How magnet is made?

Overview of rare earth permanent magnet materials

In a broad sense, all materials that can be magnetized by a magnetic field and use the magnetic properties of the material in practical applications become magnetic materials. It includes hard magnetic materials, soft magnetic materials, semi-hard magnetic materials, magnetostrictive materials, magneto-optical materials, magnetic bubble materials and magnetic refrigeration materials, among which hard magnetic materials and soft magnetic materials are the most used. The main difference between hard magnetic materials and soft magnetic materials is that hard magnetic materials have high anisotropy field, high coercivity, large hysteresis loop area, and large magnetic field required for technical magnetization to saturation. Due to the low coercivity of the soft magnetic material, it is easy to demagnetize after the technical magnetization reaches saturation and the external magnetic field is removed, while the hard magnetic material due to the high coercivity, after the technical magnetization to saturation and the magnetic field is removed, it will remain long Very strong magnetism, so hard magnetic materials are also called permanent magnetic materials or constant magnetic materials. In ancient times, people used the natural magnetite in the ore to grind into the required shape to guide or attract iron devices. The compass is one of the four ancient Chinese inventions and has made important contributions to human civilization and social progress. In modern times, the research and application of magnetic materials began after the industrial revolution, and has been rapidly developed in a short period of time. Nowadays, the research and application of magnetic materials are unparalleled in breadth and depth, with various types of high performance The development and application of magnetic materials, especially rare earth permanent magnet materials, play a huge role in promoting the development of modern industry and high-tech industries.

Performance requirements of permanent magnet materials

The main properties of permanent magnet materials are determined by the following parameters:
Maximum magnetic energy product: The maximum magnetic energy product is the maximum product of the magnetic induction intensity and the magnetic field intensity on the demagnetization curve. The larger the value, the greater the magnetic energy stored per unit volume and the better the performance of the material.
Saturation magnetization: It is an extremely important parameter for permanent magnet materials. The higher the saturation magnetization of the permanent magnet material, the higher the maximum magnetic energy product and the upper limit that the residual magnetization of the material may reach.

  • Coercive force: After the ferromagnet is magnetized to saturation, the reverse external magnetic field required to reduce its magnetization or magnetic induction to zero is called the coercive force. It characterizes the material’s ability to resist demagnetization.
  • Remanence: After the ferromagnet is magnetized to saturation and the external magnetic field is removed, the residual magnetization or residual magnetic induction remaining in the magnetization direction is called remanence.
  • Curie temperature: The critical temperature at which a strong ferromagnetic body changes from ferromagnetism and ferrimagnetism to paramagnetism is called the Curie temperature or Curie point. The high Curie temperature indicates that the use temperature of permanent magnet materials is also high.

The main types of rare earth permanent magnet materials

So far, there are two categories and three generations of rare earth permanent magnet materials:
The first category is the rare earth-cobalt alloy system (ie RE-Co permanent magnet), which includes two generations of products. In 1996, K. Strant discovered that SmCo5 alloy has a very high number of magnetic anomalies, and produced the first generation of rare earth permanent magnet 1:5 SmCo alloy. Since then, the research and development of rare earth permanent magnet materials began, and they were put into production in 1970; the second generation of rare earth permanent magnet materials, the 2:17 SmCo alloy, was put into production around 1978. They are all permanent magnet material alloys based on metallic cobalt.
The second category is NdFeB alloy (ie Nd-Fe-B permanent magnet). In 1983, both Japan and the United States discovered the NdFeB alloy, which is called the third-generation permanent magnet material. When Nd atoms and Fe atoms are replaced by different RE atoms and other metal atoms, they can develop into a variety of different compositions and different properties. Nd-Fe-B series permanent magnet material. Its preparation methods mainly include sintering method, reduction diffusion method, melt rapid quenching method, bonding method, casting method, etc., among which sintering method and bonding method are the most widely used in production. The following table lists the magnetic properties of different rare earth permanent magnet materials.

Material type

Maximum Energy Product

/Kj.m-3

Residual flux

/T

Magnetic coercivity

/kA.m-1

Intrinsic coercivity

/kA.m-1

Curie temperature

/0C

SmCo5 series

100

0.76

550

680

740

SmCo5 series(high Hc)

160

0.90

700

1120

740

Sm2Co17 series

240

1.10

510

530

920

Sm2Co17 series(High Hc)

280

0.95

640

800

920

Sintering Nd-Fe-B series

240-400

1.1-1.4

800-2400

310-510

Bonding Nd-Fe-B series

56-160

0.6-1.1

800-2100

310

Sm-Fe-N series

56-160

0.6-1.1

600-2000

310-600

It can be seen from the above table that the NdFeB permanent magnet material has the best comprehensive magnetic properties, and the sintering method is better than the bonding method. Therefore, the following mainly introduces the production process of sintered NdFeB permanent magnet materials.

What is a Neodymium Iron Boron?

Neodymium Iron Boron is an alloy made mainly from a combination of Neodymium, Iron, Boron, Cobalt and other transition metals, as well as with varying levels of Praseodymium,Dysprosium and Terbium. The exact chemical composition within NdFeB depends on the grade of the NdFeB magnet. Dysprosium and Terbium are added as a replacement for some of the Neodymium to improve the HcJ (Intrinsic coercivity) of the “Neo” magnets. An example of a typical composition is given below:

Typical composition of NdFeB

Main Elements within NdFeB Percentage by weight
Neodymium (Nd) 29% – 32%
Iron (Fe) 64.2% – 68.5%
Boron (B) 1.0% – 1.2%
Aluminium (Al) 0.2% – 0.4%
Niobium (Nb) 0.5% -1%
Dysprosium (Dy) 0.8% -1.2%

Table comparing main coating types

COATING APPLIED NICKEL EPOXY RESIN Ni + EPOXY
Electroless Powder Spray E-Coating Nickel plating
Coating + Epoxy E-Coating
Coating Thickness Range (microns) 12 to 25 25 to 40 20 to 40 15 to 25 25 to 40
Homogeneity Excellent Good Poor Excellent Good
Effectiveness versus Magnet Size Small (<20 grams) Excellent Good Fair Good Good
Large (>20 grams) Fair to Good Good Fair Good Good
Hours before coating is likely to fail Temp. & Humidity >2500 >500 >1500 >2500
(60ºC, 95%RH)
Temp. & Humidity >500 >100 >300 >500
(85ºC, 85%RH)
Salt Spray >48 <24 >100 >200
(35ºC, 5% NaCl)
Coating Colour Silver Silver Black Black Black
Heat Cycle Fair Fair Fair Fair Fair
Heat Resistance Poor Poor Poor Poor Poor
Collision Test Fair Fair Fair Fair Fair
Film to material adhesion test Fair Fair Fair Fair Fair
Glue adhesion test Fair Fair Fair Fair Fair
Tolerance accuracy Excellent Excellent Fair Fair Fair to Poor
Additional Remarks 15-30 microns Ni-Cu-Ni Standard coating Epoxy resins are not hermetic Thickness buildup can be a problem

How magnet is made?

Sintered NdFeB permanent magnets are produced by powder metallurgy. There are sixteen process links in total, and several monitoring analyses are included in different stages. Strictly speaking, these sixteen links are indispensable. The production of sintered neodymium iron boron is a systematic project, and each link must lay a solid foundation for the next link. Once a process link fails to meet the requirements, the permanent magnets made may not achieve the target performance Request and become scrap, or the yield rate is not high.

“Rare earth” elements are lanthanides (also called lanthanides), and this term is used to separate rare oxides of these elements. Rare earth metal elements were originally separated from refined rare earth oxides in an electrolytic furnace. mineral. Although the term “rare earth” is used, it does not mean that chemical elements are scarce. Rare earth elements are abundant, such as neodymium is more common than gold. The neodymium, iron and boron are measured and added to the vacuum induction furnace to form an alloy. According to the requirements of the specific grade, other elements such as cobalt, copper, gadolinium and dysprosium are also added (for example, leading to corrosion resistance).
In short, “Neo” alloy is like a cake mix, each factory has its own recipe for each grade. The molten alloy is then cooled to form an alloy ingot. Then, the alloy ingot is decomposed by hydrogen explosion (HD) or hydrogenated disproportionation desorption and recombination (HDDR), and spray-ground into micron-sized powder (about 3 microns in size) in an atmosphere of nitrogen and argon.
Molding requires tools to make replacements that are slightly larger than the required shape (because the interconnection causes electromagnetic shrinkage). The neodymium powder enters the mold cavity from the hopper and is then compacted under the condition of an external squeezing magnetic field. The applied external field is either parallel to the compressive strength (this is not commonly called pressure) or perpendicular to the direction of compaction (this is called lateral pressure). Lateral extrusion makes NdFeB have higher magnetic properties.
The neodymium iron boron powder is added to the rubber mold, and then put into a large liquid-filled container, the fluid pressure in the container rises accordingly. Volume, there is also an external magnetic field, but neodymium isostatic pressure makes neodymium iron boron have the best magnetic properties. The method used depends on the required “Neo” grade and is determined by the manufacturer.
The magnetic domains of the neodymium iron boron powder are aligned with the applied magnetic field-the more uniform the magnetic field caused, the more uniform the magnetic properties of the neodymium magnet. When the neodymium powder is pressed by the mold, the magnetization direction is locked in place-the neodymium magnet is called a preferential magnetization direction, which is called (if no external magnetic field is applied, the magnet can be magnetized in any direction, which is called Isotropic, but its magnetic properties are much lower than expected, usually only above this.
In the case of Nd2Fe14B, the easy axis of magnetization is the c-axis of the complex tetragonal structure. In the presence of an external magnetic field, its axial c-axis is separated and can be fully magnetized to saturation with a very high coercivity.
Before the magnetism of the pressurized NdFeB is released, give it a demagnetization pulse and become unmagnetized. The compacted magnet is called a “green” magnet-it is easily crushed and its magnetic properties are not good. Then the coupling process is carefully monitored (strict temperature and time curves must be used) and carried out in an inert (oxygen-free) atmosphere (such as argon). If there is an oxygen shrinkage process, it will also cause the magnet to shrink because the powder will fuse together. The shrinkage brings the magnet closer to the desired shape, but the shrinkage is usually uneven (for example, the ring may shrink into an oval shape). This is to alternatively reduce the replacement “phase” (in short, a less magnetic alloy) produced at the temperature of the gradual sintering temperature, and rapid quenching to maximize the magnetic properties of NdFeB. Due to the uneven shape of neodymium during the sintering process.
The next step is to machine the magnet to the required tolerance.

Production process of sintered NdFeB

The overall process is as follows:

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Smelting section

The smelting section is mainly responsible for smelting the proportionally weighed raw materials, which is divided into two parts: ingredients and smelting:

Ingredients

  • 1). The commonly used metals are as follows: metal neodymium, neodymium praseodymium, special boron, refined boron, copper, aluminum, gallium, terbium, cobalt, iron (Taiyuan Iron, Wuhan Iron and Steel, Shanghai Iron), dysprosium iron, and niobium iron.
  • 2). Instruments, tools, auxiliary materials, etc.: electronic scales of different specifications, steel bar cutting machines, rust removal and polishing machines, rubber gloves, masks
  • 3). Work process: According to the production requirements of the day, count the amount of various raw materials, and go to the raw material warehouse to pick up after verification; after returning, the ingredients are divided into two types, corresponding to the melting furnace in the smelting section. Used for ingot casting and small furnace casting. Relevant records must be completed when and after the ingredients are completed. Next, there will be special personnel who will come back and say that the material samples of the furnace must be inspected. After inspection, the lock car is equipped and pushed to the melting place for the next day’s material preparation. The materials of small furnaces generally need to be spot-checked, basically about 8 barrels per car, one barrel per car is tested, and small materials and others are weighed again to check whether they are qualified. Basically, the daily small furnace preparation is 55 barrels. The stock of the furnace is generally less than 10 barrels.
  • 4). Matters needing attention:
  • (1) Because there is metal powder in the air when weighing metals, you need to wear a mask during the operation. And to prevent metal from hurting your hands, you need to wear special gloves
  • (2) Since the iron rods in the raw material warehouse are long and easy to rust, they need to be cut and polished during batching to facilitate weighing and reduce impurities.
  • (3) Pay special attention to safety when operating the steel bar cutting machine, and be careful to injure your fingers.
  • (4) Master the usage of electronic scales correctly and skillfully, and strictly control the tolerance within the required range. Strict control is required when re-weighing, to ensure subsequent effective and normal production. The correctness of the operation process directly affects the quality of the product.

Smelting

Smelting is mainly responsible for casting the prepared materials into slices or ingots, which are respectively completed by a large furnace and a small furnace.
1). Cast sheet smelting

  • (1) Instruments, tools, auxiliary materials, etc. used: FMI-I-500R vacuum smelting cast furnace, crane, raw material car, spreader, hammer, iron clamp, vacuum cleaner, auxiliary lighting tool, slag bucket, stopwatch, thermocouple , nitrogen, argon, gloves, dust masks, sponges.
  • (2) Matters needing attention
  • ①When loading the material, the temperature around the crucible mouth is generally high. Wear big-toed shoes, protective gloves, and heat insulation pads during operation to avoid burns.
  • ②Work must be carried out in the hoisting area during the hoisting process; the wire ropes, hooks, and hangers should be carefully checked before hoisting to ensure that they are normal; during hoisting, ensure that no one is in the safety isolation zone and that no one is on the travel route of the equipment platform hoisting vehicle. Prevent personal injury
  • ③When pouring, the upper operator should stay in the pouring control position, observe the liquid flow at the pouring port, and always pay attention to the information feedback of the lower operator; the lower observer should continue to observe the side overflow of the tundish, the copper roller and the tundish In connection with the situation, when an abnormal phenomenon such as overflow of alloy liquid at the overflow or leakage of the tundish bottom plate is found, the upper operator should be notified in time. At this time, the pouring should be suspended, and the pouring will continue after the abnormality is eliminated.
  • ④ Wear a mask when replacing the tundish to reduce the harm of dust to the human body.
  • ⑤ Operators should wear gloves and masks when unloading and loading, and are not allowed to work with bare hands. Prevent the human body from polluting the cast piece; prevent the cast piece from scratching the human body.

The flow chart is as follows:

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2). Ingot smelting

  • (1) Instruments, tools and auxiliary materials used: vacuum induction melting furnace, raw material car, discharge car, iron clamp, slag barrel, auxiliary lighting, tool kit, discharge barrel, nitrogen, argon, refractory materials, Insulation gloves, dust mask
  • (2) Process: preparation→charging→vacuum→melting→casting→cooling→discharging
  • (3) Operating procedures: open the pre-pump valve, open the vacuum gauge → pump down below 0.08 → Cairo Roots pump → the vacuum gauge is 0 o’clock → close the pre-pump valve and Roots pump, turn off the vacuum gauge → open the inflation valve and charge argon → to When the pressure of the pressure gauge is 0.05MPa (0.04-0.06MPa) → close the charging valve and stop argon filling → turn on the main power and control power → increase the power → when the iron rod is fully dissolved into the alloy liquid, refining, let stand for 2 minutes → start casting → Cool for 25 minutes (the temperature of the furnace should be below 80 ℃) → vent (open the gas valve, manual) → turn off the power → take out the furnace.
  • (4) Matters needing attention
  • ① Wear a mask when loading and discharging to prevent inhalation of metal dust;
  • ② Attention should be paid to equipment electrical operation and inspection to prevent electric shock;
  • ③ In the smelting process, pay close attention to the flow and temperature of the cooling water in each path. When the cooling water cannot be supplied normally due to power outage or other reasons, tap water must be fed into the cooling system; if water is stopped during the smelting process, power transmission should be stopped quickly, and tap water should be connected to the cooling system to focus on cooling the induction coil. When the circulating cooling water returns to normal, turn off the tap water again, switch to circulating cooling water, and continue heating and smelting. If the molten steel splashes, stop sending power immediately, check and eliminate the fault;
  • ④ During the pouring process, if there is a large amount of water leakage when the cold ingot mold is poured through, the cooling water switch of the cold ingot mold should be quickly closed, pay attention to the change of the argon pressure gauge, and open the furnace door to take out the material; if a coil occurs during smelting If there is water leakage, stop sending power and reduce the flow of cooling water in the induction coil. Under the protection of argon gas, the furnace cover can be opened for treatment after the material in the crucible has cooled.
  • ⑤ After discharging, if there are obvious cracks or fractures in the sprue cup, it should be replaced in time to prevent the alloy liquid from flowing out during the next pouring.

Milling section

The pulverizing section is responsible for making the smelted product into fine powder. The main processes include hydrogen crushing (medium crushing), coarse powder mixing, jet milling, and fine powder mixing. The production process of low-grade products: ingredients → ingot casting → crushing → medium crushing → coarse powder mixing → jet mill → fine powder mixing. The production process of high-grade products: ingredients→casting→hydrogen crushing→coarse powder mixing→jet milling→fine powder mixing. The flow chart is as follows:

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Hydrogen smash

1. Principle of hydrogen smashing: using the hydrogen absorption characteristics of rare earth intermetallic compounds, place the neodymium-iron-boron alloy in a hydrogen environment. Cracking, so that the flakes become coarse powder.
2. Instruments, tools, auxiliary materials, etc.: domestic YS200 hydrogen crushing furnace, Nissan PHGgr50/50/200S hydrogen crushing furnace, charging device, loading and unloading truck, argon, hydrogen, nitrogen, fan.
3. Operating procedures

  • (1) Preparation: Observe that the nitrogen pressure and water source pressure meet the requirements of the hydrogen crushing process card. Set the process parameters on the controller of the hydrogen crushing furnace and review them. Check the equipment according to the “Equipment Checklist”.
  • (2) Furnace loading: Open the furnace door, clean the furnace chamber with a vacuum cleaner, remove the barrel fixing pin, put the hydrogen scrap barrel into the furnace chamber with a charging cart, lower the height of the charging cart and pull it out. Wipe the oven door and rubber ring with cotton cloth, and close the oven door. Place the completed “Product Identification Card” on the furnace door.
  • (3) Hydrogen smash:
  • ① Leak detection: press “automatic operation”, nitrogen is introduced into the furnace body, and the equipment starts positive pressure leak detection. After leak detection, the furnace body is vented to atmospheric pressure, and vacuum negative pressure leak detection is performed. When the requirements of the process card are met, the equipment will give an alarm. At this time, press the H2 valve to open, and the hydrogen smash will enter the automatic operation stage, and hydrogen will be introduced.
  • ② Hydrogen conduction: When the pressure in the furnace reaches the maximum hydrogen absorption in the process card, it is closed. After the material absorbs hydrogen, the pressure in the furnace drops, and the system automatically introduces hydrogen to the maximum value. This process is repeated. After the system confirms, the cylinder starts rotating. Keep the pressure at the maximum value and indicate that the material no longer absorbs hydrogen. Confirm that the hydrogen conduction is completed for 8 minutes.
  • ③ Replacement: The system automatically opens the exhaust valve, and closes when the exhaust reaches atmospheric pressure. The three argon inlet valves are opened one after the other. When the pressure reaches the replacement pressure, one of the argon gas inlet valves is closed, the other two are normally open, and the exhaust valve is automatically opened to exhaust, and this is repeated until the set time. The exhaust valve opens, exhausts to atmospheric pressure, and the replacement is completed.
  • ④ Dehydrogenation: The pumping system starts automatically. When the pumping rate is below 40mba, the system will automatically power on and increase the temperature, and vacuum while the temperature is rising. Generally, the temperature is 40 minutes. When the temperature reaches the set temperature of the process card, keep it for 1-3 hours. When the vacuum degree reaches the requirement of the process card, dehydrogenation is completed. If the requirements are not met, the pumping will continue until the requirements are met, the dehydrogenation is completed, and the pumping system will automatically shut down.
  • ⑤ Cooling: After the exhaust system is closed, the three argon valves are automatically opened to fill in argon at the replacement pressure value. The fan is automatically air-cooled. When the pressure in the furnace is insufficient, it is automatically supplemented. The air-cooling is about 3-5 hours to reach At 35-40 degrees, the system starts to record the cooling stop time, usually about 20 minutes. When the cooling set time is reached, the argon inlet valve is automatically closed, the fan is automatically closed, and the exhaust valve is opened to exhaust. When exhausted to atmospheric pressure, the furnace can be discharged.
  • ⑥ Baking: After the hydrogen crushing is completed, the “EDN” indicator light is on, and the device emits an alarm sound, and the furnace can be released at this time. Open the furnace door, use the charging truck to take out the barrel and place it on the barrel rack in the cooling zone, inject nitrogen into the barrel in time, and turn on the cooling fan.
  • ⑦ After the barrel reaches the cooling temperature in the cooling zone, transfer the barrel to the discharge area, replace the lid of the barrel with a funnel-shaped lid, and pour the product into the cleaned cylinder.

4. Stir the coarse powder
Coarse powder stirring is to mix the coarse powder evenly after hydrogen crushing (medium crushing) by rotating the stirring tank.
Process flow:

  • (1) Constant pressure of the mixing tank: Open the stop valve of the mixing tank, open the exhaust tank of the mixing tank, and observe the pressure gauge until it meets the requirements of the process card. Open and close the exhaust tank intermittently, observe the pressure gauge, close the exhaust valve when the specified pressure is reached, supplement air when the pressure is insufficient, and close the shut-off valve when the pressure is reached.
  • (2) Dosing: take the dosing dose in a measuring cylinder according to the requirements of the process card, then pour it into the dosing device, connect the nozzle tube and the mixing tank inflation valve, open the inflation valve, open the stop valve, set the mixing time, start the mixer, and make the mixing tank swing back and forth, open the spray device to spray.
  • (3) Stirring: After the dosing is finished, close the shut-off valve, close the inflation valve, close the dosing equipment, remove the dosing connection equipment, and then turn on the mixing tank to rotate, and it will automatically stop after the end of the mixing.

5. Matters needing attention

  • (1) When the furnace door needs to be opened in the abnormal state of the equipment, it must be replaced with argon and then vacuumed.
  • (2) In the process of hydrogen smashing, attention should be paid to check whether the hydrogen pipeline system leaks. When a leak occurs, the pipeline should be closed and repaired in time. Open flames should be eliminated during this process.
  • (3) When loading and unloading the barrel, the action should be gentle to prevent the barrel from slipping out.

Jet mill

1. Principle of jet mill: Use high-pressure airflow to blow up the stirred coarse powder, and reduce the strength through collision with each other to become fine powder.
2. Instruments, tools, auxiliary materials, etc. used: 400AFM-R jet mill, electronic scale, particle size analyzer, steel cylinder, trolley, crane, rubber ring, clamp, rubber hammer, protective mask.
3. Process flow

  • (1) Preparation: Arrange milling operations, check equipment, set parameters, and discharge materials according to the production plan.
  • (2) Startup: Switch to the automatic mode state before starting up. If the start-up state is met, press the “S11” key to return to the compressor diagram, press the “S3” key to automatically start the jet mill, record the start time, and start the air compressor.
  • (3) Connect the fine powder steel bottle: connect the fine powder steel bottle that has exhausted oxygen to the discharge port of the powder sifter.
  • (4) Feeding: use a crane to hoist the cylinder to the feeding port for feeding, and cover the feeding hopper mouth after feeding.
  • (5) Oxygen exhaust: Turn on the vibrating screen and open the discharge valve to exhaust oxygen.
  • (6) Abrasive: After the speed of the separating wheel reaches the requirement, press the feeding button, the coarse powder from the feeding port of the jet mill automatically enters the grinding chamber for grinding; the abrasive falls into the first cylinder, and the start time and related parameters of the abrasive are recorded.
  • (7) Oxygenation passivation: When the material is automatically fed to the set value, the oxygenation flow rate is adjusted for oxygenation.
  • (8) First bottle receiving and cylinder replacement: When the powder material in the first cylinder meets the requirements of the process card, replace the cylinder, and prepare for the first bottle particle size sampling.
  • (9) First bottle particle size sampling: take a plastic bag and fill it with nitrogen in advance, tie the mouth by hand and wrap the sampling gas valve, open the nitrogen tube and insert it into the plastic bag together; open the sampling ball valve momentarily and close it, and fill the powder sample into the plastic bag Inside, sampling is complete. After passivation, it is ready to be measured for particle size inspection.
  • (10) Replace steel cylinders and continue to receive materials.
  • (11) Sampling and inspection of particle size samples: According to the requirements of the jet mill process card, the sequence number of the steel cylinder is sampled. The sequence number of the particle size sample is the sequence number of the last steel cylinder when sampling.
  • (12) First inspection and disposal: The operator conducts self-inspection on the average particle size of the first bottle of powder, and continues if it is qualified, and stops feeding if three consecutive bottles are unqualified.
  • (13) Weighing and transfer: Weigh the charging cylinder and move it to the fine powder warehouse, and connect the nitrogen tube to the cylinder.
  • (14) Casting tailings processing: place the tailings in the fine powder tailings area.
  • (15) Shutdown: When there is no material in the upper hopper, it should be converted to dry running, and then press “S4” to automatically shut down the device and turn off the air compressor power supply.
  • (16) Site clearance: When the ingot material is transferred to the ingot material, the bottom material should be cleaned up.

4. Stir fine powder
Fine powder mixing is to mix fine powders of different grades after jet milling according to the ratio. The operation process is the same as that of coarse powder mixing.
5. Matters needing attention

  • (1) During operation, if air leakage is found in the pipeline, stick it with tape in time. If the air leakage is serious, stop feeding, and fill the powder in the grinding chamber with nitrogen for protection.
  • (2) During operation, if the ultra-fine powder in the grinding chamber or filter catches fire, the machine should be turned off and filled with nitrogen for protection. If the situation is serious, press “Emergency Stop”.
  • (3) If the powder material leaks when receiving the material, it should be covered with yellow sand or asbestos cloth as soon as possible, and cleaned up after cooling.
  • (4) Special attention should be paid to personnel safety during the hoisting process of steel cylinders, and personnel are strictly prohibited from entering under the hanger.
  • (5) When the steel cylinder is turned over, special care should be taken to prevent hand pinching. Protective masks must be worn during the discharging and sampling operations to prevent the powder from spraying out and harming the human body.

Forming section

The forming section is responsible for pressing the powder into shape, including forming and isostatic pressing.

Forming

1. Forming principle: Select the corresponding mold according to the requirements, and press the fine powder into the required shape.
2. Instruments, tools, auxiliary materials, etc. used: automatic magnetic field forming press, cylindrical forming press, square forming press, vacuum packaging machine, automatic powder weighing machine, circulation cart, electronic scale, caliper, small copper shovel, brush , Magnetic powder sanitary ware, magnetic column, pressure handle, protective pad, vacuum packaging bag, inner packaging film, circulation basket, circulation box.
3. Flow chart:

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4. Specific operating procedures

  • (1) Forming mold installation and disassembly: preparation → mold installation → press preparation → installation of lower indenter → mold frame installation → upper indenter → verticality inspection → demolding
  • (2) Magnetic field measurement and adjustment of forming press: calibration → magnetic field measurement and adjustment → field clearing
  • (3) Weighing powder: preparation before weighing→reclaiming→feeding→unloading→weighing→changing the barrel→cleaning and clearing the field
  • (4) Press operation
  • Cylindrical type: upper cylinder down→pause→orientation→pressing→holding pressure→demagnetization→upper cylinder up→lower cylinder up.
  • Block type: upper cylinder down→press mold→side cylinder advance→orientation→press→hold pressure→demagnetization→side cylinder retreat→upper cylinder up.
  • (5) Packaging: preparation→inspection and recording→inner film→bagging→vacuum→cartoning→marking and sequence transfer
  • (6) Cleaning: press cleaning → automatic powder weighing machine cleaning → packing box cleaning → vacuum packaging machine cleaning→ Work area ground cleaning
  • (7) Forming press cleaning site: disassemble empty barrel → automatic powder weighing machine cleaning → press cleaning → packing box cleaning → floor cleaning in work area

5. Matters needing attention

  • (1) During the magnetization process, the Teslameter probe should be placed in the middle of the magnetic poles, not in contact with any objects, and the manual magnetization time should not be too long to avoid burning the equipment.
  • (2) During the main operation of the powder weighing, the oxygen meter should be observed at any time. When the oxygen content is found to be greater than 0.05%, the operation should be suspended, the nitrogen content should be adjusted, and the operation can be continued after the oxygen content is qualified.
  • (3) When disassembling the material barrel, be sure to close the manual butterfly valve at the feed inlet first, and release the nitrogen in the material barrel before replacing it to prevent the magnetic powder from being sprayed on the human body during feeding.

Isostatic pressure

1. Isostatic pressure principle: The working principle of isostatic pressure is Pascal’s law: “The pressure of the medium (liquid or gas) in a closed container can be transmitted equally in all directions.” Specifically, after the compressed product is loaded into the equipment , The product is subjected to uniform ultra-high pressure media to increase the density of the product, and the shrinkage of the briquette depends on the compressibility of the material and the pressure during compression.
2. Apparatus, tools, auxiliary materials, etc. used: LDJ320/1500-300YS cold isostatic press (water medium), crane, cage, circulation truck, non-slip boots, plastic gloves, aprons, sleeves.
3. Operating procedures

  • (1) Preparation: The operator is responsible for checking the operation documents, equipment, instruments, tooling, and tools before the operation to make them complete. Then carry out equipment inspection.
  • (2) Parameter setting: According to the requirements of the isostatic pressing process card of the pressed product, set the parameter on the input panel.
  • (3) Loading: Place the hanging cage on the loading platform; open the hanging cage door; place the product code in the hanging cage; close the hanging cage door.
  • (4) Inlet cylinder: Turn the working cylinder (on/off) knob on the control panel to the “open” position, and the working cylinder cover will open accordingly. Use a crane to lift the cage into the working cylinder. After the cage is put into the working cylinder, observe whether the cage is completely invaded below the liquid surface. If not, add working fluid to the cylinder to completely immerse the product; turn the working state knob to the “close” position and close the cylinder cover.
  • (5) Isostatic pressure: start the isostatic press, the equipment will automatically pressurize, and the pressure light will be on; when the pressure reaches the set value, the equipment will automatically stop the pressure and the pressure light will go out; the pressure holding light will be on and the system will perform Pressure; when the pressure-holding time is up, the pressure-holding light will go out and pressure-relief will start; when the pressure-relief reaches a predetermined value, the equipment will automatically stop pressure-relief.
  • (6) Vat discharge: Open the cylinder cover; lift the cage out with a crane; drain the working fluid in the air for 40-60 seconds, then place it on the discharge table. Take the product out of the cage and place it on the circulation cart.

4. Matters needing attention

  • (1) It is strictly forbidden to pressurize when the rack has not fully entered the working position;
  • (2) During the operation of the press, closely monitor the operation panel on the electric control cabinet and the ultra-high pressure gauge on the pressure gauge bracket to prevent overpressure;
  • (3) No one is allowed to walk around the high-pressure site during the work phase of pressurizing, maintaining and depressurizing.

Sintering section

The sintering section is responsible for sintering the products after oil stripping, including two parts: oil stripping and sintering.

Oil stripping

Oil stripping is to remove the product packaging after isostatic pressing to facilitate sintering
1. Instruments, tools, auxiliary materials, etc. used: mobile glove box, oxygen meter, circulation cart, turnover box, oil stripping box, auxiliary feeding box, sintering basin, sintering bracket, scissors, mask, rubber gloves, finger cots , Garbage bag, sponge, marking iron, isolation strip
2. Operation process

  • (1) Preparation: The operator is responsible for checking the operation documents, equipment, instruments, tooling, and tools before the operation to make them complete. Then pick materials, picking materials in batches according to production batches. Be prepared before stripping the oil.
  • (2) Oxygen discharge: Open the glove box inflation valve and auxiliary feed box inflation valve, and fill it with nitrogen; observe the oxygen meter, and cut the bag when the oxygen content drops to <0.05%.
  • (3) Peel the oil and fill the basin: cut the bag→peel the packaging bag→peel the inner membrane→place the basin
  • (4) Cleaning: After the oil is peeled and filled into the basin, the glove box should be carefully cleaned to ensure that there is no remaining material; the vacuum packaging bag and inner packaging film should be put into the garbage bag; the garbage bag, transfer plastic box, and material box should be transferred to the auxiliary In the feeding box; check and ensure that there is no debris in the sintering basin and bracket (packaging bags, inner membrane fragments, etc., to prevent product contamination during the sintering process); notify the sintering section operator to enter the furnace.

3. Matters needing attention

  • (1) During the operation, the oxygen meter should be observed at all times to ensure that the oxygen content is ≤0.05%, so as to prevent the powder from oxidizing and catching fire, which may cause human injury;
  • (2) During the operation, attention should be paid to the tightness of the observation window and whether the sleeve is in good condition, so as not to cause human injury under the action of gas pressure;
  • (3) When the sintering pot is moving, the coordinated operation should be coordinated to prevent the sintering pot from tipping, slipping, and hurting fingers.

Sintering

1. The sintering process flow chart is as follows:

20201229220930 49777 - How magnet is made?

2. Instruments, tools, auxiliary materials, etc. used: VS-200RPA sintering furnace, glove box, sintering basin, hydraulic car, circulation car, thermal insulation gloves.
3. Operation process

  • (1) Preparatory work: The operator shall check the equipment, instruments, tooling, and tools before operation to make them complete.
  • (2) Vacuum inspection: Check and confirm that the furnace door is closed, and open the sintering furnace for vacuuming. Observe the degree of vacuum, calculate the vacuum time, and confirm that the requirements are met before putting the product into the furnace.
  • (3) Entering the furnace: confirm the end of the product’s oil peeling basin, and after filling the sintering furnace with nitrogen to atmospheric pressure according to the operating procedures, stop the charging. Turn on the flapper valve, turn on the screen guard valve, turn on the feeding mechanism, and slowly feed the sintering basin into the sintering furnace to make it in place. Reset the feeding mechanism. Close the screen guard valve, and close the flapper valve. Close the glove box inflation valve and turn off the oxygen meter. Then set the parameters.
  • (4) Sintering: Start the sintering furnace according to the operating procedures, and inspect the vacuum meter, voltmeter, ammeter, and cooling water of the vacuum equipment during the heating, heat preservation, and cooling process.
  • (5) Out of the furnace: After sintering, confirm that the temperature of the product in the furnace meets the process requirements, and open the furnace door; use a hydraulic forklift to take out the sintering basin in the furnace to prevent it from being on the transfer cart. Close the furnace door and turn on the vacuum device. Place the transfer truck in the area to be inspected.

4. Matters needing attention

  • (1) When an abnormal situation such as water leakage or gas leakage is found during the sintering process, the furnace should be vacuumed and then filled with argon to replace it. The furnace door can be opened only when safety is ensured.
  • (2) Wear heat-insulating gloves during the product release process to prevent human body from being burned by high temperature.
  • (3) When using hydraulic trucks to load and unload materials, they should be handled with care to prevent the sintering pot from overturning and hurting the human body.
  • (4) When moving the transfer truck, ensure that the line is barrier-free to prevent human body injury.

Magnetic property of sintered neodymium magnets

Grade Remanence  Coercive Force  Intrinsic Coercive force  Max Energy Product  Max Working Temp.
Br Hcb Hci (BH) max
KG T KOe KA/m KOe KA/m MGOe KJ/m °F
N35 11.4-11.8 1.18-1.28 ≥ 10.8 ≥ 836 ≥ 12 ≥ 955 33-36 263-287 80 176
N38 11.8-12.3 1.18-1.28 ≥ 10.8 ≥ 860 ≥ 12 ≥ 955 36-39 287-310 80 176
N40 12.7-12.9 1.27-1.29 ≥ 11.0 ≥ 876 ≥ 12 ≥ 955 38-41 303-326 80 176
N42 12.9-13.3 1.29-1.33 ≥ 10.5 ≥ 836 ≥ 12 ≥ 955 40-43 318-342 80 176
N45 13.3-13.8 1.33-1.38 ≥ 9.5 ≥ 756 ≥ 12 ≥ 955 43-46 342-366 80 176
N48 13.8-14.2 1.38-1.42 ≥ 10.5 ≥ 835 ≥ 12 ≥ 955 46-49 366-390 80 176
N50 13.8-14.5 1.38-1.45 ≥ 10.5 ≥ 835 ≥ 11 ≥ 955 47-51 374-406 80 176
N52 14.3-14.8 1.43-1.48 ≥ 10.8 ≥ 860 ≥ 11 ≥ 876 50-53 398-422 80 176
33M 11.4-11.8 1.14-1.18 ≥ 10.3 ≥ 820 ≥ 14 ≥ 1114 31-33 247-263 100 212
35M 11.8-12.3 1.18-1.23 ≥ 10.8 ≥ 860 ≥ 14 ≥ 1114 33-36 263-287 100 212
38M 12.3-12.7 1.23-1.27 ≥ 11.0 ≥ 876 ≥ 14 ≥ 1114 38-41 303-326 100 212
40M 12.7-12.9 1.27-1.29 ≥ 11.4 ≥ 907 ≥ 14 ≥ 1114 38-41 303-326 100 212
42M 12.8-13.2 1.28-1.32 ≥ 11.6 ≥ 923 ≥ 14 ≥1114 40-43 318-342 100 212
45M 13.2-13.8 1.32-1.38 ≥ 11.8 ≥ 939 ≥ 14 ≥ 1114 43-46 342-366 100 212
48M 13.6-14.0 1.36-1.40 ≥ 11.8 ≥ 939 ≥ 14 ≥ 1114 46-49 366-390 100 212
50M 14.0-14.5 1.40-1.45 ≥ 13.0 ≥ 1033 ≥ 14 ≥ 1114 48-51 382-406 100 212
30H 10.8-11.4 1.08-1.14 ≥ 10.2 ≥ 812 ≥ 17 ≥ 1353 28-31 223-247 120 248
33H 11.4-11.8 1.14-1.18 ≥ 10.6 ≥ 844 ≥ 17 ≥ 1353 31-33 247-263 120 248
35H 11.8-12.3 1.18-1.28 ≥ 11.0 ≥ 876 ≥ 17 ≥ 1353 33-36 263-287 120 248
38H 12.3-12.7 1.23-1.27 ≥ 11.2 ≥ 890 ≥ 17 ≥ 1353 36-39 287-310 120 248
40H 12.7-12.9 1.27-1.29 ≥ 11.5 ≥ 915 ≥ 17 ≥ 1353 38-41 303-326 120 248
42H 12.8-13.2 1.28-1.32 ≥ 12.0 ≥ 955 ≥ 17 ≥ 1353 40-43 318-342 120 248
45H 13.2-13.5 1.32-1.38 ≥ 12.0 ≥ 955 ≥ 17 ≥ 1353 42-46 335-366 120 248
46H 13.3-13.8 1.33-1.38 ≥ 12.2 ≥ 972 ≥ 16 ≥ 1274 44-47 350-374 120 248
48H 13.6-14.3 1.36-1.43 ≥ 12.5 ≥ 995 ≥ 16 ≥ 1274 46-49 366-390 120 248
30SH 10.8-11.4 1.081.14 ≥ 10.0 ≥ 796 ≥ 20 ≥ 1672 28-31 223-247 150 302
33SH 11.4-11.8 1.14-1.18 ≥ 10.5 ≥ 836 ≥ 20 ≥ 1672 31-34 247-276 150 302
35SH 11.8-12.3 1.18-1.23 ≥ 11.0 ≥ 876 ≥ 20 ≥ 1672 33-36 263-287 150 302
38SH 12.3-12.7 1.23-1.27 ≥ 11.4 ≥ 907 ≥ 20 ≥ 1972 36-39 287-310 150 302
40SH 12.5-12.8 1.25-1.28 ≥ 11.8 ≥ 939 ≥ 20 ≥ 1972 38-41 302-326 150 302
42SH 12.8-13.2 1.28-1.32 ≥ 11.8 ≥ 939 ≥ 20 ≥ 1672 40-43 320-343 150 302
45SH 13.2-13.8 1.32-1.38 ≥ 12.6 ≥ 1003 ≥ 20 ≥ 1592 43-46 342-366 150 302
30UH 10.8-11.4 1.08-1.14 ≥ 10.2 ≥ 812 ≥ 25 ≥ 1990 28-31 223-247 180 356
33UH 11.3-11.7 1.13-1.17 ≥ 10.7 ≥ 852 ≥ 25 ≥ 1990 31-33 247-263 180 356
35UH 11.7-12.1 1.17-1.21 ≥ 10.7 ≥ 852 ≥ 25 ≥ 1990 33-36 263-287 180 356
38UH 12.1-12.5 1.21-1.25 ≥ 11.4 ≥ 907 ≥ 25 ≥ 1990 36-39 287-310 180 356
40UH 12.5-12.8 1.25-1.28 ≥ 11.4 ≥ 907 ≥ 25 ≥ 1990 38-41 302-326 180 356
28EH 10.5-10.8 1.05-1.08 ≥ 9.5 ≥ 756 ≥ 30 ≥ 2388 26-29 207-231 200 392
30EH 10.8-11.4 1.08-1.14 ≥ 9.5 ≥ 756 ≥ 30 ≥ 2388 28-31 223-241 200 292
33EH 11.3-11.7 1.13-1.17 ≥ 10.2 ≥ 812 ≥ 30 ≥ 2388 31-33 247-263 200 392
35EH 11.7-12.1 1.17-1.21 ≥ 10.2 ≥ 812 ≥ 30 ≥ 2388 33-36 263-287 200 392
38EH 12.1-12.5 1.21-1.25 ≥ 11.4 ≥ 907 ≥ 30 ≥ 2388 36-39 287-310 200 392
30AH 10.8-11.3 1.08-1.13 ≥ 10.2 ≥ 812 ≥ 35 ≥ 2785 28-32 223-255 220 428
33AH 11.2-11.7 1.12-1.17 ≥ 10.2 ≥ 812 ≥ 35 ≥ 2785 31-34 247-271 220 428

Applications of Sintered NdFeB Magnets

  • Automotive Starters
  • Computer Rigid Disc Drives
  • DC Motors
  • Headphone
  • Halbach Arrays
  • Linear Actuators
  • Linear Motors
  • Loud Speakers
  • Magnetic Bearings
  • Magnetic Couplings
  • Magnetic Separators
  • Microphone Assemblies
  • Particle Accelerators
  • Printers
  • Relays
  • Servo Motors
  • Stepper Motors
  • Switches
  • Undulators
  • Vacuum Deposition

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

Summary
how magnet is made - How magnet is made?
Article Name
How magnet is made?
Description
Sintered NdFeB permanent magnets are produced by powder metallurgy. There are sixteen process links in total, and several monitoring analyses are included in different stages. Strictly speaking, these sixteen links are indispensable.
Author
Publisher Name
www.ymagnet.com
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