Study On The Process Of Preparing Thermoplastic Polyurethane Foam Beads By Spouted Bed Technology

Bead foaming is a kind of foaming process which has the advantages of both extrusion foaming and injection foaming,and can produce products with high foaming ratios and complex shapes.While retaining these advantages,the spouted bed bead foaming process avoids the generation of wastewater in the traditional bead foaming process,and has broad application prospects.In this paper,the empirical formula is used to determine the required gas velocity of the spouting bed,and with this as the initial value,the gas-solid characteristics of the supercritical CO2 spouting bed are studied by numerical simulation,and the effects of the CO2 flow rate and the height of the stationary bed on the spouting bed are investigated.The results show that the spouted bed can be divided into three parts:spouted region,fountain region and annulus region according to the different concentration of gas and particle velocity.Increasing gas velocity will increase the particle velocity in the spouted region,expand the fountain region,and decrease the particle concentration in the annulus region.Increasing the height of the static bed will make the bed expansion height rise,but when the height of the static bed is too high,the resistance is too large,the bed expansion height will not further riseAccording to the simulation results,the experimental device for the bead foaming of the spouted bed was designed and built.A series of thermoplastic polyurethane(TPU)foam beads were prepared by spouted bed bead foaming experiment,and the effects of CO2 flow rate,saturation temperature,saturation pressure and pressure release rate on bead foaming were investigated.The results showed that the higher the CO2 flow rate was,the more uniform the bead foaming ratio was.When the CO2 flow rate was sufficient to form a stable spouted bed,the uniformity of the bead foaming ratio remained unchanged.When the CO2 flow rate was 0.012 m/s,the saturation temperature was 150?,the saturation pressure was 10 MPa,and the pressure relief rate was 20 MPa/s,the bead foaming rate is largest,reaching 9 times,the cell density was 1.13×107/cm3,and the average cell diameter was 82.3?m.Finally,the particle movement in the pressure relief process was studied by numerical simulation,and the effects of average pressure relief rate bed height and saturation pressure on the pressure relief process were investigated.The results showed that the increase of average pressure relief rate,bed height and saturation pressure would increase the difference of pressure relief rate experienced by different particles,and the difference of foaming rate would also increase.