20 general knowledge of magnets help you grasp the basics of magnetism. To be master of magnets in mintues.
Magnetic materials are closely related to our life, from the most common refrigerator refrigeration to the high-end maglev. We collect 20 general knowledge of magnets as below:
1. Why are magnets has magnetism?
2. how to define the performance of magnet?
3. How to divide metal magnetic materials?
4. Comparison of magnetic force of several kinds of commonly used magnets
5. How to compare the properties and prices of different magnetic materials?
6. Characteristics of NdFeB magnets
7. What is a single-sided magnet?
8. Purpose of single-sided magnet?
9. What are the precautions during the transportation of magnets?
10. How to achieve magnetic isolation?
11. Which ferrite material can conduct electricity?
12. What is the Curie temperature of permanent ferrite?
13. What are the effective parameters of the core?
14. Why is the radius of the corner circle very important for winding?
15. Which type of core is suitable for making transformer?
16. What kind of core is the best?
17. What is an anti-interference magnetic ring?
18. How to demagnetize the core?
19. What is magnetoelasticity (magnetostriction)?
20. What is magnetic mismatch?
It will be not enough as encyclopedia of magnets. But it will help you grasp the basics of magnetism and be a master of magnets in minutes.
Most substances are made up of molecules, molecules are made up of atoms, and atoms are made up of nuclei and electrons. Inside an atom, the electrons rotate around the nucleus, both of which produce magnetism. However, in most materials, the direction of electron motion is different and disordered, and the magnetic effects cancel each other. As a result, most substances are not magnetic under normal conditions.
Ferromagnetic materials such as iron, cobalt, nickel or ferrite are different. The internal electron spin can be arranged spontaneously in a small range, forming a spontaneous magnetization region, which is called domain. After the ferromagnetic materials are magnetized, the internal magnetic domains are arranged neatly and in the same direction, so that the magnetism is strengthened, thus forming a magnet. The process of magnet absorbing iron is the process of magnetizing iron. The magnetized iron and different polarity of the magnet produce attraction, and the iron is firmly "stuck" with the magnet.
There are three main performance parameters 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 remanent magnetic induction strength.
Coercive force HC: to reduce the B of the permanent magnet magnetized to technical saturation to zero. The intensity of the reverse magnetic field to be added is called the magnetic inductive coercive force, which is called coercive force for short.
Magnetic energy product BH: represents the magnetic energy density established by the magnet in the air gap space (the space of two magnetic poles of the magnet), that is, the static magnetic energy per unit volume of the air gap.
Metal magnetic materials are divided into permanent magnetic materials and soft magnetic materials. Materials with intrinsic coercive force greater than 0.8ka/m are usually called permanent magnetic materials, and materials with intrinsic coercive force less than 0.8ka/m are called soft magnetic materials.
The magnetic force is arranged from large to small: neodymium iron boron magnet, samarium cobalt magnet, aluminum nickel cobalt magnet and ferrite magnet.
Ferrite: low and medium performance, lowest price, good temperature characteristics, corrosion resistance, good performance price ratio
Neodymium iron boron: highest performance, moderate price, good strength, not resistant to high temperature and corrosion
SmCo: high performance, highest price, brittleness, excellent temperature characteristics, corrosion resistance
Alnico: low and medium performance, moderate price, excellent temperature characteristics, poor corrosion resistance and interference resistance
Samarium cobalt, ferrite and neodymium iron boron can be manufactured by sintering and bonding methods. The sintered magnetic properties are high, forming is poor, forming property of bonded magnet is good, and performance is greatly reduced. Alnico can be manufactured by casting and sintering. The cast magnet has high performance, poor formability, and sintered magnet has low formability.
Neodymium iron boron permanent magnetic material is based on the intermetallic compound Nd2Fe14B. Neodymium iron boron (NdFeB) permanent magnet materials have been widely used in modern industry and electronic technology due to its high magnetic energy accumulation and coercive force and high energy density, which makes it possible to miniaturize, lighten and thin the instruments, electro acoustic motors, magnetic separation magnetization and other equipment.
Material characteristics: the advantages of NdFeB are high cost performance and good mechanical properties; the disadvantages are low Curie temperature point, poor temperature characteristics, and easy to be powdered and corroded. It must be improved by adjusting its chemical composition and adopting surface treatment methods to meet the requirements of practical application.
Manufacturing process: powder metallurgy process is used for manufacturing NdFeB.
Technological process: batching → smelting and ingot making → powder making → molding → sintering and tempering → magnetic detection → grinding → pin cutting → electroplating → finished product.
Magnets have two poles, but in some working positions, a single pole magnet is needed, so one side of the magnet needs to be wrapped by iron sheets, so that the one side of the magnet wrapped by the iron sheets is shielded, and the magnet refracted to the other side through the iron sheets can enhance the magnetic force of the other side. Such magnets are collectively referred to as single-sided magnets or single-sided magnets. There is no real one-sided magnet.
The materials used for single-sided magnets are generally arc-shaped iron sheets and NdFeB powerful magnets, and the shapes of NdFeB powerful magnets used for single-sided magnets are generally round sheets.
(1) Printing industry is widely used in gift box, mobile phone box, tobacco and wine box, mobile phone box, MP3 box, moon cake box and so on.
(2) Leather goods are widely used in the industry, such as luggage, briefcase, travel bag, mobile phone case, wallet and so on.
(3) Stationery industry is widely used, notebook, whiteboard buckle, folder, magnetic nameplate and so on have the existence of single-sided magnet.
To pay attention to the indoor humidity, it must be kept at a dry level. The temperature shall not exceed room temperature; the products in black block or blank state can be properly oiled (general engine oil is enough); the electroplated products shall be stored in vacuum sealed or isolated air to ensure the corrosion resistance of the coating; the magnetized products shall be sucked together and packed for storage so as not to suck up other metal bodies; the magnetized products shall be stored away from disk, magnetic card, magnetic tape and computer display Devices, watches and other objects sensitive to magnetic field. Magnets should be shielded during transportation in magnetized state, especially in air transportation.
Only the material that can be adsorbed on the magnet can play the role of magnetic field isolation, and the thicker the material, the better the effect of magnetic field isolation.
Soft magnetic ferrite is a kind of magnetic conducting material, which has high specific permeability and high resistivity. It is generally used at high frequency and mainly used for electronic communication. Like the computers and televisions we touch every day, there are applications in them.
The soft ferrite mainly consists of manganese zinc and nickel zinc. The permeability of manganese zinc ferrite is higher than that of nickel zinc ferrite.
It is reported that the Curie temperature of ferrite is about 450 ℃, usually more than or equal to 450 ℃. The hardness is about 480-580. Curie temperatures of NdFeB magnets are generally between 350-370 ℃. But the use temperature of NdFeB magnet can't reach Curie temperature. The magnetic properties of NdFeB magnet with temperature over 180-200 ℃ have declined a lot, the magnetic loss is also very large, and it has lost its use value.
The magnetic core, especially the ferrite material, has various geometric dimensions. In order to meet the requirements of different designs, the size of the 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.
The reason why the angle radius is important is that 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. Make sure the edge of the core is smooth. There is a certain standard roundness radius in the mold for making ferrite cores, and these cores are polished and deburred to reduce the sharpness of their edges. In addition, most cores are painted or covered to not only passivate their corners, but also make their winding surface smooth. The powder core has a pressure radius on one side and a semicircle for deburring on the other. For ferrite materials, an additional edge cover is provided.
The core 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 core should have a certain air gap to ensure that it has a certain level of permeability under the condition of high DC or AC drive. Ferrite and band core can be treated by opening air gap. The powder core has its own air gap.
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 occasions and application frequency, and there are market and other factors in the selection of any material. For example, some materials can ensure that their temperature rise is small, but their prices are expensive, so when selecting materials for higher temperature rise, it is possible to choose a larger scale Inch but lower price materials to complete such work, so the so-called best material selection should first be based on the application requirements of your inductor or transformer. In this regard, its operation frequency and cost are important factors. The optimal selection of different materials is determined according to the switching frequency, temperature rise and magnetic flux density.
Anti interference magnetic ring is also called ferrite magnetic ring. The anti-interference magnetic ring is called source because it can play an anti-interference role. For example, the electronic products are interfered by the external disorder signals and intrude into the electronic products, which cause the electronic products to receive the interference of the external disorder signals and fail to operate normally. The anti-interference magnetic ring just has this function. As long as the product is added with the anti-interference magnetic ring, it can prevent the external disorder signals from intruding into the electronic products and enable electricity The normal operation of the sub product has anti-interference effect, so it is called anti-interference magnetic ring.
Anti interference magnetic ring is also called ferrite magnetic ring, because it is made of iron oxide, nickel oxide, zinc oxide, copper oxide and other ferrite materials, because these materials contain ferrite components, and the products made of ferrite materials are like a ring, which is called ferrite magnetic ring for a long time.
The method is to apply 60Hz alternating current to the core so that the starting driving current is enough to make it saturated at both positive and negative ends, and then slowly reduce the driving level, and repeat several times until it is reduced to 0. This will make the retention point return to the original initial state.
After the magnetization of the magnetic material, there will be a small change in the geometric size. The size of the change should be a few parts per million, which is called magnetostriction. For some applications, such as ultrasonic generators, the advantages of this feature are used to obtain mechanical deformation through magnetostriction under magnetic excitation. In other applications, when working in the audible audio range, there will be a kind of howling noise. Therefore, low magnetic shrinkage materials can be used in this case.
This phenomenon occurs in ferrite, which shows that the permeability decreases when the core is demagnetized. This demagnetization can occur when the operating temperature is higher than the Curie point temperature, and the amplitude of AC or mechanical vibration can be reduced gradually.
In this phenomenon, the permeability first increases to its original level, and then decreases exponentially and rapidly. If there is no special condition for the application to expect, the permeability change will be very small, because many changes will occur within a few months after the production. High temperature accelerated the decrease of permeability. Magnetic incongruity will reappear after each successful demagnetization, so it is different from aging.
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