After annealing, the brittleness of nanocrystalline iron core is very large, so it is not suitable to cut it directly. Generally, epoxy resin is used as the curing agent to encapsulate and solidify the iron core. However, there are still some shortcomings in the epoxy resin solidified nanocrystalline iron core, such as not easy to fully fill the gap between the iron core strips, easy to produce debris when cutting, large curing shrinkage, resulting in the rapid degradation of the magnetic properties of the iron core. Epoxy + polyether amine flexible system was used as the curing agent of nanocrystalline iron core. The comprehensive influence of curing process of epoxy + polyether amine flexible system on the cutting ability and magnetic properties of nanocrystalline iron core was analyzed.

Experimental mode

The ring iron core is made of amorphous strip and annealed to prepare nanocrystalline iron core, which is then put into epoxy resin flexible curing agent for vacuum impregnation and then solidified in drying oven. The effect of curing process on the cutting ability and magnetic properties of nanocrystalline iron core was studied by orthogonal test.

Results and analysis

2.1 gap filling and cuttability of iron core strip

The gap filling effect of iron core strip is mainly determined by the lamination coefficient of iron core and the fluidity of curing agent. The lamination coefficient of each experimental group is between 0.75-0.78. The lamination coefficient of iron core of each test group after solidification is between 0.78-0.84, and the change rate of lamination coefficient of most test groups is large, which shows that the gap filling effect of strip is good. However, the lamination coefficient of sample 3 is only 0.808, and the change rate of lamination coefficient is small. This is due to the large lamination coefficient before solidification of the iron core, and the large proportion of the curing agent filler, which makes the fluidity of the curing agent poor. The joint action of the two makes the gap filling of the strip more difficult.

Wire cutting is a more intuitive way to check the gap filling effect of iron core strip. After cutting, grinding and polishing, the iron core of each test group is evenly distributed and basically free of defects such as broken band and gap. Among them, the filling of iron core is very difficult. As the key object of this test, the iron core strip shows good integrity, no broken strip, debris and other phenomena, which shows that the gap filling effect of the strip is good. Because the lamination coefficient of iron core before solidification is small, the gap of strip is too large, which increases the possibility of loss of curing agent in the process of heating and solidification, and affects the filling effect of gap of strip, which is directly reflected in the phenomenon of local fracture and breakage of strip after cutting. It shows that the smaller lamination coefficient of iron core will also affect the filling effect of strip gap.

In the core which is difficult to be filled, or at both ends of the iron core which is easy to lose curing agent, there are no cracks after solidification in some parts, the integrity of the iron core is good, showing excellent cutting ability; while in sample 4, there are different degrees of cracks and layering at both ends and inside and outside of the iron core, at the same time, in the process of grinding sample, there are a lot of debris. The macroscopical performance of the two groups of test iron cores is just corresponding to the micro morphology, which shows that even when the lamination coefficient of the iron core is large and the fluidity of the curing agent is reduced, the curing agent can still fully fill the gap between the strips to ensure that the iron core has excellent cutting ability after curing.

2.2 effect of curing process on loss

The main influence factor of iron core loss is curing temperature, and through sample process, namely curing temperature 353K, curing time 180 min, filler ratio 10%, the iron core gets the best magnetic properties after curing, at this time, the loss is low: P 1 / 1K = 7.319 w / kg, P 0.5 / 10K = 20.888 w / kg.

After winding, the iron core used in this experiment adopts a unified annealing process to prepare nanocrystalline iron core and eliminate the internal stress produced during winding. Therefore, the influence factor of magnetic properties of iron core in this test is only the internal stress produced by curing shrinkage of curing agent. Sufficient curing time can effectively release the energy generated by 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 sample 3 curing process, the loss of iron core is low, which indicates that the curing shrinkage stress of the process is low. Adjusting the curing process can improve the effect of curing agent on the loss of iron core.

2.3 effect of curing process on magnetization curve and permeability curve

At the power frequency of 50Hz, the iron core can be saturated at a very small magnetic field strength (H = 7 A / M) before solidification, and the saturation magnetic induction strength is BS = 1.02t; at the same magnetic field strength, the iron core of each test group is far from saturated after solidification, which shows a slow upward trend. Among them, the magnetic induction strength of sample 3 at this time reaches 0.85t, which is 20% lower than that before curing, but superior to other test groups; the magnetic induction strength of sample 9 with higher curing temperature is only 0.5T, which is 50% lower than that before curing. The permeability of iron core after solidification is obviously lower than before. Among them, the initial permeability before iron core solidification μ I = 163000, while after iron core solidification μ I = 73400, the change rate is 55%; the maximum permeability before iron core solidification μ max = 436000, and the maximum permeability after iron core solidification μ max = 260000, the change rate is 40%; with the increase of magnetic field strength, the permeability gap before and after iron core solidification gradually decreases, and finally basically remains at 5%. The magnetic properties of iron core decrease after solidification, and there are differences among different solidification processes, because: the solidification shrinkage stress of curing agent affects the magnetic properties of iron core, the direct result is that the permeability of iron core decreases, and the iron core is difficult to saturate; different solidification processes result in different solidification shrinkage stress in the iron core, and the stress-induced magnetic anisotropy is different, resulting in iron The magnetization curve is different after core solidification.

2.4 effect of curing process on inductance

When f = 50Hz, the inductance of iron core before solidification is 210 μ h, and after solidification