
Model 35 Viscometer Instruction Manual
208878
Revision N, February 2013
29
Table 7-1 Rotor-Bob Factor (C)
Table 7-2 Speed Factor (S)
Rotor-Bob
Combination
R-B Factor
(C)
Rotor
(rpm)
Speed Factor
(S)
R1-B1
1.000
0.9
333.3
R1-B2
8.915
1.8
166.6
R1-B3
25.392
3
100
R1-B4
50.787
6
50
R2-B1
0.315
30
10
R2-B2
8.229
60
5
R2-B3
24.707
90
3.33
R2-B4
49.412
100
3
R3-B1
4.517
180
1.667
R3-B2
12.431
200
1.5
R3-B3
28.909
300
1.0
R3-B4
57.815
600
0.5
7.2
Plastic Viscosity and Yield Point Calculation
Using R1-B1-F1 combination, test a sample at 600 rpm and record the dial reading.
Change the speed to 300 rpm and record the dial reading.
Determine the plastic viscosity (PV) and yield point (YP) using the following
equations. PV represents the slope of a straight line between the two dial readings.
YP represents the theoretical point at which the straight line, when projected, will
intercept the vertical axis.
PV (cP) =
θ
600
–
θ
300
Equation 7-2
YP (lb/100 ft
2
) =
θ
300
– PV
Equation 7-3
where
θ
is the dial reading
A spring other than F1 may be used if the dial readings are
multiplied by the proper “f” factor, but the other rotor-bob
combinations cannot be used for this two-point method.