5.
GREASE LUBRICATION
Lubricating grease is a mixture of a lubricating
fluid, a thickening agent, and usually, perfor-
mance enhancing additives. Petroleum oils
mixed with a soap thickening agent make up the
majority of the grease in use today. The soaps
are formed by the reaction of animal or vegeta-
ble fats or fatty acids with strong alkalies such
as calcium or sodium. Non soap thickening
agents, such as modified clays and polyureas,
are also used in some instances. Synthetic oils
are used in severe conditions or when a normal
petroleum oil is not adequate.
fluid, a thickening agent, and usually, perfor-
mance enhancing additives. Petroleum oils
mixed with a soap thickening agent make up the
majority of the grease in use today. The soaps
are formed by the reaction of animal or vegeta-
ble fats or fatty acids with strong alkalies such
as calcium or sodium. Non soap thickening
agents, such as modified clays and polyureas,
are also used in some instances. Synthetic oils
are used in severe conditions or when a normal
petroleum oil is not adequate.
of the common grease thickener types and their
usual properties. Some of the ratings listed In
this table are subjective and can vary greatly
depending on the manufacturer.
usual properties. Some of the ratings listed In
this table are subjective and can vary greatly
depending on the manufacturer.
The lubricating fluid, which is usually petroleum
oil, Is the main Ingredient of all greases, making
up 85 to 95 percent of the final product. While
thickening agents impart some important char-
acteristics to a grease, the oil and its additives,
perform the actual lubrication. Since the base oil
is the most important component of the grease,
many of its characteristics, such as viscosity and
pour point, influence the performance of the
grease.
oil, Is the main Ingredient of all greases, making
up 85 to 95 percent of the final product. While
thickening agents impart some important char-
acteristics to a grease, the oil and its additives,
perform the actual lubrication. Since the base oil
is the most important component of the grease,
many of its characteristics, such as viscosity and
pour point, influence the performance of the
grease.
As moving parts come in contact with the
grease, oil "bleeds" from the grease to provide
either fluid film or boundary lubrication. The oil
picked by the moving parts, will be lost due
evaporation or leakage so the grease must con-
tinually "bleed" to provide sufficient lubrication.
Eventually the grease must be replenished or
replaced
grease, oil "bleeds" from the grease to provide
either fluid film or boundary lubrication. The oil
picked by the moving parts, will be lost due
evaporation or leakage so the grease must con-
tinually "bleed" to provide sufficient lubrication.
Eventually the grease must be replenished or
replaced
Grease is used when it is not practical or con-
venient to use oil. In applications where sealing
against leakage would be difficult or where the
bearing is submerged in water, grease works
very well. Grease also has the advantages of
requiring less frequent relubrication or replen-
ishment intervals than many oil lubricated
systems and can more readily seal out dust and
dirt.
venient to use oil. In applications where sealing
against leakage would be difficult or where the
bearing is submerged in water, grease works
very well. Grease also has the advantages of
requiring less frequent relubrication or replen-
ishment intervals than many oil lubricated
systems and can more readily seal out dust and
dirt.
5.1 Grease Characteristics
Consistency. A grease's consistency, or hard-
ness, is a measure of its resistance to
deformation by an applied force and Is in most
cases, a grease's most important characteristic.
A grease's consistency is dependent on its base
oil's viscosity and the type and amount of thick-
ening agent used. Consistency is measured in
terms of the depth, in tenths of a millimeter, that
a standard cone will sink into a grease under
prescribed conditions and is referred to as the
penetration number. The National Lubricating
Grease Institute (NGLI) has established consis-
tency numbers, or grades, ranging from 000
(soft) to 6 (hard), corresponding to specified
ranges of penetration numbers. This rating sys-
tem covers most greases but there are greases
available that are softer than a NGLI No. 000 or
harder than a No. 6.
ness, is a measure of its resistance to
deformation by an applied force and Is in most
cases, a grease's most important characteristic.
A grease's consistency is dependent on its base
oil's viscosity and the type and amount of thick-
ening agent used. Consistency is measured in
terms of the depth, in tenths of a millimeter, that
a standard cone will sink into a grease under
prescribed conditions and is referred to as the
penetration number. The National Lubricating
Grease Institute (NGLI) has established consis-
tency numbers, or grades, ranging from 000
(soft) to 6 (hard), corresponding to specified
ranges of penetration numbers. This rating sys-
tem covers most greases but there are greases
available that are softer than a NGLI No. 000 or
harder than a No. 6.
The consistency of a grease should be soft
enough to allow easy application and provide
acceptable lubrication, but not so soft to leak out
of the area being lubricated. In automatic
greasing systems, a grease with a consistency
softer than is optimum for the lubrication of the
equipment may be required so that it can be
pumped through the long lines and metering
valves. As with an oil's viscosiity, grease con-
sistency becomes thinner or more fluid with an
increase in temperature and thicker or more
solid with a decrease in temperature.
enough to allow easy application and provide
acceptable lubrication, but not so soft to leak out
of the area being lubricated. In automatic
greasing systems, a grease with a consistency
softer than is optimum for the lubrication of the
equipment may be required so that it can be
pumped through the long lines and metering
valves. As with an oil's viscosiity, grease con-
sistency becomes thinner or more fluid with an
increase in temperature and thicker or more
solid with a decrease in temperature.
Consistency Stability. A grease's consistency
may change while in use primarily due to the
mechanical shearing of the thickening agent
particles. The resistance to this change is re-
ferred to Consistency Stability.
may change while in use primarily due to the
mechanical shearing of the thickening agent
particles. The resistance to this change is re-
ferred to Consistency Stability.
Dropping Point. A grease's dropping point is the
temperature at which the grease becomes soft
enough that a drop of fluid will fall from the
grease. At or above the dropping point, a grease
will act as a fluid. It should be noted that the
dropping point is not the highest allowable
operating temperature for a grease, as the
temperature at which the grease becomes soft
enough that a drop of fluid will fall from the
grease. At or above the dropping point, a grease
will act as a fluid. It should be noted that the
dropping point is not the highest allowable
operating temperature for a grease, as the
13 (FIST 2-4 11/90)