Grease is a thickened lubricant that remains in contact with moving surfaces. It is formulated from a base oil thickened with a soap, clay, or polymer. Grease properties depend on the base oil viscosity and consistency grade determined by penetration testing. Additives provide oxidation resistance, extreme pressure properties, anti-wear performance, and other characteristics. Standard tests evaluate grease properties like dropping point, oil separation, load carrying capacity, and resistance to water and corrosion. Proper grease selection depends on application parameters like temperature, speed, and load.

1. Grease Fundamentals and Analysis

2. Basic Properties

3. Simple Definition
• Grease:
– A lubricant that is a solid to semi‐fluid dispersion of a
thickening agent (thickener) in a liquid. A lubricating
grease may be formulated with additives that impart
special properties such as resistance to oxidation or
wear.
– Origin: from Old French graisse, based on Latin
crassus ‘thick, fat.’
Source: NLGI

4. Stronger Definition
• Grease:
– A grease is a lubricant which has been thickened in order that it
remain in contact with the moving surfaces and not leak out
under gravity or centrifugal action, or be squeezed out under
pressure. Thus, a major practical problem is the provision of a
structure that will stand up under shear and at all temperatures
to which it may be subjected during use. At the same time the
grease must be able to flow into the bearing through grease
guns and from spot to spot in the lubricated machine as
needed, and must not of itself add significantly to the power
required to operate the machine, particularly at the start. This is
an exacting set of rheological requirements.
Ref: Vold, J. Marjorie, and Vold, Robert D., "Lubrication and Lubricants", J. Inst. Petroleum Technology, Vol. 38, 1952, P155‐163.

5. Grease Rheology
• Rheology is the science of deformation and flow of
materials
– Most solids are considered elastic, a material that
when stressed will store deformation energy and
recoil to its original shape
– Most fluids are considered viscous, a material that
when stressed does not store deformation energy and
will start to flow
• Greases are viscoelastic materials, a little of both

6. Functionality
• Greases are thick when at rest, and thinner under
the application of shear, so they are described as
being shear thinning
– Think of the thickener as a sponge that when
squeezed will release the oil
Ref: T3‐TRI‐19560, Phillips 66 Company

7. Composition
Credit: Lubriplate Lubricants Co., 2014

8. Base Oils
• Mineral
• Synthetic
– Polyalphaolefins (PAO)
– Esters
– Polyglycols
– Polyethers
– Dialkylbenzenes
• Silicone

9. Base Oil Viscosity
VISCOSITY APPLICATION
ISO 15 ‐ 32 Used for high speeds (>3600 rpm), lower loads, good at
low temperatures
ISO 68 ‐ 100 Used for high speeds (>3600 rpm), lower loads, higher
temperatures
ISO 100 ‐ 220 Moderate speeds (<3600 rpm), good load carrying,
typical multi‐purpose grease’s oil
ISO 460 Medium speeds, high load carrying
ISO 1000 ‐ 1500 Slow speeds (<100 rpm), excellent load carrying

10. Thickeners
• Thickeners are fibrous, like a sponge, and are used to affect
grease properties:
– Texture, the appearance and feel of a grease which affects
its adhesiveness
– Dropping Point, the temperature at which the grease
releases a drop of oil
– Shear Stability, the ability to resist permanent changes in
consistency due to work
– Water Resistance, the ability to withstand water without
adverse effects
– Pumpability, the ability of a grease to flow under pressure

11. Soaps
• Lithium
• Calcium
• Sodium
• Aluminum
• Barium
Non‐Soaps
• Clays (Bentonite)
• Polyurea
Thickeners

12. Thickeners

13. Simple
• Prepared by reacting a
single organic acid with one
or more inorganic bases
Complex
• Prepared from two or more
organic acids
– Primary soap (metallic
stearate)
– Complexing agent (metallic
salt)
• The complexing agent
modifies grease
characteristics and usually
increases the dropping
point.
Soap Thickeners
Source: NLGI

14. Dropping Point (ASTM D566, D2265)
• In general, the
dropping point is the
temperature at which
the grease passes from
a semisolid to a liquid
state under the
conditions of test
• Considered to be
temperature where
thickener system fails
Ref: ASTM D566‐16, Standard Test Method for Dropping Point of Lubricating Grease, ASTM International, West Conshohocken, PA, 2016.

15. Grease Properties by Thickener
Shear
Stability
Dropping Point
(°F / °C)
Water
Resistance
Maximum
Temperature
Lithium Good 375 / 190 Yes 250 / 121
Lithium – Complex Excellent 500 / 260 Moderate 300 / 149
Calcium – Hydrated Good 190 / 88 Yes 150 / 65
Calcium – Anhydrous Poor – Good 290 / 143 Yes ‐‐‐
Calcium – Complex Good 500+ / 260+ Yes 300 / 149
Sodium Poor – Good 360 / 182 No 250 / 121
Aluminum – Normal Poor 180 / 87 Yes 150 / 65
Aluminum – Complex Good 480 / 249 Yes 300 / 149
Barium Good 400 / 204 Yes 250 / 121
Clay Good 500+ / 260+ Yes 300 / 149
Polyurea Med – Good 470 / 243 Yes 300 / 149
Ref: Tool and Manufacturing Engineers Handbook, Volume 1, p. 4‐44, Library of Congress, 1983

16. Penetration (ASTM D217)
• Cone penetration test
results provide one
measure of the consistency
of a grease
– Worked penetration results
are required to determine to
which NLGI consistency grade
a grease belongs
– Undisturbed penetration
results provide a means of
evaluating the effect of
storage conditions on grease
consistency
Ref: ASTM D217‐10, Standard Test Methods for Cone Penetration of Lubricating Grease, ASTM International, West Conshohocken, PA, 2010.

17. NLGI Consistency Number
NLGI
Number
ASTM worked (60 strokes)
penetration at 25 °C
tenths of a millimeter
Appearance
Consistency food
analogy
000 445‐475 fluid cooking oil
00 400‐430 semi‐fluid apple sauce
0 355‐385 very soft brown mustard
1 310‐340 soft tomato paste
2 265‐295 "normal" grease peanut butter
3 220‐250 firm vegetable shortening
4 175‐205 very firm frozen yogurt
5 130‐160 hard smooth pate
6 85‐115 very hard cheddar cheese
Ref: Rudnick, Leslie R. (2005). Synthetics, Mineral Oils, and Bio‐Based Lubricants: Chemistry and Technology (Chemical Industries). CRC. p. 468.

18. DIN 51502 Lubricant Codes
Ref: DIN 51502 Designation of lubricants and marking of lubricant containers, equipment and lubricating points

19. DIN 51502 Lubricant Codes
Ref: DIN 51502 Designation of lubricants and marking of lubricant containers, equipment and lubricating points

20. DIN 51502 Lubricant Codes
Ref: DIN 51502 Designation of lubricants and marking of lubricant containers, equipment and lubricating points

21. Performance Properties

22. Additives
• Structure modifiers
– modify the grease structure & properties
• Anti‐oxidants / Oxidation inhibitors
– rust and corrosion protection particularly for
applications involving high temperatures and/or
water contamination
• Extreme pressure additives
– enable greases and equipment to resist extreme heat
and extreme pressure, particularly in boundary
lubrication conditionsRef: lubimax.com

23. Additives
• Anti‐wear agents
– reduce metal wear by binding to metal surfaces,
forming a lubricious sacrificial coating
• Anti‐rust / Metal deactivators
– reduce metal reactivity to protect surfaces from
degradation
• Viscosity modifiers
– modify base fluid properties to enhance performance
in highly variable temperature applications
Ref: lubimax.com

24. Additives
• Application dependent
– Pour point depressants
– Antifoam agents
– Emulsifiers
– Demulsifiers
– Tackiness agents
– Solid additives
– Friction Modifiers
Ref: lubimax.com

25. Oil Separation (ASTM D1742)
• Results of this test
correlate directly with
the oil separation that
occurs in 35‐lb pails of
grease during storage
– Reports % wt of oil
separated after 24 hours
at 25 °C
Ref: ASTM D1742‐06(2013), Standard Test Method for Oil Separation from Lubricating Grease During Storage, ASTM International, West
Conshohocken, PA, 2013.

26. EP Properties (ASTM D2596)
• Used to differentiate
between greases
having low, medium, or
high levels of extreme
pressure characteristics
– Reports maximum load
(OK value) under which
no welding occurs
– a.k.a. Four‐Ball Method
Ref: ASTM D2596‐15, Standard Test Method for Measurement of Extreme‐Pressure Properties of Lubricating Grease (Four‐Ball Method), ASTM
International, West Conshohocken, PA, 2015.

27. AW Properties (ASTM D2266)
• Used to determine the
relative wear‐
preventing properties
of greases under the
test conditions
– Reports the wear scars
on the lower three balls
– a.k.a. Four‐Ball Method
Ref: ASTM D2266‐01(2015), Standard Test Method for Wear Preventive Characteristics of Lubricating Grease (Four‐Ball Method), ASTM
International, West Conshohocken, PA, 2015.

28. Load‐Carrying Capacity (ASTM D2509)
• Used to differentiate
between greases
having low, medium, or
high levels of extreme
pressure characteristics
– Reports maximum load
(OK value) under which
no scoring occurs
– a.k.a. Timken Method
Ref: ASTM D2509‐14, Standard Test Method for Measurement of Load‐Carrying Capacity of Lubricating Grease (Timken Method), ASTM
International, West Conshohocken, PA, 2014.

29. Corrosion Prevent (ASTM D1743)
• Uses a grease‐
lubricated tapered
roller bearings stored
under wet conditions
for 48 hours
– Pass/Fail result based on
presence of corrosion
spot >1 mm
Ref: ASTM D1743‐13, Standard Test Method for Determining Corrosion Preventive Properties of Lubricating Greases, ASTM International, West
Conshohocken, PA, 2013.

30. Water Washout (ASTM D1264)
• Estimates the
resistance of greases to
water washout from
ball bearings under
conditions of the test
– Reports % wt of grease
washed out after
spraying for 60 minutes
at 38 or 79 °C
Ref: ASTM D1264‐16, Standard Test Method for Determining the Water Washout Characteristics of Lubricating Greases, ASTM International,
West Conshohocken, PA, 2016.

31. Water Spray Off (ASTM D4049)
• Evaluates the ability of
a grease to adhere to a
metal surface when
subjected to direct
water spray
– Reports % wt of grease
removed after spraying
for 5 minutes at 38 °C
Ref: ASTM D4049‐06(2011), Standard Test Method for Determining the Resistance of Lubricating Grease to Water Spray, ASTM International,
West Conshohocken, PA, 2011.

32. Mobility (US Steel DM 43)
• Measures pumpability
of grease at lower
temperatures
– Reports g/min at 150 psi
– A factor in centralized
grease system’s lines,
nozzles and fittings
Source: SKF

33. Roll Stability (ASTM D1831)
• Can show a directional
change in consistency
that could occur in
service
– Reports change in
consistency
Ref: ASTM D1831‐11, Standard Test Method for Roll Stability of Lubricating Grease, ASTM International, West Conshohocken, PA, 2011.

34. Grease Compatibility
• Most grease manufacturers produce compatibility
charts that do not necessarily agree with one
another (often meant only for their own products)
• ASTM D6185 evaluates mixtures to confirm:
– No significant decrease in dropping point
– Mechanical stability remains in range
– Consistency remains in range after heating
Ref: ASTM D6185‐11, Standard Practice for Evaluating Compatibility of Binary Mixtures of Lubricating Greases, ASTM International, West
Conshohocken, PA, 2011.

35. In‐service Grease Testing and
Interpretation

36. Elemental Spectroscopy
• The measurement is performed by diluting a
sample with solvent and injecting into a plasma
where it is ionized (essentially burned) at a
temperature of nearly 10,000 K (hotter than the
surface of the sun)
– Each element on the periodic table emits a unique
color of light as it is ionized, and the instrument
measures the intensity of these colors to determine
the concentration (reported in part per million –
ppm).

37. Elemental Spectroscopy
• The sample must completely ionize within a very
small, measured area of the plasma. As such, only
particulate within 0‐5 microns is accurately
measured, and particles larger than 10 microns are
essentially not measured at all.
– Wear particles generated under normal conditions
and airborne contaminants easily fall within this
range, however severe wear and/or contamination
may produce particles too large for detection and
would require supplemental testing such as ferrous
wear concentration or analytical ferrography.

38. Elemental Spectroscopy
• Though additives are sub‐micron and will always be
detected by this method, a second fundamental
aspect of this test must be considered: this test only
measures elements, not compounds, alloys or
chemicals
– Though certain elements may appear in the results
and be safely assumed to be from certain types of
additives, this test does not confirm the functionality
of those additives. While additives are slowly
consumed, so long as they remain present in the fluid,
the results will not decrease significantly.

39. Elemental Spectroscopy
• Trending is important, any notable changes can
indicate mixing or incorrect grease

40. Water Contamination
• Water can soften or displace grease, leading to a
lack of lubrication
• Water can cause corrosion or pitting of parts
• Water content may correlate with wear metals or
ferrous wear concentration
– Trending is important, since a significant increase may
occur before a corresponding increase in wear

41. Ferrous Wear Concentration
• May or may not correlate with spectroscopic iron
– If ferrous wear is lower than iron, wear is considered
normal, i.e. <10 microns
– If ferrous wear increases without an increase in iron,
wear is considered severe, i.e. >10 microns
– If both increase, wear is abnormal and should be
followed up with Analytical Ferrography

42. Analytical Ferrography
• A portion of the sample is passed over a slide on
top of a magnetic plate to attract ferrous particles
• The prepared slide is then placed under a
microscope for examination
Image courtesy AZO Materials
Ferrous Particles
Near Exit are
Submicroscopic
Non Ferrous & Weakly
Magnetic Debris
Deposit Randomly
Non-Wetting
Barrier
Entry Region
Oil Flow

43. Particle Classification
• The particles are then classified by:
– Shape
– Composition
– Size
– Surface condition
• As a result of this classification, determination of an
abnormal wear mode can be made

44. Analytical Ferrography
• Levels are subjective and size dictates that results
may not correlated with elemental spectroscopy

45. Analytical Ferrography
• Pictures are of areas of interest, not necessarily
representative of complete interpretation

46. Data Interpretation Tips
• Grease samples are inherently difficult to ensure
that they are truly representative, therefore:
– Trending is the most valuable tool, try not to dwell on
absolute values or limits
– High levels of contamination without corresponding
wear often suggest poor sampling
– Sampling consistently (location, method, interval)
provide the best chance for early detection of faults

47. Thank you for listening
We will allow time for any questions