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Transient Behavior of Extruders

Transient Behavior of Extruders. by Rajath Mudalamane, Dr. David I. Bigio University of Maryland at College Park. INTRODUCTION: Research goals.

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Transient Behavior of Extruders

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  1. Transient Behavior of Extruders by Rajath Mudalamane, Dr. David I. Bigio University of Maryland at College Park

  2. INTRODUCTION: Research goals • STAGE-I: Robust screw design- ‘Minimize variations/fluctuations in the process by using the inherent damping nature of transient behavior of extruders’ • STAGE-II: Unsteady state extrusion process ‘Design for the manufacture of materials with engineered variations in quality (based on performance requirements of the material)’

  3. Theoretical modeling [8,9,10] Knowledge of transient behavior of extruders Experimental observations [1,2,3,4,5,6,7] d1 d2 Q d3 Extrusion Process N ? Temperatures d4 Research goals contd

  4. INTRODUCTION: Schematic of an Extruder • Feeder Dynamics • Feed stock variations FEEDER • Die flow instability: Spurt flow, shark skin surface roughness MELTING MIXING DIE PRESSURE GENERATION • Bed instability Downstream Processing PARTIALLY FILLED, MELT CONVEYING

  5. INTRODUCTION: Disturbance rejecting characterisics of partly filled extruders

  6. Introduction contd. Qin Qin Qout Qout

  7. FLOW DIRECTION Conveying section H Control Volume (dotted lines) Filled region Transient model: Extruder Geometry Kneading block / restrictive element Starved region Fill length(Lf)

  8. Macroscopic material balance Apply law of conservation of mass to control volume: Flow into Control Volume, supplied by starved regions Flow out of Control Volume driven by pressurization in filled region Rate of change of accumulation of material in Control Volume = - (1) = Modified White et al approach

  9. Vf - volume in the filled region • Qst - flow in the starved regions • Qfl - flow in thefilled region • Lf - length of the filled region • F – Fill fraction in starved region

  10. L is the total length of the extruder section and L= Lst+Lf For a given geometry and fluid:

  11. Simulation results: Step response

  12. Frequency response

  13. Sinusoidal disturbance in feedrate

  14. Sinusoidal disturbance in feedrate

  15. Effect of fill level in extruder

  16. Effect of Depth

  17. Step change in screw speed

  18. Sinusoidal disturbance in N

  19. Conclusions • Critical Frequency: • All higher frequencies are damped out and lower frequencies experience little damping • Function of Screw geometry and operating conditions • Critical frequency decreases with increasing fill level and vice versa • Self-leveling response by output rate to changes in screw speed • Screw speed CAN be used to control output rate with limitations on frequency

  20. Bibliography • Tadmor, Z., Klein, I., Van Nostrand Reinhold Co., N.Y., 1976. • White, F.M.,’Viscous Flow’, McGraw-Hill, 1997. • Bird, B.S., Stewart, Lightfoot, ‘Transport Phenomena’, McGraw-Hill, 1986

  21. Bibliography (contd.) • White, J.L. and Kim, E.K., SPE ANTEC, 2000. • White, J.L. and Kim, E.K., Poly. Eng. & Sci., Vol. 41, n 2, 2001. • Rauwendaal, C., ‘Polymer Extrusion’, Hanser, 1994. • Booy, M.L., Poly. Eng. & Sci., Vol. 20, 1980.

  22. INTRODUCTION contd.

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