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Identify the advantages and disadvantages of strong NdFeB neodymium magnets

As a sintered NdFeB neodymium  magnet, the powerful NdFeB neodymium magnet can be widely used in the following fields: industrial permanent magnet motor, electronics, audio and other industries.
 
The most comprehensive judgment method: one, magnet performance; two, magnet size; three, magnet plating.
 
First of all, the guarantee of the performance of the magnet comes from the control of the raw material production process. 1. According to the requirements of the enterprise to manufacture high-grade or medium-grade or low-grade sintered NdFeB neodymium, the raw materials are purchased according to the national standard.
 
2. The advanced production process directly determines the performance quality of the magnet. The most advanced technologies available today are scale ingot (SC) technology, hydrogen fragmentation (HD) technology and jet mill (JM) technology. The small-capacity vacuum induction smelting furnace (10kg, 25kg, 50kg) has been replaced by a large capacity (100kg, 200kg, 600kg, 800kg) vacuum induction furnace. SC (StripCasting) rapid solidification casting 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 grinding Machine and ball mill (wet milling) ensure the uniformity of the powder and facilitate liquid phase sintering and grain refinement.
 
Everbbeen magnet 3, magnetic field orientation, China is the only country in the world to adopt two-step press molding, vertical molding with small pressure during orientation, and finally quasi-isostatic pressing, which is the most important feature of China's sintered NdFeB neodymium industry. one.
 
4. Moreover, the monitoring of the quality of the production process is very important, and it can be controlled by the thickness measurement of the SC piece and the particle size distribution of the JM powder. High-quality products are all dependent on the control of the production process, but customers will be very confused, how to judge the performance of the products I purchased? China Institute of Metrology has developed a variety of magnetic material measuring instruments for permanent magnet materials. Pulsed Magnetic Field Magnetometer (PFM) is a test instrument for testing ultra-high-coercive permanent magnets. It is mainly used to adapt to high-coercive permanent magnets required in electric vehicles and large permanent magnet motors.
 
Customers can choose the NdFeB neodymium grades they need based on the magnet parameters Br (remanence), Hcb (coercive force), Hcj (inner coercivity), and (BH)max (maximum magnetic energy product). The parameter is the standard that determines whether the product is produced according to customer requirements.
 
Secondly, the guarantee of the size of the magnet depends on the processing strength of the factory. The shape of the NdFeB neodymium permanent magnet is various, such as wafer, cylinder, cylindrical (with inner hole); square, square, square column; Tiles, sectors, trapezoids, polygons, and various irregular shapes. Each type of permanent magnet has a different size and it is difficult to make a single molding process. The general production process is: the production of large (large size) billets, after sintering and tempering, and then through mechanical processing (including cutting, drilling) and grinding, surface coating (coating) treatment, and then Magnet performance, surface quality and dimensional accuracy are measured and then magnetized, packaged and shipped.
 
1. Machining is divided into three categories: (1) Cutting processing: cutting cylindrical and square cylindrical magnets into disc-shaped and square-shaped shapes; (2) Shape processing: processing circular and square magnets into fan-shaped or tile-shaped or A magnet having a groove or other complicated shape; (3) Punching: processing a round bar or a square rod magnet into a cylindrical or square cylindrical magnet. The processing methods are: grinding slicing, electric spark cutting and laser processing.
 
2. The surface of the sintered NdFeB neodymium permanent magnet component is generally required to be smooth and achieve a certain precision, and the surface of the magnet for the delivery of the blank needs to be surface-ground. Commonly used grinding methods for the block NdFeB neodymium permanent magnet alloy include plane grinding, double end grinding, internal round grinding, and external grinding. Cylindrical grinding, double-face grinding, etc. are commonly used for cylinders. Tile, sector and VCM magnets use multi-station grinders.
 
A qualified magnet not only requires performance compliance, but also the control of dimensional tolerance directly affects its application. The size guarantee is directly dependent on the processing strength of the factory. The processing equipment is constantly updated with the economic and market demand. The trend of more efficient equipment and industrial automation is not only to meet the increasing demand of customers for product precision, but also It saves manpower and costs, making it more competitive in the market.
 
Again, the quality of the Everbbe magnet coating directly determines the life of the product. It is known that 1 cm3 of sintered NdFeB neodymium permanent magnets stay in the air at 150 °C for 51 days and will be completely oxidized and etched away. It is more susceptible to corrosion in weak acid solutions. In order to make the NdFeB neodymium permanent magnet durable, it is required to have a service life of 20-30 years, and it must be subjected to surface anti-corrosion treatment to resist the corrosion of the magnet by the corrosive medium. At present, the sintered NdFeB neodymium permanent magnet manufacturing industry generally adopts electroplating metal, electroplating + electroless metal plating, electrophoretic coating and phosphating treatment, and 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 invading the magnet.
 
1, generally galvanized, nickel-plated + copper + nickel, nickel-plated + copper + electroless nickel plating three processes, other metal plating requirements, generally after nickel plating and then applied other metal plating.
 
2, in some special cases will also use phosphating: (1) in the NdFeB neodymium magnet products because the turnover, preservation time is 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 glue bonding, painting, etc., the bonding force of epoxy, lacquer and other epoxy organic substances requires a good infiltration property of the substrate. The phosphating process can improve the infiltration ability of the magnet surface.
 
3, electrophoretic coating has become one of the widely used anti-corrosion surface treatment technologies. Because it has good adhesion not only to the surface of the porous magnet, but also has corrosion resistance to salt spray, acid and alkali, and is excellent in corrosion resistance. However, it has poor heat and humidity resistance compared to spray coating.
 
Customers can choose the plating for their product work requirements. With the expansion of the field of motor application, customers have higher requirements for the corrosion resistance of NdFeB neodymium. The HAST experiment (also known as the PCT experiment) is specifically designed to test the corrosion resistance of sintered NdFeB neodymium permanent magnets in wet and high temperature environments.
 
How does the customer judge whether the coating meets the requirements? The purpose of the salt spray experiment is to conduct a quick anti-corrosion test on the sintered NdFeB neodymium magnet treated with anti-corrosion coating on the surface. At the end of the experiment, the sample is taken out from the test chamber and dried. Use an eye or a magnifying glass to observe the change in the color of the box on the surface of the sample with or without spots and spots.
 
In summary, customers can only correctly judge the product's eligibility if they understand their production processes and understand the requirements of the products. In a nutshell, it is the performance of the control, the control of dimensional tolerances, the detection of the coating and the evaluation of the appearance.
 
The properties of Everbbeen magnets can be tested for Br (remanence), Hcb (coercivity), Hcj (inner coercivity), (BH)max (maximum energy product) and demagnetization curves. Dimensional tolerance can be passed. The vernier caliper measures the accuracy; on the coating, the brightness of the coating can be observed by the naked eye, and the detection method by bonding force, salt spray experiment, etc.; the overall appearance, mainly with the naked eye or magnifying glass, or optical microscope (for products with linearity less than 0.2mm) ), the surface of the magnet is smooth, there are no visible particles and foreign matter, no spots, no falling corners, it is qualified.

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