Method for manufacturing electrical steel sheets and method for manufacturing cores
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- SHT CORP LTD
- Filing Date
- 2021-11-15
- Publication Date
- 2026-06-05
Smart Images
Figure 0007870520000003 
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Abstract
Description
Technical Field
[0001] The present invention relates to a method for producing an electromagnetic steel sheet material used for cores such as current transformers and in-vehicle current sensors. More specifically, it relates to a method for cutting an electromagnetic steel sheet with a fiber laser, a method for producing an electromagnetic steel sheet material with minimized deterioration of magnetic properties and imparted rust prevention effect, and a method for producing a core from the cut electromagnetic steel sheet material.
Background Art
[0002] Cores used in current transformers, current sensors, etc. are produced by winding a strip-shaped electromagnetic steel sheet material obtained by cutting an electromagnetic steel sheet, or laminating electromagnetic steel sheet materials punched by press (hereinafter, "winding" and "laminating" are collectively referred to as "laminating"). The core assembly in which electromagnetic steel sheet materials are laminated is subjected to annealing treatment and impregnated with varnish (impregnating adhesive) to fix the electromagnetic steel sheet materials to each other.
[0003] To cut an electromagnetic steel sheet into a strip shape, a slitter device is used. For example, in Patent Document 1, a long electromagnetic steel sheet is cut by a pair of upper and lower rotary blades provided in a slitter device to obtain a strip-shaped electromagnetic steel sheet material.
[0004] However, in cutting with a rotary blade, it is difficult to perform curved processing and processing with a complicated outer edge shape. Also, there is a problem that the rotary blade wears out quickly. Furthermore, the electromagnetic steel sheet may escape from the rotary blade during cutting, and it is particularly difficult to obtain a narrow strip-shaped electromagnetic steel sheet material. In addition, since the rotary blade has a thickness of about several millimeters, it causes a decrease in material yield during cutting.
[0005] Also, cutting with a rotary blade is performed with a pair of upper and lower rotary blades offset. Therefore, as shown in FIG. 8 and FIG. 10 described later, burrs 22 are generated at the cut-in portion by the cutting blade on the cut surface 21 of the electromagnetic steel sheet material 20, and the width after cutting varies. As a result, in the core assembly 23a in which a plurality of electromagnetic steel sheet materials 20 are laminated as shown in FIG. 9, a step of about ±0.1 mm occurs on the side surface.
[0006] Even in the case of electrical steel sheets obtained by press-punching, burrs form on the cut-off portion of the die, resulting in variations in width after cutting. As a result, when the electrical steel sheets are laminated, steps appear on the sides of the core assembly in the same way as described above.
[0007] If a step or unevenness occurs on the side surface of the core assembly, it can lead to dimensional defects or performance problems in the final core product.
[0008] Incidentally, in order to produce the core assembly 23a, which is made by laminating electrical steel sheets, the core 23 is subjected to an annealing treatment, followed by an impregnation treatment in which the electrical steel sheets are fixed with varnish 25 to prevent delamination between them. At this time, if the varnish 25 remains on the side surface of the core 23, it hardens into a varnish pool 24, as shown in Figure 10. The varnish pool 24 can be 0.3 mm or more in diameter and several tenths of a millimeter in height, and the core 23 in which the varnish pool 24 occurs will have a poor appearance and dimensional defects.
[0009] The inventors noticed that cores made from electromagnetic steel sheets obtained by rotary cutting or press punching tended to accumulate impregnating material. Through diligent research, they discovered that this accumulation occurs due to the following reasons.
[0010] The cause lies in the surface structure of the cut surface of the electrical steel sheet 20. The cut surface 21 of the electrical steel sheet 20, which has been cut by rotary blade or press punched, has a flat structure with few irregularities. Because a flat cut surface with few irregularities has high wettability, the varnish 26 adheres easily to the cut surface 21, as schematically shown in Figure 11. Then, as the adhered varnish 26 hardens, some of it forms varnish puddles 24 as shown in Figure 10.
[0011] Furthermore, the steps (lamination misalignment) on the core side surface caused by burrs 22 on the electrical steel sheet material 20 are also a contributing factor to varnish accumulation. This is because varnish tends to accumulate in these steps.
[0012] Therefore, the inventors considered adopting a method for cutting electromagnetic steel sheets using a laser instead of rotary blades or press punching.
[0013] For example, Patent Document 2 discloses a method for laser cutting galvanized steel sheets. A YAG laser and a CO2 laser are used as the lasers. These lasers are irradiated onto the steel sheet while blowing an assist gas of 2 to 20 volume percent oxygen and the remainder nitrogen. [Prior art documents] [Patent Documents]
[0014] [Patent Document 1] Japanese Patent Application Publication No. 5-299277 [Patent Document 2] Japanese Patent Publication No. 2001-353588 [Overview of the Initiative] [Problems that the invention aims to solve]
[0015] However, when YAG lasers and CO2 lasers are used to cut electrical steel sheets, excessive heat is applied to the cut surface during cutting. As a result, the cut surface is heated to over 1500°C up to a depth of approximately 1000 μm, altering the crystal structure of the electrical steel sheet, which affects its magnetic properties. Furthermore, when oxygen is used as the assist gas with YAG lasers and CO2 lasers, black rust forms on the cut surface of the electrical steel sheet. The magnetic properties that have deteriorated due to these changes in the surface crystal structure and the black rust that forms on the surface are difficult to recover even by annealing the electrical steel sheet. Therefore, electrical steel sheets cut with YAG lasers and CO2 lasers can be used for cores of motors and other devices where the width of the magnetic hysteresis curve (BH curve) is not a major factor, but they could not be used for cores of products such as current transformers and current sensors, where soft magnetic properties are required across the entire range of the BH curve, from the minute magnetization region to the saturation magnetization, and are affected by coercivity and residual magnetic flux density.
[0016] The object of the present invention is to provide a method for cutting an electromagnetic steel sheet with a fiber laser, a method for producing an electromagnetic steel sheet material with minimized deterioration of magnetic properties and imparted rust prevention effect, and a method for producing a core with suppressed occurrence of varnish accumulation from the cut electromagnetic steel sheet material.
Means for Solving the Problems
[0017] The method for cutting an electromagnetic steel sheet of the present invention is Irradiating a fiber laser while blowing an assist gas with an oxygen concentration of 50% by volume or more onto the electromagnetic steel sheet to perform cutting, thereby obtaining an electromagnetic steel sheet material with a rust prevention effect imparted to the cut surface.
[0018] The fiber laser Fiber core diameter: 1 μm to 25 μm, Laser output: 300 W to 1000 W, Cutting speed: 300 mm / second to 500 mm / second, and can be irradiated onto the electromagnetic steel sheet.
[0019] The oxygen concentration is 60% by volume or more, and the balance can be nitrogen.
[0020] The method for producing an electromagnetic steel sheet material of the present invention is Restoring the magnetic properties by annealing the electromagnetic steel sheet material cut by the above-described method for cutting an electromagnetic steel sheet.
[0021] The annealing treatment is preferably carried out under the conditions of 750°C to 850°C for 1 hour or more. [[ID=
[0023] It is desirable that the annealing treatment be carried out under the conditions of 750°C to 850°C for 1 hour or more.
[0024] The varnish can be a material containing an acrylic monomer and an epoxy resin.
Advantages of the Invention
[0025] According to the method for cutting an electromagnetic steel sheet of the present invention, a fiber laser is irradiated while spraying an assist gas with a high oxygen concentration onto the electromagnetic steel sheet to cut the electromagnetic steel sheet and obtain an electromagnetic steel sheet material. Since the fiber laser can concentrate energy in a narrow area, the cut surface of the electromagnetic steel sheet can be cut without being excessively heated. As a result, the obtained electromagnetic steel sheet material can minimize the change in the crystal structure of the surface layer of the cut surface and minimize the deterioration of magnetic properties. In addition, by adopting an assist gas with a high oxygen concentration, the cut surface is oxidized at high speed to form an oxide film. Since this oxide film has the effect of suppressing the generation of red rust, the electromagnetic steel sheet material obtained by cutting does not need to be subjected to rust prevention treatment or packaged with rust prevention paper.
[0026] The electromagnetic steel sheet material cut by the fiber laser has a uniformly processed cut surface, and there is no burr generation due to nibbling like rotary blade cutting or press punching. Therefore, the cut surfaces of the wound or laminated core assemblies are aligned, and the generation of steps on the side surfaces can be suppressed.
[0027] The wound or laminated core assembly is subjected to an annealing treatment. Since the region where the crystal structure changes on the cut surface of the electromagnetic steel sheet is extremely shallow, by performing the annealing treatment, the crystal structure of the surface layer of the cut surface can be restored, and the magnetic properties can be restored.
[0028] The core assembly with restored magnetic properties is immersed in varnish and then dried. Since the cut surface of the electromagnetic steel sheet material has fine irregularities, the wettability of the core assembly is reduced by the lotus effect, and the generation of steps on the side surfaces is suppressed, so the varnish accumulation can also be reduced. Therefore, the appearance defects and dimensional defects of the obtained core can be reduced.
[0029] The core produced by the present invention can be suitably used as a punched core for current transformers and as a core for in-vehicle current sensors. [Brief explanation of the drawing]
[0030] [Figure 1] Figure 1 shows (a) a photograph and (b) a magnified photograph of the cross-section of an electrical steel sheet material cut by the cutting method of the present invention. [Figure 2] Figure 2 is an enlarged schematic diagram comparing the microstructure of metals before and after annealing of cut surfaces obtained by fiber laser cutting and rotary blade cutting. [Figure 3] Figure 3 is a cross-sectional view of the core assembly of the present invention. [Figure 4] Figure 4 shows side views of the core assembly after annealing treatment by (a) fiber laser cutting and (b) and (c) rotary blade cutting. [Figure 5] Figure 5 is a graph comparing the BH curves of electrical steel sheets before and after annealing treatment using fiber laser cutting and rotary blade cutting. [Figure 6] Figure 6 is a magnified photograph showing the state of varnish accumulation in the core of the present invention. [Figure 7] Figure 7 is a cross-sectional view illustrating the mechanism by which varnish buildup is less likely to occur in the core of the present invention. [Figure 8] Figure 8 is a magnified photograph of the cross-section of an electrical steel sheet cut by a rotary blade. [Figure 9] Figure 9 is a cross-sectional view of a core assembly made by laminating electrical steel sheets cut with a rotary blade. [Figure 10] Figure 10 is a magnified photograph of varnish buildup occurring on the side surface of a core made of laminated electromagnetic steel sheets cut by a rotary blade. [Figure 11] Figure 11 is a cross-sectional view illustrating the mechanism by which varnish buildup occurs in a core made of laminated electromagnetic steel sheets cut by a rotary blade. [Modes for carrying out the invention]
[0031] The following describes a method for cutting an electrical steel sheet and a method for manufacturing a core according to one embodiment of the present invention.
[0032] The electrical steel sheets to be cut can be either grain-oriented or non-grain-oriented. The thickness of the electrical steel sheet is preferably 0.2 mm to 0.5 mm. Of course, the thickness of the electrical steel sheet is not limited to this.
[0033] The fiber laser used for cutting electrical steel sheets in this invention is supplied from a fiber laser processing machine to a laser unit via an optical fiber, and the laser is emitted from the laser head of the laser unit. The laser unit has an air nozzle built into the laser head that blows out assist gas, and the air nozzle blows high-pressure assist gas supplied from a gas cylinder towards the cutting position while the electrical steel sheet is being cut by the fiber laser.
[0034] Fiber lasers are, Fiber core diameter: 1 μm to 25 μm Laser output: 300W~1000W It can be set as follows. Of course, it is not limited to the above values.
[0035] For example, a fiber laser can be used to irradiate an electrical steel sheet with a spot diameter of 10 μm to 100 μm.
[0036] The assist gas used should have a relatively high oxygen concentration. For example, an assist gas with an oxygen concentration of 50% by volume or higher can be used, preferably 60% by volume or higher. The remainder can be substantially nitrogen. The use of a high-oxygen-concentration assist gas is to suitably oxidize the cut surface of the electrical steel sheet. The flow rate of the assist gas should preferably be between 30 liters / minute and 100 liters / minute. Of course, it is not limited to these values.
[0037] The feed rate for electrical steel sheets should preferably be adjusted to a cutting speed of 300 mm / sec to 500 mm / sec. The feed rate can be adjusted as appropriate depending on the thickness of the electrical steel sheet, the fiber core diameter, and the laser output.
[0038] By irradiating an electrical steel sheet with a fiber laser, the electrical steel sheet is cut, and electrical steel sheet material is obtained. Cutting electrical steel sheets with a fiber laser allows for curved processing and processing of complex outer edge shapes that cannot be achieved with rotary blades. Furthermore, while press punching requires a mold for each shape of electrical steel sheet material, fiber lasers do not require any molds.
[0039] In this invention, when cutting with a fiber laser, a high-oxygen assist gas is blown onto the cutting position of the electrical steel sheet, causing the cut surface to combine with oxygen and oxidize rapidly. In addition, the blowing of the assist gas blows away and purifies the dross such as molten metal that is generated on the cut surface.
[0040] Since the resulting electrical steel sheet is cut with a fiber laser while blowing a high-oxygen assist gas, an oxide film is formed on the cut surface as described above. This oxide film has the effect of suppressing the occurrence of red rust, which affects magnetic properties, etc. For example, electrical steel sheets cut with a blade or punched with a press do not have an oxide film formed on the cut surface, and red rust occurs, so they must be packaged with rust-preventive paper or the like. However, in the present invention, since an oxide film is formed on the cut surface of the electrical steel sheet, packaging with rust-preventive paper or the like is unnecessary.
[0041] When cutting with a fiber laser, the cut surface of the electrical steel sheet becomes instantaneously hot (over 1500°C), causing a change in the crystal structure of the surface layer. However, because fiber lasers can concentrate energy over a small area, the depth of the surface layer where the crystal structure changes is limited to approximately 10 μm to 50 μm. In contrast, with YAG lasers and CO2 lasers, the depth of the surface layer where the crystal structure changes is approximately 1000 μm or more. Therefore, with fiber lasers, the depth of the surface layer where the crystal changes is limited to an extremely shallow range, minimizing the degradation of magnetic properties. Since the depth to which the crystal structure changes progress on the cut surface of electrical steel sheets cut with a fiber laser is extremely shallow, the inventors discovered that by applying an annealing treatment to the electrical steel sheet material after cutting, it is possible to restore both the crystal structure and the magnetic properties. The annealing treatment will be described later.
[0042] Figure 1 shows (a) a photograph and (b) a magnified photograph of the cut surface 11 of the electrical steel sheet material 10 cut by the above cutting method. Referring to Figure 1, it can be seen that numerous fine irregularities are formed on the cut surface 11 cut by the fiber laser. When the electrical steel sheet is cut with a fiber laser, fine dome-like irregularities with a height of several tens of micrometers and a diameter of several tens of micrometers are formed on the cut surface of the electrical steel sheet material at a pitch of several tens of micrometers. On the other hand, there is no dross residue on the cut surface. Dross residue occurs due to reasons such as insufficient output of the fiber laser or cutting speed being too slow. Also, referring to Figures 1(a) and (b), the cut surface 11 is glossy, indicating that a colorless oxide film (several micrometers thick, as described later) is formed on the surface.
[0043] Figure 2 is a schematic diagram of the metallographic structure of the cut surface of electrical steel sheet material after cutting and before annealing. Figure 2(a) shows the cut surface of electrical steel sheet material cut with a fiber laser, and Figure 2(c) shows the cut surface of electrical steel sheet material cut with a rotary blade.
[0044] Referring to Figure 2(a), it can be seen that the surface of the electrical steel sheet cut by a fiber laser shows that a very shallow region of the surface (indicated by the sign α) is transformed by the heat of the fiber laser, resulting in a change in the crystal structure. On the other hand, as shown in Figure 2(c), no thermal transformation or change in crystal structure is observed in the surface cut by a rotary blade. Due to the change in crystal structure, the BH curve of the electrical steel sheet cut by a fiber laser shows a decrease in magnetic properties, i.e., a decrease in residual magnetic flux density, compared to the electrical steel sheet cut by a rotary blade (indicated by the dotted line), as shown by the solid line in Figure 5(a) later. However, as will be described later, these reduced magnetic properties can be restored by annealing.
[0045] Figure 3 is a cross-sectional view of a core assembly 13a in which multiple electromagnetic steel sheets 10, each cut to the same shape with a fiber laser, are stacked. As shown in the figure, the cut surface 11 of each electromagnetic steel sheet 10 is slightly inclined due to the cone-shaped reduction of the laser beam, but the sides of the stacked electromagnetic steel sheets 10 are aligned, indicating no stacking misalignment. Note that the inclination of the cut surface 11 is exaggerated in Figure 3, but the actual inclination is approximately 1° or less. By cutting with a fiber laser, the variation in the shape of the cut surface 11 and the variation in the width of the electromagnetic steel sheet 10 after cutting can be controlled with high precision (approximately ±0.05 mm or less).
[0046] The cut electrical steel sheets 10 are stacked to form a core assembly 13a as shown in Figure 3, and then subjected to annealing. The annealing conditions are 750°C to 850°C for 1 hour or more. Preferably, the conditions are 780°C to 820°C for 2 hours or more. The annealing atmosphere can be an inert gas atmosphere.
[0047] By applying annealing treatment to electromagnetic steel sheets cut by a fiber laser, the crystal structure of the surface layer of the cut surface, region α shown in Figure 2(a), is altered. As shown in Figure 2(b), the crystal structure is restored, and it can be seen that the fine crystal structure in the deeper layers is enlarged by the annealing treatment. As a result, the residual magnetic flux density also increases, as shown in Figure 5(b) later, and the magnetic properties can be restored.
[0048] Figure 4(a) is a side view of the core assembly 13a of the present invention after annealing, which was cut by a fiber laser. Figures 4(b) and 4(c) are side view of a core assembly 23a made of laminated electromagnetic steel sheets cut by a rotary blade, which has undergone the same annealing treatment for comparison. When the core assemblies 13a and 23a are annealed, a thin oxide film several hundred nanometers thick is formed on the side surface of the core assembly, regardless of the cutting method. However, as shown in Figure 4(a), the core assembly 13a of the present invention, which was cut by a fiber laser, does not exhibit temper color (light interference color) caused by the formation of a thin oxide film even after annealing. On the other hand, the core assembly 23a, which was cut by a rotary blade, exhibits temper color, as shown in Figures 4(b) and 4(c).
[0049] This is because a colorless oxide film several micrometers thick is initially formed on the cut surface 11 by the fiber laser. Because this colorless oxide film is formed first, even if a thin oxide film of several hundred nanometers thick is formed on top of it during the annealing process, temper color does not appear. On the other hand, on the cut surface 21 of the electromagnetic steel sheet material 20 cut by a rotary blade, a colorless oxide film several micrometers thick is not formed by cutting, and as a result of the annealing process, a thin oxide film of several hundred nanometers thick is directly formed on the cut surface 21, resulting in temper color. Cores 23 that have developed temper color generally have a poor appearance.
[0050] After annealing, the core assembly is immersed in varnish. The varnish is an impregnating adhesive, for example, a liquid containing a relatively low viscosity acrylic monomer and epoxy resin that easily penetrates between laminated electrical steel sheets.
[0051] By immersing the core assembly in varnish, the varnish penetrates between the laminated (including wound) electrical steel sheets, and the hardening of the varnish allows the electrical steel sheets to bond together, thereby creating a core. To facilitate the impregnation of the varnish between the electrical steel sheets, it is desirable to preheat the core assembly to about 80°C to 90°C and then immerse it in liquid varnish at room temperature and atmospheric pressure. This allows the varnish to effectively penetrate between the electrical steel sheets through capillary action as the preheated electrical steel sheets cool. After immersion in varnish, the varnish adhering to the sides can be dripped off by blowing air, and the varnish can be dried by holding it in a drying oven at about 110°C to 150°C for 2 to 3 hours. Referring to Figure 6, it can be seen that there is almost no varnish accumulation in the fabricated core 13. Some varnish accumulation 14 is observed, but it is in the form of a water droplet that has been repelled and rolled up at the cut surface 11. This varnish pool 14 is very small, with a diameter of about 0.05 mm and a height of about 0.02 mm, which is less than one-tenth the thickness of the electrical steel sheet, so its appearance and dimensions do not pose any practical problems.
[0052] The reason why varnish buildup is unlikely to form on the core of the present invention is as follows. As described above, on the cut surface 11 of the electromagnetic steel sheet material 10 cut by a fiber laser, numerous dome-like fine irregularities with a height of several tens of micrometers and a diameter of several tens of micrometers are formed at intervals of several tens of micrometers (see Figure 1). The core assembly is formed by laminating electromagnetic steel sheets having these cut surfaces. Because the wettability is reduced due to the lotus effect caused by the numerous fine irregularities formed on the cut surface 11, liquid varnish cannot adhere to the cut surface 11. For this reason, as shown in Figure 7, the varnish remains between the electromagnetic steel sheets 10, 10 as indicated by reference numeral 15, but the varnish that adheres to the cut surface 11 is repelled from the cut surface 11. Therefore, as shown in Figure 6, no varnish buildup occurs on the side surface of the core 13. Another reason is that, as shown in Figure 3, the electromagnetic steel sheets 10 are cut with high dimensional accuracy, so steps are less likely to occur on the sides of the core assembly 13a formed by stacking them. As a result, the amount of varnish that accumulates on the sides of the core 13 can be reduced, and the occurrence of varnish buildup can be reduced.
[0053] According to the present invention, by using a fiber laser to cut electrical steel sheets, curve processing that cannot be achieved with rotary blades can be realized, and the yield of electrical steel sheets can be improved. By cutting electrical steel sheets while blowing a high-oxygen assist gas, an oxide film is formed on the cut surface, preventing the occurrence of red rust. In addition, the cut surface of electrical steel sheets cut by a fiber laser can be made less susceptible to deterioration of magnetic properties, and these magnetic properties can be restored by annealing. Furthermore, because numerous fine irregularities are formed on the cut surface of the electrical steel sheet, varnish is less likely to adhere to the cut surface due to the lotus effect, and varnish accumulation in the core can be reduced. The core of the present invention has excellent magnetic properties and few defects in appearance or dimensions, so it can be suitably used as a core for various applications such as power transformers, choke coils, reactors, current transformers, and automotive current sensors.
[0054] As described above, the present invention can suppress the occurrence of red rust on the cut surface of electrical steel sheets, so electrical steel sheets can be cut in advance and stockpiled using the cutting method of the present invention. Later, as needed, these electrical steel sheets can be used as cores or the like and subjected to annealing and impregnation treatments.
[0055] The above description is for illustrative purposes only and should not be interpreted as limiting or restricting the scope of the invention as described in the claims. Furthermore, it goes without saying that the configuration of each part of the present invention is not limited to the above embodiments and can be modified in various ways within the technical scope described in the claims.
[0056] Furthermore, when cutting electrical steel sheets, it is possible to combine cutting methods, such as using a blade for straight sections and a fiber laser for curved sections. [Examples]
[0057] <Example 1> Electromagnetic steel sheets were cut using a fiber laser and a rotary blade, and the cut surfaces were observed before and after annealing, while the BH curve was measured.
[0058] The electrical steel sheet was a grain-oriented electrical steel sheet with a thickness of 0.23 mm, and was cut by a fiber laser under the following conditions: fiber core diameter of 14 μm, laser output of 400 W, cutting speed of 500 mm / second, oxygen concentration of 100 volume% of assist gas, and flow rate of 30 liters / minute (Example of Invention). For comparison, a grain-oriented electrical steel sheet of the same thickness was also cut by a rotary blade (Comparative Example).
[0059] Schematic diagrams of the metal structure before annealing treatment of the cut surface of the inventive example (laser cutting) and the cut surface of the comparative example (blade cutting) are shown in Figures 2(a) and 2(c), respectively. As shown in Figure 2(a), the cut surface of the inventive example is altered by the heat of the fiber laser in the region indicated by the symbol α, and the crystal structure has changed. On the other hand, as shown in Figure 2(c), no alteration or change in crystal structure is observed in the blade cutting surface. When the BH curve was measured for these electrical steel sheets before annealing treatment, as shown in Figure 5(a), it was found that the saturation magnetic flux density of the inventive example (solid line) was lower than that of the comparative example (dotted line), indicating a decrease in magnetic properties. In addition, the iron loss for both was 2.90 W / kg and 3.00 W / kg, respectively, and the average grain size of the crystal structure was 100 μm.
[0060] Next, the electrical steel sheets of the inventive example and the comparative example were subjected to annealing treatment at 800°C for 2 hours. As a result, as shown in Figure 2(b), region α in Figure 2(a) disappeared in the inventive example. Also, as shown in Figure 2(b) and Figure 2(d) for the comparative example, the average grain size of the crystals in both the inventive example and the comparative example increased to 150 μm to 200 μm. The iron loss for both was 2.37 W / kg and 2.17 W / kg, respectively, which was an improvement compared to before the annealing treatment.
[0061] Furthermore, when the BH curves of the inventive example and the comparative example were measured after annealing treatment, as shown in Figure 5(b), the inventive example (solid line) had almost the same saturation magnetic flux density as the comparative example (dotted line), indicating that the magnetic properties were restored to the same level as the comparative example through annealing treatment.
[0062] In other words, the invention demonstrates that by irradiating an electrical steel sheet with a fiber laser while blowing a high-oxygen concentration assist gas onto it, and then performing an annealing treatment, it is possible to achieve magnetic properties equivalent to those obtained when cutting with a rotary blade. On the other hand, since the fiber laser can easily process not only straight lines but also curves, it is possible to obtain a core with a circular cross-section in a wound state. Furthermore, since the laser unit does not wear out like a rotary blade, it is possible to prevent cutting defects caused by wear on the rotary blade, thus reducing the time required for blade tip maintenance by experienced craftsmen. Moreover, since the electrical steel sheet does not slip away when cutting with a rotary blade, an improvement in yield can also be achieved.
[0063] <Example 2> We cut electrical steel sheets by varying the irradiation conditions of the fiber laser and the oxygen concentration of the assist gas, and observed whether or not red rust formed in a high-temperature, high-humidity atmosphere.
[0064] The electrical steel sheets were 0.23 mm thick grain-oriented electrical steel sheets, and were cut by a fiber laser under eight different conditions (all with a flow rate of 30 liters / min): a fiber core diameter of 14 μm, laser output of 400 W, cutting speeds of 300 mm / sec and 500 mm / sec, and assist gas oxygen concentrations of 40 vol% (reference example), 50 vol%, 70 vol% and 100 vol% (all inventive examples). For comparison, grain-oriented electrical steel sheets of the same thickness were also cut using a rotary blade (comparative example). After cutting, all test materials were subjected to annealing treatment at 800°C for 2 hours.
[0065] Each of the obtained test materials was placed in a high-temperature, high-humidity environment at 85°C and 85% humidity, and the number of days until red rust was observed on the cut surface was measured. The results are shown in Table 1.
[0066] [Table 1]
[0067] Referring to Table 1, in all of the invention examples where fiber laser cutting was performed under an assist gas atmosphere with an oxygen concentration of 50 volume% or higher, no red rust was observed on the cut surface for more than three weeks. More specifically, in the invention example where cutting was performed under an assist gas atmosphere with an oxygen concentration of 70 volume% or higher, no red rust was observed for four weeks. On the other hand, in the invention example with an assist gas oxygen concentration of 40 volume% and the comparative example of cutting with a blade, red rust appeared on the cut surface within one day.
[0068] From the above, it can be seen that by performing fiber laser cutting in an assist gas atmosphere with an oxygen concentration of 50 volume% or higher, an oxide film is formed on the cut surface of the electrical steel sheet, and the formation of this oxide film suppresses the occurrence of red rust. In these inventions, red rust is unlikely to occur even when left in an oxidizing atmosphere for a long period of time, so there is no need for rust prevention treatment or packaging with rust-preventive paper, and this is especially effective when the product is large when stored in a hoop state. In order to reliably form an oxide film, it is desirable to use an assist gas with an oxygen concentration of 60 volume% or higher.
[0069] <Example 3> A current transformer was fabricated using cores created by stacking E-shaped cores, one made by cutting the entire circumference with a fiber laser, and the other by punching out the same shape with a press machine. The output voltage characteristics were then measured before and after annealing.
[0070] The electrical steel sheet was a non-oriented electrical steel sheet with a thickness of 0.35 mm. An E-shaped core was fabricated by cutting with a fiber laser under the following conditions: fiber core diameter of 14 μm, laser output of 300 W, cutting speed of 300 mm / second, oxygen concentration of 100 volume%, and flow rate of 30 liters / min for the assist gas (laser-cut core). For comparison, an E-shaped core of the same shape was also fabricated by punching out a non-oriented electrical steel sheet of the same thickness using a press (comparative example: punched core).
[0071] Using iron cores formed by stacking the E-type cores prepared as described above, current transformers with a turns ratio of 1:3000 were fabricated (Table 2, before annealing), and the output voltage characteristics were measured. Furthermore, after annealing the E-type cores of the inventive example and comparative example at 800°C for 2 hours, current transformers were fabricated again (Table 2, after annealing), and the output voltage characteristics were measured. The results are shown in Table 2.
[0072] [Table 2]
[0073] Referring to Table 2, the invention example before annealing treatment shows a 3.2% decrease in properties compared to the comparative example, but after annealing treatment, this is improved to a 0.3% decrease. The difference after annealing treatment is at a level that is sufficiently practical. In actual operation, if laser cutting is used only for processing the electrical steel sheet material and the E-type core is manufactured by punching, the part affected by the heat from laser cutting will be only one surface on the back of the E-type core, so the difference in properties will be further improved. [Explanation of Symbols]
[0074] 10 Electromagnetic steel sheet material 11 Cut surface 13 cores 13a Core Assembly 14 Varnish pooling 15 Varnish
Claims
1. A cutting step involves irradiating an electrical steel sheet with a fiber laser while blowing an assist gas with an oxygen concentration of 50 volume percent or more onto the sheet to obtain an electrical steel sheet material with a rust-preventive effect on the cut surface, The process includes an annealing step in which the cut electrical steel sheet material is subjected to an annealing treatment to restore its magnetic properties, Method for manufacturing electrical steel sheets.
2. The fiber laser in the cutting step is Fiber core diameter: 1 μm to 25 μm Laser output: 300W to 1000W Cutting speed: 300mm / sec to 500mm / sec, The electromagnetic steel sheet is irradiated with, A method for manufacturing an electrical steel sheet according to claim 1.
3. The oxygen concentration in the cutting step is 60% by volume or more, with the remainder being nitrogen. A method for manufacturing an electrical steel sheet according to claim 1 or claim 2.
4. The annealing treatment in the annealing step is carried out under conditions of 750°C to 850°C for 1 hour or more. A method for manufacturing an electrical steel sheet according to any one of claims 1 to 3.
5. A cutting step to obtain an electrical steel sheet material having a rust-preventive effect on the cut surface, by irradiating an electrical steel sheet with a fiber laser while blowing an assist gas with an oxygen concentration of 50 volume percent or more onto the electrical steel sheet, A winding or lamination step in which the electromagnetic steel sheet material cut by the cutting step is wound or laminated to obtain a core assembly, An annealing step in which the core assembly is subjected to an annealing treatment to restore the magnetic properties of the electromagnetic steel sheet material, and Immersion step of immersing the core assembly in varnish, A method for producing a core that includes [the specified element].
6. The annealing treatment in the annealing step is carried out under conditions of 750°C to 850°C for 1 hour or more. The method for manufacturing a core according to claim 5.
7. The varnish in the immersion step is a material comprising an acrylic monomer and an epoxy resin. A method for manufacturing a core according to claim 5 or claim 6.
8. The fiber laser in the cutting step is Fiber core diameter: 1 μm to 25 μm Laser output: 300W to 1000W Cutting speed: 300mm / sec to 500mm / sec, The electromagnetic steel sheet is irradiated with, A method for manufacturing a core according to any one of claims 5 to 7.
9. The oxygen concentration in the cutting step is 60% by volume or more, with the remainder being nitrogen. A method for manufacturing a core according to any one of claims 5 to 8.