MEΡΟ VI ΔΚΒΟΛΖ ΠΟΛΤΜΔΡΧΝ (POLYMER EXTRUSION) Α.Γ. Παπαζαλαζίνπ, Αλνημε 2017
ΣΗ ΔΗΝΑΗ Ζ ΔΚΒΟΛΖ? ΜΗΑ ΑΠΌ ΣΗ ΚΤΡΗΔ ΓΗΔΡΓΑΗΔ ΣΖΝ ΒΗΟΜΖΥΑΝΗΑ ΠΟΛΤΜΔΡΧΝ ΤΝΔΥΖ ΓΗΔΡΓΑΗΑ ΜΔ ΜΔΓΑΛΖ ΔΤΔΛΗΞΗΑ ΟΟΝ ΑΦΟΡΑ ΣΟ ΣΔΛΗΚΟ ΠΡΟΗΟΝ ΤΥΝΑ ΔΊΝΑΗ ΣΟ ΠΡΧΣΟ ΣΑΓΗΟ Δ ΜΗΑ ΔΗΡΑ ΓΗΔΡΓΑΗΧΝ ΜΟΡΦΟΠΟΗΖΖ Α.Γ. Παπαζαλαζίνπ, Αλνημε 2017
Δ ΠΟΗΑ ΠΟΛΤΜΔΡΖ ΔΦΑΡΜΟΕΔΣΑΗ Primary Uses are Thermoplastics: LDPE, LLDPE, HDPE, ABS, PC, PS, Nylon, PVC, PP Melt Index and Density should be matched to application Some uses for Elastomers and Thermosets Important to watch age of material and processing conditions Α.Γ. Παπαζαλαζίνπ, Αλνημε 2017
ΔΗΓΖ ΔΚΒΟΛΖ ΠΟΛΤΜΔΡΧΝ Compounding Pellets for future use Blown Film Bags, film. Cast Film Sheet Plastic Food Packaging Foam Trays, packaging via thermoforming Α.Γ. Παπαζαλαζίνπ, Αλνημε 2017
ΔΗΓΖ ΔΚΒΟΛΖ ΠΟΛΤΜΔΡΧΝ Compounding Pellets for future use Blown Film Bags, film. Cast Film Plastic Food Packaging Sheet Foam Trays, packaging via thermoforming 5/15/2017
ΔΗΓΖ ΔΚΒΟΛΖ ΠΟΛΤΜΔΡΧΝ Pipe and Tubing PVC Pipe; Garden Hoses Extrusion Coating Paper Milk Cartons with Plastic Coating Wire and Cable Coating Underground Cables Monofilament Fishing Line, Ropes Α.Γ. Παπαζαλαζίνπ, Αλνημε 2017
ΤΝ-ΔΚΒΟΛΖ Allows Opportunity for Several Layers with Different Properties All Extruders for Each Material Goes into Common Die Die Design Determines Division of Layers Α.Γ. Παπαζαλαζίνπ, Αλνημε 2017
The history of extrusion goes back to Archimedes and before BUT modern developments based on understanding of the physical phenomena are less than 50 years old. 5/15/2017
Ο ΒΑΗΚΟ ΜΟΝΟΚΟΥΛΗΟ ΔΚΒΟΛΔΑ 9 5/15/2017
Advantages of Single Screw: Low Cost Straightforward Design Reliability Disadvantages of Single Screw: Mixing is not very good (for some applications) 5/15/2017
ΘΔΡΜΑΝΖ ΚΑΗ ΦΤΞΖ Heating Bring to startup temperature Maintain desired temperatures Cooling Water or Air Cooled To shutdown an extruder quickly To cool down when the polymer overheats To keep from bridging in the feed throat To keep from melting in the grooved feed Α.Γ. Παπαζαλαζίνπ, Αλνημε 2017
ΔΝΓΟ-ΚΟΥΛΗΑ ΘΔΡΜΑΝΖ ΚΑΗ ΦΤΞΖ Cartridge Heaters to heat from both sides Fluid Heating and Cooling to control melt temperature to prevent melting in the feed zone to increase pressure generation in feed Α.Γ. Παπαζαλαζίνπ, Αλνημε 2017
ΔΠΗΠΛΔΟΝ ΔΞΟΠΛΗΜΟ ΤΣΖΜΑΣΑ ΣΡΟΦΟΓΟΗΑ Gravimetric versus RPM-based Type of hopper ΠΗΝΑΚΑ ΔΛΔΓΥΟΤ ΠΑΡΑΚΟΛΟΤΘΖΖ ΛΔΗΣΟΤΡΓΗΑ ΑΝΣΛΗΔ (GEAR PUMPS) ΤΣΖΜΑΣΑ ΜΔΣΑΓΟΖ ΚΗΝΖΖ Α.Γ. Παπαζαλαζίνπ, Αλνημε 2017
Extruder Heads and Adapters Α.Γ. Παπαζαλαζίνπ, Αλνημε 2017
ΔΠΗΠΔΓΔ ΚΔΦΑΛΔ ΔΚΒΟΛΖ (FLAT EXTRUSION DIES) 5/15/2017
Tubular Dies Schematic of a spider leg tuning die Schematic of a spiral die Schematic of a cross-head tubing die used in film blowing Α.Γ. Παπαζαλαζίνπ, Αλνημε 2017
ΠΗΡΑΛ ΚΔΦΑΛΔ ΔΚΒΟΛΖ (SPIRAL EXTRUSION DIES) 5/15/2017
ΠΑΡΑΜΔΣΡΟΗ ΠΟΤ ΔΛΔΓΥΟΝΣΑΗ ΚΑΣΑ ΣΖΝ ΛΔΗΣΟΤΡΓΗΑ Entered By Operator Set-Point temperatures along barrel and die Rotational speed of screw Output from Process Melt pressure before & after screenpack Temperature of the polymer melt at die Actual temperatures along barrel and die Α.Γ. Παπαζαλαζίνπ, Αλνημε 2017
ΓΔΧΜΔΣΡΗΚΑ ΥΑΡΑΚΣΖΡΗΣΗΚΑ ΚΟΥΛΗΑ 5/15/2017
The standard screw L ~20-30D Feed section ~ 4-8D Metering section ~6-10D q =17.66 o (E=1D) W =1D H feed ~0.15-0.2D H f /H m ~2-4 Α.Γ. Παπαζαλαζίνπ, Αλνημε 2011
ΛΔΗΣΟΤΡΓΗΚΑ ΥΑΡΑΚΣΖΡΗΣΗΚΑ ΣΟΤ ΚΟΥΛΗΑ L/D Ratio Flighted Length Outer Diameter of Screw Compressio nratio Feed Depth Metering Depth Α.Γ. Παπαζαλαζίνπ, Αλνημε 2011
Diameter Effect L/D Effect Output, pph Typical Extruder Output Versus Diameter 10000 1000 100 10 1 0.1 0.1 1 10 Diameter, inches Flighted Length L/D Ratio Outer Diameter of Screw Increasing L/D: More shear heat can be uniformly generated without degradation Better mixing opportunities Greater Residence Times Α.Γ. Παπαζαλαζίνπ, Αλνημε 2011
ΓΗΔΡΓΑΗΔ ΚΑΣΑ ΜΖΚΟ ΣΟΤ ΚΟΥΛΗΑ Α.Γ. Παπαζαλαζίνπ, Αλνημε 2011
Ζ ΕΧΝΖ ΜΔΣΑΦΟΡΑ ΣΔΡΔΧΝ (ΕΧΝΖ ΣΡΟΦΟΓΟΗΑ Solids Conveying Zone) PURPOSE: Feed Section Supply plastic at a uniform rate and pressure to the other sections of the screw Compress the solids into solid bed (by difference between barrel and screw friction) Allows air to be pressured back to hopper Be able to withstand high torque loadings Problems in feeding will manifest themselves as air entrapment in melt, melting inconsistencies and irregular extrudate rate Α.Γ. Παπαζαλαζίνπ, Αλνημε 2011
Η ΖΩΝΗ ΜΕΤΑΦΟΡΑΣ ΣΤΕΡΕΩΝ (ΖΩΝΗ ΤΡΟΦΟΔΟΣΙΑΣ Solids Conveying Zone) How the solid pellets convey???? Barrels: rough surface (sometimes intentionally grooved) Screws: smooth (polished) surface Rheology-Extrusion - Univ. Thessaly 2015 25 5/15/2017
ΑΝΑΛΤΗ ΕΧΝΖ ΣΡΟΦΟΓΟΗΑ Solid region approximated by a rigid plug in contact with all sides of channel Channel depth is constant Neglect flight clearance Coefficient of friction (COF) function of temperature but not of pressure No gravity, no density differentials in plug F r =W*dz*P*f s Α.Γ. Παπαζαλαζίνπ, Αλνημε 2011
ΑΝΑΛΤΗ ΕΧΝΖ ΣΡΟΦΟΓΟΗΑ Darnell & Mol (1956): 1 1 s q arcsin 2 1 fs H P fs 2H k ln 1 f z P f W b o b M 2 2 2 f k fsk s HWpv z b L sin sinq sin q 1 afs W 2H z Pz Po exp fb f 2 1 12 s a W H tan( q ) Max (M) when f s is small and f b is large Α.Γ. Παπαζαλαζίνπ, Αλνημε 2011
Α.Γ. Παπαζαλαζίνπ, Αλνημε 2011
Ms[kg/hr] Mass Flow Rate of the solid bed as a function of the ratio f s /f b : 4500 4000 3500 3000 2500 2000 1500 1000 500 0 0.000 0.111 0.250 0.429 0.667 fs/fb Ο ρυθμός μεταφοράς των στερεών σε σχέση με το λόγο fs/fb. Max (M) when f s is small and f b is large Rheology-Extrusion - Univ. Thessaly 2015 29 5/15/2017
Solids Conveying: COF Dependency of COF COF Depends On: Temperature Pressure Velocity (Screw Speed) COF Measurement SPR-18 Term Model Place plastic in between metal for barrel and metal for screw and measure COF (via torque). Barrel COF Effect on Conveying Solids Conveying Rate, pph at 100 RPM 400 350 300 250 200 150 100 Soilds Conveying Rate versus Coefficient of Friction on the Barrel for Soarnol EVOH 50 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Coefficient of Friction Α.Γ. Παπαζαλαζίνπ, Αλνημε 2011
600,000 500,000 Ms [kg/hr] 400,000 300,000 200,000 100,000 0,000 0 0,001 0,002 0,003 0,004 0,005 0,006 0,007 0,008 H [m] Ο ρυθμός μεταφοράς των στερεών σε σχέση με το βάθος του καναλιού. Α.Γ. Παπαζαλαζίνπ, Αλνημε 2011
Feed Section - Screw Length Length of feed section can be negligible to 1/2 the length of screw Industry Standard = 5 Diameters Feed Section - Channel Depth Solids Conveying Rate versus Channel Depth for Various Back Pressures INCREASING LENGTH: Increase output of the screw Decrease available mixing time downstream Solids Conveying Rate, in3/s 20 18 16 14 12 10 8 6 4 2 0 0.4 0.5 0.6 0.7 0.8 0.9 1 Channel Depth, inches P1/P0 = 1 P1/P0 = 100 P1/P0 = 200 P1/P0 = 500 Α.Γ. Παπαζαλαζίνπ, Αλνημε 2017
Solids Conveying - Feed properties: Bulk Density BULK DENSITY Bulk Density and Compressibility Density of the plastic including the air voids between the particles Typically 20-40 lb/ft 3 < 10 lb/ft 3, then extrusion on conventional extruder is no longer possible Screw Design For Bulk Density Bulk Density Design Rules Bulk Density > 1/2 Solid Density Feed Channel = 0.1-0.2 D 1/3 Solid < Bulk Density< 1/2 Solid Density Deeper feed Channel Required Bulk Density< 1/3 Solid Density Crammer Feeder Needed Α.Γ. Παπαζαλαζίνπ, Αλνημε 2017
Solids Conveying - Feed properties: Compressibility Bulk Density and Compressibility Bulk Density and Compressibility COMPRESSIBILITY Difference in percent between bulk density of loose particles and bulk density of packed particles > 20%, polymer is considered non-freeflowing Measure by Hand Clump Test Free flowing: No clump in hand squeeze test Angle of Repose < 45 Non-free flowing: Compressibility > 20% Easily broken clump in hand squeeze test Angle of Repose > 45 Bridge in Hopper: Compressibility > 40% Hard clump in hand squeeze test Difficult to feed a compressible powder Α.Γ. Παπαζαλαζίνπ, Αλνημε 2017
Feed Section Design Feed Section - Channel Depth Feed Section - Helix Angle SUMMARY OF COVNEYING SPEED VERSUS CHANNEL DEPTH: Parabolic Shape to curve - therefore, optimum depth can be chosen Pressure is a key variable - Increased pressure generation comes from a shallower depth Α.Γ. Παπαζαλαζίνπ, Αλνημε 2017
Feed Section Design Feed Section - # of Flights Solids C onveying Rate 30 25 20 15 10 5 0 E ffe ct o f F ee d C h an n el D ep th o n S o lid s C o n ve yin g R a te D o u b le F lig h t 0.1 0.1 5 0.2 0.2 5 0.3 0.3 5 C h a n n e l D e p th, in ch e s S in g le F lig h t *Increasing # of Flights, decreases Solids Conveying Torsion Factor Feed Section produces the most pressure, and greatest possibility of breaking screw TORSION Measurement: Where: H max 0.5D Hmax = maximum feed depth, inches D = Diameter, inches 3 5500 P motor = Power rating of the motor, horsepower N = screw speed, rpm zul = allowable shear stress of metal, psi P N motor 4140 Tensile 237,500 psi Yield 182,000 psi zul 1 3 Α.Γ. Παπαζαλαζίνπ, Αλνημε 2011
Ζ ΕΧΝΖ ΣΖΞΔΧ (Melting Zone) Solids bed in an unwrapped screw channel Screw channel cross section Predicted (Tadmor Model) and experimental solids bed profile Α.Γ. Παπαζαλαζίνπ, Αλνημε 2011
5/15/2017
Barrier Screw Α.Γ. Παπαζαλαζίνπ, Αλνημε 2017
Basic Extruder Analysis 1D Isothermal Newtonian flow between parallel plates One plate moving (screw surface) Other plate stationary (barrel inner surface) DP caused by constriction near the die Conclusion: The flowrate is the sum of the drag flow and of the pressure-driven flow Α.Γ. Παπαζαλαζίνπ, Αλνημε 2017
Now, let s (conceptually) unwind the channel, and turn it into.a CHANNEL between two flat plates (assume the screw is stationary and THE BARREL ROTATES): The barrel moves with V b =πdn where N rotational speed of screw (e.g. RPM) and z the downchannel direction. The down channel velocity component is: V bz =V b cosθ=πdncosθ and: L=z cosθ Recall the FLAT PLATE EQUATIONS for drag flow with an opposing pressure flow: Q VHW 2 3 H dp 12 dz 41 5/15/2017
Use the helical geometry of the channel: N = revs per second (rpm/60) of screw Q 1 2 D 2 2 HN sinq cosq 3 DH 12 sin 2 DP q L 42 5/15/2017
If we take into account the leakage flow rate from the small clearance (δ) between the barrel and the screw: Q 1 2 D 2 2 Q L 2 2 3 D 12e 3 DH HN sinq cosq 12 DP tanq L sin 2 DP q L in our analysis we neglect this term ~ 0 2 2 3 D 12e DP tanq L NOTE: 1. If there is no pressure build-up (e.g. no constriction of flow at the end of the extruder), the output would be maximum, i.e. drag flow only: 1 2 D 2 Q max 2 HN sinq cosq μέγιςτη παροχή 2. If the end is closed, Q=0 and we may equate drag and pressure flow which gives the MAXIMUM POSSIBLE PRESSURE: μέγιςτη 3 1 2 2 DH 2 DP 6DLN πτώςη D HN sinq cosq sin q P max 2 πίεςησ 2 12 L tanq Since μ is large for polymer melts, extremely large (AND VERY DANGEROUS!!!) pressures can develop. 5/15/2017
For the extruder: 1 2 2 Q max D HN sinq cosq 2 P max 2 6DLN tanq Careful..!! L is the length of the METERING ZONE ONLY! L For the DIE (κεφαλή) the pressure drop vs flow rate can be obtained by the usual equations: DP mh ( 2n1 ) L F 1 1 2 n Q W n 2H y x DP 2mR ( 3n1 ) 1 Q LC 3 n n r z 5/15/2017
2D Isothermal Analysis of Screw Extruders Parallel plate representation u l =u x *cos(q)+u z *sin(q) V=πDN (ι)=άμoλαο ηνπ θνριία, ζρεκαηίδεη γωλία (ζ) κε ηνλ άμoλα (ρ) (z)=helical axis Γηα ζεηηθή ξνή, u ι >0 Α.Γ. Παπαζαλαζίνπ, Αλνημε 2011
Melt Conveying simplified flow model - U z (y) (z) u z (H)=V z Flow in the y-z plane useful for flowrate predictions Α.Γ. Παπαζαλαζίνπ, Αλνημε 2011
Melt Conveying simplified flow model on x-y plane (x) (y) V x =Vsin(q) Α.Γ. Παπαζαλαζίνπ, Αλνημε 2011
Melt conveying simple flow theory u l =u x *cos(q)+u z *sin(q) The U l column shows the velocity perpendicular to the q-plane (shaded) in the direction of the screw axis u x u z u l Α.Γ. Παπαζαλαζίνπ, Αλνημε 2011
Melt conveying: fluid motion No net flow (circulation only) Pure drag flow Α.Γ. Παπαζαλαζίνπ, Αλνημε 2011
Melt conveying power calculations????? Α.Γ. Παπαζαλαζίνπ, Αλνημε 2011
Melt Conveying: geometrical corrections Effect of finite width of flow channel Shape factors Α.Γ. Παπαζαλαζίνπ, Αλνημε 2017
Melt Conveying: Effect of clearance () F pn =F p (1+f L ) And of course (H) is replaced by H- in the F D formula Pressure gradient in the presence of leackage flow Α.Γ. Παπαζαλαζίνπ, Αλνημε 2017
Parallel plate vs. annular flow vs. V=πDN (ι)=άμoλαο ηνπ θνριία, ζρεκαηίδεη γωλία (ζ) κε ηνλ άμoλα (ρ) (z)=helical axis Α.Γ. Παπαζαλαζίνπ, Αλνημε 2017
Error introduced due to flat-plate assumption Α.Γ. Παπαζαλαζίνπ, Αλνημε 2011
Melt conveying: non-newtonian fluids Α.Γ. Παπαζαλαζίνπ, Αλνημε 2017
ρεδηαζκόο θαη ιεηηνπξγία εθβνιέα θνριία The concept of combining die and screw characteristic curves to obtain operating points Screw and die characteristics for a grooved feed 45 mm diameter extruder with LDPE Α.Γ. Παπαζαλαζίνπ, Αλνημε 2017
Dimensionless screw characteristic curves for conventional and grooved feed extruders Α.Γ. Παπαζαλαζίνπ, Αλνημε 2017
ΑΛΛΔ ΓΗΟΡΘΧΔΗ Effect of channel nonuniformity in z- direction The operating curve becomes steeper Non-isothermal operation Α.Γ. Παπαζαλαζίνπ, Αλνημε 2017