Temperature - Gardco EZ ZAHN Dip Viscosity Cup Series Instruction Manual

VISCOSITY
Most materials change in viscosity as a function of temperature. Those normally measured with
viscosity cups change in the range of 3% to 8% per degree Celsius change in temperature. Usually,
the higher the viscosity the greater the change. For acceptable accuracy it is necessary to measure
temperature at the same time that viscosity cup readings are taken. When many determinations are
to be made on similar products in the same viscosity range, it may be helpful to produce a graph for
converting measured temperature and viscosity cup effl ux time in seconds to seconds at a specifi ed
temperature, normally 25° Celsius.
E
F
F
L
U
X
There are three variables to consider: viscosity, effl ux time and temperature. All three can be shown
on a graph with a family of curves as shown in the following example. Viscosity level is indicated by the
diagonal lines, increasing from the lower right to the upper left. Such a graph can be prepared for a
given material by taking readings with the EZ™ cup over a limited temperature range as shown in the
example. Within this limited range the plots of the obtained data will normally result in a straight line
such as the heavy diagonal line. Draw parallel lines as shown which represent different viscosity levels.
Enter on the graph the material represented and the EZ™ designation with cup number.
Use the prepared graph by plotting on it measured temperature and effl ux time in seconds. At "A"
in the example these values are 26.0°C and 39.5 seconds. Read parallel to the diagonal lines to the
intersection with the heavy vertical line which is 25.0°C, the target temperature. Reading horizontally
to the left it is found that the corrected effl ux time in seconds at 25°C is 41.5 seconds. Similarly, at "B"
in the example, it is found that a reading taken at 23.5°C, when corrected to 25.0°C changes from 40.5
to 37.5 seconds.
Compensating for a measured temperature near to, but not as specifi ed, must be with caution. Even
within the limited range of ±2.0°C the variation of the viscosity with temperature may not be truly linear
and any thinning materials used to adjust viscosity may also change the rate of this variation.
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Paul N. Gardner • www.gardco.com • (954) 946-9454

TEMPERATURE