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How is a powerful magnet made? - Magnet making process

How is the NdFeB powerful magnet made? The so-called strong magnet is a neodymium iron boron magnet. Compared with ferrite magnets, AlNiCo, SmCo, the magnetic properties greatly exceed those of other magnets. NdFeB magnets can absorb 640 times their own weight, so NdFeB is often used by outsiders. It is called a powerful magnet. Let's take a look at how the NdFeB magnets are made, as well as the NdFeB magnet manufacturing process, manufacturing process and equipment principles.

How is the powerful magnet made? How is the NdFeB powerful magnet made? And the principle of the magnet making process


(1) Smelting

1. According to the different process, it can be divided into two types: conventional smelting (20kg, 30kg, 50kg, 100kg) and simmering furnace (100kg, 300kg, 500kg).


2. Process

Pretreatment of A, Nd, Fe, B ingredients B, ingredient C, smelting: Firstly, the material is charged to 1Pa or less, and the low-power heating is started. The gas is continuously pumped while heating, and the gas in the adsorbed state increases with the temperature. The water is gradually desorbed and extracted, until the charge is generally dark red, the valve is filled with argon gas, and the power is increased until the charge is completely melted, and the refining is performed for about 5 minutes. After refining, the power is reduced and poured. The gate should be aligned with the cooling mold, poured and cooled.

D. Preservation of alloys In the process of placing and transporting alloy ingots, attention should be paid to the entry of impurities such as the wire of the gloves and the dust in the air. At the same time, oxygen has a destructive effect on the alloy, and oxygen permeates into the yttrium oxide. The water vapor has a destructive effect on the alloy. When the water hits the ruthenium, it will form ruthenium oxides and hydrides. Therefore, the smelting process should be protected against impurities and oxidation. .


(2) Milling

1, equipment

Hydrogen crusher, coarse crusher, medium crusher, jet mill, mixer

2, process

3. Process control points

A, the particle size of powder, 2.9 - 5.2um is appropriate, the finer the particle size, the coercivity and remanence will increase, the corrosion resistance of the product will also increase, but the subsequent process is not well controlled, the narrower the particle size distribution can be done.

B. The proper amount of air in the airflow is very important to passivate the powder. It is as if the person walks from the dark to the bright place, the eyes will be uncomfortable, sometimes it will damage the eyes. If the powder does not put some air, it will instead It is easier to oxidize in subsequent production, and it is very likely to burn.

C, stirring, because the powder properties before and after are not consistent, so the powder needs to be stirred


(3) Forming

1. Equipment Press, isostatic pressing, storage cylinder

2, process A, weighing: according to the process requirements for powder B, magnetic field oriented molding: this process in order to tens of millions of NdFeB powder in the magnetic field neatly arranged, and pressed into a set shape in the mold The basic requirement of the press is that the magnetic field must be greater than 18000 ohms in the 40mm air gap. At the same time, there should be a photoelectric protector to prevent the injury of the press C. The compacted green density is about 3.2----3.8g/cm3. The theoretical density of Nd-Fe-B after sintering is about 7.5g/cm3, so when pressing larger cylinders and squares, the deformation and size are too large due to the large amount of shrinkage, so it is necessary to pass isostatic pressing. 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 passes the isostatic pressing of the low-performance small column (below ß∂10) without the isostatic pressure and directly into the sintering furnace. In order to prevent oil immersion and surface oxidation, the isostatic green body must be vacuum-packed and stripped before entering the furnace. 4. Abrasives: The quality of the manufacturing and design of the abrasive tools directly affects the appearance quality of the product. Industry competition is fierce, and abrasive tools are an important part of cost saving. Reduce the allowance, the amount of deformation of the product to reduce the number of direct compression profiled products, the important factor in determining whether a company competitive.


(four) sintering

How is the powerful magnet made? This step is more important. After forming or isostatic pressing, the green body does not have the microstructure of high permanent magnet properties. In order to further improve the density, the contact properties between the powder particles are improved, the strength is increased, and the microstructure of the magnet with high permanent magnet properties is obtained. Characteristics, it is necessary to heat the compact to a temperature below the melting point of the powder matrix phase for a heat treatment. The sintering furnace should have good sealing performance and low leakage rate. Therefore, it should be kept tightly vacuumed to prevent gas and water vapor adsorption, and the product should not be taken out after removal. Let the furnace door open, and contact with the outside air and water vapor for a long time. The stripping tank should also be closed in time to prevent the adsorption of water vapor and affect the performance of the product. The sintering process is divided into two stages of sintering and aging, sintering temperature, and hydrogen-containing scrap Between approximately 1050 °„ C and 1085 °„ C, the ingots are crushed between 1070 °„ C and 1095 °„ C. The ingots are between 1100 °„ C and 1135 °„ C. The aging is divided into two stages of aging mechanism: 890 °„ C ~ 920 °„ C and 500 °„ C. The second stage of ~630 °„C, from sintering and aging to the entire process of the furnace generally takes between 20~38 hours.


(5) Post processing

Due to the influence of production factors, the dimensional accuracy of Nd-Fe-B blanks cannot directly meet the requirements of customers, and subsequent processing is required to meet customer requirements. ®Ļ Wire cutting (wire cutting machine) for some shaped or sliced machines that can not be directly sliced ®Ļ For sliced and medium and small squares, use a microtome for higher precision or CPK requirements (slicer, Double-sided grinding machine) ®Ļ Small cylinders that cannot be directly pressed need to be cut into small square bars and then rounded (small centerless grinding). ®Ļ Some products require small holes to be punched, and holes with holes above ß∂6 can be set. Hole machine, hole machine) ®Ļ Form-pressed cylinder (ß∂80 or less) is ground with a centerless mill (heartless mill) ®Ļ For cylinders larger than 80mm, it must be done with a hole-setting device. Flat grinding, or double-sided grinding equipment ®Ļ Some shaped products can also be completed with a direct tiling.

How is the powerful magnet made? How is the NdFeB powerful magnet made? And the principle of the magnet making process


(6) Electroplating

Since NdFeB products have poor corrosion resistance, surface treatment must be performed.

Surface treatment form

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 (environmental zinc) and hexavalent chromium and zinc. b. Nickel plating: bright nickel, black nickel, currently nickel plating is nickel, nickel and nickel three-layer plating. c. Electrophoresis (epoxy plating): black epoxy, gray epoxy. d. Phosphating. e. Gold plating, copper plating, silver plating, tin plating, etc.

2. Electroplating process

Mechanical chamfering time can be long, so plating products are not very fast and must have a cycle.


(7) Reliability test

1. Drop test: glue the product and iron sheet together with glue, free fall from 1~1.5m air and repeat it several times to see if the coating has fallen off. The drop test is basically acceptance of galvanized products.

2. Cross-cut test: Use a knife to cross-cut the coating to see the bonding of the coating (galvanized or nickel-plated).

3. Pyrolysis heat test: The product after electroplating nickel is placed in an oven for heating (about 200 °„ C), and then placed in water to chill, such that several cycles to verify the bonding strength of the nickel plating product.

4. PCT test: (pressure cook test) conditions: 2 atmospheres, 95% relative humidity, 121 °„ C temperature, check the adhesion of the coating.

5. Weight loss test: Nd-Fe-B is not the same because of easy oxidation, different processes and different added elements, and different process control. The unit of weight loss test is how many milligrams of weight lost per square centimeter. Not the same as European standards. US requirements: PCT: 2atm (atmospheric pressure) 95% RH (humidity) 121 °„ C, 96 hours, required weight loss below 10mg / cm2 European requirements: Hast test: 3atm (atmospheric pressure) 95% RH (humidity) 130 °„ C, 240 hours, It is obvious that the weight loss is below 10mg/cm2. It is obvious that the European standard is much stricter. At present, most of the PCT tests for Nd-Fe-B products produced by traditional domestic processes are 80~300 mg/cm2, and if the cobalt is added, the conventional process can be controlled. It reaches 10 mg/cm2 or less. If other processes are used, it is relatively well controlled.

6. Salt spray test: The condition is 5% sodium oxide, 35 °„ C temperature, continuous spraying for 48 hours or 72 hours, whether the coating is corrosive.

7. Constant temperature and constant test: 90% humidity, 80 °„C temperature; measure the corrosion resistance of epoxy products.

8. Aging test: Heat the product to a certain temperature for 1-2 hours, take out the cooling, compare the magnetic flux before heating and the magnetic flux after heating to measure the temperature stability of the product.


How did the powerful magnets come about? How is the NdFeB powerful magnet made? And the principle of the magnet making process, etc., this article is for reference only.


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