The magnetic powder of the magnet after orientation, forming and isostatic pressure made of green density is very low, which is a negative factor in production, green and contains more pores, easy to absorb a lot of gas including water, bring trouble and difficulty to the next process.At the same time, due to the low density of green billet, large shrinkage rate during sintering, easy deformation, size easily out of tolerance, so it must be sintering, and the process of sintering operation experience requirements are relatively high.
There are two processes: sintering and aging.
1 > sintering;During a period of insulation at the highest temperature interval, the most important sintering volume density here is increased.The relative density increased from 0.6-0.7 to 0.95.The internal composition of each grain was further homogenized.The gap between particles decreases and the adsorbed water vapor is expelled.
> aging: the sintered billet density is high, Br is high, but coercivity and magnetic energy product is not high.This is because neodymium-rich phases have not been properly distributed well.At aging temperature, neodymium - rich phase thin layer surrounds the main phase particles and insulates them from each other.After aging, the Br of billet increased slightly, and the coercivity doubled.
After sintering, the blank product shall be analyzed and tested as follows to ensure the performance of the magnet meets the standard:
A. magnetic properties test after high-temperature sintering;
B. Density test after high-temperature sintering;
C. Appearance dimension inspection after high-temperature sintering;
D. analysis of carbon, oxygen and nitrogen after high-temperature sintering;
Finally, the demagnetization curve is drawn by the magnetic measuring instrument to judge whether the blank meets the national standard.