Method for manufacturing flat enameled wire

Abstract

To provide a method for manufacturing a flat enameled wire by which it is possible to reduce occurrence of crazing even in the case of a large aspect ratio of a cross section.SOLUTION: A method for manufacturing a flat enameled wire includes: preparing an insulated wire having a conductor and an insulating layer that covers the conductor; rolling the insulated wire; heating the rolled insulated wire; applying varnish to the heated insulated wire; and baking the varnish applied to the insulated wire.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a rectangular insulated electric wire. [Background technology]

[0002] Increasing the space factor (the ratio of the conductor cross-sectional area to the coil cross-sectional area) in the coil cross section has been known as a method for improving the performance of electric vehicle motors, etc. To improve this space factor, it is effective to use rectangular wire with a rectangular cross section (a cross section perpendicular to the length direction) for the windings (see, for example, Patent Document 1).

[0003] Patent Document 1 describes a method for manufacturing a high-voltage rolled rectangular insulated electric wire, which includes a step of applying an insulating paint to the outer periphery of a round conductor and then baking it to obtain an insulated round conductor, a step of rolling the insulated round conductor to obtain an insulated rectangular conductor, and a step of applying an insulating paint again to the outer periphery of the insulated rectangular conductor and then baking it to obtain a high-voltage rolled rectangular insulated electric wire. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 11-16428 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the method for manufacturing a high-rolled rectangular insulated electric wire described in Patent Document 1, when the cross-sectional aspect ratio of the insulated electric wire is increased, the degree of processing during rolling increases, which can cause cracks in the insulating layer. Furthermore, residual stress occurs in the insulating coating after rolling, which can cause crazing on the side surfaces of the rectangular insulated electric wire when the insulating coating comes into contact with a polar solvent.

[0006] An object of the present invention is to provide a method for manufacturing a rectangular insulated electric wire that can suppress the occurrence of cracking and crazing even when the cross-sectional aspect ratio is large. [Means for solving the problem]

[0007] In order to solve the above problem, according to one aspect of the present invention, providing an insulated wire having a conductor and an insulating layer covering the conductor; rolling the insulated wire; heating the rolled insulated wire; applying a varnish to the heated insulated wire; baking the varnish applied to the insulated wire; having A method for manufacturing a rectangular insulated wire is provided. [Effects of the Invention]

[0008] According to the present invention, a method for manufacturing a rectangular insulated electric wire can be provided that can suppress the occurrence of cracking and crazing even when the cross-sectional aspect ratio is large. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a flowchart of a method for manufacturing a rectangular insulated electric wire according to one embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing an example of a manufacturing apparatus for a rectangular insulated electric wire. [Figure 3] 3A and 3B are diagrams for explaining the rolling step. [Figure 4] FIG. 4A is a cross-sectional schematic diagram of a rectangular insulated wire, and FIGS. 4B and 4C are schematic diagrams for explaining the evaluation of adhesion. DETAILED DESCRIPTION OF THE INVENTION

[0010] A method for producing a rectangular insulated electric wire according to one embodiment of the present invention will be described below. In this specification, the symbols "to" indicating a range of values include both the upper and lower limits of the range.

[0011] Fig. 1 is a flowchart of a method for manufacturing a rectangular insulated electric wire according to one embodiment of the present invention. Fig. 2 is a schematic diagram showing an example of an apparatus for carrying out the method for manufacturing a rectangular insulated electric wire. Fig. 3A is a diagram showing the main parts of a rolling mill 13, and Fig. 3B shows cross sections of an insulated electric wire 2 before and after being rolled by the rolling mill 13.

[0012] As shown in FIG. 1, the method for manufacturing a rectangular insulated electric wire according to the embodiment of the present invention includes a step (S110) of preparing an insulated electric wire 2, a step (S120) of rolling the insulated electric wire 2, a step (S130) of heating the rolled insulated electric wire 2, a step (S140) of applying varnish to the heated insulated electric wire 2, and a step (S150) of baking the varnish.

[0013] In the step (S110) of preparing an insulated wire 2, an insulated wire 2 having a conductor 2a and an insulating layer 2b covering the conductor 2a is prepared. In this step, for example, a commercially available insulated wire may be purchased, or the insulated wire 2 may be manufactured. In the present embodiment, the insulated wire 2 is manufactured. The step (S110) of preparing an insulated wire 2 is performed in the area marked S1 surrounded by a dashed line in the rectangular insulated wire manufacturing apparatus 1 shown in FIG.

[0014] In the step (S110) of preparing the insulated wire 2, when the insulated wire 2 is manufactured, first, the conductor 2a to be used for the insulated wire 2 is drawn. Specifically, the drawing is performed by feeding the conductor 2a into a wire drawing machine 10 shown in FIG. 2. The conductor 2a to be drawn is not particularly limited as long as it is conductive. In the present embodiment, the material of the conductor 2a is copper, and the cross section of the conductor 2a perpendicular to the longitudinal direction is substantially circular. That is, in the present embodiment, the conductor 2a is a round wire and is also a copper wire. The diameter of the round wire fed into the wire drawing machine 10 is not particularly limited. The diameter of the round wire before drawing is preferably within a range of, for example, 0.8 to 1.2 mm. Furthermore, it is preferable that the diameter of the round wire after drawing is not too small in order to reduce the risk of roughening the surface of the conductor 2a.

[0015] Next, the drawn conductor 2a is annealed. Specifically, the annealing is performed in an annealing furnace 11 shown in FIG. 2. In the annealing, it is preferable to remove residual stress from the drawn conductor 2a. Annealing can improve the workability in the subsequent rolling process.

[0016] Next, the annealed conductor 2a is coated with varnish and baked repeatedly to coat the conductor with an insulating layer 2b. Specifically, this process is performed in an insulating layer forming apparatus 12 having a varnish coating unit 12a and a baking unit 12b, as shown in FIG. 2. More specifically, the annealed conductor 2a is first coated with varnish in the varnish coating unit 12a, and then the coated varnish is baked in the vertical baking unit 12b. The coated varnish hardens by baking to form the insulating layer 2b. Any known varnish can be used. Examples of varnishes include varnishes containing polyesterimide, varnishes containing polyamideimide, varnishes containing polyimide, solderable varnishes, and varnishes containing polyester, and general-purpose varnishes for producing enameled wire can be used.

[0017] Furthermore, it is preferable that the application and baking of the varnish be repeated as appropriate depending on the desired thickness of the insulating layer 2b. For example, the number of times is less than about 10 times, and preferably about 3 to 8 times. In this embodiment, the insulated wire 2 obtained in the step of preparing the insulated wire 2 is a round enameled wire. The thickness of the insulating layer 2b is preferably within a range of, for example, 0.012 to 0.060 mm.

[0018] In the step (S120) of rolling the insulated wire 2, the insulated wire 2 is rolled so that its cross section becomes longer in a first direction (the width direction of the insulated wire 2) D1. This step is performed in the area marked S2 surrounded by a dashed line in the manufacturing apparatus 1 shown in FIG. 2. Specifically, this step is cold rolling performed using a rolling mill 13. In the rolling step, the aspect ratio (width / thickness) of the insulated wire 2 in a cross section perpendicular to its longitudinal direction is preferably in the range of 1:1.3 to 1:15, and more preferably in the range of 1:2 to 1:12.

[0019] As shown in Fig. 3B, the insulated wire 2 has a conductor 2a and an insulating layer 2b covering the conductor 2a. As shown in Fig. 3A, the rolling mill 13 has two rolling rollers 13a arranged to face each other in a second direction D2 (thickness direction of the insulated wire 2) perpendicular to a first direction D1 (width direction of the insulated wire 2). Each of the two rolling rollers 13a has a rolling surface parallel to the first direction D1. The shortest distance between the two rolling surfaces in the second direction D2 is set appropriately depending on the desired thickness of the insulated wire 2 after rolling. In this embodiment, the rotation axes of the two rolling rollers 13a are parallel to each other.

[0020] The insulated wire 2 passes between the two rolling rollers 13a and is rolled so that its cross section lengthens in the first direction D1. In this embodiment, the insulated wire 2 is rolled so that its cross section shortens in the second direction D2 perpendicular to the first direction D1.

[0021] The insulated wire 2 may be rolled in multiple steps. In this case, it is not necessary to roll the insulated wire 2 to the desired width and thickness in one rolling step, but rather the insulated wire 2 may be rolled to the desired width and thickness in multiple rolling steps. Furthermore, the rolling may be performed so that the cross section of the insulated wire 2 becomes shorter in both the first and second directions (up, down, left, and right).

[0022] In the step (S130) of heating the rolled insulated wire 2, the rolled insulated wire 2 is heated (baked). This makes it possible to reduce residual stress in the insulating layer 2b caused by rolling. That is, annealing is performed in the step (S130) of heating the rolled insulated wire 2. If stress remains in the insulating layer 2b, when varnish is applied in the step (S140) of applying varnish (described later), the solvent in the varnish may act on the insulating layer 2b, causing crazing. However, by reducing the residual stress in the insulating layer 2b, the occurrence of crazing can be suppressed.

[0023] The heating temperature of the insulated wire 2 is not particularly limited as long as it can reduce the residual stress in the insulating layer 2b. The heating temperature is set appropriately depending on the material of the insulating layer 2b. The heating temperature is preferably near the glass transition temperature of the material of the insulating layer 2b. For example, the heating temperature is within a range of 100 to 500°C. The heating (annealing) of the rolled insulated wire 2 is performed using an insulating layer forming apparatus 12.

[0024] In the step (S140) of applying varnish to the heated insulated wire 2, the heated insulated wire 2 is applied with varnish. Here, the insulated wire 2 may be applied with varnish before or after being cooled. In other words, the "heated insulated wire 2" does not mean the insulated wire 2 in a heated state, but rather the insulated wire 2 after being heated. For example, this step is performed by an insulating layer forming apparatus 12 shown in FIG. 2. The varnish to be applied may be the same varnish used when the insulated wire 2 was manufactured, or a different varnish may be used. Examples of varnishes include varnishes containing polyesterimide and polyamideimide, varnishes containing polyamideimide, varnishes containing polyimide, soldering varnishes, and varnishes containing polyester. A general-purpose varnish for manufacturing enameled wires can be used. In the present embodiment, the varnish used when the insulated wire 2 was manufactured is used.

[0025] In the step of baking the varnish (S150), the varnish applied to the insulated wire 2 is baked. For example, this step is performed by an insulating layer forming apparatus 12 shown in FIG. 2. The baking temperature may be the same as the temperature at which the varnish was baked when the insulated wire 2 was manufactured, or may be a different temperature. In the present embodiment, the baking temperature is the same as the temperature at which the varnish was baked when the insulated wire 2 was manufactured.

[0026] The step (S120) of rolling the insulated wire 2, the step (S130) of heating the insulated wire 2, the step (S140) of applying varnish, and the step (S150) of baking the varnish may be repeated in this order. In this case, the step (S120) of rolling the insulated wire 2 may be repeated multiple times so that the final width and thickness of the insulated wire 2 are the desired width and thickness. Similarly, the step (S140) of applying varnish and the step (S150) of baking the varnish are repeated multiple times so that the final thickness of the insulating layer 2c is the desired thickness. From the viewpoint of preventing crazing, the step (S130) of heating the insulated wire 2 is preferably performed every time between the step (S120) of rolling the insulated wire 2 and the step (S140) of applying varnish. The number of times the above four steps (S120, S130, S140, S150) are repeated is not particularly limited. The number of repetitions is preferably less than about 5 times.

[0027] The aspect ratio (width / thickness) of the rectangular insulated electric wire manufactured in this manner in a cross section perpendicular to the longitudinal direction is preferably in the range of 1:1.3 to 1:15, and more preferably in the range of 1:2 to 1:12. Generally, when the aspect ratio is within the above range, crazing occurs in conventional manufacturing methods, but the manufacturing method according to the present embodiment includes a heating step (annealing), so that crazing can be suppressed even when the aspect ratio is within the above range.

[0028] In the manufacturing apparatus 1, a take-up machine 15 shown in Fig. 2 takes up a linear body (insulated electric wire, rectangular insulated electric wire, etc.), causing the linear body to travel, thereby carrying out each process. The manufactured rectangular insulated electric wire 5 is taken up by a winding machine 16 shown in Fig. 2.

[0029] (effect) According to the method for producing a rectangular insulated electric wire according to the embodiment of the present invention, the heating step (annealing) is performed after rolling and before applying varnish, so that the occurrence of crazing can be suppressed. [Example]

[0030] The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited by these examples, and modifications of the embodiments can be made without departing from the spirit of the present invention.

[0031] Example 1 The rectangular insulated wire of Example 1 was prepared as follows. First, a copper wire with a diameter of 1.0 mm was placed in a wire drawing machine and drawn to a diameter of 0.9 mm. The drawn copper wire was then annealed in an annealing furnace. Next, an insulating layer (thickness: approximately 0.015 mm) was formed around the copper wire by repeatedly applying and baking polyamideimide varnish in an insulating layer forming device, thereby obtaining an insulated wire (round enameled wire) (step of preparing an insulated wire).

[0032] The obtained insulated wire was rolled using a rolling mill (a step of rolling the insulated wire). The rolled insulated wire was then heated using a baking machine (a step of heating the rolled insulated wire). Next, polyamideimide varnish was applied to the heated insulated wire in a varnish application unit of an insulating layer forming apparatus (a step of applying varnish). Next, polyamideimide varnish was baked onto the insulated wire coated with the polyamideimide varnish in a varnish baking unit of the insulating layer forming apparatus (a step of baking the varnish).

[0033] Next, the insulated wire with the baked varnish was rolled again in a rolling machine (a step of rolling the insulated wire). Next, the re-rolled insulated wire was heated again in a baking machine (a step of heating the rolled insulated wire). The reheated insulated wire was re-applied with polyamideimide varnish in a varnish application section of an insulating layer forming apparatus (a step of applying varnish). Next, the insulated wire with the re-applied polyamideimide varnish was re-baked with polyamideimide varnish in a varnish baking section of an insulating layer forming apparatus (a step of baking the varnish). Next, the re-rolling, re-heating, re-application, and re-baking were repeated 1 to 4 more times to obtain a rectangular insulated wire. The aspect ratio (width / thickness) in a cross section perpendicular to the longitudinal direction of the rectangular insulated wire was 1:10.

[0034] (Comparative Example 1) The rectangular insulated electric wire of Comparative Example 1 was obtained in the same manner as the rectangular insulated electric wire of Example 1, except that after rolling the insulated electric wire, varnish was applied to the rolled insulated electric wire without performing a step of heating the rolled insulated electric wire (annealing).

[0035] To evaluate the rectangular insulated electric wires obtained in Examples 1, 2, and Comparative Example 1, the following items were measured.

[0036] Dimensional measurement The length (width) in the first direction D1 and the length (thickness) in the second direction D2 of the conductor were measured at the cross section of each rectangular insulated electric wire. The thickness of each rectangular insulated electric wire in the first direction D1 and the second direction D2 were also measured at the cross section. The length (width) in the first direction D1 and the length in the second direction D2 were measured using a micrometer in accordance with Appendix JA.1 (Dimensions) of JIS C 3216-2:2019.

[0037] - Breakdown voltage measurement The breakdown voltage of each rectangular insulated wire was measured in accordance with Appendix JA.1.2(a) of JIS C 3216-5:2019, except that the load was 450 g. The results of the breakdown voltage measurements were evaluated according to the following criteria. Evaluation criteria ○: 0.8kV or more ×: Less than 0.8 kV

[0038] ·Elongation evaluation The elongation was evaluated according to JIS C 3216-3:2011 3.1.

[0039] Pinhole measurement The number of pinholes in each 5m rectangular insulated wire was measured in accordance with JIS C 3216-5:2019, Section 7 (Pinhole Test), except that the winding diameter was not specified and no pre-heating treatment was performed. The values shown in Table 1 are the average values obtained when 30 rectangular insulated wires were measured. The pinhole measurements were evaluated according to the following criteria. Evaluation criteria ○: Less than 9 pieces / 5m ×: 9 pieces / 5m or more

[0040] Flexibility evaluation Flexibility was evaluated by measuring the presence or absence of cracks that revealed the conductor in the coating when the cable was broken, in accordance with Appendix JA.5.1.1b) of JIS C 3216-3:2011. Flexibility was evaluated according to the following criteria: Evaluation criteria ○: No cracks ×: Cracks present

[0041] Adhesion evaluation FIG. 4A is a cross-sectional view of a rectangular insulated electric wire 5, FIG. 4B is a schematic diagram of a tensile tester, and FIG. 4C is a schematic diagram of a fractured portion of the rectangular insulated electric wire 5. Adhesion was evaluated using the following method. Five 35 cm long rectangular insulated electric wires 5 were tested using the tensile tester shown in FIG. 4B with a gauge length of 250 mm. Both ends of the rectangular insulated electric wire 5 were fixed to fixing portions 411 and 412. One fixing portion (fixing portion 412 in this case) was then stretched at a speed of 300 mm / min until the rectangular insulated electric wire 5 broke. The fractured rectangular insulated electric wires 5 were examined for the fracture lift length of the insulating layer 2b. The fracture lift length was measured as the length of the region where the conductor 2a and the insulating layer 2b overlap but where the insulating layer 2b was not in close contact with the conductor 2a. 4A and 4C, if both rectangular insulated electric wires 5 had areas where the conductor 2a was not in close contact with the insulating layers 2b and 2c after fracture, the fracture lift length was taken as the sum of the fracture lift lengths A and B. The adhesion was evaluated according to the following criteria. Evaluation criteria ○: The total length of the broken float is less than 11 mm ×: The total length of the broken pieces is 11 mm or more

[0042] Crazing evaluation Crazing was evaluated by observing the presence or absence of cracks on the side surfaces of the rectangular insulated wires using an optical microscope (VHX-8000) manufactured by Keyence Corporation. Evaluation criteria ○: No cracks ×: Cracks present

[0043] The results of these measurements are shown in Table 1.

[0044] [Table 1]

[0045] As shown in Table 1, the rectangular insulated wire of Example 1, which was produced by performing a heating step (annealing) after rolling the insulated wire and before applying varnish, was excellent in breakdown voltage, elongation, pinholes, flexibility, adhesion, and crazing. This is thought to be because no stress remained in the insulating layer at the time of applying the varnish after the heating step (annealing).

[0046] On the other hand, the rectangular insulated wire of Comparative Example 1, which was produced without the heating step (annealing), had poor breakdown voltage, flexibility, and crazing, as shown in Table 1. This is thought to be because the heating step (annealing) was not performed after rolling the insulated wire and before applying the varnish, so stress remained in the insulating layer at the time the varnish was applied. [Industrial Applicability]

[0047] The method for manufacturing a rectangular insulated electric wire according to the present invention is useful for manufacturing a rectangular insulated electric wire to be used in, for example, a coil. The method for manufacturing a rectangular insulated electric wire according to the present invention can be applied to either a vertical coating device or a horizontal coating device. [Explanation of symbols]

[0048] 1 Manufacturing equipment 2. Insulated wire 2a conductor 2b, 2c insulating layers 5. Rectangular insulated wire 10 Wire drawing machine 11 Annealing furnace 12. Insulation layer forming device 12a Varnish application section 12b Baking section 13 Rolling Mill 13a Roller 15. Pick-up machine 16 Winder

Claims

1. providing an insulated wire having a conductor and an insulating layer covering the conductor; rolling the insulated wire; heating the rolled insulated wire; applying a varnish to the heated insulated wire; baking the varnish applied to the insulated wire; having Manufacturing method for rectangular insulated electric wire.

2. The method for producing a rectangular insulated electric wire according to claim 1, the rolling step, the heating step, the applying step, and the baking step are sequentially repeated on the insulated wire onto which the varnish has been baked; Manufacturing method for rectangular insulated electric wire.

3. The method for producing a rectangular insulated electric wire according to claim 1, The aspect ratio of the cross section perpendicular to the longitudinal direction of the rectangular insulated electric wire is in the range of 1:1.3 to 1:

15. Manufacturing method for rectangular insulated electric wire.

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