The Fabrication Of The Grain For Injection Moulding NdFeB Permanent Magnets

In order to make full use of our country's plenty resource of Rare-earth and develop our injection moulding technique, This paper has systematically studied the problems in the process of preparation of the grain for injection moulding NdFeB permanent magnets and in basic application.This paper has got the following result:(1)This paper chose indigenous PA6 powder as the material for injection moulding NdFeB permanent magnets, they have low price and are fit to injection. The best amount of PA6 powder is from 7% to 10% wt. (2) The characteristics especial the granularity and the distribution of spun-quenched NdFeB magnetic powder have important effect on injection technics . If the powder's granularity is coarse, it's difficult to inject and if the powder's granularity is fine it's magnetic properties are poor. So the selected powder with granularity of 200 grids, average grain diameter of 35.6μm and distribution of sizes between 2-62μm has good flowing property and adapts to the injection molding process. (3) On the base of forthcoming condition, this paper chooses the double-roller mixing method to prepare the grain for injection moulding NdFeB permanent magnets by comparing the three methods. (4) During the process, KH550 silane coupling agents can treat the powder effective. The appropriate amount is 3‰wt. Add proper amount lubricant to the powder can improve the mechanics capability of injection magnets, the appropriate amount is 3‰wt too. With the increase of the PA6's amount, the thaw-exponent and mechanics capability of the mixture are enhanced, but preparation of the magnets are decreased. When the amount of PA6 powder is 7%wt, the thaw-exponent and the fluidity of the mixture are fall rapidly. It is difficult for them to be injected. (5) The injection molding granular material prepared by double-roller mixing and single screw extrudation can do more optimizing to the fabrication of the grain. The injection magnets made form the grains by this method have correspondingly higher magnet density, mechanical properties and megnetic properties compared with the magnet prepared by single granulating process. On the base of above research, this paper selects indigenous spun-quenched NdFeB magnetic powder and indigenous PA6 powder as the material for the grain of injection moulding NdFeB permanent magnets and prepared the grain .we send them to the injection magnets generative factory, and got the injection magnets .Their magnetic properties are: Br=0.5158T,Hcb=321kA/m,Hcj=730kA/m,(BH)m=40kJ/m3.These are close to that of the RNI-50 which produced by Mate company of Japan, but they have much lower costs. The magnetic and mechanical properties have exceeded the demands of the manufacturing units.