Conveyor analysis of solids conveying section of three⁃screw extruder based on discrete unit method with one⁃character arrangement

doi:10.19491/j.issn.1001-9278.2023.08.009

Abstract

Abstract:

The solids conveying section of a single⁃aligned three⁃screw extruder under metering and dosing was simulated using a discrete unit method. The transport performance of polymer particles was analyzed through both positive displacement conveying and friction drag conveying in a one⁃screw extruder. The conveying characteristics parameters of the mono⁃aligned three⁃screw extruder were calculated and then compared with those of a conventional twin⁃screw extruder. The results indicated that the filling rate of the particles in the screw groove of the extruder was increased with an increase in the engagement zone of the three⁃screw extruder. The mono⁃aligned triple⁃screw extruder exhibited better performance of the twin⁃screw extruder in the aspects of the filling degree and mass flow rate， and its conveying output was approximately 1.3 times that of the twin⁃screw extruder. This indicates a promising prospect of engineering application in the polymer processing industry.

Key words: one?way alignment of three screw, discrete unit method, solids conveying, conveyor theory

CLC Number:

TQ320.66⁺3

WANG Haolin, WANG Tingxi. Conveyor analysis of solids conveying section of three⁃screw extruder based on discrete unit method with one⁃character arrangement[J]. China Plastics, 2023, 37(8): 61-68.

Figures/Tables 20

Fig.1. Particle contact model and damping model

Fig.2. Model of three⁃screw solid conveying section

类别	机筒内径/mm	螺杆外径/mm	导程/mm	固体输送段长度/mm	螺槽深度/mm	密度/kg·m^-3	弹性模量/GPa	泊松比
机筒与螺杆参数	82	80	30	200	8	7 850	80	0.3

Tab.1. Parameters of the barrel and screw

类别	密度/kg·m^-3	弹性模量/GPa	泊松比	恢复系数	颗粒间的摩擦因数	颗粒与螺杆的摩擦因数	颗粒与机筒的摩擦因数
性能参数	595	0.17	0.44	0.5	0.81	0.25	0.35

Tab.2. Performance parameters of PE⁃LD

Fig.3. Positive displacement conveying of particles in the upper meshing zone

Fig.4. Positive displacement conveying of particles in the upper and lower meshing zone

Fig.5. Positive displacement conveying of particles in the upper and lower meshing zone

Fig.6. Coexistence of positive displacement and solid friction conveying

Fig.7. N⁃layer model of the non⁃engaging zone

挤出机类型	螺杆转速/ r·min^-1	颗粒填充率
挤出机类型	螺杆转速/ r·min^-1	0.2	0.3	0.5
双螺杆挤出机	25	3.06	4.59	7.65
	35	3.80	5.70	9.50
	45	4.83	7.25	12.09
三螺杆挤出机	25	3.98	5.97	9.95
	35	4.94	7.41	12.35
	45	6.30	9.43	15.72

Tab.3. Comparison of mass flow rates at different rotational speeds

挤出机类型	螺杆转速/ r·min^-1	螺棱宽度/mm
挤出机类型	螺杆转速/ r·min^-1	7	9	11
双螺杆挤出机	25	14.48	13.23	12.05
	35	17.22	16.10	15.73
	45	19.53	17.86	16.45
三螺杆挤出机	25	19.64	18.48	16.87
	35	24.08	22.43	21.00
	45	26.61	24.92	22.96

Tab.4. Comparison of mass flow rates at different screw rib widths

Fig.8. Structure of the three shapes of screw prongs

挤出机类型	螺杆转速/ r·min^-1	螺棱形状
挤出机类型	螺杆转速/ r·min^-1	矩形	梯形	锯齿形
双螺杆挤出机	25	13.24	14.55	15.13
	35	17.41	19.76	21.39
	45	22.42	24.92	26.88
三螺杆挤出机	25	18.48	20.37	21.18
	35	23.84	27.12	30.01
	45	30.87	34.88	36.40

Tab.5. Comparison of mass flow rates for different spiral prism shapes

Fig.9. Simplified model of the particles

颗粒形状	三螺杆质量流速率/g·s^-1	双螺杆质量流速率/g·s^-1
球形	18.47	14.29
圆柱形	21.79	15.38
椭球形	16.33	12.31

Tab.6. Mass flow rate of the particles with different shapes

Fig.10. Morphology of the particles in the extruder

Fig.11. Comparison of filling rates of the three types of particles

Fig.12. Effect of friction coefficient between particles on the flow rate

Fig.13. Effect of friction coefficient between particles and screw on the flow rate

Fig.14. Effect of friction coefficient between particles and barrel on the flow rate

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