PLASTICS EXTRUSION (ΕΚΒΟΛΗ ΠΛΑΣΤΙΚΩΝ)

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1 PLASTICS EXTRUSION (ΕΚΒΟΛΗ ΠΛΑΣΤΙΚΩΝ) 1

2 ΤΙ ΕΙΝΑΙ Η ΕΚΒΟΛΗ? ΜΙΑ ΑΠΌ ΤΙΣ ΚΥΡΙΕΣ ΔΙΕΡΓΑΣΙΕΣ ΣΤΗΝ ΒΙΟΜΗΧΑΝΙΑ ΠΟΛΥΜΕΡΩΝ ΣΥΝΕΧΗΣ ΔΙΕΡΓΑΣΙΑ ΜΕ ΜΕΓΑΛΗ ΕΥΕΛΙΞΙΑ ΟΣΟΝ ΑΦΟΡΑ ΤΟ ΤΕΛΙΚΟ ΠΡΟΙΟΝ ΣΥΧΝΑ ΕIΝΑΙ ΤΟ ΠΡΩΤΟ ΣΤΑΔΙΟ ΣΕ ΜΙΑ ΣΕΙΡΑ ΔΙΕΡΓΑΣΙΩΝ ΜΟΡΦΟΠΟΙΗΣΗΣ Rheology Extrusion Univ. Thessaly 2015

3 ΣΕ ΠΟΙΑ ΠΟΛΥΜΕΡΗ ΕΦΑΡΜΟΖΕΤΑΙ 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 3

4 ΕΙΔΗ ΕΚΒΟΛΗΣ ΠΟΛΥΜΕΡΩΝ Compounding Pellets for future use Blown Film Bags, film. Cast Film Plastic Food Packaging Sheet Foam Trays, packaging via thermoforming 4

5 ΕΙΔΗ ΕΚΒΟΛΗΣ ΠΟΛΥΜΕΡΩΝ 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 5

6 ΣΥΝ-ΕΚΒΟΛΗ (CO-EXTRUSION) Allows Opportunity for Several Layers with Different Properties All Extruders for Each Material Goes into Common Die Die Design Determines Division of Layers 6

7 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. 7

8 Ο ΒΑΣΙΚΟΣ ΜΟΝΟΚΟΧΛΙΟΣ ΕΚΒΟΛΕΑΣ 8

9 Advantages of Single Screw: Low Cost Straightforward Design Reliability Disadvantages of Single Screw: Mixing is not very good (for some applications) 9

10 ΘΕΡΜΑΝΣΗ ΚΑΙ ΨΥΞΗ 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 10

11 ΕΝΔΟ-ΚΟΧΛΙΑ ΘΕΡΜΑΝΣΗ ΚΑΙ ΨΥΞΗ 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 11

12 ΕΠΙΠΛΕΟΝ ΕΞΟΠΛΙΣΜΟΣ ΣΥΣΤΗΜΑΤΑ ΤΡΟΦΟΔΟΣΙΑΣ Gravimetric versus RPM-based Type of hopper ΠΙΝΑΚΑΣ ΕΛΕΓΧΟΥ ΠΑΡΑΚΟΛΟΥΘΗΣΗ ΛΕΙΤΟΥΡΓΙΑΣ ΑΝΤΛΙΕΣ (GEAR PUMPS) ΣΥΣΤΗΜΑΤΑ ΜΕΤΑΔΟΣΗΣ ΚΙΝΗΣΗΣ 12

13 ΕΠΙΠΕΔΕΣ ΚΕΦΑΛΕΣ ΕΚΒΟΛΗΣ (FLAT EXTRUSION DIES) 13

14 ΣΠΙΡΑΛ ΚΕΦΑΛΕΣ ΕΚΒΟΛΗΣ (SPIRAL EXTRUSION DIES) 14

15 ΛΕΙΤΟΥΡΓΙΚΑ ΧΑΡΑΚΤΗΡΙΣΤΙΚΑ ΤΟΥ ΚΟΧΛΙΑ Ζώνη τροφοδοσίας Ζώνη Συμπίεσης (τήξη) Ζώνη Άντλησης τήγματος L/D Ratio Flighted Length Outer Diameter of Screw Compression Ratio Feed Depth Metering Depth 15

16 ΓΕΩΜΕΤΡΙΚΑ ΧΑΡΑΚΤΗΡΙΣΤΙΚΑ ΤΟΥ ΚΟΧΛΙΑ Βάθος καναλιού γωνία ελίκωσης 16

17 Η ΖΩΝΗ ΜΕΤΑΦΟΡΑΣ ΣΤΕΡΕΩΝ (ΖΩΝΗ ΤΡΟΦΟΔΟΣΙΑΣ Solids Conveying Zone) How the solid pellets convey???? Barrels: rough surface (sometimes intentionally grooved) Screws: smooth (polished) surface 17

18 Darnell and Mol (1956) developed and isothermal model that relates the mass flow rate to the ratio of outlet to inlet pressure: M s HWpv H P fs 2H k ln 1 f z P f W b o b b sin sin arcsin 1 1 s f k fsk 1 f 2 s F r =W*dz*P*f s z L sin tan( ) 1afs W2H z Pz Poexp fb f s a W H 18

Mass Flow Rate of the solid bed as a function of the ratio f s /f b : Ms[kg/hr] 4500 4000 3500 3000 2500 2000 1500 1000 500 0 0.

19 Mass Flow Rate of the solid bed as a function of the ratio f s /f b : Ms[kg/hr] 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 19

20 ΗΖΩΝΗΤΗΞΕΩΣ (MELTING ZONE) 20

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23 Barrier SCREWS 23

24 BASIC EXTRUDER ANALYSIS DESIGN OF A MELT SCREW PUMP so somehow we must generate pressure from stress (from the fluid viscosity). In drag flow we have no pressure generation: 24

25 THIS DEVICE IS A PUMP BECAUSE IT GENERATES PRESSURE!!! Let s see how this principle can be put into practical use.by a (conceptional design): shallow channel of finite length covered by an infinite moving plate..but this does not represent a practical solution!! 25

26 Now, let s do what Einstein called a Gedanken (i.e. thought) construction of a practical device. twist and turn the shallow channel convert infinite plate into a barrel 26

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28 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 28

29 Use the helical geometry of the channel: Q N = revs per second (rpm/60) of screw 1 2 D 2 2 HN sin cos 3 DH 12 sin 2 P L 29

30 If we take into account the leakage flow rate from the small clearance (δ) between the barrel and the screw: Q L D 12e P tan L in our analysis we neglect this term ~ 0 Q 1 2 D DH HN sin cos 12 sin 2 P L D 12e P tan 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: Q max D HN sin cos 2 2. If the end is closed, Q=0 and we may equate drag and pressure flow which gives the MAXIMUM POSSIBLE PRESSURE: DH 2 P 6DLN D HN sin cos sin P max L tan μέγιστη παροχή μέγιστη πτώση πίεσης Since μ is large for polymer melts, extremely large (AND VERY DANGEROUS!!!) pressures can develop. 30

31 MATCHING OF DIE AND SCREW DESIGN CHARACTERISTICS We have seen that for Newtonian fluids Q versus ΔP are linear for both extruder (pressure build up) and die (pressure drop). The equation can be plotted as follow: ΣΗΜΕΙΟ ΛΕΙΤΟΥΡΓΙΑΣ ΕΚΒΟΛΕΑ 31

32 For the extruder: Q max D HN sin cos 2 P max 2 6DLN tan Careful..!! L is the length of the MELTING ZONE ONLY! L For the DIE (κεφαλή) the pressure drop vs flow rate can be obtained by the usual equations: P mh P 2mR ( 2n1 ) L F n Q W ( 3n1 ) Q LC 1 3 n n n z 32 2H y r x

33 All the previous are straightforward for NEWTONIAN FLUID ΙΝ ΤΗΕ EXTRUDER. But what happens if the fluid behaves in a NON NEWTONIAN manner??? e.g. POWER LAW mode there is not a simple closed form solution to solve problems of combined pressure and drag flow! So we will use the.equivalent VISCOSITY (ισοδύναμο ιξώδες) ( back of the envelope calculations): ref velocity gap V H 2RN H m n1 e.g. ref velocity gap V H 2 100mm 2mm s 1... s 1 ref 734Pa s ref 0. 5 The above APPROXIMATIONS apply ONLY IN THE EXTRUDER!!! 33

34 Power Requirement (κατανάλωση ισχύος εκβολέα) of the extruder: The power required by the turning screw is needed to: 1. Raise the temperature from room temperature to extrusion temperature in the die (room temperature~20 o C die temp ~ 200 o C). 2. Melt the polymer (heat of fusion). m Q ή( kg / hr ) 3. Pump the molten polymer. P o QC p T T QH pq out in Ισχύς= αύξηση Τ + τήξη + άντληση f Συνεισφορά τριών όρων! Motor power (ισχύς κινητήρα)p m : e: motor EFFICIENCY P 1 e m P o P o kW e

35 And.some calculations 1. Torque (ροπή) with power calculated from previous equation: P o F V F P / o V T o F R T o P V o R T o PO N ( D 2H ) 60 ( D 2H ) 2 T o PO N Power and Torque from.shear stress (από διατμητική τάση): P o F V P o wall Area V screw wall m n Area ( D 2H ) V screw L s N ( D 2H ) 60 L sin P o... L s 35

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