阅读说明：本技术 一种可膨胀烧结钕铁硼磁体及其制备方法和应用 (Expandable sintered neodymium-iron-boron magnet and preparation method and application thereof ) 是由 李志强 于永江 周彬 宿云婷 李雯 于 2021-06-11 设计创作，主要内容包括：本发明公开一种可膨胀烧结钕铁硼磁体及制备方法和应用,所述磁体包括烧结钕铁硼磁体及涂覆于烧结钕铁硼磁体表面的可膨胀涂层。本发明通过采用涂覆有可膨胀涂层的烧结钕铁硼磁体来代替传统的环氧树脂粘接涂层磁体加灌封树脂胶的装配方式,可将涂覆有可膨胀涂层的磁体插入磁钢槽内,利用涂层自身不可逆的膨胀,来实现磁体在磁钢槽的固定。同时本发明可膨胀涂层的使用,大大缩短了电机装配的时间,并提高了电机装配的精度。且本发明涂覆有可膨胀涂层的烧结磁体具有优异的抗高温、抗老化及耐腐蚀性能和结合力强等优异特性。(The invention discloses an expandable sintered neodymium-iron-boron magnet and a preparation method and application thereof. According to the invention, the sintered neodymium iron boron magnet coated with the expandable coating is adopted to replace the traditional assembly mode of bonding the coating magnet with epoxy resin and adding potting resin adhesive, the magnet coated with the expandable coating can be inserted into the magnetic steel groove, and the magnet is fixed in the magnetic steel groove by utilizing the irreversible expansion of the coating. Meanwhile, due to the use of the expandable coating, the motor assembling time is greatly shortened, and the motor assembling precision is improved. The sintered magnet coated with the expandable coating has excellent characteristics of high temperature resistance, ageing resistance, corrosion resistance, strong binding force and the like.)

1. The utility model provides an expandable sintered neodymium iron boron magnet which characterized in that, the magnet includes sintered neodymium iron boron magnet and coats in the expandable coating on sintered neodymium iron boron magnet surface.

Preferably, the thickness of the swellable coating is 50-300 μm, preferably 80-150 μm.

Preferably, the swellable coating softens at 60-100 ℃.

Preferably, the expandable coating has an expansion ratio of 200% to 400%, preferably 300-400%, in the pressureless state.

Preferably, after expansion of the expandable coating, the coating is cellular. Preferably, the swellable coating has a topography substantially as shown in fig. 1 after swelling.

2. The expandable sintered ndfeb magnet according to claim 1, wherein the expandable coating contains at least a water-soluble resin and a foaming agent.

Preferably, the water-soluble resin is at least one selected from the group consisting of water-soluble acrylic resins, aqueous epoxy resins, and aqueous urethane resins.

Preferably, the water-soluble resin has a solid content of 30 to 50% in the swellable coating layer.

3. An expandable sintered nd-fe-b magnet according to claim 1 or 2, wherein the foaming agent is expanded thermoplastic microspheres having a diameter of 5-30 μm, preferably 5-20 μm.

Preferably, after the expandable coating is expanded, the area of the expanded microspheres accounts for 60-90% of the cross-sectional area of the expandable coating.

Preferably, the expanded microspheres have an average diameter of 10-15 μm.

Preferably, the expansion temperature of the expanded microspheres is 110-.

Preferably, the maximum heat resistance temperature of the expanded microspheres is 145-235 ℃.

4. The expandable sintered ndfeb magnet according to any of claims 1 to 3, wherein the expandable coating is prepared by coating an expandable paint containing at least a water-soluble resin and a foaming agent component.

Preferably, the water soluble resin is present in the expandable coating in an amount of 45 to 65% by weight, for example 50 to 60% by weight.

Preferably, the expandable coating material has a blowing agent content of 10 to 30% by weight, for example 15 to 25% by weight.

5. The expandable sintered ndfeb magnet according to claim 4, wherein the expandable paint optionally also contains laponite.

Preferably, the weight percentage of the hectorite is 0.1-0.5%, such as 0.2-0.4%.

Preferably, the expandable coating also optionally contains dipropyl alcohol butyl ether.

Preferably, the weight percentage of the dipropyl alcohol butyl ether is 0.5-3%, such as 0.8-2.5%.

Preferably, the expandable coating also optionally contains propylene glycol.

Preferably, the propylene glycol is present in a weight percentage of 1-3%, such as 1.5-2.5%.

Preferably, the expandable coating also optionally contains an acrylic thickener.

Preferably, the weight percentage of the acrylic thickener is 0.2-0.8%, such as 0.3-0.6%.

Preferably, the expandable coating also optionally contains a dispersant.

Preferably, the dispersant is present in an amount of 0.1 to 0.5% by weight, such as 0.2 to 0.4% by weight.

Preferably, the dispersant is ethylene glycol, sodium oleate, carboxylate salts, and the like.

Preferably, the expandable coating also optionally contains a leveling agent.

Preferably, the weight percentage of the leveling agent is 0.1-0.5%, such as 0.2-0.4%.

Preferably, the leveling agent is silicone oil, organosiloxane, or the like.

Preferably, the expandable coating further comprises water.

Preferably, the sum of the weight percentages of the components in the expandable coating is 100%.

6. The expandable sintered ndfeb magnet according to any of claims 1 to 5, wherein the expandable coating is prepared by coating an expandable coating comprising the following components in percentage by weight: 45-65% of water-soluble resin, 10-30% of foaming agent, 0.1-0.5% of hectorite, 0.5-3% of butyl dipropyl alcohol, 1-3% of propylene glycol, 0.2-0.8% of acrylic thickener, 0.1-0.5% of dispersant and 0.1-0.5% of flatting agent.

Preferably, the sintered Nd-Fe-B magnet consists of a primary phase Nd₂Fe₁₄B. Nd-rich phase and B-rich phaseAnd (4) forming.

7. The method for preparing the expandable sintered magnet as claimed in any one of claims 1 to 6, wherein the method comprises the steps of applying an expandable coating containing the components on the surface of the sintered neodymium-iron-boron magnet, and performing pre-curing treatment to obtain the expandable sintered magnet.

Preferably, the sintered nd-fe-b magnet further comprises a step of surface pretreatment before the expandable coating is applied.

Preferably, the surface pretreatment comprises the processes of chemical ultrasonic oil removal, acid cleaning and water cleaning of the surface of the sintered neodymium iron boron magnet.

Preferably, the deoiling liquid adopted in the deoiling process is a composite solution of alkali and a surfactant.

Preferably, the alkali is sodium hydroxide or sodium carbonate, and the concentration of the alkali is 10-20 g/L.

Preferably, the surfactant is sodium dodecyl sulfate or sodium dodecyl sulfate, and the concentration of the surfactant is 2-6 g/L.

Preferably, the temperature of the oil removing liquid is 30-70 ℃, and the oil removing time is 1-20 min.

Preferably, the acid used for the acid washing may be an aqueous solution of nitric acid or citric acid.

Preferably, the acid solution concentration adopted by the acid washing is 5-30 wt%, and the acid washing time is 5-30 s.

Preferably, the coating means includes, but is not limited to, spraying, printing, dipping, painting, and the like. Preferably by spraying.

Preferably, the coating has a thickness of 50-300 μm, preferably a thickness of 80-150 μm, exemplarily 50 μm, 80 μm, 110 μm, 150 μm, 180 μm, 200 μm, 250 μm, 300 μm.

8. Use of the expandable sintered magnet according to any one of claims 1 to 6 and/or the expandable sintered neodymium iron boron magnet produced by the production method according to claim 7 in a rotor of an electric machine.

9. An electric motor rotor workpiece, characterized in that the electric motor rotor workpiece contains the expandable sintered magnet according to any one of claims 1 to 6 and/or the expandable sintered neodymium-iron-boron magnet prepared by the preparation method according to claim 7.

10. The method for assembling the motor rotor workpiece according to claim 9, wherein the method comprises assembling the expandable sintered magnet according to any one of claims 1 to 6 and/or the expandable sintered neodymium-iron-boron magnet prepared by the preparation method according to claim 7 into a magnetic steel groove, and performing thermal expansion treatment to obtain the motor rotor workpiece.

Preferably, the heating expansion treatment adopts a two-stage heating method, the expansion temperature of the first expansion stage is 110-160 ℃, and the heating rate of the first expansion stage is 5-15 ℃/min.

Preferably, the second expansion temperature of the heating expansion treatment is 180-210 ℃, and the temperature rise rate of the second expansion stage is 30-60 ℃/min.

Technical Field

The invention relates to the technical field of surface protection of magnetic materials, in particular to an expandable sintered neodymium-iron-boron magnet and a preparation method and application thereof.

Background

The sintered ndfeb magnet is called as modern 'maga' because of excellent remanence, coercive force and magnetic energy product, so that the sintered ndfeb magnet is widely applied to industries such as energy, transportation, machinery, medical treatment, IT, household appliances and the like, and particularly, the demand and application of the sintered ndfeb magnet are continuously expanded along with the development and utilization of new energy. The development of permanent magnet motors is greatly promoted by the appearance of sintered neodymium-iron-boron magnets, so that products which originally use ferrite or samarium-cobalt magnets as motor stators or rotors are replaced by sintered neodymium-iron-boron permanent magnets in an attempt to reduce the weight of the motors, improve the power coefficient and increase the output power. But the sintered Nd-Fe-B consists of a primary phase Nd₂Fe₁₄B. The Nd-rich phase and the B-rich phase are combined, and the metal Nd element has the strongest chemical activity and is extremely easy to corrode in moist, high-temperature and electrochemical environments, so that the further expansion of the application field of the sintered neodymium-iron-boron magnet is severely limited.

At present, the surface protection is generally carried out by adopting an electrophoretic epoxy resin coating in the motor industry, the thickness of the coating is 15-30 mu m, and the coating has strong bonding force with a substrate and has the outstanding advantages of acid resistance, alkali resistance and the like. However, during the assembly process of the motor, the assembly process needs to be performed by using potting resin glue, namely: and inserting the magnet into the magnetic steel groove, injecting resin glue, and heating and curing to fix the magnet in the magnetic steel groove. Therefore, in the motor assembling process, the factors such as the fluidity, the caking property, the heat conductivity, the oil resistance, the environmental protection property and the like of the resin adhesive need to be considered, and meanwhile, the time consumed for heating and curing the resin adhesive is long, so that the requirement on the caking power in the motor assembling process can be met by heating and curing for more than 24 hours. In addition, although the epoxy resin bonding coating has excellent performance, the coating has low hardness and extremely poor wear resistance, is easy to break in packaging, transportation and motor assembly, and once the coating breaks, the magnet is seriously corroded because the epoxy resin bonding coating is a cathode protection coating. Therefore, how to fix the magnet in the magnetic steel slot and make the coating have higher hardness and wear resistance becomes a technical problem to be solved in the field.

Disclosure of Invention

In order to solve the technical problems, the invention provides an expandable sintered neodymium-iron-boron magnet which comprises a sintered neodymium-iron-boron magnet and an expandable coating coated on the surface of the sintered neodymium-iron-boron magnet.

According to an embodiment of the invention, the thickness of the swellable coating is 50-300 μm, preferably 80-150 μm, exemplary 50 μm, 80 μm, 110 μm, 150 μm, 180 μm, 200 μm, 250 μm, 300 μm.

According to an embodiment of the invention, the expandable coating softens at 60-100 ℃, exemplary 60 ℃, 70 ℃, 80 ℃, 90 ℃, 100 ℃.

According to an embodiment of the present invention, the expandable coating thickness has an expansion ratio of 200% to 400%, preferably 300% to 400%, exemplary 200%, 220%, 250%, 280%, 300%, 350%, 400% in the absence of pressure.

The expandable coating provided by the invention is heated at 165-210 ℃, and the organic resin in the expandable coating is crosslinked to realize fixed molding.

According to an embodiment of the invention, after expansion of the expandable coating, the coating is cellular. Preferably, the swellable coating has a topography substantially as shown in fig. 1 after swelling.

In the present invention, the expansion ratio is the thickness of the coating layer after expansion in the free state/the thickness of the expandable coating layer before expansion.

According to an embodiment of the invention, the expandable coating comprises at least a water-soluble resin and a foaming agent.

Preferably, the water-soluble resin is at least one selected from the group consisting of water-soluble acrylic resins, aqueous epoxy resins, and aqueous urethane resins. Preferably selected from water-soluble acrylic resins.

According to an embodiment of the invention, the solids content of the water-soluble resin in the swellable coating is 30-50%, exemplarily 30%, 35%, 40%, 50%.

Preferably, the foaming agent is thermoplastic expanded microspheres having a diameter of 5-30 μm, preferably 5-20 μm, exemplary 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, 25 μm, 30 μm.

According to an embodiment of the present invention, after the expandable coating is expanded, the area of the expanded microspheres is 60 to 90% of the cross-sectional area of the expanded coating, illustratively 60%, 70%, 80%, 90%.

According to an embodiment of the present invention, the expanded microspheres inside the expandable coating are expanded in a stepwise manner at 110-.

Preferably, the expanded microspheres have an average diameter of 10-15 μm, exemplary 10 μm, 12 μm, 15 μm.

Preferably, the expansion temperature of the expanded microspheres is 110-.

Preferably, the expanded microspheres have a maximum heat resistance temperature of 145-235 deg.C, illustratively 145 deg.C, 160 deg.C, 180 deg.C, 200 deg.C, 215 deg.C, 235 deg.C.

According to an embodiment of the present invention, the expandable coating layer is prepared by coating an expandable paint containing at least a water-soluble resin and a foaming agent component.

According to an embodiment of the invention, the percentage by weight of water-soluble resin in the expandable coating is between 45 and 65%, for example between 50 and 60%.

According to an embodiment of the invention, the weight percentage of blowing agent in the expandable coating is 10-30%, for example 15-25%.

According to an embodiment of the invention, the expandable coating optionally also contains laponite. For example, the weight percent of the hectorite may be 0.1-0.5%, such as 0.2-0.4%.

According to an embodiment of the present invention, the swellable coating optionally further comprises butyl dipropionate. For example, the weight percent of the dipropyl alcohol butyl ether is 0.5-3%, such as 0.8-2.5%.

According to an embodiment of the invention, the swellable coating optionally further comprises propylene glycol. For example, the propylene glycol may be present in an amount of 1 to 3% by weight, such as 1.5 to 2.5% by weight.

According to an embodiment of the invention, the expandable coating optionally also contains an acrylic thickener. For example, the acrylic thickener may be present in an amount of 0.2 to 0.8 weight percent, such as 0.3 to 0.6 weight percent.

According to an embodiment of the invention, the swellable coating optionally further comprises a dispersant. For example, the dispersant may be present in an amount of 0.1 to 0.5% by weight, such as 0.2 to 0.4% by weight.

Preferably, the dispersant is ethylene glycol, sodium oleate, carboxylate salts, and the like.

According to an embodiment of the invention, the expandable coating further optionally contains a leveling agent. For example, the weight percentage of the leveling agent is 0.1-0.5%, such as 0.2-0.4%.

Preferably, the leveling agent is silicone oil, organosiloxane, or the like.

According to an embodiment of the invention, the swellable coating further comprises water.

According to an embodiment of the invention, the sum of the weight percentages of the components in the expandable coating is 100%. According to an embodiment of the invention, the preparation method of the expandable coating comprises the step of mixing the components to obtain the expandable coating.

Preferably, the preparation method of the expandable coating further comprises dispersing the mixed components in water to obtain a dispersion liquid. Further, the method also comprises stirring the dispersion liquid to uniformly mix the dispersion liquid.

In the invention, the expanded microspheres are screened by a screening machine to select the expanded microspheres with the particle size range of 5-30 mu m, and the expanded microspheres are mixed with water-soluble resin and stirred for 30-60min at normal temperature.

According to the embodiment of the invention, the expandable coating is prepared by coating the expandable coating comprising the following components in percentage by weight: 45-65% of water-soluble resin, 10-30% of foaming agent, 0.1-0.5% of hectorite, 0.5-3% of butyl dipropyl alcohol, 1-3% of propylene glycol, 0.2-0.8% of acrylic thickener, 0.1-0.5% of dispersant and 0.1-0.5% of flatting agent.

The inventor of the invention unexpectedly finds that in the heating expansion process, the expansion rate needs to be controlled within the range of 300-400%, and when the expansion rate is less than 200%, the gap between the magnet and the magnetic steel groove cannot be tightly filled; whereas if the expansion rate is more than 400%, the crosslinking inside the coating layer is broken, and the push-out force becomes insufficient. The expansion rate is related to the content, the grain diameter, the expansion temperature, the expansion time, the coating thickness and other conditions of the microspheres in the coating, and the expansion multiplying power can be controlled within a proper range by optimizing the using amount and the expansion conditions of the raw materials of each component in the expandable coating so as to further prepare the sintered neodymium iron boron magnet with excellent bonding and pushing force.

According to an embodiment of the invention, the sintered NdFeB magnet consists of a primary phase Nd₂Fe₁₄B. Nd-rich phase and B-rich phase.

The invention also provides a preparation method of the expandable sintered magnet, which comprises the steps of coating the expandable coating containing the components on the surface of the sintered neodymium-iron-boron magnet, and carrying out pre-curing treatment to obtain the expandable sintered magnet.

According to an embodiment of the present invention, the sintered ndfeb magnet further comprises a step of surface pretreatment before the expandable coating is applied.

According to one embodiment of the invention, the surface pretreatment comprises the processes of chemical ultrasonic degreasing, acid washing and water washing of the surface of the sintered neodymium iron boron magnet.

Preferably, the deoiling liquid adopted in the deoiling process is a composite solution of alkali and a surfactant.

Preferably, the base is sodium hydroxide or sodium carbonate at a concentration of 10-20g/L, illustratively 10g/L, 15g/L, 20 g/L.

Preferably, the surfactant is sodium dodecyl sulfate or sodium dodecyl sulfate at a concentration of 2-6g/L, illustratively 2g/L, 3g/L, 4g/L, 5g/L, 6 g/L.

Preferably, the degreasing fluid temperature is 30-70 ℃, exemplary 30 ℃, 40 ℃, 50 ℃, 60 ℃, 70 ℃. Further, the oil removing time is 1-20min, and is exemplified by 1min, 5min, 10min, 15min and 20 min.

Preferably, the acid used for the acid washing may be an aqueous solution of nitric acid or citric acid.

Preferably, the acid wash is used with an acid solution concentration of 5-30 wt%, illustratively 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%. Further, the time of the acid washing is 5 to 30s, exemplary 5s, 10s, 15s, 20s, 25s, 30 s.

Preferably, the water washing includes ultrasonic water washing using pure water. Further, the water washing time is 20-120s, exemplary 20s, 30s, 50s, 80s, 100s, 120 s.

According to embodiments of the present invention, the coating means includes, but is not limited to, spraying, printing, dipping, painting, and the like. Preferably by spraying.

According to an embodiment of the invention, the coating has a thickness of 50 to 300 μm, preferably a thickness of 80 to 150 μm, exemplary 50 μm, 80 μm, 110 μm, 150 μm, 180 μm, 200 μm, 250 μm, 300 μm.

The inventors of the present invention have surprisingly found that too thin a coating thickness of the expandable coating results in insufficient expansion force during assembly and thus a predetermined ejection force requirement is not met. However, if the thickness of the expandable coating is too large, the surface of the coating is liable to peel off and crack. And the coating thickness of the expandable coating is related to the reserved size of the magnetic steel slot, and the larger the reserved size is, the thicker the required coating thickness is. The inventor unexpectedly finds that when the coating expands, the effect is best when the expansion compression ratio of the coating in the magnetic steel groove is 35-65%, the bonding force of the magnet and the magnetic steel groove is best, and the push-out force of the magnet in the magnetic steel groove is maximum.

Expansion compression ratio m ═ H₁-H₀)/(H₂-H₀)；

Wherein: h₀Coating thickness for expandable coating, H₁The thickness of the expandable coating after expansion in the magnetic steel groove, H₂Is expandableThickness of the coating after expansion in the natural state.

According to the embodiment of the invention, the pre-curing treatment can be natural drying of the coating under normal temperature conditions (15-35 ℃) or drying under medium-low temperature (35-90 ℃) baking conditions to form a complete coating.

The invention also provides application of the expandable sintered neodymium-iron-boron magnet in a motor rotor.

The invention also provides a motor rotor workpiece which contains the expandable sintered neodymium-iron-boron magnet.

The invention also provides an assembly method of the motor rotor workpiece, which comprises the steps of assembling the expandable sintered neodymium-iron-boron magnet into a magnetic steel groove, and performing heating expansion treatment to obtain the motor rotor workpiece.

The inventor of the invention has unexpectedly found that the final service performance of the expansion coating is related to the expansion temperature, the heating rate and the holding time in the expansion assembly process, and the expansion temperature can directly influence the structure of the final expansion coating.

According to an embodiment of the invention, the thermal expansion treatment is carried out using a two-stage heating process, the expansion temperature of the first expansion stage being 110 ℃ to 160 ℃, illustratively 110 ℃, 120 ℃, 130 ℃, 140 ℃, 150 ℃, 160 ℃. Further, the temperature rise rate of the first expansion stage is 5 ℃/min to 15 ℃/min, illustratively 5 ℃/min, 10 ℃/min, 15 ℃/min.

When the expansion temperature of the first expansion stage is lower than 110 ℃, a large number of microspheres cannot be expanded and cannot reach the required expansion rate; however, when the expansion temperature of the first expansion stage is higher than 160 ℃, the microspheres will expand rapidly, but due to the different particle sizes of the microspheres in the coating, the microspheres with small particle sizes will expand rapidly and break, so that the coating collapses in advance, and thus the corresponding supporting force cannot be obtained. And when the temperature rising rate of the first expansion stage is controlled to be 5-15 ℃/min, the expansion coating can be uniformly expanded, and liquefied hydrocarbon gas in the body of the expansion microsphere is fully gasified in the temperature rising process, so that the coating is slowly and uniformly expanded.

According to an embodiment of the invention, the second expansion temperature of the heat expansion treatment is 180 ℃ to 210 ℃, exemplary 180 ℃, 190 ℃, 200 ℃, 210 ℃. Further, the temperature rise rate of the second expansion stage is 30-60 deg.C/min, illustratively 30 deg.C/min, 40 deg.C/min, 50 deg.C/min, 60 deg.C/min. After the coating is uniformly expanded, the temperature is increased at an accelerated speed, so that the thermoplastic resin in the coating is rapidly solidified.

The thermoplastic expanded microsphere consists of a thermoplastic resin shell and a propellant wrapped in the thermoplastic resin shell, wherein more than 70% of the propellant consists of isooctane. In addition to isooctane, the propellant can be selected from the group consisting of butane, pentane, heptane and other liquids within a suitable boiling point range. In the process of heating expansion, after the liquid propellant in the expanded microspheres reaches the boiling point, the propellant evaporates to raise the internal pressure of the microspheres to cause the volume change of the propellant, so that the shell which becomes soft after being heated deforms and expands, and simultaneously the shell softens to cause the microspheres to restrict expansion. The temperature at which expansion begins is Tstar and the temperature at which maximum expansion is reached is Tmax, and when the temperature exceeds Tmax, the propellant is released through the thermoplastic resin shell to the extent that the microspheres begin to rupture.

In the first expansion stage, the high boiling point solvent in the coating is volatilized to dissolve the expanded microsphere shell with the particle size less than 10 μm and the wall thickness less than 3 μm, so that the shell wall is thinned and is broken when the maximum expansion temperature is not reached. More than 60% of the microspheres in the expansion coating are cracked, after cracking, the propellant in the microspheres is released, the microspheres do not accelerate to expand any more, so that a hole structure is formed, the thermoplastic resin on the outer wall of the microspheres is crosslinked with the water-soluble resin in the coating, so that a net structure is formed, and the binding force of the magnet in the magnetic steel groove is increased.

In the second expansion stage, the expanded microsphere with the particle size of more than 10 microns in the coating continues to expand, but the high boiling point solvent in the coating is volatilized at the moment, so that the shell of the expanded microsphere is not accelerated to break. In this case, the maximum expansion temperature of the second expansion stage is lower than the maximum expansion temperature of microspheres with a particle size of > 10 μm, and the propellant release rate is slowed.

The release agent in the expanded microsphere consists of more than 70% of isooctane, so that the expansion rate of the coating can be controlled by detecting the release amount of the isooctane in the expansion process, more than 60% of microspheres in the coating are controlled to break, and the microspheres are further crosslinked with the water-soluble resin to form a net structure.

The invention can determine the gas release amount of isooctane in the expansion process by detecting the collected gas, thereby controlling the rupture proportion of the expanded microspheres. The detection method comprises the following steps:

taking a magnet (with the specification of 35.5mm 16.5mm 5.5mm) coated with an expansion coating, placing the magnet in a sealed sampling bottle, heating at the same heating temperature and heating rate as the expansion process conditions in the expansion assembly process, naturally cooling to 60 ℃ after heating, blowing the gas in the sampling bottle into a gas-phase color column by using nitrogen for detection, and recording the isooctane content w at the moment₁；

Continuously heating the magnet in the sampling bottle to a temperature higher than the maximum expansion temperature T of the expanded microspheres_maxHeating for 3 hours at the temperature of (240 ℃) to ensure that the microspheres in the expansion coating are completely broken and the isooctane in the microspheres is completely released, and recording the content w of the isooctane at the moment₂。

The rupture ratio q ═ w of the microspheres was calculated from the amount of released isooctane₁/(w₁+w₂)。

The inventor unexpectedly finds out through a large number of experiments that: the cracking proportion q of the microspheres is within the range of 60-85%, the expansion coating has excellent supporting effect, the expansion magnet has higher push-out force in the use environment, and the bonding effect of the coating is best.

The expansion coating goes through the softening process earlier, and the expansion microballon in the coating leads to the volume increase because of being heated, and the whole thickness of expansion coating increases, produces the extrusion force to motor frock inner wall, and hot melt resin in the expansion coating softens the back simultaneously and can produce certain cohesive force, is fixed in the motor frock with the sintered magnet to accomplish assembly process.

The invention has the beneficial effects that:

(1) according to the invention, the sintered neodymium iron boron magnet coated with the expandable coating is adopted to replace the traditional assembly mode of bonding the coating magnet with epoxy resin and adding potting resin adhesive, the magnet coated with the expandable coating can be inserted into the magnetic steel groove, and the magnet is fixed in the magnetic steel groove by utilizing the irreversible expansion of the coating. Meanwhile, due to the use of the expandable coating, the motor assembling time is greatly shortened, and the motor assembling precision is improved. The sintered magnet coated with the expandable coating has excellent characteristics of high temperature resistance, ageing resistance, corrosion resistance, strong binding force and the like.

(2) The invention adopts the environment-friendly water-based expansion coating with a special formula to replace the traditional potting resin, thereby reducing the VOC emission and the environmental problems caused by solvent-based adhesives.

(3) According to the invention, the content of the expanded microspheres in the expandable coating is controlled to be 10-30%, after the expandable coating is heated and expanded, the water-soluble resin and the expanded microspheres are mutually crosslinked to form a honeycomb-shaped porous structure, wherein the porosity reaches 60-90%, and the bonding thrust in the tool at normal temperature is more than 1000N/cm²。

(4) The hardness of the prepared expansion coating reaches above Mitsubishi pencil H under the condition of normal temperature (25 ℃), the wear resistance is strong, and the surface of the coating is not easy to damage in the transportation process. And the expansion coating is soaked in 10% hydrochloric acid and 10% sodium hydroxide solution for more than 24h, and the coating does not have the defects of softening, dissolving, falling and the like, so that the coating has higher acid and alkali resistance. Meanwhile, the coating is soaked in 170 ℃ engine oil for more than 500 hours, and the coating still does not have the problems of softening, bubbling, falling and the like, thereby showing higher hot oil resistance.

Drawings

FIG. 1 is an electron micrograph (300X magnification) of the expandable coating prepared in example 1 after expansion.

FIG. 2 is an electron micrograph (magnification 250) of the expandable coating (sample 5) obtained in example 5 after expansion.

FIG. 3 is an electron micrograph (250X magnification) of the expandable coating (sample 6) obtained in example 6 after expansion.

FIG. 4 is an electron micrograph (500 Xmagnification) of the expandable coating (sample 10) obtained in example 10 after expansion.

Detailed Description

The technical solution of the present invention will be further described in detail with reference to specific embodiments. It is to be understood that the following examples are only illustrative and explanatory of the present invention and should not be construed as limiting the scope of the present invention. All the technologies realized based on the above-mentioned contents of the present invention are covered in the protection scope of the present invention.

Unless otherwise indicated, the raw materials and reagents used in the following examples are all commercially available products or can be prepared by known methods.

Example 1

In this example, a sintered ndfeb magnet (not magnetized) of 35.5mm 16.5mm 5.5mm gauge was used, and the size of the magnetic steel slots of the motor rotor with assembly was 36mm 17mm 6 mm.

Magnet surface pretreatment: the method comprises the steps of removing oil from a sintered neodymium-iron-boron magnet at 60 ℃ by adopting a composite deoiling liquid with sodium hydroxide concentration of 15g/L and sodium dodecyl sulfate concentration of 3g/L for 2min, then carrying out acid washing for 15s by adopting a 25 wt% citric acid aqueous solution, and finally placing the sintered neodymium-iron-boron magnet into deionized water for ultrasonic cleaning for 2 min.

Preparing an expandable coating: the expandable coating is configured according to the following components (in weight percent): 55% of water-soluble acrylic resin, 30% of water, 10% of foaming agent, 0.2% of hectorite, 1.5% of dipropyl alcohol butyl ether, 2% of propylene glycol, 0.5% of acrylic thickener, 0.4% of ethylene glycol and 0.4% of polydimethylsiloxane, wherein the foaming agent is selected from thermoplastic expanded microspheres, and the average diameter of the foaming agent is 13 microns.

Coating treatment: the expandable coating is coated on the surface of the magnet by adopting a compressed air spraying mode, the spraying speed is 120mm/s, the coating thickness is 110 mu m, the distance between a nozzle and a workpiece is 15cm, the angle between a spray gun and the workpiece is 25 degrees, and the argon pressure of the spray gun is 0.6 MPa.

Pre-curing treatment: the surface of the magnet coated with the expandable coating is heated to 50 ℃ for pre-curing treatment to obtain a coating with the thickness of 110 mu m.

And (3) expanding the coating: putting the magnet coated with the expansion coating into a high-temperature oven under a non-pressure state, heating to 120 ℃ by adopting two-segment heating, and preserving heat for 5 min; then rapidly heating to 170 ℃, and preserving the heat for 3 min. Wherein: the heating rate of the first stage heating is 5 ℃/min, and the heating rate of the second stage heating is 50 ℃/min. As the temperature increases, the gas pressure within the shell of the expanded microspheres increases, the thermoplastic outer shell softens, the expanded volume of the microspheres increases significantly, the resin within the expanded coating softens, and the thickness of the expanded coating increases as the volume of the expanded microspheres increases. As shown in fig. 1, it can be seen that: the microspheres expand uniformly, and the microsphere walls and the resin are crosslinked with each other to form a stable supporting structure. The expansion coating is composed of water-soluble acrylic resin and expansion microspheres. The thickness of the expansion coating expands from 110 μm to 394 μm after the pre-curing treatment, and the expansion rate reaches 358%. And after expansion, the expanded coating is in a honeycomb shape, and the sectional area of the expanded microsphere accounts for 82% of that of the expanded coating. Firstly, taking a scanning electron microscope photo of the expanded coating section, then identifying gaps in the section through images, calculating the sum of the gap areas, and taking the gap areas as the proportion of the expanded microsphere section to the expanded coating section.

Assembling the magnet coated with the expansion coating into a magnetic steel groove of a motor rotor, putting the magnetic steel groove into a high-temperature oven, heating the magnetic steel groove to 120 ℃ in a two-segment mode, preserving heat for 5min, rapidly heating the magnetic steel groove to 170 ℃, and preserving heat for 3 min. Wherein: the heating rate of the first stage heating is 5 ℃/min, and the heating rate of the second stage heating is 50 ℃/min. The magnetic steel slot and the gap between the magnetic steel slot and the magnet are filled up, meanwhile, resin in the coating is crosslinked with expansion microspheres to generate a honeycomb coating structure, the coating cannot expand to the maximum limit in the expansion process due to the limitation of the inner wall of the magnetic steel slot, so that the expanded honeycomb structure is compressed and becomes wrinkled, after heating is finished, a motor rotor is cooled under natural conditions, the volume of the expansion microspheres is increased due to the change of the environmental temperature, and the change is irreversible.

In this state, the normal-temperature bonding ejection force and the high-temperature bonding ejection force of the magnet were detected, and the bonding ejection force at normal temperature (25 ℃) was: 1200N/cm²The bonding thrust at high temperature (170 ℃) is 530N/cm²。

Examples 2 to 5

The surface pretreatment method, expandable coating, and coating process were the same as in example 1, and magnets with an expansion coating thickness of 110 μm were inserted into magnetic steel slots, and the optimum assembly process conditions were obtained using different first expansion temperatures, second expansion temperatures, heating rates, and expansion times, and the results are shown in table 1 below.

TABLE 1

Wherein: w₁、W₂Is the content of isooctane and q is the microsphere rupture rate.

As can be seen from the results in table 1, the normal temperature thrust and the high temperature thrust are related to the expansion temperature and the temperature rise rate, and the optimal assembly process conditions can be obtained by optimization.

Meanwhile, the breaking rate of the microspheres is calculated by detecting the release amount of isooctane, and the breaking rate of the microspheres is 60-85%, the broken microspheres and the resin coating are mutually crosslinked, so that the obtained coating has a stable structure and can stably support the magnet and the gap in the magnetic steel groove.

FIG. 1 shows the coating state after expansion of sample 1, from which it can be seen that: the microspheres expand uniformly to crosslink the microsphere walls and the resin, thereby forming a stable support structure.

FIG. 2 is the coating state after swelling of sample 5, from which it can be seen that: the microspheres are broken more, and the microspheres are fused and adhered to each other to form larger cavities, so that the coating has lower bonding force in a high-temperature state.

Example 6

In this example, a sintered ndfeb magnet (not magnetized) of 35.5mm 16.5mm 5.5mm gauge was used, and the size of the magnetic steel slots of the motor rotor with assembly was 36mm 17mm 6 mm.

The same surface pretreatment method as that of example 1 was adopted, a composite degreasing liquid with sodium hydroxide concentration of 15g/L and sodium dodecyl sulfate concentration of 3g/L was used to degrease the sintered ndfeb magnet at 60 ℃ for 2min, then 25 wt% citric acid aqueous solution was used to pickle for 15s, and finally the sintered ndfeb magnet was placed in deionized water for 2min of ultrasonic cleaning.

The expandable powder coating produced by AKZO-Nobel company is selected, and the coating consists of 50 percent of epoxy resin powder, 20 percent of curing agent, 10 percent of elastomer resin and 20 percent of thermoplastic expandable microspheres. The expandable coating is coated on the surface of the magnet by adopting a compressed air spraying mode, the spraying speed is 60mm/s, the coating thickness is 110 mu m, the distance between a nozzle and a workpiece is 10cm, the angle between a spray gun and the workpiece is 25 degrees, and the argon pressure of the spray gun is 0.6 MPa.

And assembling the magnet coated with the expansion coating into a magnetic steel groove of a motor rotor, putting the magnetic steel groove into a high-temperature oven, and heating for 20min by applying the temperature of 190 ℃. The volume of the thermoplastic expanded microspheres is increased due to temperature change, so that the whole coating is expanded, and meanwhile, the epoxy resin is cured, so that the coating is stable and does not retract. The cross-sectional structure of the intumescent coating was observed using an electron microscope, and as shown in fig. 3, the thickness of the intumescent coating expanded from 110 μm to 180 μm after the pre-curing treatment, and the expansion rate reached 163%. And after expansion, can be clearly seen. The edges of the thermoplastic expanded microspheres are clearly visible and the expanded microspheres are only subject to increased microsphere volume under heat due to the vaporization of the liquid alkane within the microspheres. Whether the microspheres in the coating are cracked or not is estimated by detecting the release amount of isooctane in the expanded microspheres. The detection shows that when the mixture is heated at 190 ℃ for 20min, the released amount w1 of isooctane is 1.52 mg/l. The temperature is raised to 240 ℃ and kept for 3h, so that the expanded microspheres in the coating are completely cracked, and the released amount w2 of isooctane is 5.34 mg/l. According to the calculation of the formula, the fracture rate of the expanded microspheres in the actual assembly process is calculated to be q-w 1/(w1+ w2) -1.52/(1.52 +5.34) -22%.

As can be seen from fig. 3, the cross-sectional area of the expanded microspheres is 35% of the expanded coating.

In this state, the normal-temperature bonding ejection force and the high-temperature bonding ejection force of the magnet were detected, and the bonding ejection force at normal temperature (25 ℃) was: 920N/cm²The bonding thrust at high temperature (170 ℃) is 310N/cm²。

Examples 7 to 14

In this example, a sintered ndfeb magnet (not magnetized) of 35.5mm 16.5mm 5.5mm gauge was used, and the size of the magnetic steel slots of the motor rotor with assembly was 36mm 17mm 6 mm.

The magnet surface was coated with the expandable paint by compressed air spraying using the same surface pretreatment process and expandable paint as in example 1, and the sprayed thicknesses were 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, and 150 μm, respectively.

Assembling the magnet coated with the expansion coating into a magnetic steel groove of a motor rotor, putting the magnetic steel groove into a high-temperature oven, heating the magnetic steel groove to 120 ℃ in a two-segment mode, preserving heat for 5min, rapidly heating the magnetic steel groove to 170 ℃, and preserving heat for 3 min. Wherein: the heating rate of the first stage heating is 5 ℃/min, and the heating rate of the second stage heating is 50 ℃/min. The normal temperature ejection force and the high temperature ejection force of the magnet in the operating state were measured, and the results are shown in table 2 below:

expansion ratio of H₂/H₀

Compression ratio (H)₁-H₀)/(H₂-H₀)

Wherein H₀For coating thickness, H₁The thickness of the expandable coating after expansion in the magnetic steel groove, H₂The thickness of the expandable coating after expansion in its natural state.

TABLE 2

Fig. 4 shows the coating state of the sample 10 in the magnetic steel slot, and it can be seen from fig. 4 that: in the expansion process of the coating, the expansion coating is compressed and wrinkled due to the limitation of the inner wall of the magnetic steel groove.

When the expansion coating is compressed seriously, the contact surface of the expansion coating and the contact surface of the inner wall of the magnetic steel groove generate larger stress, the stress on the unit area of the coating is increased, and the internal defects of the coating are increased exponentially, so that the cohesive strength of a glue layer is reduced, and therefore, the compression ratio is controlled to be more than 35 percent, and the magnet with better normal-temperature push-out force and high-temperature push-out force can be prepared.

The greater the compression ratio, the better the economic effect is obtained, and the inventors have found through a large number of experiments that: when the compressibility is greater than 65%, the coating layer is more sensitive to shrinkage stress and thermal stress caused by temperature change, thereby causing a loss of cohesive strength of the magnet, and thus reducing normal-temperature and high-temperature extrusion forces of the magnet.

The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiment. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.