Content. Seminar on rheology. Viscometers, rheometers and measuring systems

Transcription

1 Seminar on rheology Viscometers, rheometers and measuring systems 1 Content Overview Finger, Ford cup Capillary viscometer Falling ball viscometer Rotational viscometer Rotational rheometer Sensor systems RheoScope Extensional rheometer 2

2 How can you measure viscosity? Feed back to other physical quantities, viscosity value relative or absolute. Rheometer: additional measurements of other material characteristics Principle Biosensor Volume flow Falling weight Torsion Compression Rotation sensor Device Finger Changel Ford cup (High pressure ) Capillary viscometer Falling ball viscometer Laray-viscometer Torsion viscometer Compression viscometer Krebs -Stormer-viscometer Rotational viscometer / - rheometer Measuredquantity Resistance (Force, Pressure) Time Time (Pressure, Displacement) Time Damping Force, Displacement Force, Displacement 3 Testing of viscosity: Finger... the cheapest viscometer cheap simple quick easy to clean 4

3 Testing of viscosity: Ford cup Relative values only simple quick cheap 5 Testing of viscosity: Ford cup Method Measurement of the time that a defined sample volume needs to flow through a nozzle. The diameter of the nozzle and the type of the cup have to be given with the result in "seconds", e.g. "240s with DIN cup 4" Advantage Cheap, simple and robust instrument, easy handling Disadvantage No temperature control, wrong results for non-newtonian fluids, completely unusable for samples with yield point Application Adjustion of the viscosity of the varnish or paint in the spraying cabin 6

4 Capillary viscometer (Gravity is the driving force) Advantage: + Relatively cheap + Very precise for low and medium viscosities + Can be calibrated + Absolute for Newtonian fluids Disadvantage: - Long measuring time - High cleaning effort - Labor intensive (manual version) - relative values - for Non-Newtonian fluids - Not appropriated for samples with yield stress - Limited operating temperature range Method: The time measurement how long it takes that the fluid passed two marks 7 Capillary viscometer (Gravity is the driving force) Result: ν = C 4 * t Application: Low viscous fluids i. e. oils ν - viscosity (kinematic) [ mm 2 / s ] h = n * r C 4 - Capillary constant, Depends on the used capillary and has to be determined by calibration Boundary condition: L/D > 30 (L: length, D: diameter) 8

5 High pressure capillary viscometer Advantage: + High shear rates + Less friction heating because always a new sample is feeded + Calibration possible + Absolute measurements Disadvantage : - High price, big instruments - For test with rod capillary three tests are necessary for the Bagleycorrection - Not for low viscous materials - Cleaning Method: The sample is pressed with a piston through the capillary. Measuremet of the pressure difference p und the volume flow Q Calculations: p = p 1 - p 2 τ = R/(2L) * p γ = 4/(π R 3 ) * Q η = π R 4 /8L * p/ Q Application: Polymers, printing inks 9 Falling ball viscometer: Höppler C Absolute values: Newtonian samples Relative values: Non-Newtonian samples Measuring parameter: falling time t Sample volume: 45 ml Temperature: C (circulator required) Viscosity: mpas Time curve η(t). One point measurement η(γ = const) Calibration High accuracy Limited to transparent, Newtonian liquids DIN 53015, ISO

6 Falling ball viscometer (according to Höppler DIN / ISO 12058) Result: η = K*(ρ k - ρ Fl )* t Applications: - Low viscous fluids i. e. oils - Evaporating fluids / solvents i. e. Styrol - Gases η - Viscosity (dynamic) K - Calibration factor for the ball Depends on the diameter of the ball and tube, has to be calibrated 11 Relative Viscometer Any scale reading S (time, distance, angular deflection) is set into ratio with a known viscosity standard Viscosity of unknown material is calculated as follows: η unknown = η Standard s Standard S unknown Parameters of testing (rotor, speed, filling ) strictly need to be kept constant. Good for Newtonian liquids only! 12

7 Rotational viscometer Method The torque is measured at a certain pre-set speed (controlled rate method, CR) or the speed is measured at a certain pre-set torque (controlled stress method, CS). The sensor system is designed to allow calculation of the rheological relevant quantities Advantage Flexibility in the viscosity range, temperature range and shear rate range Drawback Expensive, limited accuracy, time consuming cleaning procedure with coaxial cylinder systems Application For non-newtonian substances and temperatures different from room temperature 13 Rotational viscometer: HAAKE Viscotester 1 plus, 2 plus Absolute values: Newtonian samples Relative values: Non-newtonian samples Measuring friction of the sample at a fixed rotation speed (62.5 min -1 ) Sample volume: individual No temperature control Viscosity: VT2 plus: mpa. s Time curve One point measurement High uncertainty: 7% FS 14

8 Rotational viscometer: HAAKE Viscotester 6 & 7 plus Absolute values: Newtonian samples Relative values: Non-newtonian samples Measuring friction of the sample in dependence on defined rotation speeds (0.1 < rounds/min -1 < 200) Sample volume: min. 400 ml No temperature control (VT7: Pt100, RS232) Viscosity: L: mpa. s Time curve Flow curve Uncertainty: 1% FS R: mpa. s ISO 2555 (Brookfield-method), 15 Relative viscosity value Viscosity Curve of 2 Fluids Viscosity (mpas) Shear Rate (1/s) 16

9 Rotational viscometer: HAAKE Viscotester 550 Absolute values with all samples (Relative values with simple sensors) Measuring geometries: cylinder, plate/plate, plate/cone Sample volume: individual Temperature control (circulator required) Wide range of viscosity Time curve η (t) Flow curve η (g) Thixotropy (depends on the time of shearing) Determination of the yield stress (CR, CD) High accuracy DIN 53019/ISO 3219, DIN Relative and absolute viscosity value example Relati~2 ƒ = f (Á) Relati~3 ƒ = f (Á) Absolut ƒ = f (Á) Viscosity curve 1.00 MV-DIN with cup ƒ [Pas] 0.10 MV-DIN without cup absolute relative relative Suspension sensor E Á [1/s] 18

10 Rotational Rheometer Method The torque is measured at certain pre-set speeds (controlled rate method, CR) or the speed is measured at certain pre-set torque (controlled stress method, CS) or torque is applied as sine wave at varying frequencies (oscillation method, OSC) Advantage Flexibility in measuring methods or ranges Application For viscoelastic substances and conditions different from ambient. The sensor systems are designed to allow calculation of the rheologically relevant quantities 19 Rotational Rheometer Measurement of torque at constant or varying speed. Geometrical factors convert physical quantity into rheological quantity: τ = A Factor M Torque CS γá & = M Factor Ω RotationalSpeed CR 20

11 Rotational Rheometer: Design of a CR measuring unit Motor with speed control n Measurement of the torque M d Sensor system (cylinder, parallel plates or plate-cone) with temperature control (liquid, electrical, Peltier) 21 Rotational Rheometer: Design of a CS measuring unit Motor with torque control Measurement of speed or deformation Bearing (frictionless air bearing) with high axial and radial stiffness Sensor system (cylinder, parallel plates or plate-cone) with temperature control (liquid, electrical, Peltier) 22

12 Sensor systems: Overview Sensor system Counter part Advantage Disc, cylinder (Brookfield) Barrel Price Vane rotor, helical gooved Barrel Sedimentation Coaxial rotors Cup Price Cone Plate Flow Plate Plate Oscillation 23 Design of sensors Cylindrical Sensors - thin liquids (large rotor surface) - filled systems (wide gaps) Plate/Cone - thick substances - easy to clean - no particles - high shear rates Plate/Plate - dynamic measurements (oscillation) - inhomogeneous materials (particles, fibres) 24

13 Factors A & M τ = η γ& A = τ Md Á γ M = & Á Ω Shear stress τ [Pa]. Shear rate γ [1/s -1 ] Viscosity η [Pa. s] Torque M d [Nm] Angular velocity Ω [rad/s] η = A Md M Ω 25 Cylindrical / coaxial sensors Advantage sample filling dimensions (gap, surface) positioning sedimentation Critical Issues cleaning inertia 26

14 Coaxial cylinder sensor systems DIN Shear rate γ& Ái 2 R a = 2Ω R R 2 a 2 i 2π n Ω = δ γ& Á i = Ω = M Ω 2 δ 1 R δ = R a i test sample Ω R a L Shear stress Viscosity M 1 d τ = = M i 2 2 d 2π L R Cl 2 L R Cl i π i τ = A M i d η = M d Ω A M = [ Pa s] R i R a Shear stress τ [Pa] Shear rate γ [1/s -1 ] Shear rate factor M Torque M d [Nm] Ratio of radii δ Angular velocity Ω [rad/s] Radius of the cup R a [m] Radius of the rotor R i [m] Viscosity η [Pa s].. 27 Cone/plate sensor systems Advantage small sample volume constant shear rate easy cleaning Critical issues accurate filling correct gap setting particle size 28

15 Cone / plate sensor systems Shear rate & Á k γ 1 1 = Ω = M Ω = Ω tan α α 1 1 M = tan α α Shear stress τ K 3 = 2π R 3 K M d = A M d Shear rate γ [1/s -1 ] Shear stress τ [Pa] Viscosity η [Pas] Outer radius of cone R C Truncation radius R T Cone angle α Height of removed tip a Angular velocity Ω [rad/s] Shear rate factor M Torque M d [Nm] Sample. R C Truncation a a Viscosity M d η = Ω A M M d = G = Ω [ Pa s] a R T α 29 Plate / plate sensor systems Advantage gap setting particle size small sample volume easy cleaning Critical issues accurate filling shear rate 30

16 Plate / plate sensor systems Shear rate Shear stress Viscosity Á γ& = M Ω 2π n Ω = 60 2 τ = M d A A = 3 π R 3 + n τ = M d A 4 η = M d Ω A M = [ Pa s] test sample. R Shear rate γ [1/s -1 ] Shear stress τ [Pa] Viscosity η [Pa. s] Plate radius R Distance h Shear rate factor M Torque M d [Nm] Angular velocity Ω [rad/s] Shear stress factor A [1/m³] Rotor speed n [1/min] h 31 Recommended measuring range HAAKE Rheometer Measuring Range of two Sensors 1,E+06 1,E+05 1,E+04 Cone 35mm 1,E+03 Viscosity (Pas) 1,E+02 1,E+01 1,E+00 1,E-01 1,E-02 Cone 60mm 1,E-03 1,E-02 1,E-01 1,E+00 1,E+01 1,E+02 1,E+03 Shear rate (1/s) 32

17 How to choose a sensor system Subjective impression of the sample Low to medium viscosity easy to clean High viscous, pastes, hard to clean Large particles sedimentation, separation Coaxial cylinders in various dimensions Cone/plate (without particles) Plate/plate (with particles) Special sensors vane or helical grooved sensor 33 HAAKE Series 1 Instruments Standardized Design Compact instruments Polymer concrete stand Automatic lift system Integrated temperature control unit Temperature control options: cylinder (liquid) cone & plate (liquid) cone & plate (Peltier-element) cone & plate (electric, with additional cone heater) Manual control via display unit Control via PC + RheoWin software 34

18 HAAKE RotoVisco 1 HAAKE RotoVisco 1 is the successor of RV2/3/11/12 and replaces RV20/30 in many applications in R&D and QC. Rotational measurements (CRcontrolled) Yield-point measurement with CDmethod Measuring of viscous sample properties Torque: r.p.m.: mnm min-1 CD-mode: min-1 System: Motor: cylinder / cone-pate stepper motor Mechanical bearing 35 HAAKE RheoStress 1 HAAKE RheoStress 1 replaces the approved HAAKE line of research grade universal rheometers like CV100 Rotational testing (CR, CS, CD controlled) Oscillatory testing (CS, CD controlled) Measuring viscous -elastic sample properties Torque: r.p.m.: (0.0005) mnm (3200) rpm Frequency range: Hz Multiwave: Hz Angular resolution: 300 nano rad Motor: Air bearing low inertia drag cup with Micro Stress Control 0.5 micro Nm 36

19 HAAKE RheoScope 1 Rheometer RheoStress 1 + Microscope Rheogram + Microscopic pictures 37 HAAKE RheoStress 600 HAAKE RheoStress 600 modular high-tech rheometer Rotational testing (CR, CS, CD controlled) Oscillatory testing (CS, CD controlled) Normal force measuring Measuring viscous -elastic properties Extremely rapid motor Genuine deformation control Torque: r.p.m.: ( ) mnm (4500) rpm Frequency range: Hz Multiwave: Hz Angular resolution: 12 nano rad Normal force: Motor: Air bearing N (Option) low inertia drag cup with Micro Stress Control 0.1 micro Nm 38

20 HAAKE MARS HAAKE MARS The modular advanced rheometer system Rotational testing (CR, CS, CD controlled) Oscillatory testing (CS, CD controlled) Normal force measurements Measuring viscous -elastic properties Solid sample testing Extended temperature range with Controlled Test Chamber (CTC) Torque: Speed (CR): Speed (CS): to 200 mnm to 4500 rpm (option high shear) to 1500 rpm Frequency range: to 100 Hz Multiwave: Hz Angular resolution: 12 nano rad Normal force: Motor: Temperature: 10 to ± mn (resolution 1 mn) low inertia drag cup -150 to 600 C 39 HAAKE CaBER 1 Capillary Breakup Extensional Rheometer Probe Lasermicrometer Apparent viscosity Mathematics Measurement D=f(t) Result: Appring extensional vicosity vs. Hencky-Strai Complex flow occurs in many industrial processes and applications. The performance of products depends on the knowledge of the extensional flow behaviour. Elongational behaviour can not be measured in rotational rheometers. 40

21 Summary - HAAKE Products (LI) Falling ball viscometer Falling ball viscometer Höppler C (ISO 12058) Rotational viscometer/ -rheometer Viscotester 1 plus & 2 plus Viscotester 6 & 7 plus acc. to ISO 2555 Viscotester 550 RotoVisco 1 RheoStress 1 RheoScope 1 RheoStress 600 MARS Series 1 RheoSizer RheoSoft RheoWin Extensional rheometer CaBER 1 CaBER Software 41 Questions? 42