Judging the quality of sintered NdFeB magnets(2)


Again, the quality of the magnet coating directly deter […]

Again, the quality of the magnet coating directly determines the service life of the product.
It has been experimentally found that a 1 cm3 sintered NdFeB permanent magnet is left 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 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 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 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 bonding, painting, etc., the bonding force of epoxy, lacquer and other epoxy organic substances requires good infiltration performance 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. The HAST experiment (also known as the PCT experiment) is specifically designed to test the corrosion resistance of sintered NdFeB 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 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 eligibility of products if they understand their production processes and understand the requirements of the products. In a nutshell, it is performance control, dimensional tolerance control, coating inspection and appearance evaluation.
In terms of performance, it can be tested for Br (remanence), Hcb (coercivity), Hcj (intrinsic coercivity), (BH)max (maximum energy product) and demagnetization curve; dimensional tolerance can be performed by vernier caliper Measure 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, free of visible particles and foreign matter, no spots, no falling corners, and the appearance is acceptable.