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ACAV A2 |
| The
importance of measuring the full Range of Shear
Rates
The main reason is that the viscosity is composed
of different factors in different shear rates.
Totally different factors formulate the viscosity
in low and in high shear rates. Dominating factors
in low shears (pumping and piping) have minor
or no influence in ultra high shear (coating).
Coating colors are rheologically
complex materials:
- Their viscosity is strongly dependent on shear
rate
- Viscosity is dependent on shearing time
- They are viscoelastic
- They may have significant extensional viscosity
and/or normal stresses
Two major groups of factors define the rheology
of coating colors: Surface chemistry in low shear
rates and hydrodynamics in high shear rates.
Significance of different factors depends on shear
rate. Therefore it is not usually possible to
draw conclusion about high shear rheology by measuring
low shear area, or vice versa.
» ACAV
graphs reveal underlying runnability problems
(pdf)
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| © 2002
ACA Systems Ltd. - www.aca.fi |
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