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Appendix C
VISCOMETER RELATED VARIABLES
• Most fluid viscosities are found to be non-Newtonian. They are dependent
on Shear Rate and the spindle geometry conditions. The specifications of the
Viscometer cone and plate geometry will affect the viscosity readings. If one
reading is taken at 400 rpm, and a second at 1,000 rpm, the two viscosity values
produced may be different because the readings were made at different shear
rates. The faster the spindle speed, the higher the shear rate.
• The shear rate of a given measurement is determined by the rotational speed
and the cone angle.
• A repeatable viscosity test should control or specify the following:
1. Viscometer model
2. Cone used
3. Test temperature
4. Test speed(s) [or the shear rate(s)]
5. Length of time to record viscosity
6. Sample volume sufficient to cover the face of the cone