Brookfield BF35 - Manual (Page 10)

Brookfield Engineering Labs., Inc. Page 10 Manual No. M13-10000
Shear Stress Conversions
To convert from units on left side to units on top, multiply by factor @ intercept
Dyne/cm 2 Pa lb/100ft 2 lb/ft 2 DR
Dyne/cm 2 1 0.1 0.2084 0.002084 0.1957
Pa 10 1 2.084 0.02084 1.957
lb/100ft 2 4.788 0.4788 1 0.01 0.939
lb/ft 2 478.8 47.88 100 1 93.9
DR 5.107 0.5107 1.065 0.01065 1
What Bob and Spring Should I Use?
There is often confusion or misunderstanding about what a viscometer can actually measure. For
example, a viscometer with an R1B1 F1 combination can measure water fairly well at 100 RPM
and higher, but at 3 RPM, the readings would be shaky at best. While on the other hand, a linear
fluid with a viscosity of 15000, could not get past 6 RPM with the same combination.
To estimate which spring might be best, use the formula below to calculate a Minimum Spring
factor, where one establishes the maximum RPM the fluid is going to be tested at, as well as what
the expected “Apparent Viscosity” of the fluid at that RPM. If the Factor comes out as .87, then an
F 1.0 spring should be used. If it comes out as .16, then an F 0.2 spring would be best. To cover all
ranges, it may be necessary to use more than one spring.
Minimum Spring Factor (F) =
RPM(max) * AV(max)
BOB(F)*90000
Bob (F)
R1B1
1
R1B2 8.9
R1B3 25.4
R1B4 50.7