Consequences of Grease Viscosity on Start-Up TQ

[Slalom4me]

At start-up, how pronounced are the differences
in resistance to motion between a grease with the
following viscosities (cSt @ 40ºC)?

The values are all from NLGI #1 greases.

• 150 cSt
• 220 cSt
• 313 cSt

To a layperson, it appears as though the first grease
requires considerably less start-up torque than the
third grease.

.

 

[Tempest]

I'm not an expert on this but I believe as a "rule of thumb" you are correct. However, the type of and content % of the thickener will also come into play.

A thinner base oil will generally require more thickener to get the grease to the same NGLI #, so there can be some offset in the benefit to the thinner base oil.

The thicker base oil will also tend to protect better under high load conditions.

Maybe one of the real pros will chime in.

 

[Slalom4me]

Thanks.

Is the Viscosity reported by ASTM D 445 indicative of the
viscosity of the final grease product (ie: w/ additives)?
Or is it describing the viscosity of the base stock?

.

 

[salesrep]

Base oil properties.

 

[Slalom4me]

Originally Posted By: salesrep
Base oil properties.
Thanks, salesrep.

Would three NLGI #1 greases formulated from base oil with the
varying cSt Viscosities above (post #1) appear to have a similar
thickness/consistency when dispensed? That is to say, do the
additives bring the final product to a standard level, despite
the differences in the base oil viscosity?

.

 

[Slalom4me]

The information about grease on the following link is informative

Grease Analysis - Monitoring Grease Servicability and Bearing Condition
By Bill Herguth, Herguth Laboratories

Viscosity of Grease

"The viscosity of grease is often misunderstood. The viscosity
typically listed on a new oil data sheet is usually the
kinematic viscosity of the oil used in blending the grease
measured, using the standard ASTM D445 method. The kinematic
viscosity of the base oil is important in ensuring the correct
grease, containing the correct grade of oil is used for
lubrication purposes. However, we can also measure the viscosity
of the grease itself. Since a grease is non-Newtonian, we can
only measure the apparent viscosity because the viscosity of a
non-Newtonian fluid changes with shear stress see “Understanding
Absolute and Kinematic Viscosity” by Drew Troyer). The apparent
viscosity of a grease is determined using ASTM D1092. This test
measures the force required to force the grease through an
orifice under pressure. As such, this test is an ideal way of
determining the flow characteristics of grease through pipes,
lines, dispensing equipment as well as its pumpability."

"Rheology measurements of grease may soon replace both the cone
penetration and the apparent viscosity measurements. Rheology is
the study of the deformation and/or flow of matter when it is
subjected to strain, temperature and time. A rheometer only
requires a few grams of sample to perform the analysis, yielding
much more information than the cone penetration or the apparent
viscosity measurements. This makes the rheology measurement an
ideal test for small amounts of used grease."

 

[Slalom4me]

Originally Posted By: Slalom4me
Originally Posted By: salesrep
Base oil properties.
Thanks, salesrep.

Would three NLGI #1 greases formulated from base oil with the
varying cSt Viscosities above (post #1) appear to have a similar
thickness/consistency when dispensed? That is to say, do the
additives bring the final product to a standard level, despite
the differences in the base oil viscosity?

.
The answer to my question appears in Mr Herguth's article

Grease Analysis - Monitoring Grease Servicability and Bearing Condition
By Bill Herguth, Herguth Laboratories

Changes in Grease Consistency

"Grease is made up of base oil, a gelling agent or soap
thickener (sometimes called filler) and additives, which perform
in much the same way as oil additives. The consistency of grease
is controlled by the type and ratio of the gelling agent to the
oil and its viscosity ... "

" ... worked penetration of new greases is the property upon
which the NLGI (National Lubricating Grease Institute) grease
consistency classification system is based ... "

.

 

[Tempest]

Look for ASTM D1478 Low Temperature Torque of Ball Bearing Greases or ASTM D4693 Low Temperature Torque of Grease Lubricated Wheel Bearings in the specs on the greases.

A few high quality greases list one of these. Lower is better.

 

[Slalom4me]

Thank you.

AFAIR, neither D 1478 nor D 4693 values have been published in
the marketing information viewed to this point. Perhaps the
technical service people can provide information about these
results on request - I will inquire.

With the understanding gained during the course of the thread,
my current opinion is that the answer to the original question
is that Viscosity of Oil (D 445) has less influence on start-up
torque than Penetration (D 217) &/or Apparent Viscosity
(D 1092). This statement is based on the belief that the latter
two values represent viscosity of the final product after
thickener(s) have been added.

.