Knowledge of magnet principles

A magnet refers to an object or material that can generate a magnetic field. It is usually made of metal alloy and has strong magnetism. Traditionally, they can be divided into "permanent magnets" and "non-permanent magnets".

Permanent magnets can be natural products, also known as natural magnets, or they can be artificially manufactured (the strongest magnets are neodymium magnets).

Magnets are not permanent and sometimes lose their magnetism.

The ancient Greeks and Chinese discovered a naturally magnetized stone in nature and called it a "magnetite." This stone can magically pick up small pieces of iron and always point in the same direction after swinging at will. Early navigators used this magnet as their earliest compass to identify direction at sea.

After thousands of years of development, magnets have become powerful materials in our lives today. By synthesizing alloys of different materials, the same effect as the magnet can be achieved, and the magnetic force can also be improved. Artificial magnets appeared in the 18th century, but the process of making stronger magnetic materials was very slow until Alnico was produced in the 1920s. Subsequently, ferrite was produced in the 1950s, and rare earth magnets [Rare Earth magnets including neodymium iron boron (NdFeB) and samarium cobalt (SmCo)] were produced in the 1970s. So far,

Magnetic technology has developed rapidly, and strong magnetic materials have also made components more miniaturized.

Most magnetic materials can be magnetized to saturation in the same direction. This direction is called the "magnetization direction" (orientation direction). Magnets with no orientation direction (also called isotropic magnets) are much weaker than oriented magnets (also called anisotropic magnets).

What is the standard industry definition of "North and South Pole"?

The definition of "North Pole" is that the north pole of a magnet points to the north pole of the earth after random rotation. Likewise, the south pole of the magnet points to the south pole of the earth.

How to identify the north pole of a magnet without marking it?

Obviously it is impossible to tell the difference with the eyes alone. A compass can be held close to the magnet, and a needle pointing to the Earth's north pole will point to the magnet's south pole.

How to safely handle and store magnets?

Always be very careful as the magnets will stick together and may pinch your fingers. When magnets are attracted to each other, the magnets themselves may be damaged due to collision (corners knocked off or cracks caused).

Keep magnets away from items that are easily magnetized, such as floppy disks, credit cards, computer monitors, watches, mobile phones, medical equipment, etc.

The magnet should be kept away from the pacemaker.

For larger magnets, plastic or cardboard spacers should be added between each piece to ensure that the magnets can be separated easily.

Magnets should be stored in a dry, constant-temperature environment as much as possible.

How to achieve magnetic isolation?

Only materials that can be adsorbed to magnets can block the magnetic field, and the thicker the material, the better the magnetic isolation effect.

What is the strongest magnet?

At present, the highest performance magnets are rare earth magnets, and among rare earth magnets, neodymium iron boron is the most powerful magnet. But in an environment above 200 degrees Celsius, samarium cobalt is the most powerful magnet.

Magnet should be called magnetic steel, English Magnet. Magnetic steel is now mainly divided into two categories, one is soft magnet and the other is hard magnet;

Soft magnet includes silicon steel sheets and soft magnetic cores; hard magnets include alnico, samarium cobalt, ferrite and neodymium iron boron. Among them, the most expensive is samarium cobalt magnet, the cheapest is ferrite magnet, and the one with the highest performance is neodymium. Iron-boron magnets, but the ones with the most stable performance and the best temperature coefficient are aluminum-nickel

Cobalt magnets. Users can choose different hard magnetic products according to different needs.

How to define the performance of magnets?

There are mainly the following three performance parameters to determine the performance of the magnet:

Remanent Br: After the permanent magnet is magnetized to technical saturation and the external magnetic field is removed, the remaining Br is called is the residual magnetic induction intensity.

Coercive force Hc: To reduce the B of a permanent magnet that is magnetized to technical saturation to zero, the reverse magnetic field intensity that needs to be added is called magnetic induction coercivity, abbreviated as

Called coercive force

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 static magnetic energy per unit volume of the air gap. Since this energy is equal to the product of the magnet's Bm and Hm, it is called the magnetic energy product.

Magnetic field: The space that exerts a magnetic effect on the magnetic pole is the magnetic field

Surface magnetic field: The magnetic induction intensity at a specified position on the surface of the permanent magnet

How to choose a magnet?

Before deciding which magnet to choose, you should clearly understand what role the magnet needs to play?

Main function: moving objects, fixing objects or lifting objects.

The shape of the magnet required: disc shape, ring shape, square shape, tile shape or special shape.

Required magnet dimensions: length, width, height, diameter and tolerance, etc.

The required magnet’s suction power, expected price and quantity, etc.

The compass was invented based on the properties of magnets

1 Guide the north

2 Attract light and small objects

3 Electromagnets can do electromagnetism Relay

4. Electric motor

5 Generator

In the pre-Qin era, our ancestors have accumulated a lot of knowledge in this area and often encountered problems when exploring iron ore. To magnetite, that is, magnet (the main component is ferric oxide). These discoveries were documented very early on. These discoveries were first recorded in several chapters of "Guanzi": "

If there is a magnet on the mountain, there is gold and copper underneath."

There are similar records in other ancient books such as "The Classic of Mountains and Seas" records. The iron-attracting properties of magnets have been discovered very early. In the nine-volume mastery chapter of "Lu's Spring and Autumn Annals", it says: "Charity attracts iron, or attracts it." People at that time called "magnetism" "ci" and they attracted the magnets. Iron is regarded as the attraction of a loving mother to her children

. He also believed: "Stone is the mother of iron, but there are two kinds of stones: kind and unkind. A kind stone can attract his children, but an unkind stone cannot attract." Before the Han Dynasty, people wrote magnets as "kind stones", which means "kind stones". The meaning of loving kindness stone.

Since magnets can attract iron, can they also attract other metals? Our ancestors made many attempts and found that magnets not only cannot attract gold, silver, copper and other metals, but also cannot attract items such as bricks and tiles. During the Western Han Dynasty, people had realized that magnets could only attract iron, but not other items. When two magnets are placed close to each other, they sometimes attract each other and sometimes repel each other. Now people all know that a magnet has two poles, one is called N pole and the other is called S pole. Same-sex poles repel each other, and opposite-sex poles attract each other.

People at that time did not know this truth, but they were still aware of this phenomenon.

In the Western Han Dynasty, there was an alchemist named Luan Da. He used the properties of magnets to make two chess pieces. By adjusting the mutual position of the polarity of the two chess pieces, sometimes the two chess pieces moved toward each other. Attract and sometimes repel each other. Luan Da called it "fighting chess". He presented this new and strange gadget to Emperor Wu of the Han Dynasty and demonstrated it on the spot. Emperor Wu of the Han Dynasty was so surprised that Long Xin was so happy that he named Luan Da "General of Five Benefits". Luan Da took advantage of the properties of magnets and made novel gadgets to deceive Emperor Wu of the Han Dynasty.

The Earth is also a large magnet, with its two poles close to the geographical South Pole and the geographical North Pole respectively. Therefore, when the magnets on the earth's surface can rotate freely

they will repel each other due to the same nature of the magnets and attract each other to indicate north and south. The ancients did not understand this truth well, but they were very aware of this phenomenon.

"Applications in traditional industries":

When describing the magnetic sources, electromagnetic induction, and magnetic "devices" of magnetic materials, we have already mentioned the practical applications of some magnetic materials . In fact, magnetic materials have been widely used in various aspects of traditional industry.

For example, without magnetic materials, electrification would be impossible because generators are used to generate electricity, transformers are used in power transmission, and electric motors are used in electrical machinery, telephones, radios, and televisions. Speakers are used. Many instruments and meters use magnetic steel coils

structures.

These have already been mentioned in other chapters.

"Magnetic Applications in Biology and Medicine":

Homing pigeon enthusiasts all know that if pigeons are released hundreds of kilometers away, they will automatically return home. Why do pigeons have such a good ability to recognize their families? It turns out that pigeons are very sensitive to the earth's magnetic field, and they can use changes in the earth's magnetic field to find their home. If

you tie a magnet to a pigeon's head, the pigeon will get lost. If pigeons fly over radio towers, strong electromagnetic interference can disorient them.

In medicine, nuclear magnetic resonance imaging can be used to diagnose abnormal tissues of the human body and determine diseases. This is the nuclear magnetic resonance imaging technology that we are more familiar with. Its basic principle is as follows: the nucleus of an atom has a positive charge. , and perform spinning motion. Normally, the arrangement of the nuclear spin axes is

irregular, but when it is placed in an external magnetic field, the spatial orientation of the nuclear spin transitions from disorder to order. The magnetization vector of the spin system gradually increases from zero. When the system reaches equilibrium, the magnetization intensity reaches a stable value. If the nuclear spin system is affected by external influences at this time, such as a radio frequency of a certain frequency that excites the atomic nucleus, it can cause a oscillation effect. After the radio frequency pulse stops, the atomic nuclei that have been excited by the spin system cannot maintain this state and will return to the original arrangement state in the magnetic field. At the same time, they will release weak energy and become radio signals. This much

Multiple signals are detected and spatially resolved to obtain an image of the distribution of moving nuclei. The characteristic of NMR is that the flowing liquid does not produce a signal, which is called flow effect or flow blank effect. Therefore blood vessels are gray-white tubular structures, while blood is black with no signal.

This makes the blood vessels easy to separate from the soft tissue. The normal spinal cord is surrounded by cerebrospinal fluid. The cerebrospinal fluid is black and has white dura mater set off by fat, making the spinal cord appear as a white strong signal structure. MRI has been used in imaging diagnosis of various systems throughout the body. The best results are found in the brain, spinal cord, heart and great blood vessels, joints, bones, soft tissues and pelvic cavity. For cardiovascular diseases, not only can the anatomical changes of each chamber, great blood vessels and valves be observed, but also ventricular analysis can be performed to make qualitative and semi-quantitative diagnosis. Multiple sections can be made

with spatial resolution. High, showing the whole picture of the heart and lesions, as well as their relationship with surrounding structures, which is better than other X-ray imaging, two-dimensional ultrasound, radionuclide and CT examinations.

Magnet can not only diagnose but also help treat diseases. Magnet is a traditional Chinese medicine. Nowadays, people use the magnetic differences of different components in blood to separate red blood cells and white blood cells. In addition, the interaction between the magnetic field and the meridians of the human body can achieve magnetic therapy, which has a unique role in treating various diseases. There are already applications such as magnetic therapy pillows and magnetic therapy belts. An iron remover made of magnets can remove iron dust that may be present in flour, etc. Magnetized water can prevent boilers from scaling, and magnetized seeds can increase crop yields to a certain extent.

"Magnetic applications in astronomy, geology, archeology 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 is its connection with geological conditions? What about the magnetic field in the universe?

We have all seen the brilliant Northern Lights, at least in pictures. Our country has records of the Northern Lights since ancient times. The Northern Lights are actually the result of the interaction between particles in the solar wind and the Earth's magnetic field. The solar wind is a stream of high-energy charged particles emitted by the sun. When they arrive at the Earth, they interact with the geomagnetic field, just like a current-carrying wire is forced in the magnetic field, causing these particles to move and gather toward the North and South Pole, and interact with the thin air high in the Earth's sky. Gases collide with each other, resulting in gas molecules being excited and emitting light.

Sunspots are areas on the sun where magnetic activity is very intense. Sunspot outbursts will have an impact on our lives, such as temporarily interrupting radio communications. Therefore, studying sunspots is of great significance to us.

Geomagnetic changes can be used to explore mineral deposits. Since all substances have strong or weak magnetism, if they gather together to form mineral deposits, they will inevitably interfere with the geomagnetic field in nearby areas, causing abnormalities in the geomagnetic field.

Based on this, the magnetism of the earth can be measured on land, in the ocean, or in the air, and a geomagnetic map can be obtained. Areas with abnormal magnetic fields on the geomagnetic map can be analyzed and further explored. Unknown mineral deposits or special mineral deposits can often be discovered. geological structure.

Rocks of different geological ages often have different magnetic properties. Therefore, changes in geological time and changes in the earth's crust can be judged based on the magnetic properties of rocks.

Many mineral resources are organic, 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 substances using the different magnetism of minerals with different components and the difference in magnetic strength. Then the attraction they receive will be different. The difference results in the separation of minerals with different magnetic properties mixed together, achieving magnetic mineral separation.

"Magnetic Applications in the Military Field":

Magnetic materials are also widely used in the military field. For example, ordinary sea mines or land mines can only explode on contact with the target, so their effectiveness is limited. And if a magnetic sensor is installed on a mine or a mine, since tanks or warships are made of steel, when they approach (without touching the target), the sensor can detect changes in the magnetic field, causing the mine or mine to Explosion, increased lethality.

In modern warfare, air superiority is one of the keys to winning a battle. However, the aircraft is easily detected by enemy radar during flight, which poses a greater risk. In order to avoid enemy radar detection, a special magnetic material can be coated on the surface of the aircraft -

Absorbing material, which can absorb the electromagnetic waves emitted by the radar, so that the radar electromagnetic waves are rarely reflected, so the enemy The radar cannot detect the radar echo and cannot detect the aircraft, which makes the aircraft invisible. This is the famous "stealth aircraft". Stealth technology

Stealth technology is currently a hot topic in the field of military scientific research in the world. The American F117 stealth fighter is an example of the successful use of stealth technology.

In the United States' "Star Wars" plan, there is the development and research of a new type of weapon "electromagnetic weapon". Traditional artillery uses the thrust generated by the instantaneous expansion of ammunition when it explodes to rapidly accelerate the projectile and push it out of the barrel. The electromagnetic gun places the cannonball in a solenoid and energizes the solenoid. Then the magnetic field generated by the solenoid will produce a huge driving force for the cannonball and eject the cannonball. This is the so-called electromagnetic gun. Similar ones include electromagnetic missiles.

Edit this paragraph | Back to top knowledge There are many types of magnets. Generally divided into two categories: permanent magnets and soft magnets. The magnets we refer to generally refer to permanent magnets.

Permanent magnets are divided into two categories:

The first category: metal alloy magnets including neodymium iron boron magnets (Nd2Fe14B), samarium cobalt magnets (SmCo), and alnico Magnet (ALNiCO)

The second category: Ferrite permanent magnet material (Ferrite)

1. NdFeB magnet: It is the magnet with the highest commercial performance found so far. Known as the magnet king, it has extremely high magnetic properties and its maximum magnetic energy product (BHmax) is more than 10 times higher than that of ferrite. Its own machining performance is also quite good. The maximum working temperature can

reach 200 degrees Celsius. Moreover, its texture is hard, its performance is stable, and it has good cost performance, so its application is extremely wide. However, because of its strong chemical activity, its surface must be treated with a coating. (Such as Zn, Ni plating, electrophoresis, passivation, etc.).

2. Ferrite magnet: Its main raw materials include BaFe12O19 and SrFe12O19. Made through ceramic technology, the texture is relatively hard and is a brittle material. Because ferrite magnets have good temperature resistance, low price and moderate performance, they have become the most widely used permanent magnets. .

3. Alnico magnet: It is an alloy composed of aluminum, nickel, cobalt, iron and other trace metal elements. The casting process can be processed into

different sizes and shapes, and the machinability is very good. Cast alnico permanent magnets have the lowest reversible temperature coefficient and the operating temperature can be as high as 600 degrees Celsius or more.

Alnico permanent magnet products are widely used in various instrumentation and other application fields.

4. Samarium cobalt (SmCo) is divided into SmCo5 and Sm2Co17 according to different ingredients. Its development is limited due to the high price of its materials. Samarium

As a rare earth permanent magnet, samarium cobalt (SmCo) not only has a high magnetic energy product (14-28MGOe), reliable coercive force and good temperature characteristics

. Compared with NdFeB magnets, SmCo magnets are more suitable for working in high temperature environments.

With the development of society, magnets are used more and more widely, from high-tech products to the simplest packaging magnets. Currently, the most widely used ones are neodymium iron boron magnets.

and ferrite magnets. Judging from the development history of magnets, at the end of the 19th century and the beginning of the 20th century, people mainly used carbon steel, tungsten steel, chromium steel and cobalt steel as permanent magnet materials. In the late 1930s, the successful development of alnico magnets made the large-scale application of magnets possible. In the 1950s, the emergence of barium ferrite magnets not only reduced the cost of permanent magnets, but also expanded the application range of permanent magnet materials to high-frequency fields. By the 1960s, the emergence of samarium-cobalt permanent magnets opened up a new era for the application of magnets. In 1967, Strnat and others from Dayton University in the United States developed samarium cobalt magnets, marking the arrival of the era of rare earth magnets. So far, rare ten permanent magnets have developed from the first generation

SmCo5, the second generation precipitation hardening Sm2Co17, to the third generation Nd-Fe-B permanent magnet material. At present, ferrite magnets are still the most widely used permanent magnet material, but the output value of NdFeB magnets has greatly exceeded that of ferrite permanent magnet materials. The production of NdFeB magnets has developed into a major industry< /p>

The order of magnetic force is: neodymium iron boron magnet, samarium cobalt magnet, alnico magnet, ferrite magnet.

Magnet manufacturing process: The manufacturing processes of neodymium iron boron magnets, samarium cobalt magnets, alnico magnets and ferrite magnets are also different. In terms of technology, there are sintered NdFeB magnets and bonded NdFeB magnets. We mainly talk about sintered NdFeB magnets.

Process flow: Ingredients → Smelting and ingot making → Powder making → Pressing → Sintering and tempering → Magnetic detection → Grinding → Pin cutting and processing

→ Electroplating → Finished product. Among them, ingredients are the basis, and sintering and tempering are the key

NdFeB magnet production tools: smelting furnace, jaw crusher, ball mill, jet mill, compression molding machine, vacuum packaging machine, isostatic press,

Sintering furnace, heat treatment vacuum furnace, magnetic performance tester, Gauss meter.

NdFeB magnet processing tools: special slicers, wire cutting machines, flat grinders, double-sided machines, punching machines, chamfering machines, and electroplating equipment.

The maglev train is a maglev high-speed train system that uses contactless electromagnetic levitation, guidance and drive systems. It can reach a speed of more than 500 kilometers per hour and is the fastest ground passenger transportation vehicle in the world today. It has fast speed, strong climbing ability, low energy consumption, low noise during operation, safety and comfort, and no fuel consumption. Less pollution and other advantages. And it adopts an elevated method, occupying very little cultivated land. Maglev trains mean that these trains use the basic principles of magnetism to levitate on guide rails instead of the old steel wheel and rail trains. Magnetic levitation technology uses electromagnetic

force to lift the entire train carriage, getting rid of annoying friction and unpleasant clang sounds, achieving fast "flight" without contact with the ground and without fuel.