LU504783B1

LU504783B1 - High-density and high-strength soft magnetic composite motor stator and preparation method thereof

Info

Publication number: LU504783B1
Application number: LU504783A
Authority: LU
Inventors: Liping Liang
Original assignee: Qingdao Univ Of Technology Linyi Management Committee Office
Priority date: 2023-05-09
Filing date: 2023-07-21
Publication date: 2024-01-22
Also published as: CN116618661A

Abstract

Disclosed is a high-density and high-strength soft magnetic composite motor stator and a preparation method thereof, and belongs to the technical field of soft magnetic composites. The preparation method comprises: adjusting the particle size ratio of iron powder, carrying out pretreatment, carrying out phosphoric acid and resin coating, then carrying out primary pressing formation, with a pressure of 300-800 MPa; after completion of the pressing, sealing the formed blank through a vacuum packaging bag and then proceed to the isostatic secondary forming, with a pressure of 200-500 MPa; performing two-step low-temperature annealing heat treatment of the magnetic body after the isostatic forming in a nitrogen atmosphere, and cooling and discharging. According to the method of the present disclosure, a motor stator made of SMC with high density uniformity, high magnetic performance and high strength can be obtained while a lubricant is omitted and the heat treatment energy consumption is reduced.

Description

BL-5726

HIGH-DENSITY AND HIGH-STRENGTH SOFT MAGNETIC COMPOSITE LU504783

MOTOR STATOR AND PREPARATION METHOD THEREOF

TECHNICAL FIELD

[0001] The present disclosure relates to the technical field of soft magnetic composites, particularly to a high-density and high-strength soft magnetic composite motor stator and a preparation method thereof.

BACKGROUND

[0002] Soft magnetic composites (referred to as SMC) are prepared by coating a high-resistivity isolation layer on the surface of magnetic particles such as pure iron powder and iron-based alloy powder with different particle sizes, then carrying out pressing and heat treatment. According to its preparation process, the material has the characteristics of three-dimensional magnetocaloric isotropy, greenness, ease to manufacture and forming and high utilization rate, etc., and has broad application prospects in various fields. Particularly, the recent use of SMCs instead of traditional silicon steel sheets to make key stator materials for motors can greatly simplify the preparation process of motor stators and effectively promote the development of high-efficiency and lightweight motors, which opens up the application of motors in new fields such as new energy vehicles and electric aircrafts, and has become a research hot spot of SMCs.

[0003] In SMCs, the mass fractions of magnetic particles such as pure iron powder and magnetic alloy powder determine the magnetic properties of materials such as saturation magnetization and magnetic permeability; the isolation layer is a high-resistivity material, and after coating, the loss of the material can be effectively reduced. When used as magnetic parts in motors, SMCs are required to have good magnetic properties, i.e. high saturation magnetic induction and magnetic permeability. This requires that the pure iron powder is selected as a magnetic phase for the preparation of SMCs, and the mass fraction of the magnetic phase is high, and the magnetic body is required to have a high density. In addition, the application frequency of the motor is low, generally lower than several KHz, at this time, among the loss composition of the SMCs, the hysteresis loss dominates as 1

BL-5726 compared to the eddy current loss. Therefore, the compressive residual stress of the SMCs LUS04783 should be removed during the heat treatment.

[0004] At present, more studies focus on coating a phosphoric acid isolation layer on the surface of pure iron powder and superimposing an organic resin layer to form a multi-layer coating. However, in the subsequent pressing formation process, there are two directions for the conventional pressing pressure: upper and down directions; in order to achieve the required density for pressing, the pressing pressure is as high as 900-1,100 MPa; and a large residual stress will be formed inside the material. In order to remove this part of residual stress, it is necessary to perform stress relief heat treatment at 550-650°C. In this step, the coated phosphoric acid isolation layer will be subjected to thermal decomposition due to the poor thermal stability, which increases the material loss and affects the use of materials. Additionally, in order to achieve the required density during the material forming process, the pressing pressure in the upper and lower directions is too large; firstly, the coating layer on the surface of the iron powder will be crushed and the exposed iron powder will contact each other, resulting in a decrease in the resistivity of the magnetic body and an increase in eddy current loss; secondly, when the stator part is too high, there will be obvious density stratification in the direction of the pressing height, which will reduce the strength of the stator part and affect the use of the part in the motor; thirdly, under a large pressing pressure, the internal pressing residual stress of the material is relatively large, which cannot be completely removed after heat treatment, resulting in high hysteresis loss of the material and affecting the energy efficiency of the motor at low frequencies.

[0005] In the prior art, after coated with phosphoric acid and organic resin, the iron powder is subjected to warm-pressing formation at 80-150°C under 900-1,100 MPa, and then annealed at 550-650°C. Although the density uniformity of the material can be improved to a certain extent and the residual stress can be reduced through the utilization of the warm pressing technology, the phenomenon of density stratification still exists and there is still a problem of damage to insulating coating layer on the surface of iron powder particles during the pressing process. 2

BL-5726

SUMMARY LU504783

[0006] In order to solve the problems existing in the prior art, the present disclosure provides a high-density and high-strength soft magnetic composite motor stator and a preparation method thereof. According to the present disclosure, after coating the high resistivity isolation layer on the surface of pure iron powder, the conventional one-way/two-way pressing method is changed; and through an innovative isostatic pressing method, the overall pressing uniformity of SMCs can be effectively improved, and the density stratification phenomenon is eliminated during the stator manufacturing process. In addition, by reducing the pressing residual stress in the pressing process, the loss of materials at low frequencies can be effectively reduced, and the energy efficiency of motors with SMCs as the stator parts can be improved.

[0007] In order to solve the above technical problems, the present disclosure provides the following technical solutions:

[0008] A method for preparing a high-density and high-strength soft magnetic composite motor stator is provided, wherein the raw material of the present disclosure is pure iron powder, atomized iron powder or reduced iron powder, with a component purity of >99.0%, preferably water atomized iron powder with smoother morphology and higher purity.

[0009] The particle size ratio of iron powder: 20-40% of iron powder with a size of above 60 mesh, 50-70% of iron powder with a size of 60- 200 mesh, and the rest of iron powder with a size of below 200 mesh.

[0010] Pretreatment: a. Before coating, the surface treatment on iron powder is carried out by mechanical ball milling, so that the iron powder is exposed to a fresh surface to improve the activity of the adsorption coating medium, and meanwhile the particle size of iron powder cannot be reduced obviously, when the above conditions are met, the cemented carbide grinding balls can be used in this step, and the mass ratio of the grinding balls to the iron powder is 1:5-1:10; the speed is 300-400 rpm, and the treatment time is 5-20 minutes;

[0011] b. After ball milling, the reduction pretreatment of powder is carried out in a reducing ammonia atmosphere to eliminate the oxygen content on the surface of the iron powder caused by oxidation during storage or transportation, thereby improving the purity 3

BL-5726 and intrinsic magnetic properties of the iron powder. The temperature for reduction heat 17906783 treatment is 900-1,100°C for 1-2 h.

[0012] [Insulation coating: a. The phosphoric acid coating of the pretreated iron powder is carried out. Orthophosphoric acid, acetone, ethanol or deionized water are mixed to form a phosphoric acid solution, then heated to about 60-80°C and kept warm; the solution is mixed with iron powder evenly such that a phosphate layer is coated on the surface of the iron powder evenly, then the iron powder is dried and sieved. In order to ensure that the magnetic body has a high saturation magnetic induction and magnetic permeability, the mass fraction of phosphoric acid added in this step is 0.1-0.3wt%;

[0013] b. After the thermosetting resin and ethanol or acetone are prepared into a solution, the secondary coating of the iron powder is carried out; the drying and sieving steps are repeated to make phosphoric acid-resin-coated iron powder;

[0014] the thermosetting resin is epoxy resin, phenolic resin or polyurethane, and a solvent of the thermosetting resin solution is ethanol or acetone, and the dosage of the thermosetting resin is 0.1-0.2wt% of the dosage of the iron powder.

[0015] Pressing formation: the primary pressing formation of the powder is carried out in an ordinary upper and lower two-way press, the forming pressure is about 300-800 MPa, and the pressure holding time is 5-15 s; after completion of the pressing, the formed blank is sealed through a vacuum packaging bag and then the isostatic oil hydraulic secondary forming is proceeded, the forming pressure is 200-500 MPa, and the pressure holding time is 1-3 min.

[0016] Heat treatment: The vacuum packaging bag of the magnetic body after the isostatic forming is removed, and annealing heat treatment is performed in a nitrogen atmosphere. The heat treatment includes two steps: the first step is to heat to 180-250°C and keep warm for 20-40 minutes to discharge organic matters in the magnetic body; the second step is to heat to 350-450°C and keep warm for 5-15 minutes, and then cool and discharge from the furnace.

[0017] Compared with the prior art, the present disclosure can achieve the following beneficial effects:

[0018] In the present disclosure, the density uniformity of the SMC motor stator can be 4

BL-5726 obviously improved through the two-way pressing- isostatic pressing combined pressing LUS04783 method, especially when pressing a stator with a greater height, high density uniformity in the height direction can be obtained; firstly, the stator strength can be improved, secondly, the magnetic performance can be significantly improved and the low-frequency loss can be reduced, thereby improving the energy efficiency of the motor. Additionally, the stator is bidirectionally pressed at a lower pressure. At this time, the stator density is lower and the powder fluidity is better, and there is no need to use a lubricant; in the second stage of isostatic pressing, the isotropic pressing force in the three-dimensional space replaces the two-way pressing force, which can promote the flow and densification of the powder, and high density uniformity can be obtained at a low pressure. In this way, the use of lubricant can be omitted, the cost can be reduced, and the magnetic properties of the SMCs can be improved by increasing the mass fraction of magnetic particles. Meanwhile, the pressing stress inside the magnetic body can be reduced, thereby reducing the subsequent heat treatment temperature; and the low-frequency loss is low, the energy consumption and cost of the stator production is reduced.

[0019] Meanwhile, in the present disclosure, the phosphoric acid-organic resin composite coating on the pretreated iron powder is carried out directly, and no other particles are added subsequently to maintain a high mass fraction of magnetic particles. Therefore, according to the present disclosure, a motor stator made of SMC with high density uniformity, high magnetic performance and high strength can be obtained while a lubricant is omitted and the heat treatment energy consumption is reduced.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0020] In order to make the technical problems to be solved, the technical solutions and advantages of the present disclosure clearer, the present disclosure will be described in detail in conjunction with specific embodiments.

[0021] Unless otherwise specified, the reagents and materials used in the examples and comparative examples are commercially available.

[0022] The present disclosure provides a high-density and high-strength soft magnetic composite motor stator and a preparation method thereof. The specific examples are as follows.

BL-5726

[0023] Example 1 LUS04783

[0024] A method for preparing a high-density and high-strength soft magnetic composite motor stator comprises the following steps:

[0025] Step 1: take the water atomized iron powder which is composed of the following components in mass percent: 40% of iron powder with a size of above 60 mesh, 50% of iron powder with a size of 60- 200 mesh, and the rest of iron powder with a size of below 200 mesh; carry out mechanical ball milling pretreatment for 8 minutes at a speed of 400 rpm; the ball for ball milling is a cemented carbide ball, and the mass ratio of the cemented carbide ball to the iron powder is 1:5; then carry out a reduction heat treatment at 1,000°C for 1 h in a reducing ammonia atmosphere;

[0026] Step 2: put 1:80 orthophosphoric acid-acetone solution in a water bath at 80°C for constant temperature treatment, then mix with the pretreated water atomized iron powder evenly, dry at 70°C, and sieve through a 60-mesh sieve to prevent caking and obtain phosphoric acid-coated iron powder; the dosage of the orthophosphoric acid is 0.1wt% of the dosage of the iron powder;

[0027] Step 3: mix 1:30 epoxy resin-ethanol solution with phosphoric acid-coated iron powder evenly, dry again and sieve through a 60-mesh sieve to obtain phosphoric acid-resin-coated insulating iron powder; the dosage of the epoxy resin is 0.1wt% of the dosage of the iron powder;

[0028] Step 4: carry out primary formation of the weighed powder at room temperature and under two-way pressure, with the pressure of 400 MPa and the pressure holding time of 10 s; seal the primary-formed blank through a vacuum packaging machine and place in the pressing chamber of the isostatic press, apply an isostatic pressure of 300 MPa in each direction, with a pressure holding time of 2 min, and then carry out a secondary forming;

[0029] Step 5: remove the vacuum packaging film of the formed compact, and place in a furnace chamber of a vacuum sintering furnace, and perform annealing heat treatment in a nitrogen atmosphere, i.e. heat to temperature of 200°C, keep warm for 30 minutes, then heat to temperature of 400°C, keep warm for 10 minutes, and then cool the magnetic body and discharge from the furnace. 6

BL-5726

[0030] Example 2 LUS04783

[0031] A method for preparing a high-density and high-strength soft magnetic composite motor stator comprises the following steps:

[0032] Step 1: take the water atomized iron powder which is composed of the following components in mass percent: 30% of iron powder with a size of above 60 mesh, 60% of iron powder with a size of 60- 200 mesh, and the rest of iron powder with a size of below 200 mesh; carry out mechanical ball milling pretreatment for 10 minutes at a speed of 380 rpm; the ball for ball milling is a cemented carbide ball, and the mass ratio of the cemented carbide ball to the iron powder is 1:8; then carry out a reduction heat treatment at 950°C for 1 h in a reducing ammonia atmosphere;

[0033] Step 2: put 1:80 orthophosphoric acid-acetone solution in a water bath at 80°C for constant temperature treatment, then mix with the pretreated water atomized iron powder evenly, dry at 70°C, and sieve through a 60-mesh sieve to prevent caking and obtain phosphoric acid-coated iron powder; the dosage of the orthophosphoric acid is 0.2wt% of the dosage of the iron powder;

[0034] Step 3: mix 1:30 epoxy resin-ethanol solution with phosphoric acid-coated iron powder evenly, dry again and sieve through a 60-mesh sieve to obtain phosphoric acid-resin-coated insulating iron powder; the dosage of the epoxy resin is 0.2wt% of the dosage of the iron powder;

[0035] Step 4: carry out primary formation of the weighed powder at room temperature and under two-way pressure, with the pressure of 500 MPa and the pressure holding time of 10 s; seal the primary-formed blank through a vacuum packaging machine and place in the pressing chamber of the isostatic press, apply an isostatic pressure of 400 MPa in each direction, with a pressure holding time of 2 min, and then carry out a secondary forming;

[0036] Step 5: remove the vacuum packaging film of the formed compact, and place in a furnace chamber of a vacuum sintering furnace, and perform annealing heat treatment in a nitrogen atmosphere, i.e. heat to temperature of 200°C, keep warm for 30 minutes, then heat to temperature of 400°C, keep warm for 10 minutes, and then cool the magnetic body and discharge from the furnace. 7

BL-5726

[0037] Example 3 LUS04783

[0038] A method for preparing a high-density and high-strength soft magnetic composite motor stator comprises the following steps:

[0039] Step 1: take the water atomized iron powder which is composed of the following components in mass percent: 20% of iron powder with a size of above 60 mesh, 70% of iron powder with a size of 60- 200 mesh, and the rest of iron powder with a size of below 200 mesh; carry out mechanical ball milling pretreatment for 20 minutes at a speed of 300 rpm; the ball for ball milling is a cemented carbide ball, and the mass ratio of the cemented carbide ball to the iron powder is 1:10; then carry out a reduction heat treatment at 900°C for 1 h in a reducing ammonia atmosphere;

[0040] Step 2: put 1:80 orthophosphoric acid-acetone solution in a water bath at 80°C for constant temperature treatment, then mix with the pretreated water atomized iron powder evenly, dry at 70°C, and sieve through a 60-mesh sieve to prevent caking and obtain phosphoric acid-coated iron powder; the dosage of the orthophosphoric acid is 0.3wt% of the dosage of the iron powder;

[0041] Step 3: mix 1:30 epoxy resin-ethanol solution with phosphoric acid-coated iron powder evenly, dry again and sieve through a 60-mesh sieve to obtain phosphoric acid-resin-coated insulating iron powder; the dosage of the epoxy resin is 0.1wt% of the dosage of the iron powder;

[0042] Step 4: carry out primary formation of the weighed powder at room temperature and under two-way pressure, with the pressure of 500 MPa and the pressure holding time of 10 s; seal the primary-formed blank through a vacuum packaging machine and place in the pressing chamber of the isostatic press, apply an isostatic pressure of 400 MPa in each direction, with a pressure holding time of 2 min, and then carry out a secondary forming;

[0043] Step 5: remove the vacuum packaging film of the formed compact, and place in a furnace chamber of a vacuum sintering furnace, and perform annealing heat treatment in a nitrogen atmosphere, i.e. heat to temperature of 200°C, keep warm for 30 minutes, then heat to temperature of 400°C, keep warm for 10 minutes, and then cool the magnetic body and discharge from the furnace. 8

BL-5726

[0044] Example 4 17906783

[0045] A method for preparing a high-density and high-strength soft magnetic composite motor stator comprises the following steps:

[0046] Steps 1 to 3 are the same as those in Example 2;

[0047] Step 4: carry out primary formation of the weighed powder at room temperature and under two-way pressure, with the pressure of 300 MPa and the pressure holding time of 10 s; seal the primary-formed blank through a vacuum packaging machine and place in the pressing chamber of the isostatic press, apply an isostatic pressure of 500 MPa in each direction, with a pressure holding time of 2 min, and then carry out a secondary forming;

[0048] Step 5: remove the vacuum packaging film of the formed compact, and place in a furnace chamber of a vacuum sintering furnace, and perform annealing heat treatment in a nitrogen atmosphere, i.e. heat to temperature of 180°C, keep warm for 40 minutes, then heat to temperature of 450°C, keep warm for 5 minutes, and then cool the magnetic body and discharge from the furnace.

[0049] Example 5

[0050] A method for preparing a high-density and high-strength soft magnetic composite motor stator comprises the following steps:

[0051] Steps 1 to 3 are the same as those in Example 2;

[0052] Step 4: carry out primary formation of the weighed powder at room temperature and under two-way pressure, with the pressure of 800 MPa and the pressure holding time of 10 s; seal the primary-formed blank through a vacuum packaging machine and place in the pressing chamber of the isostatic press, apply an isostatic pressure of 200 MPa in each direction, with a pressure holding time of 2 min, and then carry out a secondary forming;

[0053] Step 5: remove the vacuum packaging film of the formed compact, and place in a furnace chamber of a vacuum sintering furnace, and perform annealing heat treatment in a nitrogen atmosphere, i.e. heat to temperature of 250°C, keep warm for 20 minutes, then heat to temperature of 350°C, keep warm for 8 minutes, and then cool the magnetic body and discharge from the furnace.

[0054] In the foregoing examples 1 to 5, there is no need to mix the phosphoric acid-resin-coated iron powder with a lubricant during the preparation of the high-density 9

BL-5726 and high-strength soft magnetic composite motor stator, and the pressing formation can be LUS04783 carried out directly.

[0055] In order to further highlight the beneficial effects of the present disclosure, comparative examples are constructed as follows.

[0056] Comparative Example 1

[0057] A method for preparing a soft magnetic composite motor stator comprises the following steps:

[0058] Step 1: take the water atomized iron powder which is composed of the following components in mass percent: 30% of iron powder with a size of above 60 mesh, 60% of iron powder with a size of 60- 200 mesh, and the rest of iron powder with a size of below 200 mesh; carry out mechanical ball milling pretreatment for 10 minutes at a speed of 380 rpm; the ball for ball milling is a cemented carbide ball, and the mass ratio of the cemented carbide ball to the iron powder is 1:8; then carry out a reduction heat treatment at 950°C for 1 h in a reducing ammonia atmosphere;

[0059] Step 2: put 1:80 orthophosphoric acid-acetone solution in a water bath at 80°C for constant temperature treatment, then mix with the pretreated water atomized iron powder evenly, dry at 70°C, and sieve through a 60-mesh sieve to prevent caking and obtain phosphoric acid-coated iron powder; the dosage of the orthophosphoric acid is 0.2wt% of the dosage of the iron powder;

[0060] Step 3: mix 1:30 epoxy resin-ethanol solution with phosphoric acid-coated iron powder evenly, dry again and sieve through a 60-mesh sieve to obtain phosphoric acid-resin-coated insulating iron powder; the dosage of the epoxy resin is 0.2wt% of the dosage of the iron powder;

[0061] Step 4: add a lubricant of 0.15wt% zinc stearate to the powder and mix them uniformly by a mixer;

[0062] Step 5: put the powder in a conventional two-way pressing hydraulic press mold for pressing at room temperature, and keep the pressing pressure at 900 MPa;

[0063] Step 6: put the formed compact in a furnace chamber of a vacuum sintering furnace, and perform annealing heat treatment in a nitrogen atmosphere, i.e. heat to temperature of 200°C, keep warm for 30 minutes, then heat to temperature of 500°C, keep

BL-5726 warm for 10 minutes, and then cool the magnetic body and discharge from the furnace. LUS04783

[0064] Comparative Example 2

[0065] A method for preparing a soft magnetic composite motor stator comprises the following steps:

[0066] Step 1: take the water atomized iron powder which is composed of the following components in mass percent: 30% of iron powder with a size of above 60 mesh, 60% of iron powder with a size of 60- 200 mesh, and the rest of iron powder with a size of below 200 mesh; carry out mechanical ball milling pretreatment for 10 minutes at a speed of 380 rpm; then carry out a reduction heat treatment at 950°C for 1 h in a reducing ammonia atmosphere;

[0067] Step 2: put 1:80 orthophosphoric acid-acetone solution in a water bath at 80°C for constant temperature treatment, then mix with the pretreated water atomized iron powder evenly, dry at 70°C, and sieve through a 60-mesh sieve to prevent caking and obtain phosphoric acid-coated iron powder; the dosage of the orthophosphoric acid is 0.2wt% of the dosage of the iron powder;

[0068] Step 3: mix 1:30 epoxy resin-ethanol solution with phosphoric acid-coated iron powder evenly, dry again and sieve through a 60-mesh sieve to obtain phosphoric acid-resin-coated insulating iron powder; the dosage of the epoxy resin is 0.2wt% of the dosage of the iron powder;

[0069] Step 4: add a lubricant of 0.15wt% zinc stearate to the powder and mix them uniformly by a mixer;

[0070] Step 5: put the powder in a conventional two-way pressing hydraulic press mold for pressing at room temperature, and keep the pressing pressure at 1,100 MPa;

[0071] Step 6: put the formed compact in a furnace chamber of a vacuum sintering furnace, and perform annealing heat treatment in a nitrogen atmosphere, i.e. heat to temperature of 200°C, keep warm for 30 minutes, then heat to temperature of 500°C, keep warm for 10 minutes, and then cool the magnetic body and discharge from the furnace.

[0072] Comparative Example 3

[0073] A method for preparing a soft magnetic composite motor stator comprises the following steps: 11

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[0074] Steps 1 to 3 are the same as those in the Comparative Example 1; LUS04783

[0075] Step 4: add a lubricant of 0.15wt% zinc stearate to the powder and mix them uniformly by a mixer;

[0076] Step 5: put the powder in a conventional two-way pressing hydraulic press mold for warm-pressing at 120°C, and keep the pressing pressure at 900 MPa;

[0077] Step 6: put the formed compact in a furnace chamber of a vacuum sintering furnace, and perform annealing heat treatment in a nitrogen atmosphere, i.e. heat to temperature of 200°C, keep warm for 30 minutes, then heat to temperature of 400°C, keep warm for 10 minutes, and then cool the magnetic body and discharge from the furnace.

[0078] Comparative Example 4

[0079] A method for preparing a soft magnetic composite motor stator comprises the following steps:

[0080] Steps 1 to 3 are the same as those in the Comparative Example 1;

[0081] Step 4: put the powder in a conventional two-way pressing hydraulic press mold for warm-pressing at room temperature, and keep the pressing pressure at 1,100 MPa;

[0082] Step 5: put the formed compact in a furnace chamber of a vacuum sintering furnace, and perform annealing heat treatment in a nitrogen atmosphere, i.e. heat to temperature of 200°C, keep warm for 30 minutes, then heat to temperature of 500°C, keep warm for 10 minutes, and then cool the magnetic body and discharge from the furnace.

[0083] Comparative Example 5

[0084] A method for preparing a soft magnetic composite motor stator comprises the following steps:

[0085] Steps 1 to 3 are the same as those in the Example 2;

[0086] Step 4: add a lubricant of 0.15wt% zinc stearate to the powder and mix them uniformly by a mixer;

[0087] Step 5: put the powder in a conventional two-way pressing hydraulic press mold for warm-pressing at room temperature, and keep the pressing pressure at 1,100 MPa;

[0088] Step 6: put the pressed blank in a nitrogen annealing furnace for annealing, i.e. heat to the annealing temperature of 200°C, keep warm for 30 minutes, then heat to temperature of 600°C, keep warm for 15 minutes, and then cool and discharge from the 12

BL-5726 furnace. LU504783

[0089] A performance test is carried out on the soft magnetic composite motor stators prepared in the above Examples 1 to 5 and Comparative Examples 1 to 5; wherein the motor stator is a cylindrical component with an inner diameter of 11 mm, an outer diameter of 30 mm and a height of 40 mm. The density is measured according to ISO3369-1975

Impermeable sintered metal materials and hardmetals—Determination of density; the saturation flux density Bs, maximum magnetic permeability Umax and coercive force He are measured according to GB/T13012-2008 Methods of measurement of d. c. magnetic properties of magnetically soft materials; the power loss Ps is measured according to

GB/T3658-2008 Methods of measurement of a. c. magnetic properties of magnetically soft materials. The results are shown in Tables 1 and 2.

[0090] Table 1

Center

Bs(T) Umax | Hc(A/m) ata

No. 1000H Botto 10000A/m 100Hz | 200Hz | 500Hz Top | height

Zz m of 20 mm

DKM

[0091] As shown in Table 1, through the innovative combination of phosphoric acid-resin inorganic-organic coating and bidirectional-isostatic combined pressing, high density uniformity can be obtained. The tests show that various parts of the stator ring have high density consistency, and the material has high saturation magnetic induction, magnetic permeability and low loss, which meets the requirements of low-frequency motors. In addition, as the number of large iron powder particles decreases, the saturation magnetic induction and magnetic permeability gradually decrease (Examples 1 to 3). In 13

BL-5726 _ . . . . LU504783 addition, the inventors have found that, compared with those of the iron powder with any two particle sizes, the magnetic properties of the iron powder with three particle sizes are increased by more than 10% and their coercive forces are decreased by more than 8%.

[0092] Table2

Ps(W/kg) Density (g/cm?)

Cent er at

Bs(T) Un Hc(A/ a

No. 10000 | ax m) 100 | 200 | 500 | 1000 | To Bott heig

A/m Hz | Hz | Hz | Hz p om ht of mm

Comparative 33 7.4 1.34 254.6 | 12.8 | 27.5 | 61.2 | 138.6 7.3 7.4

Example 1 6 1

Comparative 34 | 298.3. 7.4 1.37 16.5 | 33.1 | 68.1 | 145.2 731 | 7.42

Example 2 8 7 3

Comparative 34 7.4 1.36 246.8 | 12.2 | 26.9 | 59.1 | 135.1 7.32 | 7.41

Example 3 7 2

Comparative 32 15. 7.3 1.32 293.5 31.2 | 67.3 | 143.1 7,22 | 7.32

Example 4 5 7 3

Comparative 34 10. 7.3 1.38 205.6 22.3 | 56.4 | 205.8 7,27 | 7.37

Example 5 6 1 9

[0093] Compared with the bidirectional-isostatic combined pressing method used in the present disclosure, when pressing at room temperature, the density uniformity under the pressure of 900-1,100 MPa is poor, and the density at the center of the stator is significantly lower than that at both ends (Comparative Examples 1 and 2), resulting in lower saturation magnetic induction intensity and maximum magnetic permeability of the magnetic body and affecting the magnetic permeability of the material; in addition, the high pressing pressure brings a large internal stress of pressing; even if the heat treatment temperature rises to 500°C, the coercive force of the magnetic body is still very high, 14

BL-5726 leading to high loss of the magnetic body at low frequencies and affecting the energy LUS04783 consumption of the motor. Compared with the examples of the present disclosure, the soft magnetic composites (SMCs) obtained by the conventional pressing method and heat treatment method have poorer density uniformity, lower saturation magnetic induction intensity and maximum magnetic permeability of the magnetic body, but still have high coercive force, which affects the magnetic permeability of the material (Comparative

Example 5). When warm-pressing at 120°C is used, the density and magnetic properties are slightly improved, but the effect is still poor compared to the innovative pressing of the present disclosure (Comparative Example 3). Meanwhile, after the innovative pressing method, the use of lubricants can be omitted (Examples 1 to 3), but when no lubricant is used in ordinary pressing, the density uniformity, magnetic properties and loss of the magnetic body will be seriously affected (Comparative Example 4).

[0094] In summary, when the lubricants are omitted and the heat treatment energy consumption is reduced, motor stators made of SMC with high density uniformity, high magnetic property and high strength are obtained by the bidirectional-isostatic combined pressing method of the present disclosure.

[0095] The foregoing description merely describes the preferred embodiments of the present disclosure. It should be noted that for those of ordinary skill in the art, several improvements and modifications can be made without departing from the principle of the present disclosure, and these improvements and modifications shall also fall within the scope of protection of the present disclosure.

Claims

BL-5726 CLAIMS LU504783

1. A method for preparing a high-density high-strength soft magnetic composite motor stator, comprising: step 1: preparing iron powder, wherein the iron powder is composed of the following components in mass percent: 20-40% of iron powder with a size of above 60 mesh, 50-70% of iron powder with a size of 60- 200 mesh, and the rest of iron powder with a size of below 200 mesh; step 2: carrying out ball milling and reduction pretreatment of the iron powder; step 3: carrying out phosphoric acid and resin insulation coating on the pretreated iron powder to obtain phosphoric acid-resin coated iron powder; step 4: carrying out primary pressing formation of the phosphoric acid-resin-coated iron powder, with a forming pressure of 300-800 MPa; after completion of the pressing, sealing the formed blank through a vacuum packaging bag and then proceed to the isostatic secondary forming, with a forming pressure of 200-500 MPa; step 5: removing the vacuum packaging bag of the magnetic body after the isostatic forming, and performing annealing heat treatment in a nitrogen atmosphere: heating to temperature of 180-250°C, keeping warm for 20-40 minutes, then heating to temperature of 350-450°C, keeping warm for 5-15 minutes, and then cooling and discharging.

2. The method according to claim 1, wherein in the step 1, the iron powder is pure iron powder, atomized iron powder or reduced iron powder, and the component purity is >

99.0%.

3. The method according to claim 1, wherein in the step 2, the ball milling is carried out on the iron powder, specifically: the ball milling speed is 200-400 rpm, the pretreatment time is 5- 20 minutes; the ball for the ball grinding is a cemented carbide ball, and the mass ratio of the cemented carbide ball to the iron powder is 1:5-1:10.

4. The method according to claim 1, wherein in the step 2, the reduction pretreatment of the iron powder is carried out, specifically: the iron powder is treated at 900-1,100°C for 1-2 h in an ammonia atmosphere.

5. The method according to claim 1, wherein in the step 3, the phosphoric acid and 16

BL-5726 resin insulation coating on the pretreated iron powder is carried out, specifically: LUS04783 putting the 1:50-80 orthophosphoric acid solution in a water bath at 60-80°C to keep the temperature constant, adding the pretreated iron powder, and mixing with the orthophosphoric acid solution evenly, then drying the iron powder at 60-80°C and sieving to obtain phosphoric acid-coated iron powder; mixing the 1:30-50 thermosetting resin solution with the phosphoric acid-coated iron powder evenly, drying the iron powder again and sieving to obtain phosphoric acid-resin-coated insulating iron powder.

6. The method according to claim 5, wherein a solvent of the orthophosphoric acid solution is acetone, ethanol or deionized water, and dosage of orthophosphoric acid is

0.1-0.3wt% of the dosage of the iron powder.

7. The method according to claim 5, wherein the thermosetting resin is epoxy resin, phenolic resin or polyurethane, and a solvent of the thermosetting resin solution is ethanol or acetone, and the dosage of the thermosetting resin is 0.1-0.2wt% of the dosage of the iron powder.

8. A high-density and high-strength soft magnetic composite motor stator is prepared by the method of any one of claims 1 to 7. 17