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Orientation and molding sequence of special-shaped magnets

Magnet, special-shaped magnet in the production process is difficult to do one-time processing forming.

Magnet orientation and forming order: the magnetic powder of the magnet after orientation, molding and isostatic pressing made of blank density is very low, which is a negative factor in production, blank and contains more pores, simple adsorption of a large number of gas containing water, to the next process to bring trouble and difficulties. Because of the low density of green billet, sintering shortening rate is large, simple deformation, simple scale out of tolerance, so it is necessary to sintering, and the process of sintering operation experience requirements are relatively high.

In the sequence process of magnet orientation and molding, the blank needs to go through two processes when put into the sintering furnace:

Sintering and aging: 

1. Sintering; At the high temperature interval for a period of time, the important sintered body density progress. The relative density has improved from 0.6-0.7 to above 0.95. The internal composition of each grain is further homogenized. The space between the particles is reduced, and the adsorbed water vapor is expelled.

2. Aging: sintered NdFeb magnets billet density is high, Br is high, but coercivity and magnetic energy product is not high. This is because the neodymium-rich phase is not properly dispersed. At aging temperature, the neodymium-rich phase thin layer surrounds the main phase particles and isolates them from each other, forming an outstanding arrangement structure conducive to high coercivity. After aging, the Br of the billet is only slightly added, but the coercivity is doubled.

Orientation and forming sequence of magnet after sintering blank products need to be analyzed and tested as follows to ensure that the function of the magnet is qualified:

A. Magnetic function test after high temperature sintering;

B. Density detection after high temperature sintering;

C. Appearance scale inspection after high temperature sintering; 

D. After high temperature sintering: carbon, oxygen and nitrogen analysis;

E. After drawing the demagnetization curve through the magnetic meter to determine whether the blank is satisfied with the national standard. Since a large proportion of NdFeb magnet is made of iron, NdFeb is easily oxidized when exposed to air or moist environment. Electroplating Permanent magnet is an important way to beautify the appearance of magnets and add magnet preservation time. Magnet surface processing mainly zinc, black zinc, nickel, copper, gold, silver, epoxy resin.

Surface plating is different from its color is different, the preservation time is not the same, each has advantages and disadvantages. 

1. Zinc: the appearance is silver white, can be 12 to 48 hours of salt spray, can be bonded with some glue use (such as AB glue), if the electroplating effect is good, it can be stored for two to five years, electroplating cost is low.

2. Nickel: the appearance looks like stainless steel color, placed in the air appearance is not easy to oxidize, good appearance, good gloss, can be 12 to 72 hours of salt spray experiment. The disadvantage is that it is not simple to use glue for bonding, the appearance of lubrication adhesion is not tight, and the coating is simple to fall off. To speed up oxidation, the market is now more nickel – copper – nickel plating method to do 24-96 hours of salt spray.

3. Black Zinc: according to the customer’s customized requirements of the magnet surface is processed into black, is on the basis of galvanized chemical treatment to add a layer of black maintenance film, this film can also play the effect of magnet maintenance, increase the salt spray time. But its appearance is easy to be scratched, lose its maintenance effect.

4. Black Nickel: with the same requirements of black zinc plating, is on the basis of nickel plating after chemical treatment to add a layer of black maintenance film. 

5. Gold: commonly used in jewelry magnet accessories, now there are many very popular magnetic hand ornaments. 

6. Epoxy resin: in order to add salt spray resistance to the product, a layer of resin paint is added outside the magnet after nickel plating, which is mostly black. It is a coating with good corrosion resistance outside the magnet coating. Magnet orientation and forming in the order of magnet magnetization, meaning is to magnetize the magnetic material or the lack of magnetic magnet to add magnetic. Generally, the magnetic object to be magnetized can be placed in a strong magnetic field formed by the coil through which direct current is passed, and the magnetic field inside the magnet is catalyzed by the external magnetic field.

China High Temperature Neodymium Magnets

Post time: Aug-06-2022