Ferrite magnet

Rare Earth Magnets VS Ferrite Magnets

Magnets can produce magnetic fields that enable them to attract certain metals from afar without touching them. Some magnets are produced naturally and some are man-made. Although there are many different types of magnets, the two most popular artificial magnets are ferrite magnets and rare earth neodymium magnets.

Rare earth magnets and ferrite magnets are all types of permanent magnets. They are made up of a material that, once charged, will remain magnetic for many years unless damaged. However, not all permanent magnets are the same. Rare earth and ferrite magnets have different strength and resilience because they are made of different metal alloys.

For many years, all magnets have been natural magnets, such as lodestone, which is a kind of iron ore with magnetic properties. In 1952, magnets were first made of ferrite. By making magnets from ferrites, engineers can make magnets in any shape they want. By making the carefully manufactured mixture into ferrite magnets, a stronger magnetic field can be produced than in nature. Ferrite magnets are cheaper, stronger and soon become popular. Ferrite magnets are also called hard ferrite magnets or ferromagnets. They are made of strontium or barium ferrite.

Rare Earth magnet

There are two types of rare earth magnets: SmCo and NdFeB. SmCo and NdFeB magnets are called “rare earth” because they are made up of rare earth elements in the periodic table of elements. SmCo magnets were developed in the 1970s and were the first rare earth magnets produced. Nd-Fe-B magnets were listed in 1984.

Relative intensity

The magnetic field intensity produced by the magnet is quantified by BHmax or maximum energy product, and the BHmax or maximum energy product is measured by MGOe. The higher the BHmax is, the greater the force of the magnet is. BHmax of ferrite magnet is 3.5, BHmax of SmCo is 26, NdFeB is the most powerful rare earth magnet, its BHmax is 40.

Relative Resistance of Thermal Stress

Magnets begin to lose strength when heated to a certain temperature (Tmax), so they should not operate outside that temperature. However, when cooled below Tmax, they will regain power. The Tmax of ferrite magnet is 300℃, that of SmCo magnet is 300℃, and that of NdFeB magnet is 150℃.

Relative durability

Magnets can resist not only thermal stress, but also other stresses. NdFeB magnets are fragile and difficult to process. They are also easy to corrode. SmCo magnets are slightly less brittle and difficult to process, but have high corrosion resistance. SmCo magnets are also the most expensive type of magnet. Ferrite magnets are cheaper than SmCo and NdFeB magnets, and have good demagnetization and corrosion resistance.

Ferrite and neodymium magnet have different advantages. Ferrite magnets are easy to magnetize. They are very corrosion resistant and generally do not require additional coatings for corrosion protection. They can resist the demagnetization of external magnetic fields. They are stronger than natural magnets, although many other types of magnets are stronger than them. They are relatively cheap. Neodymium magnets are the most powerful of all permanent magnets. A neodymium magnet can lift more than any other type of magnet of the same size. They are extremely resistant to demagnetization of external magnetic fields.

Ferrites and neodymium magnets also have different disadvantages. Ferrite magnets are very fragile. They can’t be used in machinery that is under great pressure or bending. If exposed to high temperatures (over 480 degrees Fahrenheit), they will be degaussed. They only have medium intensity magnetic field, which is not suitable for applications requiring strong magnetic field. Neodymium magnets are relatively more expensive than ferrite magnets. They are easy to rust and extra measures must be taken to protect them from corrosion. Neodymium magnets are also very fragile and break under pressure. If exposed to more than 175 to 480 degrees Fahrenheit, they lose their magnetism.

Types of Permanent Magnet Materials

At present, the common permanent magnetic materials are ferrite, NdFeB, samarium cobalt, aluminium nickel cobalt, rubber magnetism and so on.
Each of the above magnets has its own characteristics and different application fields. The following are briefly introduced:
Ferrite magnet
Ferrite is a non-metallic magnetic material, also known as magnetic ceramics. We take apart the traditional radio. The horn magnet inside is ferrite. At present, the magnetic energy product of ferrite is only slightly higher than that of 4MGOe. One of the greatest advantages of this material is its low price. At present, it is still widely used in many fields. Ferrites are ceramics. Therefore, the machinability is similar to that of ceramics. Ferrite magnets are molded and sintered. If processing is needed, only simple grinding is needed. Because it is difficult to machine, most ferrite products are simple in shape and large in size tolerance. The square shape product is good and can be ground. Other dimensional tolerances are given as a percentage of nominal size. Because ferrite is widely used and inexpensive, many manufacturers will have ready-made circular rings of conventional shapes and sizes, such as diamonds and other products to choose from. Because ferrite is made of ceramics, there is basically no corrosion problem. The finished product does not need surface treatment or coating such as electroplating.

Rubber coated magnet
Rubber magnet is one of the series of ferrite magnets. It is made of bonded ferrite magnetic powder and synthetic rubber by extrusion, calendering and injection molding. It can be processed into the strip, roll, sheet, block, ring, and various complex shapes. Its magnetic energy product ranges from 0.60 to 1.50 MGOe in the application fields of rubber magnets: refrigerators, message boards, fasteners that fix objects to metal bodies for advertising, and magnetic discs for toys, teaching instruments, switches, and sensors. Mainly used in micro and special motors, refrigerators, disinfection cabinets, kitchen cabinets, toys, stationery, advertising, and other industries.

Samarium cobalt
Samarium-cobalt magnets consist mainly of samarium and cobalt. Samarium cobalt magnets are also the most expensive of several magnets because of the high price of the two materials themselves. The magnetic energy product of samarium-cobalt magnet can reach 30MGOe or even higher at present. In addition, samarium cobalt magnets have high coercivity and high-temperature resistance. They can be used at 350 degrees Celsius, so they can not be replaced in many applications. Samarium cobalt magnet belongs to powder metallurgy products. Generally, according to the size and shape of the finished product, the manufacturer sinters the block blank and then uses the diamond blade to cut into the finished product size. Because samarium cobalt is conductive, it can be processed by wire cutting. In theory, samarium and cobalt can be cut into shapes that can be cut by wire cutting, without considering magnetization and larger size. Samarium cobalt magnet, corrosion resistance is good, generally, do not need to carry out anti-corrosion plating or coating. In addition, the texture of samarium cobalt magnet is very brittle, so it is difficult to process small size or thin-walled products.

NdFeB
The neodymium magnet is a magnet product with wide application and rapid development. Neodymium iron boron has been widely used since its invention, and it has not been more than 20 years. Because of its high magnetic properties and processability, the price is not very high, so the application field expands rapidly. At present, the magnetic energy product of commercialized NdFeB can reach 50MGOe, which is 10 times that of ferrite. NdFeB is also a powder metallurgical product, and its processing method is similar to that of SmCo. At present, the highest working temperature of NdFeB is about 180 degrees Celsius. If it is used in harsh environments, it is generally recommended not to exceed 140 degrees Celsius. NdFeB is very susceptible to corrosion. Therefore, most of the finished products need to be electroplated or coated. Conventional surface treatments include nickel plating, zinc plating, aluminum plating, electrophoresis, etc. If working in a closed environment, phosphating can also be used. Because of the high magnetic properties of NdFeB, NdFeB has been used to replace other magnetic materials on many occasions to reduce the volume of products. If we use ferrite magnets, the size of mobile phones today will not be less than half a brick.
Samarium cobalt magnet and neodymium iron boron magnet have better processing performance. Therefore, the dimension tolerance of the product is much better than that of ferrite. General products, size tolerance can be achieved (+/-) 0.05 mm.

AlNiCo
Aluminum-nickel-cobalt magnet has two processes: casting and sintering. AlNiCo magnets have a magnetic energy product of up to 9MGOe, which has the greatest characteristic of high-temperature resistance and working temperature of 550 degrees Celsius. However, Al-Ni-Co is very easy to demagnetize in reverse magnetic field. If you push two poles of Al, Ni, and Co together, the magnetic field of one of the magnets will be withdrawn or reversed. Therefore, it is not suitable to work in the reverse magnetic field (such as magnet rotor). Aluminum, nickel, and cobalt have high hardness. Although they can be ground and cut by wire, they are expensive. Generally supplied products, there are two kinds of ground or non-grinded. Aluminum, nickel, and cobalt are widely used in the sensor field.

What are the Types of Magnets?

There are many kinds of magnets, generally divided into permanent magnets and soft magnets.

Permanent magnet is divided into two categories:

The first category is: metal alloy magnets include NdFeB, SmCo and AlNiCo magnets.

The second category is ferrite permanent magnet.

1. Neodymium-iron-boron magnet: It is the most commercially available magnet, known as the magnet king, with extremely high magnetic properties, its maximum magnetic energy product is more than 10 times higher than that of ferrite. Its mechanical properties are quite good. The working temperature can reach up to 200 degrees Celsius. Moreover, its texture is hard, its performance is stable, and its cost performance is very good, so its application is extremely extensive. But because of its strong chemical activity, the surface layer must be treated.

2. Ferrite magnet: its main raw materials include BaFe12O19 and SrFe12O19. It is a brittle material with hard texture. Ferrite magnet has been widely used because of its good temperature resistance, low price and moderate performance.

3. Aluminum nickel cobalt magnet: an alloy consisting of aluminum, nickel, cobalt, iron and other trace metals. The casting process can be made into different sizes and shapes, with good workability. The cast aluminum nickel cobalt permanent magnet has the lowest reversible temperature coefficient, and the working temperature can reach up to 600 degrees Celsius. Al Ni Co permanent magnet products are widely used in various instruments and other applications.

4. Samarium cobalt (SmCo) is divided into SmCo5 and Sm2Co17 according to their components. Because of the high price of materials, their development is limited. SmCo, as a rare earth permanent magnet, not only has a high magnetic energy product, reliable coercivity, and good temperature characteristics. Compared with NdFeB magnets, samarium cobalt magnet is more suitable for working in a high-temperature environment.