Seminar Basics on Rheology. Common sources of errors in viscosity measurements

Transcription

1 The world leader in serving science Seminar Basics on Rheology Common sources of errors in viscosity measurements

2 Overview Reasons for measuring errors - Instrument related - Handling related - Sample related 2

3 Source of trouble Reasons Instrument Handling Sample Torque measurement r.p.m. measurement Geometry factors (A, M) Geometry Choice of sensor Test definition Sample history Sample loading Particles, trapped air Solvent loss Chemical reaction Swelling / shrinking Gap setting Temperature control Zero point Friction heat Slipping Elasticity Taylor vorticis Sedimentation 3

4 Error sources DIN Viscosity = Geometry * M d /n Geometry +/- 0.5 % ABS - Tolerance of the dimensions (diameter, radius, length, angle) - Tolerance of positioning (excentricity, inclination, distances) Revolutions n +/- 0.5% ABS - the speed is very accurately recorded with digital encoders (+/-1bit) - speed is very constant and accurate with stepper motors - tachometer generators are less accurate -Torque M+/- 1% FSD or +/-0.5 % ABS - +/- 1% for traditional instruments and +/- 0.5% for modern rheometer - Full Scale Deflection leads to greater tolerance range 4

5 Viscosity (mpas) Measuring uncertainty ( error trumpet ) Mess-Unsicherheit der Viskosität 560,0 RS C3 5 /2 RV 1 C3 5 /2 S oll- V isosity mp a s +/- 5 % Error 540,0 520,0 500,0 480,0 460,0 440,0 420,0 RS 300 with C35/2 RV 1 with C35/2 400,0 1,E-01 1,E+00 1,E+01 1,E+02 1,E+03 1,E+04 ThermoHaake Shear rate (1/s) 5

6 Air bearing friction Air bearing friction is proportional to: rotational speed viscosity of air Remedy: friction correction Measuring gap Rotating bearing shaft Air Thin liquids and low shear 6

7 Position-dependent torque The torque value is dependent on: excentricity of the rotating shaft tolerance of the bearing housing Remedy: Micro Stress Control Thin liquids und Low Shear 7

8 Torsion of the shaft If samples are very rigid and a high torque is applied there is a torsion shaft to be observed Remedy: compensation of the torsion Torque Shaft 8

9 [Pa] Inertia correction I_on_2 = f (Á) I_off_2m = f (Á) 25 Flow curve Without inertia correction 10 5 With inertia correction Á [1/s] 9

10 Source of trouble Reasons Instrument Handling Sample Torque measurement r.p.m. measurement Geometry factors (A, M) Geometry Selected geometry Test definition Sample history Sample loading Particles, trapped air Solvent loss Chemical reaction Swelling / shrinking Gap setting Temperature control Zero point Friction heating Slipping Elasticity Taylor vorticis Sedimentation 10

11 Handling Selection of measuring geometry Consideration of - Measuring range - Sample properties Type [-] - factor - factor [Pa/Nm] Min. Viscosity [mpas] Max. Viscosity [mpas] DG Z40DIN Z20DIN DC60/ C35/ PP PP Z43DIN/E HS

12 Shear stress (Pa) Viscosity (mpas) Handling Selection of measuring geometry Measuring range in comparison with RS1&PP20+ RS1&PP60 RS1 ThermoHaake Rheometer Measuring Range RS1 1,0E+12 1,E+12 PP20 PP60 1,0E+10 1,E+10 PP20 PP60 RS1 1,0E+08 1,E+08 RS1 PP20 PP A A 10 M 1,0E+06 1,E M Gp (1/s) Gp (1/s) 1,0E+04 1,E+04 Eta (mpas) 1,0E+02 1,E+02 Eta (mpas) Tau (Pa) 1,0E+00 1,E+00 Tau (Pa) 1,0E-02 1,E-02 1,0E-04 1,E-04 1,E-04 1,E-03 1,E-02 1,E-01 1,E+00 1,E+01 1,E+02 1,E+03 1,E+04 Shear rate (1/s) 12

13 Viscosity Error / Viskositätsfehler (%) Handling Gap Setting and Error Cone & Plate Gap Error / Platte-Kegel Abstandsfehler 4,5% 4,0% 3,5% A Winkel 1,0 Radius 30,0mm B Winkel 2,0 Radius 30,0mm C Winkel 4,0 Radius 30,0mm 1 3,0% 2,5% 2,0% 2 1,5% 1,0% 0,5% 0,0% Gap error / Abstandsfehler (microns) 4 Cone angle 13

14 Viscosity error / Viskositätsfehler (%) Handling Sample Loading and Error Reduced effective Radius / Einschnürungsfehler 40,0% 35,0% 30,0% A Winkel 1,0 Radius 10,0mm B Winkel 2,0 Radius 17,5mm C Winkel 4,0 Radius 30,0mm 20 mm 25,0% 20,0% 15,0% 35 mm 60 mm 10,0% 5,0% 0,0% 0 0,5 1 1,5 2 Reduced effective radius / Einschnürung (mm) 14

15 [Pas] [Pa] Handling Lost of gap filling 80 Flow- and Viscosity curve CR-Modus [1/s]

16 Handling Lost of gap filling Measurements on viscoelastic materials: measuring geometry plate / plate 35mm with different gaps ( mm) 16

17 [Pa] T [ C] ƒ [Pas] Friction heating Fr-heat1 = f (Á) ƒ = f (Á) T = f (Á) 3000 Flow and viscosty curve Viscosity Shear stress Temperature Á [1/s] 17

18 Source of trouble Reasons Instrument Handling Sample Torque measurement r.p.m. measurement Geometrya factors (A,M) Geometry Selected geometry Test definition Sample history Sample loading Particles, trapped air Solvent loss Chemical reaction Swelling / shrinking Gap setting Temperature control Zero point Friction heating Slipping Elasticity Taylor vorticis Sedimentation 18

19 Shear Stress Slippage CS/CR-Measurement Shear Rate 19

20 [Pa s] Taylor vortex Taylor1. = f ( ) [1/s] 20

21 Loss of solvent 21

22 Any questions? Thank you for your attention 22