Study on Safe Mixing Radial Clearance of Conical Twin⁃screw for Extrusion of Energetic Materials

doi:10.19491/j.issn.1001-9278.2021.11.019

Abstract

Abstract:

Taking the extrusion section， transition body， and extruder head of a conical twin?screw extruder as an research object， the non?isothermal steady?state and transient finite element simulation of Polyflow was conducted to analyze the distributions and change curves of each field in the flow field， their safe mixing issues of energetic materials in the flow channel were studied. Considering both safety performance and mixing effect， a comprehensive evaluation method was established， and the radial clearance was optimized. The results indicated that the maximum shear rate， highest shear stress， and highest viscous heat dissipation of the channel all took place near the entrance of the extruding segment. The highest pressure and temperature were located at the exits of the extruding section flow channel and extruder head， respectively. The mixing effect of the conical twin screw increased with an increase in radial clearance. When the radial gap was 0.5mm， the safety performance of flow channel was the worst. However， the screw exhibited the best safety performance at a radial gap of 1 mm.

Key words: energetic material, conical twin-screw, radial clearance, safety performance, mixing effect

CLC Number:

TQ 320.66

ZHANG Junwei, DONG Liqun, MA Yun, ZHANG Jun, XUE Ping. Study on Safe Mixing Radial Clearance of Conical Twin⁃screw for Extrusion of Energetic Materials[J]. China Plastics, 2021, 35(11): 125-132.

Figures/Tables 18

参数	熔体稠度/N·sⁿ ? m^-2	幂律指数（无量纲参数）	温度敏感系数/K^-1	密度/kg·m^-3	比热容/J·（kg·K）^-1	热导率/W·（m·K）^-1	参考温度/K
符号	m	n	b	ρ	C_p	k	T_r
数值	5.5×10⁵	0.154	0.024 9	1 780	1 250	0.35	363.15

Tab. 1. Rheological and physical parameters of energetic materials

螺杆代号	G0.5	G1	G1.5	G2
间隙/ mm	0.5	1	1.5	2

Tab. 2. Radial clearance

Fig.1. 3D model of conical screw conveying section under G1 and G2 type

Fig.2. 3D model of flow channels

Fig.3. Flow channel finite element model

位置	流动边界条件	热边界条件
入口	inflow	338.15 K
机筒内壁面	壁面无滑移	Flux density imposed
锥形双螺杆	转速	328.15 K
挤出出口	自由流动	热出口

Tab. 3. Flow boundary conditions and thermal boundary conditions

Fig.4. Distribution of each field in flow channel

Fig.5. Curves of pressure and maximum pressure under different gap

Fig.6. The curve of viscous heating and maximum viscous heating under different gap

Fig.7. The curve of temperature and maximum temperature under different gap

Fig.8. The curve of shear stress and maximum shear stress under different gap

Fig.9. The cumulative residence time distribution of different gap flow field

Fig.10. The weighted average shear rate of flow field under different gap

Fig.11. The weighted average shear stress of flow field under different gap

Fig.12. The average backflow coefficient of flow field under different gap

Fig.13. The curve of safety coefficient and maximum safety coefficient under different gap

Fig.14. The mixing coefficient under different radial clearance

Fig.15. The safety mixing coefficient of flow field under different radial clearance

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