Grain orientation is an extremely important variable that affects the permeability. Improved orientation results in the greater permeability which in turn lowers the core loss. Recent developments have made it possible to produce greater permeability material.
In the case of 3% Si-Fe (110)[001] crystal, the core loss depends strongly upon the tilt angle of the [001] direction from the sheet plane. When the tilt angle is about 2
°, the core loss becomes minimum, that is, when the tilt angle is less than about 2
°, increase in the 180
° domain wall spacing gives rise to increase in the core loss.
It is also known that the core loss takes minimum at B
8 of about 1.95 T at 800 A/m for the laboratory products. A great part of increment in the loss in the range of B
8 higher than 1.95 T is thought to be due to the coarsening of magnetic domains caused by increase in the number of grains having the ideal (110)[001] orientation.
These results were obtained by using the laboratory products, for which the samples were annealed in the form of flat sheet. In the manufacturing process, however secondary recrystallized grains grow during box annealing in coiled strip, and rounded grains are heat flattened by subsequent annealing. Even if (110) plane in the middle part of grain is parallel to the sheet plane, at the grain boundaries the tilt angle of [001] axis from the sheet plane is about 2
° for large grains. Therefore, the 180
° domains appear at the grain boundaries and the 180
° domain wall spacing decreases so as to reduce the magnetostatic energy. The core loss of the products annealed in a coil form decreases as B
8 increases higher than 1.95 T.
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