At present, commonly used permanent magnets are ferrite magnets, neodymium magnets, SmCo magnets, AlNiCo magnets, rubber magnets, and so on. Each type of the above magnets has its properties, and their pros & cons are also different. So in this article, let's take a deeper look at the permanent magnet types, pros & cons.
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Permanent Magnets Types, Pros & Cons
Ferrite magnets are a non-metallic magnetic material, also known as magnetic ceramics. They have a wide range of applications. Ferrite magnets do not have high magnetic properties. Typically, the magnetic energy product (one of the parameters to measure the performance of magnets) can only be slightly higher than 4MGOe.
The biggest advantage of this kind of magnet is its low price. At present, they are still widely used in many fields. For example, the horn magnet in the traditional radio is made of ferrite magnets. Besides, since ferrite magnets are made of ceramic material, there are few corrosion problems. The finished products do not need surface treatment such as electroplating or coating.
Ferrite magnets are generally formed by molds and then sintered. Therefore, it is difficult to machine ferrite magnets. So most ferrite products have simple shapes and large dimensional tolerances.
Rubber magnet is one of the series of ferrite magnetic materials. It is a flexible, elastic, and twistable magnet made by bonding ferrite magnetic powder and synthetic rubber and extruding, calendering, injection molding, and other processes. Generally, its magnetic energy product is 0.60&#;1.50 MGOe. Rubber magnets can be processed into strips, rolls, sheets, blocks, rings, and other various complex shapes.
Rubber magnets are mainly used in refrigerators, teaching instruments, switches, sensor magnets, micro motors, disinfection cabinets, kitchen cabinets, toys, stationery, advertising, and other industries.
The main components of SmCo magnets are samarium and cobalt. Since the above two materials are expensive, SmCo magnets are one of the most expensive magnets available on the market today.
The magnetic energy product of SmCo magnets can reach 30MGOe, or even higher. In addition, the SmCo magnet has a high coercive force and high-temperature resistance and can be applied to a high temperature of 350 degrees Celsius, so it cannot be replaced in many applications. Besides, since SmCo magnets have electrical conductivity, they can be processed by wire cutting. Moreover, SmCo magnets have good corrosion resistance and generally do not require anti-corrosion plating or painting.
The SmCo magnet is very brittle, so it is difficult to process small-sized or thin-walled products.
Due to their excellent magnetic properties and ease of processing, relatively low price, neodymium magnets, or NdFeB magnets are currently widely used and rapidly-developing magnet products.
The magnetic energy product of NdFeB magnets can reach 50MGOe, which is 10 times that of ferrite magnets. Due to the excellent magnetic properties of neodymium magnets, on many occasions, they are used to replace other magnetic materials to reduce product volume. In addition, just like SmCo magnets, NdFeB magnets also have good processing performance. Therefore, the dimensional tolerance of NdFeB products is much better than that of the ferrite products. Generally, the dimensional tolerance of general NdFeB products can be (+/-) 0.05mm.
The maximum operating temperature of NdFeB magnets is around 180 degrees Celsius. If in a harsh environment, it is generally recommended that the maximum operating temperature of NdFeB magnets does not exceed 140 degrees Celsius. In addition, neodymium magnets are easily corroded. Therefore, most NdFeB products need to be plated or painted. Commonly used surface treatments include nickel plating (nickel-copper nickel), zinc plating, aluminum plating, electrophoresis, etc. If they work in a closed environment, phosphating can also be used.
AlNiCo magnet is an alloy composed of metals aluminum, nickel, cobalt, iron, and other trace metal elements, and its magnetic energy product can reach 9MGOe. AlNiCo magnets are widely used in the field of sensors.
The biggest pro of AlNiCo magnets is their high-temperature resistance, and their working temperature can reach 550 degrees Celsius.
AlNiCo magnets are very easy to demagnetize under the reverse magnetic field. If you force the same pole direction (two N or two S) of two Alnico magnets together, the magnetic field of one of the magnets will be reversed or reversed. Therefore, they are not suitable to work under the reverse magnetic field (such as a motor).
Thank you for reading our article and we hope it can help you to have a better understanding of the permanent magnet types, pros & cons. If you want to know more about permanent magnets, we would like to recommend you visit Stanford Magnets for more information. Stanford Magnets is a leading magnet supplier across the world, that has been involved in R&D, manufacturing, and sales of strong magnets and ferrite magnets since the s. It provides customers with high-quality rare earth permanent magnetic products such as neodymium magnets, SmCo magnets, AlNiCo magnets, and other non-rare earth permanent magnets at a very competitive price.
A rotating electric machine is an energy converter; we call it a motor when electrical energy is converted to mechanical energy, and an alternator when the conversion is reversed. In either case, the electric machine may be the same device even though its function is reversed.
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Some attractive benefits that high-speed alternators or motors can offer include:
There are different machine topologies for high-speed applications, and each has its own benefits and drawbacks. The permanent magnet machine type is considered the most superior in terms of performance due to its unique characteristics, including robust construction that is well suited for high-speed operation, and zero excitation power requirements that result in unity power factor operation.
When efficiency and weight are primary concerns, a machine with a permanent magnet rotor is clearly superior in most applications. This is because of the following:
Other considerations that are also taken into account when selecting this type of permanent magnet machine for high-speed applications include:
The motors require a synchronous start-up procedure; induction starting can overheat and demagnetize the rotor.
Induction machines are the workhorse of industry. They are used everywhere and have many good features. The simple, low cost squirrel cage rotor structure is particularly appealing. Excitation is provided by the stator current, which induces and reacts with current in conductive rotor bars. This type of machine has the following characteristics:
Synchronous reluctance machines have a very stiff, high strength rotor that can operate at surface speeds up to 1,100 feet/second. The rotor can also operate at fairly high temperatures without detriment &#; possibly 600-700 &#;F. The rotor is constructed of layers of ferromagnetic steel separated by equal layers of non-magnetic material to form salient poles of low reluctance in the direct axis, but high reluctance in the cross axis. Both materials are brazed together and have very high strength. The rotor is a smooth bimetallic cylinder. This type of machine has the following characteristics:
Excitation can be varied to reduce losses at partial load; even turned off. The machine cannot produce a sustained short circuit current. Alternators may not self-excite with load circuit connected.
Due to their high-efficiency, compact size, and robustness, PM machines are used in electric vehicles, renewable energy systems, aerospace, industrial automation, and any other application that requires high-speed and efficient energy conversion.
PM machines operate reliably without lubricants in diverse environments. They feature superior efficiency, low maintenance, and quiet operation in a compact, lightweight package, making them ideal for many high-speed applications.
They require zero excitation power, allowing unity power factor operation, smooth rotor design, large air gaps, high resistivity, and low rotor permeability. These factors enable PM machines to minimize losses while supporting efficient cooling.
Key factors include the cost of magnet material, magnet temperature limits, the need for synchronous start-up procedures, and ensuring that the rotor is designed for optimal stability and durability.
While PM Machines offer many advantages, their magnets have temperature limitations. The safe operating temperature depends on the magnet material, but most have a practical temperature limit of approximately 200°C due to the risk of irreversible demagnetization.
While induction machines are pervasive and cost-effective, they typically have lower efficiency
and power factor. Synchronous reluctance machines offer high rotor strength and temperature
resistance but require significant reactive power for excitation, which negatively impacts the machine&#;s efficiency and power factor.
Challenges include the high cost of rare earth magnets used in PM Machines, thermal management, and the need for precise control systems to handle the synchronous operation while protecting against fault conditions seamlessly.
Ongoing R&D primarily focuses on developing new magnet materials with higher temperature tolerance, improving cooling techniques, and advancing control strategies. These improvements will significantly enhance the performance and reliability of PM Machines.
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