COMPUTATIONAL ANALYSIS AND DESIGN OF SINGLE SCREW EXTRUDERS HAVING SCREWS OF COMPLEX GEOMETRY WITH MIXING ELEMENTS
Nick Polychronopoulos *
Hyper Advanced Simulation Laboratory (H.A.S.L.)
SPE EUROTEC 2011 BARCELONA, SPAIN
The “heart” of every extruder is an ARCHIMEDEAN SCREW attributed to Archimedes287-212 BC but, actually known to Egyptians for irrigation in the Nile Delta and the auger (screw drill) for carpentry was known to the Greeks before the 3rd Century BC. See: Chris Rorres, J.Hydraul.Eng.,Vol.126, 71-80, (January 2000)
SINGLE SCREW EXTRUDER: Rotating screw in a heated barrel. Early developments for rubber due to Thomas Hancock in 1820 in England. Modern developments started in the1950’s.
MODELING of EXTRUSION started in the 1950’s
Prominent names at DUPONT (USA) o Maillefer (parallel o McKelvey developments in o Gore Switzerland, 1950’s) o Squires 1950’s - Maddock (UnionCarbide) 1950’s - McKelvey’s book on P.P. appeared in 1962 - The book by Z. Tadmor and I. Klein appeared in 1970
MODELING OF EXTRUSION IS 60 YEARS OLD, BUT MANY CHALLENGES REMAIN
SINGLE SCREWEXTRUSION IS THE MOST COST-EFFECTIVE WAY TO MELT AND PUMP A POLYMER SCREW DESIGN calls for OUTPUT MAXIMIZATION MELT TEMPERATURE MINIMIZATION EXTRUSION STABILITY MELT QUALITY
OPTIONS: - CONVENTIONALsingle flighted screws - BARRIER screws - Screws with MIXING SECTIONS
Conventional single screw (also called: plasticating) extruders are composed of three sections:
In all screws at least thefirst 70% or so of melting is due to the shear stress in the melt film between the barrel and the solid bed surface.
BARRIER SCREW PRINCIPLE
- Increased melting. - At least 80% is melted byshear over the solid bed (i.e. very little conductive melting).
MADDOCK (Union Carbide) MIXING SECTION
SOLID PARTICLES TRANSPORT (pellets, size, properties, powders, difficult to...
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