Why are magnets magnetic?
Most matter is composed of molecules, which are composed of atoms, and atoms are composed of nuclei and electrons. Inside an atom, electrons spin constantly and revolve around the nucleus. Both movements of electrons produce magnetism. But in most materials, electrons move in different and chaotic directions, and the magnetic effects cancel each other out. Therefore, most substances are not magnetic under normal circumstances. Ferromagnetic materials such as iron, cobalt, nickel, or ferrite are different. The electron spins inside them can spontaneously arrange themselves in a small range to form a spontaneous magnetization area. This spontaneous magnetization area is called a magnetic domain. After ferromagnetic substances are magnetized, the internal magnetic domains are arranged neatly and in the same direction, which strengthens the magnetism and forms a magnet. The magnet's process of attracting iron is the process of magnetizing the iron block. The magnetized iron block and the magnet have different polarities of attraction, and the iron block "sticks" to the magnet.
How to define the performance of magnets?
There are mainly the following 4 performance parameters to determine the performance of the magnet:
Residual magnetism Br: After the permanent magnet is magnetized to technical saturation and the external magnetic field is removed, the remaining Br is called the residual magnetic induction intensity.
Coercive force Hcj: To reduce the Br of a permanent magnet that is magnetized to technical saturation to zero, the reverse magnetic field intensity that needs to be added is called magnetically induced 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 static magnetic energy per unit volume of the air gap. Hcb, Hcj The reverse magnetic field intensity required to reduce the Br (magnetic induction intensity) of a permanent magnet magnetized to technical saturation to zero is called the magnetic induction coercivity. In the same way, the intrinsic magnetic induction intensity UoM or Mr is reduced to zero. The required reverse magnetic field strength is called the intrinsic coercive force.
Intrinsic coercive force (Hcj): The unit is Oersted (Oe) or A/m (A/m): the reverse magnetic field strength required to reduce the residual magnetization Mr of the magnet to zero, which we call Innate coercion. Intrinsic coercive force is a physical quantity that measures the ability of a magnet to resist demagnetization. It represents the coercive force when the magnetization M in the material returns to zero.
How to classify magnetic materials?
Metal magnetic materials are divided into two categories: permanent magnetic materials and soft magnetic materials. Generally, materials with an intrinsic coercive force greater than 0.8kA/m are called permanent magnetic materials, and materials with an intrinsic coercive force less than 0.8kA/m are called soft magnetic materials. Comparison of the magnetic force of several commonly used magnets. The magnetic force from large to small is neodymium iron boron magnet, samarium cobalt magnet, alnico magnet, and ferrite magnet.
Cost-effectiveness comparison of different magnetic materials?
Ferrite: low and medium performance, lowest price, good temperature characteristics, corrosion resistance, good performance-price ratio.
NdFeB: highest performance, medium price, good strength, 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, and neodymium iron boron can be manufactured by sintering and bonding methods. The sintered magnet has high magnetic properties but poor molding. The bonded magnet has good formability but a lot of performance reduction. AlNiCo can be manufactured by casting and sintering methods. Cast magnets have higher performance but poor formability, while sintered magnets have lower performance and better formability.
Characteristics of NdFeB magnets
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, and the advantages of high energy density make NdFeB permanent magnet materials widely used in modern industry and electronic technology, thus making instrumentation, electroacoustic motors, and magnetic separation It becomes possible to make equipment such as magnetization smaller, lighter, and thinner. Material characteristics: The advantages of NdFeB are high-cost performance and good mechanical properties; its disadvantages are low Curie temperature point, poor temperature characteristics, and ease of pulverizing and corroding. It must be made by adjusting its chemical composition and adopting surface treatment methods. Only by improving it can it meet the requirements of practical applications. Manufacturing process: NdFeB is manufactured using a powder metallurgy process. Process flow: ingredients → smelting and ingot making → powder making → pressing → sintering and tempering → magnetic detection → grinding processing → pin cutting processing → electroplating → finished product.
Ferrite magnet:
Features: Its main raw materials include BaFe12O19 and SrFe12O19. Made through ceramic technology, the texture is relatively hard and brittle. Because ferrite magnets have good temperature resistance, low price, and moderate performance, they have become the most widely used permanent magnets. Characteristics: It has high magnetic properties, good time stability, and low-temperature coefficient. Ferrite magnet application areas: widely used in electricity meters, instruments, motors, automatic controls, microwave devices, radar and medical equipment, etc. Ferrite magnet magnetizing direction: axial, radial, or as required. Ferrite magnet shapes: cylindrical, circular, rectangular, flat, tile-shaped, and axe-shaped can be produced.
What is a single-sided magnet?
Magnets have two poles, but in some working positions, single-pole magnets are required, so one side of the magnet needs to be wrapped with an iron sheet so that the magnetism of the side covered by the iron sheet is shielded and the magnets on the other side are refracted by the iron sheet. Magnets enhance 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 such thing as a true single-sided magnet. The materials used for single-sided magnets are generally arc-shaped iron sheets and powerful NdFeB magnets. The shapes of NdFeB powerful magnets used for single-sided magnets are generally disk shapes.
What is the use of single-sided magnets?
(1) It is widely used in the printing industry. Single-sided magnets are found 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. Single-sided magnets are found in bags, briefcases, travel bags, mobile phone cases, wallets, and other leather goods.
(3) It is widely used in the stationery industry. Single-sided magnets exist in notebooks, whiteboard buckles, folders, magnetic nameplates, etc.
What precautions should be taken during the transportation of magnets?
Pay attention to indoor humidity, which must be maintained at a dry level. The temperature should not exceed room temperature; black block or blank products can be properly oiled when stored (general engine oil is sufficient); electroplated products should be vacuum sealed or stored in isolation from air to ensure the corrosion resistance of the coating; magnetized products should be attracted Store them together and in boxes to avoid attracting other metal objects; magnetized products should be stored away from disks, magnetic cards, tapes, computer monitors, watches and other objects that are sensitive to magnetic fields. Magnets in the magnetized state should be shielded when transported, especially when transported by air, they must be completely shielded.
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. The main products of Xiangci Magnets include sintered ferrite magnets (isotropic, anisotropic, and polar anisotropy), injection molded magnets (encoder magnetic rings, injection molded integrated rotor components, Hall magnetic rings), with good consistency, and strong stability.
Which ferrite material can conduct electricity?
Soft magnetic material ferrite is a magnetically permeable material with high magnetic permeability and high resistivity. It is generally used at high frequencies and is mainly used in electronic communications. Computers and televisions that we come into contact with every day have applications inside them. Soft ferrites mainly include manganese-zinc and nickel-zinc. The magnetic permeability of manganese-zinc ferrite is greater than that of nickel-zinc ferrite.
What is the Curie temperature of permanent magnet ferrite?
It is reported that the Curie temperature of ferrite is around 450°C, usually greater than or equal to 450°C. Hardness is around 480-580. The Curie temperature of NdFeB magnets is basically between 350-370℃. However, the operating temperature of NdFeB magnets cannot reach the Curie temperature. When the temperature exceeds 180-200°C, the magnetic properties have been greatly attenuated, the magnetic loss is also very large, and the use value has been lost. Curie point is also known as Curie temperature (Tc) or magnetic transition point. It refers to the temperature at which the spontaneous magnetization in magnetic materials drops to zero and is the critical point at which ferromagnetic or ferrimagnetic substances transform into paramagnetic substances. Below the Curie point temperature, the material becomes a ferromagnet, and the magnetic field associated with the material is difficult to change. When the temperature is higher than the Curie point, the material becomes a paramagnet, and the magnetic field of the magnet changes easily with changes in the surrounding magnetic field. The magnetic sensitivity at this time is approximately 10 to the power of negative 6. The Curie point is determined by the chemical composition and crystal structure of the substance.
What are the generally effective parameters of magnetic cores?
Magnetic cores, especially ferrite materials, have various geometries and sizes. To meet the requirements of various designs, the size of the magnetic core is also calculated to suit the optimization requirements. These existing magnetic core parameters include physical parameters such as magnetic path, effective area, effective volume, etc.
Why is the corner radius important for winding?
The reason why the corner radius is important is that if the edge of the core is too sharp, it is possible to nick the insulation of the wire during the precise and tight winding process. Pay attention to ensure that the edges of the magnetic core are rounded. Ferrite core production molds have a certain standard roundness radius, and these cores are ground and deburred to reduce the sharpness of their edges. In addition, most magnetic cores are painted or covered to not only blunt their corners but also make their winding surfaces smooth. Powder cores have a semicircle with a pressure radius on one side and a deburring process on the other side. For ferrite materials, an edge covering is additionally provided.
Which type of magnetic core is suitable for making a transformer?
The magnetic core that meets the needs of the transformer should have high magnetic induction intensity on the one hand, and keep its temperature rise within a certain limit on the other hand. For inductors, the magnetic core should have a certain air gap to ensure that it has a certain magnetic permeability level under high DC or AC driving conditions. Both ferrite and tape cores can be treated with air gaps, and the powder core has its own Comes with air gap.
What kind of magnetic core is best?
It should be said that there is no answer to this question because the selection of magnetic core is determined based on the application situation and application frequency. The selection of any material also has a market and other factors to consider. For example, some materials can guarantee a temperature rise. Smaller, but expensive. In this way, when selecting materials for higher temperature rises, it is possible to choose larger-sized but lower-priced materials to complete such work. Therefore, the so-called best material The selection must first be based on the application requirements of your inductor or transformer. From this point of view, its operating frequency and cost are important factors. The optimal selection of different materials is determined based on switching frequency, temperature rise, and magnetic flux density.
What is an anti-interference magnetic ring?
Anti-interference magnetic ring is also called a ferrite magnetic ring. The origin of the name anti-interference magnetic ring is that it can play an anti-interference role. For example, electronic products are affected by external disordered signals and invade the electronic products, causing the electronic products to receive interference from external disordered signals and fail to operate normally. The anti-interference magnetic ring, Just to have this function, as long as the product is equipped with an anti-interference magnetic ring, it can prevent external chaotic signals from intruding into electronic products, enable the electronic products to operate normally, and play an anti-interference effect, so it is called an anti-interference magnetic ring. Anti-interference magnetic ring is also called a ferrite magnetic ring, because a ferrite magnetic ring is made of ferrite materials such as iron oxide, nickel oxide, zinc oxide, copper oxide, etc., because these materials contain ferrite Composition, and the product is made of ferrite material is like a ring, so it is called ferrite magnetic ring over time.
How to demagnetize a magnetic core?
The method is to apply 60Hz alternating current to the magnetic core so that its initial drive current is enough to saturate both the positive and negative ends, and then gradually and slowly reduce the drive level, repeating several times until it drops to 0. This will restore its retention point to its original initial state.
What is magnetoelasticity (magnetostriction)?
After the magnetic material is magnetized, a small geometric change will occur. The size of this change should be on the order of a few parts per million, which is called magnetostriction. Some applications, such as ultrasonic generators, take advantage of this property to obtain mechanical deformation through magnetically excited magnetostriction. In some other applications, when working in the audible frequency range, a howling noise will appear. Therefore, low magnetic shrinkage materials can be applied in this case.
What is magnetic mismatch?
This phenomenon occurs in ferrite and manifests itself as a decrease in magnetic permeability when the core is demagnetized. This demagnetization can occur after the operating temperature is above the Curie point temperature, the application of gradually decreasing amplitude of alternating current or mechanical vibration, etc. In this phenomenon, the magnetic permeability first increases to its original level and then decreases exponentially and rapidly. If no special conditions are desired for the application, then the change in permeability will be small, since many changes can occur within a few months of fabrication. High temperatures accelerate this decrease in magnetic permeability. Magnetic dissonance will recur after each successful demagnetization and is therefore different from aging.
What kind of magnets can be used in water?
Depending on the material, not every magnet can be used in water. A corroded and rusty magnet can be hazardous to aquatic life. Ferrite has strong corrosion resistance and oxidation resistance and can be used normally in water.
What are magnetic tiles?
Magnetic tile is a kind of tile-shaped magnet among permanent magnets, which is mainly used in permanent magnet motors.
What are the production processes of ferrite magnet tiles?
Ferrite magnets are mainly made of sintered ferrite. The production process of sintered ferrite magnet tiles is mainly divided into wet-pressing anisotropic, dry-pressing isotropic, and dry-pressing anisotropy. The difference between anisotropic and isotropic is whether there is an orientation magnetic field when the press is forming. Here we mainly introduce the process of wet pressing of the opposite sex. The wet pressing process flow is: raw materials → pre-calcination → coarse grinding (primary ball milling) → batching → secondary ball milling (wet grinding) → magnetic field forming → sintering → grinding → cleaning → magnetization. Because the molding slurry contains moisture, the molded particles are easy to turn in the magnetic field, so they can obtain a higher degree of orientation than dry pressing, and their performance is also higher.
NdFeB magnetic tile production process flow
Sintered NdFeB magnetic tiles: ingredients → smelting → crushing → powder making → magnetic field molding → isostatic pressing → vacuum sintering and tempering → wire cutting and other processing → electroplating → magnetization.
What is the choice of workpiece cleaning method?
The way the workpiece is placed in the cleaning tank has a great relationship with the quality of the cleaning. Its placement is also related to the size, shape, and structure of the workpiece. Generally speaking, overlapping stacks of workpieces or too many stacks at one time will affect the cleaning effect. Although NdFeB magnetic materials have different shapes, they are mostly small parts. You can put it on a nylon net and shake it in the cleaning tank for cleaning. This will help the dirt on the surface of the workpiece fall off, and it will also help destroy the water film on the workpiece with blind holes, making the cavitation effect easy to occur in the blind holes. Another way to place the workpiece is to directly flatten the workpiece on the bottom plate of the cleaning tank (that is, the ultrasonic transducer radiating plate) so that the workpiece can withstand strong ultrasonic impact. The practice has proved that this method of directly placing the workpiece on the bottom plate for cleaning has the best cleaning effect and the highest efficiency.
What precautions should be taken during the transportation of magnets?
Pay attention to indoor humidity, which must be maintained at a dry level. The temperature should not exceed room temperature; black block or blank products can be properly oiled when stored (general engine oil is sufficient); electroplated products should be vacuum sealed or stored in isolation from air to ensure the corrosion resistance of the coating; magnetized products should be attracted Store them together and in boxes to avoid attracting other metal objects; magnetized products should be stored away from disks, magnetic cards, tapes, computer monitors, watches and other objects that are sensitive to magnetic fields. Magnets in the magnetized state should be shielded when transported, especially when transported by air, they must be completely shielded.
What is a powerful magnet?
Powerful magnets refer to neodymium iron boron magnets. Its magnetic properties greatly surpass ferrite magnets, alnico, and samarium cobalt. NdFeB magnets can absorb 640 times their weight, so NdFeB magnets are often called powerful magnets by outsiders.
How to demagnetize a strong magnet?
A certain method for demagnetization can be developed according to the different usage conditions of powerful magnets.
1) High-temperature demagnetization method: The main operation of the high-temperature demagnetization method is to put the magnet into a high-temperature furnace for heating. After high-temperature treatment, the magnetism of the powerful magnet will be removed. However, during the heating process, the effect of high temperature will directly cause The structure of the objects inside the magnet to undergo drastic changes, so this demagnetization method is generally used for scrapped and recycled magnets.
2) Vibration demagnetization method: This method is very simple to operate. It vibrates a powerful magnet violently and violently. After the vibration operation, the internal structure of the magnet changes, thereby changing the physical properties of the magnet. Generally speaking, The effect of this demagnetization method is not great, and only a small amount of demagnetization can be used temporarily.
3) Magnet AC demagnetization method: This method of demagnetization is to put the magnet into a space that can generate an AC magnetic field. After the interference of the AC magnetic field, the internal structure of the magnet will be disrupted, thus achieving the demagnetization effect. This method is a relatively common demagnetization method.
The above three methods are all effective for demagnetizing powerful magnets, but in normal times we still prefer the AC demagnetization method. It has a better demagnetization effect than the high-temperature demagnetization method and the vibration demagnetization method and is also highly efficient. It is currently the most commonly used method in industrial production. method.
How to check coating quality? The quality of the coating directly affects the service life of NdFeB. The main methods for testing the quality of NdFeB coating are:
1) Visual inspection of appearance The appearance is mainly observed with the naked eye, preferably under natural light (sunlight, indirect sunlight), or under a fluorescent lamp with an illumination equivalent to 40W. There should be no blistering, peeling, partial plating, uneven color tone, stains, water stains, etc.
2), coating thickness measurement
3). Drop test (mainly for galvanized products)
4) Cross-hatch test (generally used for nickel-plated products)
5), Chill and heat test
6), PCT pressure test
7), SST salt spray test
8), constant temperature and humidity test, etc.