Sequence of magnet orientation and forming
Magnets are difficult to be processed and formed at one time in the production process. The following introduces the sequence of magnet orientation and forming:
The density of the green body made of the magnetic powder of the magnet after orientation, forming and isostatic pressing is very low, which is a negative factor in the production. This process brings time and difficulty. At the same time, because the green density is low, the shrinkage rate during sintering is large, the deformation is simple, and the size is simple and out of tolerance, so it is necessary to sinter, and the process requires relatively high sintering operation experience.
In the sequential process of magnet orientation and forming, the green body needs to go through two processes in the sintering furnace: sintering and aging.
- Sintering; in the high temperature range for a period of time, the density of the important sintered body increases. The relative density of the green body increases from 0.6-0.7 to above 0.95. The internal components of each crystal grain are further homogenized. The voids between the particles are reduced and the adsorbed water vapor is expelled.
- Aging: The density of the sintered billet is high, and the Br is high, but the coercive force and magnetic energy product are not high. This is because the neodymium-rich phase is not properly dispersed. At the aging temperature, the thin layer of neodymium-rich phase surrounds the main phase particles and isolates them from each other, forming an excellent structure conducive to high coercivity. After aging, the Br of the billet was only slightly increased, and the coercivity increased exponentially.
The order of magnet orientation and forming After sintering, the blank product needs to be analyzed and tested as follows to ensure that the function of the magnet is qualified:
A. Magnetic function detection after high temperature sintering;
B. Density detection after high temperature sintering;
C. Appearance size inspection after high temperature sintering;
D. After high temperature sintering: analysis of carbon, oxygen and nitrogen;
E. Then draw the demagnetization curve through the magnetic tester to judge whether the blank meets the national standard.
Because a large proportion of NdFeB is composed of iron, NdFeB is easily oxidized when exposed to air or humid environment. Magnet electroplating is an important process to beautify the appearance of magnets and increase the preservation time of magnets. Magnet surface treatment mainly includes zinc, black zinc, nickel, copper, gold, silver, epoxy resin, etc.
The appearance of electroplating is different, its color is also different, and the time of preservation is also different, each with its own advantages and disadvantages.
1) Zinc: The appearance is silver-white, and it can pass 12-48 hours of salt spray. It can be used with some glues (such as AB glue). If the electroplating effect is good, it can be stored for two to five years. The cost of electroplating is relatively low.
2) Nickel: The appearance looks like stainless steel color, it is not easy to be oxidized when left in the air, the appearance is good, the gloss is good, and it can pass the salt spray test for 12-72 hours. The disadvantage is that it is not easy to bond with glue, the surface lubrication and adhesion are not tight, and it is easy to make the coating fall off. To speed up the oxidation, most of the nickel-copper-nickel electroplating methods on the market are salt spray for 24-96 hours.
3) Black zinc: The surface of the magnet is treated black according to the customer’s customized requirements. On the basis of galvanizing, a layer of black protective film is added after chemical treatment. This film can also play a role in protecting the magnet and increase the salt spray time. However, its appearance is easily scratched and loses its maintenance effect.
4) Black nickel: The same as the requirement of black zinc plating, a layer of black maintenance film is added after chemical treatment on the basis of nickel plating.
5) Gold: Commonly used in the magnet accessories of jewelry, there are many very popular magnetic jewelry now.
6) Epoxy resin: In order to increase the time when the product is resistant to salt spray, a layer of resin paint is added on the outside of the magnet after nickel plating, which is mostly black, which is a kind of coating with good corrosion resistance outside the magnet encapsulation.
Magnetization of magnets in the sequence of magnet orientation and forming, literally means to magnetize magnetic substances or add magnetism to magnets lacking magnetism. Generally, the magnetic object to be magnetized is placed in a strong magnetic field formed by a coil through which DC current passes, and the magnetic field in the magnet is catalyzed by the external magnetic field.