Arc magnets in motors, also known as motor magnets, are fixed to circular rotors or stators.
Definition of Arc Magnets in Motors
Arc magnets in motors are a type of permanent magnet primarily applied in permanent magnet motors. Their arc shape is the reason they are called arc magnets.
Functions of Arc Magnets in Motors
Arc magnets have vast applications in motors, especially in permanent magnet synchronous and brushless DC motors. By installing arc magnets on the rotor or stator, they create a stable magnetic field that interacts with the motor’s windings, driving the motor to rotate.
For instance, in electric vehicle drive motors, neodymium arc magnets provide a strong magnetic field, enhancing the motor’s power density and efficiency, thereby improving the vehicle’s performance and range.
Types of Arc Magnets in Motors
Motor materials are generally categorized into three common types based on their composition: neodymium arc magnets, ferrite magnets, and aluminum-nickel-cobalt and samarium-cobalt arc magnets.
Application of Arc Magnets in Motors
Arc magnets have different performance and magnetic field waveform requirements based on their application:
| For Rotors: The outer arc surface field demands high quality, with typical waveforms resembling saddle shapes, square waves, or sinusoidal waves, sometimes incorporating multiple harmonics.
| For Stators: The inner arc surface field is high, depending on the motor’s output requirements, which are determined by the shape and production characteristics of the arc magnets. This primarily yields a saddle-shaped waveform that offers greater output.
Magnetization Direction of Arc Magnets in Motors
The distribution of the N and S poles of arc magnets is not fixed but designed flexibly based on specific magnetization methods and application scenarios. In most motor applications, arc magnets are typically magnetized in pairs: one magnet has its N pole on the outer arc surface and S pole on the inner arc surface, while the other magnet is the opposite. This design ensures uniform distribution of the motor’s magnetic field and achieves higher operational efficiency through polar symmetry.
Magnetization Methods for Arc Magnets in Motors
| Open-Circuit Magnetization: The magnets are magnetized individually before assembly. This method does not create a closed magnetic loop, making saturation difficult and influencing the magnetic flux density of the magnets.
| Closed-Circuit Magnetization After Assembly: After gluing the magnets into the casing, they are magnetized in a closed circuit. This increases the density of the magnets, allowing for adjustment of the magnetic density waveform through the shape of the magnetization head, although it complicates assembly.
Complete Assembly Then Magnetization: The finished product is assembled first and then magnetized, resulting in a magnetic flux density that falls between the previous two methods. Among these, the first method is the most convenient and efficient for production, but the residual magnetic field will be about 10% lower than the second and third methods. The second method is the most reasonable, allowing for external or internal magnetization, and should involve prior gluing and drying for convenience. The third method is suitable for small motors.
Polarity Detection of Arc Magnets in Motors
There are two practical methods:
| Gauss Meter Detection: If a company has a gauss meter, the detection process is straightforward. Bringing the magnet close to the gauss meter probe displays the polarity (N or S) directly, which is both quick and highly accurate.
| Magnetic Comparison: In the absence of specialized equipment, known-polarity magnets can be used for comparison tests. Based on the principle that like poles repel and opposites attract, observing the interaction between magnets can easily indicate the polarity of an unknown magnet.
Impact of Arc Magnets in Motors
| High remanence (Br) produces greater torque and power output, leading to higher efficiency because, with the same air gap surface area, higher Br can generate substantial torque.
| High Hcb: High coercivity (Hcb) ensures the motor can meet its required electromotive force, aligning the motor’s operating point with maximum energy product to fully exploit the capabilities of the magnets.
| High Hcj: Ensures resistance to demagnetization under overload and aging, as well as strong low-temperature resistance.
| High (BH)max: A higher value indicates better operational coefficients for permanent magnets in the motor, improving efficiency.
| Better Rectangularity in Demagnetization Curves: Results in lower dynamic losses in the motor.
Arc Magnets Manufacturer
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Image Source: Idealmagnetsolutions & Jdamagnet & Kjmagnetics & Nature & Pmtndt & Magkraftndt
