Punching edge effects and induction heating
Decrease of the magnetic properties by the processing of finally annealed steels
For their use in the magnet cores of electrical machines magnetic steels are cut or punched. In general the structure of edgenear areas is destroyed by this processing.
These microstructural changes cause changes of characteristic magnetic properties . It is to be usually expected with a less steep B(H) magnetizability and with higher hysteresis losses P(B) than in the material in the delivered state.
Electrical steel in the semi-processed state to alternative
The manufacturers of the electrical steels offer a magnetic steel, which is delivered weakly cold-rolled (= deformed critically) and which after a recrystallizing annealing in special annealing furnaces reaches its good magnetic properties.
For the processing plants these semi finished or semi processed electrical steels have got apart from the advantages (= exzellente magnetic characteristics of the punching parts) also disadvantages:
high investment and operating cost for the annealing technology an atypical additional production stage (annealing), the space requirement and the small flexibility of the conventional furnaces.
Inductive heating of small laminations
In co-operation with a partner from the lighting industry and an enterprise for inductive heating equipment technology the inductive annealing of punching laminations from electrical steels in the annaeled and in the semi-processed state were examined.
The heating parameters for the two qualility groups differ clearly from each other. While with the laminations from annealed electrical steel a short time annealing is sufficient at relatively low temperatures, the annealing of punching parts of semi-processed quality has to be longer and at higher temperatures, in order to secure the recrystallisation of the structure with a sufficient grain growth.
Beside the temperature the gas atmosphere is crucial. It was annealed in an inert gas-flow.
Demands on the heating technology for semi-processed qualities are a reducing atmosphere during the recrystallisation and a temporarily oxidizing atmosphere during the cooling. These demands can be gone around by the use of low-decarburized qualities with a permanent heat resistance surface insulation.
Both with the glowing of the laminations from the annealed electrical steel as well as with the glowing from laminations rom the semi-processed qualities in first attempts very good results were reached.
The decrease of the magnetic properties of annealed electrical steel during its processing can be compensated by a reheating.
In an attempt the possibilities were examined, which can be get by an inductive heating.