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Vacuum heat treatment of soft magnetic materials

The raw materials of soft magnetic alloy are mainly bars, strips and plates. The parts are cut, punched, punched or wound by cold working. In the process of machining, the original grain structure of the material will be destroyed, which will reduce the magnetic conductivity of the material. At the same time, the machining stress produced in the process of machining will lead to the instability of the part size. Therefore, the parts made of soft magnetic alloy must be annealed after processing, so that the material can get regular equiaxed grain structure again, reduce the content of impurities in the material, restore and improve the magnetic properties of the material, eliminate the processing stress and stabilize the size of the parts.


According to different materials and application requirements, high temperature annealing (1150-1250 ℃) and medium temperature annealing (800-850 ℃) can be used for the annealing of soft magnetic alloy parts. Permalloy with high magnetic conductivity is usually annealed at high temperature. Sometimes, in order to further improve the magnetic conductivity, magnetic field annealing is also used. For the stacked or rolled silicon steel sheet (usually called core) of transformer, transformer or motor, medium temperature annealing is used.

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Square vacuum annealing furnace


At present, the annealing of soft magnetic materials mainly adopts the well type external hot atmosphere furnace, which is protected by nitrogen or hydrogen. There are obvious defects in this way, especially when nitrogen is used as the protective atmosphere. First of all, when nitrogen protection is used for treatment, the purity of atmosphere obtained by nitrogen replacement in the furnace is not enough, and the flow direction of nitrogen has a great influence on the surface quality of the workpiece, and there is often the phenomenon that the color of parts in the same furnace is inconsistent after treatment.


This is caused by slight oxidation of some workpieces due to the poor nitrogen flow area in the furnace. Secondly, the temperature uniformity of the external furnace is poor, the performance of the treated parts is different greatly, and the qualification rate is low. In addition, in terms of energy consumption, the furnace lining of the external heat furnace is thick, and the power consumed on the furnace lining in the heating process is large, and the thermal efficiency is low; in the heating process, high-purity nitrogen needs to be continuously filled, and the consumption of nitrogen is large; the service life of the heat-resistant steel furnace under high temperature is low, which results in high operation cost of the external heat furnace. For example, if hydrogen is used as the protective atmosphere, the performance and surface quality of workpieces can be improved depending on the strong decarburization ability and reduction effect of hydrogen, but the problems of uneven temperature and high operation cost are still inevitable.


Round vacuum annealing furnace


The use of internal heated vacuum annealing furnace is of great significance to the annealing of soft magnetic alloy parts. Internal heated vacuum furnace has obvious advantages in the aspects of workpiece treatment effect, operation cost, production efficiency and production environment.


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