Brookfield DV2+Pro Viscometer - Manual (Page 25)

Brookfield Engineering Labs., Inc. Page 25 Manual No. M03-165-F0612
Please see our publication, “More Solutions to Sticky Problems”, for more detail relating to
sample preparation.
III.3 Selecting a Spindle/Speed
The DV-II+Pro has the capability of measuring viscosity over an extremely wide range. For
example, the RVDV-II+Pro can measure fluids within the range of 100-40,000,000 cP. This
range is achieved through the use of several spindles over many speeds. See Appendix B for
details.
The process of selecting a spindle and speed for an unknown fluid is normally trial and error. An
appropriate selection will result in measurements made between 10-100 on the instrument
% torque scale. Two general rules will help in the trial and error process.
1) Viscosity range is inversely proportional to the size of the spindle.
2) Viscosity range is inversely proportional to the rotational speed.
In other words: to measure high viscosity, choose a small spindle and/or a slow speed. If the
chosen spindle/speed results in a reading above 100%, then reduce the speed or choose a smaller
spindle.
Experimentation may reveal that several spindle/speed combinations will produce satisfactory
results between 10-100%. When this circumstance occurs, any of the spindles may be selected.
Non-Newtonian fluid behavior can result in the measured viscosity and yield stress changing if
the spindle and/or speed is changed. See our publication, “More Solutions to Sticky Problems,”
for more details.
When viscosity data must be compared, be sure to use the same test methodology: namely
the same instrument, spindle, speed, container, temperature and test time.
III.4 Multiple Data Points
The majority of viscosity and yield stress measurements are made at the quality control level
and often consist of a single data point. The test is conducted with one spindle at one speed.
The data point is a useful bench mark for the go/no-go decision in a production setting. The
DV-II+Pro can be used for single point measurement.
Many fluids exhibit a characteristic change in viscosity and yield stress with a change in applied
force. This non-Newtonian flow behavior is commonly seen in paints, coatings and food products
as a decrease in viscosity as shear rate increases or an increase in yield stress as a rotational speed
increases. This behavior cannot be detected or evaluated with the single point measurement.
Non-Newtonian flow is analyzed through the collection of viscosity data over a range of shear
rates and the generation of a graph of viscosity versus shear rate (a rheogram). This information
will allow for a more complete characterization of a fluid and may help in formulation and
production of a product. The DV-II+Pro is capable of collecting multiple data points for
comprehensive analysis of flow behavior.
More information on flow behavior, shear rate and rheograms is available in our publication,
“More Solutions to Sticky Problems.”