Common problem

Sintered NdFeB permanent magnet, as one of the important materials to promote contemporary technology and social progress, is widely used in the following areas: computer hard disk, nuclear magnetic resonance imaging, electric vehicles, wind power, industrial permanent magnet motor, consumer electronics (CD, DVD, mobile phones, audio, copiers, scanners, cameras, cameras, refrigerators, televisions, air conditioners, etc.) and magnetic machinery, magnetic levitation technology, magnetic drive and other industries.

Since 1985 in Japan, China and Europe and the United States at the same time began to industrialization, which nearly 30 years, the global permanent magnet material industry to flourish, magnetic properties continue to refresh the record, the variety of materials and grades continue to increase. With the expansion of the market, its manufacturers are also increasing, and many customers will inevitably fall into such a confused, how to judge the merits of the product?

The most comprehensive way to determine: First, the magnet performance; Second, the size of the magnet; Third, the magnet coating.

First of all, the protection of magnet performance from the raw material production process control

1, according to the enterprise manufacturing high-grade or mid-range or low-grade sintered NdFeB requirements, in accordance with national standards of raw materials to buy raw materials.

2, the production process of advanced or not directly determine the performance of the magnet quality. At present, the most advanced technology is scale ingot (SC) technology, hydrogen crushing (HD) technology and airflow grinding (JM) technology. The small capacity vacuum induction smelting furnace (10kg, 25kg, 50kg) has been replaced by large capacity (100kg, 200kg, 600kg, 800kg) vacuum induction furnace. SC (StripCasting) quick-setting chip technology has gradually replaced the large ingot (cooling direction of the thickness of more than 20-40mm of the ingot), hydrogen crushing (HD) technology and air mill (JM) to replace the jaw crusher, Machine, ball mill (wet milling), to ensure the uniformity of the powder, and is conducive to liquid phase sintering and grain refinement.

3, the magnetic field orientation, China is the world's only two-step compression molding of the country, the orientation with a small pressure vertical molding, and finally the use of quasi-isostatic pressing, which is China's sintered NdFeB industry, one of the most important features The

4, and the quality of the production process monitoring is very important, can be measured by SC film thickness and JM powder particle size distribution and other detection methods for control. Quality products are determined by the production process control, but the customer will be very puzzled, how to judge the performance of the products I buy it? China Institute of Metrology has developed a variety of models of permanent magnet material technology magnetic parameters measuring instruments. Pulsed Magnetic Field Magnetometer (PFM) is a test instrument for testing ultra-high coercivity permanent magnets, primarily to accommodate the high coercivity permanent magnets required in the field of electric vehicles and large permanent magnet motors.

The customer can select the desired NdFeB grade according to the magnet parameters Br (remanence), Hcb (coercivity), Hcj (intrinsic coercivity), (BH) max (maximum magnetic energy product) Parameter is to determine whether the product is in accordance with customer requirements of the production standards.

Second, the protection of the size of the magnet depends on the processing strength of the factory

The actual application of NdFeB permanent magnet shape is a variety of, such as discs, cylinders, cylindrical (with holes); square, square, square column; tile, fan, trapezoidal, polygonal and various Irregular shape and so on. Each shape of the permanent magnets have different sizes, the production process is difficult to achieve a molding. The general production process is: Mr. production of large (large size) of the blank, after sintering and tempering treatment, and then through the mechanical processing (including cutting, drilling) and grinding processing, surface coating (coating), and then Magnet performance, surface quality and dimensional accuracy of the test, and then magnetizing, packaging and factory.

1, mechanical processing is divided into three categories:

(1) cutting: the cylindrical, square column magnets cut into a round, square-like;

(2) shape processing: the circular, square magnets into a fan-shaped, tile or groove or other complex shape of the magnet;

(3) drilling processing: the rod, square rod-shaped magnet into a cylindrical or square tube magnet. The processing methods are: grinding section processing, EDM cutting and laser processing.

2, sintered NdFeB permanent magnet components on the surface of the general requirements of smooth and achieve a certain accuracy, rough delivery of the surface of the magnet surface grinding required. Square NdFeB permanent magnet alloy commonly used grinding processing methods are surface grinding, double-face grinding, the round grinding, cylindrical grinding and so on. Cylindrical commonly used coreless grinding, double face grinding and so on. Watt-type, fan-shaped and VCM magnets with multi-station grinder.

A qualified magnet, not only the performance of the standard, the size of the tolerance control also directly affect its application. And the size of the protection depends directly on the processing strength of the factory, processing equipment with the economic and market demand is constantly updated, more efficient equipment and industrial automation trends, not only to meet customer demand for increasing product precision, but also Saving manpower and cost, so that it has more market competitiveness.

Again, the quality of the magnet coating directly determines the service life of the product

Experiments show that 1cm3 sintered NdFeB permanent magnet placed in the air at 150 ℃ for 51 days, will be all oxidized corrosion. It is more susceptible to corrosion in weak acid solutions. In order to make the NdFeB permanent magnet durable, it requires 20-30 years of service life, which must withstand the surface corrosion resistance, in order to resist corrosion of the corrosion medium on the magnet. At present, the sintered NdFeB permanent magnet manufacturing industry commonly used electroplating metal, electroplating + electroless plating, electrophoresis coating and phosphating treatment and other methods, in the magnet surface coated with a layer of additional isolates, the magnet surface and corrosive media isolation , To prevent the media against the magnet.

1, generally to galvanized, nickel + copper + nickel, nickel + copper + electroless nickel plating three main technology, other metal plating requirements, are generally applied after the nickel plating and other metal plating.

2, in some special circumstances will also use phosphating: (1) in the NdFeB magnet products because of the turnover, the preservation of the time is too long and not clear follow-up surface treatment methods, the use of phosphate is simple; 2) When the magnet needs epoxy adhesive bonding, painting, glue, paint and other epoxy organic adhesive force requires a good substrate invasion performance. The phosphating process can improve the invasion of the magnet surface.

3, electrophoretic coating has become widely used anti-corrosion surface treatment technology. Because it is not only with the porous magnet surface of the binding force is very good, but also with salt spray, acid, alkali and other corrosion, excellent corrosion resistance. But compared with the spray coating its poor resistance to heat and humidity.

Customers can choose the coating for their product requirements. With the expansion of the field of motor applications, customers of NdFeB corrosion resistance has a higher demand. The HAST experiment (also known as the PCT experiment) is specifically designed to test the corrosion resistance of sintered NdFeB permanent magnets in humid and high temperature environments.

And the customer how to determine whether the coating meets the requirements? Salt spray experiments aimed at the surface by the anti-corrosion coating of sintered NdFeB magnets to do rapid anti-corrosion experiments, the end of the experiment, the sample from the test chamber, With the eyes or magnifying glass to observe the surface of the sample spots, spot size of the box size changes.

In summary, the customer only understand its production process, understand the requirements of the product factors, in order to correctly determine the product's eligibility. Simple summary is the performance of the grasp, the size of the tolerance control, the detection of the coating and the appearance of the assessment.

(BH) max (maximum magnetic energy product) and demagnetization curve; dimensional tolerances can be performed by means of a vernier caliper, and the thickness of the caliper can be measured by the performance of the Br (remanence), Hcb (coercivity), Hcj (intrinsic coercivity) The overall appearance, mainly with the naked eye or magnifying glass, or optical microscope (for less than 0.2mm degree of the following products), the brightness of the coating can be observed by the naked eye, Magnet surface smooth, no visible particles and foreign body, no spots, no drop off the corner, it is the appearance of qualified.

NdFeB permanent magnet is also known as modern industrial monosodium glutamate, as a modern industry important high-performance magnetic materials to promote the field of modern technology and social progress, widely used in various fields, how to determine the most comprehensive advantages of permanent magnet products: Can; Second, the size of the magnet; Third, the surface coating.

First, the magnetic properties

First, the key to the decision is to control the magnetic properties of the raw materials of the production process.

1, raw material manufacturers according to business needs or mid-range or low-grade sintered NdFeB, raw materials in the purchase of raw materials, the provisions of the national standard, the company only sell high-grade NdFeB.

2, the advanced nature of the production process also determines the performance quality of the magnet.

3, the production process of quality control is very important.

Second, the size of the magnet and the value of tolerance

The use of NdFeB magnets in various shapes, such as round, shaped, square, tile-shaped, trapezoidal. Different sizes of materials are machined with different machine tools for cutting rough materials, and advanced technology and machine operators determine the accuracy of the product.

Third, the surface coating treatment

Surface coating quality of the coating, zinc, nickel, nickel copper and nickel electroplating copper and gold plating process. According to customer requirements for the product plating options work. NdFeB product quality of the pros and cons, a brief summary, is to grasp the performance, size tolerance control, to determine the appearance of coating inspection and evaluation. The thickness of the coating, the color and brightness of the coating and the adhesion of the coating, and can observe the appearance of the magnet through the appearance of the smooth, with or without spots, and whether or not the surface of the magnet can be measured. Drop the corners to assess the quality of the product.