The past and present of NdFeB

NdFeB magnets can be divided into bonded NdFeB magnets and sintered NdFeB magnets. Bonding is actually injection molding, while sintering is vacuum molding through high temperature heating. NdFeB magnet is the most powerful permanent magnet so far. The material grade is N35-N52; various shapes can be processed according to the specific requirements: round, square, drilling, magnetic tile, magnetic bar, convex, trapezoid, etc.; despite these advantages, the surface is easy to rust, so some protective surface treatment is usually required: nickel plating, zinc plating, gold plating, epoxy resin plating, etc. Ordinary Nd-Fe-B magnets are suitable for the environment temperature below 80 degrees, but there are several kinds of magnets that can withstand 200 degrees. Mainly used in electronics, electrical appliances, packaging, motor, toys, leather goods, automotive machinery, etc.
Let’s see how we define it? Today, I would like to share with you a “different” Nd-Fe-B and tell you about its past and present lives.

Rare earth elements

There are 17 kinds of rare earth elements:

  • Scandium (SC)
  • Yttrium (y)
  • Lanthanum (CA)
  • Cerium (CE)
  • Praseodymium (PR)
  • Neodymium (nd)
  • PM (PM)
  • Samarium (SM)
  • Europium (EU)
  • Gadolinium (GD)
  • Terbium (TB)
  • Dysprosium (Dy)
  • Holmium (HO)
  • Erbium (ER)
  • Thulium (TM)

Ytterbium (Yb) and lutetium (Lu) rare earth metals commonly used in NdFeB products are neodymium, praseodymium, dysprosium, terbium, gadolinium and holmium.

Rare earth metals are active metals

The chemical activity of rare earth metals is between alkali metals (lithium, sodium) and alkaline earth metals (magnesium, calcium). Under certain conditions (sodium is very active and can only be stored in kerosene), the following reactions will occur, and a lot of heat will be generated. The supply of heat will further promote the reaction, such as:

  • 2Nd+3O2=2Nd2O3+Q
  • 2Nd+6H2O=2Nd(OH)3+3H2+Q
  • Nd2O3+3H2O=2Nd(OH)3+Q

From the above equation, it can be seen that anti-oxidation and anti moisture should be carried out in the production of NdFeB, among which anti moisture is the key. In wet days and rainy days, all workshops should pay full attention to anti moisture.

Distribution of rare earth metals

According to statistics, rare earths have been found in Inner Mongolia, Jiangxi, Zhejiang, Guangdong, Fujian, Guangxi, Hunan and other places in China. Due to the different state of existence, Baotou rare earth in Inner Mongolia is in the form of bastnaesite, and mainly in the form of light rare earth (rare earth in front of neodymium), while Jiangxi is in the form of ion type, mainly in the form of medium and heavy rare earth. Most of the world’s rare earth is in China, which accounts for about 80% of the world’s rare earth, while 80% of China’s rare earth is in Baotou, Inner Mongolia. Rare earths have been found in the United States, Russia, Australia, Vietnam and other countries in the world.

Magnetic material

The main magnetic materials used are ferrite magnets, alnico magnets, SmCo magnets and NdFeB magnets.
At present, ferrite is the most widely used in the world, and its products are cheap, followed by NdFeB. The temperature stability of alnico and SmCo is better than NdFeB, so alnico and SmCo are indispensable in some pointer instruments, military products and high-end consumer goods.
The Curie temperature of ferrite is 465 ℃, the Curie temperature of NdFeB is 310 ℃, the Curie temperature of alnico is 800 ℃, and the Curie temperature of SmCo is 700-800 ℃. Therefore, the temperature stability of NdFeB is the worst, but its performance is the highest, so it is called “ciwang”. At present, there are two processes for the production of magnetic materials: sintering and bonding, but the precision of the product is high.

Application fields of NdFeB

  • 1. Application of microwave communication technology: it is used in radar technology, satellite communication, remote control and telemetry technology, electronic tracking and electronic countermeasure technology, and NdFeB is used in magnetic control electron tube, magnetic control traveling wave tube, cathode ray tube, circulator, etc.
  • 2. Application in electrical engineering: more than one third of the output of rare earth permanent magnet materials is used to manufacture all kinds of permanent magnet motors. The advantages of permanent magnet motors are copper saving, power saving, light weight, small volume and high specific power. Electric bicycle motor, computer-driven motor, lathe speed and speed measurement motor, elevator traction motor, mahjong motor, refrigerator air conditioning motor, wind engine motor, automobile engine motor and so on are widely used.
  • 3. Application in electroacoustic devices: such as loudspeaker, microphone, hearing aid, stereo headset (MP3, MP4), telephone receiver and electroacoustic sensor, etc.
  • 4. Application in magnetic mechanical engineering: magnetic machinery includes magnetic driver, magnetic gear, magnetic brake, magnetic clamp, magnetic fishing device, magnetic bearing, magnetic pump, magnetic valve, magnetic seal door, magnetic lock, permanent magnet hoist, permanent magnet carrier, etc.
  • 5. The application in transportation means: the maglev train based on the principle of same-sex repulsion; modern luxury cars need 15-70 permanent magnet devices, such as windshield wiper motor, oil pump motor, window opening motor, door lock motor, defogging motor, automatic car controller, starting motor, etc.
  • 6. Application in magnetic separation technology: the technology of separating ferromagnetic material from non ferromagnetic material by magnetic method is called magnetic separation technology. Magnetic separation technology has been widely used in mineral processing, coal preparation, raw material treatment, water treatment, garbage treatment, medical treatment, chemical industry and food industry.
  • 7. Application in magnetization technology: magnetization of material by magnetic field, change the bonding state and properties of magnetized material; or change the atomic and electronic state, promote the chemical reaction of material and combustion of fuel; or change the crystalline form or freezing point of material. This technology is called magnetization technology. Magnetizer, fuel economizer in automobile, oil paraffin preventer in oil exploitation, etc.
  • 8. Applications in magnetic therapy and fitness equipment: such as magnetic therapy cup, magnetic ball, magnetic therapy machine, magnetic therapy shoes, magnetic therapy hat, Magnetic Therapy Bracelet, necklace, etc., as well as the rapid development of medical equipment in recent years, the consumption of magnetic resonance imaging (MRI) is 3-4 tons per set. Imagine how much neodymium iron boron should be used for each hospital in China if equipped with an MRI.

In a word, since the invention of NdFeB in 1983, new application fields have appeared every year, with an annual growth rate of more than 30%.

Development of NdFeB

  • 1. Product development. Since its invention in 1983, neodymium iron boron has not developed rapidly in the first ten years, but it has developed rapidly in the last ten years. In 1996, China produced 360 tons, Japan produced 2000 tons, and the United States produced 1000 tons. But in 2006, China produced 60000 tons, Japan produced 2000 tons, and almost no other countries. The world’s output of neodymium iron boron combined with sintering and bonding is about 100000 tons (including 20000 tons of bonding).
  • 2. Enterprises: before 1998, the western world developed faster than China, while China developed slower. But so far, there are only four enterprises in Japan, only one in the United States and only one in Europe, while there are more than 100 in China. Therefore, China is the world’s largest producer of NdFeB, but not a powerful country. 60% of China’s NdFeB production is in Zhejiang, and the rest is in Shanxi, Beijing and Tianjin. The sales bases of NdFeB are in Shenzhen, Ningbo and Beijing.
  • 3. Performance development: the development of NdFeB performance depends on the improvement of technology and the application of advanced equipment. Before 1996, the best performance in China was N38, and the best performance in the world was N48. By 2006, the best performance in China was n52, and the best performance in the world was n52 (large-scale production). The performance of NdFeB in China has improved rapidly, and China has gradually transformed from a big producer into a powerful producer.
  • 4. Process development: the first NdFeB process is wet production, using toluene or gasoline as protective agent, ball milling production, low performance, later developed to dry production (jet mill) performance has been greatly improved, but the best performance can only be N45, but since the invention of strip casting (SC) process, the performance has been greatly improved, at present batch production can reach n52.
  • 5. Equipment development: from ball mill to jet mill, from ingot to casting piece to hydrogen crushing, from single type sintering furnace to continuous multi type sintering furnace, from simple press to automatic press, equipment development and process breakthrough are the key to reduce cost and improve performance of NdFeB.
  • 6. Development of post-processing technology: the follow-up processing technology of early NdFeB is relatively monotonous and wasteful. The main processing technologies include slicing, wire cutting, drilling, centerless grinding, vertical grinding, etc. with the rapid development of NdFeB and the continuous expansion of its application field, great changes have taken place in processing technology and equipment, such as casing (improving the comprehensive utilization rate of materials), casing and grinding Grinding and other new processing technologies are widely used, which create conditions for NdFeB to reduce cost and improve precision.

Basic properties and microstructure of NdFeB

Metal properties
Sintered NdFeB is a solid with a density of 7.2-7.7g/cm3 and a melting point of about 1150 ℃ (different melting points of trace elements are also different). It is a metal conductor and can be electroplated.
Strong permanent magnet
The theoretical magnetic energy product of sintering is 64Mgoe, and the saturation magnetization is 1.6T. At present, the largest magnetic energy product in mass production at home and abroad is 52Mgoe.
It can be used at different temperatures according to different properties
1. 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 ℃;
  • The maximum temperature of M material Hcj ≥ 17koe 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 ℃.

2. According to the difference of remanence BR and maximum magnetic energy product (BH) max, it can be divided into different grade series.

  • N35,N38,N42,N45,N48,N50,N52, etc
  • 35M,38M,40M,42M,45M,48M,50M,52M, etc

Microstructure of NdFeB

Matrix structure Nd2Fe14B

The main physical parameters are (BH) max, Br, Hcj and HCD, as shown in the following figure: (BH) max = BD * HD

20210221042054 55252 - The past and present of NdFeB

Boron rich phase

It is a compound of B, ND1 + ∑ fe4b4. In Nd-Fe-B permanent magnet alloy, the boron rich phase is harmful, and the smaller its volume fraction, the better.

Neodymium rich phase

The nd rich phase plays an important role in the magnetic hardening of sintered Nd-Fe-B alloy. The proper nd rich phase can promote the coercivity of sintered Nd-Fe-B alloy.

Impurities

There are also some oxides such as Nd2O3, α – Fe, chloride and voids in sintered Nd-Fe-B.

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 ~ 345 mpa.

Manufacturing technology and equipment principle of NdFeB

Nd-Fe-B sintered magnet is an essential part in the drive motor of hybrid electric vehicle and electric vehicle. Compared with other magnets, neodymium magnet not only has strong magnetic force and can achieve high power enough to drive the vehicle, but also can reduce the motor to the size suitable for vehicle use.
So, do you know how this powerful NdFeB magnet is made? It needs to first crush the alloy containing the necessary materials into particles, gather these particles to form, and then sinter. Then it can be cut to the required size. This process always feels like making a cake.
What is the production process of NdFeB permanent magnet? What are the processing procedures of NdFeB magnets? See the flow chart of NdFeB magnet for details.
20210221040134 93273 - The past and present of NdFeB

It can be seen that there are 11 steps to go from raw materials to finished products. In fact, the processing and production details of magnets are not limited to these 11 production links. We start from a blank material, because most magnet manufacturers buy magnet blanks directly and then process them. First of all, when the materials are bought back, they need to be polished. Why? Because the blanks are bought back The surface of the material is very rough and uneven. Only glue is needed to polish it well. The glue link is very important. It is necessary to glue the magnet wool embryo to the asbestos board, and then glue the asbestos board to a clamp. After bonding, install the clamp to the slicer, adjust it well, and then start cutting.
Usually, a square magnet needs to be cut at least three times, that is to say, it needs to be glued three times, and after each cut, it needs to be boiled with water, so that the glue can be boiled off and the material can be glued again. A square magnet needs to be chamfered after it is cut, because the water chestnut of the cut magnet is very sharp, which is not conducive to electroplating and product safety. After electroplating, magnetization, testing, packaging and shipment of the product are carried out. Therefore, a small magnet seems to be very simple, but its production process is very troublesome. It is unreasonable for some customers to ask for goods when their orders are sent. According to our magnet processing technology, it takes three days to complete a product as soon as possible, and it also needs to ignore all the costs and conditions to reach the delivery date. The magnet seems simple, but it is not easy Production and processing are complicated.

Manufacturing technology of permanent magnet:

(1) Sintering process

Sintering process is the most widely used production process by powder metallurgy, which is suitable for the production of sintered NdFeB, permanent ferrite, SmCo and sintered AlNiCo magnets. The production process diagram is shown in Figure 1.

20210221040715 19782 - The past and present of NdFeB

(2) Foundry Technology

Casting is a kind of processing method that melts the solid metal into liquid and pours it into the mold of a specific shape, waiting for it to solidify. For permanent magnets, the casting process is mainly used to produce cast AlNiCo magnets. Compared with sintered al NiCo, cast AlNiCo has higher magnetic properties, and can be processed into different sizes and shapes. The process of sintered al NiCo is simple, the tolerance of blank size is small, and the machinability is good. The production process diagram is shown in Figure 2.

20210221041025 80383 - The past and present of NdFeB

3) Bonding process

The bonding process is a kind of production process in which permanent magnet powder with certain magnetic properties is evenly mixed with adhesive and other additives in a certain proportion, and then composite permanent magnet materials are prepared by pressing, extrusion and injection molding. Compared with sintered and cast permanent magnets, bonded permanent magnets have the following advantages: high dimensional accuracy, no deformation, no need of secondary processing; large degree of freedom in shape, which can produce products of various shapes, such as long strip, sheet, tube, ring or other complex shapes, according to the actual use needs; convenient for mass automatic production; and high mechanical strength. Its disadvantages are low magnetic properties and low temperature. The key technologies in the bonding process are: the preparation of magnetic powder, the selection of coupling agent and adhesive, the amount of binder, molding pressure and orientation magnetic field strength. The manufacturing methods of magnetic powder used for bonding NdFeB mainly include melt rapid quenching, HDDR, mechanical alloying and gas spraying. Among them, the most popular method is HDDR. The production flow chart of bonding process is shown in Figure 3.

20210221041225 12785 - The past and present of NdFeB

(4) Hot pressing and hot deformation process

Hot pressing and hot deformation process is another process to produce NdFeB magnets. Isotropic and anisotropic NdFeB magnets can be produced by this process. The NdFeB magnet produced by this process has high magnetic properties, and the maximum radial magnetic energy product can reach 240 ~ 360 kJ / m3. And it has high heat resistance, the use temperature can reach 180 ℃, the magnetic ring is nanocrystalline structure, high density, using epoxy resin electrophoresis coating, excellent corrosion resistance. Hot pressed anisotropic radially oriented ring magnets are mainly used in EPS motors, servo motors, electric tool motors and various DC motors. The flow chart of hot pressing and hot deformation process is as follows:

Turn left | turn right

20210221041423 14512 - The past and present of NdFeB

Permanent magnet is a kind of magnet which can keep its magnetism for a long time. Such as natural magnetite (magnetite) and artificial magnetic steel (iron nickel cobalt magnetic steel) and so on. Permanent magnet is also called hard magnet, which is not easy to lose magnetism or be magnetized. The materials used as magnets and electromagnets are mostly soft magnets. The polarity of the permanent magnet does not change, but the polarity of the soft magnet changes with the polarity of the applied magnetic field. They all attract iron objects, which we call magnetism.

Manufacturing process of NdFeB magnet

(1) Melting

1. According to the different process, it can be divided into conventional smelting (20kg, 30kg, 50kg, 100kg) and strip throwing furnace (100kg, 300kg, 500kg).
2. Process
A. Pretreatment of Nd,Fe, B ingredients
B. Ingredients
C. Melting:
First of all, charge the material and pump it to below 1pA, then start to send low-power heating, and continue to pump gas while heating. With the increase of temperature, the adsorbed gas and water are gradually desorbed and pumped out until the charge is generally dark red. Close the valve and fill argon, increase the power and raise the temperature until the charge is completely melted, and then refine for about 5 minutes. After refining, reduce the power and pour it The opening should be aligned with the cooling mold, and the pouring should be completed and cooled.
D. Preservation of alloy
Attention should be paid to the entry of impurities in the process of ingot placement and transportation, such as the silk of gloves, dust in the air, etc. At the same time, oxygen has a destructive effect on the alloy, and oxygen penetrates into it, making neodymium become neodymium oxide; water vapor has a destructive effect on the alloy, and water will produce neodymium oxide and hydride when it touches neodymium, so impurities and oxidation should be prevented in the smelting process.

(2) Milling

1. Equipment
Hydrogen crushing furnace, coarse crusher, medium crusher, jet mill and mixer

2. Craft

20210221043155 75655 - The past and present of NdFeB

3. Key points of process control

  • A. The smaller the particle size is, the higher the coercivity and remanence will be, and the corrosion resistance of the product will also be improved. However, the follow-up process is not easy to control, and the smaller the particle size distribution is, the higher the performance can be.
  • B. It is very important to passivate the powder with proper amount of air in the air jet mill. It is just like people walking from the dark to the bright place will feel uncomfortable and sometimes damage their eyes. If there is no air in the powder, it is easier to oxidize in the follow-up production, and it is very likely to burn.
  • C. Because the properties of the powder before and after stirring are not consistent, the powder needs to be stirred.

(3) Molding

1. Equipment
Press, isostatic pressure, storage barrel
2. Craft

  • A. Weighing: according to the process requirements.
  • B. Magnetic field oriented molding: in order to arrange tens of thousands of NdFeB powder particles under the action of magnetic field and form a set shape in the mold, the basic requirement of the press is that the magnetic field must be greater than 18000 Ω when the air gap is 40mm, and there should be a photoelectric protector to prevent the press from hurting people.
  • C. The density of green compact is about 3.2-3.8g/cm3, while the theoretical density of sintered Nd-Fe-B is about 7.5g/cm3. Therefore, the density of green compact needs to be improved by isostatic pressing because of the large shrinkage, easy cracking, angular distortion and size out of tolerance when pressing large cylinders and squares. The density of green compact is 4.5g/cm3 after isostatic pressing, At present, except for the low-performance small column (below 10) with unequal static pressure, the company directly swings the box and then enters the sintering furnace, other parts pass through the isostatic pressure. In order to prevent oil immersion and surface oxidation, the isostatic pressing green body must be vacuum sealed and oil stripped before entering the furnace.

3. Abrasive tools
The manufacturing and design level of abrasives directly affect the appearance quality of products. With the fierce competition in the industry, abrasives are an important part of cost saving. The reduction of machining allowance, the reduction of product deformation and the direct pressing production of some special-shaped products will determine whether an enterprise has competitiveness

(4) Sintering

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 compact to the temperature below the melting point of powder matrix for a period of heat treatment
Sintering furnace should have good sealing and low leakage rate. Therefore, it is often necessary to close and vacuum to prevent the adsorption of gas and water vapor. Do not leave the furnace door open after the product is taken out and contact with the outside air and water vapor for a long time. The stripping oil tank should also be closed in time to prevent the adsorption of water vapor and affect the product performance

The sintering process is divided into two stages: sintering and aging. The sintering temperature is about 1050 ℃ ~ 1085 ℃, the hydrogen crushing of ingot is about 1070 ℃ ~ 1095 ℃, the ingot is about 1100 ℃ ~ 1135 ℃. The aging process is divided into two stages: 890 ℃ ~ 920 ℃ and 500 ℃ ~ 630 ℃. Generally, it takes 20 ~ 38 hours from sintering and aging to discharging.

20210221043517 22794 - The past and present of NdFeB

(5) Post processing

Due to the influence of production factors, the dimensional accuracy of Nd-Fe-B billet can not directly meet the customer’s requirements, so it needs to be processed later to meet the customer’s requirements.
For some special-shaped or slicing machine can not directly slice with wire cutting (wire cutting machine).
The slicer is used for wafer and small and medium square, and the double-sided grinder (slicer, double-sided grinder) is also needed for those with higher accuracy or CPK requirements.
The small cylinder that can not be pressed directly needs to be cut into small squares first, and then rounded (small centerless grinding).
Some products that need small holes need to be punched, and those with holes above Ф 6 can be holed (punching machine, holing machine).
The formed and pressed cylinder (below Ф 80) is ground with centerless mill (centerless mill).
If the diameter of the cylinder is larger than 80mm, it must be completed by the casing equipment.
Square need to be ground with large vertical mill or flat mill, or double-sided mill equipment.
Some special-shaped products can also be completed with direct set tile.

(6) Electroplating

Due to the poor corrosion resistance of NdFeB products, surface treatment must be carried out.
1. Form of surface treatment

  • a. Zinc plating: blue white zinc, white zinc, color zinc, black zinc. According to the requirements of environmental protection, it can be divided into trivalent chromium zinc (environmental protection zinc) and hexavalent chromium zinc.
  • b. Nickel plating: bright nickel and black nickel. At present, nickel plating is a three-layer nickel copper nickel plating method.
  • c. Electrophoresis (epoxy plating): black epoxy, gray epoxy.
  • d. Phosphating.
  • e. Gold plating, copper plating, silver plating, tin plating, etc.

2. Electroplating process

20210221044230 54330 - The past and present of NdFeB

Mechanical chamfering time may be long, so electroplating products are not very fast, there must be a cycle.

Reliability test

1. Drop test: stick the product and the iron sheet with glue, fall freely from the air of 1~1.5m and repeat it for many times to see whether the coating falls off. The drop test is basically the acceptance of galvanized products.
2. Scoring Test: use a knife to mark the coating, and see the combination of the coating.
3. Induced cold and heat test: heat the nickel-plated product in the oven (about 200 ℃), and then cool it in the water for several cycles to check the binding force of the nickel-plated product.
4. PCT test: (pressure boiling test) conditions: 2 atmospheric pressure, 95% relative humidity, 121 ℃ temperature, test the binding capacity of the coating.
5. Weight loss test: Nd-Fe-B due to easy oxidation, different processes and different added elements, and different process control, weight loss is different, weight loss test unit is per square centimeter to lose how much weight milligrams of American and European standards are not the same.
U.S. requirements: PCT: 2atm (atmospheric pressure) 95%RH( humidity) 121 ℃,96 hours, requiring weight loss below 10mg/cm2.
European requirements: AST test: 3atm (atmospheric pressure )95%RH( humidity) 130 ℃,240 hours, requires weight loss below 10mg/cm2.
Obviously, the European standards are much stricter, and at present, most of the PCT tests of Nd-Fe-B products produced by the domestic traditional technology are 80~300mg/cm2, if cobalt is added, the conventional process can reach below 10mg/cm2. If you use other processes, it is relatively easy to control.
6. Salt spray test: The condition is 5% sodium oxide, 35 ℃ temperature, continuous spray 48 hours or 72 hours, whether there is corrosion in the coating.
7. Constant temperature and constant temperature test: 90% humidity, 80℃ temperature; Measure the anti-corrosion performance of epoxy products.
8. Aging test: heat the product to a certain temperature, keep it for 1-2 hours, take it out for cooling, compare the magnetic flux before heating with the magnetic flux after heating, and measure the temperature stability of the product.

Some problems encountered in the production and sales of NdFeB are listed.

(1) Some problems encountered in production

  • 1. Oxidation
  • 2. Cracking
  • 3. Low density (low residual magnet, low magnetic energy product, can be improved by sintering)
  • Low coercive force (can be improved by aging)
  • 4. Corners
  • 5. Can’t be worn out
  • 6. Size difference
  • 7. Poor coating
  • 8. Poor temperature stability

(2) Problems encountered in sales

1. Performance
2. Plating and coating quality (such as salt spray test)
3. Temperature coefficient
4. Machinability
5. Density:

  • The density of N series is generally 7.3~7.55g/cm3.
  • The density of H series is generally 7.4~7.6g/cm3.
  • The density of SH series is generally 7.48~7.62g/cm3.
  • The density of UH series is generally 7.52~7.7g/cm3.
  • The density of the EH series is generally 7.55~7.75g/cm3.
  • AH series is generally between 7.6~7.8g/cm3.

The density of the same series of ingot materials is low, and the density of hydrogen crushes is high. The higher the density, the better the electroplating performance of the product.
6. Weightlessness: special requirements can generally be 10mg/cm2 (more than 100 hours)
7. Sintered NdFeB and bonded NdFeB: sintered Nd-Fe-B are mutually directional products with high magnetic energy accumulation, while the bonded Nd-Fe-B is pressed and bonded by binder, which is isotropic and low magnetic energy accumulation (5-10mgoe)
8. Patent issue: the patent of NdFeB is jointly owned by Sumitomo in Japan (now known as NEOMAX company by Hitachi merger) and MQ in the United States.

Safety of NdFeB production

Nd-Fe-B is inflammable. At the same time, in order to prevent oxidation, inert gas is added in the production process, so it is explosive. Therefore, safety is very important. The safety problems in the production process of the industry are listed
1. Smelting:

  • A. After pouring, the product of smelting furnace will expand at high temperature due to water leakage, resulting in explosion.
  • B. The alloy ingot fell to the ground and broke the operator’s toenails.
  • C. The argon gas was not discharged completely during the cleaning of belt throwing furnace, resulting in suffocation and death of employees.

2. Milling: the most safety accidents occurred in milling, and many of them were fatal.

  • A. The filter tube of jet mill exploded.
  • B. Stock powder burning.
  • C. The blender exploded.
  • D. The hydrogen furnace exploded.
  • E. Ultrafine powder combustion.

3. Molding

  • A. There was positive pressure in the powder storage bucket after mixing, and the accident was caused by improper operation of the staff.
  • B. Press broken fingers (neodymium iron boron enterprises have occurred, but after the installation of light control, the accident decreased).

4. Centerless grinding: grinding fingers.
5. Auxiliary work: the staff injured their fingers by illegal operation when drilling the sintering plate.
6. Magnetization: the finger of the magnetic product is broken because it is not marked.

Three Preventions in NdFeB production

Anti oxidation: because neodymium is very active and oxygen affinity is very strong, easy to cause product oxidation.
Damp proof: the water vapor in the air has a great influence on the quality of NdFeB. If the equipment leaks in the process, the product will produce ammonia smell, and the ingot (piece) will be exposed to the air for a long time, which has a great influence on the product quality.
Prevention of impurities: due to the lax control of various process links (especially smelting and pulverizing), the entry of dust and foreign matters, a large number of products will be scrapped. 

Source: Network Arrangement – China Permanent Magnet Manufacturer – www.ymagnet.com

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