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1. Basics of viscosity
Rheology is the study of the flow and deformation of materials. Two hundred
years ago all materials then known could be classed as either Newtonian
liquids or Hookean solids. These days almost all materials of commercial
or industrial importance are known to exhibit the characteristics of both,
that is, under some conditions they behave as solids and under other conditions
they behave as liquids. The development of instrumentation to measure
material properties has paralleled our understanding of their molecular
properties. Thus from the use of U tube viscometers to measure the viscosity
of Newtonian liquids we now use viscometers that routinely measure viscosity
as a function of shear rate together with rheometers that can characterize
the solid-like properties of the same material. Grace Instrument Company
is committed to providing a range of state of the arts instrumentation
that meets the needs of today's research or field engineer.
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2. Coaxial Cylinder Viscometers
Grace Instrument Company produces a range of Couette coaxial cylinder rotational viscometers.
The test fluid is contained in the annular space or shear gap between
the cylinders. Rotation of the outer cylinder at known velocities is accomplished
through precision gearing. The viscous drag exerted by the fluid creates
a torque on the inner cylinder or bob. This torque is transmitted to a
precision spring where its deflection is measured. Viscosity is calculated
from shear rate, deflection and instrument constants.
The Grace Instrument Company viscometers range from 60,000 different speeds
to 1,000,000 speeds models to variable-speed, high- temperature, and high-pressure
models.
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