Physical Simulation Of Particle Dispersion Behavior And Foam Stability In Metal Melt

Aluminum foam material,a new kind of light weight functional material,which has widely applications and plays a great role in national security and economic construction.In many preparation methods,melt foaming method has been widely studied due to its advantages of low production cost,simple technological process and easy large-scale production.The mixing process plays an important role in this method and has a great influence on the quality of aluminum foam.Mixing behavior and transformation of the melt are difficulty to investigate at high temperature,so this paper carried out the physical simulation of the particles dispersion behavior in the melt and the foam stablility based on the water-base system.This paper is aim to establish a theoretical basis of the melt foaming method.The viscosity and surface tension of the solution were measured.In the case of adding the baffles in solution,the effect of stirring paddle type,stirring height,viscosity,particle size and stirring speed on the dispersion behavior of particles in solution was studied.In the whole stirring experimental,video information was collected by industrial camera.Then the image information was converted into digital information by gray histogram,which realized the transformation of physical simulation from traditional qualitative research to quantitative research.PIV(Particle image velocimetry)technology was used to visually measure the flow field under different test parameters.The effect of solution properties and particle parameters on foam stability was studied.The main conclusions are as follows:(1)The viscosity of aqueous solution increased exponentially with the increase of the volume fraction of propylene triol,and the surface tension decreased sharply with the addition of PEG2000.(2)The installation of the baffle can eliminate the adverse influence of the swirling effect on the stirring effect;compared with other paddle types,the axial circulation flow generated by the propeller is more conducive to the uniform dispersion of the solid phase particles in the solution;under the physical simulation conditions,the optimum technologic parameters on the suspension and dispersibility of the solid phase particles in the solution has been detrmined,i.e.the propeller paddle,H/4 height of stirring,the viscosity is 4 mPa·s and the 1200 r/min of the stirring speed.(3)Changing the wettability between the particles and the solution can adjust the adhesion state of the particles at the liquid film interface.The adsorption of a large amount of particles on the gas/liquid interface can inhibit the liquid film discharge and improving the stability of the foam.(4)The smaller the particle size,the better the suspension of the particles in the solution.However,if the particle size is too small,the agglomeration phenomenon will be easy occur,because desorption energy of the particles will be decrease,and get detached from the adsorption interface,which is harmful for the stability of the foam.The oversize of particle influences the adsorption arrangement of the solid phase particles at the gas-liquid interface,which inhibits the formation of foam and not conducive to the stability of the foam.The foam stability is best when the particle size is 25 ?m under physical simulation conditions.(5)The drainage rate of the liquid film decreases with the increase of viscosity and the decrease of surface tension,respectively.The foam stability can be improved by increasing viscosity and decreasing surface tension at a certain particle concentration.Foam life first increases and then decreases with the increase of particle concentration.When the viscosity is 2 mPa·s and 4 mPa·s,the maximum value of foam life is obtained at about 3%particle concentration;when the viscosity is 6 mPa·s and 8 mPa·s,the maximum value of foam life is obtained at about 5%particle concentration.