【正文】 C 051015202530351 6 . 8 1 6 . 9 17 1 7 . 1 1 7 . 2 1 7 . 3 1 7 . 4 1 7 . 5 1 7 . 6 1 7 . 7V o l u m e (c c )Pressure (MPa)12. Fibre spinning test Test: Data obtained: Uses: Special hauloff motor amp。 dies: 1015,000 s1 2mm 216。 A deeper look inside What happens in the entrance zone of a capillary die ? ? a change in crosssection leads to a entrancepressuredrop because of : ? Elastic stringing ? Acceleration ? secondary flow ? Extensional, viscous flow Pressure transducer Capillary die Comparison of Typical Shear Data 11010010001 10 100 1000 10000 100000Shear Rate ( /s )Shear Stress (kPa)LLDPEPPHDPELDPEPPNy l on 66 ( 13% glas s fi l l ed)uPV CComparison of Typical Extension Data 0. 010. 11101001 10 100 1000 10000 100000Sh ea r Rat e (/s)Entry Pressure (MPa)LL DPEPPHDPELDP EPPNy lo n 66 ( 1 3 % .)u PVCTypical Polymer Processing Temperatures 1. Polyolefins: ~190176。 ? 適當(dāng)升高熔體溫度是另一個(gè)典型例子。實(shí)驗(yàn)發(fā)現(xiàn)，當(dāng)入口區(qū)為平口型（入口角 ）時(shí)，擠出破裂現(xiàn)象嚴(yán)重。釋能后的熔體又會(huì)再次與模壁粘著，從而再集中能量，再發(fā)生滑移。但當(dāng)剪切速率 后，入口區(qū)出現(xiàn)強(qiáng)烈的拉伸流，其造成的拉伸形變超過熔體所能承受的彈性形變極限，強(qiáng)烈的應(yīng)力集中效應(yīng)使主流道內(nèi)的流線斷裂，使死角區(qū)的環(huán)流或渦流乘機(jī)進(jìn)入主流道而混入口模。很高時(shí)，出現(xiàn)無規(guī)破裂?？梢钥隙ǖ卣f，這些現(xiàn)象與高分子液體的非線性粘彈行為，尤其是彈性行為有關(guān)，是高分子液體彈性湍流的表現(xiàn)。 D a t a f ro m R o s a n d O L R8010012014016018020022050 70 90 110 130 150 170 190 210 230 250Sh e a r St ra i n R a t e (/ s )Shear Stress (kPa) 8 x 0 . 5 m m1 2 x 0 . 7 5 m m1 6 x 1 m mL i n e o f c o n s t a n tSh e a r St re s sWall Slip Correction No Wall Slip gapp 1/R ? Result: Dependency of wall slip velocity on shear stress (true shear rate) slip shear full Q Q Q ? ? R v 4 slip true app ? g ? g . . 2 slip 3 true 3 app R v 4 R 4 R ? ? ? ? ? g ? ? ? g . . Mooney, M., J. Rheology 2, 210 (1931) Wall Slip Measurement ?Slip ponent of flowrate, Q = ? R2 v [Vs] mm/s [?w] kPa PE Vs = (?w/100) ?w 90 kPa ? PVC Vs = (?w/100) ?Some typical slip velocities ?Many materials only slip above a critical stress, typically MPa Extensional Flow Analysis 4 Extensional Flow Analysis 4 Extensional Flow Analysis 4 Extensional Flow Analysis 4 Extensional Flow Analysis ? 拉伸黏度是在實(shí)際紡絲過程即非穩(wěn)態(tài)拉伸流中的黏度。High Pressure Capillary Rheometry 1 Introduction Polymers are used because: ? They are cheap to form into shape in molten state Therefore, ? We need to understand how they flow when molten also important in: food processing, pharmaceuticals, paints, inks, pastes, slurries etc... Very important in Polymer Processing But, molten polymers are plicated systems... ? Temperature dependent ? Rate dependent ? Time dependent ? Work dependent (and that’s before we add lubricants, fillers, plasticisers, foaming agents etc…!) ? In between a liquid and a solid Influences on Viscosity ? molecular structure of sample ? temperature ? pressure ? time ? shear rate ? ? (T, p, t, g) = g . . Shear viscosity definition g shear rate . ? shear stress ? ? = g . ? shear viscosity ?Viscosity is a measure of resistance of a fluid against the applied shear force. ?Shear viscosity is only one part of Rheology. ?It is the dominant effect for pressure in extruders, injection moulding machines and dies. 1 . E + 0 01 . E + 0 21 . E + 0 41 . E + 0 61 . E + 0 81 . E 0 5 1 . E 0 3 1 . E 0 1 1 . E + 0 1 1 . E + 0 3 1 . E + 0 5S he a r r a t e ( s1)Viscosity (Pa.s)Typical process shear rates Relaxation Coating Free surface Mixing Extrusion Injection moulding Why do we need a highpressure capillary rheometer? The application is important log g/s1 DMA Osc. / Rot. rheometer High pressure capillary rheometer Viscosities: (low), middle to highviscous Quantities: Shear and extensional viscosity, wall slip relaxation, PVT, Flow instabilities 101 103 Levelling 104 101 Extrusion, Injection Moulding 100 102 Mixing 103 106 Roll Coating, Spraying Viscosities: low viscous to solidlike Quantities: Shear viscosity, yield, viscoelastic properties, relaxation etc. Nondestructive Oscillarory shear ? rot. rheometer: structural/low shear measurements – highpressure capillary: processing flow behaviour ? Single point test (generates one number) MFI die ( diameter) ? Defined by standards (ISO1133) ? Simple ? Cheap ? Easy to use ? Pressure driven Melt Flow Indexer (MFI) Melt Flow Indexer (MFI) ? Single point test ? Does not generate engineering units (grams per 10 minutes) ? Mainly a shear flow measurement neglects extension ? Very low shear rate test (gapp = MFI) But, 1 . E + 0 01 . E + 0 21 . E + 0 41 . E + 0 61 . E + 0 81 . E 0 5 1 . E 0 3 1 . E 0 1 1 . E + 0 1 1 . E + 0 3 1 . E + 0 5S he a r r a t e ( s1)Viscosity (Pa.s)Typical process shear rates Relaxation Coating Free surface Mixing Extrusion Injection moulding MFI test Capillary Rheometer Measure: Pressure drop Piston Capillary die Pressure transducer Polymer melt Set: Piston speed Die Dim’s Capillary rheometry We set: Temperatur