Magnets refer to objects or materials that can generate magnetic fields. They are usually made of metal alloys and have strong magnetism. Traditionally it can be divided into "permanent magnets" and "non-permanent magnets".
Permanent magnets can be natural products, also known as natural magnets, or artificial (the strongest magnet is neodymium magnet).
Non-permanent magnets sometimes lose magnetism.
The ancient Greeks and China discovered that there was a naturally magnetized stone in nature, called a "magnet". This kind of stone can magically pick up a small piece of iron and swing it at will and always point in the same direction. Early navigators used this magnet as their earliest finger.
The south needle knows the direction at sea.
After thousands of years of development, magnets have become a powerful material in our life today. By synthesizing alloys of different materials, we can achieve the same effect as magnets and improve the magnetic force. In the18th century, artificial magnets appeared, but those who made stronger magnetic materials.
This process was very slow, and Al-Ni-Co alloy was not produced until the 1920s. Subsequently, ferrite was manufactured in 1950s and [rare earth magnets [including NdFeB and SmCo]] was manufactured in 1970s. At this moment,
With the rapid development of magnetic technology, ferromagnetic materials also make components more miniaturized.
Most magnetic materials can be magnetized to saturation in the same direction, which is called "magnetization direction" (orientation direction). Non-oriented magnets (also called isotropic magnets) are much weaker than oriented magnets (also called anisotropic magnets).
What is the standard industrial definition of "North and South Pole"?
The definition of "North Pole" is that after a magnet rotates at will, its North Pole points to the North Pole of the Earth. Similarly, the south pole of the magnet also points to the south pole of the earth.
How can you tell the north pole of a magnet without labeling it?
Obviously, eyes alone can't tell the difference. You can use a compass to get close to the magnet, and the pointer pointing to the north pole of the earth will point to the south pole of the magnet.
How to handle and store magnets safely?
Be very careful, because magnets attract each other and may pinch your fingers. When magnets attract each other, they may also be damaged by collision (knocking off corners or cracking).
Keep the magnet away from easily magnetized objects, such as floppy disks, credit cards, computer monitors, watches, mobile phones, medical devices, etc.
Magnets should be kept away from pacemakers.
For larger magnets, plastic or cardboard washers should be added between each magnet to ensure that the magnets can be easily separated.
Magnets should be stored in a dry and constant temperature environment as much as possible.
How to achieve magnetic isolation?
Only the material that can be adsorbed on the magnet can isolate the magnetic field, and the thicker the material, the better the magnetic isolation effect.
What is the strongest magnet?
At present, the magnet with the highest performance is rare earth magnet, and NdFeB is the magnet with the strongest performance among rare earth magnets. But in the environment above 200 degrees Celsius, samarium and cobalt are the strongest magnets.
Magnets, which should be called magnetic steel, are mainly divided into two categories, one is soft magnetic and the other is hard magnetic;
Soft magnetic includes silicon steel sheet and soft magnetic core; Hard magnets include Al-Ni-Co, Sm-Co, ferrite and NdFeB, among which Sm-Co magnetic steel is the most expensive, ferrite magnetic steel is the cheapest, and NdFeB magnetic steel has the highest performance, but Al-Ni has the most stable performance and the best temperature coefficient.
Cobalt magnetic steel, users can choose different hard magnetic products according to different needs.
How to define the performance of a magnet?
There are mainly the following three performance parameters to determine the performance of the magnet:
Remanence Br: The permanent magnet is magnetized to technical saturation, and the retained Br is called remanence induction intensity after the external magnetic field is removed.
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 induction coercive force, which is very simple.
Called coercivity
Magnetic energy product BH: indicates the magnetic energy density established by the magnet in the air gap space (the space between the two poles of the magnet), that is, the static magnetic energy per unit volume of the air gap. Because this energy is equal to the product of Bm and Hm of the magnet, it is called magnetic energy product.
Magnetic field: the space that produces magnetic effect on the magnetic pole is the magnetic field.
Surface magnetic field: the magnetic induction intensity at a specific position on the surface of a permanent magnet.
How to choose a magnet?
What role should the magnet play before deciding which kind of magnet to choose?
Main functions: moving objects, fixing objects or lifting objects.
Required magnet shape: disc, ring, square, tile or special shape.
Required magnet dimensions: length, width, height, diameter and tolerance, etc.
Attraction of required magnets, expected price and quantity, etc.
The compass was invented according to the characteristics of magnets.
1 refers to the north and south.
Attract light and small objects.
Electromagnets can be used as electromagnetic relays.
4. Engine
5 generator
In the pre-Qin period, our ancestors had accumulated a lot of knowledge in this field. When exploring iron ore, they often encountered magnetite, that is, magnetite (mainly composed of ferroferric oxide). These findings have long been recorded. These findings were first recorded in several articles in Pipe: "
There is a magnet on the mountain with gold and copper under it. "
There are similar records in other ancient books, such as Shan Hai Jing. The iron-absorbing characteristics of magnets have long been discovered. The main chapter of the nine volumes of Lu's Spring and Autumn Annals is: "Kindly absorb iron, or absorb it." At that time, people called "magnetism" "kindness". They think that magnets are the loving mothers of their children.
Attraction. And think: "Stone is the mother of iron, but there are two kinds of stones: kind and unkind. Kindness can attract his children, but not kindness. " Before the Han Dynasty, people wrote magnets as "Guanyin Stone", which means love stone.
Since magnets can attract iron, can they attract other metals? Our ancestors made many attempts and found that magnets can not only attract metals such as gold, silver and copper, but also attract bricks and tiles. It was not until the Western Han Dynasty that people realized that magnets could only attract people.
Iron, and can't attract other items. When two magnets are put together and close to each other, sometimes they attract each other and sometimes they repel each other. Now people all know that magnets have two poles, one is called N pole and the other is called S pole. Like-sex repulsion, opposites attract.
People didn't know this truth at that time, but they could still perceive this phenomenon.
In the Western Han Dynasty, there was an alchemist named Luan Da. He used this characteristic of magnet to make something similar to two chess pieces. By adjusting the mutual position of the polarities of two chess pieces, sometimes the two chess pieces attract each other and sometimes repel each other. Luan Da called it "playing chess". He put this new one
Strange things are dedicated to Emperor Wu of the Han Dynasty and demonstrated live. Emperor Wu of the Han Dynasty was pleasantly surprised. He was named "General Five Blessingg". Luan made great use of the properties of magnets to make novel things to deceive Emperor Wu of Han Dynasty.
The earth is also a big magnet, and its poles are close to the geographical south pole and the geographical north pole respectively. So the magnets on the earth's surface can rotate freely.
When moving, magnets will repel each other because of the same sex, and the nature of opposites attracting will indicate the north and south. The ancients did not understand this truth, but they knew this phenomenon very well.
"Application in traditional industries":
When talking about magnetic sources, electromagnetic induction and magnetic "devices" of magnetic materials, we have mentioned some practical applications of magnetic materials. In fact, magnetic materials have been widely used in all aspects of traditional industry.
For example, electrification is impossible without magnetic materials, because power generation requires generators, power transmission requires transformers, motors require motors, and telephones, radios and televisions require speakers. Magnetic steel coils are used in many instruments.
Structure. These have been mentioned in other contents.
"Application of magnetism in biology and medicine";
Pigeon lovers know that if pigeons are released hundreds of kilometers away, they will automatically return to their nests. Why do pigeons have such a good housekeeping skill? It turns out that pigeons are very sensitive to the earth's magnetic field, and they can use the changes of the earth's magnetic field to find their own home. if
Tie a magnet to the pigeon's head and it will get lost. If pigeons fly over the radio tower, strong electromagnetic interference will also disorientate them.
In medicine, we can diagnose abnormal tissues of human body and judge diseases by using the familiar nuclear magnetic resonance imaging technology. Its basic principle is as follows: the nucleus is positively charged and spins. Usually, the arrangement of nuclear spin axes is
Irregular, but placed in an external magnetic field, the spatial orientation of nuclear spin changes from disorder to order. The magnetization vector of the spin system increases gradually from zero, and when the system reaches equilibrium, the magnetization reaches a stable value. If the nuclear spin system is influenced by external factors, such as
Radio frequency with constant frequency excites nucleus, which can cause vibration effect. After the radio frequency pulse stops, the nucleus strengthened by the spin system can't maintain this state, and will return to the original arrangement state in the magnetic field, and at the same time release weak energy into radio signals, which makes this possible.
Multi-signal detection and time-space resolution can get the distribution image of moving nuclei. The characteristic of NMR vibration is that the flowing liquid does not produce signal, which is called flow effect or flow blank effect. So blood vessels are gray-white tubular structures, while blood is black and has no signal.
This makes it easy for blood vessels to separate soft tissues. Normal spinal cord is surrounded by cerebrospinal fluid, which is black and has white dura mater set off by fat, which makes the spinal cord show white strong signal structure. Nuclear magnetic resonance (NMR) vibration has been applied to imaging diagnosis of various systems in the whole body. Most effective
The best are the skull and brain, as well as its spinal cord, heart blood vessels, joint bones, soft tissues and pelvic cavity. For cardiovascular diseases, we can not only observe the anatomical changes of heart cavity, great vessels and valves, but also make ventricular analysis, qualitative and semi-quantitative diagnosis and make multiple sections.
Figure, with high spatial resolution, shows the whole picture of the heart and lesions and their relationship with surrounding structures, which is superior to other X-ray imaging, two-dimensional ultrasound, nuclide and CT examination.
Magnetism can not only diagnose, but also help treat diseases. Magnets were used blindly in ancient medicine in China. Now people use the magnetic differences of different components in blood to separate red blood cells from white blood cells. In addition, the interaction between magnetic field and human meridians can realize magnetic therapy.
It has a unique function in treating many diseases and has been applied to magnetic therapy pillows, magnetic therapy belts and so on. The iron remover made of magnet can remove iron powder that may exist in flour, magnetized water can prevent boiler from scaling, and magnetized seeds can improve crop yield to some extent.
"The application of magnetism in astronomy, geology, archaeology and mining";
We already know that the earth is a huge magnet, so where does its magnetism come from? Has it existed since ancient times? What does it have to do with geological conditions? What is the magnetic field in the universe?
At least in the pictures, we have all seen the splendid Northern Lights. China has recorded the Northern Lights since ancient times. The northern lights are actually the result of the interaction between particles in the solar wind and the geomagnetic field. The solar wind is a stream of high-energy charged particles emitted by the sun. When they reach the earth,
The interaction with the geomagnetic field, like a wire with a current, is forced in the magnetic field, which makes these particles move and gather to the north and south poles and collide with the thin gas in the high altitude of the earth. As a result, gas molecules are excited and emit light.
Sunspots are areas where solar magnetic field activity is very strong. The eruption of sunspots will have an impact on our lives, such as temporarily interrupting radio communication. Therefore, the study of sunspots is of great significance to us.
Geomagnetic changes can be used to explore mineral deposits. Because all substances have strong or weak magnetism, if they gather together to form sediments, it will inevitably interfere with the geomagnetic field in the nearby area and make the geomagnetic field abnormal. According to this, it can be on land.
By measuring the magnetism of the earth, ocean or air, we can obtain the geomagnetic map, and analyze and further explore the abnormal areas of the magnetic field on the geomagnetic map, so we can often find unknown mineral deposits or special geological structures.
Rocks of different geological ages often have different magnetic properties. Therefore, we can judge the geological age change and crustal change according to the magnetism of rocks.
Many mineral resources are * * *, which means that several minerals are mixed together and have different magnetic properties. Taking advantage of this feature, people have developed a magnetic separator, which uses magnets to attract these objects by taking advantage of the different magnetism of minerals with different components and the difference of magnetic strength.
Quality, then their attraction is different, and as a result, mixed minerals with different magnetism can be separated to realize magnetic beneficiation.
"The application of magnetism in the military field";
Magnetic materials are also widely used in the military field. For example, ordinary mines or mines can only explode when they hit the target, so their functions are limited. And if magnetic sensors are installed on mines or mines, because tanks or warships are made of steel, in them,
When approaching (without touching the target), the sensor can detect the change of magnetic field, which makes the mine or mine explode and improves the lethality.
In modern warfare, air superiority is one of the keys to winning the battle. However, the aircraft is easily found by enemy radar during flight, which is very dangerous. In order to avoid being monitored by enemy radar, the plane surface can be coated with a special magnetic material-
Absorbing materials can absorb the electromagnetic waves emitted by radar, so that the radar electromagnetic waves are rarely reflected, so the enemy radar cannot detect the radar echo, find the aircraft, and make the aircraft achieve the purpose of stealth. This is the famous "stealth plane". hide
Human body technology is a hot spot in the field of military scientific research in the world. The American F 1 17 stealth fighter is an example of the successful application of stealth technology.
In the "Star Wars" plan of the United States, there is a new weapon "electromagnetic weapons". Traditional artillery uses the thrust generated by the instantaneous expansion of ammunition when it explodes to accelerate the projectile quickly and push it out of the bore. The electromagnetic gun put that shell into the solenoid,
When the solenoid is energized, the magnetic field generated by the solenoid will generate a huge impetus to the shell and shoot it. This is the so-called electromagnetic gun. Similar to electromagnetic missiles.
Edit this paragraph | There are many kinds of knowledge magnets. Generally divided into two categories: permanent magnet and soft magnet. When we say magnets, we usually mean permanent magnets.
Permanent magnets are divided into two categories:
Category I: Metal alloy magnets include neodymium magnets (Nd2Fe 14B), samarium cobalt magnets (SmCo) and aluminum nickel cobalt magnets (ALNiCO).
Category II: Ferrite.
1, neodymium magnet: it is the magnet with the highest commercial performance found at present, and it is called the magnetic king. It has extremely high magnetism and its magnetism reaches the maximum.
The energy product (BHmax) is 10 times higher than that of ferrite. Its machinability is also quite good. Working temperature can be as high as
Up to 200 degrees Celsius. But also because of its hard texture, stable performance, good cost performance and wide application. But because of its chemical activity
It is very strong, so its surface must be treated. (such as zinc plating, nickel plating, electrophoresis, passivation, etc. ).
2. Ferrite magnet: Its main raw materials include BaFe 12O 19 and SrFe 12O 19. Made of ceramic technology, hard texture, belonging to
Brittle materials have become the most widely used permanent magnets because of their good temperature resistance, low price and moderate performance.
3. Al-Ni-Co magnet: It is an alloy composed of trace metal elements such as aluminum, nickel, cobalt and iron. The casting process can be processed into
Different sizes and shapes, good machinability. The reversible temperature coefficient of cast Al-Ni-Co permanent magnet is the lowest, and the working temperature can reach 600℃.
Above degrees. Al-Ni-Co permanent magnet products are widely used in various instruments and other application fields.
4.SmCo can be divided into SmCo5 and Sm2Co 17 according to different components. Its development is limited by the high price of its materials. samarium (Sm)
As a rare earth permanent magnet, cobalt (SmCo) not only has high magnetic energy product (14-28MGOe), reliable coercivity and good temperature characteristics.
Make love. Compared with neodymium magnet, samarium cobalt magnet is more suitable for working in high temperature environment.
With the development of society, magnets are widely used, ranging from high-tech products to the simplest packaging magnets.
Or neodymium magnets and ferrite magnets. From the development history of magnets, people mainly used carbon at the end of 19 and the beginning of the 20th century.
Steel, tungsten steel, chromium steel and cobalt steel are used as permanent magnet materials. At the end of 1930s, Al-Ni-Co magnet was successfully developed, which led to its large-scale application.
Use becomes possible. In 1950s, the appearance of barium ferrite magnets not only reduced the cost of permanent magnets, but also broadened the application scope of permanent magnet materials to
High frequency field. In 1960s, the appearance of samarium-cobalt permanent magnets opened up a new era for the application of magnets. Dayton, USA 1967
University Strnat, etc. The development of samarium cobalt magnet marks the arrival of the era of rare earth magnets. So far, the rare ten permanent magnets have experienced the first generation.
SmCo5, the second generation precipitation hardening Sm2Co 17, has developed into the third generation NdFeB permanent magnet. At present, ferrite magnets are the most widely used.
Permanent magnet materials, but the output value of neodymium magnet has greatly exceeded that of ferrite permanent magnet materials, and the production of neodymium magnet has developed into a big industry.
The magnetic force is arranged as follows: neodymium magnet, samarium cobalt magnet, Al-Ni-Co magnet and ferrite magnet.
Manufacturing technology of magnets: Nd magnets, Sm-Co magnets, Al-Ni-Co magnets and ferrite magnets have different manufacturing technologies. Technically, there are sintered neodymium magnets and bonded neodymium magnets. We mainly talk about sintered neodymium magnets.
Process flow: batching → smelting and ingot making → milling → pressing → sintering and tempering → magnetic detection → grinding → pin cutting and adding.
Work → electroplating → finished product. Among them, batching is the foundation and sintering tempering is the key.
Neodymium magnet production tools: melting furnace, crusher, ball mill, jet mill, pressure forming machine, vacuum packaging machine, isostatic press,
Sintering furnace, heat treatment vacuum furnace, magnetic performance tester, Gauss meter.
Neodymium magnet processing tools: special slicer, wire cutter, flat grinder, double-sided machine, punch, chamfering machine, plating equipment.
Maglev train is a high-speed maglev train system with contactless electromagnetic levitation, guidance and drive system. Its speed can reach more than 500 kilometers per hour, and it is the fastest ground passenger transport in the world today, with fast speed, strong climbing ability, low energy consumption and low running noise.
Small, safe and comfortable, no oil consumption, less pollution. And the overhead way is adopted, which occupies less cultivated land. Maglev train refers to the use of the basic principle of magnetic force to suspend these trains on the guide rail to replace the old steel wheels and track trains. Magnetic levitation technology uses electromagnetism.
Force lifts the whole train car, gets rid of annoying friction and unpleasant clang, and realizes fast "flying" without touching the ground and fuel.