preferred embodiment of the present invention and does not limit the implementation and protection scope of the present invention. Those skilled in the art should realize that any equivalent substitutions and obvious changes made based on the description and illustrations of the present invention should be included within the protection scope of the present invention.

Claims

1. A method of manufacturing an enameled flat wire, characterized by the steps of The method comprises the following steps: S1, continuously extruding soft oxygen-free copper rod to obtain round wire blank; S2, four-roll rolling the round wire blank to obtain rolled flat blank; S3, multi-pass stretching the rolled flat blank to obtain first flat wire core material; S4, sequentially ultrasonic cleaning and annealing the first flat wire core material to obtain second flat wire core material; S5, sequentially coating and curing each layer of paint layer of the second flat wire core material to obtain the enameled flat wire; The extrusion speed of the continuous extrusion is 80 m / min-150 m / min; The four-roll rolling machine adopts a rotating speed of 80 r / min-150 r / min and a roll gap of 0.2 mm-0.5 mm; The stretching speed of the multi-pass stretching is 6 m / min-30 m / min; The annealing temperature is 400 ℃-650 ℃, and the speed is 6 m / min-30 m / min; The curing zone temperature of the oven used for the sequential coating and curing of each layer of paint layer is 350 ℃-700 ℃, the rotating speed of the circulating fan in the oven is 1000 r / min-4000 r / min, the rotating speed of the exhaust fan in the oven is 1000 r / min-4000 r / min, and the line speed in the sequential coating and curing of each layer of paint layer is 6 m / min-30 m / min; The taper angle of the last stretching die used for the multi-pass stretching in the compression zone and the outlet zone is 16°-20°; The fillet radius of the first flat wire core material is 0.24 mm-0.5 mm; The taper angle of the paint coating die used for the sequential coating and curing of each layer of paint layer in the paint coating zone is 6°-14°; The four-side arc height in the cross section of the paint coating die used for the sequential coating and curing of each layer of paint layer in the paint coating zone and the sizing zone is 2.5 μm-10 μm.

2. The production method according to claim 1, characterized by, The processing deformation of the four-roll rolling is 0.5 mm-1.5 mm.

3. The preparation method according to claim 1, characterized in that, The method further comprises the following steps: After the sequential coating and curing of each layer of paint layer of the second flat wire core material, sequentially cooling, lubricating and winding the enameled flat wire.

4. A flat enamelled wire produced by the production method according to any one of claims 1 to 2, characterised in that, The conductor volume fraction of the enameled flat wire is not less than 78%, and the wear resistance of the enameled flat wire is not less than 22500 times.

Images