Why are magnets magnetic?
Matter is mostly composed of molecules, molecules are composed of atoms, and atoms are composed of nuclei and electrons. Inside the atom, the electrons are constantly rotating on their own axis and orbiting the nucleus. Both of these movements of the electrons will generate magnetism. But in most substances, the electrons move in different directions and are chaotic, and the magnetic effects cancel each other out. Therefore, most substances are not magnetic under normal conditions.
Ferromagnetic substances such as iron, cobalt, nickel, or ferrite are different. The electron spins inside it can be spontaneously arranged in a small range to form a spontaneous magnetization region, which is called a magnetic domain. After the ferromagnetic material is magnetized, the internal magnetic domains are arranged neatly and in the same direction, which strengthens the magnetism and constitutes a magnet. The iron-absorbing process of the magnet is the magnetization process of the iron block. The magnetized iron block and the different polarities of the magnet generate attractive force, and the iron block is firmly "sticked" to the magnet.
How to define the performance of the magnet?
There are mainly three performance parameters as follows to determine the performance of the magnet:
Remanence Br: After the permanent magnet is magnetized to technical saturation and the external magnetic field is removed, the retained Br is called the residual magnetic induction.
Coercive force Hc: To reduce the B of the permanent magnet magnetized to technical saturation to zero, the required reverse magnetic field strength is called the magnetic induction coercive force, or coercive force for short.
Magnetic energy product BH: It 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.
How to divide metal magnetic materials?
Metal magnetic materials are divided into two categories: permanent magnetic materials and soft magnetic materials. Generally, materials with intrinsic coercive force greater than 0.8kA/m are called permanent magnetic materials, and materials with 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 is arranged from large to small: NdFeB magnets, SmCo magnets, AlNiCo magnets, and ferrite magnets.
What is the cost-effective comparison of different magnetic materials?
Ferrite: low and medium performance, lowest price, good temperature characteristics, corrosion resistance, good cost performance 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. Sintered magnets have high magnetic properties but poor molding. Bonded magnets have good formability and much lower performance. AlNiCo can be manufactured by casting and sintering methods. Cast magnets have higher performance and poor formability, while sintered magnets have lower formability and better formability.
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, so that instruments and meters, electroacoustic motors, magnetic separation and magnetization Miniaturization, light weight, and thinning of equipment such as equipment become possible.
Material characteristics: NdFeB has the advantages of high-cost performance and good mechanical properties; the disadvantage is that the Curie temperature is low, the temperature characteristics are poor, and it is easy to powder and corrode. It must be used by adjusting its chemical composition and adopting surface treatment methods. It can be improved to meet the requirements of practical application.
Manufacturing process: The manufacture of NdFeB adopts powder metallurgy process. Process flow: batching → smelting ingot making → powder making → pressing → sintering and tempering → magnetic testing → grinding → pin cutting → electroplating → finished product.
What is a single-sided magnet?
Magnets have two poles, but in some working positions a single-sided pole magnet is required, so it is necessary to wrap one side of the magnet with an iron sheet, so that the magnetism of the side covered by the iron sheet is shielded, and the magnetism on the other side is refracted through the iron sheet. Magnets can enhance the magnetic force of the magnet on the other side. Such magnets are collectively referred to as single-sided magnets or single-sided magnets. There are no true single-sided magnets.
The materials used for single-sided magnets are generally arc-shaped iron sheets and NdFeB strong magnets, and the shape of NdFeB strong magnets used for single-sided magnets is generally in the shape of a disc.
What is the purpose of single-sided magnet?
It is widely used in the printed matter industry. There are single-sided magnets in gift packaging boxes, mobile phone packaging boxes, tobacco and alcohol packaging boxes, mobile phone packaging boxes, MP3 packaging boxes, moon cake packaging boxes, etc.
It is widely used in the leather goods industry. There are single-sided magnets in leather goods such as bags, briefcases, travel bags, mobile phone cases, and wallets.
It is widely used in the stationery industry, and there are single-sided magnets in notebooks, whiteboard clasps, folders, magnetic nameplates, etc.
What precautions should be taken during the transportation of magnets?
Pay attention to the humidity in the room, which must be maintained at a dry level. The temperature should not exceed room temperature; when storing products in the black block or rough state, oil can be properly applied (ordinary engine oil is enough); electroplated products should be stored in a vacuum seal or isolated from the air to ensure the corrosion resistance of the coating; magnetized products should be closed Store together and in a box to avoid picking up 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. The magnet should be shielded when transported in a magnetized state, especially air transport must be completely shielded.
How to achieve magnetic isolation?
Only materials that can be adsorbed to the magnet can play the role of isolating the magnetic field, and the thicker the material, the better the effect of magnetic isolation.
Which ferrite material can conduct electricity?
Soft magnetic material Ferrite is a magnetic material with high magnetic permeability and high resistivity. It is generally used at high frequencies and is mainly used for electronic communications. Like computers and TVs that we touch every day, there are applications in them. Soft ferrites mainly include manganese zinc and nickel zinc, etc., and the magnetic permeability of manganese zinc ferrite is higher 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. The hardness is around 480-580. The Curie temperature of NdFeB magnets is basically between 350-370 °C. However, the use temperature of NdFeB magnets cannot reach the Curie temperature, and the magnetic properties have been attenuated a lot when the temperature exceeds 180-200 °C, and the magnetic loss is also very large, which has lost its use value.
What are the effective parameters of the magnetic core?
Magnetic cores, especially ferrite materials, come in a variety of geometries and dimensions. In order to meet the requirements of various designs, the size of the magnetic core is also calculated to meet the optimization requirements. These existing core parameters include physical parameters such as magnetic path, effective area, and effective volume.
Why is the corner radius very important for winding?
The corner radius is important because if the edge of the core is too sharp, it is possible to cut the insulation of the wire during the precise and tight winding process. Take care to ensure that the edges of the core are rounded. Ferrite core molds have a certain standard roundness radius, and these cores are polished and deburred to reduce the sharpness of their edges. In addition, most magnetic cores are painted or covered to not only passivate the corners, but also make the winding surface smooth. Powder cores have a pressure radius on one side and a deburring semicircle on the other. For ferrite materials, an additional edge cover is provided.
Which type of magnetic core is suitable for making a transformer?
The magnetic core that meets the needs of the transformer should have a 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 level of magnetic permeability under high dc or ac driving conditions. Both ferrite and ribbon cores can be treated with air gaps. Powder cores have their own Comes with air gap.
What kind of magnetic core is the best?
It should be said that there is no answer to this question, because the selection of the magnetic core is determined according to the application occasion and application frequency, etc. The selection of any material also has factors such as the market to consider. Smaller, but it is expensive, so that when choosing a material for a higher temperature rise, it is possible to choose a larger size but lower price material to complete such a job, so the so-called best material The choice of the inductor or transformer should 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 based on switching frequency, temperature rise, and magnetic flux density.
What is the anti-interference magnetic ring?
Anti-interference magnetic rings are also called ferrite magnetic rings. The source of the name of the anti-jamming magnetic ring is that it can play an anti-jamming role. For example, electronic products are disturbed by external turbulent signals and invade electronic products, so that electronic products receive interference from external turbulent signals and fail to operate normally, while anti-jamming magnetic rings, It happens to have this function, as long as the product is added with an anti-jamming magnetic ring, it can prevent external disturbance signals from invading electronic products, make electronic products operate normally, and play an anti-interference effect, so it is called anti-jamming magnetic ring.
Anti-interference magnetic ring is also called ferrite magnetic ring, because 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 made of ferrite material is like a ring, so it is called ferrite magnetic ring over time.
How to demagnetize the core?
The method is to apply 60Hz alternating current to the core so that its initial drive current is sufficient to saturate both the positive and negative terminals, and then gradually and slowly reduce the drive level, repeating several times until it drops to zero. This will restore its holding point back to its original initial state.
What is magnetoelasticity (magnetostriction)?
After the magnetic material is magnetized, there will be a small geometric change. The size of this change should be at the level of a few parts per million, which is called magnetostriction. Some applications, such as sonotrodes, take advantage of this property to obtain mechanical deformation through magnetically actuated magnetostriction. In some other applications, when working in the audible frequency range, there will be a whistling noise. Therefore, low magnetic shrinkage materials can be applied in this case.
What is magnetic mismatch?
This phenomenon occurs in ferrites and manifests itself as a drop in permeability that occurs when the core is demagnetized. This demagnetization can occur after the operating temperature is higher than the Curie point temperature, the application of alternating current or mechanical vibration with a gradually decreasing amplitude, etc.
In this phenomenon, the permeance first increases to its original level and then rapidly decreases exponentially. If no special conditions are desired for the application, then the change in permeability will be small, since many changes occur within a few months of fabrication. High temperatures accelerate this decrease in permeability. Magnetic dissonance will repeat after each successful demagnetization, so it is not the same as aging.