China permanent magnet manufacturer:

Summary of characteristics, technology and testing knowledge of magnetic materials

Magnetic materials are closely related to our lives, from the most common refrigerator refrigeration to high-end maglev, are inseparable from them. So, let’s get to know about this amazing material.

Why does the magnet have magnetism?

Most of the matter is composed of molecules, which are composed of atoms, and atoms are composed of atomic nuclei and electrons. Inside the atom, electrons rotate constantly and rotate around the nucleus, and both of these movements produce magnetism. But in most materials, the direction of electron motion is different and disorderly, and the magnetic effect is offset. Therefore, most substances do not normally appear magnetic.
Ferromagnetic substances such as iron, cobalt, nickel or ferrite are different. The internal spin of ferromagnetic materials can be arranged spontaneously in a small range, forming a spontaneous magnetization region, which is called magnetic domain. After magnetization of ferromagnetic materials, the inner magnetic domains are arranged in a uniform and uniform direction, which makes the magnetic stronger, and forms a magnet. The process of iron absorption of magnet is the magnetization process of iron block. The magnetized iron block and magnet have different polarity attraction. The iron block is firmly “stuck” with the magnet.

How to define the performance of the magnet?

The main performance parameters are 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 residual magnetic induction strength.
Coercive force HC: to reduce the magnetization to zero of the technically saturated permanent magnet, the required reverse magnetic field strength is called magnetic sense coercivity, or coercivity.
Magnetic energy product BH: represents the magnetic energy density established by the magnet in the air gap space (the magnetic two pole space), that is, the static magnetic energy per unit volume of the air gap.

How to divide the metal magnetic materials?

Metal magnetic materials are divided into permanent magnet materials and soft magnetic materials. Generally, the materials with intrinsic coercive force greater than 0.8ka/m are called permanent magnet materials, and those with intrinsic coercive force less than 0.8ka/m are called soft magnetic materials.

Comparison of magnetic force of several kinds of common magnets

The magnetic force is arranged from large to small: neodymium iron boron magnet, samarium cobalt magnet, aluminum nickel cobalt magnet and ferrite magnet.

Analogy of the properties and prices of different magnetic materials?

Ferrite: low and medium performance, lowest price, good temperature characteristics, corrosion resistance, good performance price ratio.
NdFeB: the highest performance, high price, good strength, high temperature and corrosion resistance
Samarium cobalt: high performance, highest price, brittle, excellent temperature characteristics, corrosion resistance.
Aluminum nickel cobalt: low and medium performance, price, excellent temperature characteristics, corrosion resistance and poor interference resistance.
Samarium cobalt, ferrite, Nd-Fe-B can be manufactured by sintering and bonding methods. The sintering magnetic properties are high, forming is poor, and the forming property of bonded magnets is good and the properties are reduced. Alnico can be manufactured by casting and sintering methods. The casting magnet has high properties, poor formability, low sintering magnet and good formability.

Characteristics of NdFeB magnet

NdFeB permanent magnet is a permanent magnet material based on the intermetallic compound Nd2Fe14B. NdFeB has high magnetic energy accumulation and coercion, and the advantages of high energy density make NdFeB permanent magnet materials widely used in modern industry and electronic technology, so that the miniaturization, lightweight and thin shape of instruments, electro acoustic motors, magnetic separation magnetization and other equipment can be made possible.
Material characteristics: NdFeB has the advantages of high cost performance and good mechanical properties; the disadvantage is that Curie temperature is low, temperature characteristics are poor, and it is easy to be powdered and corroded. It is necessary to improve it by adjusting its chemical composition and surface treatment method, so as to meet the requirements of practical application.
Manufacturing process of NdFeB magnet: powder metallurgy is used for the manufacture of NdFeB.
Process flow: ingredients → smelting ingot → powder making → pressing → sintering and tempering → magnetic testing → grinding → marketing cutting → electroplating → finished products.

What is a single magnet?

Magnets have two poles, but in some working positions, one side magnet needs to be wrapped with iron sheet, so that the magnetic field covered by the iron sheet is shielded, and the magnet on the other side is enhanced by refraction of the iron sheet to enhance the magnetic force of the other side. Such magnets are collectively referred to as single-sided magnet or single-sided magnet. There is no real single-sided magnet.
The materials used for single-sided magnets are generally arc-shaped iron sheet and NdFeB strong magnet, while the shape of NdFeB powerful magnet used for single-sided magnet is generally round.

The use of single side magnet?

  • (1) Printing products are widely used in the gift packaging box, mobile phone packaging box, tobacco and wine packaging box, mobile phone packaging box, MP3 packaging box, moon cake packaging box and other products.
  • (2) Leather industry is widely used, bags, briefcase, travel bags, mobile phone cases, wallets and other leather goods have the existence of single-sided magnets.
  • (3) Stationery industry is widely used, notebook, white buckle, folder, magnetic nameplate and so on have the existence of single-sided magnet.

What precautions are there in the process of magnet transportation?

To pay attention to 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 coated (general oil can be used); electroplating products shall be stored in vacuum sealed or isolated air to ensure the corrosion resistance of coating; magnetizing products shall be sucked together and packed to avoid absorbing other metal bodies; the magnetizing products shall be stored away from disk, magnetic card, tape and computer display A device, watch, etc. sensitive to magnetic field. The magnet should be shielded when it is transported in magnetization state, especially in air transportation.

How to achieve magnetic isolation?

Only the material that can be adsorbed on the magnet can play the role of separating magnetic field, and the thicker the material, the better the magnetic isolation effect.

Which ferrite material can conduct electricity?

The ferrite of soft magnetic material belongs to magnetic guide material, which is generally used in high frequency and mainly used in electronic communication. Like the computers and TV we touch every day, there are applications in it.
The main soft ferrite is manganese zinc and nickel zinc, and the permeability of Mn Zn ferrite is higher than that of Ni Zn ferrite.

What is the Curie temperature of permanent magnet oxygen body?

It is reported that the Curie temperature of ferrite is about 450 ℃, usually greater than or equal to 450 ℃. The hardness is about 480-580. The Curie temperature of NdFeB magnets is between 350-370 ℃. But the temperature of NdFeB magnets can not reach the Curie temperature. The magnetic properties of NdFeB magnets are much reduced and the magnetic loss is very large, which has lost the use value.

What are the effective parameters of the core?

Magnetic core, especially ferrite material, has many kinds of geometric dimensions. To meet the requirements of various 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.

Why is the radius of the corner circle very important for winding?

The reason why the angular radius is important is that if the edge of the core is too sharp, it is possible to break the insulation of the wire during the precise and tight winding process. Pay attention to ensure the edge of the core is smooth. The mold for ferrite core manufacturing has a certain standard radius of roundness, and these cores are polished and deburring to reduce the sharpness of its edges. In addition, most cores are painted or covered to not only passivate the angle, but also make the winding surface smooth. The powder core has a pressure radius on one side and a semicircle for deburring. For ferrite materials, an additional edge cover is provided.

Which type of core is suitable for transformer production?

The core which meets the needs of transformer should have high magnetic induction strength on one hand and keep its temperature rise within a certain limit.
For inductors, the core should have a certain air gap to ensure that it has a certain permeability level under the condition of high DC or AC drive. Both ferrite and band core can be opened air gap treatment, and the powder core has its own air gap.

What kind of core is the best?

It should be said that there is no answer to this question, because the choice of magnetic core is determined according to the application situation and application frequency. For example, some materials can ensure that the temperature rise is small, but the price is expensive. Therefore, when selecting materials to meet the higher temperature rise, it is possible to choose a larger ruler The materials with low price are used to complete such work. Therefore, the selection of the best materials should be based on the application requirements of your inductor or transformer. In this regard, the operating frequency and cost are important factors. The optimization of different materials is determined according to the switching frequency, temperature rise and flux density.

What is the anti-interference magnetic ring?

The anti-interference magnetic ring is also known as ferrite magnetic ring. The source of anti-interference magnetic ring is that it can play an anti-interference role. For example, electronic products are subject to external disturbance signals, and invade electronic products, so that electronic products receive interference from external disturbance signals and can not operate normally. The anti-interference magnetic ring can have this function. As long as the product is added with anti-interference magnetic ring, it can prevent the external disturbance signal from invading electronic products and make electric power The sub-product is in normal operation and has the anti-interference effect, so it is called anti-interference magnetic ring.
The anti-interference magnetic ring is also called ferrite magnetic ring, because it is made of ferrite materials such as iron oxide, nickel oxide, zinc oxide, copper oxide, etc. because these materials contain ferrite components, and the products made of ferrite materials are like a ring, which has been called ferrite magnetic ring for a long time.

How to demagnetize the core?

The method is to apply 60Hz AC to the core so that the starting driving current is enough to saturate the core at both positive and negative ends, then slowly reduce the driving level gradually, repeat several times until it is reduced to 0. This will make its hold point return to its original state.

What is magnetoelasticity (magnetostriction)?

After magnetization of magnetic materials, there will be a small change in geometric size. This change should be at a level of a few millionths, which is called magnetostriction. For some applications, such as ultrasonic generators, it uses the advantages of this feature to obtain mechanical deformation through magnetostriction excited by magnetic excitation. In other applications, when working in the audible range, there will be a kind of noise. Therefore, the low shrinkage materials can be applied to this situation.

What is magnetic mismatch?

This phenomenon occurs in ferrite, which shows that the permeability decreases after the core demagnetization. This demagnetization can be found after the operating temperature is higher than the Curie point temperature, and the AC or mechanical vibration with decreasing amplitude can be applied.
In this phenomenon, the permeability increases to its original level first, and then decreases exponentially. If there are no special conditions expected for the application, the permeability will change very little, because many changes will change within months after fabrication. The high temperature accelerated the decrease of the permeability. Magnetic incongruity will occur repeatedly after each successful demagnetization, so it is different from aging.

Knowledge of processing technology

Characteristics and processing technology of ferrite magnet?

Features: its main raw materials include BaFe12O19 and SrFe12O19. It is made by ceramic technology, which is of relatively hard texture and belongs to brittle material. Because of its good temperature resistance, low price and moderate performance, ferrite magnet has become the most widely used permanent magnet.
Characteristics: it has high magnetic properties, better time stability and lower temperature coefficient.
Ferrite magnet application: widely used in meters, meters, motors, automatic control, microwave devices, radar and medical devices.
Direction of magnetization of ferrite magnet: it can be magnetized axially, radially or as required.
Ferrite magnet shape: can produce cylindrical, circular, rectangular, flat, tile, axe shaped.

Characteristics and processing technology of aluminum nickel cobalt magnet

Characteristics of aluminum nickel cobalt magnet: it is an alloy composed of aluminum, nickel, cobalt, iron and other trace metal elements. Casting process can be processed into different sizes and shapes, and it has good processability. The permanent magnet of casting aluminum nickel cobalt has the lowest reversible temperature coefficient, and the working temperature can be as high as 600 ℃. Aluminum nickel cobalt permanent magnet products are widely used in various instruments and other applications.
Classification of aluminum nickel cobalt magnets: it can be divided into two categories: cast aluminum nickel cobalt and sintered aluminum nickel cobalt.
Application site: casting aluminum nickel cobalt products are mainly used in automobile parts, instruments, electroacoustic, motor, teaching and aerospace and military fields, and have the advantages of low temperature coefficient, high temperature resistance, humidity resistance, non oxidation and good working stability. Sintered aluminum nickel cobalt is made by powder metallurgy, which is suitable for the production of complex, light, thin and small products, and widely used in instruments, communication, magnetoelectric switches and various sensors.
Shape of aluminum nickel cobalt magnet: it can produce cylindrical, circular, rectangular, flat, tile and horseshoe.

Characteristics and processing technology of samarium cobalt magnet?

Samarium cobalt magnet is also called samarium cobalt magnetic steel, samarium cobalt permanent magnet, samarium cobalt permanent magnet, samarium cobalt strong magnet, rare earth cobalt permanent magnet, etc. It is a kind of magnetic material made of samarium, cobalt and other metal rare earth materials after mixing, melting into alloy, crushing, pressing and sintering. It has high magnetic energy product and very low temperature coefficient. The maximum working temperature can reach 350 ℃, negative temperature is unlimited. When the working temperature is over 180 ℃, the maximum magnetic energy product, temperature stability and chemical stability are higher than NdFeB permanent magnet materials. It has strong anti-corrosion and anti-oxidation properties, so it is widely used in aerospace, national defense and military industry, microwave devices, communication, medical equipment, instruments, instruments, various magnetic transmission devices, sensors, magnetic processors, motors, magnetic cranes, etc.
The production process of samarium cobalt magnet: ingredients → ingot smelting → powder making → pressing → sintering and tempering → magnetic detection → grinding → cutting and marketing processing → finished products.
Samarium cobalt magnet shape: round plate, ring, square piece, square strip, tile shape, special shape can be processed according to requirements.

Magnetic field orientation and pressure type

The orientation of powder magnetic field is one of the key technologies for manufacturing high performance sintered magnet. The purpose of magnetic field orientation is to make the magnetization direction (c axis) of each powder particle oriented in the same direction, and to make anisotropic magnet. Then there is the largest residual magnet br along the direction of the c axis orientation of the powder particle, thus improving the maximum magnetic energy product of the magnet. The orientation of powder has an important influence on the residual magnetic BR and the maximum magnetic energy product (BH) max of the magnet. There are two purposes for powder pressing: one is to press the powder into a certain shape and size blank according to the user’s needs; the other is to maintain the crystal orientation obtained in the magnetic field orientation. There are three commonly used pressing methods: die pressing, cold isostatic pressure and rubber die pressing (cold isostatic pressure). The molding process is the main process of oxygen absorption of magnetic powder, so there are strict oxidation prevention measures in the forming process, which requires the magnetic particle weighing or pressing process to work under the protection of inert gas. The equipment used in this process is a molding press.

Orientation direction of magnet?

Sintered NdFeB permanent magnet is an anisotropic magnet. Orientation direction: the direction in which anisotropic magnets can obtain the best magnetic properties is called the orientation direction of magnet, also known as “orientation axis”, “easy magnetization axis”.

How to judge the magnetization direction of magnet?

Magnetic pole test piece can be used. The principle of pole test piece is to put some iron powder in the partition layer and clamp it with transparent things. When there is magnetic force, the magnetic particle of interlayer will attract past, and the magnetic field is no magnetic particle, so the distribution of magnetic pole can be observed.

Which magnet can be used in water?

Not every magnet can be used in water, depending on the material. A corrosion and rust magnet can harm aquatic life. Ferrite has strong corrosion resistance and oxidation resistance, and can be used in water normally.

What is magnetic tile?

Magnetic tile is a kind of tile magnet which is mainly used in permanent magnet motor.

What are the production processes of ferrite magnetic tile?

The ferrite magnetic tile is mainly sintered ferrite.
The production process of sintered ferrite magnetic tile is mainly divided into wet pressure, dry pressure and dry pressure. The difference between the two is whether there is a magnetic field orientation during press forming. This paper mainly introduces the wet pressure heterosexual process.
The wet pressing process is as follows: raw material → pre burning → coarse grinding (primary ball milling) → ingredients → secondary ball milling (wet grinding) → magnetic field forming → sintering → grinding → cleaning → magnetization.
Because the molding slurry contains water, the particles can be easily turned in magnetic field, so the higher orientation degree is obtained than the dry pressure difference performance, and the performance is higher.

Production process of NdFeB magnetic tile

Sintering nd Fe-B magnetic tile: ingredients, melting, crushing, powder making, magnetic field forming, isostatic pressure, vacuum sintering and tempering, wire cutting, etc. → electroplating → magnetization.

Selection of cleaning method of workpiece?

The placement of workpiece in the cleaning tank has a great relationship with the cleaning quality, and its placement mode is related to the size, shape and structure of the workpiece. Generally speaking, overlapping stacking between workpieces or excessive stacking at a time will affect the cleaning effect.
Although the NdFeB magnetic materials are of different shapes, they are mostly small parts. It can be placed on nylon net and shaken in the cleaning tank, which will help the dirt on the surface of the workpiece to fall off, and also to the damage of water film with blind hole workpiece, which makes the blind hole easy to produce cavitation effect. Another way is to spread the workpiece directly on the bottom plate of the cleaning tank (that is, the radiation plate of ultrasonic transducer), so that the workpiece can bear strong ultrasonic impact. The practice shows that the method of cleaning the workpiece directly on the bottom plate has the best cleaning effect and the highest efficiency.

What precautions are there in the process of magnet transportation?

To pay attention to 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 coated (general oil can be used); electroplating products shall be stored in vacuum sealed or isolated air to ensure the corrosion resistance of coating; magnetizing products shall be sucked together and packed to avoid absorbing other metal bodies; the magnetizing products shall be stored away from disk, magnetic card, tape and computer display A device, watch, etc. sensitive to magnetic field. The magnet should be shielded when it is transported in magnetization state, especially in air transportation.

What is a strong magnet?

Strong magnet refers to NdFeB magnet. Its magnetic properties greatly exceed ferrite magnets, aluminum nickel cobalt and samarium cobalt. NdFeB magnets can absorb 640 times the weight of their own, so NdFeB is often called a strong magnet by people outside the industry.

How to demagnetize the strong magnet?

According to the use of strong magnet, a certain method can be developed to demagnetize.
1) High temperature demagnetization method:
The main operation of high temperature demagnetization is to put the magnet into the high temperature furnace for heating. After high temperature treatment, the magnetic properties of the strong magnet will be removed. However, in the heating process, the structure of the objects inside the magnet will be changed dramatically because of the high temperature effect. Therefore, the demagnetization method will be used for the scrap and recovery magnets.
2) Vibration demagnetization method:
This method is simple to operate, which is to vibrate strongly and violently. After the vibration operation, the internal structure of the magnet has changed, so as to change the physical properties of the magnet. Generally speaking, the demagnetization method has little effect, and can only be used temporarily with less demagnetization.
3) Magnetic AC demagnetization method:
This method of demagnetization is to say that the magnet is put into a space that can produce AC magnetic field. After the interference of AC magnetic field, the internal structure of the magnet will be disrupted, thus the demagnetization can be achieved. This method is a common method of demagnetization.
The above three methods are effective for demagnetization of strong magnets. But in general, we should choose AC demagnetization method. It is better than that of high temperature demagnetization and vibration demagnetization, and it is also highly efficient. It is the most widely used method in industrial production.

How to detect the coating quality?

The quality of coating directly affects the service life of NdFeB. The main methods of quality detection of NdFeB coating are as follows:
1. Visual inspection of appearance
The appearance is mainly observed by naked eye, and it is best under natural light (sunlight, non direct direction), or under fluorescent lamp with illumination equivalent to 40W. There should be no blistering, peeling, partial plating and uneven color, stains, water stains, etc.
2. Coating thickness measurement;
3. Drop test (mainly for galvanized products);
4. Grid test (generally used for nickel plating products);
5. The experiment of heat shock;
6. PCT pressure test;
7. SST salt spray test;
8. Constant temperature and humidity test, etc.

What should be paid attention to when measuring the particle size distribution of Nd-Fe-B powder by laser particle size meter?

NdFeB particles have strong magnetic properties, and generally measure the average particle size by air permeability method. At present, it is mainly used for measuring the particle size distribution by dry laser particle size meter. NdFeB powder has the characteristics of spontaneous combustion in air, and when the ambient temperature is slightly high, it will ignite itself when the concentration reaches a certain degree. It will often lead to the burning of vacuum cleaner pipeline and filter screen and burn the vacuum cleaner. The following measures should be taken to prevent spontaneous combustion: (1) inert gas such as high pressure nitrogen shall be used as the source; (2) the vacuum cleaner pipe shall be replaced with polyethylene pipe with smooth surface so that particles will not deposit in the pipeline; (3) water filter vacuum cleaner shall be selected.

Which motors will use NdFeB magnetic tile?

NdFeB is a permanent magnet material and an indispensable part of permanent magnet. Rare earth permanent magnet motor is the largest application field of NdFeB magnet, accounting for 70% of the total magnet, and the number of VCM (ring motor) matched by computer hard disk accounts for 40% – 50%. Therefore, the computer industry is the largest user of permanent magnet motor.
The common permanent magnet motors are: permanent magnet DC motor and permanent magnet alternating current motor.
Permanent magnet DC motor: Brush DC motor, brush less motor, step motor, etc.
Permanent magnet AC motor: synchronous permanent magnet motor, permanent magnet servo motor, etc.

How to apply NdFeB magnetic tile in brush less motor?

As we all know, NdFeB magnetic tile or NdFeB radial magnetic ring is as important as human heart in motor products. When the current is energized, the magnetic field generated by the coil drives the magnetic field of NdFeB magnetic tile or NdFeB radial magnetic ring. Therefore, the magnetic field of NdFeB magnetic tile or NdFeB radial magnetic ring is strong and weak, and the operation efficiency of the motor is very important. Let’s first look at the advantages of the BLDCM:

  • 1. The brush is removed by the brush free and low-interference BLDCM. The most direct change is that there is no spark generated when the brush motor is running, which greatly reduces the interference of the electric spark to the remote control radio equipment.
  • 2. The advantages of low noise, smooth operation without brush, greatly reduced friction, smooth operation and low noise, this advantage is a huge support for the stability of the model operation.
  • 3. The service life is long, the low maintenance cost is less brush, the wear of the brush motor is mainly on the bearing. From the mechanical point of view, the brush free motor is almost a maintenance free motor. If necessary, only some dust removal maintenance is required.

As the name implies, the brush element is definitely not needed. A magnetic field around the winding coil is formed which rotates around the geometric axis of the motor. This magnetic field drives the permanent magnet steel on the rotor to rotate, and the motor turns. The performance of the motor is related to the number of NdFeB magnetic tiles, the magnetic flux strength of Nd-Fe-B radial magnetic ring, the input voltage of the motor and other factors, which really determines its making The performance of the electronic governor is still brush free. The good electronic governor needs the overall control of the process of single chip control program design, circuit design, complex processing technology, so the price is much higher than that of the brush motor.

Comparison of the properties of ferrite and NdFeB?

Appearance: iron oxygen constitution is loose and has no metal luster, generally does not electroplate, usually black. NdFeB should be electroplated basically, otherwise it is easy to rust. The surface has silver and white metallic luster.
Magnetic force: according to the data, it is found that the ferrite magnetic force is usually 800-1000 Gauss and the density is 5 (g/cm3). In the state of bare magnetic, the magnetic force of NdFeB can reach 3500 Gauss. The density was 7.5 (g/cm3).
Performance: the ferrite has good temperature and stability, compared with the normal temperature resistance of NdFeB is only 80 degrees. And the price is cheap. NdFeB has the characteristics of small volume, light weight and strong magnetism, and the magnetic properties are completely different from ferrite.
Price: ferrite is usually cheap, many of which are calculated by piece, and the price has influence on the shape, size and processing difficulty of ferrite. NdFeB: the price of NdFeB is changing almost every day, depending on the brand and special requirements you need to use.

How to preserve NdFeB magnetic materials?

  • 1. NdFeB magnets should not approach electronic equipment, because there are positive and negative poles in the magnet itself. There is a circuit circuit. If it is close, it will affect the use of electronic equipment and control circuit.
  • 2. Magnets should not be stored in wet environment to avoid oxidation, which may cause appearance, physical properties and magnetic properties to change.
  • 3. People who are sensitive to metal objects will be rough and reddish if they approach magnets. If the above reaction occurs, do not contact the magnet.
  • 4. Do not approach magnets to floppy disks, hard drives, credit cards, tapes, memory cards, TV tubes, etc. If magnet is close to magnetic recorder, it will affect or even destroy the recorded data.


  • 1. Magnet must not be placed around strong current;
  • 2. Magnet can not be baked on fire, and it is heated;
  • 3. The magnet can not be knocked and vibrated violently;
  • 4. Small magnets cannot be put together with large magnets;
  • 5. The shoe magnet should also add a piece of soft iron to the two poles to connect the two poles, and invert the north and south poles of the adjacent magnets;
  • 6. Small magnets (such as magnetic needles) cannot be placed with large magnets.

When saving NdFeB magnets, the environmental requirements are drying, and also to prevent NdFeB magnets from meeting acid and alkali chemicals, so as to avoid the influence of NdFeB magnetic materials, corrosion, rust and other phenomena. So placing NdFeB magnetic material on a board is still good for avoiding moisture. Always be careful when storing magnets, because they will be absorbed together by themselves and may pinch your fingers. When magnets are adsorbed, they may also damage the magnet itself (by touching the edge angle or by striking cracks).
Source: China Permanent Magnet Manufacturer –



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