[edit]Basic Knowledge
The ancient Greeks and Chinese discovered a naturally magnetized stone in nature and called it "iron absorption stone". This stone could magically pick up small pieces of iron and always point in the same direction when swung around. Early mariners used this magnet as their earliest compass to find their way at sea.
After thousands of years of development, today magnets have become a powerful material in our lives. By synthesizing alloys of different materials can achieve the same effect as an iron absorber, but also increase the magnetic force. Man-made magnets appeared in the 18th century, but the process of making stronger magnetic materials was slow until the 1920s when aluminum nickel cobalt (Alnico) was made. Then, in the 1950s, ferrite was produced, and in the 1970s, rare earth magnets [Rare Earth magnets include neodymium-iron-boron (NdFeB) and samarium cobalt (SmCo)] were produced. Since then, magnetic science and technology have developed rapidly, and strong magnetic materials have made components more miniaturized.
[edit]Direction of magnetization
Most magnetic materials can be magnetized to saturation in the same direction, which is called the "direction of magnetization" (direction of orientation). Magnets without orientation (also called isotropic magnets) are much less magnetic than oriented magnets (also called anisotropic magnets).
What is the standard industrial definition of "north and south poles"?
The definition of "North Pole" is that the North Pole of a magnet is pointing towards the North Pole of the Earth when the magnet is rotated randomly. Similarly, the south pole of a magnet points to the south pole of the earth.
How do you recognize the north pole of a magnet without labeling it?
Obviously you can't tell by eye alone. You can use a compass close to the magnet, and the needle pointing to the Earth's North Pole will point to the magnet's South Pole.
How do I safely handle and store a magnet?
Always be very careful, as magnets can attract themselves together and can pinch your fingers. It is also possible to damage the magnets themselves by bumping them against each other (knocking off corners or cracking them).
Keep magnets away from magnetized objects such as floppy disks, credit cards, computer monitors, watches, cell phones, and medical devices.
Keep the magnet away from pacemakers.
Larger magnets should have plastic or cardboard spacers between each piece to ensure that the magnets can be easily separated.
Magnets should be stored in a dry, temperature-controlled environment.
How do I insulate my magnets?
Only materials that attach to the magnet can act as a magnetic field barrier, and the thicker the material, the better the barrier.
What is the strongest magnet?
The highest performance magnets are rare earth magnets, and NdFeB is the most powerful of the rare earth magnets. However, Samarium Cobalt is the most powerful magnet in environments above 200 degrees Celsius.
[edit]Types of magnets
Magnets, should be called magnets, English Magnet, magnets are now divided into two main categories, one is a soft magnet, a class of hard magnets;
Soft magnets, including silicon steel sheet and soft magnet core; hard magnets, including alnico, samarium cobalt, ferrite and neodymium-iron-boron, which, the most expensive is samarium cobalt magnets, and the most inexpensive is ferrite magnets, the highest performance is NdFeB magnets. The highest performance is NdFeB magnet, but the most stable performance and the best temperature coefficient is Alnico magnet, users can choose different hard magnetic products according to different needs.
How to define the performance of a magnet?
There are 3 main performance parameters to define the performance of a magnet:
Residual Br : After the permanent magnet is magnetized to technical saturation and the external magnetic field is removed, the Br retained is called the residual magnetic induction strength.
Coercivity Hc :The reverse magnetic field strength that needs to be added to reduce the B of a permanent magnet magnet magnetized to technical saturation to zero is known as the magnetic coercivity, which is briefly
referred to as the coercivity
Magnetic energy product BH :It represents the magnetic energy density that is built up by the magnet in the space of the air-gap (the space of the magnet's two poles), i.e., 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 produces magnetic action on the poles is the magnetic field
Surface magnetic field:The magnetic induction at a specified location on the surface of a permanent magnet
How to choose a magnet?
Before deciding which magnet to choose, it should be clear what the magnet is needed to do?
The main function: to move an object, to fix it or to lift it.
The shape of the magnet required: circular, toroidal, square, tile or special shape.
Dimensions of the magnet required: length, width, height, diameter and tolerances, etc.
The size of the magnet required: length, width, height, diameter and tolerances.
The suction power of the magnet, the desired price and quantity, and so on.
The compass was invented on the basis of the nature of magnets
[edit]Role of magnets
1 Pointing north and south
2 Attracting light objects
3 Electromagnet can be used as an electromagnetic relay
4 Generator
The discovery of the phenomenon of magnetism
In the pre-Qin era, our ancestors had already accumulated many knowledge in this area. Much of this knowledge was already accumulated by our ancestors during the pre-Qin era, when they often encountered magnetite, or magnetite (the main component is tetraoxo
tri-iron oxide), when exploring for iron ore. These discoveries were documented early on. The first of these discoveries was recorded in several passages of the Pipe: "He who has magnetite on the mountain has gold and copper underneath."
Other ancient texts such as the Classic of Mountains and Seas contain similar accounts. The iron absorbing properties of magnets were discovered very early, and the nine volumes of Lüshi Chunqiu (吕氏春秋), which is a masterpiece, reads:
"Ci recruits iron, or attracts it." At that time, the people called "magnet" for "Ci" they regarded the magnet to attract iron as a mother's attraction to her children. And think: "Stone is the mother of iron
, but there are two kinds of stone charity and not charity, charity stone can attract his children, not charity stone can not attract."
Before the Han Dynasty, people wrote magnet as "Ci Shi", which means loving stone.
Since magnets can attract iron, can they also attract other metals? Our ancestors made many attempts, and found that magnets not only can not attract gold,
silver, copper and other metals, but also can not attract bricks and tiles and other items. In the Western Han Dynasty, people had already realized that magnets could only attract iron, but not other objects.
When two magnets were put together near each other, sometimes they attracted each other and sometimes they repelled each other. Now people know that magnets have two poles, one
called the N pole and one called the S pole. The same poles repel each other and the opposite poles attract each other. People didn't know this, but they were able to
notice the phenomenon.
To the Western Han Dynasty, there is a square priest named Luan Da, he used this nature of the magnet to make two chess-like things, by adjusting the polarity of the two pieces
mutual position, sometimes the two pieces attract each other, and sometimes repel each other. Luan Da called it "fighting chess". He offered this novelty to Emperor Wu of Han, and demonstrated it on the spot. Han Wu Di was surprised, the dragon heart pleased, and even appointed Luan Da as "General Wuli". Luan big use of the nature of the magnet, the production of novelties to deceive
Han Wu Di.
The Earth is also a large magnet, and its two poles are in close proximity to the geographic South Pole and the geographic North Pole. Therefore, the magnet on the surface of the Earth, can be free to rotate
movement, it will be due to the nature of the magnet same sex repulsion, opposite sex attraction indication of the north and south. This reasoning was not understood by the ancients, but this type of phenomenon is very clear to them.
Applications of Magnetic Phenomena
"Applications in Traditional Industries":
We have already mentioned some of the practical applications of magnetic materials when we talked about the source of magnetism, electromagnetic induction, and magnetic devices. In fact, magnetic materials have been used in a wide range of applications in various aspects of conventional industry.
For example, without magnetic materials, electrification would have been impossible because generators are used for power generation, transformers for power transmission, electric motors for electrical machinery, and loudspeakers for telephones, radios, and televisions. Numerous instruments and meters are used in the magnet coil structure. All of this has already been covered in the rest of the story.
Magnetic Applications in Biology and Medicine:
Pigeon fanciers know that pigeons return to their nests automatically if they are released hundreds of kilometers away. Why are pigeons so good at recognizing home? Originally, pigeons are very sensitive to the earth's magnetic field, they can use the earth's magnetic field changes to find their own home. If a magnet is tied to the pigeon's head, the pigeon will get lost. If pigeons fly over radio towers, the powerful electromagnetic interference will also disorient them.
In medicine, the use of nuclear magnetic **** vibration can diagnose abnormal tissue in the human body, to determine the disease, which is more familiar with the nuclear magnetic **** vibration imaging technology, the basic principle is as follows: the atomic nucleus with a positive charge, and spin movement. Normally, the arrangement of the spin axis of the nucleus is irregular, but when it is placed in an applied magnetic field, the nuclear spin space orientation transitions from disorder to order. The magnetization vector of the spin system grows gradually from zero, and when the system reaches equilibrium, the magnetization strength reaches a stable value. If the nuclear spin system is subjected to external effects, such as a certain frequency of radio frequency excitation of the nucleus can cause *** vibration effect. In the radio frequency pulse stops, the spin system has been excited nuclei, can not maintain this state, will return to the magnetic field in the original arrangement of the state, at the same time to release a weak energy, become radio signal, the many signals detected, and make it when the spatial resolution, you get the distribution of nuclei in the movement of the image. Nuclear magnetic **** vibration is characterized by the flow of liquid does not produce a signal called the flow effect or flow blanking effect. Thus blood vessels are grayish-white tubular structures, while blood is black with no signal. This makes the blood vessels easily soft tissue separated. The normal spinal cord is surrounded by cerebrospinal fluid, which is black, and has white dura mater lined with fat so that the spinal cord shows up as a white, strongly signaling structure. MRI*** vibration has been applied to diagnostic imaging of systems throughout the body. The best results are the cranial brain, and its spinal cord, the heart large blood vessels, joints bones, soft tissues and pelvis. For cardiovascular disease can not only observe the anatomical changes of the chambers, great vessels and valves, but also ventricular analysis, qualitative and semi-quantitative diagnosis, can be made for a number of cross-sectional maps, high spatial resolution, showing the whole picture of the heart and the lesion, and its relationship with the surrounding structures, superior to other X-ray imaging, two-dimensional ultrasound, nuclide and CT examination.
Magnets are not only diagnostic, but can also help treat disease. Magnets are an herb used in ancient Chinese medicine. Nowadays, the magnetic difference between different components of blood is utilized to separate red and white blood cells. In addition, the interaction between magnetic field and human meridians can realize magnetic therapy, which has unique effects in treating many diseases, and has been applied to magnetic therapy pillows, magnetic therapy belts and so on. With magnets made of iron remover can remove flour and other iron powder may exist, magnetized water can prevent boiler scaling, magnetized seeds can be to a certain extent to make crop yield.
"Magnetic Applications 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 been there since ancient times? How is it related to geological conditions? And what about magnetic fields in the universe?
We have all seen the brilliant Northern Lights, at least in pictures. The Northern Lights have been recorded in our country 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, and the geomagnetic field interaction, as if the wire with electric current in the magnetic field force, making these particles to the north and south poles of the movement and aggregation, and and the Earth's high altitude of the thin gas collision, the result of gas molecules by the excitation, and thus the light.
Sunspots are regions on the Sun where magnetic activity is very intense. Sunspot eruptions can have an impact on our lives, such as temporarily disrupting radio communications. Therefore, it is important for us to study sunspots.
Changes in geomagnetism can be used to explore for mineral deposits. Since all substances have strong or weak magnetic properties, if they come together to form a deposit, they will inevitably interfere with the geomagnetic field of the neighboring area, causing anomalies in the geomagnetic field. According to this, the magnetic field of the earth can be measured on land, at sea, or in the air, and a geomagnetic map can be obtained, and the areas with abnormal magnetic fields on the geomagnetic map can be analyzed and further explored, and unknown mineral deposits or special geological formations can often be found.
Rocks of different geological ages often have different magnetic properties. Therefore, the magnetic properties of rocks can be used to help determine changes in geological age and crustal changes.
Many mineral resources are ****ogenic, meaning that several minerals are mixed together and have different magnetic properties. Using this feature, people developed a magnetic separator, the use of different components of the different magnetic properties of minerals as well as the difference between the strength of the magnetic properties, with a magnet to attract these substances, then they are subject to the attraction of the difference, the result can be mixed together with different magnetic properties of the minerals to separate, the realization of the magnetic separation of minerals.
"Magnetic applications in the military":
Magnetic materials are also widely used in the military. For example, ordinary mines or landmines can only explode on contact with the target and therefore have limited effect. However, if a magnetic sensor is installed on a mine or a landmine, since tanks or warships are made of steel, when they are close to (without touching the target), the sensor can detect changes in the magnetic field and make the mine or landmine explode, thus increasing the lethality.
In modern warfare, air control is one of the keys to victory. However, the aircraft in the flight process is easily detected by the enemy's radar, and thus has a greater danger. In order to avoid enemy radar monitoring, can be coated with a special layer of magnetic material on the surface of the aircraft - wave-absorbing material, which can absorb the electromagnetic waves emitted by the radar, making the radar electromagnetic waves rarely reflect, so the enemy radar can not detect the radar echo, can not find the aircraft, which makes the aircraft to achieve the purpose of stealth. This is the famous "stealth aircraft". Stealth technology is currently the world's military research in the field of a major hot spot. The U.S. F117 stealth fighter is an example of the successful use of stealth technology.
In the U.S. "Star Wars" program, there is a new type of weapon "electromagnetic weapons" development research. Traditional artillery is to use the instantaneous expansion of the ammunition explosion generated by the thrust of the shell quickly accelerated, out of the gun. On the other hand, an electromagnetic cannon puts the shell in a solenoid, energizes the solenoid, and the magnetic field generated by the solenoid generates a huge push force on the shell, which shoots the shell out. This is called an electromagnetic cannon. Similarly there are electromagnetic missiles etc.
[edit]Knowledge of magnets
There are many types of magnets, generally divided into two categories of permanent magnets and soft magnets, the magnets we say, generally refers to permanent magnets
Permanent magnet magnets are divided into two categories:
The first category is: metal alloy magnets, including neodymium-iron-boron magnets Nd2Fe14B), samarium cobalt (SmCo) magnets, aluminum nickel cobalt (ALNNi) magnets (Nd2Fe14B), smarium cobalt magnets, aluminum nickel cobalt (ALNiCo), aluminum nickel cobalt (AlNiCo) magnets (AlNiCo) magnets (AlNiCo) magnets (AlNiCo). Cobalt magnets (ALNiCO)
The second category is: ferrite permanent magnet materials (Ferrite)
1, NdFeB magnets: it is currently found in the commercialization of the highest performance of the magnet, known as the king of magnets, has a very high magnetic performance of its maximum magnetic
energy product (BHmax) is higher than the ferrite (Ferrite) more than 10 times. It also has excellent machinability. The maximum working temperature can
reach 200 degrees Celsius. And its texture is hard, stable performance, has a very good cost performance, so its application is extremely wide. But because of its chemical activity
strong, so it must be its surface tinting treatment. (such as plating Zn, Ni, electrophoresis, passivation, etc.).
2. Ferrite magnets: its main raw materials include BaFe12O19 and SrFe12O19, through the ceramic process method of manufacturing and become, the texture is relatively hard, is
brittle materials, because of the ferrite magnets have a very good temperature resistance, low price, moderate performance, has become the most widely used permanent magnets.
3. Alnico magnets: an alloy composed of aluminum, nickel, cobalt, iron and other trace metal elements. The casting process allows for the production of magnets in different sizes and shapes with excellent machinability. Cast Alnico magnets have the lowest reversible temperature coefficient and can operate at temperatures up to 600 degrees Celsius and above. Alnico permanent magnets are widely used in a variety of instrumentation and other applications.
4. Samarium Cobalt (SmCo) is divided into SmCo5 and Sm2Co17 according to the different composition, and its development is limited due to its expensive material price. Samarium cobalt (SmCo) as a rare earth permanent magnet, not only has a high magnetic energy product (14-28MGOe), reliable coercivity and good temperature
performance. Compared with NdFeB magnets, SmCo magnets are more suitable to work in high temperature environment.
[edit]History of magnets
With the development of society, the application of magnets is also more and more extensive, from high-tech products to the simplest packaging magnets, the most widely used
is still neodymium-iron-boron magnets and ferrite magnets. From the perspective of the history of the development of magnets, the late nineteenth century, the early twentieth century, people mainly use carbon
steel, tungsten steel, chromium steel and cobalt steel for permanent magnetic materials. At the end of the 1930s, the successful development of Alnico magnets to make 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 broadened the scope of application of permanent magnet materials to
high-frequency field. To the sixties, the emergence of samarium cobalt permanent magnets, the application of magnets opened up a new era. 1967, the United States Dayton
University of Strnat, developed into samarium cobalt magnets, marking the arrival of the rare earth magnets. So far, rare-earth permanent magnets have experienced the first generation
SmCo5, the second generation of precipitation hardening type Sm2Co17, the development of the third generation of Nd-Fe-B permanent magnet materials. At present, ferrite magnets are still the largest amount of
permanent magnetic materials, but the output value of Nd-Fe-B magnets has greatly exceeded that of ferrite permanent magnetic materials, and the production of Nd-Fe-B magnets has developed into a major industry
Magnetic force magnets are arranged as follows: Nd-Fe-B magnets, Samarium Cobalt magnets, Alnico magnets, ferrite magnets.
Magnet production process: neodymium iron boron magnets, samarium cobalt magnets, alnico magnets, ferrite magnets production process is also different
1, neodymium iron boron magnets from the process, there are sintered neodymium iron boron magnets and bonded neodymium iron boron magnets, we mainly talk about sintered neodymium iron boron magnets.
[edit]NdFeB magnet process
Process: Ingredients → Ingot melting → Powder → Pressing → Sintering and tempering → Magnetic detection → Grinding → Pins and cuts
Work → Electroplating → Finished products. Among them, batching is the foundation, sintering and tempering is the key
NdFeB magnet production tools: smelting furnace, jaw machine, ball mill, air mill, press molding machine, vacuum sealing machine, isostatic press,
sintering furnace, heat treatment vacuum furnace, magnetic performance tester, gaussmeter.
NdFeB magnet processing tools: there are special slicing machine, wire cutting machine tools, flat grinding machine, double-sided machine, punching machine, chamfering machine, plating equipment.
[edit]What is a maglev train
The maglev train is a magnetic levitation high-speed train system that uses a contactless electromagnetic levitation, guidance and drive system. Its speed can reach more than 500 kilometers per hour, is today the world's fastest ground passenger transportation, has the advantages of fast speed, strong climbing ability, low energy consumption, low noise when running, safe and comfortable, no fuel, less pollution. And it adopts the use of elevated methods, taking up very little arable land. Maglev trains mean that these trains utilize the basic principles of magnetism to levitate on rails instead of the old steel wheel and rail trains. Maglev technology uses electromagnetic force to lift the entire train car, getting rid of the annoying friction and unpleasant clanking sound, and realizing no contact with the ground, no fuel fast "flight".