Study On Binder System And Debinding Process Of Strontium Ferrite Powder Injection Molding

Nowadays,the electronic industry demands small and complex parts as a consequence of the miniaturization of electronic devices.Some complex soft and hard magnetic parts of Sr-ferrite ceramics have already been made using powder injection molding(PIM)technology,compared with the parts obtained by the conventional sintered magnets and resin-bonded magnets.Successful production of parts by PIM are closely related to the binder system and debinding process.In this study,new binder system with the addition of microcrystalline wax(MW)or ethylene vinyl acetate(EVA)was used for the Sr-ferrite powder injection molding.The optimum binder composition was determined based on rheological measurement,mircrostructure observation by SEM,thermal change by DSC,mechanical properties and debinding process.The results are as follows:(1)Compared with the binder system of high density polyethylene(HDPE),paraffin(PW)and stearic acid(SA),the addition of MW significantly improved the debinding defects such as deformation and cracking.The grains become small and uniform when MW is added in the pure binder system,which implies that the MW separates the PW in the mixing and makes PW easily distributing in the binder system containing HDPE.This causes the homogeneous distribution between the components of the binder.The MW with 10 vol.% addition in the binder system decreases the defects of the green parts after solvent debinding because the distribution of the binder system between the Sr-ferrite particles becomes more homogeneous.(2)The addition of MW at low dissolution rate to PW/MW systems or binder systems leads to the gradually decrease of weight loss of the soluble binders in n-heptane,which is beneficial to the step of gradual degeneration of injection parts in the solvent debinding process and improve the debinding defects.Moreover,it is found that the amount of extracted soluble binders increases with the MW addition and the increase of ferrite filler contents in the same solvent debinding time,which decreases the time of the solvent debinding.99.2 wt.% of the binders in the M55 sample can be successfully removed in 12.4h and no obvious defects remain after optimal two-stage debinding,which benefits producing the Sr-ferrite ceramics with defect-free and dense microstructure. The mechanism of solvent debinding is the process of dissolution-diffusion,and the debinding rate increases with the increase of debinding temperature and time.(3)The addition of EVA on the HDPE-PW-MW-SA binder system to improve the conformal property and thermal debinding process of Sr-ferrite injection parts.With the increase of EVA content,the viscosity of HDPE/EVA mixture decreased gradually,which improved the processing fluidity of feedstock.Among them,the impact strength and flexural strength of Sr-ferrite injection parts increased with the increase of EVA content.The impact strength and flexural strength increased obviously with 10 vol.% EVA addition in the skeleton binder,reaching 1.13KJ/m2 and 11.9MPa,respectively.The EVA with the size of about 38.9mm×9.9mm×3.77 mm were performed by immersing in n-heptane at 40 °C for 6h,the swelling rate of thickness,width and length were 49.9%,51.9%,and 37.8%,respectively.A binder formulation with a volume ratio of 4EVA-36HDPE-40PW-10MW-10 SA was determined.Optimize the thermal debinding program to shorten the thermal debinding time to 6.1h.