VISCOSITY
ASTM D 88, D 445, Redwood, and Engler
Viscosity is probably the most significant phys-
ical property of a petroleum lubricating oil. It is
the measure of the oil's flow characteristics. The
thicker the oil, the higher its viscosity, and the
greater its resistance to flow. The mechanics of
establishing a proper lubricating film depend
largely upon viscosity.
ical property of a petroleum lubricating oil. It is
the measure of the oil's flow characteristics. The
thicker the oil, the higher its viscosity, and the
greater its resistance to flow. The mechanics of
establishing a proper lubricating film depend
largely upon viscosity.
To evaluate the viscosity of an oil numerically,
any of several standard tests may be applied.
Though these tests differ to a greater or lesser
extent in detail, they are essentially the same in
principle. They all measure the time required for
a specified quantity of oil at a specified temper-
ature to flow by gravity through an orifice or
constriction of specified dimensions. The thicker
the oil, the longer the time required for its
passage.
any of several standard tests may be applied.
Though these tests differ to a greater or lesser
extent in detail, they are essentially the same in
principle. They all measure the time required for
a specified quantity of oil at a specified temper-
ature to flow by gravity through an orifice or
constriction of specified dimensions. The thicker
the oil, the longer the time required for its
passage.
Close control of oil temperature is important.
The viscosity of ally petroleum oil increases
when the oil is cooled and diminishes when it is
heated. For this same reason, the viscosity
value of an oil must always be accompanied by
the temperature at which the viscosity was de-
termined. The viscosity value by itself Is
meaningless.
The viscosity of ally petroleum oil increases
when the oil is cooled and diminishes when it is
heated. For this same reason, the viscosity
value of an oil must always be accompanied by
the temperature at which the viscosity was de-
termined. The viscosity value by itself Is
meaningless.
The two commonest methods of testing the
viscosity of a lubricating oil are the Saybolt and
the kinematic. Of these, the Saybolt (ASTM D
88) is the method more frequently encountered
in conjunction with lubricating oils. However, the
kinematic method (ASTM D 445) is generally
considered to be more precise. There are also
the Redwood and the Engler methods, which are
widely used in Europe, but only to a limited
extent in the United States. Each test method
requires its own apparatus--viscosimeter (or
viscometer).
viscosity of a lubricating oil are the Saybolt and
the kinematic. Of these, the Saybolt (ASTM D
88) is the method more frequently encountered
in conjunction with lubricating oils. However, the
kinematic method (ASTM D 445) is generally
considered to be more precise. There are also
the Redwood and the Engler methods, which are
widely used in Europe, but only to a limited
extent in the United States. Each test method
requires its own apparatus--viscosimeter (or
viscometer).
Apparatus: The Saybolt Universal viscosimeter
is used for oils of low and intermediate viscosity.
It consists of a cylindrical container for the oil
sample with a receiving flask under it to catch
is used for oils of low and intermediate viscosity.
It consists of a cylindrical container for the oil
sample with a receiving flask under it to catch
and measure oil discharged from the container.
At the bottom of the container is an orifice of
specified dimensions through which the oil
flows. Flow of oil is stopped and started with a
cork.
At the bottom of the container is an orifice of
specified dimensions through which the oil
flows. Flow of oil is stopped and started with a
cork.
The oil container is jacketed with a water bath to
facilitate maintenance of a constant oil tem-
perature. Temperatures are checked by two
thermometers, one in the oil and one in the
water bath. To adjust the temperature, an ex-
ternal source of heat is applied to the bath. Flow
of oil into the receiver is timed with a stop watch
or equivalent device.
facilitate maintenance of a constant oil tem-
perature. Temperatures are checked by two
thermometers, one in the oil and one in the
water bath. To adjust the temperature, an ex-
ternal source of heat is applied to the bath. Flow
of oil into the receiver is timed with a stop watch
or equivalent device.
For very viscous oils, the Saybolt Furol
viscosimeter is used. This apparatus differs from
the Saybolt Universal viscosimeter only in that
it has a larger orifice. For heavy oils, the larger
orifice helps confine the testing time to a
reasonable length.
viscosimeter is used. This apparatus differs from
the Saybolt Universal viscosimeter only in that
it has a larger orifice. For heavy oils, the larger
orifice helps confine the testing time to a
reasonable length.
The kinematic viscosimeter performs very much
the same function as the Saybolt viscosimeter,
but its construction is quite different. Kinematic
viscosity is usually determined by the
Ubbelohde instrument, a sort of glass U-tube in
which certain necessary bulbs and constructions
have been incorporated. Each tube is rated
according to velocity at which water passes
through it, and there are different classes of
tubes for different ranges of oil viscosity.
the same function as the Saybolt viscosimeter,
but its construction is quite different. Kinematic
viscosity is usually determined by the
Ubbelohde instrument, a sort of glass U-tube in
which certain necessary bulbs and constructions
have been incorporated. Each tube is rated
according to velocity at which water passes
through it, and there are different classes of
tubes for different ranges of oil viscosity.
The Redwood apparatus and the Engler
apparatus are of the same general type as the
Saybolt.
apparatus are of the same general type as the
Saybolt.
Procedures:
(a) Saybolt Method--With the oil at test temper-
ature, usually 100° F or 210° F, the cork is
removed from the oil container, allowing oil to
flow into the receiving flask. The time required
to fill the flask to the 60-cc graduation mark is
observed.
(a) Saybolt Method--With the oil at test temper-
ature, usually 100° F or 210° F, the cork is
removed from the oil container, allowing oil to
flow into the receiving flask. The time required
to fill the flask to the 60-cc graduation mark is
observed.
(FIST 2-4 11/90)
A-18