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China Magnets Source Material Limited provides tailor-made magnets for many types of motors, generators, and actuators.
Magnetic materials play important roles in a wide range of devices for industry. By far the most important of the many industrial uses of magnet is motor.
The magnets create motion for motor. And the permanent magnet motor has the advantages of high efficiency, large torque, and constant speed with load. Compared with synchronous motors, it can draw less amount of current.
When designing a motor, the choice of magnet has a significant impact on the overall performance of the motor and the cost of the project. So you need to know how to choose the right magnets for motor.
Broadly speaking, there are four main types of commercial magnets currently: Neodymium (NdFeB), Samarium Cobalt (SmCo), AlNiCo and ferrite (also called ceramic). Among them, ferrite, rare earth samarium cobalt and neodymium magnet can be used in permanent magnet motor and vehicle magnet applications.
As rare earth magnets have stronger magnetic force than ferrite permanent magnets, they can be used to make smaller and lighter motors. However, rare earth magnets are also more expensive than the ferrite magnet option.
Keyword: strongest magnet available commercially
NdFeb magnets are the one most commonly used in traction motors for hybrids and EVs. The high energy NdFeB magnets make motor as small, light, compact and efficient as possible.
Working Temperature Effects
NdFeB magnets has poor temperature resistance over other permanent magnets. As neodymium magnet has a negative coefficient, their coercivity along with the magnetic energy density (BHmax) decreases with temperature. Their max. use temp. Ranges from 60℃ to 220℃, Curie temperatures range from 310–370°C.
However they can be added Dysprosium (Dy) or terbium (Tb) to curb the fall in performance from temperature changes. But this makes the magnet even more expensive.
The traction motors for hybrid and electric automobiles, railroad vehicles and the motors for industrial equipment operate at relatively high temperatures. Therefore, heat-resistant neodymium magnets are generally used in these applications.
Corrosion Problems
Neodymium magnets have poor resistance to corrosion if no coating protection. Meanwhile, they can also corrode from the inside out if proper pre-treatment processes are not followed. Often, a multi-layer Nickel-Copper-Nickel plating is applied. But for motor applications, epoxy and Zn coatings are used more. What’s more, another new surface treatment everlube can be utilized in high requirement of humidity & salt spray resistance environments as well.
Keyword: extremely resistant to demagnetization
Smco magnets are a type of rare earth permanent magnets – brittle, and prone to cracking and chipping. They are available in two “series”, namely SmCo5 magnets and Sm2Co17 magnets.
Good Temperature Stability
Samarium magnets are the second strong magnets. And at typical operating temperatures, the samarium-cobalt magnet has superior magnetic properties to the strongest heat-resistant neodymium magnets currently used in motors. The maximum operating temperatures ranges from 250 and 350℃; Curie temperatures range from 700 to 800 °C.
Strong Resistance To Corrosion & Oxidation Resistance
SmCo magnets offer outstanding corrosion resistance (neodymium magnets do not). Plating or surface coatings are not necessary for most applications, making them advantageous for medical applications as well.
Broad-Based Source Of Supply
Unlike neodymium magnets, which need high levels of rare dysprosium (Dy) to function at moderate temperatures, SmCo magnets use materials that are more widely available and are inherently stable at temperatures well above the Curie point of NdFeB. This makes SmCo pricing more stable and less prone to market changes.
Keyword: cheapest magnet in the world
Ceramic magnets, a type of permanent magnet, have low energy compared to rare earth magnets. In addition to low price, they are also have strong resistance to demagnetization and exceptional corrosion resistance. They are commonly used in most types of DC electric motors.
Operating Temperatures
Ferrite magnets have a maximum operating temperature of approximately 250 degrees Celsius or higher and a Curie temperature of about 450 degrees Celsius.
Good Corrosion
Ceramic magnets offer good corrosion resistance and generally do not require a coating or plating.
When designing PM motor, the shape and size of permanent magnets have also an important effect on performance and commutation of electromotor. It is significant to choose appropriate shape and size of permanent magnets.
For example, most of the rotor modification techniques for cogging reduction are mainly based on magnet shape variation, which is comparatively more practical and cost-effective.
As sintered NdFeB is an anisotropic material. It is very difficult to make them into a complicated magnetization direction.
Arc shape magnets can be formed into radial rings. They are still the most common motor magnet shape, especially for PM DC motor and magnet rotor.
The curved magnets will allow magnets get closer to the stator. So it can decrease air gap and increase the flux between them.
Theoretically, ring shape magnets are the best shape for motor magnets. To be more precise, these rings are radial oriented ring motor magnets. They have many advantages as follows:
However, restricted by magnet material property and manufacture technology, not all magnets can be made into radial oriented ring. There are two main radial ring magnets. One is bonded magnet, the other one is sintered neodymium magnet.
Molded magnets are designed for different motors, such as pump motor, vacuum cleaner motor, gated motor, stepper motor, brushless motor, DC motor, starter motor and conveyor motor. They are made by hot extrusion and deformation.
Compared with sintered NdFeB, plastic ferrite, smco or plastic ndfeb magnet have advantages in control accuracy and high yield. They are the most flexible permanent magnet and can be made into different complex shapes with various magnetizing ways. But the magnetic field is much lower than sintered ndfeb.
Sintered neodymium magnets can be made into radial oriented ring too. But the cost is very expensive as they need extra magnetizing fixture and magnetization coil. there are many restrictions on the size and grade as well.
Flat (trapezoidal and rectangular) shape is another common choice for motor magnets.
Flat plate-shaped is convenient for motor magnet manufacturers to process.
That means cheaper cost than segment motor magnet.
For high-speed permanent magnet synchronous motors, how to fix motor magnets and prevent them from flying out has always been the focus of engineers.
The important is to design a safe structure to overcome centrifugal force, such as linear, V and SPOKE embedded structures.
But if the rotational speed enter ultra-high-speed field. The embedded structure will encounter a bottleneck. This requires the use of a surface mounted structure.
The general approach is to make a sleeve or frame to put arc magnets in that will keep them in order and don’t jump around. The sleeve here has to be made of something sturdy and nonmagnetic, such as aluminum, copper, Q235 low carbon steel, glass fiber Sheath and carbon fiber sheath. The most promising one is the carbon fiber sheath.
Auxiliary fixation can be applied as well. For example, using metal glue (such as LOCTITE industrial-strength epoxy glue or other motor magnet glue) to bond curved magnets to the outer surface of the rotor.
Our engineers suggest using mechanical fixing as the main method, and adhesive fixing as the auxiliary method. And here is the reason:
Manufacturers need light, extremely strong magnets to power electric-vehicle motors, and they have long relied on the rare-earth metals neodymium and dysprosium to create them.
But those metals are expensive and subject to wild price jumps and shaky supply chains—problems that have become more acute as demand for electric cars grows.
More and more researchers began to find new solution. Currently, there are three main trends:
Dy is a rare earth mineral that is in extremely short supply and increasingly expensive.
“GBD Neo” magnets offer a combination of high energy density and temperature stability at moderate cost by reducing the amount of Dysprosium (Dy) (GBDD) and Terbium (Tb) (GBDT) used.
This process enhances coercivity while limiting the adverse effects on remanence, when compared to traditional neo manufacturing methods.
This process favors smaller magnets with a thickness of less than 6mm or laminated materials. For high frequency applications at working temperatures approaching 180°C, consider using this product.
Urban Mining Company (UMC), USA, has made a new process for reclaiming magnets containing rare earth metals to produce new, higher performance neodymium iron boron (Nd2Fe14B)-type sintered magnets.
The methodology offers a practical way to reuse the minerals that are readily available in domestic e-waste.
UMC’s objective is to use 100% recycled Nd2Fe14B powder for the production of new permanent magnets, providing producers with the benefit of a more economical source of rare earth raw metals. (Anthony Caggiano, Materials World magazine)
As a professional manufacturer of motor magnets, China Magnets Source Material Limited provides magnets fabricated & assembled for motor, rotor, generator & torque coupler applications.
Our industrial magnet materials include high energy rare earth neodymium (NdFeB), samarium cobalt, ferrite permanent magnets. Injection & compression molded magnets & laminated magnets are also available.
We are committed to providing immediate design assistance from prototype to production capabilities.
If you are looking for an exceptional motor magnet manufacturer that will listen to you and deliver what you expect, email us, we are ready to serve you.
When you ask for arc / flat motor magnets price, engineering drawing is important and necessary to provide us to avoid any misunderstanding on the magnet or magnetic assembly dimensions. For assistance from a technical representative, click here for the contact info.
China Magnets Source Material Limited
