Heat treatment of amorphous alloy core strip

  Amorphous alloy has the advantages of high saturation magnetic induction strength, small coercive force, low loss, etc., so it is widely used in power transformers with high efficiency, energy saving and environmental protection. However, before 2009, almost all of the amorphous strip used in amorphous alloy transformers in China's entire industry market was produced by Hitachi Metals Corporation of Japan. The construction of a 10,000-ton amorphous alloy strip production line with independent intellectual property rights by China's technology companies has been put into operation, breaking the passive situation of amorphous raw materials relying on imports and accelerating the development of a low-carbon economy in China's power industry.

 

Heat treatment of amorphous alloy core strip

  The current amorphous alloy core adopts an approximately rectangular lap winding structure. The internal stress of the formed core is very large, and the magnetic properties are severely damaged. These stresses must be eliminated by heat treatment annealing. The heat treatment annealing process is the most critical and most difficult process in the entire manufacturing process of the amorphous alloy core. Domestic amorphous alloy strips are horizontally arc-shaped, and their internal stress is greater than that of imported strips. In addition, the difference in composition makes them more sensitive to temperature during heat treatment. Therefore, an appropriate heat treatment annealing process is developed to The final core performance and quality of domestic amorphous alloy strips are critical.

  1. Heat treatment annealing temperature. The proper core annealing temperature should not only ensure the elimination of the internal stress of the core and restore its magnetic properties, but also be able to reduce the brittleness of the amorphous alloy strip as much as possible and reduce the risk of breakage in the subsequent operation of the core. The test shows that the final annealing temperature of the domestic amorphous alloy strip core is controlled at 375 ～ 380 ℃.

  2. Heat treatment holding time. Experiments show that the unit excitation power decreases with the extension of the annealing time, while the unit no-load loss of the core increases with the extension of the annealing time, and the brittleness of the core strip also increases with the increase of the annealing time . Therefore, we must choose the best heat preservation time according to the user's requirements on the performance of the core.

  3. Heat treatment to protect the atmosphere. The iron core is easily oxidized during high temperature heat treatment annealing. After the core surface is oxidized, in addition to the rust on the surface, the main reason is that the no-load loss of the core will increase significantly. Therefore, the core must be protected by atmosphere during the entire heat treatment annealing process. The currently used process protective gas is nitrogen or argon.

  4. Heating and cooling speed. Since the core is mass-loaded and batch heat-treated during mass production, a reasonable heating and cooling rate not only affects the performance results of the amorphous alloy core, but also affects the production efficiency and production costs. In general, the faster the heating rate, the greater the dispersion. However, experiments show that the temperature dispersion of the domestic amorphous alloy strip core when reaching the high temperature region and approaching the optimal annealing temperature point is small, and can be controlled within 3 ℃. Therefore, in the heating stage, the domestic amorphous alloy strip core can be directly heated rapidly. In addition, the fast cooling speed is beneficial to reduce the no-load loss of the core, but at the same time it will increase the excitation power of the core. Therefore, the best cooling rate requires accumulated experience data to make the best choice.

  5. External magnetic field. After forming, the amorphous alloy core needs an additional DC magnetic field to obtain a good magnetic domain orientation during annealing to improve its magnetic properties. The test shows that the field strength of the domestic amorphous alloy strip core during annealing needs to be about 2000A / m or the magnetic field current is 1400A to ensure that the core material is saturated during annealing, so as to achieve the best annealing effect.