Handling Of Abnormal Magnetization In The Design Of Permanent Magnet Mechanism With High Field

Sintered Nd-Fe-B which has excellent properties can be used to product high field permanent magnetic mechanism. There is a kind of special permanent magneticmechanism--high field magic ring which is made up of permanent magnet segments withdifferent magnetization directions. A magnetic flux density level several times as much as the remanence of permanent magnet material can be achieved if we design the magic ring properly.However, abnormal magnetization including local saturation, local demagnetization and rotational magnetization occur in the assembly process of high field permanent magnetic mechanism, which result in operating point of the material move in all the four quadrants, so accurate design of high field permanent magnet mechanism is very difficulty. Though some foreign researchers producted some mechanisms which flux densities reached 4-5T, the theoretical values were greater than the actual results evidently, because abnormal magnetization were not considered comprehensively. We can't design expected permanent magnet mechanism if simulation abnormal magnetization unaccuratlly in finite element analysis. But certain vector hysteresis models which can simulation rotational magnetization were related to magnetic recording mediums or soft magnetic materials, otherwise, the varying pattern referred was circularly or elliptically rotational field, which is different from the arbitrary magnetization pattern, and the application of these models were very complicated. The information about rotational magnetization of hard magnetic material in the condition of high field which is chage arbitrarily is very little.Based on analysising microstructure and microscopic mechanism of magnetization and demagnetization of sintered Nd-Fe-B, a 2D simplified vector Preisach model is presented in this paper. Using this vector Preisach model in finite element analysis, abnormal magnetization occur in the assembly process of high field permanent magnetic mechanism are considered comprehensively. The method only requires the data of limiting magnetic hysteresis loops of the material along easy and hard axis, so the application of vector Preisach model become convernient and efficient.Combining the vector Preisach hysteresis model and finite element analysis, a dynamic magnetic field analysis is implemented for a new magic ring in the process of assembling.A series of methods such as adding soft magnetic material, adjusting magnetization directions, utilizating two grades permanent magnet materials and replacing anti-magnetic shell to magnetic shielded shell are adopted in the new magic ring. Furhtermore, dimensions of every part and certain directions of magnetization are optimized by method of exhaustion and orthogonal testing method. All these methods can reduce local saturation and local demagnetization to enhance magnetic strength in air cavity of magic ring.Finally, after the model is completed and measured, the magnetic field strength is 4.10 T and is smaller than the results of expectation. The error is effect of assembly process, machining precision, material performance and measurement etc. The model verifies reasonablity of the construction of magic ring and validity of the optimization method. The proposed method provides a theoretical foundation for the design of high field permanent magnetic mechanism.