How to buy NdFeB permanent magnet?
How to buy NdFeB permanent magnet?
The main raw materials of NdFeB permanent magnet are 32% Nd, 64% Fe and 1% B (a small amount of Dy, TB, Co, Nb, GA, Al and Cu) Nd2Fe14B compound is used as the matrix of Nd2Fe14B ternary system permanent magnet material, and its composition should be similar to the molecular formula of Nd2Fe14B compound. However, when the distribution ratio of Nd2Fe14B is completely adopted, the magnetic properties of the magnet are very low, or even non-magnetic. Only when the content of Nd2Fe14B is more than that of Nd2Fe14B compound, the better permanent magnetic properties can be obtained.
Neodymium iron boron permanent magnetic material is an alloy of neodymium and iron oxide. As the latest result of the development of rare earth permanent magnetic materials, it is widely used because of its excellent magnetic properties, and is known as the “king of magnets” in the magnet industry Neodymium iron boron (NdFeB) has very high magnetic energy product and coercivity, and the advantages of high energy density make NdFeB permanent magnet materials widely used in modern industry and electronic technology. Many customers choose to buy magnets because there are many kinds of NdFeB permanent magnet materials. They may have such concerns. How should I choose a corresponding NdFeB permanent magnet material I need to customize this product. What’s the magnetic force specification, maximum magnetic energy product, working temperature, coercivity and so on? Now let’s talk about how to buy the NdFeB permanent magnet you need?
First of all, you need to determine the size of the magnetic force, and then choose a grade that can meet the requirements of the magnetic force, and the size is appropriate. You also need to consider the working temperature. For the working temperature above 80 degrees, you need to use the high temperature resistant model. You also need to pay attention to whether there is corrosiveness in the working environment, and electroplating is needed to work in the corrosive environment.
Production control of raw materials
Raw material production control, the production of raw materials must comply with national standards. Many businesses in order to benefit, drilling holes in raw materials, not up to national standards, so the performance of the magnet is reduced.
Testing of magnet materials
Vibration probe magnetometer, open circuit test BH curve, from room temperature to 300 ℃.
Magnetic force and temperature requirements for NdFeB magnets
According to the intrinsic coercivity Hcj, sintered NdFeB can be divided into N, m, h, SH, uh, eh and ah materials. According to a certain aspect ratio (L / d > 0.5) and environmental conditions, sintered NdFeB can be divided into three types.
- The maximum temperature of N material Hcj ≥ 12koe is 80 ℃;
- The maximum temperature of M material Hcj ≥ 14koe is 100 ℃;
- H material Hcj ≥ 17koe, the maximum temperature is 120 ℃;
- The maximum service temperature of SH material Hcj ≥ 20koe is 150 ℃;
- The maximum service temperature of uh material Hcj ≥ 25koe is 180 ℃;
- The maximum service temperature of EH material Hcj ≥ 30koe is 200 ℃;
- The maximum temperature of ah material Hcj ≥ 33koe is 230 ℃.
The Curie temperature of NdFeB is 312 ℃.
From the perspective of magnetism: NdFeB’s excellent magnetism is its biggest feature, which is also the reason why it can quickly base on the market. Choosing NdFeB magnet first depends on what kind of magnetism you need, and what kind of suction the size of the magnet needs. Of course, the shape of the magnet can be customized according to the needs of customers. On the premise of determining the size, we can choose the magnet From N35 to n52, the larger the number is, the stronger the magnetic force is. The magnetic force can be selected according to your specifications. The temperature is specific, below 80 degrees, choose n series, above 80 degrees, H series, 120 degrees resistance; SH series, 150 degrees resistance; uh series, 180 degrees resistance; and Eh and ah above 200 degrees.
Note: Curie point is also known as Curie temperature (TC) or magnetic transition point. It refers to the temperature at which the spontaneous magnetization of magnetic materials drops to zero, and it is the critical point at which ferromagnetic or ferromagnetic materials turn into paramagnetic materials. When the temperature is lower than Curie point, the material becomes a ferromagnet, and the magnetic field related to the material is difficult to change. When the temperature is higher than the Curie point, the material becomes paramagnetic, and the magnetic field of the magnet is easy to change with the change of the surrounding magnetic field. At this time, the magnetic sensitivity is about the negative sixth power of 10. The Curie point is determined by the chemical composition and crystal structure of a substance.
Temperature coefficient: the characteristic of NdFeB material is that with the increase of temperature, remanence, intrinsic coercivity and maximum magnetic energy product will decrease.
- The remanence temperature coefficient α BR is generally in the range of – 0.09 ~ 0.128% / ℃;
- The intrinsic coercivity temperature leads to α Hcj in the range of – 0.45 to – 0.8% / ℃;
- For example, a NdFeB material α br = – 0.10% / ℃ α Hcj = – 0.5% / ℃;
- The remanence is 12kgs and the coercivity is 20koe at 20 ℃.
BR and Hcj: at 80 ℃
- Br80℃= Br20℃+αBr.(T80-T20).Br20℃= Br20°-(80-20)*0.10%/℃.Br20℃=12(1-0.06)=11.28KGS
- Hcj80℃= Hcj20°-(80-20).0.005* Hcj20℃=20(1-0.3)=20*0.7=14KOe
Other physical properties of NdFeB
- 1. Hardness (HV): 620
- 2. Young’s modulus: 1.6 * 1011 N/m2
- 3. Compression ratio: 9.8 * 10-12 M/n
- 4. Resistivity: 1.8 ~ 2.0 * 10-4 Β.Cm
- 5. Bending strength: 295 ～ 345mpa
Shape, size and tolerance of NdFeB magnets
Various shapes of NdFeB magnets are used, such as round, irregular, square, tile and trapezoid. Different sizes of materials are processed by different machine tools. Advanced technology and machine operators determine the accuracy of products. The strength and technology of the factory determine the size of magnets Because in the production process of NdFeB, the process is more complex, it can not be formed at one time, but also through the cutting and reprocessing process. Different shapes of magnets have different sizes. If we want to achieve the size and quality required by customers, then the technical strength of the factory is very critical.
Neodymium iron boron is an important part of many kinds of manufacturing products, such as motors, horns, testing instruments and so on. Users generally have certain requirements for the dimensional tolerance and geometric tolerance of neodymium iron boron, because the unqualified product size will lead to the failure of neodymium iron boron components to install, or even damage the machine. Substandard size often leads to the risk of batch returns.
The dimensional tolerance of NdFeB refers to a product determined to be produced within the allowable size range. The purpose of the tolerance is to specify the allowable defect margin for the manufacture of NdFeB magnets.
The following is the dimensional tolerance range of various specifications.
Tolerance range of NdFeB block magnet:
The processing difficulty beyond this size range will be greatly increased. The price of NdFeB will also increase greatly due to the increase in loss rate.
Do you want to magnetize? If you want to magnetize, which way, axial direction? Radial?
What is magnetization?
To magnetize a magnetic substance or to increase the magnetism of a magnet that is not sufficiently magnetic. In general, the magnetic object to be magnetized is placed in the magnetic field formed by the coil with direct current passing through.
The magnetization direction can be divided into thickness magnetization and radial magnetization. When affected by the external energy, such as heating and impact, the magnetic distance direction of each domain will become inconsistent, and the magnetism will weaken or disappear. At this time, it will be degaussed. In order to retain the original properties, magnetization is needed.
Magnetization in the process of powder production needs to set the orientation, magnetization methods include radial, axial, plane, etc.
- Constant current magnetization (low voltage large capacity capacitance discharge), suitable for low coercivity magnets, such as ferrite magnets.
- Pulse magnetization (high voltage small capacity capacitance discharge) is suitable for magnets with high coercivity, such as NdFeB magnets.
Working principle of magnetizer
Constant current magnetizer
Working principle: the coil generates a constant magnetic field through constant current DC in the coil. It is suitable for magnetization of low coercivity permanent magnetic materials.
Working principle: through the instantaneous pulse current in the coil, the coil produces a short super magnetic field. It is suitable for high coercivity permanent magnet materials or complex multipole magnetization. It is widely used in permanent magnet material production and application enterprises, suitable for magnetization of all kinds of permanent magnet material parts and components, such as aluminum nickel cobalt series, ferrite series, rare earth permanent magnet series, etc., with high efficiency and reliability. The equipment has no special requirements for the power configuration of the workplace, and is easy to use and flexible.
Specifically, the capacitor is first charged with high DC voltage, and then discharged through a coil with minimal resistance. The peak value of discharge pulse current can reach tens of thousands of amperes. This current pulse generates a strong magnetic field in the coil, which makes the hard magnetic material in the coil permanent magnetized. The peak value of pulse current is very high when the magnetizer is working, which requires the capacitor to withstand the impulse current. The structure of the magnetizing machine is relatively simple. In fact, it is an electromagnet with extremely strong magnetic force. It is equipped with iron blocks of various shapes as additional magnetic poles, so as to form a closed magnetic circuit with the charged magnet. When magnetizing, the additional magnetic poles and the charged magnet can be set up. As long as the exciting current is added, the brushing can be completed instantly.
Disk NdFeB magnets can be magnetized axially or radially.
Magnetization direction of NdFeB
Length, width and thickness: square magnets are defined in three dimensions. It is consistent that we define the thickness dimension along the magnetization axis. Thickness is usually the smallest size, but not always! Sometimes, the longer side is used as the magnetization direction, but we still call the long side thickness, but the longer number is usually placed in the last number. It is easy to see clearly the magnetizing direction of the square magnet at a glance. For example, for F8 * 5 * 20, the magnetization direction is 20.
Magnetization by thickness
Magnetization (magnetization) direction of middle hole NdFeB magnets
The middle hole magnet can be magnetized axially or radially.
Magnetization direction of NdFeB magnet
Magnetizable tile in one direction.
North pole side
South pole side
Magnetization by circumference
Magnetization by thickness
It can also be multi pole magnetization.
According to the external environment to choose the required coating magnet.
The neodymium iron boron magnet contains metal neodymium, so it is easy to oxidize. The surface must be processed.
The coatings of NdFeB magnets include nickel, copper, nickel, zinc, gold, silver, epoxy resin, black nickel, and chromium.
Nickel, copper and nickel are usually referred to as NI or nickel. It can also be plated with environmentally friendly nickel and black nickel. It can be divided into bright nickel and dark nickel on its surface.
Electrogalvanized zinc can be divided into blue zinc, white zinc, environmentally friendly zinc, color zinc, and black zinc.
Gold and silver
Gold and silver plating are actually four-layer plating: nickel + copper + nickel + gold/silver
In order to improve the corrosion resistance of the magnet and meet the specific surface condition requirements, the following surface treatment can be performed on the magnet according to the customer’s needs. According to the different application environments of permanent magnets, it can also provide a variety of customized composite coating designs to ensure the durability of the magnet.
|Coating category||Coating code||colour||Minimum local thickness||Neutral salt spray test||Damp heat experiment||Pressure cooker experiment||Recommended temperature|
|Electroplated nickel copper nickel (rolling)||NiCuNi||silver||15μm||72h||500h||48h||＜200℃|
|Electroplated nickel copper nickel (hanging)||NiCuNi||silver||10μm||48h||500h||48h||＜200℃|
|Electroplating blue and white zinc||Zn||Blue and white||4μm||48h||48h||N/A||＜200℃|
|Electroplating color zinc||CZn||colourful||4μm||48h||48h||N/A||＜200℃|
|Nickel copper + tin||NiCu+Sn||Silver white||15μm||72h||500h||96h||＜200℃|
|Electroless Ni plating||Ni||silver||8μm||96h||500h||48h||＜200℃|
|Electrophoresis black / grey epoxy||Black EP||black||15μm||240h||500h||96h||＜200℃|
|Nickel copper + electrophoresis||NiCu+ EP||black||25μm||500h||1000h||200h||＜200℃|
|Zinc + electrophoresis||Zn+ EP||black||18μm||240h||1000h||200h||＜200℃|
|SSR coating||SSR||Golden gray||10μm||1000h||1000h||300h||＜200℃|
In order to avoid high temperature oxidation and weak acid liquid corrosion, and to extend the service life of magnets, the usual way is to coat the surface of magnets. The common coatings are nickel, nickel, copper, nickel, zinc, color zinc, epoxy, Perrin, etc. according to the different needs of customers, different coatings are selected, and there are other problems If you don’t know much about the magnet industry, you can tell me the demand of your products. We recommend a scheme for you to choose, please contact us: [email protected].
Manufacturer’s equipment and production process
Look at the equipment and production process of magnet manufacturers. China’s production of NdFeB generally adopts the two-part pressing method. Of course, advanced technology not only improves the output, but also improves the quality. At present, SC, HD and JM are the most advanced technologies
Production process of NdFeB magnets
Sintered Nd-Fe-B permanent magnets are produced by powder metallurgy. There are sixteen process steps, including monitoring and analysis in different stages. Strictly speaking, none of these 16 links is indispensable. The production of sintered Nd-Fe-B is a systematic project, which is closely linked with each other. Every link should lay a good foundation for the next link. Once a process link fails to meet the requirements, the permanent magnet may not meet the target performance requirements and become a scrap, or the yield is not high.
As the saying goes, “good medicine, good medicine”, this sentence is very suitable for the production of sintered NdFeB magnets, good raw materials are the basis for the production of high-quality magnetic materials. Raw materials are generally purchased according to the requirements of high-grade, medium grade or low-grade sintered NdFeB magnets produced by magnetic material manufacturers and corresponding national standards. Before smelting, raw materials should be cut off and surface treated.
The composition design of sintered NdFeB is very important, which relates to the quality of products and whether the magnetic properties can meet the requirements of customers, because many intrinsic magnetic properties of materials, such as magnetic polarization and Curie temperature, are determined by the composition of materials. The basic principle of composition design is to ensure high enough intrinsic properties and to consider the material cost. (the cost of raw materials accounts for about 65% – 90% of the total cost of sintered Nd-Fe-B materials. On the premise of meeting the requirements of users’ magnetic properties, we should try our best to use cheap components and use less rare earth metals and other precious metal materials.)
Melting ingot / slab
Smelting is the first process for sintered NdFeB magnets to enter the production process. The melting furnace produces alloy strip slivers. The process needs the furnace temperature to reach about 1300 ℃ and lasts for four hours. After this process, raw materials are processed into alloy sheets by hot melting and cooling, and then the next process is carried out.
(vacuum flaking furnace)
The purpose of powder making is to break large alloy ingots into powders of a certain size. The latest powder making process is to make Nd-Fe-B strip (SC) powder by hydrogen breaking and jet milling. In order to obtain a well oriented magnet, it is required that the powder particle size is small (3-4 μ m) and the size distribution is concentrated, and the powder particles are spherical or nearly spherical.
Orientation and pressing
In the last issue, we have introduced the magnetic orientation of sintered NdFeB. The magnetic orientation of powder is one of the key technologies to produce high-performance sintered NdFeB. After the broken magnetic powder is put into the mold, an external magnetic field is applied for orientation, and then the powder is pressed. At present, there are three common pressing methods: film pressing, cold isostatic pressing and rubber mold isostatic pressing. Under the same neodymium content, rubber mold isostatic pressing can obtain greater magnetic energy product.
(cold isostatic press)
Sintering and tempering
The relative density of sintered Nd-Fe-B powder compacts is high, the contact between particles is mechanical contact, and the bonding strength is low. In order to further improve the density, improve the contact properties between powder particles, improve the strength, and make the magnet have the microstructure characteristics of high permanent magnetic properties, it is necessary to heat the compacts to the temperature below the melting point of the basic phase of the powder for a period of time The process is called sintering.
After high temperature quenching, the distribution of grain boundary phase is not uniform and the grain boundary is not clear, so it is necessary to temper at a certain temperature to optimize the structure and obtain the best magnetic properties. Tempering means that the sintered magnetic powder billet is cooled to a certain temperature and then heated again. The tempering temperature needs to be determined by test or thermal difference analysis.
Vacuum sintering furnace
Machining and surface treatment
The shapes of sintered NdFeB magnets used in practice are various, such as disc, cylinder, ring, square, tile, sector and various irregular shapes. Due to the different shapes and sizes of permanent magnet components, it is difficult for other magnets to be formed at one time except for large size regular permanent magnet components. Therefore, in general, in the process of powder metallurgy, we produce large billets. After sintering and tempering treatment, we can produce magnetic materials of shape and size that meet the needs of customers through mechanical processing (including cutting, drilling, etc.) and grinding and surface coating treatment. There are three types of machining:
- 1. Cutting cylindrical and square cylindrical magnets into circular and square pieces is called cutting
- 2. Machining round and square magnets into fan-shaped, tile shaped, grooved or other complex shapes is called shape machining
- 3. Machining round bar or square bar magnet into cylinder or square cylinder element is called drilling
- Machining methods include grinding slicing, EDM and laser processing.
(multi wire cutting machine)
The quality control in the production process of sintered NdFeB permanent magnet and the quality inspection of the final product should include the items listed in the table below, but not every item should be inspected, which should be determined by the requirements of the product order contract.
Table.1 Quality control in the production process of sintered NdFeB permanent magnet and quality inspection of final product
|Process stage||Project||Nature of detection||Necessity|
|Raw material||Chemical composition analysis of materials||Quality control||Necessary|
|HD + JM magnetic powder||Thickness distribution and surface quality of SC sheet||Quality control||Necessary|
|Analysis of hydrogen, oxygen and carbon content||Quality control||Necessary|
|Tempered billet||Powder particle size distribution||Quality control||Necessary|
|Average grain size||Quality control||Phased|
|Orientation degree of basic phase grains||Quality control||Phased|
|Technical magnetic parameter measurement||Quality control||Necessary|
|Final product quality inspection||Density measurement||Quality control||Necessary|
|Thickness test of surface anticorrosive coating||Quality control||According to the contract|
|Coating adhesion test||Final product quality inspection||According to the contract|
|Experiment on humidity resistance of magnet||Final product quality inspection||According to the contract|
|Experiment on salt spray resistance of magnet||Final product quality inspection||According to the contract|
|Thermomagnetic stability experiment||Final product quality inspection||According to the contract|
|Stability test of cold and hot shock resistance||Final product quality inspection||According to the contract|
|Mechanical property test||Final product quality inspection||According to the contract|
|Magnetic comparison test (surface magnetic field, magnetic flux or magnetic moment)||Final product quality inspection||According to the contract|
|Appearance quality inspection||Final product quality inspection||According to the contract|
|Dimension and tolerance inspection||Final product quality inspection||According to the contract|
|Other testing items specified in the contract||Final product quality inspection||According to the contract|
Generally, the quality of NdFeB is evaluated from two aspects:
- 1. Appearance: check whether there are missing edges and corners, whether the electroplated coating is in good condition, and whether the size meets the design requirements.
- 2. Properties: there is a unified standard for the properties of Nd-Fe-B.
A brief summary of the quality of NdFeB products is to grasp the performance, control the dimensional tolerance, and judge the appearance inspection and evaluation of the coating Test the Gauss surface of the magnetic flux of the magnet, and other tests; dimensional tolerance, precision that can be measured with vernier caliper; coating, color and brightness of the coating and adhesion of the coating, and observe the smooth surface of the magnet, whether there are spots, whether there are edges and corners, so as to evaluate the quality of the product.
Instructions for transportation and storage of magnets
When the magnet is transported in magnetized state, especially when transported by airlines, it should be shielded. The magnet material is hard and brittle. During the whole transportation and installation process, it is necessary to ensure that the magnetic field will not collide strongly. If the method is improper, the magnetic field is easy to be damaged During the whole use of the magnet, the workplace should be kept clean to prevent the iron pin and other small residues from adsorbing on the surface of the magnet and endangering the normal use of the product. The magnetic frame is suitable for placing in the naturally ventilated drilling room. The natural environment of acid, alkaline, solvent, water, high temperature and high humidity makes the magnetic field easy to rust, and the coating explodes, and the magnetic field is demagnetized layer by layer
Magnets should be far away from magnetic disks, magnetic cards, magnetic tapes, computer monitors, watches and other magnetic fields, as well as electronic equipment such as cardiac pacemakers and medical machinery, otherwise the risk is great. Magnets with strong magnetism (plastic antistatic tweezers, samarium cobalt) should not be placed together with magnets with poor magnetism (al Ni Co, ferrite core), especially those with opposite polarity, otherwise magnets with poor magnetism are easy to demagnetize Attention should be paid to obtain one by one during operation and installation to prevent collision and damage of opposite sex attraction, and prevent floating debris generated by magnet attraction from entering eyes and causing human injury.
Because the neodymium magnet is very strong and its adsorption force is more than 600 times of its own weight, it is necessary to prevent hands or other parts of the human body from being clamped by the magnet during the operation, and pay more attention to personal safety and safety protection for the magnet with large restrictions During operation and installation, attention should be paid to obtain one by one to prevent the opposite sex attraction from colliding and damaging, and to prevent the floating debris generated by the magnet attraction from entering the eyes and causing human injury. Please do not swallow the magnet or put it out of the reach of children.
How to identify NdFeB permanent magnets?
The newly produced NdFeB is a gray black solid, with rough surface and black powder falling. 4102 is not corrosion-resistant, and its surface will be oxidized to form reddish brown rust in the air. The chemical formula is Nd2Fe14B. In fact, the proportion of neodymium is about 35%. Only when neodymium rich crystals are formed can it produce greater attraction. The density is 7.5g/cm3.
- 1. All the magnetic flux of the whole magnet can be measured by Helmholtz co vibrating coil test.
- 2. Hall effect detection, the conventional test method is reflected in the form of Gaussian value, the principle is that the TWT in the magnetic field shows Hall effect in the magnetic field.
- 3. Axial field description. Used to describe the magnetic field distribution of magnetic combination.
- 4. Fixed suction test.
- 5. High resolution test can measure the magnetic field change of one in 100000.
How to choose the appropriate grade of NdFeB permanent magnet material?
- When it is used at room temperature and the stability requirement is not high, ordinary coercivity grade products, such as n grade, can be selected. At this time, the magnet with high magnetic energy product can be selected as far as possible.
- If the stability requirements are strict, first, according to the magnetic circuit design, calculate the required Br and appearance size; take br as the ordinate, h as the abscissa to establish the rectangular coordinate system, passing through points a (0, Br), B (Hcb, 0) is a straight line, which is the ideal b-hcb demagnetization curve of the selected magnet; according to the aspect ratio corresponding to the external dimension, the magnetic permeability coefficient PC is calculated; at the o point, take – | PC | as the slope, make a straight line, PC parallel to ob, and the corresponding value at C point is the minimum HCB value of the magnet; the HK value of the magnet is greater than HCB, and the Hcj only needs HK. Finally, according to Hcj value, the brand of the magnet should be selected.
- If the magnet is used at high temperature, it can be selected by referring to the service temperature corresponding to each magnet brand, and aging treatment can be carried out if necessary.
How to choose the type of NdFeB permanent magnet material according to the electromagnetic parameters of permanent magnet motor?
The most important thing is to know the temperature produced by the maximum speed of permanent magnet motor.
In the working environment, what factors affect the magnetic force of NdFeB magnets?
Temperature is the factor that affects the magnetic force of NdFeB magnet: the strong NdFeB magnet has a strict working temperature limit. Above the working temperature, the magnet may demagnetize, while above the Curie temperature, the demagnetization will not be reversible.
Humidity: sintered NdFeB is a kind of magnetic material pressed by magnetic powder metallurgy process. Its internal structure is porous and easy to be oxidized. Therefore, sintered NdFeB will adopt coating for anti-corrosion treatment. However, the coating can not fundamentally deal with the influence of environmental humidity on the magnet. The drier the environment, the more permanent the magnetic properties of the magnet.
Magnetic field: the existence of alternating magnetic field of NdFeB magnets. People who have a certain understanding of magnets know that magnets can be divided into N, S poles or multipoles. If there is another magnetic field around the NdFeB magnet, it will counteract part of the magnetic force of the magnet. It is also said that it will demagnetize in the temperature range.
The factors that affect the magnetic force of NdFeB magnet – Vibration: the mechanical vibration of NdFeB magnet is related to the assembly. The magnet rubs the product during the assembly process. Because the material property of NdFeB magnet is fragile, the body is worn and the size becomes smaller. So the magnet will slowly weaken.
Price of NdFeB permanent magnet
From the perspective of price: price may not be the necessary condition to choose a magnet, but customers’ choice of what price segment they need is often an important aspect of choosing NdFeB permanent magnet materials. When purchasing magnets, customers usually choose the brand of NdFeB materials of different value segments according to their own needs
Source: China Permanent Magnet Manufacturer – www.rizinia.com