China permanent magnet manufacturer:

How to judge the quality of sintered NdFeB magnets?

Sintered NdFeB permanent magnets, as one of the important materials to promote contemporary technology and social progress, are widely used in the following fields: computer hard disks, nuclear magnetic resonance imaging, electric vehicles, wind power generation, industrial permanent magnet motors, consumer electronics (CD, DVD, mobile phone, audio, copier, scanner, video camera, camera, refrigerator, TV, air conditioner, etc.) and magnetic machinery, magnetic levitation technology, magnetic transmission and other industries.
Since the industrialization in Japan, China, and Europe and the United States began in 1985, the global permanent magnet material industry has been booming in the past 30 years, with record-breaking magnetic properties, and increasing material varieties and grades. With the expansion of the market, its manufacturers are increasing, and many customers are inevitably caught in such confusion. How to judge the quality of sintered NdFeB magnets? The most comprehensive judgment method: 1. Magnet performance; 2. Magnet size; 3. Magnet Plating.

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

1. According to the company’s requirements for manufacturing high-end or mid-range or low-end sintered NdFeB, raw materials are selected according to the raw material composition specified by the national standard.
2. Whether the production process is advanced or not directly determines the performance and quality of the magnet. At present, the most advanced technologies are scale ingot (SC) technology, hydrogen crushing (HD) technology and jet mill (JM) technology.
Small-capacity vacuum induction smelting furnaces (10kg, 25kg, 50kg) have been replaced by large-capacity (100kg, 200kg, 600kg, 800kg) vacuum induction furnaces. SC (StripCasting) quick-setting cast sheet technology has gradually replaced large ingots (ingots with a thickness greater than 20-40mm in the cooling direction), and hydrogen crushing (HD) technology and jet mill (JM) have replaced jaw crushers and disc mills. The machine and ball mill (wet milling) ensure the uniformity of the powder and are beneficial to liquid phase sintering and grain refinement.
3. In terms of magnetic field orientation, my country is the only country in the world that adopts two-step compression molding. It uses low pressure vertical compression molding during orientation, and finally uses quasi-isostatic compression molding. This is one of the most important features of my country’s sintered NdFeB industry.

Secondly, the guarantee of magnet size depends on the processing strength of the factory

The practically used neodymium iron boron permanent magnet shapes are various, such as discs, cylinders, cylinders (with internal holes); square plates, squares, square columns; tiles, sectors, trapezoids, polygons and various Irregular shapes, etc.

20200619094747 759015249 - How to judge the quality of sintered NdFeB magnets?

Sintered NdFeB Magnet

The permanent magnets of each shape have different sizes, and it is difficult to form them in one production process. The general production process is: firstly produce large (large size) blanks, after sintering and tempering, and then through mechanical processing (including cutting, punching) and grinding, surface plating (coating) treatment, and then the magnet performance and surface quality And dimensional accuracy testing, then magnetizing, packaging and leaving the factory.

  • 1. Mechanical processing is divided into three categories: (1) Cutting processing: cutting cylindrical and square columnar magnets into discs, squares, (2) Shape processing: processing round and square magnets into sector, tile or For magnets with grooves or other complex shapes, (3) Drilling: processing round or square bar magnets into cylindrical or square cylindrical magnets. Its processing methods include: grinding and slicing processing, electric discharge cutting processing and laser processing.
  • 2. The surface of the sintered NdFeB permanent magnet element is generally required to be smooth and reach a certain accuracy. The surface of the magnet delivered as a blank needs to be surface ground. Common grinding methods for square NdFeB permanent magnet alloys include surface grinding, double-end grinding, internal grinding, and external grinding. Cylinders are commonly used for coreless grinding and double-end grinding. Multi-station grinders are used for tile, sector and VCM magnets.

Whether a magnet is qualified or not, not only needs to meet the performance standards, but also the control of dimensional tolerances directly affects its application. The guarantee of size directly depends on the processing strength of the factory. Processing equipment is constantly updated with economic and market demand. More efficient equipment and the trend of industrial automation not only meet the increasing demand of customers for product accuracy, but also Save manpower and cost, make it more competitive in the market.

Thirdly, the quality of the magnet coating directly determines the application life of the product

Experiments have shown that 1cm3 of sintered NdFeB permanent magnets will be completely oxidized and corroded if they stay in the air at 150°C for 51 days. It is more susceptible to corrosion in weak acid solutions. In order to make the NdFeB permanent magnet durable, it is required to have a service life of 20-30 years.
It must be subjected to surface anti-corrosion treatment to resist the corrosive damage of corrosive media to the magnet. At present, the manufacturing industry of sintered NdFeB permanent magnets generally uses methods such as electroplating metal, electroplating + electroless metal plating, electrophoretic coating and phosphating treatment. An additional spacer is plated on the surface of the magnet to isolate the surface of the magnet from the corrosive medium. , To prevent the media from harming the magnet.

  • 1. Generally, zinc plating, nickel plating + copper + nickel, nickel plating + copper + chemical nickel plating are the main processes. Other metal plating requirements are generally applied to other metal plating after nickel plating.
  • 2. Phosphating is also used in some special cases: (1) When the NdFeB magnet products are turned over and stored for too long and the subsequent surface treatment method is not clear, the use of phosphating is simple and easy; 2) When the magnet needs epoxy adhesive bonding, painting, etc., the bonding force of the epoxy organic matter such as glue and paint requires the matrix to have good wettability. The phosphating process can improve the wettability of the magnet surface.
  • 3. Electrophoretic coating has become one of the widely used anti-corrosion surface treatment technologies. Because it not only has a good bonding force with the porous magnet surface, but also has corrosion resistance such as salt spray, acid and alkali resistance, and excellent corrosion resistance. However, compared with spray coating, its resistance to humidity and heat is poor.

Customers can choose the plating layer according to their product work requirements. With the expansion of motor application fields, customers have higher requirements for the corrosion resistance of NdFeB. The HAST experiment (also known as the PCT experiment) is to test the corrosion resistance of sintered NdFeB permanent magnets in humid and high temperature environments.

And how do customers judge whether the coating meets the requirements? The purpose of the salt spray test is to do a quick anti-corrosion test on the sintered NdFeB magnets whose surface has been treated with anti-corrosion coating. At the end of the experiment, the sample is taken out of the test box and dried. Use your eyes or a magnifying glass to observe whether there are spots on the surface of the sample, and the change in color of the size box of the spot area.

Source: China Permanent Magnet Manufacturer –



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