Method for manufacturing insulated wire, method for detecting defect, and system for manufacturing insulated wire

Abstract

Provided is a method for manufacturing an insulated wire that has a conductor and an insulating film covering the periphery of the conductor, the method comprising: a coating and baking step for providing, on the periphery of the conductor, an insulating film including a multilayer insulating layer by repeatedly forming an insulating layer through coating and baking a resin varnish; and a detection step for detecting a defect occurring in the conductor or the insulating layer in parallel with the repetition of insulating layer formation through coating and baking the resin varnish.

Description

Method for manufacturing insulated wire, method for detecting defective part, and manufacturing system for insulated wire

[0001] The present invention relates to a method for manufacturing an insulated wire, a method for detecting a defective part, and a manufacturing system for an insulated wire.

[0002] If there are defects in the conductor or insulating film of an insulated wire, insulation failure occurs at the defective part. Therefore, the manufactured insulated wire is inspected before shipment to identify and mark the defective part, and if necessary, the area having the defective part is removed before shipment.

[0003] As a method for accurately detecting surface defects of a rectangular enameled wire, for example, in Patent Document 1, bright-field imaging light is irradiated onto the flat surface and corner surfaces of a rectangular enameled wire moving in the longitudinal direction, and a step of imaging bright-field images of the flat surface and the corner surfaces, a step of irradiating dark-field imaging light along the longitudinal direction of the rectangular enameled wire, and imaging dark-field images of the flat surface and the corner surfaces, and a step of determining the presence or absence of defects on the flat surface and the corner surfaces from the bright-field images and the dark-field images are provided. An invention of an appearance inspection method for a rectangular enameled wire is disclosed. Further, in Patent Document 2, there is disclosed an invention of a film abnormality detection device for an enameled wire, which includes a contact member that contacts the surface of the enameled film of an enameled wire linearly moving in a certain direction and is displaced according to the height of film abnormality generated on the surface of the enameled film, and a displacement meter that acquires the amount by which the contact member is displaced.

[0004] Japanese Patent Application Laid-Open No. 2016-102724 Japanese Patent Application Laid-Open No. 2020-85647

[0005] Rotating electric machines such as motors are manufactured by, for example, shortening (segmenting) insulated wires, bending them into hairpin shapes to form segment coils, and then inserting these segment coils into slots in a stator core. When insulated wires are used after being bent in this way, minute defects that are difficult to detect in the wire's pre-bending state (straight state) can cause insulation failure in the bent or curved sections. Furthermore, our studies have revealed that among defects in insulated wires, conductor defects and defects located on the conductor side (closer to the conductor) in the thickness direction of the insulating coating (insulating coating defects closer to the conductor) are more likely to cause insulation failure due to bending, while defects on or near the surface of the insulating coating do not significantly affect insulation failure.Focusing on the defective parts of the insulating coating, Figure 1 shows a graph of the relationship between the position of the defect in the thickness direction and the dielectric breakdown voltage.As shown in Figure 1, the further inward the location of the defect in the insulating coating (left side of the graph in Figure 1) the smaller the dielectric breakdown voltage. Therefore, by detecting defects occurring deeper within the insulating coating and conductor defects with greater accuracy, it is possible to more efficiently avoid insulation defects that tend to become apparent due to bending and other processes. Referring to the above-mentioned Patent Documents 1 and 2 from the above perspective, the technologies described in Patent Documents 1 and 2 are methods for inspecting the appearance of finished enameled wires, making it difficult to detect internal defects that do not appear on the surface. For example, one method of detecting insulation defects by applying a voltage to a manufactured insulated wire and measuring the leakage current can also be considered. However, in order to detect defects occurring on the conductor side of the insulating coating of a finished insulated wire (an insulated wire with a sufficiently thick insulating coating), as well as conductor defects, it is necessary to apply a very high voltage, which can cause damage to the insulating coating or lead to false positives.

[0006] The present invention aims to provide a method for manufacturing an insulated wire, a method for detecting defects, and a manufacturing system for insulated wires, which enable the detection of defects in the conductor and defects occurring on the conductor side of the insulating coating with higher accuracy.

[0007] The inventors of this invention have conducted extensive research to solve the above problems and have found that, in the manufacturing of insulated wires, by repeatedly applying and baking a resin varnish to form an insulating layer (enamel layer) and simultaneously detecting defects, conductor defects and defects on the conductor side of the insulating coating can be detected with greater accuracy. Furthermore, by marking the defective areas or, if necessary, removing the areas containing the defective areas, the use of insulated wires that are prone to insulation failure due to bending and other processes can be efficiently avoided. This invention was completed after further research based on these findings.

[0008] In other words, the above problems of the present invention have been solved by the following means: [1] A method for manufacturing an insulated wire having a conductor and an insulating film covering the outer circumference of the conductor, comprising: a coating and baking step of providing a multilayer insulating film on the outer circumference of the conductor by repeatedly forming an insulating layer by coating and baking a resin varnish; and a detection step of detecting a defect occurring in the conductor or the insulating layer in parallel with the repeated formation of the insulating layer by coating and baking the resin varnish. [2] The method for manufacturing an insulated wire according to [1], wherein in the detection step, the detection of the defect is performed by measuring leakage current. [3] The method for manufacturing an insulated wire according to [1] or [2], wherein in the detection step, the detection of the defect is performed two or more times during the repeated formation of the insulating layer by coating and baking. [4] The method for manufacturing an insulated wire according to any one of [1] to [3], wherein in the detection step, the first detection of the defect is performed when the total thickness of the insulating layer is 5 to 90 μm. [5] A method for manufacturing an insulated wire according to any one of [1] to [4], wherein the thickness of the insulating coating is 25 μm or more. [6] A method for detecting defects in an insulated wire having a conductor and an insulating coating covering the outer circumference of the conductor, wherein a multilayer insulating coating is provided on the outer circumference of the conductor by repeatedly applying and baking a resin varnish to form an insulating layer, and the method includes detecting defects in the conductor or the insulating layer in parallel with the repeated application and baking of the resin varnish to form the insulating layer. [7] A manufacturing system for an insulated wire having a conductor and an insulating coating covering the outer circumference of the conductor, comprising: an application and baking device for repeatedly applying and baking a resin varnish to form an insulating layer on the outer circumference of the conductor; and a detector for detecting defects in the conductor or the insulating layer in parallel with the repeated application and baking of the resin varnish to form the insulating layer. [8] The manufacturing system for an insulated wire according to [7], wherein the detector is a spark tester. [9] The insulated wire manufacturing system according to [7] or [8], comprising two or more of the detectors.

[0009] According to the present invention, the method for manufacturing an insulated wire, the method for detecting defects, and the manufacturing system for an insulated wire can detect defects in the insulated wire with higher accuracy.

[0010] Figure 1 is a graph showing the relationship between dielectric breakdown voltage and the location of defects. Figure 2 is a schematic diagram illustrating the configuration of the manufacturing system used in the method for manufacturing insulated wires of the present invention. Figure 3 is a schematic diagram illustrating a cross-sectional view of an insulated wire obtained by the method for manufacturing insulated wires of the present invention. Figure 4(a) is a schematic diagram illustrating how defects are detected in an insulated wire manufactured without using the method for manufacturing insulated wires of the present invention. Figure 4(b) is a schematic diagram illustrating how defects are detected in an insulated wire manufactured by the method for manufacturing insulated wires of the present invention.

[0011] In this invention and specification, when the term "insulating layer" is used, it refers to a layer (enamel layer) formed by applying and baking a resin varnish once. In this invention, insulating layers formed by repeating the application and baking of the same resin varnish multiple times are considered to be multilayer insulating layers. In other words, whether the resin varnish is the same or different, the layer formed by one application and baking is counted as one insulating layer. To put it another way, when the application and baking is repeated, a multilayer insulating layer is formed in which the same number of insulating layers as the number of repetitions are stacked. In this specification, the shape of an insulated wire, including the conductor and insulating film, in terms of the cross-sectional shape perpendicular to the longitudinal direction of the insulated wire, may be simply referred to as the cross-sectional shape. In this invention, the cross-sectional shape does not mean that only the cut surface has a specific shape, but rather that this cross-sectional shape is continuously connected in the longitudinal direction of the entire insulated wire, and unless otherwise specified, the cross-sectional shape perpendicular to this direction is substantially the same for any part of the longitudinal direction of the insulated wire. In this specification, numerical ranges indicated by "~" mean a range that includes the numbers listed before and after it as the lower and upper limits, respectively.

[0012] [Method for Manufacturing Insulated Wires] In one embodiment, the present invention provides a method for manufacturing insulated wires (hereinafter also referred to as "the manufacturing method of the present invention"). The manufacturing method of the present invention is a method for manufacturing an insulated wire having a conductor and an insulating film covering the outer circumference of the conductor, comprising: a coating and baking step for forming an insulating layer on the outer circumference of the conductor by repeatedly applying and baking a resin varnish to provide an insulating film of a multilayer insulating layer; and a detection step for detecting defects (also simply referred to as defects) that have occurred in the conductor or the insulating layer, in parallel with the repeated application and baking of the resin varnish to form the insulating layer. In other words, it is a method for manufacturing insulated wires that incorporates a detection step for detecting defects that have occurred in the conductor or the insulating layer during an intermediate stage in the process of repeatedly applying and baking the resin varnish on the outer circumference of the conductor. The insulating film is a multilayer insulating layer (multilayer enamel layer) formed by repeatedly applying and baking a resin varnish. In the manufacturing method of the present invention, defects can be detected with high accuracy by repeatedly applying and baking resin varnish to form an insulating layer while simultaneously detecting defects (i.e., detecting defects during the formation of the insulating film).

[0013] In the present invention and this specification, a "defective part" of an insulated wire means a part that may cause insulation failure. Examples of such defects include surface scratches (scratches, peeling) on ​​the conductor, internal defects in the conductor, foaming within the insulating film (insulating layer), inclusion of foreign matter (resin varnish gel, film carbides, fibers, metals, dust, etc.) within the insulating film (insulating layer), and scratches on the surface of the conductor or insulating film (insulating layer) (such as contact scratches with contact parts). Examples of internal defects in the conductor include cracks such as fissures, cracks caused by blowholes (or pinholes), and surface bulges.

[0014] Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. However, the present invention is not limited to the embodiments shown below, except as specified herein. Figure 2 is a schematic diagram illustrating the insulated wire manufacturing system 100 used in the manufacturing method of the present invention, which includes a varnish coating apparatus 101 and a baking furnace 102 for applying and baking resin varnish, a roller 103, and a detection device 104 (104A, 104B1, 104B2, 104C) for detecting defects in the insulated wire. In the resin varnish application and baking process, the varnish coating apparatus 101 applies resin varnish to the outer circumference of the conductor 201, and then bakes it in the subsequent baking furnace 102 to form an insulating layer. By repeating this application and baking operation multiple times, an insulating film of a multilayer insulating layer is formed. In one example shown in Figure 2, an insulated wire manufacturing system 100 is shown in which the application and baking operation is repeated 12 times (providing a first pass line to a twelfth pass line). In the manufacturing method of the present invention, defect detection is performed in parallel with the repeated formation of the insulating layer by applying and baking the resin varnish. In one example shown in Figure 2, the application and baking of the resin varnish is performed on the front side of the manufacturing system 100, and defect detection of the insulated wire is performed on the back side. The four detection units 104 for detecting the defects are arranged such that one unit (detector 104A) is on the third pass line, two units (detectors 104B1, 104B2) are on the sixth pass line, and one unit (detector 104C) spans the ninth to eleventh pass lines. In other words, by detecting defects at an appropriate timing in parallel with the repeated formation of the insulating layer by applying and baking the resin varnish, a high detection accuracy for defects can be achieved.

[0015] Figure 3 is a schematic cross-sectional view showing an example of the configuration of an insulated wire 200 manufactured by the method for manufacturing an insulated wire of the present invention. The insulated wire 200 has a conductor 201 and an insulating film 202 that is in contact with the conductor 201 and covers the circumferential surface of the conductor 201. In Figure 3, the conductor 201 is a conductor (flat rectangular conductor) with a rectangular cross-sectional shape perpendicular to the longitudinal direction. The insulating film 202 is a multilayer insulating layer in which multiple insulating layers 203 formed by coating and baking a resin varnish are laminated. Note that in Figure 3, some of the boundaries between the insulating layers 203 are omitted. The cross-sectional shape of the insulated wire 200 is preferably similar to that of the conductor 201, and in particular, the overall shape of the insulating film 202, that is, the cross-sectional shape of the outermost surface of the insulating film 202 opposite to the conductor 201, is preferably similar to that of the conductor 201. Note that similarity is not limited to a perfectly similar shape, but is sufficient if it is substantially similar.

[0016] In the manufacturing method of the present invention, the conductor used for the insulated wire can be one that has been conventionally used as a conductor for insulated wires. Examples include metal conductors such as copper wire and aluminum wire. The cross-sectional shape perpendicular to the longitudinal direction of the conductor used in the manufacturing method of the present invention is not particularly limited. Examples include conductors with a circular or rectangular (square, rectangular (flat-angled)) cross-sectional shape. In the present invention, a conductor with a rectangular cross-sectional shape is preferred, and a flat-angled conductor is more preferred. A conductor with a rectangular cross-sectional shape has a higher space-filling ratio in the stator core slots compared to a conductor with a circular cross-sectional shape. For this reason, it is preferred for applications where many insulated wires are incorporated into a certain narrow space.

[0017] The characteristic configuration of the manufacturing method of the present invention will be described in more detail below.

[0018] <Coating and Baking Process> The manufacturing method of the present invention has a coating and baking process in which a resin varnish is applied to the outer circumference of a conductor and baked multiple times, thereby forming an insulating film of a multilayer insulating layer on the outer circumference of the conductor. The method of applying the resin varnish to the conductor can be a conventional method, for example, using a die that is similar in shape to the conductor in a varnish coating apparatus, or, if the cross-sectional shape of the conductor is rectangular, using a die called a "universal die" that is formed in a grid shape. The conductor coated with the resin varnish is baked in a baking furnace by a conventional method. The specific baking conditions depend on the shape of the baking furnace used, but in a natural convection type vertical furnace of approximately 10 m, it can be achieved by setting the furnace temperature to 400 to 650°C and the passage time to 10 to 90 seconds.

[0019] The number of repetitions of coating and baking the resin varnish to form the insulating film is not particularly limited and can be set as appropriate to satisfy the provisions of the present invention. In this invention, "number of repetitions of coating and baking" is synonymous with the number of layers in the multilayer insulating layer. For example, the number of repetitions of coating and baking can be 10 or more, 12 or more, or 15 or more. The number of repetitions can also be 35 or less, 30 or less, or 25 or less. If the number of repetitions is shown as a preferred range, it is preferably 10 to 35, more preferably 12 to 30, and even more preferably 15 to 25. Similarly, the number of layers in the insulating layer constituting the insulating film can be 10 or more, 12 or more, or 15 or more. The number of layers can also be 35 or less, 30 or less, or 25 or less. If the number of layers is shown as a preferred range, it is preferably 10 to 35, more preferably 12 to 30, and even more preferably 15 to 25. Furthermore, the resin varnish used for coating and baking may be the same for all insulating layers, or different types of resin varnish may be used for each insulating layer.

[0020] In the manufacturing method of the present invention, the resin varnish coating and baking operation is carried out such that the thickness of the formed insulating film (the total thickness of the multilayer insulating layer in the finished product) is preferably 25 μm or more, more preferably 30 μm or more, even more preferably 40 μm or more, even more preferably 50 μm or more, and even more preferably 60 μm or more. Furthermore, the resin varnish coating and baking operation is carried out such that the thickness of the formed insulating film is preferably 230 μm or less, more preferably 200 μm or less, even more preferably 170 μm or less, and even more preferably 140 μm or less. If the thickness of the formed insulating film is shown as a preferred range, it is preferably 25 to 230 μm, more preferably 30 to 230 μm, even more preferably 40 to 200 μm, even more preferably 50 to 170 μm, and even more preferably 60 to 140 μm. The thickness of the insulating film is measured by 16-point measurement. The 16-point measurement method is a commonly used measurement method in this field, and the specific measurement method is described in International Publication No. 2013 / 073397.

[0021] The insulating layer is an enamel layer formed by applying a resin varnish containing an insulating resin (insulating polymer) to a conductor and baking it. For the formation of this enamel layer, any resin suitable for forming an enamel layer can be appropriately applied depending on the purpose. The resin can be either a thermosetting resin or a thermoplastic resin, and the insulating layer is preferably an enamel layer formed by curing a thermosetting resin. Examples of thermosetting resins that can be used to form the enamel layer include polyimide (PI), polyamide-imide (PAI), polyurethane, thermosetting polyester (PEst), H-type polyester (HPE), polybenzimidazole, polyesterimide (PEsI), melamine resin, and epoxy resin, and one or more of these can be used.

[0022] The organic solvents (organic solvents) used to varnish the resin included in the aforementioned resin varnish include, for example, amide solvents such as N,N-dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), and N,N-dimethylformamide (DMF); urea solvents such as N,N-dimethylethylene urea, N,N-dimethylpropylene urea, and tetramethylurea; lactone solvents such as γ-butyrolactone and γ-caprolactone; carbonate solvents such as propylene carbonate; methyl ethyl ketone; and methyl isobutyl ether. Examples of suitable solvents include ketones and cyclohexanone, ester solvents such as ethyl acetate, n-butyl acetate, butyl cellosolve acetate, butyl carbitol acetate, ethyl cellosolve acetate, and ethyl carbitol acetate, glyme solvents such as diglyme, triglyme, and tetraglyme, hydrocarbon solvents such as toluene, xylene, and cyclohexane, phenolic solvents such as cresol, phenol, and halogenated phenol, sulfone solvents such as sulfolane, and dimethyl sulfoxide (DMSO). In particular, from the viewpoint of varnish stability due to hydrogen bonding with the resin, the organic solvent is preferably an aprotic solvent, preferably contains DMAc and / or NMP, and more preferably contains DMAc and / or NMP. Furthermore, the above organic solvents may be used individually or in combination of two or more.

[0023] The resin varnish may optionally contain various additives such as adhesion promoters, foaming agents for bubble formation, antioxidants, antistatic agents, UV inhibitors, light stabilizers, fluorescent whitening agents, pigments, dyes, compatibilizers, lubricants, strengthening agents, flame retardants, crosslinking agents, crosslinking aids, plasticizers, thickeners, devisers, and elastomers. The resin varnish may also contain inorganic fine particles to the extent that they do not affect its properties. Examples of such inorganic fine particles include zinc oxide, titanium oxide, tin oxide, silicon carbide, and strontium titanate.

[0024] <Detection Step> The manufacturing method of the present invention includes a detection step for detecting defects in the conductor or the insulating layer in parallel with the repeated formation of an insulating layer by applying and baking a resin varnish. Note that "detecting defects in the conductor or the insulating layer in parallel with the repeated formation of an insulating layer by applying and baking a resin varnish" means, for example, when the resin varnish application and baking operation is repeated n times, detecting defects in the insulated wire at least once during that time (i.e., from after the first application and baking operation to before the nth application and baking operation).

[0025] The number of times defects in the insulated wire are detected can be appropriately set according to the thickness of the insulating coating and the number of insulating layers formed. The detection of defects performed during the repeated formation of the insulating layer by applying and baking the resin varnish is preferably performed two or more times, more preferably three or more times, even more preferably four or more times, and even more preferably five or more times. For example, in the example shown in Figure 2, detection is performed once on the third pass line, twice on the sixth pass line, and once each on the ninth to eleventh pass lines, resulting in a total of six detections during the repeated formation of the insulating layer by applying and baking the resin varnish. When defects are detected multiple times as described above, the detection method for each defect may be the same method, or different methods may be combined. When defects are detected multiple times, the detection may be performed multiple times on the same pass line, multiple times across multiple different pass lines, or multiple times on the same pass line while also multiple times across multiple different pass lines. For example, in the example shown in Figure 2, detection is performed twice on the sixth pass line while detection is also performed across the third, sixth, and ninth to eleventh pass lines.

[0026] In the detection process described above, the overall thickness of the insulating layer at the time of the first detection is not particularly limited, and the first detection can be performed at a desired timing depending on the purpose. For example, the overall thickness of the insulating layer at the time of the first detection is preferably 5 μm or more, more preferably 10 μm or more, even more preferably 20 μm or more, and may be 30 μm or more, or 40 μm or more. Furthermore, the thickness is preferably 90 μm or less, more preferably 80 μm or less, and even more preferably 70 μm or less. If the thickness is shown as a preferred range, it is preferably 5 to 90 μm, more preferably 10 to 90 μm, even more preferably 20 to 90 μm, and may also be 30 to 80 μm, or 40 to 70 μm. By performing the first defect detection when the overall thickness of the insulating layer is within the above thickness range, defects in the conductor and defects occurring in the insulating layer on the conductor side of the insulating film can be detected with greater accuracy. Furthermore, when detecting defects multiple times, each subsequent detection is preferably performed when the thickness of the insulating layer has increased by 3 to 20 μm from the thickness of the insulating layer at the time of the previous detection, more preferably when it has increased by 4 to 15 μm, and even more preferably when it has increased by 5 to 10 μm. For example, if the thickness of the insulating layer at the time of the first detection is 50 μm, the second detection can be performed when the thickness of the insulating layer is preferably in the range of 53 to 70 μm, more preferably 54 to 65 μm, and even more preferably 55 to 60 μm. It is also preferable to perform the first detection when the thickness of the insulating layer at the time of detection is in the range of 1 / 3 to 2 / 3 of the thickness of the insulating coating when the insulated wire is completed, or in the range of 1 / 2 to 2 / 3.

[0027] The method for detecting defects is not particularly limited and includes, for example, leakage current measurement, image inspection, ultrasonic inspection, partial discharge initiation voltage (PDIV) measurement, corona discharge measurement, eddy current testing, laser external measurement, and contact measurement. Among these, it is preferable to detect defects in insulated wires by measuring leakage current. With leakage current measurement, it can be determined that a defect exists at the location where leakage current is measured. Examples of devices used for leakage current measurement include spark testers (manufactured by Shintoyo Kiki Co., Ltd. and DSE Test Solutions). It should be noted that the application of these measuring devices (detection devices) to detect defects in finished insulated wires is publicly known. The present invention has a distinctive technical perspective in that the inventors recognized the problems in conventional methods for detecting defects using these measuring devices and set a new problem, and the present invention has a distinctive technical element in that it has solved the above new problem by devising the timing of detection as described above. Furthermore, as shown in the example in Figure 2, when two detections are performed on the sixth pass line, for example, the first detection (detection by detector 104B1) may be performed by a spark tester and the second detection (detection by detector 104B2) may be performed by image inspection, or the first detection may be performed by image inspection and the second detection by a spark tester. In the former case, the shape of the sparked defect (insulation failure) can be recorded and confirmed by the spark tester, and in the latter case, minute defects that could not be detected by the image sensor can be detected by the spark tester. In addition, by performing analysis processing using artificial intelligence (AI) on the data obtained by the above detection method (e.g., image data), it is possible to reduce the chances of overlooking defects and to detect defects with even greater accuracy.

[0028] When detecting defects in insulated wires by measuring leakage current, the measurement conditions can be appropriately set according to the purpose. For example, the applied voltage is preferably 500V or higher, more preferably 2kV or higher, and even more preferably 4kV or higher. Also, from the viewpoint of reducing damage to the insulating coating, the voltage is preferably less than 10kV, more preferably 8kV or lower, and even more preferably 6kV or lower. Furthermore, when detecting defects, the applied voltage may be set lower if the overall thickness of the insulating layer is thin, and higher if the overall thickness of the insulating layer is thick. In addition, in leakage current measurement, it is also possible to set it so that a defect exists when the detected current value exceeds a certain value (threshold). Such a threshold can be appropriately set depending on the applied voltage and the type of insulated wire (type of conductor and insulating layer, thickness of insulating layer, etc.).

[0029] In the manufacturing method of the present invention, an example of detecting a defect by measuring leakage current is schematically shown in Figure 4. In the insulated wire 200 shown in Figure 4, the defect 204 is located close to the conductor in the insulating film 202. As shown in Figure 4(a), when detecting a defect 204 in a finished insulated wire 200, the thickness of the insulating film 202 is sufficiently thick, so the defect 204 cannot be detected by simply applying a certain voltage (a voltage that does not damage the insulating film) with the spark tester 300. In Figure 4(a), a high voltage is required to detect a defect 204 in a finished insulated wire 200, in which case the insulating film 202 may be damaged. In contrast, as in the manufacturing method of the present invention shown in Figure 4(b), when measuring leakage current during the formation of the insulating film 202, the overall thickness of the insulating layer 203 is thin, so the defect 204 can be detected by applying only a low voltage, and damage to the insulating film 202 can also be suppressed. Furthermore, even if the thickness of the insulating layer 203 increases due to repeated application and baking of resin varnish, the leakage current is measured at the same location due to the spark generation point 205 (with the spark generation point 205 as the starting point). Therefore, the defect 204 can be detected without applying a high voltage to the finished insulated wire 200.

[0030] In the manufacturing method of the present invention, it is preferable to detect defects in the insulated wire (insulated wire after the formation of the insulating film) even after the resin varnish application and baking process (after all repetitions of forming the insulating layer by applying and baking the resin varnish have been completed). The detection of defects after the application and baking process may be performed on the pass line after the final resin varnish application and baking operation, or at any time, such as after winding the finished insulated wire or before shipment. By detecting defects in the insulated wire after the resin varnish application and baking process, it is possible to reliably identify defects on the surface of the insulated wire, mark the location of the defects, and, if necessary, remove the area containing the defects before shipment. The method for detecting defects in the insulated wire after the formation of the insulating film can be applied as a method for detecting defects in parallel with the repetitions of forming the insulating layer by applying and baking the resin varnish, and it is preferable to combine multiple detection methods. Furthermore, it is preferable that the multiple detection methods include the same detection method as the method for detecting defects in parallel with the repeated formation of the insulating layer by applying and baking the resin varnish. For example, the detection method for detecting defects in parallel with the repeated formation of the insulating layer by applying and baking the resin varnish may be leakage current measurement, and the method for detecting defects in the insulated wire after the insulating film has been formed may be a combination of leakage current measurement, image inspection, and laser outside measurement.

[0031] The manufacturing method of the present invention may include steps that are normally performed in the manufacturing of insulated wires, in addition to the coating and baking steps and the detection steps described above. Examples of such steps include a wire drawing step, an annealing step, a lubricant application step, and a winding step. It may also include a marking step for recording the location of a defect and a removal step for removing the area having a defect.

[0032] [Method for detecting defects] In relation to the manufacturing method of the present invention described above, the present invention provides, in one embodiment, a method for detecting defects in a conductor or insulating layer during the manufacture of an insulated electric wire (the detection method of the present invention). That is, according to the present invention: In the manufacture of an insulated electric wire having a conductor and an insulating film covering the outer circumference of the conductor, when forming an insulating layer on the outer circumference of the conductor by repeatedly applying and baking a resin varnish to form an insulating film of a multilayer insulating layer, the present invention provides a method for detecting defects in the conductor or the insulating layer in parallel with the repeated application and baking of the resin varnish to form the insulating layer. In the detection method of the present invention, the method for forming an insulating film of a multilayer insulating layer by repeatedly applying and baking a resin varnish to form an insulating layer, and the method for detecting defects in the conductor or the insulating layer in parallel with the repeated application and baking of the resin varnish to form the insulating layer, etc., are as described in the manufacturing method of the present invention, and the preferred form is also the same. That is, the matters described in the manufacturing method of the present invention can be directly applied to the detection method of the present invention. Furthermore, in one embodiment of the present invention, a method for manufacturing an insulated wire is provided, which includes marking and / or removing the defective portion detected by the above detection method.

[0033] [Insulated Wire Manufacturing System] In another embodiment, the present invention provides an insulated wire manufacturing system (hereinafter also referred to as "the manufacturing system of the present invention"). The manufacturing system of the present invention is a manufacturing system for an insulated wire having a conductor and an insulating coating covering the outer circumference of the conductor, comprising: a coating and baking device that repeatedly forms an insulating layer on the outer circumference of the conductor by coating and baking a resin varnish; and a detection device that detects defects occurring in the conductor or the insulating layer in parallel with the repeated coating and baking of the resin varnish to form the insulating layer. The manufacturing system of the present invention is a suitable system for carrying out the manufacturing method of the present invention described above.

[0034] In the manufacturing system of the present invention, the coating and baking apparatus comprises at least a varnish coating apparatus for coating a resin varnish and a baking furnace. The coating and baking apparatus can be one that is commonly used in the manufacture of insulated wires. The number of pass lines provided in the coating and baking apparatus can be appropriately set according to the number of insulating layers of the insulated wire to be manufactured. For example, in the example shown in Figure 2, the manufacturing system 100 of the present invention has 12 pass lines, from the first pass line to the twelfth pass line.

[0035] In the manufacturing system of the present invention, it is preferable that the detector is incorporated into the coating and baking apparatus. More specifically, it is preferable that it is provided between the baking furnace and the varnish coating apparatus, which are located within the coating and baking apparatus. The manufacturing system of the present invention preferably has multiple detectors (or detection units) (two or more). For example, in the example shown in Figure 2, the manufacturing system 100 of the present invention has a total of four detectors 104: one on the third pass line (detector 104A), two on the sixth pass line (detectors 104B1, 104B2), and one spanning the ninth to eleventh pass lines (detector 104C). In the detector 104C, each detection unit for detecting defects is provided on the ninth to eleventh pass lines, respectively.

[0036] In the manufacturing system of the present invention, defects are detected in insulated wires during the formation of the insulating coating, so at least one detector is provided on at least one pass line, excluding the final pass line. The manufacturing system of the present invention preferably has two or more pass lines, more preferably three or more pass lines, even more preferably four or more pass lines, and even more preferably five or more pass lines. The number of detectors provided on the same pass line may be two or more, three or more, four or more, or five or more. By providing multiple detectors on the same pass line, the chances of overlooking defects can be reduced. The multiple detectors may be the same detector or a combination of different detectors.

[0037] In the manufacturing system of the present invention, the first detector (the detector that first detects the defective part) is installed on the pass line between the baking furnace and the varnish coating apparatus when the total thickness of the insulating layer is preferably 5 μm or more, more preferably 10 μm or more, and even more preferably 20 μm or more. The thickness may also be 30 μm or more, or 40 μm or more. The thickness is preferably 90 μm or less, more preferably 80 μm or less, and even more preferably 70 μm or less. The preferred range for the thickness is preferably 5 to 90 μm, more preferably 10 to 90 μm, and even more preferably 20 to 90 μm, and may also be 30 to 80 μm, or 40 to 70 μm. Furthermore, if multiple detectors are provided, it is preferable that the second and subsequent detectors be installed on the pass line between the baking furnace and the varnish coating apparatus after the total thickness of the insulating layer has increased by preferably 3 to 20 μm, more preferably 4 to 15 μm, and even more preferably 5 to 10 μm from the total thickness of the insulating layer at the detector installed immediately before it. In addition, the installation position of the first detector can be set to a position where the total thickness of the insulating layer at the installation position of the first detector is 1 / 3 or more and 2 / 3 or less, or 1 / 2 or more and 2 / 3 or less, based on the thickness of the insulating coating when the insulated wire is completed.

[0038] The type of detector is not particularly limited, and examples include a spark tester for measuring leakage current, an image inspection device for acquiring images, an ultrasonic generator, a partial discharge initiation voltage (PDIV) measuring device, a corona discharge measuring device, an eddy current testing device, a laser outside measuring device, a contact-type measuring device, etc., with the spark tester being preferred. In addition, a computer for analyzing and recording the detection signal may be provided in conjunction with the detector. The computer may be capable of performing data processing using artificial intelligence (AI). Furthermore, in the case where two detectors (104B1, 104B2) are provided on the sixth pass line, as shown in the example in Figure 2, for example, the first detector (detector 104B1) may be a spark tester and the next detector (detector 104B2) may be an image inspection device, or the first detector (detector 104B1) may be an image inspection device and the next detector (detector 104B2) may be a spark tester. In the former case, the shape of the sparked defect (insulation failure) can be recorded and confirmed using a spark tester, while in the latter case, minute defects that could not be detected by the image sensor can be detected using a spark tester.

[0039] The manufacturing system of the present invention preferably includes a detector for detecting defects in the insulated wire after the insulating film has been formed, independently of the repeated application and baking of the resin varnish to form the insulating layer (hereinafter, such a detector will also be referred to as a "final detector" to distinguish it from a detector that detects defects in parallel with the repeated application and baking of the resin varnish to form the insulating layer). The final detector may be installed on the pass line after the last resin varnish application and baking operation, or it can be installed at any position, such as after winding the finished insulated wire or before shipment. By detecting defects in the insulated wire after the repeated application and baking of the resin varnish to form the insulating layer has been completed, it is possible to reliably identify defects on the surface of the insulated wire, mark the location of the defects, and remove the area containing the defects as needed. The above-described detector can be used as the final detector, and it is preferable to use a combination of multiple detectors. Furthermore, it is preferable that the combination of detectors includes the same type of detector as the detector that detects defects in parallel with the repeated application and baking of the resin varnish to form the insulating layer. For example, a spark tester can be used as a detector to detect defects in parallel with the repeated formation of an insulating layer by applying and baking resin varnish, and the final detection device can be a combination of a spark tester, a visual inspection device, and a laser outside measuring device.

[0040] The manufacturing system of the present invention can be configured similarly to a conventional insulated wire manufacturing system, except that it has a coating and baking device that repeatedly forms an insulating layer by coating and baking a resin varnish, and a detection device that detects defects in parallel with the repeated coating and baking of the insulating layer by the resin varnish. For example, in addition to the coating and baking device and the detection device, it may also have a cleaning device, a drying device, a cooling device, a straightening device, an extrusion device, etc. It may also be equipped with a marking device for recording the location of defects and a removal device for removing areas containing defects. Furthermore, the manufacturing system of the present invention may be equipped with a recording device for recording the location and condition of defects detected by the detection device.

[0041] The problem and solution of the present invention will be fully understood by those skilled in the art based on the above description. The present invention will be further explained below with reference to specific examples.

[0042] [Evaluation of Foam Detection Rate] <Example 1> A conductor with a rectangular cross-section (copper wire) was used as the conductor. Using a die in which the outer shape of the cross-section of the innermost insulating layer in contact with the conductor is similar to the cross-sectional shape of the conductor, polyimide resin varnish (manufactured by Essex Solutions) was applied to the surface of the conductor and baked for 60 seconds in a baking furnace with a length of 15 m set to 550°C. The linear speed was set to 15 m / min. This coating and baking process was performed a total of 17 times to form an insulating film (thickness: 60 μm) consisting of 17 polyimide insulating layers. In parallel with the repeated formation of the insulating layer by coating and baking the resin varnish as described above, a spark tester (manufactured by Shintoyo Kiki Co., Ltd.) was placed at a position where the total thickness of the insulating layer at the time of manufacture was the thickness shown in Table 1 below, and a voltage of 4 kV was applied to cause sparks in the defective areas.

[0043] (Evaluation Method) For 2000m of insulated wire (finished product) obtained by the manufacturing method of Example 1, the defective parts were sparked again under the same conditions (applied 4kV), and the defects at the locations where sparks occurred were identified visually or by magnifying glass. Then, a voltage of 10kV was applied using a spark tester to forcibly spark even minute defects. The defects at each location where a spark occurred were identified by cutting the insulated wire at that location and observing it under a microscope. The number of bubbles among the defects detected under each application condition was counted, and the detection rate was calculated using the following formula (Formula 1), and the evaluation was performed based on the evaluation criteria below. The results are shown in Table 1 below. Detection rate (%): [Number of bubbles detected with applied 4kV] / [Number of bubbles detected with applied 10kV] × 100 ... (Formula 1) -Evaluation Criteria- ◎: Detection rate of 95% or more ○: Detection rate of 80% or more and less than 95% △: Detection rate of 50% or more and less than 80% ×: Detection rate of less than 50%

[0044] <Examples 2 to 4, Comparative Example 1> Insulated electric wires were manufactured in the same manner as in Example 1, except that the thickness of the insulating film, the number of insulating layers, the number of detectors, and the total thickness of the insulating layers at the positions of the respective detectors were as described in Table 1 below (Examples 2 to 4). For each of the obtained insulated electric wires, the detection rate was evaluated in the same manner as above. The results are shown in Table 1 below. Also, for the insulated electric wire obtained by the manufacturing method of Comparative Example 1, which was the same as in Example 1 except that the thickness of the insulating film and the number of insulating layers were as described in Table 1 below and no detection of defective portions was performed in the manufacturing stage of the insulated electric wire, the detection rate was evaluated in the same manner as above. The results are shown in Table 1 below.

[0045] [Evaluation of Detection Rate of Foreign Matter Inclusion] <Examples 5 to 7, Comparative Examples 2 and 3> Insulated electric wires were manufactured in the same manner as in Example 1, except that the thickness of the insulating film, the number of insulating layers, the number of detectors, and the total thickness of the insulating layers at the positions of the respective detectors were as described in Table 2 below (Examples 5 to 7). For each of the obtained insulated electric wires, after causing a spark at the defective portion in the same manner as above, the defects were identified, the number of foreign matter inclusions among the identified defects was counted, and the detection rate was evaluated. The method for calculating the detection rate and the evaluation criteria were the same as above, except that the number of foreign matter inclusions was used instead of the number of foams. The results are shown in Table 2 below. Also, for each of the insulated electric wires obtained by the manufacturing methods of Comparative Examples 2 and 3, which were the same as in Example 1 except that the thickness of the insulating film and the number of insulating layers were as described in Table 2 below and no detection of defective portions was performed in the manufacturing stage of the insulated electric wire, the detection rate of foreign matter inclusion was evaluated in the same manner as in Examples 5 to 7. The results are shown in Table 2 below. <>

[0046] [Evaluation of Detection Rate of Conductor Defects] <Examples 8 to 10, Comparative Example 4> Insulated electric wires were manufactured in the same manner as in Example 1, except that the thickness of the insulating film, the number of insulating layers, the number of detectors, and the total thickness of the insulating layers at the position of each detector were as described in Table 3 below (Examples 8 to 10). For each of the obtained insulated electric wires, after sparking the defective part in the same manner as above, the defect was identified, and the number of conductor defects (surface flaws and internal defects of the conductor) among the identified defects was counted to evaluate the detection rate. Regarding the calculation method and evaluation criteria of the detection rate, it was the same as above, except that the number of conductor defects was used instead of the number of foams. The results are shown in Table 3 below. Also, regarding the insulated electric wire obtained by the manufacturing method of Comparative Example 4, which was the same as in Example 1 except that the thickness of the insulating film and the number of insulating layers were as described in Table 3 below and no detection of defective parts was performed at the manufacturing stage of the insulated electric wire, the detection rate of conductor defects was evaluated in the same manner as in Examples 8 to 10. The results are shown in Table 3 below.

[0047]

[0048]

[0049]

[0050] Tables 1-3 above show that for each insulated wire obtained by the manufacturing methods of Comparative Examples 1-4, in which the thickness of the insulating coating was 60 μm, 100 μm, and 130 μm, and no defect detection was performed during the manufacturing process, the detection rate for defects in the finished insulated wires was low for all defects, including foaming, foreign matter contamination, and conductor defects. The reason for this is thought to be that, as shown in Figure 4(a), in Comparative Examples 1-4, no defect detection was performed during the manufacturing process, so there were no spark generation sites within the insulating coating, and the final detection machine could not detect defects that occurred further inside the insulating coating or conductor defects. In contrast, for each insulated wire obtained by the manufacturing methods of Examples 1-10, in which defect detection was performed in parallel with the repeated application and baking of resin varnish to form the insulating layer during the manufacturing process, the detection rate for defects in the finished insulated wires was high in all cases (Tables 1-3). The reason for this is that, as shown in Figure 4(b), in Examples 1 to 10, spark generation sites exist within the insulating film. Therefore, during detection by the final detection device, new sparks are generated at these spark generation sites, making detection possible regardless of the location of the defect in the thickness direction.

[0051] Although we have described the present invention along with its embodiments, we do not intend to limit our invention in any detail of the description unless specifically designated, and we believe that it should be interpreted broadly without contradicting the spirit and scope of the invention as set forth in the appended claims.

[0052] This application claims priority based on Japanese Patent Application No. 2025-026203, filed in Japan on February 20, 2025, the contents of which are incorporated herein by reference as part of this specification.

[0053] 100 Insulated wire manufacturing system 101 Varnish coating machine 102 Baking oven 103 Roller 104, 104A, 104B1, 104B2, 104C Detector 200 Insulated wire 201 Conductor 202 Insulating coating 203 Insulating layer 204 Defect 205 Spark generation location 300 Spark tester

Claims

1. A method for manufacturing an insulated wire having a conductor and an insulating coating covering the outer circumference of the conductor, comprising: a coating and baking step of repeatedly applying and baking a resin varnish to form an insulating layer on the outer circumference of the conductor to provide a multilayer insulating coating; and a detection step of detecting defects occurring in the conductor or the insulating layer in parallel with the repeated application and baking of the resin varnish to form the insulating layer.

2. The method for manufacturing an insulated wire according to claim 1, wherein the detection of the defect is performed by measuring leakage current in the detection step.

3. The method for manufacturing an insulated wire according to claim 1 or 2, wherein in the detection step, the detection of the defective portion is performed two or more times during the repeated formation of the insulating layer by coating and baking.

4. The method for manufacturing an insulated wire according to any one of claims 1 to 3, wherein in the detection step, the first detection of a defect is performed when the total thickness of the insulating layer is 5 to 90 μm.

5. A method for manufacturing an insulated wire according to any one of claims 1 to 4, wherein the thickness of the insulating coating is 25 μm or more.

6. A method for detecting defects in an insulated electric wire having a conductor and an insulating coating covering the outer circumference of the conductor, wherein a multilayer insulating coating is provided on the outer circumference of the conductor by repeatedly forming an insulating layer by applying and baking a resin varnish, and the method includes detecting defects occurring in the conductor or the insulating layer in parallel with the repeated application and baking of the insulating layer by the resin varnish.

7. A manufacturing system for an insulated wire having a conductor and an insulating coating covering the outer circumference of the conductor, comprising: a coating and baking device that repeatedly forms an insulating layer on the outer circumference of the conductor by coating and baking a resin varnish; and a detection device that detects defects occurring in the conductor or the insulating layer in parallel with the repeated coating and baking of the resin varnish to form the insulating layer.

8. The insulated wire manufacturing system according to claim 7, wherein the detector is a spark tester.

9. The insulated wire manufacturing system according to claim 7 or 8, comprising two or more of the aforementioned detectors.

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