CN115762944A - High-precision encoder magnetic grid material and preparation method of encoder magnetic grid - Google Patents
High-precision encoder magnetic grid material and preparation method of encoder magnetic grid Download PDFInfo
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Abstract
The invention relates to the technical field of magnetic encoders, and discloses a high-precision encoder magnetic grid material and a preparation method of the encoder magnetic grid, wherein the encoder magnetic grid material comprises the following raw materials in parts by weight: 20 to 95 portions of anisotropic samarium iron nitrogen or composite magnetic powder thereof, 0.1 to 1 portion of coupling agent, 5 to 80 portions of macromolecular resin and 0.1 to 1.5 portions of assistant. The preparation method comprises the steps of mixing raw materials, carrying out injection molding orientation, demagnetizing to obtain a semi-finished product, and magnetizing to obtain the high-precision encoder magnetic grid.
Description
Technical Field
The invention relates to the technical field of magnetic encoders, in particular to a high-precision encoder magnetic grid material and a preparation method of an encoder magnetic grid.
Background
The magnetic encoder has the advantages of simple structure, low possibility of being influenced by dust, high response speed, small size, low cost and the like, and is widely applied to the industrial automation fields of precision machinery, numerical control machines, robots and the like.
The magnetic encoder mainly comprises a magnetic grid, a detection sensitive element and a signal processing circuit. The magnetic grid is the most core part of the magnetic encoder and is made of permanent magnetic materials, the structural shape of the magnetic grid is divided into a plurality of different structures such as a magnetic drum, a magnetic disk, a magnetic ring, a linear magnetic scale and the like, and the magnetic grid is used for meeting the structural and installation requirements of different magnetic encoders. The alternating N-pole and S-pole magnetic poles can be formed on the magnetic grid by adopting different manufacturing processes, the magnetic field information of the magnetic poles, such as surface magnetic strength and precision, magnetic pole waveform zero crossing precision, coercive force, temperature characteristic and the like, has important influence on the precision and resolution of a magnetic encoder, and the magnetic field information of the magnetic grid magnetic poles is completely determined by the material of the magnetic grid and the manufacturing method of the magnetic grid.
The encoder magnetic grid material is required to have the magnetic characteristics of high remanence, high coercivity, high magnetic energy product, wide temperature range and the like, and most of the existing encoder magnetic grid permanent magnetic materials adopt ferrite, neodymium iron boron and the like. For example, CN10968860A and CN102873325A are made of ferrite or neodymium iron boron.
CN10968860A discloses an absolute type magnetic rotary encoder, which comprises a rotating shaft, a plurality of rotating wheels capable of rotating along with the rotating shaft, a plurality of encoding units corresponding to the rotating wheels one by one, and one or more permanent magnet assemblies for providing magnetic field bias for the encoding units. Each coding unit comprises a magnetic conductivity encoder disc and a sensor unit, wherein the magnetic conductivity encoder disc is structurally arranged on each coding unit and can enable the magnetic conductivity of each coding unit to be different along with the difference of the position of the coding unit relative to the rotating shaft, the sensor unit comprises a plurality of magnetic sensors, and the permanent magnet assembly of each coding unit is made of one of barium ferrite, cobalt ferrite, neodymium iron boron and ferrite.
CN102873325A discloses a layered feeding method for die pressing neodymium iron boron magnetic powder, the common manufacturing method of these material magnetic grids is to use ferrite and rubber to press and form or use the ferrite magnetic powder coating process of oil-mixed adhesive to make, etc., the above materials and manufacturing method have the problems of low surface magnetic strength and precision, poor zero crossing precision of magnetic pole waveform, low coercive force, weak anti-electromagnetic interference capability, poor corrosion resistance, etc. for the occasion of the precise magnetic grid which needs to satisfy the complex structure, compact size and multiple magnetic poles.
Disclosure of Invention
The invention provides a material of an encoder magnetic grid taking anisotropic samarium-iron-nitrogen as a main body material, aiming at the problems of poor precision, low coercive force, weak anti-electromagnetic interference capability and the like of the magnetic grid taking ferrite and neodymium-iron-boron as materials.
In order to realize the purpose, the invention adopts the technical scheme that:
a high-precision encoder magnetic grid material comprises the following raw materials in parts by weight: 20 to 95 portions of anisotropic samarium iron nitrogen or composite magnetic powder thereof, 0.1 to 1 portion of coupling agent, 5 to 80 portions of macromolecular resin and 0.1 to 1.5 portions of assistant.
The anisotropic samarium iron nitrogen or the composite magnetic powder thereof comprises anisotropic samarium iron nitrogen magnetic powder and/or composite magnetic powder of anisotropic samarium iron nitrogen and anisotropic ferrite.
The anisotropic samarium iron nitrogen magnetic powder has excellent magnetic performance, is equivalent to the anisotropic neodymium iron boron, is far higher than the isotropic neodymium iron boron and the anisotropic ferrite magnetic powder, and has higher corrosion resistance than neodymium magnetic powder; the magnetic grating is used for preparing the encoder magnetic grating, so that higher surface magnetic strength can be obtained, and the resolution space and the signal-to-noise ratio of a magnetic signal are enhanced. Meanwhile, the anisotropic samarium-iron-nitrogen magnetic powder has higher coercive force which is more than 2 times of that of the anisotropic ferrite magnetic powder, and the reliability of the encoder magnetic grid in an electromagnetic environment can be improved.
But the research of being used for preparing the encoder magnetic grid with samarium iron nitrogen magnetic powder among the prior art is very few, and based on the magnetic property unstability of samarium iron nitrogen magnetic powder, the encoder magnetic grid for making fluctuates greatly, and surface magnetic accuracy and magnetic pole wave form zero cross precision are all relatively poor, and the encoder magnetic grid that samarium iron nitrogen magnetic powder was made has higher requirements such as magnetic field orientation size, orientation uniformity.
In the invention, the anisotropic samarium-iron-nitrogen or the composite magnetic powder thereof, the polymer resin, the additive and the additive are uniformly mixed, melted, mixed and extruded by a high-speed mixer to obtain granules, and the encoder magnetic grid is obtained by injection molding. The samarium iron nitrogen magnetic powder is coated by the coupling agent in advance, so that the problem of unstable magnetism of the samarium iron nitrogen magnetic powder is solved, the compatibility with high polymer resin is improved, and reasonable formula components are adjusted, so that the encoder magnetic grid made of the obtained permanent magnet material has good corrosion resistance, impact resistance, good thermal stability, high uniform surface magnetic strength and zero crossing precision of magnetic pole waveform.
Preferably, the composite magnetic powder contains at least 20% by mass of anisotropic samarium-iron-nitrogen magnetic powder. The magnetic performance of the encoder magnetic grid can be effectively adjusted by adding part of the ferrite magnetic powder, and meanwhile, the ferrite magnetic powder also has good oxidation resistance.
Preferably, the anisotropic samarium iron nitrogen or the composite magnetic powder thereof is subjected to coating modification treatment by a coupling agent before use. In order to solve the problems of unstable magnetism and easy oxidation of the surface of the samarium iron nitrogen magnetic powder, the coupling agent is adopted to firstly coat and modify the samarium iron nitrogen or the composite magnetic powder thereof, so that the magnetic powder performance is more stable, the adverse effects of the magnetic powder performance such as oxidation and the like can not occur when the samarium iron nitrogen or the composite magnetic powder thereof is contacted with air for a long time, and meanwhile, the coated and modified magnetic powder is easy to orient under the action of a magnetic field, thereby ensuring the surface precision and the quality of the manufactured encoder magnetic grid.
Further preferably, the coating modification treatment process of the anisotropic samarium iron nitrogen or the composite magnetic powder thereof specifically comprises the following steps: soaking the anisotropic samarium iron nitrogen or the composite magnetic powder thereof into a solvent containing a coupling agent, stirring for 0.1 to 3 hours at the temperature of between 30 and 60 ℃, fully and uniformly mixing the mixture, and drying the mixture to obtain the magnetic powder with the surface treated. Too high a temperature may volatilize the organic solvent during mixing, resulting in uneven mixing.
The drying temperature is 80-120 ℃, and the drying time is 1-6 h; the aim is to remove the solvent, and to ensure that the coupling agent is uniformly coated and combined on the surface of the magnetic powder, the temperature is lower than 80 ℃, the full drying is difficult and the combination strength of the coupling agent and the magnetic powder is low; the temperature is higher than 120 ℃, which easily causes the magnetic powder performance attenuation.
The solvent comprises any one of ethanol, isopropanol and acetone;
the coupling agent comprises one or more of aluminate coupling agent, silane coupling agent and titanate coupling agent;
the auxiliary agent comprises one or more of palmitamide, N' -ethylene bis stearamide and bis (1, 2, 6-pentamethyl-4-piperidyl) sebacate;
the polymer resin comprises one or more of nylon, polyphenylene sulfide, polyethylene and polypropylene;
preferably, the coupling agent is an aluminate coupling agent and a silane coupling agent, so that the coating effect is better; the auxiliary agent is at least two of palmitamide, N' -ethylene bisstearamide and bis (1, 2, 6-pentamethyl-4-piperidyl) sebacate; the polymer resin is nylon or polyphenylene sulfide.
The average grain diameter of the anisotropic samarium iron nitrogen magnetic powder is 1-5 μm; the anisotropic samarium iron nitrogen magnetic powder has fine and concentrated granularity, generally 1-5 mu m, is much thinner than neodymium magnetic powder (generally 50-200 mu m) such as neodymium iron boron and the like, and can be more uniformly distributed in the magnetic grid of the encoder, so that the waveform zero crossing precision of the magnetic pole is higher, and the thinner magnetic grid of the encoder can be prepared.
The invention also provides a preparation method of the high-precision encoder magnetic grid, which comprises the following steps:
step 1, soaking 20-95 parts of anisotropic samarium iron nitrogen or composite magnetic powder thereof into a solvent containing 0.1-1 part of coupling agent, stirring and mixing for 0.1-3 hours at 30-60 ℃, and drying to obtain surface-treated magnetic powder;
step 2, mixing the magnetic powder subjected to surface treatment in the step 1, 5-80 parts of polymer resin and 0.1-1.5 parts of auxiliary agent, and then performing melt extrusion granulation to obtain composite granules; the maximum magnetic energy product of the composite granules is 3.0-16.0 MGOe; the density is 3.60-16.0 g/cm 3 . The larger the maximum magnetic energy product is, the more the magnetized encoder isThe higher the surface magnetic strength of the grid is, the composite granules with different properties can be flexibly selected according to the use requirements of the encoder magnetic grid in practical application.
Step 3, performing injection molding and orientation on the composite granules, and demagnetizing the oriented encoder magnetic grid to obtain a semi-finished encoder magnetic grid product;
and 4, magnetizing the encoder magnetic grid semi-finished product according to the magnetic pole requirement of the encoder magnetic grid to obtain the high-precision encoder magnetic grid meeting the requirement.
The anisotropic samarium iron nitrogen and the composite material thereof obtained by granulation are subjected to injection molding in a molding die cavity of an encoder by adopting an injection molding mode, an electromagnetic field or a permanent magnetic field is adopted for orientation in the injection molding process, and the magnetic powder can be orderly arranged according to the orientation direction under the magnetic field orientation.
In step 3, adopting an electromagnetic field or a permanent magnetic field for orientation; in the orientation process, a forming die of the encoder magnetic grid is provided with a magnetic path channel on the induction surface of the magnetic grid;
the magnetic field intensity of the orientation magnetic field and the induction surface of the magnetic grid form 90 degrees during injection molding, and the magnetic field intensity is not lower than 0.6T; if the orientation strength is lower than 0.6T, the orientation is incomplete or insufficient, and the magnetic powder cannot be completely arranged according to the orientation direction, so that the performance of the encoder magnetic grid in the subsequent magnetizing process cannot be exerted, and the surface magnetic strength of the obtained magnetic grid is low.
After injection molding, the magnetic domain orientation degree of the induction surface of the magnetic grid is 60-99%, and the difference of the magnetic domain orientation degrees of all points is not more than 5%; the magnetic domain orientation degree is too low, namely the magnetic domain arrangement consistency is poor, the performance of the encoder magnetic grid can not be exerted in the subsequent magnetizing process to a certain extent, the apparent magnetic strength is low, the heterogeneity of the surface of the magnetic grid can be reduced when the difference of the orientation degree of each point magnetic domain exceeds 5%, and the zero crossing precision of the magnetic pole waveform in the magnetizing process is reduced.
The surface magnetism of the encoder magnetic grid semi-finished product is below 1mT after demagnetization; the surface magnetic residue exceeding 1mT after demagnetization can cause the deterioration of the surface magnetic precision during the magnetizing process of the encoder magnetic grid, and can also affect the zero crossing precision of the magnetic pole waveform of the encoder magnetic grid.
In step 4, the semi-finished product of the encoder magnetic grid is magnetized by adopting pulse single pole or the whole fixture;
and pulse single-pole magnetizing is adopted for the encoder magnetic grid with the pole spacing below 1mm, and the width of a magnetizing pole head is smaller than 87% of the pole spacing of the encoder magnetic grid. If the width of the magnetizing pole head exceeds 87% of the distance between the magnetic grids of the encoder, interference can be generated on adjacent magnetic poles in the magnetizing process, so that the magnetized magnetic poles are covered, and the non-magnetized magnetic poles are endowed with magnetism, so that the precision of the magnetic grids of the encoder is directly influenced.
Preferably, the encoder magnetic grid comprises a magnetic drum, a magnetic disk, a magnetic ring, a linear magnetic scale and other different structural shapes. The encoder magnetic grid manufactured based on the precise injection molding has the advantages of high size precision, no deformation, no need of secondary processing, large degree of freedom of shape structure forming and the like, the proportion of the anisotropic samarium-iron-nitrogen magnetic powder is adjusted to manufacture the encoder magnetic grid with different performance requirements, meanwhile, the heat fluidity of materials can be changed to customize encoder magnetic grids with various shapes and structures according to use requirements, and the development of high-resolution and high-precision magnetic encoders structurally provides guarantee.
Compared with the prior art, the invention has the following beneficial effects:
(1) The magnetic pole zero-crossing point precision of the fine magnetized anisotropic samarium iron nitrogen powder is higher, the magnetic pole is not easy to rust in salt fog and other environments compared with neodymium iron boron materials, the surface magnetic strength is higher compared with ferrite materials, and the influence of demagnetization and the like is not easy to occur due to higher coercive force.
(2) The encoder magnetic grid with a complex and thin structure can be manufactured by adopting an injection molding mode, and meanwhile, the insert can be taken or integrally injected, so that the requirement of large-scale production is met.
(3) The maximum magnetic energy product of the anisotropic samarium-iron-nitrogen and the composite material thereof is 3.0-16.0 MGOe, the encoder magnetic grids with different performance requirements can be manufactured, and the output magnetic signals and the signal-to-noise ratio of the encoder magnetic grids can be improved.
Drawings
FIG. 1 is a schematic view of the process for manufacturing the encoder magnetic grid of embodiment 1.
FIG. 2 shows the orientation requirements of the encoder grating blank of example 1.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not limit the invention. Those skilled in the art should understand that they can make modifications and equivalents without departing from the spirit and scope of the present invention, and all such modifications and equivalents are intended to be included within the scope of the present invention.
The raw materials used in the following embodiments are all available on the market, and the particle size of the ferrite magnetic powder is 1-3 μm; the grain diameter of the anisotropic samarium iron nitrogen magnetic powder is 1-5 μm.
The following embodiment is to manufacture an encoder magnetic grating having an outer diameter of 30mm, an inner diameter of 24mm, a height of 2mm, and 64 poles in the axial direction.
Example 1
The schematic diagram of the preparation process of the high-precision encoder magnetic grid is shown in figure 1:
(1) Dissolving 0.5 part of aluminate in ethanol, immersing 88.5 parts of anisotropic samarium iron nitrogen magnetic powder in the ethanol, immersing the coated magnetic powder by using the ethanol, stirring and homogenizing the mixture at 40 ℃, and drying the mixture at 95 ℃ in vacuum;
(2) The coated magnetic powder obtained in step (1) was mixed with 10.5 parts of nylon 12, 0.1 part of palmitamide, 0.3 part of N, N' -ethylenebisstearamide, and 0.1 part of bis (1, 2, 6-pentamethyl-4-piperidyl) sebacate. Proportioning, namely uniformly mixing the proportioned raw materials in a high-speed mixer at the rotating speed of 800r/min to obtain mixed raw materials;
(3) Melting and mixing the mixed raw materials prepared in the step (2) at 200 ℃, extruding and granulating to prepare composite granules, wherein the maximum magnetic energy product of the composite granules is 9.42MGOe, and the density is 4.33g/cm 3 ；
(4) And (3) melting and injecting the composite material prepared in the step (3) into a mold cavity by adopting an injection molding mode, wherein in the orientation process, a magnetic path channel is arranged on a magnetic grid induction surface of a forming mold of the encoder magnetic grid, and in the injection molding process, the encoder magnetic grid is oriented under the magnetic field intensity of 0.7T by using an electromagnetic field, as shown in figure 2, the magnetic field intensity of the orientation magnetic field and the magnetic grid induction surface form a 90-degree angle in the injection molding process. Demagnetizing the encoder magnetic grid, wherein the surface magnetism of the demagnetized encoder magnetic grid is 0.5mT, and manufacturing a semi-finished product of the encoder magnetic grid;
carrying out orientation degree test on the encoder magnetic grid semi-finished product, wherein the magnetic domain orientation degree of the magnetic grid induction surface is 85%, and the difference of the magnetic domain orientation degrees of all points is 3%;
(5) And (4) magnetizing the whole clamp by 64 poles according to the magnetic pole requirement of the encoder magnetic grid to obtain the finished product of the encoder magnetic grid.
Comparative example 1: without being coated
(1) Proportioning 88.5 parts of anisotropic samarium-iron-nitrogen magnetic powder, 10.5 parts of nylon 12 resin, 0.5 part of aluminate coupling agent, 0.1 part of palmitamide, 0.3 part of N, N' -ethylene bis stearamide and 0.1 part of bis (1, 2, 6-pentamethyl-4-piperidyl) sebacate, and directly and uniformly mixing the proportioned raw materials in a high-speed mixer at the rotating speed of 800r/min to obtain a mixed raw material;
(2) Melting and mixing the mixed raw materials prepared in the step (1) at 200 ℃, extruding and granulating to obtain the composite granules with the maximum magnetic energy product of 9.36MGOe and the density of 4.33g/cm 3 ；
(3) And (3) melting and injecting the composite granules prepared in the step (2) into a mold cavity in an injection molding mode, wherein a magnetic path channel is arranged on a magnetic grid induction surface of a forming mold of the encoder magnetic grid, the encoder magnetic grid is oriented under the magnetic field intensity of 0.7T in the injection molding process, and the magnetic field intensity of an oriented magnetic field and the magnetic grid induction surface form an angle of 90 degrees in the injection molding process. Demagnetizing the encoder magnetic grid, wherein the surface magnetism of the demagnetized encoder magnetic grid is 0.5mT, and manufacturing a semi-finished product of the encoder magnetic grid;
carrying out orientation degree test on the encoder magnetic grid semi-finished product, wherein the magnetic domain orientation degree of the magnetic grid induction surface is 82%, and the difference of the magnetic domain orientation degrees of all points is 5%;
(4) And magnetizing the encoder by 64 poles according to the magnetic pole requirement of the encoder magnetic grid to obtain the finished encoder magnetic grid.
Comparative example 2 Low oriented magnetic field Strength
(1) Dissolving 0.5 part of aluminate coupling agent in ethanol, immersing 88.5 parts of anisotropic samarium-iron-nitrogen magnetic powder in the ethanol, stirring and homogenizing the coated magnetic powder at 40 ℃, and then drying the magnetic powder at 95 ℃ in vacuum;
(2) Proportioning the coated magnetic powder obtained in the step (1) with 10.5 parts of nylon 12, 0.1 part of palmitamide, 0.3 part of N, N' -ethylene bis-stearamide and 0.1 part of bis (1, 2, 6-pentamethyl-4-piperidyl) sebacate, and uniformly mixing the proportioned raw materials in a high-speed mixer at the rotating speed of 800r/min to obtain a mixed raw material;
(3) Melting and mixing the mixed raw materials prepared in the step (2) at 200 ℃, extruding and granulating to obtain the composite granules with the maximum magnetic energy product of 9.42MGOe and the density of 4.33g/cm 3 ；
(4) And (3) melting and injecting the composite granules prepared in the step (3) into a mold cavity in an injection molding mode, wherein a magnetic path channel is arranged on a magnetic grid induction surface of a forming mold of the encoder magnetic grid, the encoder magnetic grid is oriented under the magnetic field intensity of 0.4T in the injection molding process, and the magnetic field intensity of an oriented magnetic field and the magnetic grid induction surface form an angle of 90 degrees in the injection molding process. Demagnetizing the encoder magnetic grid, wherein the surface magnetism of the demagnetized encoder magnetic grid is 0.5mT, and manufacturing a semi-finished product of the encoder magnetic grid;
carrying out orientation degree test on the encoder magnetic grid semi-finished product, wherein the magnetic domain orientation degree of a magnetic grid induction surface is 55%, and the difference of the magnetic domain orientation degrees of all points is 7%;
(5) And magnetizing the encoder by 64 poles according to the magnetic pole requirement of the encoder magnetic grid to obtain the finished encoder magnetic grid.
Comparative example 3: the surface magnetism is higher after demagnetization
(1) Dissolving 0.5 part of aluminate in ethanol, immersing 88.5 parts of anisotropic samarium iron nitrogen magnetic powder in the ethanol, immersing the coated magnetic powder by using the ethanol, stirring and homogenizing the mixture at 40 ℃, and drying the mixture at 95 ℃ in vacuum;
(2) Mixing the coated magnetic powder obtained in the step (1) with 10.5 parts of nylon 12 resin, 0.1 part of palmitamide, 0.3 part of N, N' -ethylene bis stearamide and 0.1 part of bis (1, 2, 6-pentamethyl-4-piperidyl) sebacate, and uniformly mixing the mixed raw materials in a high-speed mixer at the rotating speed of 800r/min to obtain a mixed raw material;
(3) Melting and mixing the mixed raw materials prepared in the step (2) at 200 ℃, extruding and granulating to obtain the composite granules with the maximum magnetic energy product of 9.42MGOe and the density of 4.33g/cm 3 ；
(4) And (3) melting and injecting the composite granules prepared in the step (3) into a mold cavity in an injection molding mode, wherein a magnetic path channel is arranged on a magnetic grid induction surface of a forming mold of the encoder magnetic grid, the encoder magnetic grid is oriented under the magnetic field intensity of 0.7T in the injection molding process, and the magnetic field intensity of an oriented magnetic field and the magnetic grid induction surface form an angle of 90 degrees in the injection molding process. Demagnetizing the encoder magnetic grid, wherein the surface magnetism of the demagnetized encoder magnetic grid is 1.5mT, and manufacturing a semi-finished product of the encoder magnetic grid;
(5) And magnetizing the encoder magnetic grid by 64 poles according to the magnetic pole requirement of the encoder magnetic grid to obtain the finished product of the encoder magnetic grid.
Example 2
(1) Dissolving 0.5 part of aluminate in ethanol, immersing 45 parts of anisotropic samarium iron nitrogen magnetic powder and 41 parts of anisotropic ferrite magnetic powder in the ethanol, immersing the coated magnetic powder by using the ethanol, stirring and homogenizing the coated magnetic powder at 40 ℃, and then drying the coated magnetic powder in vacuum at 95 ℃;
(2) Mixing the coated magnetic powder obtained in the step (1) with 13 parts of nylon 12 resin, 0.1 part of palmitamide, 0.3 part of N, N' -ethylene bis stearamide and 0.1 part of bis (1, 2, 6-pentamethyl-4-piperidyl) sebacate, and uniformly mixing the mixed raw materials in a high-speed mixer at the rotating speed of 800r/min to obtain a mixed raw material;
(3) Melting and mixing the mixed raw materials prepared in the step (2) at 200 ℃, extruding and granulating to obtain the composite granules with the maximum magnetic energy product of 3.62MGOe and the density of 3.55g/cm 3 ；
(4) And (4) melting and injecting the composite granules prepared in the step (3) into a mold cavity in an injection molding mode, wherein in the orientation process, a magnetic path channel is arranged on a magnetic grid induction surface of a forming mold of the encoder magnetic grid, the encoder magnetic grid is oriented under the magnetic field intensity of 0.7T in the injection molding process, and the magnetic field intensity of an orientation magnetic field forms 90 degrees with the magnetic grid induction surface in the injection molding process. Demagnetizing the encoder magnetic grid, wherein the surface magnetism of the demagnetized encoder magnetic grid is 0.5mT, and manufacturing a semi-finished product of the encoder magnetic grid;
(5) And magnetizing the encoder by 64 poles according to the magnetic pole requirement of the encoder magnetic grid to obtain the finished encoder magnetic grid.
Comparative example 4: neodymium iron boron magnetic powder
(1) Dissolving 0.5 part of aluminate in ethanol, immersing 91 parts of isotropic neodymium iron boron magnetic powder in the solution, immersing the coated magnetic powder just by using the ethanol, stirring and homogenizing the solution at 40 ℃, and then drying the solution in vacuum at 95 ℃;
(2) Mixing the coated magnetic powder obtained in the step (1) with 8 parts of nylon 12 resin, 0.1 part of palmitamide, 0.3 part of N, N' -ethylene bis-stearamide and 0.1 part of bis (1, 2, 6-pentamethyl-4-piperidyl) sebacate, and uniformly mixing the mixed raw materials in a high-speed mixer at the rotating speed of 800r/min to obtain a mixed raw material;
(3) Melting and mixing the mixed raw materials prepared in the step (2) at 200 ℃, extruding and granulating to obtain the composite granules with the maximum magnetic energy product of 5.61MGOe and the density of 4.82g/cm 3 ；
(4) Melting and injecting the composite granules prepared in the step (3) into a mold cavity in an injection molding mode to manufacture a semi-finished product of the encoder magnetic grid;
(5) And magnetizing the encoder magnetic grid by 64 poles according to the magnetic pole requirement of the encoder magnetic grid to obtain the finished product of the encoder magnetic grid.
Comparative example 5: injection molding anisotropic ferrite for manufacturing encoder magnetic grid
(1) Dissolving 0.5 part of aluminate in ethanol, immersing 89.5 parts of anisotropic ferrite magnetic powder in the ethanol, stirring and homogenizing the ethanol at 40 ℃, and then drying the mixture in vacuum at 95 ℃;
(2) Mixing the coated magnetic powder obtained in the step (1) with 9.5 parts of nylon 12 resin, 0.1 part of palmitamide, 0.3 part of N, N' -ethylene bis stearamide and 0.1 part of bis (1, 2, 6-pentamethyl-4-piperidyl) sebacate, and uniformly mixing the mixed raw materials in a high-speed mixer at the rotating speed of 800r/min to obtain a mixed raw material;
(3) Melting and mixing the mixed raw materials prepared in the step (2) at 200 ℃, extruding and granulating to obtain the composite granules with the maximum magnetic energy product of 1.96MGOe and the density of 3.58g/cm 3 ；
(4) And (3) melting and injecting the composite granules prepared in the step (3) into a mold cavity in an injection molding mode, wherein in the orientation process, a magnetic path channel is arranged on a magnetic grid induction surface of a forming mold of the encoder magnetic grid, the encoder magnetic grid is oriented under the magnetic field intensity of 0.7T in the injection molding process, and the magnetic field intensity of an oriented magnetic field and the magnetic grid induction surface form an angle of 90 degrees in the injection molding process. Demagnetizing the encoder magnetic grid to obtain demagnetized encoder magnetic grid surface magnetic of 0.5mT and making semi-finished encoder magnetic grid product;
(5) According to the magnetic pole requirement of the encoder magnetic grid, 64 poles of the encoder magnetic grid are magnetized to obtain a finished encoder magnetic grid product;
the encoder magnetic grids prepared in examples 1 to 2 and comparative examples 1 to 5 were subjected to surface magnetic strength and accuracy, zero crossing accuracy of magnetic pole waveform, corrosion resistance, anti-electromagnetic interference capability, and other performance tests, and the obtained test results are shown in table 1. The surface magnetic strength and precision and the magnetic pole waveform zero crossing precision are tested by a waveform measuring instrument: standard T/MBJX 0008-2021; the corrosion resistance is tested by a salt spray test: the standard GB/T2423.17 (the corrosion degree is taken as the standard for judging the good and bad performance, the corrosion resistance is judged to be good when the corrosion degree is not rusted and the corrosion resistance is judged to be bad when the corrosion degree is rusted after the salt spray test for 12 hours); standard GB/T17626.8 (testing the magnetic strength, accuracy and zero crossing accuracy of encoder magnetic grid in electromagnetic interference environment if the change rate is within 3%, within 3% -5% the strength is strong, more than 5% the strength is weak)
Table 1 results of performance test of examples and comparative examples
As can be seen from Table 1: the encoder magnetic grid made of the anisotropic samarium iron nitrogen has higher surface magnetic strength and precision, higher zero crossing precision of magnetic pole waveform and better corrosion resistance than the encoder magnetic grid made of the isotropic neodymium iron boron, and the encoder magnetic grid made of the anisotropic samarium iron nitrogen and the anisotropic ferrite has higher surface magnetic strength and precision, higher zero crossing precision of magnetic pole waveform and stronger anti-electromagnetic interference capability than the encoder magnetic grid made of the anisotropic ferrite.
From a comparison of example 1 and comparative example 1, the samarium iron nitrogen magnetic powder of comparative example 1 was not coated with a coupling agent, resulting in a surface thereof being easily oxidized and thus having poor corrosion resistance; wherein comparative example 2 has low apparent magnetic strength due to incomplete orientation due to low magnetic field strength during orientation.
The composite magnetic powder of samarium iron nitrogen and ferrite is selected in the embodiment 2, the magnetic powder contains the ferrite, the maximum magnetic energy product is lower, and the surface magnetic strength is low, but the coercive force of the ferrite magnetic powder is lower, and the coercive force of the ferrite magnetic powder can be improved after the ferrite magnetic powder is compounded with the samarium iron nitrogen magnetic powder, so that the anti-electromagnetic interference capability is better than that of the ferrite magnetic powder, the surface magnetic precision and the anti-electromagnetic interference capability are good, and the excellent encoder magnetic grid manufacturing characteristics can be realized.
In comparative example 3, because the surface magnetism is remained after demagnetization, the surface magnetism intensity and the waveform distribution of the encoder magnetic grid are uneven in the subsequent magnetizing process, so that the surface magnetism precision and the zero crossing point precision are reduced.
The common neodymium iron boron magnetic powder and the common ferrite magnetic powder in the prior art are respectively selected in the comparative example 4 and the comparative example 5, and the neodymium iron boron magnetic powder has larger particle size, the surface is very easy to be oxidized by oxygen, the surface magnetic precision is poorer after magnetization, and the neodymium iron boron magnetic powder is very easy to rust after being used for a period of time and cannot be used for a long time. The ferrite magnetic powder has low coercive force, so that demagnetization and other phenomena are easy to occur in an electromagnetic interference environment, and the working performance of the magnetic grid of the encoder is influenced.
Therefore, the encoder magnetic grid made of the anisotropic samarium iron nitrogen and the composite material thereof has good various performances and has a plurality of advantages in the aspects of manufacturing and application of the encoder magnetic grid.
Claims (10)
1. A high-precision encoder magnetic grid material is characterized by comprising the following raw materials in parts by weight: 20 to 95 portions of anisotropic samarium iron nitrogen or composite magnetic powder thereof, 0.1 to 1 portion of coupling agent, 5 to 80 portions of polymer resin and 0.1 to 1.5 portions of auxiliary agent; the anisotropic samarium iron nitrogen or the composite magnetic powder thereof comprises anisotropic samarium iron nitrogen magnetic powder and/or composite magnetic powder of anisotropic samarium iron nitrogen and anisotropic ferrite.
2. The high precision encoder magnetic grid material of claim 1, characterized in that the composite magnetic powder comprises at least 20% by mass of anisotropic samarium iron nitrogen magnetic powder.
3. The high-precision encoder magnetic grid material according to claim 1, characterized in that the anisotropic samarium iron nitrogen or its composite magnetic powder is modified by coating with a coupling agent before use.
4. The high-precision encoder magnetic grid material according to claim 3, characterized in that the modified treatment process of coating of anisotropic samarium iron nitrogen or its composite magnetic powder specifically comprises the steps of: soaking the anisotropic samarium-iron-nitrogen or the composite magnetic powder thereof into a solvent containing a coupling agent, stirring and mixing for 0.1 to 3 hours at the temperature of between 30 and 60 ℃, and drying to obtain the magnetic powder with the surface treated.
5. The high precision encoder grating material of claim 1 or 4, wherein the coupling agent comprises one or more of an aluminate coupling agent, a silane coupling agent, a titanate coupling agent.
6. The high precision encoder grid material according to claim 1, wherein the auxiliaries comprise one or more of palmitamide, N' -ethylene bis stearamide, bis (1, 2, 6-pentamethyl-4-piperidyl) sebacate;
and/or the polymer resin comprises one or more of nylon, polyphenylene sulfide, polyethylene and polypropylene;
and/or the average grain diameter of the anisotropic samarium iron nitrogen magnetic powder is 1-5 μm.
7. A preparation method of a high-precision encoder magnetic grid is characterized by comprising the following steps:
step 1, soaking 20-95 parts of anisotropic samarium iron nitrogen or composite magnetic powder thereof into a solvent containing 0.1-1 part of coupling agent, stirring and mixing for 0.1-3 hours at 30-60 ℃, and drying to obtain surface-treated magnetic powder;
step 2, mixing the magnetic powder subjected to surface treatment in the step 1, 5-80 parts of polymer resin and 0.1-1.5 parts of auxiliary agent, and then performing melt extrusion granulation to obtain composite granules; the maximum magnetic energy product of the composite granules is 3.0-16.0 MGOe;
step 3, performing injection molding and orientation on the composite granules, and demagnetizing to obtain a semi-finished product of the encoder magnetic grid;
and 4, magnetizing the encoder magnetic grid semi-finished product according to the magnetic pole requirement of the encoder magnetic grid to obtain the high-precision encoder magnetic grid meeting the requirement.
8. The method for preparing the high-precision encoder magnetic grid according to claim 7, wherein in the step 3, an electromagnetic field or a permanent magnetic field is used for orientation, and in the orientation process, a magnetic path channel is arranged on the induction surface of the magnetic grid by a forming die of the encoder magnetic grid;
the magnetic field direction of the oriented magnetic field and the induction surface of the magnetic grid form 90 degrees during injection molding, and the magnetic field intensity is not lower than 0.6T; after injection molding, the magnetic domain orientation degree of the induction surface of the magnetic grid is 60-99%, and the difference of the magnetic domain orientation degrees of all points is not more than 5%.
9. The method for preparing the high-precision magnetic grid of the encoder according to claim 7, wherein the surface magnetism of the semi-finished product of the magnetic grid of the encoder is below 1mT after demagnetization;
and 4, magnetizing the semi-finished product of the encoder magnetic grid by adopting a pulse single pole or integrally magnetizing by using a clamp.
10. The method for preparing the high-precision encoder magnetic grid according to claim 7, wherein pulse single-pole magnetizing is adopted for the encoder magnetic grid with the pole spacing below 1mm, and the width of a magnetizing pole head is less than 87% of the pole spacing of the encoder magnetic grid.
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