Study on mixing characteristics in conveying section of new eccentric tri⁃screw extruder

doi:10.19491/j.issn.1001-9278.2022.07.021

Abstract

Abstract:

A new eccentric three?screw extruder was designed on the basis of the traditional tri?screw extruder. The tri?screw extruder had the characteristics of eccentric screw geometry， special gradient change of screw groove configuration， and high area utilization coefficient. The three?dimensional numerical simulation of the flow and mixing law of polypropylene （PP） melt in the new eccentric three?screw extruder was carried out using the finite element method. The distribution law of pressure and velocity in the eccentric tri?screw extruder were presented. The mixing characterization parameters such as the residence time distribution， distribution index， separation scale， and maximum shear stress of the tri?eccentric screw extrusion flow fields were calculated. The results indicated that the screw eccentricity not only determined the shape of the screw end face but also changed the variation degree of the screw groove gradient. The particle agglomeration effect in the extruder decreased but the material shear effect increased with a gradual decrease in the spiral groove gradient. Among the three new eccentric tri?screw extruders， the new eccentric screw extruder with an eccentricity of 3 mm had relatively good mixing performance.

Key words: tri?screw extruder, eccentricity, screw end face, spiral groove gradient

CLC Number:

TQ320.64

LIU Yang, ZHU Xiangzhe. Study on mixing characteristics in conveying section of new eccentric tri⁃screw extruder[J]. China Plastics, 2022, 36(7): 150-156.

Figures/Tables 14

Fig.1. End face meshing curve of new eccentric three head screw

Fig.2. Screw combination with different eccentricity

Fig.3. Sectional view of screw combination with different eccentricity

Fig.4. Sectional view of different screws along XZ plane

Fig.5. Mesh division of the screw and runner

Fig.6. Pressure nephogram of X?Z section at Y=-20 mm on Y axis

Fig.7. Pressure nephogram of X?Z section at Y=0 on Y axis

Fig.8. Velocity vector diagram of X?Z section at Z=-1 mm （outlet position Z= 0） and T = 1.7 s on Z axis

Fig.9. Velocity change curve along the positive direction of Z axis at different positions

Fig.10. Spatial distribution of tracer particles at time of 3.83 s

Fig.11. Residence time distribution curve of the three groups of the new eccentric tri?screw extruders

Fig.12. Distribution index and separation scale curve of the three groups of the new eccentric tri?screw extruders

Fig.13. Maximum shear stress

Fig.14. Mean shear stress

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