CN111638477A - Method for nondestructive testing of sheet metal magnetic powder magnetic permeability - Google Patents
Method for nondestructive testing of sheet metal magnetic powder magnetic permeability Download PDFInfo
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- CN111638477A CN111638477A CN202010418877.8A CN202010418877A CN111638477A CN 111638477 A CN111638477 A CN 111638477A CN 202010418877 A CN202010418877 A CN 202010418877A CN 111638477 A CN111638477 A CN 111638477A
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Abstract
The invention provides a method for nondestructive testing of sheet metal magnetic powder magnetic permeability, which is characterized by comprising the following steps: the sheet metal magnetic powder is molded into an ordered body to be tested after the magnetic field orientation step and the radial compaction step, and the ordered body to be tested is subjected to an electromagnetic characteristic test to obtain magnetic permeability or parameters capable of being used for calculating the magnetic permeability; the magnetic field orientation step is as follows: the sheet metal magnetic powder is arranged in parallel under the action of a magnetic field; the radial compaction step is as follows: providing radial pressure for the sheet metal magnetic powder; the magnetic field orientation step may be performed prior to the radial compaction step, or the magnetic field orientation step and the radial compaction step may be performed simultaneously. The flaky metal magnetic powder is regularly arranged in a certain direction under the orientation effect of the magnetic field and is more easily compacted and formed, the regularly arranged flaky metal magnetic powder is closer to the state of the flaky metal magnetic powder in a final product, and the reliability and the reference value of magnetic conductivity detection can be improved. The sample preparation and detection processes do not damage the sheet metal magnetic powder and can be recycled.
Description
Technical Field
The invention belongs to the field of magnetic material performance detection, and particularly relates to a method for nondestructively detecting the magnetic permeability of sheet metal magnetic powder.
Background
The magnetic conductivity parameter is an important electromagnetic characteristic parameter, and is accurate in measurement and significant, and the magnetic conductivity of the sheet metal magnetic powder cannot be directly measured. One of the existing measuring methods is to prepare a final product for testing, for example, a sample to be tested is mixed with a certain adhesive and an additive to prepare slurry, the slurry is cast into a raw belt, then the raw belt is hot-pressed and molded, and then the raw belt is punched into a specific shape, such as a ring shape, and the specific shape is used as a magnetic core of a coil to measure self-inductance/mutual inductance; and determining the magnetic permeability of the material by utilizing the relation between the coil inductance and the magnetic permeability of the magnetic core material. The test method has the advantages of complex sample preparation process, time and labor waste, difficulty in mastering and stable implementation. In addition, after mixing with the binder and hot press molding, the sample to be tested is partially damaged and cannot be separated out alone, so that the sample to be tested cannot be reused after the magnetic permeability test.
In addition, the sample powder to be tested can also be mixed with the molten paraffin in a certain proportion, shaped in a mould and tested. Thus, the sample preparation is simple, and the paraffin can be melted by heating and then the sample to be detected can be recycled. However, it is not considered that the magnetic permeability of the sample to be measured is influenced by the arrangement of the sample to be measured. In the magnetic core for conducting the permeability test, the sample to be tested is in a disordered isotropic stacked state, however, in a product in which the sample to be tested is used as a production raw material, the sample to be tested is generally arranged anisotropically in a certain orientation. Therefore, the magnetic permeability test result of the magnetic core prepared by the method is adopted to evaluate the magnetic permeability of the product prepared by the sample to be tested, and a larger error is generated.
Disclosure of Invention
The invention aims to provide a method for nondestructively testing the magnetic permeability of sheet metal magnetic powder so as to improve the speed and reliability of the magnetic permeability test of the sheet metal magnetic powder.
According to one aspect of the present invention, there is provided a method for non-destructive testing of magnetic permeability of sheet metal magnetic powder, comprising: the sheet metal magnetic powder is molded into an ordered body to be tested after the magnetic field orientation step and the radial compaction step, and the ordered body to be tested is subjected to an electromagnetic characteristic test to obtain magnetic permeability or parameters capable of being used for calculating the magnetic permeability; the magnetic field orientation step is as follows: the sheet metal magnetic powder is arranged in parallel under the action of a magnetic field; the radial compaction step is as follows: providing radial pressure for the sheet metal magnetic powder; the magnetic field orientation step may be performed prior to the radial compaction step, or the magnetic field orientation step and the radial compaction step may be performed simultaneously.
The magnetic powder is arranged regularly according to a certain orientation, and is more easily compacted and molded, and the formed ordered body to be detected can reach higher density. The magnetic conductivity of the ordered object to be measured by the method has higher reliability on the judgment of the magnetic conductivity of the finished product, so that the magnetic conductivity of the final product of production activities can be accurately predicted by using the sheet metal magnetic powder produced in the research and development and preparation stages of the magnetic material, unqualified magnetic materials can be rapidly checked without being put into production for detection, the research and development cost is saved, and the efficiency of technical improvement and innovation is improved. In the sample preparation process, the flaky metal magnetic powder does not need to be mixed with other materials, the flaky metal magnetic powder cannot be irreversibly damaged by a radial compaction mode, and the flaky metal magnetic powder can be recycled and reused after the magnetic conductivity is detected, so that nondestructive detection in the true sense is achieved. In addition, the method also eliminates the processes of material input, energy consumption and production for sample preparation, reduces the detection cost and improves the detection efficiency.
Preferably, in the radial compaction step: (1) filling the sheet metal magnetic powder into a mold with a sample accommodating cavity, wherein the radial cavity wall of the sample accommodating cavity is made of a heat-shrinkable material; (2) heating the mold to enable the radial cavity wall to contract radially and provide radial pressure for the sheet metal magnetic powder in the sample accommodating cavity; (3) rapidly cooling the contracted radial cavity wall. The sheet metal magnetic powder can be radially compacted and molded into an ordered to-be-detected body by utilizing the shrinkage of the thermal shrinkage material, no complex and expensive equipment is needed in the sample preparation process, and the operation is convenient. The contraction direction of the radial cavity wall is vertical to the direction of the parallel arrangement of the sheet metal magnetic powder. Therefore, the radial pressure on the flaky metal magnetic powder does not influence the arrangement direction of the flaky metal magnetic powder, so that the flaky metal magnetic powder can still be arranged in parallel in the same direction before and after compaction and is consistent with the arrangement state of the flaky metal magnetic powder in a final product.
Preferably, the gel content in the heat-shrinkable material is 60 to 70% by mass. The gel content of the heat-shrinkable material is limited, so that the heat-shrinkable material has good contractility and expansibility, can be quickly shrunk to the original position when the sheet metal magnetic powder is compacted, and is easily expanded when being reheated so as to be convenient for taking out the ordered object to be measured from the die.
Preferably, the raw materials for preparing the heat-shrinkable material comprise 150-180 parts of ethylene-vinyl acetate copolymer and 0-50 parts of linear low-density polyethylene according to parts by weight. The heat-shrinkable material prepared from the raw materials can be shrunk in place at 90-100 ℃, the shrinking temperature is low (the shrinking temperature of a common heat-shrinkable material is about 130 ℃), the safety of the operation process is improved, and the energy consumption of heating is also reduced. In addition, the introduction of linear low density polyethylene improves the mechanical strength of the heat shrinkable material.
Preferably, the sample holding chamber comprises radial chamber wall and holding chamber bottom plate, and the periphery of holding chamber bottom plate is located to radial chamber wall cover, and the material of holding chamber bottom plate does not have pyrocondensation nature. In the heating process, the bottom plate of the accommodating cavity cannot deform along with the temperature change, so that the bottom of the mold is kept flat, and the deformation of the bottom plate, such as tilting, concave recessing, convex protruding and the like, is avoided. Optionally, the bottom plate of the accommodating cavity is made of 100% epoxy resin. The epoxy resin has better heat resistance below 180 ℃.
Preferably, in the magnetic field orienting step, the magnetic field direction of the magnetic field is a vertical direction.
Preferably, the gradient direction of the magnetic field is a vertically downward direction.
The resultant force direction of the sheet metal magnetic powder in the magnetic field is always vertical downward, so that the sheet metal magnetic powder can be tightly stacked on the lower part of the mold under the action of the vertical downward resultant force.
Preferably, the magnetic field has a field strength of 0.01T-1.0T.
Preferably, the magnetic field orientation step is carried out for a time of not less than 2 minutes before the temperature of the radial chamber walls is brought to their melting point.
The flaky metal magnetic powder can be ensured to fully interact with a magnetic field, and disordered stacking is converted into ordered arrangement.
Preferably, before the radial compaction step is carried out, a notch is made on the top edge of the radial cavity wall; the method also comprises a sample recovery step after the electromagnetic property test is carried out on the ordered object to be tested: and heating the mold containing the ordered body to be detected, tearing the notch to stretch the radial cavity wall after the plasticity of the radial cavity wall is restored, and taking the ordered body to be detected out of the mold. Before contraction, the radial cavity walls are of a small thickness and are easily notched.
Drawings
FIG. 1 is a schematic view of the assembly of a heat shrinkable material and a bottom plate of a receiving chamber;
FIG. 2 is a schematic perspective view of the mold in an unretracted condition;
FIG. 3 is a schematic perspective view of components of the magnetic field orientation device;
FIG. 4 is a schematic perspective view of a component for measuring permeability of a material;
FIG. 5 is a schematic view of a configuration in which the mold is placed in a magnetic field orientation device;
fig. 6 is a schematic perspective view of the radial cavity wall of the mold when it is contracted to the original position.
The correspondence of the various components to the numbers in the drawings is as follows:
1. the magnetic field orientation device comprises a mold, 11 parts of a heat shrinkable material, 12 parts of an accommodating cavity bottom plate, 13 parts of a sample accommodating cavity, 14 parts of a notch, 2 parts of a magnetic field orientation device, 21 parts of a yoke frame, 211 parts of a lower pole head, 212 parts of an upper pole head, 22 parts of a magnet, 23 parts of an inner cavity of the magnetic field orientation device, 3 parts of an LCR tester and 4 parts of a test coil.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The mold 1 referred to in the following examples was prepared by the following method:
preparation of the heat-shrinkable material 11: putting the mixture into a smelting cavity of a double-roll open mill, melting and mixing the mixture at 130 ℃, then pressing the mixture on a flat vulcanizing machine for 10 minutes at 130 ℃ and 10MPa to form a sheet, irradiating the sheet by using an ELV-8 type electron accelerator with the irradiation dose of 100kGy, and naturally cooling the sheet to room temperature to obtain a finished product;
molding of the mold 1: and (3) heating the heat-shrinkable material 11 in an oven at 130 ℃ for 4 minutes, then winding the heat-shrinkable material 11 into a hollow tubular object, and rapidly cooling and shaping. As shown in fig. 1, the tubular object is sleeved on the periphery of a circular bottom plate with an inner diameter matched with the tubular object, the circular bottom plate is made of 100% epoxy resin, so as to prepare a mold 1, a space enclosed by the inner surface of the tubular object and the upper surface of the circular bottom plate is used as a sample accommodating cavity 13 of the mold 1, a heat shrinkable material 11 is used as a radial cavity wall of the sample accommodating cavity 13, and the circular bottom plate is used as an accommodating cavity bottom plate 12. The mold 1 is shaped as shown in fig. 2.
As shown in fig. 3, the magnetic field orientation device 2 used in the following embodiment includes a yoke frame 21 and a magnet 22, the yoke frame 21 is in a square frame shape, the inside of the yoke frame 21 is hollow, a lower pole head 211 penetrating the upper surface is opened in the middle of the upper surface of the bottom side of the yoke frame 21, the lower pole head 211 protrudes upward relative to the upper surface, an upper pole head 212 penetrating the lower surface is opened in the middle of the lower surface of the top side of the yoke frame 21, and the upper pole head 212 protrudes downward relative to the lower surface. The lower pole head 211 and the upper pole head 212 are symmetrical about the geometric center of the yoke frame 21, the distance between the hole of the lower pole head 211 and the hole of the upper pole head 212 is smaller than the height of the die 1, the hole diameter of the hole of the upper pole head 211 is slightly larger than the maximum outer diameter of the die 1, so that the bottom and the top of the die 1 can respectively extend into the lower pole head 211 and the upper pole head 212, and the die 1 is limited by the mutual matching of the lower pole head 211 and the upper pole head 212. One magnet 22 is fixedly mounted inside each of the opposite sides of the yoke frame 21 distributed on the left and right, the two magnets 22 are symmetrical about the central axis of the yoke frame 21, the magnetic lines of force of the magnets 22 are led out of the yoke frame 21 through the lower pole head 211 and the upper pole head 212, and a magnetic field of 0.05-0.1T is generated between the lower pole head 211 and the upper pole head 212.
The components and parts that embodiment 1, embodiment 2, embodiment 3 and comparative example 1 are used for testing material magnetic permeability include LCR tester 3, test coil 4 and a plurality of wire, and test coil 4 is for having 100 circles around, and the epoxy piece of the copper wire coil of 0.5mm of wire diameter, and the middle part of epoxy piece is equipped with the cavity that runs through its upper and lower surface, and the internal diameter of this cavity is equal with the external diameter of holding chamber bottom plate 12 of mould 1, and wire connection LCR tester 3 and test coil 4. The permeability test principle of the test objects prepared in example 1, example 2, example 3 and comparative example 1 is as follows:
as shown in FIG. 4, the test module port is connected to the LCR tester 3, and when an alternating current flows through the loop, the LCR tester 3 will read the inductance (L) of an air coil0) When the ordered object to be tested or the wave-absorbing sheet sample formed by stacking the soft magnetic powder is placed in the hollow cavity of the test coil 4, the LCR tester 3 will read the inductance (L) of the iron core, and then the L/L0Is a function of the height h, radius r, cavity influence factor m and magnetic permeability u of the hollow cavity, and is derived as follows:
L/L0＝((h-r)/h+u×r/h+m)/(1+m)。
the test results of some materials with known performance are substituted into the model, and u and L, L can be obtained through simulation calculation and coefficient correction0Semi-quantitative relationships within a certain range.
The sheet metal magnetic powder referred to in the following examples is a same batch of Fe-Si-Al soft magnetic powder with an average particle size of 60 μm.
Example 1
Two notches 14 symmetrical relative to the central axis of the mold 1 are cut in the top edge of the radial cavity wall of the mold 1, the notches 14 are V-shaped, and the distance from the bottom to the top edge of the radial cavity wall is one fifth of the height of the sample accommodating cavity 13. Filling the sheet metal magnetic powder to be measured into a sample accommodating cavity 13 with the mold 1, wherein the filling height is not more than one third of the height of the sample accommodating cavity 13. The magnetic field aligning device 2 is placed on the heating surface of the heating device so that the bottom edge of the yoke frame 21 is in contact with the heating surface. The bottom of a mould 1 filled with the sheet metal magnetic powder extends into a lower pole head 211, the top of the mould 1 extends into an upper pole head 212, the mould 1 is limited in an effective magnetic field area between the lower pole head 211 and the upper pole head 212 (as shown in figure 5), a heating device is started immediately, the temperature is increased to 93-95 ℃ at the speed of 15 ℃/min, the temperature is kept for 4 minutes until a heat-shrinkable material 11 serving as a radial side wall shrinks to the original position (as shown in figure 6), and the sheet metal magnetic powder in a sample accommodating cavity 13 is compacted into an ordered body to be measured with certain apparent density in the process. In the process of heating up, the die 1 is prevented from moving out of the inner cavity 23 of the magnetic field orientation device, so that the uncompacted flaky metal magnetic powder is prevented from shaking. After the thermal shrinkage material 11 shrinks to the original position, the thermal shrinkage material is rapidly cooled and shaped, and then the mold 1 with the ordered object to be measured is taken out from the inner cavity 23 of the magnetic field orientation device.
Starting the LCR tester 3, adjusting the frequency of the LCR tester 3 to 100kHz, and recording the inductance value L at the moment when the sample to be tested is not placed0Then the mould 1 with the ordered body to be tested is placed into the hollow cavity of the test coil 4, and the inductance value L at the moment is recorded. By u and L, L0And (4) calculating the semi-quantitative relational expression of the (a) to obtain u.
After the test is finished, the mold 1 with the ordered body to be tested is placed on the heating surface of the heating device, the temperature is raised to 90-100 ℃, the forceps are used for tearing the two notches 14 on the radial cavity wall to break the radial cavity wall, and then the ordered body to be tested is taken out of the mold 1. Finally, the orderly body to be tested is made by ultrasonic beating and is re-dispersed into loose flaky metal magnetic powder. In other embodiments, if the radial cavity wall contracted to the original position is thin, the radial cavity wall can be directly cut after the magnetic permeability measurement is performed, so that the ordered object to be measured can be taken out of the mold 1.
Example 2
Two notches 14 symmetrical relative to the central axis of the mold 1 are cut in the top edge of the radial cavity wall of the mold 1, the notches 14 are V-shaped, and the distance from the bottom to the top edge of the radial cavity wall is one fifth of the height of the sample accommodating cavity 13. Filling the sheet metal magnetic powder to be measured into a sample accommodating cavity 13 with the mold 1, wherein the filling height is not more than one third of the height of the sample accommodating cavity 13. The magnetic field orienting device 2 is placed on the heating surface of the heating device such that the bottom edge of the yoke frame 21 is in contact with the heating surface by the bottom edge of the magnet mounting frame 21 in which the magnet 22 is embedded. The bottom of a mould 1 filled with the sheet metal magnetic powder extends into a lower pole head 211, the top of the mould 1 extends into an upper pole head 212, the mould 1 is limited in an effective magnetic field area between the lower pole head 211 and the upper pole head 212, the magnetic field is oriented for 2 minutes, then a heating device is started, the temperature is increased to 93-95 ℃ at the speed of 25 ℃/min, the temperature is kept for 4 minutes until a heat-shrinkable material 11 serving as a radial side wall shrinks to the original position, and the sheet metal magnetic powder in a sample accommodating cavity 13 is compacted into an ordered body to be measured with certain loose packing density in the process. In the process of heating up, the die 1 is prevented from moving out of the inner cavity 23 of the magnetic field orientation device, so that the uncompacted flaky metal magnetic powder is prevented from shaking. After the thermal shrinkage material 11 shrinks to the original position, the thermal shrinkage material is rapidly cooled and shaped, and then the mold 1 with the ordered object to be measured is taken out from the inner cavity 23 of the magnetic field orientation device.
Starting the LCR tester 3, adjusting the frequency of the LCR tester 3 to 100kHz, and recording the inductance value L at the moment when the sample to be tested is not placed0Then the mould 1 with the ordered body to be tested is placed into the hollow cavity of the test coil 4, and the inductance value L at the moment is recorded. By u and L, L0And (4) calculating the semi-quantitative relational expression of the (a) to obtain u.
After the test is finished, the mold 1 with the ordered body to be tested is placed on the heating surface of the heating device, the temperature is raised to 90-100 ℃, the forceps are used for tearing the two notches 14 on the radial cavity wall to break the radial cavity wall, and then the ordered body to be tested is taken out of the mold 1. Finally, the orderly body to be tested is made by ultrasonic beating and is re-dispersed into loose flaky metal magnetic powder. In other embodiments, if the radial cavity wall contracted to the original position is thin, the radial cavity wall can be directly cut after the magnetic permeability measurement is performed, so that the ordered object to be measured can be taken out of the mold 1.
Example 3
Two notches 14 symmetrical relative to the central axis of the mold 1 are cut in the top edge of the radial cavity wall of the mold 1, the notches 14 are V-shaped, and the distance from the bottom to the top edge of the radial cavity wall is one fifth of the height of the sample accommodating cavity 13. Filling the sheet metal magnetic powder to be measured into a sample accommodating cavity 13 with the mold 1, wherein the filling height is not more than one third of the height of the sample accommodating cavity 13. The mould 1 with the ordered body to be measured is placed on the heating surface of a heating device, the temperature is raised to 93-95 ℃ at the speed of 15 ℃/min, the temperature is kept for 4 minutes until the heat shrinkable material 11 as the radial side wall shrinks to the original position, and the cooling and the shaping are rapidly carried out. In the process, the sheet metal magnetic powder in the sample accommodating cavity 13 is compacted into a stacked body to be measured with certain apparent density.
Starting the LCR tester 3, adjusting the frequency of the LCR tester 3 to 100kHz, and recording the inductance value L at the moment when the sample to be tested is not placed0Then, the mold 1 with the stacked body to be tested is placed in the hollow cavity of the test coil 4, and the inductance L at this time is recorded. By u and L, L0And (4) calculating the semi-quantitative relational expression of the (a) to obtain u.
After the test is finished, the die 1 with the stacked body to be tested is placed on the heating surface of the heating device, the temperature is raised to 90-100 ℃, the tweezers are used for tearing the two notches 14 on the radial cavity wall to break the radial cavity wall, and the tweezers are used for taking out the stacked body to be tested from the die 1. Finally, the stacked body to be tested is manufactured by ultrasonic beating and is re-dispersed into loose flaky metal magnetic powder. In other embodiments, if the radial cavity wall contracted to the original position is thin, the radial cavity wall can be directly cut after the magnetic permeability measurement is performed, so that the stacked object to be measured can be taken out of the mold 1.
Comparative example 1
Uniformly mixing the flaky metal magnetic powder and the molten paraffin according to the mass ratio of 80:20, and cooling the mixture in a mold to form a cylindrical to-be-detected body with the diameter of 20 mm.
Starting the LCR tester 3, adjusting the frequency of the LCR tester 3 to 100kHz, and recording the inductance value L at the moment when the sample to be tested is not placed0Then, the cylinder of the body to be tested is placed in the hollow cavity of the test coil 4, and the inductance value L at the moment is recorded. By u and L, L0And (4) calculating the semi-quantitative relational expression of the (a) to obtain u.
Comparative example 2
Preparing the wave absorbing plate stamping ring by using the sheet metal magnetic powder according to the following steps:
step 1: taking 0.30 part by weight of polyurethane into 0.70 part by weight of cyclohexanone, and stirring and dissolving in an open container to prepare glue;
step 2: 1, putting 1 part by weight of flaky Fe-Si-Al soft magnetic powder, 0.040 part by weight of BIBP and a small amount of vulcanizing agent into the glue obtained in the step 1, and stirring and dissolving in an open container to obtain a wave-absorbing sheet raw material solution;
and step 3: taking the wave-absorbing sheet raw material liquid obtained in the step (2), coating the wave-absorbing sheet raw material liquid on a high polymer film at the speed of 2.3m/min, and controlling the thickness of the coating to be 0.17mm in the coating process;
and 4, step 4: heating and curing the coated coating through segmented temperature control to obtain a semi-finished product;
and 5: putting the semi-finished product into a vulcanizing machine, controlling the heating temperature to be 180 ℃, and vulcanizing the semi-finished product of the wave-absorbing material at the speed of 2.5m/min under the condition of 8MPa of pressure to obtain a wave-absorbing sheet;
step 6: and stamping the wave-absorbing sheet into a stamping ring with the outer diameter of 20mm and the inner diameter of 10 mm.
The punched ring obtained as described above was fixed to a jig 16454A for magnetic permeability measurement, and a magnetic permeability (u) was measured using a 9441B impedance analyzer (german technology).
The deviation ratios of the magnetic permeability data obtained by using the ordered test object, the stacked test object or the paraffin cylinder test object of example 1, example 2, example 3 and comparative example 1, respectively, with respect to the magnetic permeability test result of the stamp ring prepared in this example were counted, and the calculation formula of the deviation ratio was as follows (the "test object" in the following formula is the ordered test object of example 1 or the ordered test object of example 2 or the stacked test object of example 3 or the paraffin cylinder test object of comparative example 1)
The statistical results of the deviation ratios are shown in table 1.
TABLE 1 magnetic conductivity test deviation ratio statistics
According to the test result, for the wave-absorbing sheet product prepared from the sheet metal magnetic powder, the magnetic conductivity measured by the ordered object to be tested obtained by adopting the combination of magnetic field orientation and radial compaction sample preparation is closer to the magnetic conductivity of the wave-absorbing sheet product.
Although the present invention has been described in detail with reference to the preferred embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the true spirit and scope of the present invention.
Claims (10)
1. A method for nondestructive testing of sheet metal magnetic powder magnetic permeability is characterized in that:
forming the sheet metal magnetic powder into an ordered object to be tested after the magnetic field orientation step and the radial compaction step, and carrying out an electromagnetic property test on the ordered object to be tested to obtain magnetic permeability or a parameter capable of being used for calculating the magnetic permeability;
the magnetic field orientation step is as follows: the sheet metal magnetic powder is arranged in parallel under the action of a magnetic field;
the radial compaction step comprises the following steps: providing radial pressure for the parallel arrangement of the sheet metal magnetic powder;
the magnetic field orientation step may be performed prior to the radial compaction step, or the magnetic field orientation step and the radial compaction step may be performed simultaneously.
2. The method for non-destructively testing magnetic powder permeability of sheet metal according to claim 1, wherein in the radial compacting step:
(1) filling the sheet metal magnetic powder into a mold with a sample accommodating cavity, wherein the radial cavity wall of the sample accommodating cavity is made of a heat-shrinkable material;
(2) heating the die to enable the radial cavity wall to shrink radially so as to provide radial pressure for the sheet metal magnetic powder in the sample accommodating cavity;
(3) rapidly cooling the contracted radial cavity wall.
3. The method for non-destructive testing of magnetic permeability of sheet metal powder according to claim 2, wherein: the gel content in the heat-shrinkable material is 60-70% by mass percent.
4. A method for non-destructive examination of the permeability of magnetic powders in sheet form as claimed in claim 3, characterized in that: the raw materials for preparing the thermal shrinkage material comprise, by mass, 150-180 parts of ethylene-vinyl acetate copolymer and 0-50 parts of linear low density polyethylene.
5. The method for non-destructive testing of magnetic permeability of sheet metal powder according to claim 2, wherein: the sample holding cavity is composed of a radial cavity wall and a holding cavity bottom plate, the radial cavity wall is sleeved on the periphery of the holding cavity bottom plate, and the holding cavity bottom plate is made of a material without thermal shrinkage.
6. The method for non-destructive testing of magnetic permeability of flake metal particles according to any of claims 2 to 5, wherein: in the magnetic field orienting step, a magnetic field direction of the magnetic field is a vertical direction.
7. The method for non-destructive testing of magnetic permeability of sheet metal powder according to claim 6, wherein: the gradient direction of the magnetic field is a vertical downward direction.
8. The method for non-destructive testing of magnetic permeability of flake metal particles according to any of claims 2 to 5, wherein: the magnetic field intensity of the magnetic field is 0.01T-1.0T.
9. The method for non-destructive testing of magnetic permeability of sheet metal powder according to claim 8, wherein: the magnetic field orientation step is carried out for a time of not less than 2 minutes before the temperature of the radial chamber wall is brought to its melting point.
10. The method for non-destructive testing of magnetic permeability of flake metal particles according to any of claims 2 to 5, wherein:
before performing the radial compaction step, creating a notch on a top edge of the radial cavity wall;
the method also comprises a sample recovery step after the electromagnetic property test is carried out on the ordered body to be tested: and heating the mold containing the ordered body to be measured, tearing the notch to stretch the radial cavity wall after the radial cavity wall recovers plasticity, and taking the ordered body to be measured out of the mold.
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