Motor core manufacturing method and heat treatment device used therein

Abstract

To provide a method for manufacturing a motor core capable of simultaneously performing strain removal and grain growth in a laminate.SOLUTION: A method for manufacturing a motor core comprises: a preparation step S001 for preparing a laminate S of an electromagnetic steel sheet processed into a predetermined shape; a first heating step S003 for heating the laminate S at an atmospheric temperature of 500-800°C in an atmospheric gas having a dew point of -20°C or less composed of a low oxidizing gas and / or a reducing gas; and a second heating step S004 for soaking the laminate S at 1000-1200°C in a vacuum of 100 Pa or less after the first heating step.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a motor core and a heat treatment apparatus used therefor. [Background technology]

[0002] Motor cores, such as rotor cores and stator cores, are manufactured by stamping strip-shaped electromagnetic steel sheets into a predetermined shape and then laminating these steel sheets of the predetermined shape. During this process, processing distortion occurs during stamping and crimping during lamination. It is known that if a motor core is manufactured with this processing distortion remaining, the magnetic path will become distorted, preventing the motor from performing as designed. Therefore, efforts are being made to reduce processing distortion by annealing the laminate of electromagnetic steel sheets (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-161243 Summary of the Invention [Problem to be solved by the invention]

[0004] In order to obtain motor cores with excellent magnetic properties, it is believed that it is effective to grow the crystal grains of electrical steel sheets to 100 μm or more. However, the annealing temperature used in conventional stress relief annealing is low, and only a small amount of grain growth can be expected. While it is possible to use steel sheets that have been adjusted to the desired crystal grain size through prior heat treatment, this increases the cost of material procurement.

[0005] SUMMARY OF THE INVENTION In view of the above circumstances, an object of the present invention is to provide a method for manufacturing a motor core that can simultaneously remove distortion and grow grains in a laminate, and a heat treatment apparatus used therefor. [Means for solving the problem]

[0006] Thus, the motor core manufacturing method according to the first aspect of the present invention is defined as follows: a preparation step of preparing a laminate of electromagnetic steel sheets processed into a predetermined shape; a first heating step of heating the laminate at an atmospheric temperature of 500 to 800°C in an atmospheric gas consisting of a low oxidizing gas and / or a reducing gas having a dew point of -20°C or less; After the first heating step, a second heating step is performed in which the laminate is uniformly heated at 1000 to 1200° C. in a vacuum of 100 Pa or less.

[0007] According to the motor core manufacturing method of the first aspect defined in this manner, the laminate is heated to a temperature (1000 to 1200°C) at which grain growth is possible in a short period of time through a series of heat treatments including the first heating step and the second heating step, so that distortion relief and grain growth can be performed simultaneously in the laminate. In addition, in the first aspect of the motor core manufacturing method, the laminate is heated in two stages: convection heating using atmospheric gas and subsequent vacuum heating, which allows the laminate to be efficiently heated to a temperature at which grain growth is possible while suppressing oxidation of the laminate.

[0008] Here, in the temperature range of 1000 to 1200°C, the rigidity of the laminate decreases during treatment, making it prone to deformation. For this reason, it is desirable to heat-treat the laminate while it is placed on a jig made of a C / C composite (second aspect).

[0009] Furthermore, the less oxidizing gas may be nitrogen, and the reducing gas may be hydrogen and / or carbon monoxide (third aspect).

[0010] As described above, according to the motor core manufacturing method of the present invention, distortion relief and grain growth of the laminate can be carried out simultaneously, so that the average crystal grain size of the electromagnetic steel sheet before the first heating step can be made less than 100 μm (fourth aspect), and then grain growth can be carried out to make the average crystal grain size of the electromagnetic steel sheet after the second heating step 100 to 300 μm (fifth aspect). The average grain size of the electrical steel sheets that make up the laminate is measured as follows: A test piece is cut so that the cross section of the sheet thickness can be observed, and the grain boundaries are etched by nital etching to reveal them. The grain sizes of 100 or more grains are then measured by the line segment method to determine the average grain size.

[0011] A heat treatment apparatus according to a sixth aspect of the present invention is defined as follows: A heat treatment apparatus for carrying out the manufacturing method according to the first aspect, a plurality of heat treatment chambers for heat treating the laminate; a roller disposed in the heat treatment chamber and supporting and transporting the laminate; The heat treatment chamber is a roller hearth type heat treatment apparatus in which a first heating chamber in which the first heating step is performed, a second heating chamber in which the second heating step is performed, and an annealing chamber in which the laminate is annealed after the second heating step are arranged in series. By using the heat treatment apparatus of the sixth aspect defined in this way, the motor core manufacturing method of the first aspect can be carried out.

[0012] A heat treatment apparatus according to a seventh aspect of the present invention is defined as follows: A heat treatment apparatus for carrying out the manufacturing method according to the first aspect, (A) a batch-type heating chamber arranged along the conveying track, which performs the first heating step and / or the second heating step; (B) a batch-type cooling chamber arranged along the conveying track, which slowly cools the laminate after the second heating step; (C) a transport unit having a heat-retaining chamber that accommodates the workpiece and keeps it warm with a heater, and a delivery chamber that delivers the laminate between the heating chamber or the cooling chamber and the heat-retaining chamber; A heat treatment device comprising: The heat treatment apparatus of the seventh aspect defined in this manner can also be used to carry out the motor core manufacturing method of the first aspect. [Brief explanation of the drawings]

[0013] [Figure 1] 3 is a flowchart showing the steps of a method for manufacturing a motor core according to one embodiment of the present invention. [Figure 2] 2 is a diagram showing the overall configuration of a roller hearth type heat treatment device used in the manufacturing method of the embodiment. FIG. [Figure 3] FIG. 10 is a diagram showing a jig on which a laminate is placed. [Figure 4] FIG. 4 is a diagram showing an example of a heat pattern in the manufacturing method of the embodiment. [Figure 5] FIG. 10 is a diagram showing the overall configuration of a heat treatment apparatus according to another embodiment of the present invention. [Figure 6] 6 is a diagram showing the internal structure of the heating chamber and the transfer unit of FIG. 5. [Figure 7] FIG. 2 is a plan view of the heating chamber and the transport unit. DETAILED DESCRIPTION OF THE INVENTION

[0014] Next, embodiments of the present invention will be described in detail below.

[0015] The motor core manufacturing method according to one embodiment of the present invention can be performed as one step in the manufacture of motor cores such as rotor cores, stator cores, etc. The laminated body S that constitutes the motor core is formed in a separate step (not shown) by laminating steel sheets of a predetermined shape obtained by punching strip-shaped electromagnetic steel sheets by press working, and then joining them by caulking or the like.

[0016] As shown in FIG. 1, the manufacturing method of this example can be a method including a preparation step S001 of preparing a laminate S of electromagnetic steel sheets processed into a predetermined shape, a degreasing step S002 of evaporating oil adhering to the steel sheets that make up the laminate S, a first heating step S003 of heating the laminate S at an ambient temperature of 500 to 800°C in an ambient gas with a dew point of −20°C or lower, a second heating step S004 of soaking the laminate S at 1000 to 1200°C in a vacuum, a slow cooling step S005 of slowly cooling the laminate S, and a rapid cooling step S006 of rapidly cooling the laminate S after slow cooling. In the manufacturing method of this example, by carrying out this series of steps, strain relief and grain growth can be carried out simultaneously in the laminate S, so the grain size (average crystal grain size) of the electrical steel sheet prepared in preparation step S001 is desirably less than 100 μm from the viewpoint of workability. After carrying out the series of steps, the average crystal grain size of the electrical steel sheet can be made 100 to 300 μm, which provides excellent magnetic properties.

[0017] 2 shows a schematic overall configuration of a roller hearth type heat treatment device 1 used in this manufacturing method. This heat treatment device 1 continuously heat-treats a laminate S of electromagnetic steel sheets placed on a jig 80.

[0018] As shown in Fig. 3(A), the jig 80 on which the laminate S is placed includes a plurality of plate-like trays 81 (81A, 81B, 81C, and 81D in this example) and short columnar spacers 82 erected at the four corners of the trays 81A, 81B, and 81C, excluding the top tray 81D. As shown in Fig. 3(B), a plurality of laminates S are placed on the flat upper surface of each tray 81. The laminates S and the jig 80 are transported together as a workpiece W. The jig 80 in this example is made of a C / C composite, which has high heat resistance and little loss of strength in the temperature range of 1000 to 1200°C. A C / C composite is made of a carbon composite material reinforced with high-strength carbon fiber. By placing the laminate S on a jig made of the C / C composite, deformation of the laminate during high-temperature annealing can be suppressed.

[0019] Next, the configuration of the heat treatment apparatus 1 will be described. As shown in Fig. 2, the heat treatment apparatus 1 has an inlet 6 for loading on the left side of the furnace body 3 in the figure, and an outlet 7 for unloading on the right side of the furnace body 3 in the figure. The inlet 6 and the outlet 7 are provided with doors 23 and 24, respectively, which are opened and closed by an air cylinder type opening and closing device 22. That is, in this example, the stack S loaded from the left side in the figure is transported toward the right side in the figure.

[0020] Inside the furnace body 3, a front chamber 10, a degreasing chamber 12, a first heating chamber 14, a second heating chamber 16, a slow cooling chamber 18, and a rapid cooling chamber 20 are arranged in series along the direction in which the laminate S is transported. Air cylinder type opening and closing devices 26 are provided between each chamber, and drive opening and closing doors 27, 28, 29, 30, and 31 formed in each chamber.

[0021] Anterior chamber 10 is a section that prevents atmospheric air from entering downstream degreasing chamber 12. A degassing pipe 34 connected to vacuum pump 33 is connected to anterior chamber 10, and the pressure inside anterior chamber 10 is reduced to a vacuum of 100 Pa or less by vacuum pump 33.

[0022] The degreasing chamber 12 is a section where oil adhering to the steel plates (the steel plates that constitute the laminate S) during the punching process is evaporated. A degassing pipe 37 connected to a vacuum pump 36 is connected to the degreasing chamber 12, and the interior of the degreasing chamber 12 is depressurized to a vacuum state of 100 Pa or less by the vacuum pump 36. An electric heater 38 is also provided as heating means for heating the interior of the degreasing chamber 12 to a temperature at which degreasing is possible (300 to 500°C). As a result, the laminate S contained in the degreasing chamber 12 is heated under vacuum, and the oil adhering to the laminate S can be evaporated. The oil vapor is discharged to the outside through the degassing pipe 37 and is collected in a cold trap as necessary.

[0023] The first heating chamber 14, together with the downstream second heating chamber 16 and slow cooling chamber 18, is a section for annealing the laminate S. A heater 40 is provided inside the first heating chamber 14 as a heating means. Also connected to the first heating chamber 14 are a degassing pipe 42 connected to a vacuum pump 41, and an atmospheric gas supply pipe 44, which can supply nitriding gas (low-oxidizing gas) with a dew point of −20° C. or lower as atmospheric gas into the chamber.

[0024] In the first heating chamber 14, the interior temperature is set to an ambient temperature of 500 to 800°C, and convection heat transfer heating is performed on the laminate S in the first heating chamber 14 using nitrogen gas. By using convection heat transfer heating via gas, the heating time for the laminate S can be shortened compared to vacuum heating. If the gas is pressurized, the heating capacity can be further improved. Although the C / C composite jig 80 has the problem of being vulnerable to high-temperature oxidizing atmospheres, the first heating chamber 14 contains an atmosphere of low-oxidizing gas and / or reducing gas with a dew point of -20°C or less, which effectively prevents the oxidation resistance of the C / C composite jig 80 from decreasing.

[0025] The second heating chamber 16 is a section in which the laminate S is uniformly heated to 1000 to 1200° C. in a vacuum of 100 Pa or less, causing grain growth of the crystal grains of the electrical steel sheets. For this reason, an electric heater 48 is provided as heating means inside the second heating chamber 16. In addition, a degassing pipe 50 connected to a vacuum pump 49 is connected to the second heating chamber 16, and the inside of the second heating chamber 16 is depressurized to a vacuum state of 100 Pa or less by the vacuum pump 49. In a high-temperature atmosphere, the number of gas molecules in the atmosphere decreases, and the ability of convection heating using gas decreases. For this reason, in consideration of cost benefits, vacuum heating is performed in the second heating chamber 16, which does not require the introduction of gas.

[0026] The slow cooling chamber 18 is a section in which the soaked laminate S is slowly cooled at a predetermined cooling rate. The slow-cooling chamber 18 is connected to a degassing pipe 53 connected to a vacuum pump 52, and also to an atmospheric gas supply pipe 54, through which nitrogen gas having a dew point of −20° C. or less can be supplied into the chamber as atmospheric gas. The annealing chamber 18 is also equipped with a heat exchanger 57 for cooling the ambient gas and a fan (not shown) for circulating the ambient gas, and the ambient gas in the annealing chamber 18 can be cooled by the heat exchanger 57, thereby annealing the laminate S at a predetermined cooling rate.

[0027] The rapid cooling chamber 20 is a section for rapidly cooling the slowly cooled laminate S. Similar to the slow cooling chamber 18, the rapid cooling chamber 20 is also connected to an atmospheric gas supply pipe 60, and is equipped with a heat exchanger 63 for cooling the atmospheric gas and a fan (not shown) for circulating the atmospheric gas.

[0028] Conveying rollers 70 are arranged in parallel along the conveying direction in each chamber constituting the heat treatment apparatus 1. The rollers 70 arranged in the antechamber 10, the degreasing chamber 12, the first heating chamber 14, the second heating chamber 16, the slow cooling chamber 18, and the rapid cooling chamber 20 respectively constitute roller groups 71, 72, 73, 74, 75, and 76. These roller groups 71, 72, 73, 74, 75, and 76 are each independently driven to sequentially convey the laminate S placed on the jig 80 downstream in the conveying direction (to the right in the drawing).

[0029] The rollers 70 can be made of metal such as stainless steel or heat-resistant cast steel, but these are prone to deformation when used at temperatures above 900°C. Therefore, in this example, rollers 70 installed in the first heating chamber 14, the second heating chamber 16, and the slow cooling chamber 18 are made of a C / C composite, which has little loss of strength at high temperatures.

[0030] Next, a series of heat treatment operations in the heat treatment apparatus 1 when the laminate S is loaded will be described. The series of operations in the heat treatment apparatus 1 is based on the heat pattern shown in FIG.

[0031] First, the laminate S is prepared in a state in which it is placed on a jig 80 . Then, roller group 71 is driven to load laminate S into front chamber 10. When door 23 is closed, vacuum pump 33 releases the air inside the chamber to the outside, and the pressure inside front chamber 10 is reduced to a vacuum pressure similar to that of degreasing chamber 12.

[0032] Thereafter, the exit door 27 of the anterior chamber 10 and the entrance door 27 of the degreasing chamber 12 are opened, the roller groups 71 and 72 are driven, the laminate S is transferred into the degreasing chamber 12, and the door 27 is closed. The interior of the degreasing chamber 12 is maintained at a temperature at which degreasing is possible (here, 350°C), and the laminate S loaded into the degreasing chamber 12 is heated to the degreasing temperature of 350°C, and the oil adhering to the laminate S is evaporated.

[0033] Then, with the pressure inside the degreasing chamber 12 and the first heating chamber 14 reduced to the same vacuum pressure, the exit door 28 of the degreasing chamber 12 and the entrance door 28 of the first heating chamber 14 are opened, the roller groups 72, 73 are driven, the laminate S is transported into the first heating chamber 14, and the door 28 is closed. The inside of the first heating chamber 14 is maintained at a predetermined set temperature (700°C in this case), and the laminate S placed in the first heating chamber 14 is heated to 700°C, which is the set temperature of the first heating chamber 14. In order to accelerate the temperature rise at this time, nitrogen gas is supplied into the first heating chamber 14, and the temperature rise of the laminate S is accelerated by convective heating by the nitrogen gas and heat radiation by the heater 40.

[0034] When the temperature of the laminate S reaches near the set temperature of 700°C, the nitrogen gas inside the first heating chamber 14 is evacuated, and the inside of the first heating chamber 14 is depressurized to a vacuum pressure (100 Pa or less) similar to that inside the second heating chamber 16. The exit door 29 of the first heating chamber 14 and the entrance door 29 of the second heating chamber 16 are opened, and the roller groups 73, 74 are driven to transfer the laminate S into the second heating chamber 16, and the door 29 is closed. The interior of the second heating chamber 16 is maintained at a predetermined set temperature (here, 1100°C), and the laminate S loaded into the second heating chamber 16 is heated to the set temperature by heat radiation from the heater 48 in a vacuum of 100 Pa or less, and then maintained at a uniform temperature.

[0035] After the predetermined time of soaking, the exit door 30 of the second heating chamber 16 and the entrance door 30 of the annealing chamber 18 are opened, the roller groups 74, 75 are driven, the laminate S is transported into the annealing chamber 18, and the door 30 is closed. In the slow cooling chamber 18, the laminate S is slowly cooled to 500°C at an average cooling rate of 200°C / H by convection heat transfer caused by nitrogen gas supplied into the slow cooling chamber 18.

[0036] After annealing, the exit door 31 of the annealing chamber 18 and the entrance door 31 of the rapid cooling chamber 20 are opened, the roller groups 75, 76 are driven, the laminate S is transferred into the rapid cooling chamber 20, and the door 31 is closed. In the rapid cooling chamber 20, the ambient gas is circulated while being cooled by the heat exchanger 63, thereby cooling the laminate S. After cooling, the door 24 is opened and the laminate S is carried out, completing a series of operations related to the heat treatment of the laminate S.

[0037] As described above, according to the motor core manufacturing method using the heat treatment device 1 of this embodiment, the laminate S is heated to a temperature (1000 to 1200°C) at which grain growth is possible through a series of heat treatments including the first heating step S003 and the second heating step S004, so that distortion removal and grain growth of the laminate S can be performed simultaneously. In addition, in this manufacturing method, the laminate S is heated in two stages: convection heating using an atmospheric gas with a dew point of -20°C or less, followed by vacuum heating. This allows the laminate S to be efficiently heated to a temperature at which grain growth is possible while suppressing oxidation of the laminate S.

[0038] Here, in the temperature range of 1000 to 1200°C, the rigidity of the laminate S decreases during processing, making it more susceptible to shape deformation. In this embodiment, the laminate S is placed on a jig 80 made of a C / C composite and subjected to heat processing, thereby making it possible to suppress deformation of the laminate S.

[0039] According to the manufacturing method of this embodiment, distortion removal and grain growth of the laminate S can be performed simultaneously, so that the average crystal grain size of the electromagnetic steel sheet before the first heating step is less than 100 μm, and by performing grain growth, the average crystal grain size of the electromagnetic steel sheet after the second heating step can be made 100 to 300 μm, which has excellent magnetic properties.

[0040] Next, a heat treatment apparatus 1B according to another embodiment of the present invention will be described. 5 is a diagram showing the overall configuration of heat treatment apparatus 1B. In the figure, reference numeral 90 denotes a rail serving as a conveying track extending linearly from side to side in the figure, and multiple batch-type processing chambers (here, a degreasing chamber 93, a heating chamber 94, and a cooling chamber 95) are arranged linearly along this rail 90 with their openings 100 facing in the same direction, upward in the figure. Also, a loading table 92 is provided on the right end side of the figure, and an extraction table 96 is provided on the left end side.

[0041] In the heat treatment device 1B, a workpiece W consisting of a laminate S and a jig 80 (see Figure 3) is subjected to a degreasing process (see Figure 1) in a degreasing chamber 93, a first heating process and a second heating process (see Figure 1) in a heating chamber 94, and a slow cooling process and a rapid cooling process (see Figure 1) in a cooling chamber 95.

[0042] The heat treatment apparatus 1B of this example has, in addition to the above-mentioned degreasing chamber 93, heating chamber 94, and cooling chamber 95, a transport unit 97 that runs on rails 90. The transport unit 97 has a delivery chamber 98 and a heat retention chamber 99, and delivers the workpiece W between the loading table 92, each of the treatment chambers 93, 94, and 95, and the extraction table 96.

[0043] FIG. 6 shows the internal structure of the heating chamber 94 and the transfer unit 97. As shown in the figure, the heating chamber 94 has a cylindrical furnace shell 122 with a bottom and a heat insulating material 124 disposed inside the shell. The heat insulating material 124 forms a cylindrical heat insulating wall 125 with a bottom. The heat insulating wall 125 forms a processing chamber 126 inside. The heating chamber 94 is provided with a suction port 132. The suction port 132 is connected to a vacuum pump (not shown) through a suction pipe, so that the inside of the heating chamber 94 is suctioned to a vacuum by the vacuum pump.

[0044] The heating chamber 94 is also provided with a supply port 134 for supplying nitrogen gas (low-oxidizing gas) as atmospheric gas with a dew point of −20° C. or lower into the heating chamber 94. The nitrogen gas supplied from the supply port 134 is first guided to a header 136, and then introduced into the heating chamber 94, more specifically, into the processing chamber 126 inside the insulating wall 125, through a branch pipe 137 connected to the header 136 and a nozzle 138 provided on the branch pipe 137.

[0045] The heat insulating wall 125 is provided with a convection fan 139 that agitates and convects the nitrogen gas supplied within the processing chamber 126, thereby promoting the temperature rise of the workpiece W during the temperature rise period, and a motor 140 that rotates the fan 139. The heat insulating wall 125 is also provided with a water-cooled panel 141 near the motor 140 to protect the motor 140 from heat. A heater 128 is also provided within the processing chamber 126 as a heating means.

[0046] The processing chamber 126 is provided with a stand 130. The workpiece W in the processing chamber 126 is placed and supported on the stand 130. The heating chamber 94 is also provided with a sliding door 142 that opens and closes the opening 100.

[0047] The structure of the heating chamber 94 has been described above, but the other chambers, such as the degreasing chamber 93 and the cooling chamber 95, have basically the same structure. However, the cooling chamber 95 is provided with a heat exchanger (not shown) therein that lowers the temperature of the ambient gas by heat exchange.

[0048] The transport unit 97 has a delivery chamber 98 at the front on the side of the processing chambers 93, 94, 95, and a heat-retaining chamber 99 at the rear on the opposite side for keeping the workpiece W warm.

[0049] The delivery chamber 98 has a pressure-resistant rectangular cylindrical wall 158, and defines therein a storage chamber 160 for storing the workpiece W. A delivery mechanism 162 is provided in this storage chamber 160. The transfer mechanism 162 transfers the workpiece W between each processing chamber 93, 94, 95 and the rear heat-retaining chamber 99, and has a fork portion 162A and horizontal slide members 162B, 162C, which are slid horizontally to transfer the workpiece W using the fork portion 162A.

[0050] This delivery chamber 98 is provided with a suction port 163, which is connected to a vacuum pump 164 shown in Figure 7 through a suction pipe 166A, so that the inside of the delivery chamber 98 is suctioned to a vacuum by the vacuum pump 164. An on-off valve 168A made of a solenoid valve is provided on the suction pipe 166A, and the on-off valve 168A opens and closes the suction port 163 and the vacuum pump 164 so as to communicate with each other or cut off communication therebetween.

[0051] 7, the delivery chamber 98 is also provided with a supply port 170 through which nitrogen gas is supplied into the delivery chamber 98. The delivery chamber 98 has an opening 172 without a door at its front end, i.e., the left end in FIG. 6. The delivery chamber 98 is provided with a flat frame-shaped packing 174 around the opening 172. The delivery chamber 98 is docked with each of the processing chambers 93, 94, and 95 by moving forward toward the processing chambers 93, 94, and 95 so that the frame-shaped packing 174 is in airtight contact with the outer surfaces of the processing chambers 93, 94, and 95.

[0052] On the other hand, the latter heat-retaining chamber 99 has a heat insulating material 178 inside a bottomed cylindrical furnace shell 176, and the heat insulating material 178 constitutes a heat insulating wall 180. The heat insulating wall 180 forms a storage chamber 182 inside, which is configured to store the workpiece W. A stand 184 is provided in the storage chamber 182. The workpiece W in the storage chamber 182 is placed on the stand 184 and supported.

[0053] 7, the heat-retaining chamber 99 is provided with a suction port 186 for drawing a vacuum inside the chamber, and this suction port 186 is connected to the vacuum pump 164 through a suction pipe 166B. An on-off valve 168B made of an electromagnetic valve is provided on the suction pipe 166B, and the suction port 186 and the vacuum pump 164 are connected or disconnected by opening and closing the on-off valve 168B.

[0054] The heat-retaining chamber 99 is provided with a heater 220 for keeping the workpiece W warm inside the heat-retaining wall 180. As shown in Fig. 2, the heat-retaining chamber 99 is provided with doors 210, 212 made of a heat-insulating material that open and close an upper opening 204 and a lower opening 206 of the heat-retaining wall 180, and these are opened and closed by cylinders 214, 216.

[0055] The heat-retaining chamber 99 also has a supply port (not shown) in the furnace shell 176 for supplying nitrogen gas as a cooling gas into the chamber. Inside the chamber 99, there is a heat exchanger (not shown) that lowers the temperature of the supplied nitrogen gas through heat exchange, a cooling fan 200 that agitates the nitrogen gas and circulates it within the heat-retaining chamber 56, and a motor 202 that rotates the cooling fan, which together form a gas cooling device for the workpiece W. That is, in this embodiment, the heat-retaining chamber 56 has a cooling function in addition to a heat-retaining function for keeping the workpiece W warm.

[0056] As shown in Figure 6, an opening 222 is provided between the heat-retaining chamber 99 and the delivery chamber 98, more specifically, at the end of the heat-retaining chamber 99 on the delivery chamber 98 side, and this opening 222 is opened and closed by a door 228.

[0057] Next, a series of heat treatment operations in the heat treatment apparatus 1B will be described. The series of operations in the heat treatment apparatus 1B is based on the heat pattern shown in Figure 4. Furthermore, when the workpiece W is transferred between the transport unit 97 and each of the treatment chambers 93, 94, and 95, the workpiece W is transferred in a state where the atmospheres of both chambers (low dew point atmosphere, vacuum) are matched.

[0058] First, the transport unit 97 receives and transports the workpiece W on the loading table 92 shown in Figure 5, and loads it into the degreasing chamber 93. The degreasing chamber 93 that has received the workpiece W performs degreasing on the workpiece W therein.

[0059] Thereafter, the transport unit 97 removes the degreased workpiece W from the degreasing chamber 93, keeps it warm in the heat-retaining chamber 56, and then loads the workpiece W into the heating chamber 94. The heating chamber 94 then performs a heating and soaking treatment on the workpiece W. Specifically, when the workpiece W is loaded into the heating chamber 94, the heater 128 heats the workpiece W to a temperature of approximately 700° C., which is the set temperature in the first heating step.

[0060] To accelerate the temperature rise, nitrogen gas is supplied into the heating chamber 94 from the supply port 134, and the convection fan 139 is rotated, so that the workpiece W is quickly heated to around 700°C by the convection heating from the convection fan 139 and the radiant heat from the heater 128.

[0061] When the temperature of the workpiece W rises to around 700°C, the nitrogen gas inside the heating chamber 94 is evacuated through the suction port 132, and the inside of the heating chamber 94 is depressurized to a set vacuum pressure (100 Pa or less). After that, vacuum heating by the heater 128 continues in a vacuum of 100 Pa or less, and the workpiece W is soaked at 1100°C.

[0062] After the heating and soaking treatment is completed, the transport unit 97 removes the workpiece W from the heating chamber 94 , keeps it warm in the heat-retaining chamber 99 , and then transfers it to the cooling chamber 95 . The cooling chamber 95 receives this and slowly cools the workpiece W at a predetermined cooling rate. At this time, nitrogen gas is supplied into the cooling chamber 95 from the supply port 134, and the convection fan 139 is rotated, so that the workpiece W is cooled (slowly cooled) at the predetermined cooling rate by convection heat transfer by the convection fan 139.

[0063] After cooling, the transport unit 97 removes the workpiece W from the cooling chamber 95 and ejects it onto the extraction table 96. This completes the heat treatment of the workpiece W including the stack S.

[0064] As described above, the motor core manufacturing method of this embodiment can be carried out even when heat treatment apparatus 1B is used. In this heat treatment apparatus 1B, the first and second heating steps are carried out in one heating chamber 94, but it is also possible to configure the first and second heating steps to be carried out in separate heating chambers. Also, in heat treatment apparatus 1B, the slow cooling step and rapid cooling step are carried out in one cooling chamber 95, but it is also possible to configure the slow cooling step and rapid cooling step to be carried out in separate cooling chambers. In addition, the heat-retaining chamber 99 in this example has a cooling function, and it is possible to carry out part of the slow cooling process or the rapid cooling process in the heat-retaining chamber 99.

[0065] Although the embodiments of the present invention have been described in detail above, this is merely an example. For example, in the above-described embodiments, nitrogen gas (low-oxidizing gas) was used as the atmospheric gas consisting of low-oxidizing gas and / or reducing gas with a dew point of −20° C. or less. However, if nitrogen compounds are generated in high-temperature gas containing nitrogen and the grain growth of the laminate is inhibited, hydrogen gas can be used instead of nitrogen gas. Furthermore, a mixed gas can be used as the atmospheric gas, and examples include nitrogen + hydrogen, nitrogen + carbon monoxide, and nitrogen + hydrogen + carbon monoxide. The present invention can be configured in various modified forms without departing from the spirit and scope of the present invention. [Explanation of symbols]

[0066] 1,1B Heat treatment equipment 14 1st heating chamber 16 Second heating chamber 18 Cooling room 70 Laura 80 Jig 94 Heating Chamber 95 Cooling Chamber 97 Transport Unit 98 Delivery Chamber 99 Heating Chamber S laminate S001 Preparation process S003 1st heating process S004 2nd heating process W Processing object

Claims

1. a preparation step of preparing a laminate of electromagnetic steel sheets processed into a predetermined shape; a first heating step of heating the laminate at an atmospheric temperature of 500 to 800°C in an atmospheric gas consisting of a low oxidizing gas and / or a reducing gas having a dew point of -20°C or less; a second heating step of soaking the laminate at 1000 to 1200°C in a vacuum of 100 Pa or less after the first heating step; A method for manufacturing a motor core comprising:

2. The method for manufacturing a motor core according to claim 1 , wherein the heat treatment is performed while the laminate is placed on a jig made of a C / C composite.

3. 3. The method for manufacturing a motor core according to claim 1, wherein the low-oxidizing gas is nitrogen, and the reducing gas is hydrogen and / or carbon monoxide.

4. 4. The method for manufacturing a motor core according to claim 1, wherein the average crystal grain size of the electromagnetic steel sheet before the first heating step is less than 100 μm.

5. The method for manufacturing a motor core according to claim 4, wherein the average crystal grain size of the electromagnetic steel sheet after the second heating step is 100 to 300 μm.

6. A heat treatment apparatus for carrying out the manufacturing method according to claim 1, a plurality of heat treatment chambers for heat treating the laminate; a roller disposed in the heat treatment chamber and supporting and transporting the laminate; The heat treatment chamber is a roller hearth type heat treatment apparatus in which a first heating chamber in which the first heating step is performed, a second heating chamber in which the second heating step is performed, and an annealing chamber in which the laminate is annealed after the second heating step are arranged in series.

7. A heat treatment apparatus for carrying out the manufacturing method according to claim 1, (A) a batch-type heating chamber arranged along a conveying track, the heating chamber performing the first heating step and / or the second heating step; (B) a batch-type cooling chamber arranged along the conveying track, the cooling chamber slowly cooling the laminate after the second heating step; (C) a transport unit having a heat-retaining chamber that accommodates the workpiece and keeps it warm with a heater, and a delivery chamber that delivers the laminate between the heating chamber or the cooling chamber and the heat-retaining chamber; A heat treatment device comprising:

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