POLYMER PROCESSING LABORATORY UNIVERSITY OF MARYLAND Transient Behavior of Extruders by Rajath Mudalamane, Dr. David I. Bigio University of Maryland at College Park

POLYMER PROCESSING LABORATORY UNIVERSITY OF MARYLAND 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)’

POLYMER PROCESSING LABORATORY UNIVERSITY OF MARYLAND Research goals contd Knowledge of transient behavior of extruders Experimental observations [1,2,3,4,5,6,7] Extrusion Process Q N Temperatures d1d1 d2d2 d3d3 d4d4 ? Theoretical modeling [8,9,10]

POLYMER PROCESSING LABORATORY UNIVERSITY OF MARYLAND INTRODUCTION: Schematic of an Extruder FEEDER MELTING PARTIALLY FILLED, MELT CONVEYING MIXING DIE PRESSURE GENERATION Downstream Processing Feeder Dynamics Feed stock variations Bed instability Die flow instability: Spurt flow, shark skin surface roughness

POLYMER PROCESSING LABORATORY UNIVERSITY OF MARYLAND INTRODUCTION: Disturbance rejecting characterisics of partly filled extruders

POLYMER PROCESSING LABORATORY UNIVERSITY OF MARYLAND Introduction contd. Q in Q out Q in Q out

POLYMER PROCESSING LABORATORY UNIVERSITY OF MARYLAND Transient model: Extruder Geometry Kneading block / restrictive element Starved region Fill length (L f ) Filled region Conveying section FLOW DIRECTION Control Volume (dotted lines) H

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

POLYMER PROCESSING LABORATORY UNIVERSITY OF MARYLAND V f - volume in the filled region Q st - flow in the starved regions Q fl - flow in the filled region L f - length of the filled region  – Fill fraction in starved region

POLYMER PROCESSING LABORATORY UNIVERSITY OF MARYLAND L is the total length of the extruder section and L= L st +L f For a given geometry and fluid:

POLYMER PROCESSING LABORATORY UNIVERSITY OF MARYLAND Simulation results: Step response

POLYMER PROCESSING LABORATORY UNIVERSITY OF MARYLAND Frequency response

POLYMER PROCESSING LABORATORY UNIVERSITY OF MARYLAND Sinusoidal disturbance in feedrate

POLYMER PROCESSING LABORATORY UNIVERSITY OF MARYLAND Sinusoidal disturbance in feedrate

POLYMER PROCESSING LABORATORY UNIVERSITY OF MARYLAND Effect of fill level in extruder

POLYMER PROCESSING LABORATORY UNIVERSITY OF MARYLAND Effect of Depth

POLYMER PROCESSING LABORATORY UNIVERSITY OF MARYLAND Step change in screw speed

POLYMER PROCESSING LABORATORY UNIVERSITY OF MARYLAND Sinusoidal disturbance in N

POLYMER PROCESSING LABORATORY UNIVERSITY OF MARYLAND 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

POLYMER PROCESSING LABORATORY UNIVERSITY OF MARYLAND Bibliography 1.Tadmor, Z., Klein, I., Van Nostrand Reinhold Co., N.Y., White, F.M.,’Viscous Flow’, McGraw-Hill, Bird, B.S., Stewart, Lightfoot, ‘Transport Phenomena’, McGraw-Hill, 1986

POLYMER PROCESSING LABORATORY UNIVERSITY OF MARYLAND 8.White, J.L. and Kim, E.K., SPE ANTEC, White, J.L. and Kim, E.K., Poly. Eng. & Sci., Vol. 41, n 2, Rauwendaal, C., ‘Polymer Extrusion’, Hanser, Booy, M.L., Poly. Eng. & Sci., Vol. 20, Bibliography (contd.)

POLYMER PROCESSING LABORATORY UNIVERSITY OF MARYLAND INTRODUCTION contd.