1、INTERNATIONAL STANDARD IS0 12644 First edition 1996-l 2-01 ANSI Intern W is the total weight of the rod and the weight loads; A is the apparent shearing area; g is the gravitational acceleration; in is the total mass; r is the radius of the rod; 1 is the length of the aperture. 2 The shearing length
2、 of the aperture of a falling rod viscometer usually contains both a tapered and a parallel section; therefore, it is understood that A is not the true shearing area but an apparent shearing area. 1 IS0 12644:1996(E) 0 IS0 2.3 shear rate, y: Velocity gradient through a stressed liquid in a direction
3、 perpendicular to the shearing area. Unit: s-1. NOTE - For the falling rod viscometer, yis inversely proportional to all fall time according to the equation y= L r. In (R/r) . f (3) where Y is the shear rate; L is the falling distance of the rod; r is the radius of the rod; R is the radius of the ap
4、erture; t is the fall time. If the ratio of the radii of the rod and aperture is close to unity, the term may be simplified to Y=$ (4) where s is the thickness of the ink in the nip determined by the difference between radii of the aperture and of the rod. 2.4 apparent viscosity, qa: Ratio of the sh
5、ear stress oto the shear rate yfor a given shear stress or shear rate. Unit: Pa. s. 2.5 Newtonian liquid: Liquid whose shear stress is proportional to shear rate. 2.6 non-Newtonian liquid: Liquid whose shear stress is not proportional to shear rate. NOTES 1 There are two types of non-Newtonian liqui
6、ds: With shear thickening liquids, the viscosity increases with shear rate; with shear thinning liquids, the viscosity decreases with shear rate. 2 If the viscosity of a liquid decreases with application of steady mechanical stress from a value at the state of rest to a final value and increases aga
7、in if the stress ceases, the liquid is called thixotropic. 2.7 flow curve: Graph of the shear stress oas a function of the shear rate yor vice versa. 2.8 Casson model (see A.l): Flow model which assumes a non-linear increase of shear stress owith increasing shear rate 7 A minimum stress 00 is requir
8、ed to initiate flow. 2.9 Bingham model (see A.2): Flow model which assumes a linear increase of the shear stress (3 with increasing shear rate y A minimum stress 00 is required to initiate flow. 2.10 Power Law model (see A.3): Flow model which assumes an increase of the shear stress CT of a liquid p
9、roportional to the Nth power of the shear rate y 2.11 yield stress, 00: Minimum stress required to initiate flow of a liquid. Unit: 1 Pa. 2.12 pseudo yield stress, CT,: Shear stress at a defined low shear rate when applying the Power Law model, typically to 2,5 s-1. 2 0 IS0 IS0 12644:1996(E) 2.13 re
10、ference temperature: Temperature (25 “C) for which all results are reported. Unit: “C. NOTE - Measurements made at temperatures different from this temperature are corrected (see 6.2.2) 2.14 test temperature: Actual temperature of the aperture ring during measurements. Unit: “C. 2.15 shortness ratio
11、: Ratio of yield stress or pseudo yield stress to the apparent viscosity. Unit: 1 s-1. 3 Test method 3.1 Principle The principle of this test is the measurement of the relative velocity between a vertical rod and an aperture ring. The bottom of the rod is inserted into the aperture. The gap is fille
12、d with the test fluid, which is sheared when the rod falls. By loading the rod with different load weights, different shear rates are obtained. By applying linear regression methods to the measured fall times as a function of load weight, the viscosity and the yield stress can be calculated. 3.2 App
13、aratus 3.2.1 Falling rod viscometer The viscometer consists of - a cylindrical rod (figure 1) made from metal or any other hard material. In order to obtain comparable values for shear stress and resulting shear rate the mass of the steel rod should be (I 32 * I) g. - a metal ring (figure 2) with a
14、defined cylindrical or conical aperture. The ring is fixed on a support and should be temperature controlled. Since the diameter of rod and aperture are critical they are manufactured within low tolerances. These dimensions shall be supplied by the manufacturer. To minimize possible gap differences,
15、 only matching sets of rod and aperture ring shall be used. - load weights to be loaded on top of the rod. Series of load weights are combined to sets. Sets of load weights with the following masses should be used: A: 5 000, 4 000, 3 000, 2 000, 1000 B: 3 000, 2 000, 1 500, 500 c: 1 500, 1 000, 800,
16、 500 D: 800, 600, 400, 200 E: 400, 300, 200, 100 F: 200, 100, 50, 0 The tolerance for the masses of load weights shall be f 0,2 g; - a designated measuring distance marked on the strut. The tolerance shall be I!I 0,2 mm. Sensors may be placed at the marks. - a levelling device. - a timing device. Th
17、e tolerance shall be + 0,l s (should be + 0,Ol s) 3 IS0 12644:1996(E) Ring Aperture Rod Support Measuring distance, upper mark Measuring distance, lower mark Weight Water jacket 9 Level 10 Horizontally adjusting screw 11 Strut r Radius of the rod R Radius of the aperture 1 Length of the aperture L M
18、easuring distance Figure 1 - Falling rod viscometer 4 IS0 12644:1996(E) Figure 2 -Aperture ring 3.2.2 Temperature control Means shall be provided for measurement and control of the test temperature. 3.2.3 Others Non-scratching spatulas. Standard viscosity oils (at least 2) for calibration. NOTE - Th
19、e viscosity of the standard viscosity oils shall be in the same range as that of the test samples. The viscosity of these oils shall be traceable to a standards institution. An internal standard may be used for comparative studies only. 3.3 Ambient temperature control The test shall be carried out u
20、nder controlled ambient temperature. This can be achieved either by placing the viscometer in a thermostatically controlled cabinet or by working under constant room temperature. If working in a cabinet, the inner temperature should not vary from the test temperature by more than is the shear stress
21、; is the shear rate; is the mass; is the gravitational acceleration; is the radius of the rod; is the length of the aperture; is the thickness of the ink in the nip; is the fall time; is the measuring distance. (5) 6 0 is0 IS0 12644:1996(E) Fixed parameters and constants are combined as device facto
22、rs a and p and p=L 2rcrl The unit of a is 1 and the unit of /I is Pa/kg. Since the shear rate (6) . . . (7) . . . (8) and shear stress o=IJm . (9) the viscosity of a Newtonian fluid can be calculated from the slope of a plot of yversus ofor different masses. The measured viscosity is the reciprocal
23、slope of the linear regression line. If a certain set of rod and aperture ring shows viscosity variations of 20 % from the specifications of the standard viscosity oil it shall be discarded. Smaller differences are compensated by using a correction factor 0: = qtrue / qmeasured . (I 0) The correctio
24、n factor di is specific for a single set of rod and aperture. It is recommended that a calibrated set of aperture and rod be kept as an internal standard. 4.2 Calibration for the Power Law model For determination of the device factor /I (stress constant) defined in equation (7) it is necessary to me
25、asure the radius r of the rod and the length 1 of the aperture. Both dimensions shall be measured to 0,Ol mm. Given these data the device factor p is calculated according to equation (7). The value of the device factor a defined in equation (6) shall be computed from fall time runs of the standard v
26、iscosity oils. For that purpose, measurements shall be taken with at least two such oils, covering the viscosity range of interest, and at least four fall times. The known viscosity of the oils is divided by the fall time t for each weight load with the mass m and this quotient is plotted versus the
27、 mass for each standard viscosity oil. According to equation (1 I), the slope of the regression line is the quotient p/a of the two device factors. qstd = p m t a . (11) where qstd is the viscosity of the standard viscosity oil; t is the fall time; m is the mass of the weight load. Having calculated
28、 /3 from the geometric dimensions of rod and aperture according to the above method, a can easily be calculated. With the device factors a and p determined, values for the shear rate yand shear stress o can be calculated from the fall time t and the mass m used as shown in equations (8) and (9). 7 I
29、S0 12644:1996(E) 5 Calculation 5.1 Calculation for Casson and Bingham models (see A.1 and A.2) Calculation for Casson and Bingham models requires: - at least 4 fall times as a function of different mass of the weight loads; - the device factors cx, j3; - the correction factor 0; - the test temperatu
30、re at the beginning and the end of the test. Equations (8) and (9) together with the device factors a! and fi are used to calculate yand ovalues. For the Casson model, the linear regression of dyas a function of 40 leads to 77 as described in A.I. For the Bingham model the linear regression of yas a
31、 function of CT leads to 17 as described in A.2. The correlation coefficient should be calculated as a measure of the repeatability of the test. For correlation coefficient values of 0,999 or better the results are reliable. In case of lower correlations the test shall be repeated. 5.2 Calculation f
32、or Power Law model (see A.31 Calculation for Power Law model requires: - at least four fall times as a function of different mass of the weight loads; - the device factors a and p; - the test temperature at the beginning and end of the test. Equations (8) and (9) are used together with the device fa
33、ctors a and j3 to calculate y and D values. A linear regression of these values plotted double logarithmically according to equation (18) in A.3 is used to determine k and N. These values are used with equation (18) in A.3 to calculate apparent viscosity (772scc), the pseudo yield stress (02,s), and
34、 optionally, the shortness ratio. Correlation coefficients for the regression line shall be 0,999 or better for reliable results. Temperature corrections may be applied as described in 6.2. 6 Corrections 6.1 Corrections for Casson and Bingham models 6.1.1 Viscosity corrections According to the calib
35、ration procedure, the viscosity is corrected by 17 = qmeasured CD (12) (see 4.1). 6.1.2 Temperature corrections Viscosity is strongly temperature dependent. Therefore the temperature shall be checked before and after the test. The test temperature is defined to be the arithmetical average of these v
36、alues. Principally, if the test temperature varies from reference temperature (25 “C) by more than 0,2 “C before the runs the thermostatic equipment shall be reset. If the temperature during the test varies more than 1 “C, the test shall be repeated. If the variation is less, the following equation is used to correct the fall time to the reference temperature of 25 “C: rEtmeasured I+ 6 (,-25) (13) 8
