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ICI Rotothinner
The Rotothinner, originally developed by ICI Paints, is
driven by a constant-speed motor and utilizes a large, diskshaped
rotor which is immersed in the sample under test. A
standard sample container is used, which is held magnetically
to a turntable. The torque transmitted through the sample
rotates the turntable until a steady position is reached.
(The rotary motion is resisted by a spring.) The turntable is
graduated in poise units, and the viscosity is indicated by a
pointer attached to the instrument base. The viscosity range
of a given model is somewhat narrow, and measurement over
a wide viscosity range necessitates purchase of separate instruments.
The instrument is calibrated for use only with
standard containers. There is no provision for temperature
control of the specimen. For "rheologically structured" materials,
the manufacturer recommends to allow up to 4 min
under shear for the reading to become steady, thus providing
for a more or less constant shear history. However, temperature
may vary during this period due to the input of energy
resulting from the 575-rpm rotor speed.
Although the instrument has a scale graduated in poise
units, the shear rate of test is unknown since the flow field is
not viscometric. Flow in the vicinity of a rotating disk can be
quite complex, especially for non-Newtonian and viscoelastic
materials. Consequently, the apparent Rotothinner viscosity
must be considered only approximate and the scale graduations
arbitrary for such materials.
The Rotothinner is manufactured by Sheen Instruments,
Ltd. and is widely used in Europe. |
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