NLG~
Understanding Open Gear Lubricants: Product Design Considerations
John J. Lorimor CLS, CLGS, Chris Hsu, PhD., The Lubrizol Corporation, Wickliffe, Ohio, USA
Presented at NLGI’s 79th Annual Meeting, June, 2012, Palm Beach, Florida, USA
Introduction
Q
general
lubricants.
Instead
they areasoften
pen gearpurpose
lubricants
are seldom
developed
formulated to meet the specific needs of a particular
application or even a unique piece of equipment.
Equipment builders frequently specify lubricant physical
and performance characteristics designed around the
operating conditions that will be encountered by the
equipment during normal operation. Once the actual
operating conditions are known, the lubricant’s physical
and compositional properties can be customized to suit
the unique needs of the application. These significant
factors in lubricant design can include3:
1. Operating load
2. Operating temperature
3. Sliding speed
4. Gear size and surface condition
The extremely high operating stress and slow speed
that can be encountered in open gear applications
mean that in many cases it is difficult to operate in any
lubrication regime except boundary, For this reason,
selecting a lubricant using a suitable high viscosity base
fluid is typically required to provide acceptable real
world performance. In most cases the performance of
this lubricating film must be further supplemented by
appropriate extreme pressure/anti-wear additives. This
is necessary to prevent gear damage that may occur
during start up, under shock loading, in the presence
of severe contamination, or even under worst-case
conditions such as during temporary loss of lubricant.
Consideration of operating temperature includes
both ambient conditions as well as the temperature at
the working tooth flank. Ambient temperature consider
ations are important because of the significant effect it
has on lubricant viscosity and the overall dispensability
of the lubricant from bulk storage. For this reason,
some lubricants used in low temperature climates
can require the use of low pour point synthetic fluid
components or alternatively use of a diluent solvent to
enhance pumpability. Heat which is generated at the
working tooth flank through sliding motions and friction
can have the opposite effect, reducing the effective vis
cosity of the lubricant and decreasing the actual lubri
cant film thickness. For high operational temperatures,
resistance to oxidation can be very important.
The overall dimensions of the gear and pinion and
the rotational speed of the gear set can itself be an
obstacle to effective lubrication. The manufacture of
large open gears is generally not as precise in its manu
facturing tolerances, and for this reason the surface
finish is likely to be rougher than that found in enclosed
gears. Surface finish plays a role in the ease of develop
ing a suitable lubricating film, and new gears will have a
dramatically higher surface roughness than “broken-in”
surfaces. The size of the large gears also means that
lubricant “run-off” or “fling-off” must be controlled, and
most open gear lubricants are formulated to be tena
cious in their adhesion to gear surfaces.
Open Gear Lubrication
The finished lubricant marketplace is filled with
numerous variations in open gear lubricant composi
tions, resulting in significant differences in physical and
performance properties. These compositional differ
ences have been explained in several prior papers123
as necessary to address the specific needs of various
market segments. For the formulator, the many prod
uct variations can make understanding the underlying
product design considerations difficult. Despite the
confusion that can exist because of the wide array of
lubricant types and varied composition in the market
place designed to suit these many different applica
tions, there exist a set of common principles to which
all open gear lubricants adhere.
—18—
VOLUME 77, NUMBER 5
NLGI
The most basic of the lubricant principles ful
filled by all open gear lubricants is the effective
separation of teeth in rolling or sliding motion.
Without effective separation of these parts in
motion, there is a continuous wear on metal
surfaces that can eventually lead to component
failure. Separation of moving parts specifically
means establishing an effective lubricating film.
At a constant temperature and speed, the film
thickness produced is directly proportional to
the fluid’s kinematic viscosity. As the following
chart in Figure 1 demonstrates using an optical
EHD film tester, two radically different viscosity
oils can each produce the same film thickness
when adequate speed can be achieved. At the
same speed, the lower viscosity oil will have a
much thinner fluid film.
Since lubricating film thickness directly relates Figure 1
to viscosity, it is common for equipment build
ers to specify minimum viscosity requirements in their
approved lubricant specifications. This requirement
ensures an adequate lubricating film is produced at the
unique speed, load and operating temperature of their
equipment. When using greases, it has been reported45
that the thickener can contribute to an increased lubri
cating film thickness. When a minimum fluid viscosity
is specified, the presence of a grease thickener acts as
a safety margin to further improve film thickness and
encourage elastohydrodynamic (EHD) lubrication.
Film Thickness in Optical EHD Tests at 1OO~C
Speed (rn~s)
—
Optical EHD film thickness comparison
from the standard has been reproduced and is included
as Table 1.
For industrial applications, most OEM recommenda
tions defer to the published AGMA guidelines and con
sist of imparting a minimum fluid viscosity to the service
lubricant. The goal of a minimum base fluid viscosity
is to provide a wear inhibiting elastohydrodynamic
(EHD) supporting film that is thick enough to span the
particle size of contaminants. The term “hydrodynamic
lubrication” is applied to the lubrication state ensuring
complete separation of the mating elements of the tn
bological system. Viscosity has a significant role to play
in the formation of a satisfactory lubricating film under
load and at operating temperature. For gears operating
at slow peripheral velocities, it has been reported that
by doubling the lubricant viscosity, the service life can
be tripled14. By contrast, the reduced film thickness
Viscosity Requirements
The guidelines published within the ANSI/AG MA
9005-E02 standard for industrial gear lubrication has
the following in its annex D regarding minimum viscos
ity recommendations for open gear lubricants. The data
Table 1
ANSI/AGMA 9005-E02 annex D minimum OGL viscosity recommendations
Intermittent spray
Ambient temperature, °C
Non-residual lubricant
Residual type lubricant
Gravity feed or forced drip
-10 to +5
4140 cSt @ 40°C
428.5 cSt @ 100°C
4140 cSt @ 40°C
+5 to +20
6120 cSt © 40°C
857 cSt © 100°C
6120 cSt © 40°C
+20 to +50
190 cSt © 10000
857 cSt © 100°C
190 cSt © 100°C
—19—
NLGI SPOKESMAN, NovEMBER/DEcEMBER 2013
NLGft
average surface roughness of the gearing (Ral + Ra2)/2.
If lambda is greater than 2 the lubricant film thickness
is twice as high as the surface roughness. Under such
full-film hydrodynamic lubrication, the tooth flanks are
completely separated by the lubricant film. It is gener
ally recognized that higher lambda ratios can dramati
cally reduce wear and increase the gear set life.
If lambda is between 0.7 2, the gear is operat
ing under mixed friction conditions, and there can be
some opportunity for metal-to-metal contact to occur
between the mating tooth surfaces. If the lambda value
is less than 0.7, the gear is operating under boundary
lubrication conditions, meaning that there is definitely
metal-to-metal contact between the tooth flank surfaces.
It is assumed by these equipment builders that in the
mixed-friction range, the risk of rupture of the oil film is
greater if the viscosity separating contacting surfaces is
low. Lower base fluid viscosity can, however, produce
acceptable lambda values when surfaces are properly
conditioned. It is reported that for industrial applica
tions, surface finishing through proper running-in can
produced by lower viscosity base fluids can more easily
rupture and allow metal surfaces to contact, especially
as the temperature rises from operation under continu
ous boundary conditions. Under low ambient tempera
ture conditions reduced viscosity base fluids can still
function because of the low temperature thickening
effect of the oil.
The example shown in Table 2 is a comparison of
two commercial high viscosity fluid type open gear
lubricants. The example shows that two commercial
products each designed to fulfill the demands of the
same industrial open gear application can have radi
cally different rated viscosity. As the data demonstrates,
at their operating temperature “mid-point” they are
extremely similar in viscosity, which in a constant speed
application corresponds to providing a similar film
thickness.
Maintaining a lubricating film thickness greater
than the dimensions of surface asperities is generally
regarded as key to proper lubrication. Lambda (2~) is
the ratio of the oil film thickness (hc) divided by the
—
Table 2
Comparison of commercial OGL product effective viscosity at operating temperature
Published
Viscosity ©
40°C (cSt)
Published
Viscosity ©
100°C (cSt)
Published
Operating
Temperature
Range (°C)
Midpoint
Temp (°C)
Calculated
Viscosity (cSt) ©
Midpoint
temperature
Commercial
Product A
3100
165
Oto 110
55
1346
Commercial
Product B
25500
750
4Oto 140
90
1245
Table 3
Comparison of Mining OGL EP requirements
ASTM
Test Method
Bucyrus SD4713
OGL Spec
P&H Revised
464 Spec
P&H Multi-Service
520 Spec
Four Ball Wear Scar
(max), mm
D2266
0.7
1 .0
0.7
Four Ball EP
Weld Point, kg
LWI (mm)
D2596
800
120
400
500
—
—
Timken OK Load, lbs
D2509
—
50
-_~/
—20—
VOLUME 77, NUMBER 5
NLG~
a>
be reduced from a typical of around 4pm to as low as
0.3pm13. Some gear manufacturers strongly discourage
the use of running-in lubricants due to the impact of
forced wear on tooth modifications.
Rack-type gear configurations are common to
mining equipment, and in these specific applications
speeds can decrease to zero velocity with frequent
directional changes. Under these variable speed condi
tions the formation of an EHD film will not be possible
and mixed and boundary friction will be present. In
such extreme cases the use of supplemental compo
nents such as chemically active EP additives, or combi
nations of such additives with significant solid lubricant
content is necessary to prevent metal-to-metal contact,
and to protect these highly loaded surfaces from wear.
Load Carrying Capacity (LCC)
Requirements
For industrial “fixed plant” applications such as rotary
grinding mills or rotary kilns and dryers, the load car
rying performance of open gear lubricants is typically
governed by conformance to specifications such as
ANSI/AGMA 9005-E02. The current AGMA 9005-E02
standard requires that EP gear oils having oil viscosity
>3200 cSt © 4000, must at a minimum achieve FZG
test performance under A/8.3/90 conditions of >12
stage failure load. In older AGMA standards such as
AGMA 251 .02, the use of the Timken OK load (ASTM
D2782) as a measure of EP performance has also
been specified, requiring a minimum 45 lb. OK load for
acceptable open gear lubricants.
For mining “mobile plant” applications such as
shovels, excavators and draglines, OEM requirements
for load carrying performance have been previously
reported2. Some of the more common LOG require
ments of current specifications are detailed in Table 3.
Due to the high potential for severe loading, slow
speeds, and reversing direction, extreme pressure
protection in these applications is considered a critical
lubricant performance parameter with four ball weld
points of up to 800kg required.
Figure 3
—
Timken test spedmens
Laboratory Evaluation of Open Gear
Lubricants
Bench test selection and field application
Bench tests are used as screening tools by lubricant
formulators before undertaking field trials. The results
of bench testing do not always correlate with field tests
mainly because the greater complexity of the actual
application. The friction and wear properties can be
determined under four important parameters: load,
speed, temperature, and the materials used. The most
severe case is under high load, low speed, and high
temperature. This can be explained by reviewing the
Stribeck curve for the situation under study. In the most
—21 —
NLGI SPOKESMAN, NOVEMBER/DECEMBER 2013
NLGII
severe case, the frictional pairs are under boundary
lubrication conditions. As wear occurs, the contact
surface area increases and the contact pressure is
reduced. Temperature will also rise in the contact.
As the contact conditions change, the friction changes
accordingly. We used the following bench tests to
study the open gear lubricant formulation:
L
Timken Test, ASTM D2509/D2 7836
The Timken test is a common laboratory technique
for the evaluation of lubricant film strength properties as
imparted by EP additives. Film strength is a key prop
erty of open gear lubricants. The lubricant is applied to
a rotating test ring and a test block is pressed against
it. The test is run under conditions of progressively
increasing load stages, until rupture of the lubricating
film occurs. The purpose of the test is to make deter
mination of the load capacity (O.K. load) and weld load.
It has been generally assumed that the unit pressure
measurement relates to the film strength of the lubricant.
The machine is a ring-on-block setup with carbu
rized steel test pieces, hardened to HRG 58 to 62
and having ground surfaces with a roughness of 0.51
to 0.76 pm Ra. The sliding speed is approximately
2 meters per second and the starting temperature is
room temperature. During the test, the temperature of
the contact interface rises to >150°C. The test duration
is 10 minutes, with a constant lubricant feed until either
the test reaches its time limit and stops or scuffing
occurs and the rig is stopped. The test blocks are visu
ally inspected for scuffing, and the OK load is deter
mined as being the highest load used in which scuffing
did not occur. The test blocks and rings are shown in
Figure 3. Full details can be found in the ASTM D2509
test method.
A
Figure 4 — Four Ball Tester
Figure 5 — Four ball test specimens
The contacts in a four-ball EP tester consists of the
triangular loading of three lower fixed and stationary
balls against a rotating upper ball, which gives three
point contacts. The balls are ANSI Grade 25 Extra Polish
12.7mm (0.Sin) in diameter and composed of AISI
E-521 00 chromium steel hardened to HAG 64 66.
The top ball is then rotated at 1770 rpm for 10 seconds.
Tests are repeated at successively higher load stages
until welding occurs. The machine and the test balls are
shown in Figure 4 and Figure 5.
–
Four Ball Weld Point, ASTM D25967
The lubricant is tested in a four-ball system con
sisting of a rotating ball (running ball), sliding with
an adjustable test force on three balls identical to it
(starting balls). The test load is increased in stages
until welding of the four-ball system occurs. Evaluation
is made to determine the weld load or the O.K. load
beneath it.
FZG Gear Rig8’9
The FZG test rig has proven itself to be the most
realistic test for gear lubricants, providing information
relating to load carrying capacity and scuffing load
—22—
VOLUME 77, NUMBER 5
NLG~
limits for lubricants. The sliding velocities of different
laboratory test machines have been reported to vary
between 0.09 rn/s for the Falex machine to 11 .56 rn/s
for the FZG machine. Based upon these numbers, the
FZG is closer to the sliding found in an actual open
gear application. AGMA and CEO guidelines utilize the
test version N8.3/90, standardized in DIN 51 354 as a
basic testing procedure for gear oils. The FZG grease
test defined by ISO 14635 part 3 provides information
about the load carrying properties of gear greases.
It is applicable to semi-fluid greases of NLGI grades
0, 00 and 000. The FZG machine utilizes a locked
clutch in which the load is applied to two spur gears
and specially profiled (A type) to be mis-matched. The
gears are case hardened to HRC 60 to 62. The shaft
rotates at 500 rpm and the pitch line velocity is 2.7 rn/s.
Typical OGL Formulation Components
Base fluid
The selection of a base fluid depends upon many
factors. For sorne applications, low ternperature char
acteristics can be very important in this selection pro
cess. For others the environmental profile of the oil can
also be a concern. Film strength is generally of primary
importance, so higher viscosity oil cuts are predomi
nately used.
Viscosity builders are used in a formulation to
increase the overall fluid viscosity, improve the viscositytemperature relationship, and to promote better adhe
sive properties. In order to provide separation the
lubricant must remain in contact with the gear surfaces
and must not be removed by the sliding gear contacts.
In addition, the lubricant must not run off between
lubrication application intervals. Viscosity has a signifi
cant impact upon products adhesiveness, and higher
viscosity fluids promote greater adhesion to the gear
surface. While asphalt has been generally regarded as
old technology, it is still in use due to its acceptable
performance and low cost. Substitutes for asphalt
can include petroleurn resins, high viscosity grades of
polyisobutylene, and heavy oil fractions, which have all
becorne common constituents of these modern high
viscosity systems.
Chemically active additives
Chemically active additives contained as a certain
percentage in oil or grease react chemically with the
iron of the steel in tribological contact under sufficiently
high temperatures. These activation temperatures are
easily generated from the intense pressures that occur
during gear contact. Chemical additives decompose
at a particular temperature and attack the surface of
the metal, forming with the metal surface sacrificial lay
ers that can absorb heavy loads and a~e resistant to
wear. Chemically active additives can be destroyed if
the lubricant is overheated, and thereby be rendered
ineffective. Water contamination of the lubricant can
also cause additives to be rendered ineffective. Typical
chemical additives have been well discussedboH and
include extreme pressure, antiwear, anti-corrosion, and
anti-oxidant functionalities. These ingredients can be
found as individual components or pre-blended as
optimized mixtures or “packages”.
Solid lubricants
In the real world there are conditions in which suffi
ciently high temperatures do not occur, so that no reac
tion film can be formed from the chemical additives.
In such cases, solid lubricants are deposited in tribo
logical contact as a result of the pressure between
—23—
NLGI SPOKESMAN, NOVEMBER/DECEMBER 2013
NLG~
the elements in contact. Solid lubricants do not break
down with temperature, and in order to be effective
need only a minimum pressure to form effective films
of lubricant on metal surfaces. These solid lubricant
films can absorb heavy loads, prevent wear and reduce
friction. Solid lubricants also exhibit excellent hightemperature stability, making them ideal for such
applications.
Molybdenum disulfide (M0S2) lubricant films can
support very heavy loads, prevent wear and reduce
the coefficient of friction12. In addition to molybdenum
disulfide, a number of other solid lubricants such as
polytetrafluoroethylene (PTFE) and calcium carbonate
(CaCO3) are commonly used in synergistically-acting
combinations, so that the mixture exhibits consider
ably better tribqlogical properties than molybdenum
disulfide on its own. Proper selection of solid lubricants
for open gear application can be crucial to meeting
OEM requirements, as some solid lubricants such as
synthetic graphite have been shown to adversely affect
wear protection.
Grease thickener
The function of a grease thickener is to contribute
desirable rheological properties to the open gear
lubricant. A physical matrix structure creates a semi
solid consistency, which allows solid lubricants and
other insoluble additives to be suspended within the
lubricant. The grease thickener also creates a supple
mentary constituent to the fluid portion of the formula,
contributing to increased film thickness at the loaded
contact. Some thickener types such as gelled calcium
sulfonate can add to the load carrying capacity of
the finished lubricant. Grease thickeners in common
use include alkali metal soaps based upon aluminum,
lithium, or calcium ions. Inorganic thickeners are also
commonly used, and examples include converted
overbased calcium sulfonate gels, bentonite clay and
fumed silica.
Diluent solvents
Mining operations can be located in remote areas
subject to wide temperature extremes. For these
reasons, some lubricants will also contain solvents in
order to dispense in conditions of low ambient tem
perature, or where methods of application requires fluid
consistency such as by spray system. Solvents have
become more regulated, and chlorinated materials
once known for their high load carrying capacity, good
volatility and safe flash points are no longer used. In
their place, most formulations today typically include an
aliphatic hydrocarbon, the selection of which is based
upon consideration of both the flash point and accept
able evaporative tendencies. With modern solvents it
is important not to spray the product too frequently,
as the solvent needs sufficient time to evaporate and
produce the correct operational viscosity. Testing of the
solvents impact upon product dispensability is typically
performed by simulated dispensing systems such as
the Lincoln Ventmeter.
Developmental Formulations
A frequently presented global trend is the desire by
lubricant consumers to move away from asphaltic
(bitumen) based residual lubricants. Residual lubricants
are considered older technology and for this reason
were not selected for use in the developmental formula
tions. Environmental considerations have also resulted
in the trend to formulate products free from heavy met
als and chlorinated solvents. Current trends in industrial
maintenance point to improved condition monitoring of
capital equipment. For this reason, one selling point of
open gear products offering semi-transparent lubricant
films is that the surface condition of large gears can
be more easily assessed by maintenance personnel.
For these reasons, open gear lubricant product lines of
major manufacturers have become more diverse, offer
ing products designed to suit these emerging needs
in the marketplace. The following example open gear
lubricants were developed attempting to incorporate
these modern OGL formulation trends.
For mining applications, the product design begins
with a suitable grease base, and for our work a gelled
calcium sulfonate was selected for its high inherent EP
and antiwear characteristics. The base fluid viscosity
was calculated to meet OEM requirements, and then
blended from a mixture of high-viscosity polyisobutyl
ene (PIB) and bright stock, providing high film-strength
—24—
VOLUME 77, NUMBER 5
NLG~
ment attempts, the following example formulations
were developed and are included in Table 4.
and excellent adhesive “cling” to metal surfaces. PIB
was selected over other polymeric tackifiers because
of its excellent shear stability. In order to meet the
demanding four-ball EP requirements of the mining
specification, two chemical additive components were
selected based upon a reported synergistic EP effect
promoting high four-ball EP weld loads11.
For industrial applications, the example lubricant
was prepared as a super-high-viscosity fluid. Medium
molecular weight (Mn=3500) PIB was selected for
the base fluid because it is colorless, chemically inert,
extremely shear stable, and offers a very high viscos
ity (4500 cSt @ 100°C). This combination of attributes
produces adhesive, high film-strength, nearly transpar
ent coatings on gear surfaces that will not build up in
the roots of gear teeth. The bench test performance of
the fluid had requirements that necessitated a different
additive approach than the grease. Upon review of the
desired performance requirements, it was determined
that an existing commercially available and well opti
mized additive package would be the most suitable
choice.
Both examples were targeted to provide superior
EP performance exceeding general industry and OEM
minimum requirements. Based upon several develop-
Benchmark Lubricants
The candidate developmental formulations were
compared to industry benchmark lubricants in order to
evaluate their potential field performance. These refer
ence lubricants were selected because they are widely
used and recommended by OEM’s, and especially
because they carry recommendations by trained field
personnel familiar with the actual field performance of
lubricants in service.
BENCH TEST RESULTS AND DISCUSSION
Comparison of mining OGL formulations
The example grease-based OGL formulation was
evaluated using typical ASTM standards against a field
proven mining industry benchmark commercial greasebased product. The industry benchmark claims to meet
the Bucyrus (now CAT Mining) SD4713 specification for
OGL included in Table 5, and both the developmental
formulation and the industry benchmark were com
pared to this standard.
Table 4
Developmental OGL Formulations
Function
Description
%_Weight
Example Mining OGL
Formulation
Base Fluid
150 Bright Stock
Polyisobutylene (Mn
35.60%
=
3500)
14.40%
Grease thickener
Calcium Sulfonate Grease Base
24%
Solid Lubricants
MoS2, technical fine grade
5%
CaCO3, precipitated
10%
PTFE, particle size 4 micron
5%
Sulfurized Olefin, 44% S
3%
400TBN Overbased Ca Sulfonate
3%
Chemical additives
Example High viscosity
fluid OGL
Commercial OGL Additive Package
Total
94%
6%
100%
—25—
NLGI SPOKESMAN, NOVEMBER/DECEMBER 2013
100%
NLGI
Table 5
Comparison of Mining OGL products
Test Description
ASTM/ISO
Method
Bucyrus
SD4713
Requirement
Example
Mining OGL
Commercial
Reference
Texture
Visual
Tacky
Tacky
Color
Visual
Black
Black
0
0
362
370
Calcium
sulfonate
Aluminum
complex
<1 40°C
<1 40°C
<1 40°C
15
<15
800
167
800
137
≤0.70
0,53
0.71
<600 @
lowest
expected
temp
29
30
100
850
9.1
1.24
0.9
0.04
+40°C
-1 to 121 °C
≥
US mobility, g/sec
@25°C
@-1°C
Useful temp range
FZG N2.76/50
wear rate, mg/kWh
-20 to +40°C
ISO 14635-3
Timken retention
>
14 stages
100
70
4 ball weld point, kg
D2783
250
315
315
400
500
4 Ball LWI
D2783
50.1
76.2
72.5
80
83.9
FZGA/8.3/90
05182
>14
>14
>14
>14
>14
4 baIl wear scar, mm
D2266
0.40
0.39
0.37
0.37
0.44
~
~
—27—
NLGI SPOKESMAN, NOVEMBER/DECEMBER 2013
NLGU
Under standard ASTM D51 82 conditions the FZG
test can successfully differentiate lubricants of different
gears in use are 20mm in width. In order to increase
additive concentration in the degree of gear tooth
the loading per unit area, special half-width gears of
distress. FZG modified procedures are an area of inter
10mm were used resulting in significantly increased
est, and possible future research could include running
contact pressure from the standard test. In addition,
this test at a slower speed in order to see what may
the gears were run in a reverse direction so that the
be revealed.
gear contact begins at the tip and goes to the root,
Conclusion
which is opposite normal gear tooth interaction. The
effect of these combined changes is that all pressure
Proper design of open gear lubricants requires
is concentrated on a smaller initial contact area, and
consideration of many operating variables and per
undergoes a significantly higher degree of sliding than
formance requirements. Speeds, loads, temperatures
under normal conditions13. Based upon our experience,
and surface finish are four significant considerations in
the net result of these modifications is
that the gearing becomes significantly
Table 7
more aggressive in its failure modes.
Comparison of OGL performance in the FZG “shock” test
Finally, the test was conducted
Sample
Visual Rating
Wear Image
at a higher linear speed of 16.6 m/s
in order to promote increased gear
surface temperatures, and was run for
2% OGL
longer duration of 43400 cycles. The
Additive
Scuffing
Package
test is typically run 21700 cycles for
each load stage. The result of these
modifications is to severely stress the
lubricant film and promote wear.
4% OGL
The results of the testing are shown
Additive
Scratches
in the following Table 7:
Package
As expected, the gear ratings fol
lowing the completion of this round
of testing were much more severe
than those run under standard condi
6% OGL
tions. The developmental formulation
AddiUve
Scratches
containing the lowest level of addi
tive treatment produced the first test
failure, by experiencing a measured
degree of scuffing above the maximum
8% OGL
allowable limit. Scuffing is defined as
Additive
Scratches
the displacement of metal by momen
Package
tary welding and ripping apart of the
mating surfaces of gear teeth, and is
characterized visually by the appear
A
ance of a matte (dull), frosted, or
Heavy
Commercial
granular surface appearance.
Surface
Benchmark
As demonstrated in the testing, the
Distress
special “shock” version of the FZG
y
~
—28—
VOLUME 77, NUMBER 5
NLGA
“Tribotest journal 5-1, September 1998. (5) 79
the formulation of this type of product. Proper viscosity
is important to assure the formation of a suitable film
thickness necessary to separate the surfaces of gears
in motion, and for the film to span the dimensions of
particulate contaminants. For speeds too low to estab
lish EHD lubrication, special additives must be included
in the formulation to prevent metal-to-metal contact.
Open gear lubricants designed for industrial or mining
applications have distinct compositional differences,
which are necessary to address OEM requirements.
Formulations for open gear lubricants can be tailored to
meet the unique needs of each application, and labora
tory bench testing can be used to characterize and
even differentiate performance of the finished
lubricants.
FZG remains a versatile and valuable tool for the
evaluation of wear prevention and load carrying char
acteristics of additive systems for open gear lubricants.
Modification to the traditional testing methods such as
the previously disclosed “shock” test can provide clear
differentiation among high-EP lubricant candidates,
something standard test versions could not.
4. Cann, PM. “Grease Lubricant Film Distribution in
Rolling Contacts” NLGI Spokesman (1997) Vol 61(2)
p22 29.
—
5. Cann, PM. and Hurley, S. “Grease Composition
and Film Thickness in Rolling Contacts” NLGI
Spokesman (1999) Vol 63(1) p12-22.
6. ASTM D2509-03(2008) Standard Test Method
for Measurement of Load-Carrying Capacity
of Lubricating Grease (Timken Method) ASTM
International, West Conshohocken, PA.
7. ASTM D2596-97(2008) Standard Test Method
for Measurement of Extreme-Pressure Properties
of Lubricating Grease (Four-Ball Method) ASTM
International, West Conshohocken, PA.
8. ASTM D51 82-97(2008) Standard Test Method
for Evaluating the Scuffing Load Capacity of Oils
(FZG Visual Method) ASTM International, West
Conshohocken, PA.
9. ISO 14635-3:2005 FZG Test Method A12,8/50
for Relative Scuffing Load-Carrying Capacity and
Wear Characteristics of Semifluid Gear Greases
International Standards Organization (2007)
Acknowledgements
The authors would like to thank the Lubrizol
Corporation for permission to publish this paper. They
would also like to acknowledge the contributions of
the Lubrizol mechanical testing group, blend services,
and film strength testing laboratory. Special thanks to
Dwight Parham, Dr. Gareth Fish and Bill Hankes for
their knowledge and advice.
10. Rudnick, L. “Lubricant Additives: Chemistry and
Applications (Second Edition)”
11. Ward, W.C. and Fish, G. “Extreme Pressure
Performance of Greases: Passive EP Additives”
Presented at the NLGI 79th Annual Meeting Palm
Beach, Florida June 9-12, 2012.
References
12. Risdon, T.J. “Molybdenum Disulfide in Greases
A Review” (2005) Presented at the NLGI 72nd
Annual Meeting San Antonio, Texas October 30
November 1, 2005.
1. Brown, TO., Hildebrant, K.A., and Slack, D.A.,
“Development of an Improved Open Gear Lubricant”
Journal of the Society of Tribologists and Lubrication
Engineers
–
13. Fish, G. “A Comparison of Laboratory Scuffing
Load Tests” presented at Load Capacity Testing
of Lubricants, 23rd May 1990, published by I.
Mech. E.
2. Nicholas Samman and Shek N. Lau. “Grease-based
Open Gear Lubricants: Multi-service Products
Development and Evaluation.” NLGI Spokesman,
1998, Vol. 62, No. 9, p.34.
–
14. Molykote® 1991 English Edition, Henderson, G.
and Wersig, S. eds Molykote (1991)
3. Philip L. De Vaal, “Open-Gear Lubrication: Meeting
Industrial Requirements using Laboratory Techniques
—29—
NLGI SPOKESMAN, NOVEMBER/DECEMBER 2013
—
NLG~
ABOUT THE AUTHORS
John Lorimor, CLS, CLGS The Lubrizol
Corporation Lorimor is currently Global
—
—
f
~
Commercial Manager, Grease Additives
within the Lubrizol Corporation. He has
been employed at Lubrizol’s Wickliffe,
Ohio headquarters since 2006. John has
over 18 years total lubricants industry
experience, previously holding the posi
was the recipient of the NLGI Author Award at the 2010 annual
meeting. John is an STLE Certified Lubrication Specialist (C.L.S.®),
and was among the first to receive the NLGI Certified Lubricat
ing Grease Specialist (CLGS®) designation. He is a long-standing
member of STLE, and an active participant in the NLGI.
Chris Hsu, Ph.D. The Lubrizol Cor
poration Chris received his Ph.D. from
the Department of Chemical Engineer
ing; Penn State University in 1990, He is
currently a Senior Research Chemist for
Lubrizol, focusing on grease formulation
and ASTM bench testings.
—
—
Grease Additives, also for Lubrizol. Prior
to joining Lubrizol, John held several technical positions with NLGI
member companies, including leadership roles in research and
development, technical service, and grease manufacturing opera
tions. John obtained his B.S. degree in Chemical Science from
Kansas State University in 1994, and his MBA from the University
of Phoenix in 2001. He has authored multiple papers for NLGI, and
Auburn University Student, Tim Hall
Receives Tribology Minor Scholarship from NLGI
T
of
im the
HallNLGI
was Scholarship
selected by Auburn
for the new
University
Tribology
as the
Minor
recipient
program. Hall was born in Dothan, Alabama and moved to
Tallahassee, Florida when he was four years old. Growing up,
he had an affinity for fixing things. In high school, Tim owned
his own lawn business and did maintenance on his own
equipment. This love for fixing mechanical things is what led
him to major in Mechanical Engineering at Auburn University.
Being from Florida, attending Auburn was only made possible
due to the generosity of scholarships. The Tribology Minor
was something that Hall hadn’t planned on until his junior
year at Auburn. After co-opping in maintenance for a paper mill, he began to learn about
the extreme importance of lubrication, and witnessed how merely changing the type of
grease used in the rope sheaves could double the life of the bearings. Upon returning to
Auburn the following semester, he learned about the Tribology minor degree program and
immediately became interested. Tim looks forward to using the added knowledge from the
Tribology Minor with his Mechanical Engineering degree in industry upon graduation.
—30—
VOLUME 77, NUMBER 5