Improvement Of Vacuum Induction Atomization Device And Preparation Of Spherical Aluminum Powde

Vacuum induction melting gas atomization technology is one of the cost-effective and widely used methods in the industrial production of metal powder.The powder prepared by this method still has the disadvantages of wide particle size distribution,low yield of a fine powder,and many satellite particles.To further improve the performance of the powder,the research in recent years has focused on atomization mechanism research and process optimization while ignoring the influence of equipment design defects on the atomization process and powder quality.Based on the comprehensive debugging of the entire air atomization system,this paper optimizes and improves the shortcomings of the gas atomization system and device according to the design concept of the existing powder system.The mechanism and influence of different parameters on the axial pressure of the nozzle were studied under pure gas conditions.Under the guidance of the pressure test results,the effects of process parameters on the particle size distribution,acceptable powder yield,and powder morphology were determined by atomization experiments.The results are as follows:The formation of the positive and negative pressure zones in the central axis of the nozzle is the result of the combined action of airflow entrainment and scattering.When the pressure at the tip of the infusion tube is larger than the hydraulic pressure P generated by the melt gravity,the airflow flows through the infusion tube to the holding crucible under the action of pressure difference.The essential condition for the infusion tube not to be blocked is P’<P=1.83 k Pa.The natural supplementary flow will supplement or release the gas in the recirculation zone.The extensive range of the infusion tube corresponding to the successful completion of the atomization of the 30°,40°and 50°nozzles accounts for 89.5%,72.9%and 60.4%of the total extension range,respectively,which is more suitable for the actual atomization process.The injection angle will affect the flow rate of the scattered gas entering the recirculation zone and the volume of the recirculation zone.The larger the injection angle,the greater the tip pressure when the extension length of the infusion tube is the same.When the angle of the nozzle is 30°,blockage occurs in the range of 22mm～32 mm,and the extension length range corresponding to smooth atomization accounts for the highest proportion of 79.1%.The pressure at the tip of the infusion tube is not positively correlated with the atomization pressure.Under the pressure of2 MPa,the infusion tube will be blocked in the extension range of 25 mm～32 mm.Under the pressure of 3 MPa～5 MPa,the infusion tube cannot complete the atomization in the extension range of 20 mm～32 mm.Increasing the atomization pressure can increase the kinetic energy of the atomized gas and play a positive role in the refinement of the aluminium powder.When the atomization pressure increases from 1 MPa to 3 MPa,the liquid flow breaks into finer droplets,and the D50 decreases from 155.55μm to 83.525μm,which decreases by 46.3%.The yield of aluminium powder with particle size less than 200μm increases from 36.5%to 59.8%.The melt temperature mainly affects the surface tension and viscosity of the melt.When the temperature of an aluminium liquid increases from 800℃ to 850℃,the D50 decreases from 111.669μm to 103.221μm,and the yield of aluminium powder with particle size less than 200μm increases from 49.75%to 53.64%.The different extension lengths will change the tip pressure of the infusion tube,and the tip pressure strongly affects the melt flow.When the extension length of the infusion tube is 21 mm,the melt flow is hindered by the reverse airflow,and the mass flow rate of the melt is the smallest.The maximum gas-liquid ratio is 9.7,the minimum powder D50 obtained by atomization is 70.436μm,and the highest powder yield below 200μm is 67.3%.The capillary resistance is inversely proportional to the diameter of the infusion tube.When the diameter of the infusion tube is 3.5 mm,the minimum D50 is 90.278μm,and the yield of spherical aluminium powder with particle size less than 200μm is up to 53.67%.The powder has high sphericity.When the nozzle atomization angle is 30°,the particle size distribution of aluminium powder is narrow,and the aluminium powder in the range of 5～100μm occupies more than 60%.The total yield of aluminium powder with particle size less than 200μm is 59.8%,which is more suitable for the actual atomization process.The optimized process parameters are as follows:gas pressure 3 MPa,melt temperature 850℃,extension length of the infusion tube 21 mm,the diameter of infusion tube 3.5 mm,and injection angle 30°.