Brookfield DV-III Rheometer - Manual (Page 20)

Brookfield Engineering Laboratories, Inc. Page 20 Manual No. M/98-211-A0701
III.3 Selecting a Spindle/Speed
The DV-III+ has the capability of measuring viscosity over an extremely wide range (for
example, the RVDV-III+ can measure fluids within the range of 100-40,000,000 cP) (see
Appendix B). This range is achieved through the use of several spindles over many speeds.
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 changing if the spindle and/
or speed is changed. See our publication, "More Solutions to Sticky Problems," for more detail.
When viscosity data must be compared, be sure to use the same spindle, speed, container
and temperature.
III.4 Multiple Data Points
The majority of viscosity measurements are made at the quality control level and 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-III+ can be used for
single point measurement.
Many fluids exhibit a characteristic change in viscosity 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. This behavior cannot be detected or evaluated with
the single viscosity 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 formulating and
production of the product. The DV-III+ is capable of collecting multiple data points for the
analysis of flow behavior. See Section IV on Programming and Analysis.
More information on flow behavior, shear rate and rheograms is available in our publication,
"More Solutions to Sticky Problems."
III.5 Cleaning
All immersed components are stainless steel. Use cleaning solutions that are not corrosive and
avoid scratching the measurement surfaces. The instrument housing should be cleaned with a
soft damp cloth.