Magnetic materials are closely related to our lives, from the most common refrigerator refrigeration to high-end magnetic levitation, they are inseparable. So, let's take a look at this magical material now!
Why are magnets magnetic?
Most matter is composed of molecules. Molecules are composed of atoms, and atoms are composed of nuclei and electrons. Inside the atom, the electron keeps spinning and revolving around the nucleus. Both of these movements of the electron will produce magnetism. But in most materials, the directions of electron movement are different and chaotic, and the magnetic effects cancel each other out. Therefore, most substances do not exhibit magnetism under normal conditions.
Ferromagnetic substances such as iron, cobalt, nickel, or ferrite are different. The electron spins in it can spontaneously arrange in a small range to form a spontaneous magnetization zone. This spontaneous magnetization zone is called a magnetic domain. After the ferromagnetic substance is magnetized, the internal magnetic domains are arranged neatly and in the same direction to strengthen the magnetism and form a magnet. The magnetization process of the magnet is the magnetization process of the iron block. The magnetized iron block and the magnet with different polarities generate attractive force, and the iron block is firmly "sticked" with the magnet.
2. How to define the performance of the magnet?
There are mainly the following 3 performance parameters to determine the performance of the magnet:
Remanence Br: After the permanent magnet is magnetized to technical saturation and the external magnetic field is removed, the retained Br is called the residual magnetic induction.
Coercive force Hc: To reduce the B of a permanent magnet magnetized to technical saturation to zero, the required reverse magnetic field strength is called magnetic coercive force, or coercive force for short.
Magnetic energy product BH: represents the magnetic energy density established by the magnet in the air gap space (the space between the two magnetic poles of the magnet), that is, the magnetostatic energy per unit volume of the air gap.
3. How to divide metallic magnetic materials?
Metal magnetic materials are divided into permanent magnetic materials and soft magnetic materials. Generally, materials with intrinsic coercivity greater than 0.8kA/m are called permanent magnetic materials, and materials with intrinsic coercivity less than 0.8kA/m are called soft magnetic materials.
4. Comparison of the magnetic force of several types of commonly used magnets
The magnetic force is arranged from large to small: neodymium iron boron magnet, samarium cobalt magnet, alnico magnet, ferrite magnet.
5. What are the price comparisons of different magnetic materials?
Ferrite: low and medium performance, lowest price, good temperature characteristics, corrosion resistance, good performance-to-price ratio
NdFeB: The highest performance, the price is good, the strength is good, and it is not resistant to high temperature and corrosion
Samarium cobalt: high performance, highest price, brittle, excellent temperature characteristics, corrosion resistance
AlNiCo: low and medium performance, medium price, excellent temperature characteristics, corrosion resistance, poor interference resistance
Samarium cobalt, ferrite, neodymium iron boron can be manufactured by sintering and bonding methods. The sintered magnetic properties are high and the molding is poor. The bonded magnets have good moldability and much lower performance. AlNiCo can be manufactured by casting and sintering methods. Cast magnets have higher performance and poor formability, while sintered magnets have lower formability and better formability.
6. The characteristics of neodymium iron boron magnets
The NdFeB permanent magnet material is a permanent magnet material based on the intermetallic compound Nd2Fe14B. NdFeB has extremely high magnetic energy product and coercive force. At the same time, the advantages of high energy density make NdFeB permanent magnet materials widely used in modern industry and electronic technology, thereby making instrumentation, electroacoustic motors, and magnetic separation magnetization The miniaturization, weight reduction, and thinning of equipment are possible.
Material characteristics: NdFeB has the advantages of high cost performance and good mechanical properties; the disadvantage is that the Curie temperature is low, the temperature characteristics are poor, and it is easy to pulverize and corrode. It must be adjusted by its chemical composition and surface treatment methods. It can be improved to meet the requirements of practical applications.
Manufacturing process: NdFeB is manufactured using powder metallurgy technology.
7. What is a single-sided magnet? Magnets have two poles, but in certain working positions, single-pole magnets are needed. Therefore, one side of the magnet needs to be covered with iron sheets, so that the side covered by the iron sheets is magnetically shielded, and the iron sheet is refracted to the other side. Magnets increase the magnetic force of the magnet on the other side. Such magnets are collectively called single-sided magnets or single-sided magnets. There is no real single-sided magnet. The materials used for single-sided magnets are generally arc-shaped iron sheets and powerful neodymium iron boron magnets. The shape of the powerful neodymium iron boron magnets used for single-sided magnets is generally a disc shape.
8. What is the purpose of single-sided magnets?
(1) It is widely used in the printed matter industry. There are single-sided magnets in gift packaging boxes, mobile phone packaging boxes, tobacco and alcohol packaging boxes, mobile phone packaging boxes, MP3 packaging boxes, moon cake packaging boxes and other products.
(2) It is widely used in the leather goods industry. There are single-sided magnets in leather goods such as suitcases, briefcases, travel bags, mobile phone cases, wallets and so on.
(3) It is widely used in the stationery industry. Notebooks, whiteboard buttons, folders, magnetic nameplates, etc. all have single-sided magnets.
9. What are the precautions during the transportation of magnets? Pay attention to the indoor humidity, which must be maintained at a dry level. The temperature should not exceed room temperature; when storing products in black or rough state, oil can be applied appropriately (normal engine oil is sufficient); electroplated products should be stored in a vacuum sealed or isolated from air to ensure the corrosion resistance of the coating; magnetized products should be attracted Store them together and in a box to avoid picking up other metal objects; storage of magnetized products should be away from magnetic disks, magnetic cards, magnetic tapes, computer monitors, watches and other objects that are sensitive to magnetic fields. Magnets should be shielded when transported in a magnetized state, especially air transportation must be completely shielded.
10. How to achieve magnetic isolation? Only the material that can be adsorbed to the magnet can cut off the magnetic field, and the thicker the material, the better the magnetic shielding effect.
11. Which ferrite material can conduct electricity? Ferrite, a soft magnetic material, is a magnetic material with high magnetic permeability and high resistivity. It is generally used at high frequencies and is mainly used for electronic communications. There are applications in the computers and TV sets that we come into contact with every day. Soft ferrites mainly include manganese-zinc and nickel-zinc, etc. The permeability of manganese-zinc ferrite is greater than that of nickel-zinc ferrite.
12. What is the Curie temperature of permanent ferrite? It is reported that the Curie temperature of ferrite is about 450°C, usually greater than or equal to 450°C. The hardness is around 480-580. The Curie temperature of neodymium iron boron magnets is basically between 350-370℃. However, the use temperature of NdFeB magnets cannot reach the Curie temperature. The magnetic properties of NdFeB magnets at temperatures exceeding 180-200°C have been attenuated a lot, the magnetic loss is also very large, and they have lost their use value.
