Method for eliminating internal stress generated by sintering of soft magnetic ferrite core

Abstract

The application discloses a method for eliminating internal stress generated by sintering of a soft magnetic ferrite core, and belongs to the technical field of magnet sintering. In the application, secondary sintering is performed in a low-temperature range, compared with traditional primary annealing, residual stress is effectively eliminated, and excessive grain growth is avoided, so that good microstructure stability is maintained. In the sintering process, oxygen partial pressure is adopted in combination with closed-loop regulation, so that the stability and repeatability of the sintering environment are ensured, the batch consistency of product magnetic properties is significantly improved, the method can be realized through a standard controllable atmosphere furnace and an online oxygen sensor, special and complex equipment is not needed, the process route is clear, and the method is easy to popularize and apply on an existing production line.

Description

Technical Field

[0001] This invention belongs to the field of magnet sintering technology, and particularly relates to a method for eliminating internal stress generated during the sintering of soft magnetic ferrite cores. Background Technology

[0002] Soft magnetic ferrite materials are widely used in electronic fields such as transformers, inductors, magnetic antennas, and electromagnetic shielding components due to their high resistivity, low eddy current loss, and excellent magnetic properties. Their fabrication typically involves high-temperature sintering to achieve grain densification and performance improvement. However, the sintering process inevitably introduces thermal and structural stresses into the material. These residual stresses lead to decreased permeability, increased coercivity, and increased losses, severely impacting the overall performance and lifespan of soft magnetic ferrite cores.

[0003] In existing technologies, high-temperature annealing is often used to eliminate internal stress after sintering of soft magnetic ferrites. This type of process is generally carried out in the temperature range of 800℃ to 1000℃. While it can partially release stress, it also has significant drawbacks: abnormal grain growth: high temperatures can easily cause excessive grain growth, leading to instability in the material's microstructure and consequently reducing magnetic properties; insufficient atmosphere control: traditional annealing is mostly carried out in an inert gas environment, making it difficult to stably control the oxygen partial pressure inside the furnace. This can easily cause insufficient oxidation or reduction on the magnetic core surface, resulting in large performance fluctuations. Therefore, there is room for improvement. Summary of the Invention

[0004] The purpose of this invention is to address the problem that excessive grain growth under high-temperature conditions can easily lead to microstructural instability in materials, which in turn reduces magnetic properties, and to propose a method for eliminating internal stress generated during the sintering of soft magnetic ferrite cores.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for eliminating internal stress generated during the sintering of soft magnetic ferrite cores specifically includes the following steps:

[0007] Loading and preparation: The soft magnetic ferrite products to be processed are placed in the furnace cavity of the controlled atmosphere furnace. The soft magnetic ferrite products are cleaned before loading to remove oil and impurities. During loading, the air flow in the furnace is ensured and the products are kept out of direct contact with the furnace lining.

[0008] The atmosphere is replaced by replacing the atmosphere in the furnace cavity of the controllable atmosphere furnace. This is done by vacuum pumping or repeatedly filling the furnace with inert gas and then venting it, so as to reduce the residual oxygen content in the furnace and create an inert environment.

[0009] During the heating process, the product is heated in stages under inert or reducing atmosphere conditions in the furnace cavity:

[0010] The first stage involves raising the temperature to 85-110℃ at a rate of 1-10℃ / min and holding it at that temperature for 10-30 minutes to remove adsorbed moisture from the surface or pores of the product. The second stage involves raising the temperature to the predetermined reheating temperature at a rate of 1-5℃ / min.

[0011] The soft magnetic ferrite product is reheated in a temperature range of 250-700℃ and kept in a reducing atmosphere with an oxygen partial pressure of 200-1000ppm for 10-24 hours.

[0012] Controlled cooling: After the reheating is completed, the furnace temperature is gradually reduced to below 200°C at a cooling rate of 1~10°C / min. During the cooling process, a reducing or inert atmosphere is maintained. Once the temperature drops to a safe range, air is introduced to complete the cooling.

[0013] After the product has cooled, it is removed from the oven and its surface is cleaned and its performance is tested as needed.

[0014] As a further description of the above technical solution:

[0015] When the furnace cavity is in a reducing atmosphere, the volume fraction of reducing gas should be 99.98-99.9%, and the remaining oxygen content should be 0.02%-0.1%. The gas ratio is precisely controlled by an atmosphere control device.

[0016] As a further description of the above technical solution:

[0017] It also includes using an online oxygen concentration sensor to monitor the oxygen partial pressure inside the furnace in real time, and adjusting the ratio of hydrogen to inert gas through a closed-loop control method, so that the oxygen partial pressure during the reheating process is stably maintained in the range of 200-1000ppm.

[0018] As a further description of the above technical solution:

[0019] It also includes verifying the reheating effect through magnetic performance testing, specifically including detecting the initial permeability, coercivity and loss value, and confirming the stress relief effect of soft magnetic ferrite products through X-ray diffraction and microscopic observation.

[0020] As a further description of the above technical solution:

[0021] This also includes temperature control for heat preservation during reheating, specifically including:

[0022] Receive the process recipe containing the target temperature profile and target oxygen partial pressure value from the control terminal of the controlled atmosphere furnace, and generate the current recipe instruction;

[0023] The system acquires real-time temperature and oxygen partial pressure measurements, and, in conjunction with the current formulation instructions, calculates a linkage adjustment instruction through a coupled control model.

[0024] Based on the aforementioned linkage adjustment command, the heater power output and mixed gas flow rate are synchronously controlled to achieve coordinated control of the back-burning process.

[0025] As a further description of the above technical solution:

[0026] The step of calculating the linkage adjustment command through the coupled control model includes:

[0027] The real-time temperature measurement value is compared with the target temperature curve to generate a temperature deviation, and the real-time oxygen partial pressure measurement value is compared with the target oxygen partial pressure value to generate an oxygen partial pressure deviation;

[0028] The temperature deviation and the oxygen partial pressure deviation are processed by the proportional-integral-derivative control algorithm to obtain the initial power adjustment signal and the initial gas ratio signal.

[0029] The initial power adjustment signal and the initial gas ratio signal are coupled and weighted to generate the linkage adjustment command.

[0030] As a further description of the above technical solution:

[0031] It also includes the following steps:

[0032] Monitor the changes in the temperature deviation and oxygen partial pressure deviation over time, and extract dynamic response characteristics;

[0033] Based on the dynamic response characteristics, the optimized parameter set of the proportional-integral-derivative control algorithm is calculated through an automatic tuning model;

[0034] The proportional-integral-derivative control algorithm is updated using the optimized parameter set to improve the adaptability of generating the linkage adjustment command.

[0035] As a further description of the above technical solution:

[0036] The step of calculating the optimization parameter set through the automatic tuning model includes:

[0037] Identify the process range to which the real-time temperature measurement value belongs, determine whether it is a low-temperature stress relief range or a high-temperature stability range, and obtain the range identifier;

[0038] Based on the interval identifier, call the automatic tuning model that matches the low temperature stress relief interval or the high temperature stability interval;

[0039] The matching automatic tuning model generates a targeted set of optimized parameters to achieve fine control over different process ranges.

[0040] As a further description of the above technical solution:

[0041] It also includes the following steps:

[0042] The real-time oxygen partial pressure measurement value is monitored, and when it continuously deviates from the target oxygen partial pressure value and exceeds the recovery threshold, it is determined to be an atmosphere runaway event.

[0043] Based on the aforementioned atmosphere runaway event, a stop insulation command and a forced cooling command are generated.

[0044] Execute the stop heat preservation command and the forced cooling command to switch the process to a safe cooling procedure under an inert atmosphere.

[0045] As a further description of the above technical solution:

[0046] It also includes the following steps:

[0047] During the reverse combustion process, the real-time temperature measurement value, the real-time oxygen partial pressure measurement value, and the linkage adjustment command are collected to form a process dataset.

[0048] The process dataset is associated with the current recipe instruction to generate a timestamp traceability data package with a recipe identifier;

[0049] The timestamp traceability data packet is stored in the database for subsequent quality analysis and process reproduction.

[0050] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0051] 1. In this invention, a second reheating process is performed in the low-temperature range of 250-700℃. Compared with traditional single annealing, this effectively eliminates residual stress and avoids excessive grain growth, thereby maintaining good microstructure stability. Furthermore, the oxygen partial pressure is controlled in combination with closed-loop regulation during the reheating process to ensure the stability and repeatability of the reheating environment. The batch consistency of the magnetic properties of the products is significantly improved. The method can be implemented using a standard controllable atmosphere furnace and an online oxygen sensor. No special or complex equipment is required. The process route is clear and easy to promote and apply on existing production lines.

[0052] 2. In this invention, by ensuring that the actual furnace temperature quickly and accurately follows the preset target temperature curve, and through the synergistic effect of the proportional-integral-derivative control algorithm, the common overshoot and oscillation problems in the temperature control process can be suppressed, making the entire heating and holding process smoother and more controllable. This is crucial for stress relief of soft magnetic ferrite cores in a specific temperature range, significantly improving the uniformity and repeatability of the heat treatment process, and ensuring the magnetic properties of the final product. Attached Figure Description

[0053] Figure 1 This is a process flow diagram of a method for eliminating internal stress generated during the sintering of soft magnetic ferrite cores, as proposed in this invention. Detailed Implementation

[0054] The following will be combined with the appendix Figure 1 The technical solutions in this invention will be described below.

[0055] In this embodiment of the invention, "instruction" can include direct and indirect instructions, as well as explicit and implicit instructions. The information indicated by a certain piece of information is called the information to be instructed. In specific implementation, there are many ways to instruct the information to be instructed, such as, but not limited to, directly instructing the information to be instructed, such as the information to be instructed itself or its index. It can also indirectly instruct the information to be instructed by instructing other information, where there is a correlation between the other information and the information to be instructed. It can also instruct only a part of the information to be instructed, while the other parts are known or pre-agreed upon. For example, the instruction of specific information can be achieved by using a pre-agreed (e.g., protocol-defined) arrangement of various pieces of information, thereby reducing instruction overhead to some extent. Simultaneously, common parts of various pieces of information can be identified and uniformly indicated to reduce the instruction overhead caused by individually indicating the same information.

[0056] Furthermore, the specific indication method can also be any existing indication method, such as, but not limited to, the above-mentioned indication methods and their various combinations. Specific details of various indication methods can be found in existing technologies, and will not be elaborated upon here. As described above, for example, when multiple pieces of information of the same type need to be indicated, the indication methods for different pieces of information may differ. In specific implementation, the required indication method can be selected according to specific needs. This embodiment of the invention does not limit the selected indication method; therefore, the indication methods involved in this embodiment of the invention should be understood to cover various methods that enable the party to be indicated to obtain the information to be indicated.

[0057] It should be understood that the information to be indicated can be sent as a whole or divided into multiple sub-information messages sent separately, and the sending period and / or timing of these sub-information messages can be the same or different. The specific sending method is not limited in this embodiment of the invention. The sending period and / or timing of these sub-information messages can be predefined, for example, according to a protocol, or configured by the sending device by sending configuration information to the receiving device.

[0058] "Predefined" or "pre-configured" can be achieved by pre-saving corresponding codes, tables, or other means that can be used to indicate relevant information in the device. This embodiment of the invention does not limit the specific implementation method. "Saving" can refer to saving in one or more memories. These memories can be separate installations or integrated into the encoder, decoder, processor, or electronic device. Alternatively, some memories can be separately installed, while others are integrated into the decoder, processor, or electronic device. The type of memory can be any form of storage medium, and this embodiment of the invention does not limit this.

[0059] In the embodiments of this invention, the “protocol” may refer to a protocol family in the field of communication, a standard protocol with a similar protocol family frame structure, or a related protocol applied to a future intelligent monitoring system for ridge bifurcation defects in lithium niobate growth. The embodiments of this invention do not specifically limit this.

[0060] In this embodiment of the invention, descriptions such as "when," "under the circumstances," "if," and "if" all refer to the device making corresponding processing under certain objective circumstances, and are not limited to a specific time. They do not require the device to make a judgment action during implementation, nor do they imply any other limitations.

[0061] In the description of the embodiments of the present invention, unless otherwise stated, " / " indicates that the objects before and after are in an "or" relationship. For example, A / B can represent A or B. "And / or" in the embodiments of the present invention is merely a description of the relationship between the related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, and B alone, where A and B can be singular or plural. Furthermore, in the description of the embodiments of the present invention, unless otherwise stated, "multiple" refers to two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, at least one of a, b, or c can represent: a, b, c, ab, ac, bc, or abc, where a, b, and c can be single or multiple. Additionally, to facilitate a clear description of the technical solutions of the embodiments of the present invention, the terms "first" and "second" are used in the embodiments of the present invention to distinguish identical or similar items with essentially the same function and effect. Those skilled in the art will understand that the terms "first," "second," etc., do not limit the quantity or order of execution, and that "first," "second," etc., are not necessarily different. Furthermore, in the embodiments of this invention, words such as "exemplary" or "for example" are used to indicate that something is being described as an example, illustration, or description. Any embodiment or design scheme described as "exemplary" or "for example" in the embodiments of this invention should not be construed as being more preferred or advantageous than other embodiments or design schemes. Specifically, the use of words such as "exemplary" or "for example" is intended to present the relevant concepts in a concrete manner for ease of understanding.

[0062] The network architecture and business scenarios described in the embodiments of this invention are for the purpose of more clearly illustrating the technical solutions of the embodiments of this invention, and do not constitute a limitation on the technical solutions provided by the embodiments of this invention. As those skilled in the art will know, with the evolution of network architecture and the emergence of new business scenarios, the technical solutions provided by the embodiments of this invention are also applicable to similar technical problems.

[0063] For a better understanding of the embodiments of this application, please refer to Figure 1 This paper provides a technical solution: a method for eliminating internal stress generated during the sintering of soft magnetic ferrite cores, specifically including the following steps:

[0064] Loading and preparation: The soft magnetic ferrite products to be processed are placed in the furnace cavity of the controlled atmosphere furnace. The soft magnetic ferrite products are cleaned before loading to remove oil and impurities. During loading, the air flow in the furnace is ensured and the products are kept out of direct contact with the furnace lining.

[0065] The atmosphere is replaced by replacing the atmosphere in the furnace cavity of the controllable atmosphere furnace. This is done by vacuum pumping or repeatedly filling the furnace with inert gas and then venting it, so as to reduce the residual oxygen content in the furnace and create an inert environment.

[0066] During the heating process, the product is heated in stages under inert or reducing atmosphere conditions in the furnace cavity:

[0067] The first stage involves raising the temperature to 85-110℃ at a rate of 1-10℃ / min and holding it at that temperature for 10-30 minutes to remove adsorbed moisture from the surface or pores of the product. The second stage involves raising the temperature to the predetermined reheating temperature at a rate of 1-5℃ / min.

[0068] The soft magnetic ferrite product is reheated in a temperature range of 250-700℃ and kept in a reducing atmosphere with an oxygen partial pressure of 200-1000ppm for 10-24 hours.

[0069] Controlled cooling: After the reheating is completed, the furnace temperature is gradually reduced to below 200°C at a cooling rate of 1~10°C / min. During the cooling process, a reducing or inert atmosphere is maintained. Once the temperature drops to a safe range, air is introduced to complete the cooling.

[0070] After the product has cooled, it is removed from the oven and its surface is cleaned and its performance is tested as needed.

[0071] As a further description of the above technical solution:

[0072] When the furnace cavity is in a reducing atmosphere, the volume fraction of reducing gas should be 99.98-99.9%, and the remaining oxygen content should be 0.02%-0.1%. The gas ratio is precisely controlled by an atmosphere control device.

[0073] It also includes using an online oxygen concentration sensor to monitor the oxygen partial pressure inside the furnace in real time, and adjusting the ratio of hydrogen to inert gas through a closed-loop control method, so that the oxygen partial pressure during the reheating process is stably maintained in the range of 200-1000ppm.

[0074] It also includes verifying the reheating effect through magnetic performance testing, specifically including detecting the initial magnetic permeability, coercivity and loss value, and confirming the stress relief effect of soft magnetic ferrite products through X-ray diffraction and microscopic observation.

[0075] This also includes temperature control for heat preservation during reheating, specifically including:

[0076] Receive the process recipe containing the target temperature profile and target oxygen partial pressure value from the control terminal of the controlled atmosphere furnace, and generate the current recipe instruction;

[0077] The system acquires real-time temperature and oxygen partial pressure measurements, and, in conjunction with the current formulation instructions, calculates a linkage adjustment instruction through a coupled control model.

[0078] Based on the aforementioned linkage adjustment command, the heater power output and mixed gas flow rate are synchronously controlled to achieve coordinated control of the back-burning process;

[0079] The step of calculating the linkage adjustment command through the coupled control model includes:

[0080] The real-time temperature measurement value is compared with the target temperature curve to generate a temperature deviation, and the real-time oxygen partial pressure measurement value is compared with the target oxygen partial pressure value to generate an oxygen partial pressure deviation;

[0081] The temperature deviation and the oxygen partial pressure deviation are processed by the proportional-integral-derivative control algorithm to obtain the initial power adjustment signal and the initial gas ratio signal.

[0082] The initial power adjustment signal and the initial gas ratio signal are coupled and weighted to generate the linkage adjustment command;

[0083] It also includes the following steps:

[0084] Monitor the changes in the temperature deviation and oxygen partial pressure deviation over time, and extract dynamic response characteristics;

[0085] Based on the dynamic response characteristics, the optimized parameter set of the proportional-integral-derivative control algorithm is calculated through an automatic tuning model;

[0086] The proportional-integral-derivative control algorithm is updated using the optimized parameter set to improve the adaptability of generating the linkage adjustment command;

[0087] The step of calculating the optimization parameter set through the automatic tuning model includes:

[0088] Identify the process range to which the real-time temperature measurement value belongs, determine whether it is a low-temperature stress relief range or a high-temperature stability range, and obtain the range identifier;

[0089] Based on the interval identifier, call the automatic tuning model that matches the low temperature stress relief interval or the high temperature stability interval;

[0090] The matching automatic tuning model generates a targeted set of optimization parameters to achieve fine control over different process ranges.

[0091] It also includes the following steps:

[0092] The real-time oxygen partial pressure measurement value is monitored, and when it continuously deviates from the target oxygen partial pressure value and exceeds the recovery threshold, it is determined to be an atmosphere runaway event.

[0093] Based on the aforementioned atmosphere runaway event, a stop insulation command and a forced cooling command are generated.

[0094] Execute the stop heat preservation command and the forced cooling command to switch the process to a safe cooling procedure under an inert atmosphere;

[0095] It also includes the following steps:

[0096] During the reverse combustion process, the real-time temperature measurement value, the real-time oxygen partial pressure measurement value, and the linkage adjustment command are collected to form a process dataset.

[0097] The process dataset is associated with the current recipe instruction to generate a timestamp traceability data package with a recipe identifier;

[0098] The timestamp traceability data packet is stored in the database for subsequent quality analysis and process reproduction.

[0099] Experimental Example 1

[0100] To verify the effectiveness of the low-temperature reheating process of the present invention, the following comparative experiments were conducted;

[0101] Sample preparation:

[0102] Twenty iron-based soft magnetic alloy ring samples (approximately 20 mm inner diameter, 40 mm outer diameter, and 5 mm thickness) were prepared using powder metallurgy. They were divided into four groups of five samples each.

[0103] Group 0 (control group): The products were cooled directly after sintering and were not subjected to re-firing.

[0104] Group 1 (Traditional Annealing Group): The samples were held at 900℃ in an inert atmosphere for 2 hours and then cooled in a controlled manner.

[0105] Group 2 (Example A of the Invention): According to the process of the present invention, the gas is reheated at 500°C for 3 hours in an atmosphere of 5% H2 / N2 mixture, and the oxygen partial pressure is stably controlled at about 300 ppm.

[0106] Group 3 (Invention Embodiment B): According to the process of the present invention, the sample is reheated at 600°C for 1 hour under the same atmospheric conditions as above.

[0107] Process conditions: Each reheating group uses a controlled atmosphere furnace, which is first purged with inert gas before heating. The heating rate is divided into two stages: the first stage heats to 250℃ at 10℃ / min and holds for 20min to remove moisture; the second stage heats to the target reheating temperature at 2℃ / min. During reheating, the gas ratio is adjusted using an online oxygen sensor and a mass flow controller to stabilize the oxygen partial pressure in the furnace at 300±50ppm. After reheating, the furnace is cooled to below 200℃ at a rate of 1~5℃ / min, and then air is introduced to complete the cooling process.

[0108] Test method:

[0109] After processing, each group of samples was tested separately:

[0110] Initial permeability μi (low field measurement), coercivity Hc (BH loop test), and residual stress (X-ray diffraction sin²ψ method determination).

[0111] The test results for each group of samples are shown in Table 1:

[0112] Table 1. Comparison of sample performance under different treatment processes (mean, expressed as a percentage relative to the group 0)

[0113]

[0114] Conclusion: As shown in Table 1, the samples (Group 2 and Group 3) treated by the low-temperature reheating process of the present invention have significantly higher initial permeability than the control group, significantly reduced coercivity, and reduced residual stress by 35% to 45%. Compared with traditional high-temperature annealing, the process of the present invention achieves more complete stress relief while avoiding abnormal grain growth, and the magnetic properties are improved more significantly, which fully proves the technical effect of the present invention.

[0115] It should be understood that the term "and / or" in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural. Additionally, the character " / " in this article generally indicates an "or" relationship between the preceding and following related objects, but it can also represent an "and / or" relationship. Please refer to the context for a more accurate understanding.

[0116] In this invention, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of a single item or a plurality of items. For example, at least one of a, b, or c can represent: a, b, c, ab, ac, bc, or abc, where a, b, and c can be a single item or multiple items.

[0117] It should be understood that, in various embodiments of the present invention, the order of the above-mentioned process numbers does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0118] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0119] Those skilled in the art will understand that, for the sake of convenience and brevity, the specific working processes of the systems, devices, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0120] In the embodiments provided by this invention, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between devices or units may be electrical, mechanical, or other forms.

[0121] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0122] In addition, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit.

[0123] If the aforementioned functions are implemented as software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this invention, or the part that contributes to the prior art, or a part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0124] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for eliminating internal stress generated during the sintering of soft magnetic ferrite cores, characterized in that, Specifically, the following steps are included: Loading and preparation: The soft magnetic ferrite products to be processed are placed in the furnace cavity of the controlled atmosphere furnace. The soft magnetic ferrite products are cleaned before loading to remove oil and impurities. During loading, the air flow in the furnace is ensured and the products are kept out of direct contact with the furnace lining. The atmosphere is replaced by replacing the atmosphere in the furnace cavity of the controllable atmosphere furnace. This is done by vacuum pumping or repeatedly filling the furnace with inert gas and then venting it, so as to reduce the residual oxygen content in the furnace and create an inert environment. During the heating process, the product is heated in stages under inert or reducing atmosphere conditions in the furnace cavity: The first stage involves raising the temperature to 85-110℃ at a rate of 1-10℃ / min and holding it at that temperature for 10-30 minutes to remove adsorbed moisture from the surface or pores of the product. The second stage involves raising the temperature to the predetermined reheating temperature at a rate of 1-5℃ / min. The soft magnetic ferrite product is reheated in a temperature range of 250-700℃ and kept in a reducing atmosphere with an oxygen partial pressure of 200-1000ppm for 10-24 hours. Controlled cooling: After the reheating is completed, the furnace temperature is gradually reduced to below 200°C at a cooling rate of 1~10°C / min. During the cooling process, a reducing or inert atmosphere is maintained. Once the temperature drops to a safe range, air is introduced to complete the cooling. After the product has cooled, it is removed from the oven and its surface is cleaned and its performance is tested as needed.

2. The method for eliminating internal stress generated during the sintering of soft magnetic ferrite cores according to claim 1, characterized in that, When the furnace cavity is in a reducing atmosphere, the volume fraction of reducing gas should be 99.98-99.9%, and the remaining oxygen content should be 0.02%-0.1%. The gas ratio is precisely controlled by an atmosphere control device.

3. The method for eliminating internal stress generated during the sintering of soft magnetic ferrite cores according to claim 1, characterized in that, It also includes using an online oxygen concentration sensor to monitor the oxygen partial pressure inside the furnace in real time, and adjusting the ratio of hydrogen to inert gas through a closed-loop control method, so that the oxygen partial pressure during the reheating process is stably maintained in the range of 200-1000ppm.

4. The method for eliminating internal stress generated during the sintering of a soft magnetic ferrite core according to claim 1, characterized in that, It also includes verifying the reheating effect through magnetic performance testing, specifically including detecting the initial permeability, coercivity and loss value, and confirming the stress relief effect of soft magnetic ferrite products through X-ray diffraction and microscopic observation.

5. The method for eliminating internal stress generated during the sintering of a soft magnetic ferrite core according to claim 1, characterized in that, This also includes temperature control for heat preservation during reheating, specifically including: Receive the process recipe containing the target temperature profile and target oxygen partial pressure value from the control terminal of the controlled atmosphere furnace, and generate the current recipe instruction; The system acquires real-time temperature and oxygen partial pressure measurements, and, in conjunction with the current formulation instructions, calculates a linkage adjustment instruction through a coupled control model. Based on the aforementioned linkage adjustment command, the heater power output and mixed gas flow rate are synchronously controlled to achieve coordinated control of the back-burning process.

6. The method for eliminating internal stress generated during the sintering of a soft magnetic ferrite core according to claim 5, characterized in that, The step of calculating the linkage adjustment command through the coupled control model includes: The real-time temperature measurement value is compared with the target temperature curve to generate a temperature deviation, and the real-time oxygen partial pressure measurement value is compared with the target oxygen partial pressure value to generate an oxygen partial pressure deviation; The temperature deviation and the oxygen partial pressure deviation are processed by the proportional-integral-derivative control algorithm to obtain the initial power adjustment signal and the initial gas ratio signal. The initial power adjustment signal and the initial gas ratio signal are coupled and weighted to generate the linkage adjustment command.

7. The method for eliminating internal stress generated during the sintering of a soft magnetic ferrite core according to claim 6, characterized in that, It also includes the following steps: Monitor the changes in the temperature deviation and oxygen partial pressure deviation over time, and extract dynamic response characteristics; Based on the dynamic response characteristics, the optimized parameter set of the proportional-integral-derivative control algorithm is calculated through an automatic tuning model; The proportional-integral-derivative control algorithm is updated using the optimized parameter set to improve the adaptability of generating the linkage adjustment command.

8. The method for eliminating internal stress generated during the sintering of a soft magnetic ferrite core according to claim 7, characterized in that, The step of calculating the optimization parameter set through the automatic tuning model includes: Identify the process range to which the real-time temperature measurement value belongs, determine whether it is a low-temperature stress relief range or a high-temperature stability range, and obtain the range identifier; Based on the interval identifier, call the automatic tuning model that matches the low temperature stress relief interval or the high temperature stability interval; The matching automatic tuning model generates a targeted set of optimized parameters to achieve fine control over different process ranges.

9. A method for eliminating internal stress generated during the sintering of a soft magnetic ferrite core according to claim 5, characterized in that, It also includes the following steps: The real-time oxygen partial pressure measurement value is monitored, and when it continuously deviates from the target oxygen partial pressure value and exceeds the recovery threshold, it is determined to be an atmosphere runaway event. Based on the aforementioned atmosphere runaway event, a stop insulation command and a forced cooling command are generated. Execute the stop heat preservation command and the forced cooling command to switch the process to a safe cooling procedure under an inert atmosphere.

10. A method for eliminating internal stress generated during the sintering of a soft magnetic ferrite core according to claim 9, characterized in that, It also includes the following steps: During the reverse combustion process, the real-time temperature measurement value, the real-time oxygen partial pressure measurement value, and the linkage adjustment command are collected to form a process dataset. The process dataset is associated with the current recipe instruction to generate a timestamp traceability data package with a recipe identifier; The timestamp traceability data packet is stored in the database for subsequent quality analysis and process reproduction.

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