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이석희(S. H. Lee),최준환(J. W. Choi),문탁진(T. J. Moon),정원용(W. Y. Jeung) 한국자기학회 1998 韓國磁氣學會誌 Vol.8 No.3
The purpose of this study is to investigate the variations of rheological and magnetic properties with powder loading in plastic anisotropic ferrite magnets. The measured relative viscosities with powder loading were compared with the calculated ones. The variation of relative viscosities with powder loading was in good agreement with that of particle alignment. Remanent flux density and maximum energy product increased linearly with the increase of powder loading, and then showed maximum values. The decrease of magnetic properties at high powder loading was caused by rapid decrease of particle alignment due to the drastic increase of mixture viscosity. The powder loading for maximum magnetic properties is dependent on magnetic field during injection molding and melt viscosity of binder, so the binder with low melt viscosity is necessary to fabricate the magnet with high properties.
플라스틱 자석 혼합물의 균질도 평가방법과 균질도가 자기특성에 미치는 영향
이석희(S. H. Lee),최준환(J. W. Choi),문탁진(T. J. Moon),정원용(W. Y. Jeung) 한국자기학회 1998 韓國磁氣學會誌 Vol.8 No.2
Homogeneous feedstock is necessary to make plastic magnets with uniform magnetic properties, therefore the optimized mixing route and the homogeneity evaluation method are demanded. In this paper, method of homogeneity evaluation and effect of homogeneity on the magnetic properties were investigated using Srferrite /EVA plastic magnets. The feedstocks with different homogeneity were prepared using batch mixer and single screw extruder. The homogeneities of feedstocks were tested by torque sensor, capillary rheometer, and measurement of magnetic properties. Mixing torque measurement using torque sensor was an effective method to determine the critical powder loading, but it was not suitable to determine the feedstock mixing quality. Particle alignment measurement of a plastic magnet was very accurate to evaluate the homogeneity, but expensive equipments were required to make and measure the samples. Pressure measurement using capillary rheometer was a very effective and easy method with high accuracy. Homogeneous feedstock increased the particle alignment of plastic magnet. Remanent flux density and maximum energy product increased linearly and quadratically with increasing particle alignment, respectively.
이방성 Sr - 페라이트 / 레진본드 영구자석에서 Sr - 페라이트 자성분말의 방향성
정원용(W. Y. Jeung),조태식(T. S. Cho),문탁진(T. J. Moon) 한국자기학회 1994 韓國磁氣學會誌 Vol.4 No.3
The alignment of Sr-ferrite magnetic powders, which is usually related to the fluidity and the applied magnetic field, is investicated in the anisotropic Sr-ferrite /resin-bonded permanent magnets. The magnetic powder alignment is observed to increase with the applied magnetic field and the fluidity which is a function of molding temperature and powder packing ratio. The rest magnetic powder alignment is achieved at the following conditions; Sr-ferrite packing ratio of 56vol%, apparent viscosity of about 3000 poise in 1000sec-¹ shear rate, and applied magnetic field of about 5kOe. The degree of preferred orientation of the magnetic powders in the field direction, as determined by the dc hysterisis graphs, is 84~85%(0.84~0.85). This result is in agreement with the value of 0.85 obtained by the X-ray experiments in the 2θ range of 23~40^0. The best magnetic properties obtained are; 2.2kG of remanent flux density, 2.2MGOe of maximum energy product.
커플링제가 플라스틱 페라이트 자석의 레올로지와 자기특성에 미치는 영향
이석희(S. H. Lee),최준환(J. W. Choi),문탁진(T. J. Moon),정원용(W. Y. Jeung) 한국자기학회 1998 韓國磁氣學會誌 Vol.8 No.5
Effects of coupling agents on the rheological and magnetic properties of plastic ferrite magnets were investigated. Magnetic powder used was Sr-ferrite, and binder used was polypropylene (PP), and coupling agents used were γ-methacryloxypropyl trimethoxy silane (A174) and isopropyl triisostearoyl titanate (TTS). It was found that the addition of coupling agents to the PP / ferrite system reduced the melt viscosity and increased the magnetic properties considerably, and the treatment with TTS showed greater effect than A174 did. By comparison with that of the untreated one, the apparent viscosities of the mixtures treated with A174 and TTS decreased 23 % and 50 %, respectively, at the shear rate of 1280 sec-¹. Untreated plastic magnets showed remanent flux density (Br) of 1.89 kG and maximum energy product (BHmax) of 0.84 MGOe, and A174 treated magnets showed of Br 2.25 kG and BH(max) of 1.23 MGOe. TTS treated magnets showed Br of 2.35 kG and BH(max) of 1.33 MGOe.