Preparation process of motor iron core

Abstract

The invention discloses a preparation process of a motor iron core, and particularly relates to the technical field of motor iron core manufacturing, and the technical scheme comprises the following steps: taking atomized silicon steel powder as a matrix, adding expanded graphite and nano silicon dioxide to construct a heat conduction enhanced interface, and matching with a melamine resin low-temperature cross-linked network and a manganese phosphate-lithium chloride composite additive to prepare the motor iron core. The iron core is prepared through dry premixing, spray granulation, cold press forming, sub-melting point self-diffusion sintering and a secondary curing process. Through the synergistic effect of the graphite phase and the nanometer interface, the eddy current loss is remarkably reduced, and meanwhile the heat dissipation efficiency of the iron core is improved; the problem of grain coarsening caused by traditional high-temperature annealing is avoided by utilizing a low-temperature crosslinking and sub-melting point diffusion process, and the characteristics of high magnetic conductivity and low iron loss are obtained while the process flow is simplified; the compound additive system effectively stabilizes the grain boundary structure, and ensures the dimensional stability and mechanical strength of the iron core under the high-frequency working condition. The technology is suitable for high-performance application scenes such as new energy automobile driving motors and high-speed motorized spindles.

Description

Technical Field

[0001] This invention relates to the field of motor core manufacturing, and in particular to a process for preparing a motor core. Background Technology

[0002] Currently, motor cores are mainly manufactured using silicon steel sheet laminated structures or powder metallurgy processes. Traditional silicon steel sheet laminated cores are widely used in industrial motors and transformers, possessing high magnetic permeability, but suffer from complex processing, high stamping losses, and limitations in shape design. Powder metallurgy core technology has been increasingly applied to high-frequency motors and motors with complex structures in recent years. Common manufacturing methods include pressing, annealing, and organic insulating coating. To reduce iron losses, existing technologies typically improve magnetic properties by reducing the carbon content in the silicon steel powder, using high-temperature annealing to relieve stress, or coating with an insulating layer.

[0003] However, existing technologies still have many shortcomings in practical applications. On the one hand, traditional high-temperature annealing processes tend to cause excessive coarsening of silicon steel powder grains, reducing the material's mechanical properties and dimensional stability, thus limiting the development of miniaturized and high-speed motors. On the other hand, existing coating-type insulation treatments lead to reduced interfacial thermal conductivity, causing excessive temperature rise in the motor core under high-frequency operating conditions. Furthermore, conventional powder metallurgy motor cores struggle to simultaneously meet the dual requirements of high permeability and low loss in terms of magnetic properties and thermal management, lacking effective grain boundary control and composite reinforcement methods.

[0004] Therefore, this invention proposes a manufacturing process for an electric motor core. Summary of the Invention

[0005] The main objective of this invention is to provide a manufacturing process for motor cores. By introducing techniques such as graphite phase reinforcement, low-temperature crosslinking of melamine resin, and sub-melting point grain boundary induced diffusion, the invention solves the technical problems existing in the manufacturing of motor cores, such as high-temperature annealing dependence, insufficient interfacial thermal conductivity, and high iron loss.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] An electric motor core is made of the following components in parts by weight: 80-120 parts of atomized silicon steel powder, 1-3 parts of expanded graphite, 1-5 parts of melamine resin, 0.2-0.7 parts of manganese phosphate, 0.1-0.5 parts of lithium chloride, 1-1.5 parts of nano-silica, and 1-2 parts of polyvinyl alcohol.

[0008] Preferably, the motor core is made of the following components in parts by weight: 100 parts atomized silicon steel powder, 2 parts expanded graphite, 3 parts melamine resin, 0.5 parts manganese phosphate, 0.3 parts lithium chloride, 1.2 parts nano-silica, and 1.5 parts polyvinyl alcohol.

[0009] The present invention also discloses a process for preparing the above-mentioned motor core, the specific steps of which are as follows:

[0010] Step 1: Dry premix the atomized silicon steel powder, expanded graphite, and nano-silica in a closed high-shear mixer for 30 min at a shear rate of 1200 r / min.

[0011] Step 2: Melamine resin, manganese phosphate, and lithium chloride are dissolved in hot water at 70°C and stirred to form a uniform solution. Polyvinyl alcohol is then added to form a composite colloidal system. This system is then spray-granulated with the mixed powder obtained in Step 1. The spray temperature is 80°C, the nozzle diameter is 0.8 mm, and the drying wind speed is 3 m / s to form particles with a particle size of 80-120 μm.

[0012] Step 3: Place the spray-granulated powder into a mold for cold pressing. The pressing pressure is 700 MPa, and the pressure is held for 2 minutes to obtain a dense preform.

[0013] Step 4: Place the molded preform in a tube furnace under a nitrogen atmosphere and heat it to 320°C. Hold it at that temperature for 90 minutes. The atmosphere flow rate is controlled at 100 ml / min to complete grain boundary induced diffusion and structural densification.

[0014] Step 5: Perform a secondary heat curing treatment on the iron core after step 4 at 180°C for 1 hour to obtain the motor iron core.

[0015] Preferably, the expanded graphite is a layered graphite with an initial particle size of 50-100 μm, and it forms a composite coating layer in synergy with nano-silica during the mixing process.

[0016] Preferably, the melamine resin is a thermosetting modified melamine-formaldehyde resin with a crosslinking temperature range of 280℃-350℃.

[0017] Preferably, the hot air drying velocity used in step 2 for spray granulation is 2.5 to 3.5 m / s, and the spray drying process is continuous to ensure that the particles are dense inside and have a surface roughness of less than 2 μm.

[0018] Preferably, in step 4, the nitrogen atmosphere can be replaced by argon or a mixture of nitrogen and hydrogen, with a mixing ratio of 9:1 and a flow rate of 80-120 ml / min.

[0019] Preferably, before the secondary thermosetting treatment in step 5, a mechanical vibration pretreatment of 1 to 3 minutes is performed, and the vibration frequency of the mechanical vibration pretreatment is 50 to 70 Hz.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. This invention introduces a graphite phase thermal conductivity enhancement mechanism and a nanoscale insulating distribution layer into the material system by constructing a composite coating structure of atomized silicon steel powder, expanded graphite, and nano-silica. This effectively reduces eddy current losses under AC operating conditions and improves the thermal conductivity of the iron core, solving the problem of traditional insulating coatings hindering heat dissipation. Furthermore, melamine resin is used as the low-temperature crosslinking phase, and manganese phosphate and lithium chloride are synergistically used to induce a dense interface structure at the grain boundaries. This allows the iron core to achieve grain boundary ordering and improved magnetic properties without relying on high-temperature annealing, significantly enhancing the material's permeability and dimensional stability under medium- and low-temperature conditions.

[0022] 2. This invention utilizes a diffusion rearrangement and interface solidification process under sub-melting point temperature conditions to simplify the traditional multi-stage heat treatment process in powder metallurgy, while obtaining a densely formed iron core structure with uniform magnetic properties and good mechanical strength, suitable for the manufacturing needs of complex geometric motor structures. This process system takes into account the synergistic optimization of material properties and preparation processes, providing a low-energy-consumption and green technical path for high-frequency, high-efficiency, and high-stability motor iron cores. Detailed Implementation

[0023] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0024] This invention discloses an electric motor core, which is made of the following components in parts by weight: 80-120 parts of atomized silicon steel powder, 1-3 parts of expanded graphite, 1-5 parts of melamine resin, 0.2-0.7 parts of manganese phosphate, 0.1-0.5 parts of lithium chloride, 1-1.5 parts of nano-silica, and 1-2 parts of polyvinyl alcohol.

[0025] By utilizing melamine resin to form a micro-crosslinked network under medium-temperature conditions, the magnetic matrix structure is stabilized. Simultaneously, the introduction of trace amounts of manganese phosphate and lithium chloride composite additives regulates the self-diffusion process of grain boundaries within the iron core, significantly reducing the grain coarsening caused by traditional high-temperature annealing. A dual-layer reinforcement of relative magnetic permeability and thermal conductivity, composed of expanded graphite and nano-silica, effectively reduces AC hysteresis loss and improves thermal stability.

[0026] Based on the formula, this invention also discloses a specific process for preparing the motor core, the steps of which are as follows:

[0027] Step 1: Dry premixing atomized silicon steel powder, expanded graphite, and nano-silica in a closed high-shear mixer for 30 min and a shear rate of 1200 r / min; wherein, the expanded graphite is a layered graphite with an initial particle size of 50-100 μm, and forms a composite coating layer with nano-silica during the mixing process.

[0028] Step 2: Melamine resin, manganese phosphate, and lithium chloride are dissolved in hot water at 70°C and stirred to form a uniform solution. Polyvinyl alcohol is then added to form a composite colloidal system. This system is then spray-granulated with the mixed powder obtained in Step 1. The spray temperature is 80°C, the nozzle diameter is 0.8 mm, and the drying wind speed is 3 m / s to form particles with a particle size of 80-120 μm.

[0029] It should be noted that the melamine resin is a thermosetting modified melamine-formaldehyde resin, and its crosslinking temperature range is 280℃-350℃.

[0030] The hot air drying velocity used in spray granulation is 2.5 to 3.5 m / s, and the spray drying process is continuous to ensure that the particles are dense inside and have a surface roughness of less than 2 μm.

[0031] Step 3: Place the spray-granulated powder into a mold for cold pressing. The pressing pressure is 700 MPa, and the pressure is held for 2 minutes to obtain a dense preform.

[0032] Step 4: Place the molded preform in a nitrogen atmosphere tube furnace and heat it to 320℃. Hold the temperature for 90 minutes, and control the atmosphere flow rate at 100 ml / min to complete grain boundary induced diffusion and structural densification. In this step, the nitrogen atmosphere can be replaced by argon or a mixture of nitrogen and hydrogen with a mixing ratio of 9:1 and a flow rate of 80-120 ml / min.

[0033] Step 5: Perform mechanical vibration pretreatment on the iron core processed in Step 4 for 1 to 3 minutes. The vibration frequency of the mechanical vibration pretreatment is 50 to 70 Hz. Then, perform a secondary heat curing treatment at 180°C for 1 hour to obtain the motor iron core.

[0034] The present invention is further disclosed below with reference to specific embodiments and comparative examples:

[0035] Example 1

[0036] The raw materials for preparing the motor core in this embodiment specifically include, by weight: 100 parts of atomized silicon steel powder, 2 parts of expanded graphite, 3 parts of melamine resin, 0.5 parts of manganese phosphate, 0.3 parts of lithium chloride, 1.2 parts of nano-silica, and 1.5 parts of polyvinyl alcohol.

[0037] In this embodiment, the motor core is prepared according to steps 1-5 of the aforementioned preparation process. The process parameters used have not been adjusted, so they will not be described in detail.

[0038] Example 2

[0039] The raw materials for preparing the motor core in this embodiment specifically include, by weight: 80 parts of atomized silicon steel powder, 1 part of expanded graphite, 1 part of melamine resin, 0.2 parts of manganese phosphate, 0.1 parts of lithium chloride, 1 part of nano-silica, and 1 part of polyvinyl alcohol.

[0040] The steps for preparing the motor core in this embodiment are the same as in Embodiment 1, and the process parameters used have not been adjusted, so they will not be described again.

[0041] Example 3

[0042] The raw materials for preparing the motor core in this embodiment specifically include, by weight: 120 parts of atomized silicon steel powder, 3 parts of expanded graphite, 5 parts of melamine resin, 0.7 parts of manganese phosphate, 0.5 parts of lithium chloride, 1.5 parts of nano-silica, and 2 parts of polyvinyl alcohol.

[0043] In this embodiment, the motor core is prepared according to steps 1-5 of the aforementioned preparation process. The process parameters used have not been adjusted, so they will not be described in detail.

[0044] Example 4

[0045] The raw materials for preparing the motor core in this embodiment specifically include, by weight: 90 parts of atomized silicon steel powder, 2 parts of expanded graphite, 2 parts of melamine resin, 0.3 parts of manganese phosphate, 0.2 parts of lithium chloride, 1.1 parts of nano-silica, and 1.3 parts of polyvinyl alcohol.

[0046] In this embodiment, the motor core is prepared according to steps 1-5 of the aforementioned preparation process. The process parameters used have not been adjusted, so they will not be described in detail.

[0047] Example 5

[0048] The raw materials for preparing the motor core in this embodiment specifically include, by weight: 110 parts of atomized silicon steel powder, 2 parts of expanded graphite, 4 parts of melamine resin, 0.6 parts of manganese phosphate, 0.4 parts of lithium chloride, 1.4 parts of nano-silica, and 1.8 parts of polyvinyl alcohol.

[0049] In this embodiment, the motor core is prepared according to steps 1-5 of the aforementioned preparation process. The process parameters used have not been adjusted, so they will not be described in detail.

[0050] To verify the synergistic effect mechanism of graphite phase composite coating structure, low-temperature cross-linking network and sub-melting point diffusion process on iron core performance, this invention designed comparative examples 1-3. The aim is to systematically verify the key effects of the coupling of material composition design and process parameters on magnetic permeability improvement, iron loss suppression and thermal stability by respectively eliminating the expanded graphite / nano silica composite system, replacing melamine resin and canceling the grain boundary diffusion step, and changing the diffusion temperature parameters.

[0051] Comparative Example 1

[0052] Compared to Example 1, this comparative example did not include expanded graphite and nano-silica, while all other components and process parameters remained the same. The specific formulation was adjusted to: 100 parts atomized silicon steel powder, 3 parts melamine resin, 0.5 parts manganese phosphate, 0.3 parts lithium chloride, and 1.5 parts polyvinyl alcohol. This comparative example was used to verify the effect of the graphite phase and nano-interface reinforcement on magnetic properties and thermal conductivity.

[0053] All other parts are the same as in Example 1.

[0054] Comparative Example 2

[0055] Compared to Example 1, this comparative example replaces the melamine resin with an equal amount of epoxy resin and omits the diffusion treatment process in step 4, directly curing at 180°C. This comparative example is used to verify the effects of the low-temperature crosslinking network and grain boundary diffusion process on magnetic permeability and dimensional stability.

[0056] All other parts are the same as in Example 1.

[0057] Comparative Example 3

[0058] Compared to Example 1, this comparative example increases the diffusion treatment temperature to 450°C and shortens the holding time to 30 minutes in step 4, while keeping the other parameters the same. This comparative example is used to verify the criticality of the sub-melting point diffusion process for grain refinement and iron loss control.

[0059] All other parts are the same as in the embodiment.

[0060] The motor core samples prepared in Examples 1-5 and Comparative Examples 1-3 were subjected to the following tests, and the test results are shown in Table 1.

[0061] Test 1: Magnetic permeability and iron loss test, according to standard: GB / T 3655-2008 "Methods for measuring AC magnetic properties of soft magnetic materials";

[0062] Experimental procedure: The iron cores prepared in each embodiment and comparative example were processed into ring-shaped samples (outer diameter 50 mm, inner diameter 30 mm, thickness 5 mm); the initial permeability (μi) and iron loss (P15 / 50) were measured using an AC hysteresis loop tester under a magnetic field strength of 1.0 T at 50 Hz; the test environment temperature was controlled at 25 ± 1 ℃, and each group of samples was tested 3 times and the average value was taken.

[0063] Test 2: Thermal conductivity and temperature rise test, according to standard: GB / T 22588-2008 "Measuring thermal diffusivity or thermal conductivity by flash method".

[0064] Experimental procedure: Prepare a circular sample with a diameter of 20 mm and a thickness of 2 mm; measure the thermal conductivity (λ) using a laser flash thermal conductivity meter, with a test temperature range of 25-150℃; place the sample in a high-frequency magnetic field generator (frequency 1 kHz, magnetic field strength 0.5 T) for 30 minutes and record the surface temperature rise (ΔT).

[0065] Test 3: Compressive strength and dimensional stability test, according to standard: GB / T 228.1-2010 "Metallic materials, tensile testing - Part 1: Test method at room temperature" (compressive strength conversion).

[0066] Experimental procedure: The specimen was processed into a 10mm×10mm×15mm rectangular block; a universal testing machine was used to apply pressure at a rate of 1mm / min, and the fracture strength (σc) was recorded; the specimen was placed in an oven at 150℃ for 24 hours, and the dimensional change rate (ΔL / L0) was measured after cooling.

[0067] Table 1: Experimental test results data of Examples 1-5 and Comparative Examples 1-3

[0068]

[0069] It can be seen that, in terms of magnetic permeability, the 1.25 × 10⁻³ H / m of Example 1 is significantly higher than that of Comparative Example 1 (0.82 × 10⁻³ H / m). This is because Comparative Example 1 did not add expanded graphite and nano-silica, resulting in a lack of synergistic effect between the graphite phase and the nano-interface layer on the surface of the silicon steel powder, exacerbating the disorder of magnetic domain arrangement. In Comparative Example 2, after replacing melamine resin with epoxy resin, the magnetic permeability further decreased to 0.75 × 10⁻³ H / m, indicating that epoxy resin cannot form an effective cross-linked network at low temperatures, making it difficult to stabilize the microstructure of the magnetic matrix. Although Comparative Example 3 retained the graphite phase, it used a high-temperature diffusion process, and its magnetic permeability of 0.91 × 10⁻³ H / m was still lower than that of Example 1, indicating that the 450℃ treatment caused grain coarsening, weakening the optimizing effect of sub-melting point diffusion on grain boundary magnetic domains.

[0070] In the iron loss data, Example 1's 2.8 W / kg was 43% lower than Comparative Example 1's 4.9 W / kg. This was directly attributed to the absence of the composite insulating layer composed of nano-silica and expanded graphite in Comparative Example 1, leading to a significant increase in eddy current loss. Comparative Example 2, due to the omission of diffusion treatment and mismatched resin crosslinking temperatures, saw its iron loss rise to 5.3 W / kg, reflecting the presence of numerous magnetic domain wall pinning points within the preform that had not completed grain boundary diffusion rearrangement. Comparative Example 3 controlled the iron loss at 4.1 W / kg through high-temperature short-time diffusion, which, while better than Comparative Example 1, was still higher than all other examples, demonstrating that the submelting point diffusion time and temperature window have a decisive impact on reducing iron loss.

[0071] Thermal conductivity tests showed that Example 1's thermal conductivity of 35.2 W / m·K was 82% higher than Comparative Example 1's 19.3 W / m·K, clearly verifying the synergistic enhancement mechanism of the layered thermally conductive network of expanded graphite and the interface filling effect of nano-silica. Comparative Example 2, due to the formation of a dense insulating layer after epoxy resin curing, had a thermal conductivity of only 22.1 W / m·K, indicating that the open cross-linked structure of melamine resin is more conducive to the construction of thermal conduction pathways. Comparative Example 3, due to partial oxidation of graphite caused by high-temperature diffusion, had a thermal conductivity reduced to 27.5 W / m·K, highlighting the necessity of a low-temperature diffusion process under nitrogen protection for maintaining the integrity of the graphite phase.

[0072] In terms of compressive strength, Example 1's 285 MPa is significantly higher than Comparative Example 2's 180 MPa. This is because the three-dimensional cross-linked network formed by the melamine resin during the diffusion stage effectively enhances the interparticle bonding force, while the rigid curing characteristics of the epoxy resin lead to increased interfacial brittleness. Comparative Example 1, lacking the particle reinforcement effect of nano-silica, has a compressive strength of only 195 MPa, further demonstrating the dispersion strengthening effect of nanofillers. Comparative Example 3 obtained a strength of 245 MPa through high-temperature treatment, which is higher than Comparative Example 1 but still lower than Example 1, indicating that excessively high diffusion temperatures may induce internal microcracks, weakening the overall mechanical properties of the material.

[0073] In the dimensional stability test, the 0.07% change rate of Example 1 was significantly better than that of Comparative Example 2 (0.38%). This is directly related to the fact that Comparative Example 2 did not undergo grain boundary diffusion treatment, and the shrinkage stress of resin curing could not be effectively released. Comparative Example 1, due to the lack of a graphite-silica composite interface buffer layer, suffered from a mismatch in thermal expansion coefficients, resulting in a dimensional change rate of 0.21%. Comparative Example 3, after high-temperature diffusion, had a dimensional change rate of 0.18%, which, although improved compared to Comparative Example 1, was still higher than the Example group, indicating that the submelting point diffusion temperature plays an irreplaceable role in suppressing lattice distortion.

[0074] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A motor core, characterized in that, The motor core is made of the following components in parts by weight: 80-120 parts of atomized silicon steel powder, 1-3 parts of expanded graphite, 1-5 parts of melamine resin, 0.2-0.7 parts of manganese phosphate, 0.1-0.5 parts of lithium chloride, 1-1.5 parts of nano-silica, and 1-2 parts of polyvinyl alcohol.

2. The manufacturing process of the motor core according to claim 1, characterized in that, The motor core is made of the following components in parts by weight: 100 parts atomized silicon steel powder, 2 parts expanded graphite, 3 parts melamine resin, 0.5 parts manganese phosphate, 0.3 parts lithium chloride, 1.2 parts nano silicon dioxide, and 1.5 parts polyvinyl alcohol.

3. A process for preparing the motor core according to claim 1 or 2, characterized in that, The specific steps are as follows: Step 1: Dry premix the atomized silicon steel powder, expanded graphite, and nano-silica in a closed high-shear mixer for 30 min at a shear rate of 1200 r / min. Step 2: Melamine resin, manganese phosphate, and lithium chloride are dissolved in hot water at 70°C and stirred to form a uniform solution. Polyvinyl alcohol is then added to form a composite colloidal system. This system is then spray-granulated with the mixed powder obtained in Step 1. The spray temperature is 80°C, the nozzle diameter is 0.8 mm, and the drying wind speed is 3 m / s to form particles with a particle size of 80-120 μm. Step 3: Place the spray-granulated powder into a mold for cold pressing. The pressing pressure is 700 MPa, and the pressure is held for 2 minutes to obtain a dense preform. Step 4: Place the molded preform in a nitrogen atmosphere tube furnace and heat it to 320°C. Hold it at that temperature for 90 minutes. Control the atmosphere flow rate at 100 ml / min to complete grain boundary induced diffusion and structural densification. Step 5: Perform a secondary heat curing treatment on the iron core after step 4 at 180°C for 1 hour to obtain the motor iron core.

4. The manufacturing process of the motor core according to claim 3, characterized in that, The expanded graphite is a layered graphite with an initial particle size of 50-100 μm, and it forms a composite coating layer in synergy with nano-silica during the mixing process.

5. The manufacturing process of the motor core according to claim 3, characterized in that, The melamine resin is a thermosetting modified melamine-formaldehyde resin with a crosslinking temperature range of 280℃-350℃.

6. The manufacturing process of the motor core according to claim 3, characterized in that, In step 2, the hot air drying velocity used for spray granulation is 2.5 to 3.5 m / s, and the spray drying process is continuous to ensure that the particles are dense inside and have a surface roughness of less than 2 μm.

7. The manufacturing process of the motor core according to claim 3, characterized in that, In step 4, the nitrogen atmosphere can be replaced by argon or a mixture of nitrogen and hydrogen, with a mixing ratio of 9:1 and a flow rate of 80–120 ml / min.

8. The manufacturing process of the motor core according to claim 3, characterized in that, Before the secondary heat curing treatment in step 5, a mechanical vibration pretreatment of 1 to 3 minutes is performed, with the vibration frequency of the mechanical vibration pretreatment being 50 to 70 Hz.

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