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How to make annealed nanocrystalline iron cores easy to cut

How to make annealed nanocrystalline iron cores easy to cut

2021-10-20

The brittleness of the nanocrystalline iron core after annealing is extremely large, and it is not suitable for cutting directly. Usually epoxy resin is used as a curing agent to encapsulate and cure the iron core, but the epoxy resin cured nanocrystalline iron core is not easy to fully fill the gap of the iron core strip, and it is easy to produce debris during cutting, and the curing shrinkage rate is large, resulting in The magnetic performance of the iron core is sharply inferior. The epoxy resin + polyether amine flexible system is used as the curing agent of the nanocrystalline iron core, and the comprehensive influence of the curing process of the epoxy resin + polyether amine flexible system on the cutability and magnetic properties of the nanocrystalline iron core is analyzed.

nanocrystalline cores

Experimental method


A toroidal iron core is made by winding an amorphous strip material, annealed to prepare a nanocrystalline iron core, and then put into an epoxy resin flexible curing agent for vacuum impregnation, and then cured in a drying box. Orthogonal experiment was used to study the effect of curing process on the cutability and magnetic properties of nanocrystalline iron cores.


results and analysis


2.1 Gap filling and cutability of core strip


The gap filling effect of the core strip is mainly determined by the core lamination coefficient and the fluidity of the curing agent. The lamination coefficients of the iron cores of each experimental group before curing are distributed between 0.75-0.78. The lamination coefficients of the iron cores of each test group after curing are distributed between 0.78-0.84, and the lamination coefficients of most test groups have a large change rate, which indicates that the gap filling effect of the strip is good. However, the lamination coefficient of sample 3 after curing is only 0.808, and the change rate of lamination coefficient is small. This is because the lamination coefficient of the iron core is large before curing, and the curing agent filler ratio is large, which makes the curing agent fluidity worse. The two work together, which makes it more difficult to fill the gap of the strip.


Wire cutting is a more intuitive way to test the gap filling effect of the core strip. After the iron cores of each test group have undergone cutting, grinding and polishing, the strips are evenly distributed, and there are basically no defects such as broken strips and voids. Among them, the filling of the iron core is more difficult. As the focus of this test, the iron core strip shows good integrity, without broken bands, debris and other phenomena, which shows that the gap filling effect of the strip is good. Because the lamination coefficient of the iron core before curing is small, the gap between the strips is too large, which increases the possibility of the loss of curing agent during the heating and curing process, and affects the filling effect of the gap between the strips. The direct manifestation is the partial strip after cutting. There is a phenomenon of fracture and fragmentation. It shows that the smaller lamination factor of the iron core will also affect the filling effect of the strip gap.


In the core part that is difficult to fill, or the two ends of the iron core where the curing agent is easy to lose, there are no local gaps after curing. The iron core has good integrity and exhibits excellent cutability; while the sample 4 has two iron cores. The ends and the inner and outer sides show different degrees of gaps and stratification. At the same time, there are a lot of debris in the process of grinding. The macroscopic performance of the two sets of test iron cores exactly corresponds to the microscopic appearance, indicating that the vacuum impregnation process is adopted, even when the core lamination coefficient is large and the fluidity of the curing agent is reduced, the curing agent can still fully fill the belt. The material gap ensures that the iron core has excellent cutability after curing.


2.2 The effect of curing process on loss


The main influencing factor of the iron core loss is the curing temperature; and after the sample process, that is, the curing temperature is 353K, the curing time is 180 min, and the filler ratio is 10%. The magnetic properties of the iron core are obtained after curing, and the loss is lower at this time: P 1/1k = 7.319 W/kg, P 0.5/10k = 20.888 W/kg.


After the iron core used in this experiment is wound, a uniform annealing process is adopted to prepare the nanocrystalline iron core while eliminating the internal stress generated in the iron core winding. Therefore, the influencing factor of the magnetic properties of the iron core in this test is only the internal stress caused by the curing shrinkage of the curing agent. Adequate curing time can effectively release the energy generated by the cross-linking reaction, reduce internal stress, and avoid energy waste caused by too long time. The filler can effectively reduce the curing shrinkage and help to adjust the fluidity of the curing agent. Under the curing process of Sample 3, the loss of the iron core is lower, indicating that the curing shrinkage stress of this process is lower, and adjusting the curing process can improve the effect of the curing agent on the loss of the iron core.


2.3 The effect of curing process on magnetization curve and permeability curve


Under the power frequency of 50 Hz, the iron core can be saturated with a very small magnetic field intensity (H=7 A/m) before curing, and the saturation magnetic induction intensity Bs =1.02T; under the same magnetic field intensity, the iron cores of each test group after curing The cores are far from being saturated, and they all show a slow upward trend. Among them, the magnetic induction intensity of sample 3 at this time reaches 0.85T, which is 20% lower than that before curing, but is better than other test groups; the magnetic induction intensity of sample 9 with a higher curing temperature is only 0.5T, which is compared with that before curing A decrease of 50%. The magnetic permeability of the iron core after solidification is significantly lower than before solidification. Among them, the initial permeability of the iron core before curing is μi=163000, while the after curing of the iron core is μi=73400, and the rate of change is 55%; the large permeability of the iron core before curing is μmax=436000, and after the iron core is cured The large permeability μmax=260000, the rate of change is 40%; as the magnetic field intensity increases, the magnetic permeability gap before and after the iron core is solidified gradually decreases, and finally remains at 5%. The magnetic performance of the iron core after curing has decreased, and there are differences in the reduction of magnetic performance caused by different curing processes. The reason is that the curing agent curing shrinkage stress affects the magnetic performance of the iron core, and the direct result is that the magnetic permeability is reduced, and the iron core is difficult to saturate. ; Different curing processes cause differences in the curing shrinkage stress inside the iron core, and the stress-induced magnetic anisotropy is different, resulting in different magnetization curves after the iron core is cured.


2.4 The effect of curing process on inductance


When f=50Hz, the inductance of the iron core before curing is 210μH, and the inductance is significantly reduced after curing. Among them, 3 iron cores perform better, and the inductance is 100μH; as the frequency increases, the difference in inductance before and after curing of the iron core gradually decreases. When f=100kHz, it almost reaches the same level, and the inductance is 5~6 μH. Since curing will reduce the magnetic properties of the iron core, the inductance change rate is negative. It can be seen that in the range of f=50Hz~1kHz, the inductance change rate of each test group is -50%~-80%, and each curve basically maintains the level. Among them, the inductance change rate of the 3 iron core is significantly lower than that of other test groups. , Keep at about -50%; in the range of f=1~100 kHz, the inductance change rate shows an obvious decreasing trend, while the gap between the test groups is reduced. When f=100 kHz, the inductance of each test group changes The rates are maintained at around -10%. This shows that in the range of f=50 Hz~1kHz, the curing shrinkage stress of the curing agent has a greater impact on the inductance of the iron core. Adjusting the curing process can effectively reduce the effect of curing on the inductance of the iron core; while at f=1~100 kHz Within the range, the curing agent has little effect on the inductance of the iron core, and the change rate of inductance is very small by adjusting the curing process.


in conclusion


(1) Under vacuum impregnation conditions, epoxy resin + polyetheramine flexible system is used to cure the nanocrystalline iron core, and the gap filling effect of the iron core strip is better, and it has excellent cutability after curing.


(2) Orthogonal test analysis shows that the main influencing factor of iron core loss is curing temperature. The curing process is: curing temperature 353K, curing time 180min, and filler ratio 10%. The core loss cured by this process is relatively low: P1/1k =7.319 W/kg, P 0.5/10k = 20.888W/kg, the magnetic induction intensity (H=7 A/m) is reduced by 20%, and the initial permeability μi Decrease by 55%, and the large permeability μmax decreased by 40%.


(3) In the range of 50 Hz~1 kHz, the curing shrinkage of the curing agent has a greater impact on the inductance of the iron core. The effect of curing on the inductance of the iron core can be effectively reduced by adjusting the curing process; while in the range of 1-100 kHz, the curing The influence of the agent on the inductance of the iron core is small, and the influence on the rate of change of the inductance is very small.

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