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4.3 Selecting a spindle/speed
The DVNext has the capability of measuring viscosity over an
extremely wide range. For example, the DVNext RV can measure
fluids within the range of 100-40,000,000 cP. This range is achieved
by using 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. There are two general rules that will help in the trial and error
process:
•
Viscosity range is inversely proportional to the size of the
spindle.
•
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. DVNext LV Rheometers are
provided with a set of four spindles and a narrow guard leg; DVNext
RV Rheometers come with a set of six spindles and a wider guard
leg; DVNext HA and DVNext HB Rheometers come with a set of six
spindles and no guard leg. (See Appendix G for more information on
the guard leg.)
The spindles are attached to the rheometer by screwing them onto the coupling nut on the lower shaft (see Figure
3-4). Note that the spindles have a left-hand thread. The lower shaft should be secured and slightly lifted with one
hand while screwing the spindle to the left. The face of the spindle nut and the matching surface on the lower shaft
should be smooth and clean to prevent eccentric rotation of the spindle. Spindles can be identified by the number on
the side of the spindle coupling nut.
The motor should be OFF whenever spindles are being removed or attached.
Note: Keep the Magnetic Coupling and inner sleeve as clean as possible and free from debris that could become
lodged inside the adapter.
M19-2101 REVISION 2.0
D V N E X T R H E O M E T E R - O P E R AT I O N A L M A N U A L
Figure 4-1
Figure 4-2
52
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