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How to make a strong magnet-magnet making process
Time:08/05/2021
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How are NdFeB powerful magnets made? The so-called powerful magnets usually refer to neodymium iron boron magnets. Compared with ferrite magnets, aluminum nickel cobalt, and samarium cobalt, its magnetic performance greatly surpasses other types of magnets. Neodymium iron boron magnets can absorb 640 times the weight of its own weight, so neodymium iron boron is often used by outsiders. It is called a powerful magnet. Let's take a look at how the NdFeB strong magnet is made, as well as the production process, manufacturing process and equipment principle of the NdFeB magnet.
How is a powerful magnet made? How are NdFeB powerful magnets made? And the principle of the magnet manufacturing process
 
(1) Smelting
1. According to different processes, it can be divided into two types: conventional smelting (20kg, 30kg, 50kg, 100kg) and belt spinning furnace (100kg, 300kg, 500kg). 
 
2. Craft  
Pretreatment of A, Nd, Fe, B ingredients B, ingredient C, smelting:  First charge the material and then pump it to below 1Pa, start low-power heating, continue to pump air while heating, as the temperature rises, the gas in the adsorbed state , The water is gradually desorbed and drawn out, until the charge is generally dark red, close the valve and fill with argon gas, increase the power and heat up until the charge is completely melted, and perform refining for about 5 minutes. After the refining is completed, the power is reduced and pouring is performed. The gate should be aligned with the cooling mold, and the pouring is completed and cooled. 
D. Preservation of the alloy. Pay attention to the entry of impurities such as glove wire, dust in the air, etc. during the placement and transportation of alloy ingots. At the same time, oxygen has a destructive effect on the alloy. Oxygen permeates in and turns neodymium into neodymium oxide; water vapor has a destructive effect on the alloy. When water encounters neodymium, neodymium oxides and hydrides will be generated. Therefore, the smelting process must be protected from impurities and oxidation. . 
 
(2) Flour milling 
1. Equipment  
Hydrogen crusher, coarse crusher, medium crusher, jet mill, mixer 
2. Process
3. Key points of process control
A. The particle size of the powder is 2.9-5.2um. The finer the particle size, the corresponding coercive force and remanence will increase, and the corrosion resistance of the product will also increase, but the subsequent process is not easy to control, and the narrower particle size distribution can be made higher.
B. It is very important to put some air in the jet mill to passivate the powder. It is just as if people go from the dark to the bright place, the eyes will be uncomfortable and sometimes damage the eyes. If the powder does not put some air, it will be It is easier to oxidize in subsequent production, and it is very likely to burn
C. Stirring, because the performance of the powder coming out before and after is not consistent, the powder needs to be stirred
 
(3) Forming
1. Equipment   press, isostatic press, storage cylinder
2. Process A, powder weighing: Weigh powder B and magnetic field orientation molding according to the process requirements: this process is to arrange thousands of NdFeB powders neatly under the action of a magnetic field and press them into a set shape in the mold , The basic requirement of the press is that the magnetic field must be greater than 18,000 ohms at a 40mm air gap, and there should be a photoelectric protector to prevent the press from hurting people. The density of the pressed green body is about 3.2----3.8g/cm3, The theoretical density of Nd-Fe-B after sintering is about 7.5g/cm3. Therefore, when pressing relatively large cylinders and squares, due to the large shrinkage, it is easy to crack and deform the corners and the size is out of tolerance. Therefore, isostatic pressing is required. To increase the density of the green body, the density of the green body after isostatic pressing is 4.5 g/cm3. The company now directly swings the box and enters the sintering furnace except for low-performance small columns (below Ф10). In order to prevent oil immersion and surface oxidation, the isostatic green body must be vacuum sealed and stripped before entering the furnace. 4. Abrasive tools: The production and design level of abrasive tools directly affects the appearance quality of the product. The competition in the industry is fierce, and abrasive tools are an important link in saving costs.The reduction of processing allowances, the reduction of product deformation, and the direct production of some special-shaped products will determine one of the important factors of whether an enterprise is competitive.
 
(4) Sintering
How is a powerful magnet made? This step is more important. After forming or isostatic pressing, the green body does not have a microstructure with high permanent magnetic properties. In order to further increase the density, improve the contact properties between powder particles and increase the strength, so that the magnet has a microstructure with high permanent magnetic properties. Features: the compact needs to be heated to a temperature below the melting point of the powder matrix phase for a period of heat treatment. The sintering furnace should have good sealing and low leakage rate. Therefore, it should always be closed and vacuumed to prevent the adsorption of gas and water vapor. Keep the furnace door open for a long time in contact with the outside air and water vapor. The oil stripping 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 used to remove hydrogen scrap It is between 1050℃~1085℃, the hydrogen smash of ingot is about 1070℃~1095℃, and the ingot material is between 1100℃~1135℃. The aging is divided into two-stage aging mechanism 890℃~920℃ and 500℃ ~630°C for the second stage, the whole process from sintering and aging to baking generally takes between 20 to 38 hours.
 
(5) Post-processing
Due to the influence of production factors, the dimensional accuracy of Nd-Fe-B blanks cannot directly meet customer requirements, and subsequent processing must be carried out to meet customer requirements. ü Use wire cutting (wire cutting machine) for some special-shaped or slicing machines that cannot be directly sliced.  ü For wafers and small and medium squares, use a slicing machine. For higher precision or CPK requirements, a double-sided grinder is required for processing (slicing machine, Double-sided grinder) ü Small cylinders that cannot be directly pressed need to be cut into small squares with squares and then rounded (small centerless grinding) ü Some products require small holes to be punched, and holes above Ф6 can be punched (punched) Hole machine, punching machine)  ü Molded and pressed cylinders (under Ф80) are ground with a centerless grinder (centerless grinder)  ü Cylinders larger than 80mm must be completed with a punching device ü For squares that need to be ground, use a large vertical mill or Flat grinding or double-sided grinding equipment ü Some special-shaped products can also be directly covered with tiles.
How is a powerful magnet made? How are NdFeB powerful magnets made? And the principle of the magnet manufacturing process
 
(6) Electroplating
Because NdFeB products have poor corrosion resistance, surface treatment must be carried out.
1. The form of surface treatment
a. Galvanizing: blue and white zinc, white zinc, color zinc, black zinc. According to environmental protection requirements, it can be divided into trivalent chromium zinc (environmentally friendly 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 and gray epoxy. d. Phosphating. e. Gold-plated, copper-plated, silver-plated, tin-plated, etc.
2. Electroplating process
The mechanical chamfering time may be long, so electroplating products are not very fast, and there must be a cycle.
 
(7) Reliability test
1. Drop test: Use glue to stick the product and the iron sheet together, drop it freely from 1~1.5m in the air and repeat it many times to see if the coating has fallen off. The drop test is basically to check and accept the galvanized product.
2. Cross-cut test: Cross-cut the coating with a knife to see the combination of the coating (galvanized or nickel-plated is ok).
3. Chill and heat test: Put the nickel-plated product in an oven for heating (about 200°C), and then chill it in water for several cycles to test the bonding force of the nickel-plated product.
4. PCT test: (pressure cooking test) conditions: 2 atmospheres, 95% relative humidity, 121 ℃ temperature, test the adhesion of the coating.
5. Weight loss test: Nd-Fe-B is easy to oxidize, different processes, different added elements, and different process controls. The weight loss is different. The unit of weight loss test is how many milligrams of weight per square centimeter is lost. The United States It is not the same as the European standard. American requirements: PCT: 2atm (atmospheric pressure) 95%RH (humidity) 121°C, 96 hours, with a weight loss of less than 10mg/cm2, European requirements: Hast test: 3atm (atmospheric pressure) 95%RH (humidity) 130°C, 240 hours, The requirement that the weight loss is less than 10mg/cm2 is obviously much stricter in Europe. At present, most of the PCT tests of Nd-Fe-B products produced by traditional domestic processes are 80~300 mg/cm2. If cobalt is added and the conventional process can be controlled at the same time Reached below 10mg/cm2. If other processes are used, it is relatively easy to control.
6. Salt spray test: The condition is 5% sodium oxide, 35℃ temperature, continuous spraying for 48 hours or 72 hours, whether there is corrosion in the coating.
7. Constant temperature and constant 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 and cool it, compare the magnetic flux before heating and the magnetic flux after heating to measure the temperature stability of the product.
 
How is a powerful magnet made? How are NdFeB powerful magnets made? As well as the principle of the magnet making process, this article is for reference only!
 
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