Applying Open

Gear Lubricants
Lawrence G. Ludwig Jr., Schaeffer Manufacturing

Reprinted with permission of Machinery Lubrication magazine

When selecting an open gear lubri-

cant for use in a particular application,
the method of application used must be
considered. The typical methods of ap-
plication used in open gear systems are:
• Spray/atomization systems
• Gravity feed or drip feed
• Oil bath (splash and idler
immersion systems)
• Hand, brush or pour on

Generally, if the open gear lubricant

is to be applied by a drip system, force-
feed lubricator or spray system, it must
be sufficiently fluid in order to flow eas-
ily through the application equipment.
For brush applications, the open gear
lubricant must be fluid enough to al-
low uniform, brush-on coverage on the
teeth. In any case, during operation, the
open gear lubricant must be viscous and
tacky enough to resist squeeze-out from
the gear teeth. When open gears are lu-
bricated by dripping into a splash pan
or through the use of splash and idler
immersion systems, the open gear lubri-
cant must not be so heavy that it chan-
nels as the gear teeth dip into it. Finally,
when open gears are lubricated, the con-
sistency or grade and its ease of pump-
ing must permit easy application under Figure 1 — Correct lubricant spray patterns on tooth flanks.
prevailing, ambient conditions.

Spray/Atomization Systems
The most common type of spray/
atomization system used in the lubri-
cation of open gearing is the intermit-

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 Figure 2 — Placement of spray nozzles; example of three-nozzle spray bar with
spray nozzle spaced apart at 150 mm.

tent, mechanical spray system. Its usage sent down a passage in a spray manifold,
depends upon the open gear lubricant where the open gear lubricant is direct-
remaining on the gear teeth through ed to a nozzle. A second passage of pres-
several revolutions. Intermittent spray surized air (usually in the range of 80
systems utilize metering valves that di- to 120 pounds-per-square-inch) is di-
rect the lubricant to an air/grease nozzle rected to the same nozzle. This pressur-
that sprays the lubricant onto the open ized air blows the open gear lubricant
gears with the assist of air pressure. The out of the nozzle and onto the open
basic components of this type of system gear. After a predetermined amount of
are a pump, controller, metering valve, open gear lubricant is dispensed, both
spray manifold and spray nozzles. the air system and the pump shut off
The operation of this type of system until the next lubrication cycle. Usually
is very straightforward; a signal from a there is a delay in shutting off the air, so
controller turns on the pump to supply as to ensure that the open gear lubricant
the open gear lubricant to a positive-dis- has cleared the nozzle. This removes the
placement metering valve. The metering open gear lubricant from the nozzle
valve can be a progressive, two-line or tip, thus preventing it from drying and
injector type. The metered lubricant is clogging the nozzle.

Table 1 — Lubricant quantity guidelines for intermittent methods of application (Ref. 1)

Gear ¼ Hour 1 1 Hour1 2 Hour1,2
diameter Face width in meter Face width in meter Face width in meter
in (inches) (inches) (inches)
meters 0.2 0.4 0.6 0.8 1.0 0.2 0.4 0.6 0.8 1.0 0.2 0.4 0.6 0.8 1.0
(feet) (8) (16) (24) (32) (40) (8) (16) (24) (32) (40) (8) (16) (24) (32) (40)
3.0 (10) 5.9 8.9 11.8 14.8 7.8 23.7 35.5 47.3 59.2 71 59.1 88.8 118 148 178
3.7 (12) 8.9 8.9 11.8 14.8 17.8 35.5 41.4 53.3 65.1 76.9 88.8 104 133 163 192
4.3 (14) 8.9 11.8 14.8 17.8 20.7 41.4 47.3 59.2 71.0 82.8 104 118 148 178 207
4.9 (16) 11.8 14.8 17.8 20.7 23.7 47.3 59.2 71.0 82.8 94.7 118 148 163 207 237
5.5 (18) 14.8 17.8 20.7 23.7 26.6 59.2 71.0 82.8 94.7 107 148 178 207 237 266
6.1 (20) 17.7 20.7 23.7 26.6 29.6 71.0 82.8 94.7 107 130 178 207 237 266 325
6.7 (22) 20.7 23.7 26.6 29.6 32.5 82.8 94.7 107 118 142 207 237 266 296 355
7.3 (24) 23.7 26.6 29.6 32.5 35.5 94.7 107 118 130 154 237 266 296 325 385
7.9 (26) 26.6 29.6 32.5 35.5 38.5 107 118 130 142 166 266 196 325 355 414
8.5 (28) 29.6 32.5 35.5 8.5 41.4 118 130 142 154 178 296 325 355 385 444
1 The spraying time should equal the time for one and preferably two revolutions of the gear to insure complete coverage.
Periodic inspections should be made to insure that sufficient lubricant is being applied to give proper protection.
2 Two hours is the maximum interval permitted between applications of lubricant. More frequent application of smaller
quantities is preferred. However, where diluents are used to tin lubricants for spraying, intervals must be so short as to
prevent diluent evaporation.

36 powertransmissionengineering february 2012 www.powertransmission.com

 The spraying time should equal the
amount of time it takes for one or two
revolutions to ensure complete cover-
age. Periodic inspections must be made
to ensure that a sufficient amount of
open gear lubricant is being applied to
provide proper protection. Two hours
is the maximum interval time permit-
ted between applications, per AGMA
9005-D94 guidelines.
The amount of open gear lubricant
to use is dependent upon the applica- Figure 3 — Inadequate spray pattern on the tooth flank; inadequate spray
tion—e.g., mills, kilns, dragline, etc.— patterns normally lead to scuffing in these highlighted areas. Additional,
correctly spaced spray nozzles and higher air pressure are required to improve
and the pitch line velocity of the gear- the lubrication film.
ing; the rated electrical power draw on
the electric motor powering the gear
(for mills and kilns); the type of gearing; to provide adequate lubricant coverage
and the type of open gear lubricant to across the entire face of the gear teeth.
be applied. In many applications, your As a guideline, for slow-speed, open
lubricant supplier can recommend the gearing operating up to 2,000-feet-per-
starting amount to use. These applica- minute (10 meters per second), the end
tion rates are expressed in grams-per- nozzles should be placed 2 to 2.5 inches
centimeter-face width-per-hour. In lieu (50 to 65 millimeters) from the gear face
Figure 4 — Recommended spray bar
of a starting recommendation from the edge, with the remaining nozzles spaced design for easy checking of spray
lubricant supplier, AGMA has issued 5 to 7 inches (130 to 180 millimeters) pattern.
lubricant quantity guidelines in the from center. Nozzle location is also a
AGMA 9005-D94 standard that can function of the spray pattern. Spray
be used for intermittent methods of ap- nozzles are generally positioned to di-
plication. rect the open gear lubricant at the loaded
• The spraying time should equal profiles of the gear teeth (not the pinion)
the time for one—preferably at a maximum distance of 6 to 8 inches
two—revolutions of the gear to (150 to 200 millimeters) from the gear
ensure complete coverage. Periodic teeth (Ref. 2). The correct spray pattern
inspections should be made to ensure on the tooth flanks and an illustration of Figure 5 — Spray bars can be located at
four different directions of rotation.
that sufficient lubricant is being the correct spacing of spray nozzles are
applied to give proper protection. illustrated in Figures 1 and 2.
• Two hours is the maximum interval The air pressure to the spray bar also
permitted between lubricant must be properly set; otherwise, the
applications, although a more open gear lubricant will not be atom-
frequent application of smaller ized correctly. Insufficient air pressure
quantities is ideal. However, will result in a splattering, lumpy or
where diluents are used to thin stringy appearance (Fig. 3), while exces-
lubricants for spraying, intervals sive air pressure will tend to blow the
must be brief enough so as to open gear lubricant off of the gear. For
prevent diluent evaporation. most open gear lubricants, the air pres-
sure seating must not be set lower than
To ensure that the correct amount of 75 psi (35 kilopascals or 5 bar) and not
open gear lubricant is applied and oper- higher than 90 psi (42 kpa or 6 bar).
ation reliability maintained, it is impor- Even if the spray nozzles are moni-
tant to maintain a perfect spray pattern, tored using control flow mechanisms,
without any gaps. Distribute the open periodic checks of the spray pattern
gear lubricant evenly over the entire are recommended as part of maintain-
height and width of the tooth flank on ing full and even coverage of the open
the loaded side of the gear. The number gearing on the gear face. Spray bars have
of spray nozzles to use for a given appli- many different designs, and many of the
cation is determined by the gear width. older spray systems do not allow easy
Typically, four to six spray nozzles are access to check the spray pattern while
required; they must be properly spaced the open gearing is operational. If the

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 onto the drive or loaded side of the
pinion or girth gear. Setting the spray
angle at 30° (Fig. 5.) will achieve a very
good distribution of the lubricant in an
upward or downward direction—always
to the load-carrying tooth flank. The
spray nozzle distance set back from the
gear is approximately eight inches, plus
or minus two inches (200 millimeters
plus or minus 50 mm)—depending on
the air pressure and tooth height. The
width of the gear tooth will determine
the amount of spray nozzles required to
adequately lubricate the gear drive.
To further ensure that the proper
amount of lubricant is being applied
once the spray bar nozzles and pat-
terns are set, it is recommended that
the amount of lubricant being ex-
pelled from each injector be weighed.
Over time, injector spray nozzles do
Figure 6 — Properly lubricated open gear.
not deliver the appropriate amount of
lubricant-per-cycle that they are de-
spray bar does not swing out or open signed to deliver. Too much open gear
outward with the door, the safest way lubricant being applied can cause waste,
to check the spray pattern is when the while under-lubrication can lead to in-
machine is shut down. A recommended creased wear and eventual component
procedure for inspecting spray patterns failure. The amount of lubricant needed
is as follows: to be expelled from each injector can
• Ensure isolation procedures are be obtained from the manufacturer of
adhered to, then open the inspection the automatic lubrication system. For
door and place a clean piece of example, a Lincoln SL-1 style injec-
cardboard or paper on the gear set, tor typically expels 0.046 ounces (1.31
where the spray nozzle atomizes the grams) per cycle of lubricant.
open gear lubricant onto the gear set. The timer settings on the automatic
• Operate the lube system and lubrication system should eventually be
check the lubricant coverage set to the shortest frequency, depending
on the cardboard or paper. The upon the type of open gear lubricant
coverage should overlap from one used. For asphaltic and high-viscosity
spray nozzle to the next, and there synthetic/ high-viscosity base fluids, the
should not be any gaps within the typical time-setting interval is 10 to 20
appropriate height and width to minutes, while for semi-fluid greases
cover the load-carrying gear teeth. and gel/polymer-thickened type open
• If gaps are found, the air pressure, gear lubricants, the typical time-setting
spray angle and spray cap interval is 15 to 30 minutes.
need to be adjusted to obtain A strobe light can be used to check
the appropriate coverage. the appearance of the gears during op-
• Once the adjustments have eration. The strobe light should be set at
been made, repeat the process the same speed that the gear is turning.
until the perfect spray pattern A well-lubricated gear will have a dark-
(Fig. 1) is achieved. color to semi-transparent appearance—
depending upon the type of open gear
If the spray bar requires changing, lubricant being used—and strings of lu-
the spray bar design should be altered bricant will appear as the gear and pin-
so that the spray pattern can be checked ion teeth separate. An over-lubricated
during equipment operation (Fig. 4). gear will be black, with excess lubricant
The spray bar should be set at a 30° dripping and flinging off, or built up on
angle to spray the open gear lubricant the teeth and root zones of the gear.

38 powertransmissionengineering february 2012 www.powertransmission.com

 Taking temperature readings across
the gear face using a non-contact ther-
mometer can be also be done to check
if the open gearing is being properly
lubricated. An even temperature across
the gear tooth indicates that the gear is
being properly lubricated.
In addition to being used to check
for proper lubrication, strobe lighting
and temperature reading can be used to
check for misalignment. Any misalign-
ment results in less contact across the
meshing gears, resulting in increased
wear. Roughly a 30°F difference across
the gear tooth and darker to lighter ar-
eas of lubricant across the contact film
indicate misalignment.
Gravity-feed or drip-feed systems.
Gravity-feed or drip-feed systems are
found on mills, kilns, shovels, draglines
and excavators. These systems consist of
Figure 7 — Over-lubricated open gear.
one or more oilers, cascade pans, pres-
surized feed lines or applicator wheels.
They allow the open lubricant to drip lubricant is an asphaltic or high-viscos-
into the gear mesh at a set rate. This ity, synthetic-based fluid-type, the vis-
method of application is limited to cosity of the fluid should be a minimum
open gearing with pitch line velocities of 1,000 centistokes (cSt), at 40°C.
of 1,500-feet-per-minute (7.5 meters- Hand-, brush- or pour-apply it. Man-
per-second) or less. ual application is one of the oldest—and
For these types of systems, asphaltic, most dangerous—methods used to ap-
high-viscosity-synthetic-oil open gear ply open gear lubricants. It has been
lubricants are generally used. If pres- used to apply open gear lubricants on
sured feed lines or applicator wheels mills, kilns, shovels, draglines and ex-
are used in these systems, a semi-fluid cavators. Generally, asphaltic-type and
grease or gel/polymer-thickened type of high-viscosity synthetic-type open gear
open gear lubricant can be used. lubricants are applied by this method.
Oil bath (splash and idler immersion) But using this method can result in
system. Oil bath systems are the sim- not only the improper amount of open
plest method of lubricating open gears. gear lubricant being applied, but also
The gear or an idler in mesh with the can result in the introduction of con-
gear is allowed to dip into the open taminants into the gearing. Further ap-
gear lubricant, carrying it around to the plication by this method while the open
mesh. Idler immersion systems are gen- gearing is operational can compromise
erally limited to open gear systems with safety and result in injury—or death—
pitch line velocities below 300 feet-per- to the person applying the open gear
minute (1.5 meters-per-second). Some lube.
systems will also include re-circulating Lubricating film thickness and selec-
pumps and filtration systems. A splash tion criteria. The primary lubrication re-
and idler immersion system can be gime required to lubricate open gearing
found on mill and kiln applications. is elastrohydrodynamic (EHD) lubrica-
As a general recommendation, as- tion. According to the EHD theory, the
phaltic, high-viscosity synthetic oil, critical factor is the open gear lubricant’s
semi-fluid grease-type and gel/poly- film thickness, which is dependent upon
mer-type open gear lubricant can be the dynamic viscosity of the open gear
used in these systems. If a semi-fluid lubricant at operating temperatures, av-
grease-type of gel/polymer is used, the erage surface velocity of the gear tem-
open gear lubricant must be semi-fluid perature, the loads and geometry of the
to fluid in consistency. If the open gear gearing, etc. It has been established that

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the lubrication condition present in • Ambient temperature encountered in farther than two inches apart.
most gears is predominately elastrohy- the area where the machine operates Procedure for switching from one type
drodynamic. Gear teeth are subject to • Climate condition where the of open gear lube to another: Although it
enormous contact pressures over rela- machine operates, e.g.—ice, is best to completely clean the gear, pin-
tively small areas (possibly as great as snow, wet, dusty, etc. ion and gear guards, conversion of one
435,000 psi), and yet they are success- • How lubricant is applied type of open gear lubricant to another
fully lubricated with very thin films of • If applied by a spray or automatic can be made by applying the open gear
lubricant. There are two reasons for this: lubrication system, the type of lube lubricant to be used directly over most
• The high pressure causes the system that is installed—Farval, existing applications.
surfaces to deform elastically and Lincoln, Worner, Droppsa, etc. Procedure:
spread the load over a wider area. • Type and ratio of the pump utilized
• The viscosity of the lubricant on the automatic lube system • Purge the lube lines thoroughly.
increases considerably with • Width of pinion gear • Start the timing settings 50
pressure, thus increasing the • Is gearing double or single pinion? percent higher than the operational
lubricant’s load-carrying capacity. • Power rating of the electric motor settings to ensure all of the lines
Once the film thickness is deter- • Position and number of spray nozzles are purged and flushed and have
mined, another important parameter Once all of these conditions are built up a sufficient lubricant
to be calculated is the Lambda ratio. known, the proper open gear lubricant coverage film before reducing
This ratio is defined as the ration of for the given application can be selected the lubricant consumption rate
EHD film thickness of the lubricant based upon the different topics, meth- to the operational settings.
to the composite surface roughness of ods of application and characteristics • Readjust the timer to maintain
the contacting metal surfaces. As the discussed in this paper. an adequate lubricant film. The
Lambda ratio approaches one—i.e., the Finally, when switching open gear lubricant quantity should not be
film thickness is of the same order as the lubricants or applying open gear lubri- reduced abruptly, but at five-minute
surface roughness—one can expect that cants on new equipment where no prior intervals of 150 to 200 hours for
there will be increased contact between lubricant was used, the following proce- mills and 100 to 150 hours for
the two contacting gears. dures should be followed: shovels, draglines and excavators.
It should be noted that this calcula- Procedure to follow on new • Product performance
tion is based solely on the base oil vis- equipment: should be monitored.
cosity of the open gear lubricant; it does • When reducing consumption
not take into account any film thickness • Clean all coating and quantity to the control unit of the
contribution that may be made by the debris from the gears. spray system, it should be set to
open gear lubricant’s thickener system • Coat the gear and pinion ensure the intervals between spray
or its solid lubricants. In addition, some with a light film of open gear cycles are as short as possible.
types of open gear lubricants, such as lubricant employing some Short and frequent spray cycles
grease-like and gel/polymer-thickened sort of spray method. ensure the lubricant is supplied
types, may contain light-viscosity base Start-up procedure: evenly to the component, which
fluids. These light-viscosity base fluids increases functional reliability.
are used as a cutback of the heavy-vis- • Run equipment slowly under no • Adjust the air pressure and
cosity base fluids present in the formu- load to verify that there is lubricant volume as needed.
lation in order to enhance pumping of throughout the entire load zone. • Inspections of the lubricating
the product during low-ambient-tem- • Gradually increase speed and systems, tooth flank conditions
perature conditions. The light-viscosity load while turning on the and spray pattern are required
base fluids are volatile and dissipate un- automatic lube system. to ensure reliable operation. The
der operating conditions. Subsequently, • Monitor continuously until a spray system should be maintained
the base viscosity of these open gear proper coating is maintained. thoroughly in accordance with the
lubricants increases, generating a tacky, For spray systems: manufacturer’s instructions.
durable lubricant film that adheres to
the gearing. • Prior to startup, purge the lube References
Besides taking into consideration the lines and check spray patterns 1. ANSI/AGMA 9005-D-94. “Industrial
lubricant film thickness provided by the for complete coverage. Gear Lubrication,” Table 10, Page 10.
selected open gear lubricant, other con- • Adjust the air pressure and 2. Ibid, Page 11.
siderations must be taken into consid- volume as needed.
eration when recommending the proper For drip systems: Lawrence G. Ludwig Jr. is the
type, grade and amount to be applied: chief chemist and technical direc-
• OEM requirements • Most open gear lubricants are tor for Schaeffer Manufacturing
• Type of open gear application— designed to adhere where applied. (lludwig@schaefferoil.com).
mills, kilns, shovels, draglines, etc. Drip tubes should be spaced no

40 powertransmissionengineering february 2012 www.powertransmission.com