When spray finishing, viscosity measurements will help you understand
the size of needle and nozzle required
to effectively atomize your finish. By
recording these measurements, you
can duplicate your material “recipe” to
ensure consistency in production.
To save you from dusting off your
high school chemistry book, listed be-
low is some information about viscosity
in relation to spray finishing:
What is viscosity?
Viscosity is the measurement of a
fluid’s resistance to flow. Typically, vis-
cosity is measured in centipoise which
is one hundredth of a poise.
How do I measure viscosity?
To measure the viscosity of your finish,
you will require (a) your desired finish,
(b) a viscosity cup and (c) a stopwatch.
The most common viscosity cup sizes
are the #4 Ford or the #2 Zahn.
Viscosity is measured by submerging the viscosity cup into the finish
then removing it to see the amount of
time your finish takes to pass through
the orifice at the bottom of the viscosity cup. Start your timer the moment
you begin lifting the cup out of the
finish. Once the cup drains completely
or you notice a break in the stream,
stop your timer. The amount of time
elapsed is called your run- out time.
What does it all mean?
Most manufacturers of spray finishing equipment will include a viscosity index in their manual for you to
compare your run-out time with the
recommended run-out time as per the
coating or equipment manufacturer.
By referencing this index, you will be
able to confidently choose the needle
and nozzle size best suited for spraying
Source: Jim Larin is director of sales at Fuji
Spray. For information call 800-650-0930 or
Spray finishing: Understanding & measuring viscosity
By Jim Larin
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