The sixth process of the magnet production process: sintering and aging

The density of the green blank made of magnetic powder after orientation, forming and isostatic pressure is very low, which is a negative factor in production. The green blank contains more pores, which are easy to absorb a large amount of gas including water, bringing troubles and difficulties to the next process.At the same time, because of the low density of green, sintering shrinkage rate, easy deformation, size is easy to out-of-tolerance, so must be sintered, and the process of sintering operation experience requirements are relatively high.

The raw material needs to go through two processes: sintering and aging when it is put into sintering furnace.

1>Sintering;The density of the most important sintered body increases at the highest temperature for a period of time.The relative density of green leaves increased from 0.6-0.7 to above 0.95.The internal composition of each grain is further homogenized.The gap between the particles is reduced and the adsorbed water vapor is expelled.

2>Aging: Sintered blank density is high, Br is high, but the coercivity and magnetic energy product is not high.This is because the neodymium rich phase has not been properly distributed.At the aging temperature, the neodymium-rich phase thin layer surrounds the main phase particles and isolates them from each other, forming a good tissue structure conducive to high coercive force.After aging, the billet Br increased only slightly and the coercivity multiplied.

The sintered blank products shall be analyzed and tested as follows to ensure that the performance of the magnet reaches the standard:

A. Detection of magnetic properties after high temperature sintering;

B. Density detection after high temperature sintering;

C. Inspection of appearance size after high temperature sintering;

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

Finally, the demagnetization curve is drawn by the magnetic tester to determine whether the blank meets the national standard.

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