Rapid stress relief annealing of electrical steel
Through flash annealing process, the stamped laminate of electrical steel is subjected to uneven heat treatment, which solves the problem of core loss caused by residual stress after stamping and cutting of electrical steel, and achieves more efficient heat treatment, reducing production costs and iron losses.
Patent Information
- Application Number
- CN201811480957.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Priority Date
- 2017-12-11
- Filing Date
- 2018-12-05
- Publication Date
- 2024-12-27
- Estimated Expiration
- 2038-12-05
AI Technical Summary
In the prior art, residual stress generated by electrical steel during stamping and cutting leads to core loss and energy efficiency reduction. The traditional stress-removing annealing process has a long time, which increases production costs.
The flash annealing process is used to flash anneale the laminates stamped into hardened outer edge areas of the steel, and the inner and outer edge hardness is brought close to the central hardness through uneven heat distribution, thereby eliminating residual stress and reducing iron losses.
It significantly reduces iron loss, improves the efficiency and performance of electrical components, reduces heat treatment time, and reduces production costs.
Smart Images
Figure CN109897948B_ABST
Abstract
Description
Technical Field
[0001] The present disclosure relates to a heat treatment process for steel used in electric machines. Background Art
[0002] Electrical steel is a unique steel used to produce specific magnetic properties. Electrical steel is usually manufactured in cold rolled strips with a thickness of less than 2mm. These strips are cut to shape to form the laminated core of transformers, and the stators and rotors of electric motors. Electrical steel is usually formed by punch cutting, which is a process of placing a flat section of steel into a die and pressing it with a tool to form the desired surface. Stamping electrical steel may cause residual stresses, which are internal stress distributions that are locked into the material. This stress is present even when no external load is applied to the material.
[0003] Residual stress in electrical components can lead to core losses and reduced energy efficiency. Core losses exist in certain devices that include cores that are subjected to changing magnetic fields, such as transformers, inductors, AC motors, and alternators. Ideally, the magnetic field transmitted through the device would be lost in the core and dissipated as heat or noise, or both. Residual stresses, and thus core losses, can be reduced by a metalworking process called annealing. Annealing is a heat treatment process that changes the physical properties and sometimes the chemical properties of the material being processed. Typically, annealing is performed by applying 750°C for at least 30 minutes or even several hours. Cycle times greater than 30 minutes result in expensive production processes. Summary of the invention
[0004] According to one embodiment of the present disclosure, a method for manufacturing a stator is provided. The method may include stamping a fully processed steel into a set of laminations having a hardened outer edge region. The method may also include flash annealing the laminations to concentrate heat energy in the inner edge region and the outer edge region relative to the central region of the laminations to drive the hardness of the inner edge region and the outer edge region close to the hardness of the central region to eliminate residual stress and reduce the iron loss of the laminations.
[0005] According to another embodiment of the present disclosure, a method for manufacturing an electric motor is provided. The method may include stamping a fully processed steel into a set of laminations having a hardened outer edge region. The method may also include flash annealing the laminations to produce an uneven heat distribution on the laminations to drive the hardness of the inner edge region and the outer edge region to approach the hardness of the center region to eliminate residual stress and reduce the iron loss of the laminations.
[0006] According to another embodiment of the present disclosure, a method for manufacturing an electric motor is provided. The method may include punching a fully processed steel into a group of laminations having a hardened outer edge, and perforating the group of laminations to define at least one hole having a hardened inner edge region. The method may also include stacking the laminations to form a lamination assembly. The method may also include flash annealing the lamination assembly to concentrate heat energy in the inner edge region and the outer edge region relative to the central region of the lamination to drive the hardness of the inner edge region and the outer edge region to approach the hardness of the central region to eliminate residual stress and reduce the iron loss of the lamination. BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a flow chart showing a prior art process involving conventional stress relief annealing for electrical steel.
[0008] Figure 2 is a flow chart showing a process including a rapid thermal treatment process for annealing electrical steel.
[0009] Figure 3 is a graph showing the temperature and duration of a rapid thermal processing process.
[0010] Figure 4 is a perspective view of an exemplary thermal furnace and components for performing a rapid thermal processing process.
[0011] Figure 5A is a top view of an exemplary lamination and designated hardness measurement points.
[0012] Figure 5B is a detailed view taken along line 5B.
[0013] Figure 6 is a graph of hardness measurements at various locations on the lamination before and after the flash annealing heat treatment process.
[0014] Figure 7 and Figure 8 is a graph showing the iron loss reduction associated with flash annealed electrical steel. DETAILED DESCRIPTION
[0015] Embodiments of the present disclosure are described herein. However, it should be understood that the disclosed embodiments are merely examples and that other embodiments may take various and optional forms. The drawings are not necessarily drawn to scale; some features may be enlarged or minimized to show the details of specific components. Therefore, the specific structural and functional details disclosed herein are not to be interpreted as limitations, but merely as representative bases for teaching those skilled in the art to adopt the present invention in various ways. As will be understood by those skilled in the art, the various features shown and described with reference to any one of the figures may be combined with the features shown in one or more other figures to produce embodiments that are not explicitly shown or described. The combination of features shown provides representative embodiments for typical applications. However, specific applications or implementations may expect various combinations and modifications of features consistent with the teachings of the present disclosure.
[0016] Electrical steel is used in electrical applications to construct electrical devices such as power transformers, distribution transformers and electrical machines (motors and generators). Electrical steel can include a range of alloys that have favorable magnetic properties for electrical machine structures. Ferroalloys suitable for electrical steel can include silicon percentages up to 6.5%. Electrical steel is typically formed into steel sheets that can be cut or punched to form laminations. In use, the periodic variation of the applied magnetic field dissipates energy in the electrical steel, a phenomenon known as core losses. By reducing core losses in electrical steel, the efficiency of electrical components can be improved.
[0017] Electrical devices or components (e.g., stators, rotors, transformers) can be constructed from stacks of electrical steel sheets. Electrical devices can include motors, transformers, inductors, and other devices consisting of laminated cores. A flow chart of a conventional manufacturing process includes receiving fully processed electrical steel 12 and punching the electrical steel sheets into a final shape through a punch and die 14. Fully processed steel refers to electrical steel with an insulating coating, full heat treatment, and defined magnetic properties. After punching at 14, the laminations can be stacked and assembled as indicated at 16. The punching process prior to operation 16 involves strong shear forces at the cut edges of the shape, so there is plastic deformation in these areas. Plastic deformation or strain causes residual stresses, which affect the magnetic properties of the core. More specifically, core losses reduce the performance and efficiency of electrical devices. Core losses can be referred to as iron losses and can be interchangeable.
[0018] Various techniques can be used to remove residual stress caused by the cutting process. For example, stress relief annealing (SRA)18 can be used. SRA involves heat treating the punched electrical steel sheets or assembled cores at high temperatures for a long time. Previous stress relief annealing techniques subject the punched electrical steel sheets or components to a temperature of 750° for at least 30 minutes. In some cases, the time required for annealing may exceed 240 minutes. The lengthy time required for annealing increases costs due to long cycle times. A vacuum or protective gas environment is required during SRA to prevent oxidation of the electrical steel.
[0019] refer to Figure 2 , a flow chart showing a process 100 including rapid thermal processing is shown. As indicated at 102, fully processed electrical steel is received and punched into a desired shape and size as indicated at 104. As described above, fully processed steel refers to electrical steel with an insulating coating, full heat treatment, and defined magnetic properties. After punching at 104, the laminations are stacked and assembled as indicated at 106. The assembly can be used for a rotor, stator, or transformer or any suitable component that forms an electric machine when assembled. Then, as indicated at 108, the assembly or lamination stack can then be subjected to a rapid thermal processing process. As indicated at 110, the lamination stack can be assembled to other components to form an electric machine or transformer.
[0020] Reference now Figure 3 and Figure 4 , a graph depicting the temperature and duration of a flash annealing heat treatment process is shown. The flash annealing heat treatment process can be performed by placing the assembly 210 into a continuous annealing furnace 202. The continuous annealing furnace moves the assembly by moving a rod 206 along a direction arrow D. The duration can be controlled by the speed at which the assembly moves within the hot furnace or the amount of time the assembly is within the hot furnace, or both. Although a lamination assembly for a stator 210 is shown, the flash annealing process can be applied to various other components of an electric machine, such as a transformer core or a rotor.
[0021] Figure 5A and Figure 5B A top view of an exemplary rotor lamination 138 and a detail view taken along line BB are depicted. Figure 6 6 is a graph depicting hardness measurements taken at various locations along the lamination before and after the flash annealing heat treatment process. Figure 4, the rotor lamination 138 is one of many rotor laminations that can be stacked to form the rotor core assembly 210. The lamination includes an inner edge 160 that defines a circular central opening for accommodating a drive shaft having a keyway that can receive a drive key 162. The rotor lamination 138 can define a plurality of magnet openings 142 that are symmetrically disposed relative to adjacent pairs of magnet openings 142. The magnet openings 142 can be grouped in pairs, each pair forming a V-shape. The lamination 138 includes an outer edge or periphery 150 that constitutes the outermost portion of the lamination. Typically, the outer edge 150 is formed by a cutting or blanking operation, while the central opening, the inner edge 160, and the magnet openings 142 can be formed by a punching operation.
[0022] Five concentric dashed lines D1, D2, D3, D4, and D5 are shown on the surface of the rotor laminations 138. Each of these dashed lines represents a linear distance from the outer edge or outer perimeter 150 of the laminations 138. For example, dashed line D1 is spaced approximately 12.5 mm from the outer edge 150. Dashed line D2 is spaced approximately 25 mm from the outer edge 150. Dashed line D3 is spaced approximately 50 mm from the outer edge 150. Dashed line D4 is spaced approximately 75 mm from the outer edge 150. Finally, dashed line D5 is spaced approximately 175 mm from the outer edge 150. As will be described in more detail below, these dashed lines correspond to distances from the edge represented on the x-axis.
[0023] Figure 6 The graph 600 in FIG. 600 shows the hardness (HV) at different locations on the lamination 138. An area near the stamped edges (outer edge 150 and inner edge 160) that exhibits increased hardness relative to the hardness across the area may indicate the presence of residual stress. As previously described, residual stress increases core losses, resulting in reduced performance and efficiency of the electrical device. Hardness measurements were taken before and after the flash annealing heat treatment process. HV is the unit of measurement for the Vickers hardness test. The Vickers hardness test is a common test for determining the hardness of an object's surface or for determining the hardness of thinner materials. The thickness of the laminations shown is between 0.1 mm and 0.3 mm, making the Vickers hardness test more appropriate than another type of hardness test. For thicker parts, another hardness test may be used.
[0024] A plurality of concentric hidden lines are provided between the outer edge 150 and the circular central opening 160. The outer edge 150 corresponds to the Figure 5B The x-axis marks the location of the outer edges and corresponds to Figure 6600. As shown in the graph 600, the hardness of the area between 0 mm and 12.5 mm before the flash annealing heat treatment process is between 250 HV and 300 HV. After the flash annealing heat treatment process, the hardness is reduced or normalized to have a range between 200 HV and 225 HV. Similarly, the inner edge 160 is aligned with the circle marked 175 mm ( Figure 5A ) has a hardness range of 250 HV to 300 HV (before the flash annealing heat treatment process). After the flash annealing heat treatment process, the hardness is reduced or standardized to between 200 HV and 225 HV.
[0025] Reference now Figure 7 and Figure 8 , graphs depicting iron loss reduction versus time are shown. Each graph includes a y-axis representing iron loss or core loss and an x-axis representing the duration of heat treatment. Figure 7 The graphs in depict the iron loss versus rapid heat treatment time for samples or parts cut, stamped, or punched along the rolling direction. Figure 8 The graph in depicts the iron loss for rapid heat treatment time for a sample or part cut, stamped or punched in the transverse direction. Steel coils are usually rolled to form coils or sheets of desired thickness. The longitudinal direction is the direction in which the metal sheet moves through the coil. The transverse direction is at an angle of about 90° to the longitudinal direction.
[0026] Figure 7 The line S1 shown in FIG. 1 indicates that the stack is punched (eg, Figure 2 The core loss (10.5 W / kg) before the punching operation (as shown in FIG. 104) is shown in FIG. 10.5 W / kg. The core loss 10.5 W / kg represents the average value obtained from various samples. Line S2 indicates the punching operation (as shown in FIG. Figure 2 The core loss after (represented by operation 104 in FIG. 1 ) is (12 W / kg).
[0027] Line S3 represents the core loss of the stacked laminations subjected to a flash annealing heat treatment process at a temperature of 900°C. Figure 4 ) had core losses of about 12.3 W / kg after about one minute. The core losses dropped to about 11.7 W / kg after two minutes and reached their lowest point of 11 W / kg after five minutes. The benefit of the additional time in the oven was eliminated after 5 minutes; the core losses increased linearly between 5 minutes (11 W / kg) and 10 minutes (12 W / kg).
[0028] Line S4 represents the core loss of the stacked laminations subjected to the flash annealing heat treatment process at a temperature of 1,000°C. Figure 4) has a core loss of about 12 W / kg after about one minute. The core loss drops to its lowest point (about 11.3 W / kg) after two minutes. The core loss increases linearly between 2 minutes and 5 minutes (12.7 W / kg). The core loss increases further to about 13.5 W / kg after 10 minutes.
[0029] Line S5 represents the core loss of the stacked laminations subjected to the flash annealing heat treatment process at a temperature of 1,100°C. Figure 4 ) has a core loss of about 12.3 W / kg after about one minute. The core loss drops to its lowest point (about 11.8 W / kg) after two minutes. The core loss increases linearly between 2 minutes and 5 minutes (14 W / kg).
[0030] Now specific reference Figure 8 , line S6 indicates that the stack is punched (e.g. Figure 2 The core loss (12.4 W / kg) before the punching operation (as shown in FIG. 104) is shown in FIG. 104. The core loss 12.4 W / kg represents the average value obtained from various samples. Line S7 indicates the punching operation (as shown in FIG. Figure 2 The core loss after the operation 104 in FIG. 1 is 13.6 W / kg. The core loss 13.6 W / kg represents an average value obtained from various samples.
[0031] Line S8 represents the core loss of the stacked laminations subjected to the flash annealing heat treatment process at a temperature of 900°C. Figure 4 ) has a core loss of about 13.4 W / kg after about one minute. The core loss drops to about 13 W / kg after two minutes and reaches its lowest point of 12 W / kg after about 5 minutes. The core loss increases to about 12.3 W / kg after 10 minutes.
[0032] Line S9 represents the core loss of the stacked laminations subjected to the flash annealing heat treatment process at a temperature of 1,000°C. Figure 4 ) has a core loss of about 13.6 W / kg after about one minute. The core loss drops to its lowest point (about 12.4 W / kg) after two minutes. The core loss increases linearly to 13.3 W / kg between 2 minutes and 5 minutes. The core loss increases further to about 14.9 W / kg after 10 minutes.
[0033] Line S10 represents the core loss of the stacked laminations subjected to the flash annealing heat treatment process at a temperature of 1,100° C. The stacked laminations are placed in a hot furnace 202 ( Figure 4) has a core loss of about 13.8 W / kg after about one minute. The core loss drops to its lowest point (about 12.5 W / kg) after two minutes. The core loss increases linearly to 16 W / kg between 2 minutes and 5 minutes.
[0034] Although exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the present invention. On the contrary, the words used in this specification are descriptive rather than restrictive, and it should be understood that various changes can be made without departing from the spirit and scope of the present invention. Additionally, the features of various implementation embodiments can be combined to form other embodiments of the present invention.
[0035] According to the present invention, a method for manufacturing a stator assembly includes: stamping fully processed steel into a group of laminations having a hardened inner edge region and a hardened outer edge region; and flash annealing the laminations to concentrate heat energy in the inner edge region and the outer edge region relative to the central region of the laminations to drive the hardness of the inner edge region and the outer edge region to approach the hardness of the central region to eliminate residual stress and reduce the iron loss of the laminations.
[0036] According to one embodiment, the flash annealing is performed such that an average grain size of the laminate after the flash annealing is within 20% of an average grain size before the flash annealing.
[0037] According to one embodiment, the flash annealing comprises placing the stator assembly in a hot furnace at a temperature equal to or higher than 1000° C. for a time between 1 minute and 2 minutes.
[0038] According to one embodiment, the flash annealing includes placing the stator assembly in a hot furnace at a temperature between 901° C. and 999° C. for a time between 2 minutes and 5 minutes.
[0039] According to one embodiment, the flash annealing comprises placing the stator assembly in a hot furnace at a temperature of 900° C. for a time between 5 minutes and 10 minutes.
[0040] According to one embodiment, the flash annealing is done by placing the stator in a continuous annealing furnace.
[0041] According to one embodiment, the continuous annealing furnace comprises infrared lamps.
[0042] According to the present invention, a method for manufacturing an electric motor includes: stamping fully processed steel into a group of laminations having a hardened outer edge region and a hardened inner edge region; and flash annealing the laminations to produce an uneven heat distribution on the laminations to drive the hardness of the outer edge region and the inner edge region to approach the hardness of the central region to eliminate residual stress and reduce the iron loss of the laminations.
[0043] According to one embodiment, the flash annealing is performed such that an average grain size of the laminate after the flash annealing is within 20% of an average grain size before the flash annealing.
[0044] According to one embodiment, the flash annealing comprises placing the stack in a hot furnace at a temperature equal to or higher than 1000° C. for a time between 1 minute and 2 minutes.
[0045] According to one embodiment, the flash annealing includes placing the stack in a hot oven at a temperature between 901° C. and 999° C. for a time between 2 minutes and 5 minutes.
[0046] According to one embodiment, the flash annealing comprises placing the stack in a hot furnace at a temperature of 900° C. for a time between 5 minutes and 10 minutes.
[0047] According to one embodiment, the flash annealing is accomplished by placing the laminate in a continuous annealing furnace.
[0048] According to the present invention, a method for manufacturing an electric motor includes: punching fully processed steel into a group of laminations having hardened outer edges; perforating the group of laminations to define at least one hole having a hardened inner edge region; stacking the laminations to form a lamination assembly; and flash annealing the lamination assembly to concentrate heat energy in the inner edge region and the outer edge region relative to the central region of the lamination to drive the hardness of the inner edge region and the outer edge region to approach the hardness of the central region to eliminate residual stress and reduce the iron loss of the lamination.
[0049] According to one embodiment, the flash annealing is performed such that an average grain size of the laminate after the flash annealing is within 20% of an average grain size before the flash annealing.
[0050] According to one embodiment, the flash annealing comprises placing the stack assembly in a hot furnace at a temperature equal to or higher than 1000° C. for a time between 1 minute and 2 minutes.
[0051] According to one embodiment, the flash annealing includes placing the stack assembly in a hot oven at a temperature between 901° C. and 999° C. for a time between 2 minutes and 5 minutes.
[0052] According to one embodiment, the flash annealing includes placing the stack assembly in a hot furnace at a temperature of 900° C. for a time between 5 minutes and 10 minutes.
[0053] According to one embodiment, the flash annealing is accomplished by placing the lamination assembly into a continuous annealing furnace.
Claims
1. A method for manufacturing a stator assembly, comprising: stamping the fully processed steel into a set of laminations having a hardened inner edge region and a hardened outer edge region; as well as flash annealing the lamination in a hot furnace to concentrate heat energy in the inner edge region and the outer edge region relative to the central region of the lamination to drive the hardness of the inner edge region and the outer edge region close to the hardness of the central region to eliminate residual stress and reduce iron loss of the lamination, Among them, flash annealing is performed in one of the following three ways: placing the laminate in a hot furnace at a temperature equal to or greater than 1000° C. for a period between 1 minute and 2 minutes; placing the laminate in a hot oven at a temperature between 901°C and 999°C for a time between 2 minutes and 5 minutes; and The stack is placed in a hot oven at a temperature of 900°C for a period of between 5 minutes and 10 minutes.
2. The method of claim 1, wherein the flash annealing is performed such that an average grain size of the laminate after the flash annealing is within 20% of an average grain size before the flash annealing.
3. The method of claim 1, wherein: The heating furnace is a continuous annealing furnace. The method of claim 3 , wherein the continuous annealing furnace comprises infrared lamps.
5. A method for manufacturing a motor, comprising: stamping the fully processed steel into a set of laminations having hardened outer edge regions and hardened inner edge regions; as well as flash annealing the lamination in a hot furnace to produce a non-uniform heat distribution on the lamination to drive the hardness of the outer edge region and the inner edge region to approach the hardness of the central region to eliminate residual stress and reduce the iron loss of the lamination, Among them, flash annealing is performed in one of the following three ways: placing the laminate in a hot furnace at a temperature equal to or greater than 1000° C. for a period between 1 minute and 2 minutes; placing the laminate in a hot oven at a temperature between 901°C and 999°C for a time between 2 minutes and 5 minutes; and The stack is placed in a hot oven at a temperature of 900°C for a period of between 5 minutes and 10 minutes.
6. The method of claim 5, wherein the flash annealing is performed such that an average grain size of the laminate after the flash annealing is within 20% of an average grain size before the flash annealing.
7. The method of claim 5, wherein: The heating furnace is a continuous annealing furnace.
8. A method for manufacturing a motor, comprising: Blanking the fully processed steel into a set of laminations having hardened outer edges; perforating the set of laminations to define at least one hole having a hardened inner edge region; stacking the laminations to form a lamination assembly; as well as flash annealing the lamination assembly in a hot furnace to concentrate heat energy in the inner edge region and the outer edge region relative to the central region of the lamination to drive the hardness of the inner edge region and the outer edge region close to the hardness of the central region to eliminate residual stress and reduce iron loss of the lamination, Among them, flash annealing is performed in one of the following three ways: Placing the laminate assembly in a hot furnace at a temperature equal to or greater than 1000° C. for a period of time between 1 minute and 2 minutes; placing the stack assembly in a hot oven at a temperature between 901°C and 999°C for a time between 2 minutes and 5 minutes; and The stack assembly is placed in a hot furnace at a temperature of 900°C for a period of between 5 minutes and 10 minutes.
9. The method of claim 8, wherein the flash annealing is performed such that an average grain size of the laminate after the flash annealing is within 20% of an average grain size before the flash annealing.