# D445_11 (17a)

0 (0 Likes / 0 Dislikes)

Charge the viscometer in the
manner dictated by the design
of the instrument.
This operation being
in conformity with that
employed when the
instrument was calibrated.
If the sample is
thought or known
to contain fibers
or solid particles,
filter through a 75
unit of measure screen,
either prior to or
during charging.
See Specifications D446.
To minimize the potential
of particles passing
through the filter
from aggregating,
it is recommended
that the time lapse
between filtering and
charging be kept to a minimum.
In general, the viscometers
used for transparent liquids
are of the type
listed in table A 1.1
of the written
standard, A and B.
With certain products which
exhibit gel-like behavior,
exercise care that flow
time measurements are
made at sufficiently high
temperatures for such materials
to flow freely, so that
similar kinematic viscosity
results are obtained
in viscometers
of different
capillary diameters.
Allow the charged viscometer
to remain in the bath
long enough to reach
the test temperature.
Where one bath is
used to accommodate
several viscometers,
never add or withdraw,
or clean the viscometer, while
any other viscometer is in use
for measuring a flow time.
Because this time will vary
for different instruments,
for different temperatures,
and for different kinematic
viscosities, establish a safe
equilibrium time by trial.
30 minutes should be sufficient,
except for the highest
kinematic viscosities.
Where the design of the
viscometer requires it,
adjust the volume of
the sample to the mark
after the sample has reached
temperature equilibrium.
Use suction if the
sample contains
no volatile constituents or
pressure to adjust the head
level of the test sample to a
position in the capillary arm
of the instrument,
about 7 millimeters
above the first timing mark,
unless any other value is
stated in the
operating instructions
for the viscometer.
With the sample
flowing freely, measure
in seconds to within
0.1 second the time
required for the meniscus
to pass from the first
to the second timing mark.
If this flow time is less
than the specified minimum,
see 10.2 of the
written standard.
Select a viscometer with a
capillary of smaller diameter,
and repeat the operation.
Repeat the procedure described
in 11.2 of the written standard
to make a second
measurement of flow time.
Record both measurements.
From the two measurements
of flow time,
calculate two determined
values of kinematic viscosity.
Reference section
11.2.3 and 11.2.4
of the written standard for
information on determining
values of kinematic viscosity.
Verify that the calibration
constant for the viscometer
being used is appropriate
for the temperature at which
the measurement is being made.
Refer to the viscometer
calibration certificate
for more details.
In this particular case, the
viscometer tube calibration
constant, C, equals
0.01512 millimeters
squared per second squared.
Using the flow time
measurement from test number
1, 226.44 seconds, calculate
the kinematic viscosity
determination using
the following equation.
Nu equals 226.44 seconds times
0.01512 millimeters squared
per second squared equals 3.424
millimeters squared per second.
Calculate the second kinematic
viscosity determination
using the flow time
measurement from test number 2,
226.75 seconds.
Nu equals to 226.75 seconds
times 0.01512 millimeters
squared per second
squared equals
3.428 millimeters
squared per second.
Determine the difference between
the two kinematic viscosity
results.
Average kinematic viscosity
determination number 1 and 2.
Use the determine
ability calculation
for gas oils from
section 17.1.1.
0.0013 times y plus 1, where
y is the average of determined
values being compared.
0.0013 times 3.426 millimeters
squared per second plus 1
equals 0.005754 millimeters
squared per second.
Because the difference between
the two kinematic viscosity
determinations, 0.004, is less
than the calculated determined
ability, 0.005754,
the measurement
is considered to meet ASTM
D445 determined ability.
Therefore, report the
kinematic viscosity result
as the average of the
2 determined values,
3.426 millimeters squared
per second, rounded to 4
significant figures
as per section
15.1 of the written standard.