In the design of motors by motor manufacturers, the shape and size of permanent magnets have a crucial impact on the overall performance of the motor. Therefore, selecting motor magnets with suitable shapes and sizes is of great significance.
Commonly used shapes for motor magnets include arc-shaped, flat-shaped, ring-shaped, and other forms. In this article, we will discuss the advantages of different shapes of motor magnets.
Arc-shaped Motor Magnets
Arc-shaped magnets are also called tile magnets which are often used in different electric motors or generators. Due to their south and north polarities, they are used in torque couplings as well. Arc-shaped magnets are still the most common shape for motor magnets, especially for DC motors and magnetic rotors.
The Advantages of Arc-shaped Motor Magnets
Reduced Air Gap: The bent or curved shape of arc magnets allows them to bring the magnetic field closer to the stator. This reduction in the air gap between the magnet and the stator contributes to increased magnetic efficiency and improved overall motor performance.
Image Source: Celeramotion
Radial Flux Arrangement: Arc-shaped magnets facilitate the formation of radial magnetic rings. This radial flux arrangement is well-suited for various motor types, especially for applications like DC motors and magnetic rotors.
There are four main types of arc magnets: curved bottom arc, chord arc, flat bottom arc, and bread loaf.
Image Source: Bunting
Each of these shapes has different advantages and disadvantages when considering the impact on a motor design. Priority is given to selecting the optimum arc design, not the production costs. the reason is that the shape is fundamental to the performance. The cost of the magnet materials are far higher than the production costs.
Image Source: Bunting
Ring-shaped Motor Magnets
In theory, ring-shaped magnets are considered the optimal shape for motor magnets. More precisely, these are radial ring-shaped motor magnets. There are two main types of radial ring-shaped magnets. One is bonded magnets, and the other is sintered NdFeB magnets.
Bonded magnets are designed for different motors, such as pump motors, vacuum cleaner motors, brushless motors, DC motors, and conveyor motors. Compared to sintered NdFeB, bonded magnets, such as ferrite magnets, SmCo magnets, or NdFeB magnets, have advantages in terms of control precision and better-finished product yield. They can be made into different complex shapes through various magnetization methods. However, their magnetic fields are much lower than sintered NdFeB magnets.
Sintered NdFeB magnets can also be made into radial-oriented magnetic rings. However, they are very expensive because they require additional magnetization fixtures and magnetization coils. There are also many limitations in terms of size and grade.
Ring-shaped Motor Magnets Possess Many Advantages
Uniform magnetic field distribution: The circular shape of the magnet helps create a more uniform magnetic field across its surface. This uniformity contributes to stable and efficient motor operation.
Image Source: Science Photo Library
Easy to assemble: The circular shape of the magnet simplifies the assembly process, making it easier for manufacturers to integrate these magnets into motor systems. This can lead to cost savings in the production process.
Multiple magnetization directions: Ring-shaped magnets offer flexibility in magnetization directions, enabling customization to suit specific motor designs. This versatility is advantageous in applications where magnetic field requirements vary. The ability to select the most suitable magnetization direction enhances the efficiency of the motor by aligning the magnetic field with the desired motion, whether it be axial or radial.
Excellent motor performance: The manufacturing process for ring-shaped magnets allows for tighter tolerances and minimized variability in dimensions. This precision is particularly beneficial in motors that demand high reliability and performance.
Flat Motor Magnets
Flat magnets(trapezoidal magnets or rectangular magnets) are another common choice for motor magnets.
Cost: Flat shapes are convenient for motor magnet manufacturers to process. This means that they cost less than segmented motor magnets.
Reduced Eddy Currents: The planar shape of flat magnets can help minimize eddy currents, which are undesirable circulating currents induced in conductive materials. This reduction in eddy currents contributes to improved motor efficiency.
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