Study On The Flowability And Compressibility Of Bonded Magnetic Powder

Due to its outstanding properties such as high magnetic properties,high dimensional accuracy,complicated shapes,low eddy current loss and multi-polar magnetization,bonded NdFeB magnets are widely used to fabricate electric motors in automotive industry,hard disk drives and household appliances,etc.In the context of energy conservation,the trend of miniaturization,lighter weight and higher speed of devices such as motors and sensors requires smaller size,thinner annular magnetic ring walls,lower compression pressures and higher properties of magnets.Therefore,it is vital to keep a good flowability,apparent density and mechanical properties of the bonded magnet during the magnet molding process.However,the present evaluation method for powder flowability is limited.And there exist some obstacles especially poor filling,extremely high compression pressure and under-improved mechanical properties for preparation high-density,thin-walled/complex-shaped bonded magnets.In this paper,new evaluation method was used to manifest the flowability of magnetic powders,and the influence of magnetic powders,coupling agent,adhesive on the flowability and compressibility was studied to reveal their internal relationship and provide a theoretical basis for the preparation of rare earth bonded magnet with good processability and excellent performance.The L9(34)orthogonal experiment method was used to explore the influence of the particle size on the flowability.After orthogonal optimization,the flowability of the melt-spun magnetic powder is increased by 15.2%,and the apparent density is increased by 0.25 g/cm3 to 3.21 g/cm3.The flowability of compounds is increased by 31.7%after mixing,however the flowability of the compounds is no longer affected by the particle size.In addition,the compressing process conforms to the Huang's pressing theory.The special energy(SE)is used to evaluate the flowability of the bonded magnetic powder.The results show that the special energy of the bonded magnetic powder has a linear negative correlation with its apparent density,which can indicate the force between the magnetic powders on a macro scale,providing a new direction for the study of the interface compatibility of two-phase or multiphase composite materials.Four different silane coupling agents were employed to pretreat the surface of the NdFeB powders.In result,the epoxy resin is more evenly distributed on the surface of the compounds treated by silane coupling agents and some agglomerated particles produced.Also,the apparent density is increased by 0.3 g/cm3 and compression pressure is dropped by 63.7%.In addition,the radial crushing strength is significantly increased by about 3?4 times.Silane coupling agent could help to improve the interface compatibility of the compounds and reduce the force between powders.In order to improve the impact resistance of bonded NdFeB composites,thermoplastic resin polysulfone modified epoxy resin is introduced and active diluent is used to reduce the viscosity of the polysulfone-epoxy system to improve its flowability.The results show that the compounds prepared by the modified resin has good flowability and compressibility while the radial crushing strength of the magnetic ring is increased by about 4?5 times.In addition,the corrosion resistance of the composite material is also significantly improved.