HANGZHOU TENGYE MAGNETIC MATERIALS CO., LTD.
Laminated magnets are also known as segmented magnets. They are composed of two or more individual magnets bonded yet insulated to one other. Laminated NdFeB magnets were developed for the purpose of enhancing the performance of electric machines. This is achieved by preventing the magnets from overheating. In addition to NdFeB, Sm2Co17 magnet also served as the base magnetic material for magnet segmentation technology.
With the development of electric motors for vehicles and generators for wind power constructions, the demand for sintered NdFeB magnets is growing fast. Being the main components of these devices, NdFeB magnets enable them to work at high speed. However, eddy current will be produced during the high-speed operation in the magnets and consequently cause NdFeB magnets to heat up. As a result, demagnetization takes place when the temperature in the magnets reaches a certain point. By segmenting complete NdFeB blanks and then laminating them together with adhesive, each magnet becomes an independent part and insulates each other. This will effectively reduce eddy current loss and keep the temperature of NdFeB magnets down during the operation.
One drawback of NdFeB magnet is its poor resistance to high temperature. The magnets demagnetize at high temperature. By laminating and insulating NdFeB blank, the eddy current path is broken into several paths. Thus, it reduces the eddy current density and eddy current loss decreases as well. To provide you with a better understanding, we recommend you to read JMAG’s article – Analysis of the Eddy Current in the Magnet of an IPM Motor.
Depending on the technical requirement in the application, individual NdFeB magnets are glued together to form complete laminated NdFeB magnets either “before” or “after” coating. The segmented magnets mounted on the rotor shown above belongs to “after-coating type”, where individual magnets are coated and then glued in a certain way to form a larger unit. So-called “before-coating type” is shown on the right picture, which requires a complicated manufacturing process and is therefore costly to process.
To start with, individual NdFeB blanks are sliced (segmented) into several single pieces of the same thickness and laminated with glue for the purpose of insulation. The whole laminated NdFeB blank is then considered as a normal blank, which is to be cut, sliced and ground into the desired geometry and dimension. The maximum insulation that the bonding adhesive can typically achieve is 95%. The final product – complete laminated NdFeB magnets, cannot be electroplated due to the existence of adhesive because the whole magnet body is no longer electrically conductive. Instead, epoxy-painting (usually black) or phosphorization are common alternative coating solutions
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