LUBE SELECTION
REPRINT FROM MACHINERY LUBRICATION
NOVEMBER - DECEMBER 2008
Selecting the Right
Industrial Gear Oil
BY TIM COOPER, THE LUBRIZOL CORPORATION
t would be great if industrial gears ran in cool, clean and
dry environments. However, conditions in gear-driven
operations such as steel mills, manufacturing plants and
other strenuous industrial applications are anything but cool,
clean and dry. That’s why lubricant selection can be so challenging.
I
Changes Impacting
Gear Oil Lubricants
Harsher Environments
Even with regular lubricant maintenance, heat, higher
loads and pressures, and contaminants such as water can
compromise a gear system. Today’s gear-driven equipment,
and the lubricants that protect and allow them to perform
well over the long haul, must withstand increasingly harsh
environments that also cause quick consumption of essential gear oil additives. This is partly due to the trend toward
smaller machines and exposure to diverse applications and
punishing operating conditions. In addition, maintenance
and plant managers expect higher performance, less downtime and more productivity to decrease costs and improve
profits.
Gearbox Size
Today’s gearboxes typically are smaller and made from
newer, lighter-weight materials than before. But, these
smaller, lighter pieces of equipment are pushed to produce
more power and, at the same time, be more durable and reliable than before.
Downsizing gearboxes means less oil and additive to lubricate and protect gears. However, at the same time,
equipment loads are increasing. That translates into higher
temperatures and more rapid oxidation. Oxidation harms
industrial gear oils because it can form sludge that can
shorten both oil and gear life. The results are expensive downtime, repair or replacement costs.
Selecting the Right Oil
To handle increased demands, today’s industrial gear oils
must contain high-performance additive chemistry. The goal
is to keep the lubricant thermally stable and robust enough
to ensure that it lasts longer, protects better and performs
more efficiently, while at the same time keeping the system
clean and carrying away heat and contaminants. This is no
easy task. Consider industrial gear oils that at one time were
widely acceptable for a given application. Even if these oils
meet minimum industry specifications, which can remain
unchanged for up to 10 years, they may not be durable
enough to protect your equipment.
There are five factors to keep in mind when selecting
industrial gear oil that will provide you optimum performance and profitability. Each is discussed in this article.
1 November - December 2008
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Fluid Cleanliness
Smaller gearboxes must do the same amount of work as,
or even more than, their larger predecessors. But spaces are
smaller and tolerances are tighter. That translates to higher
speeds and loads. The trend toward smaller reservoirs means
the system must cycle the fluid more often with less time to
dissipate heat, release foam, settle out contaminants and
demulsify water.
Constant gear rolling and sliding produces friction and
heat. The heavier operating loads common in today’s industrial settings increase metal-to-metal contact or boundary
lubrication, producing even more heat and pressure. To meet
longer drain intervals for environmental and cost reasons, the
fluid stays in the system longer. Therefore, fluid cleanliness
and performance retention becomes critical.
Highly viscous lubricants generate heat from internal fluid
friction and also may consume more power to turn the gears.
The rate of oxidation in the fluid can increase, which
decreases the fluid’s effectiveness and life. In addition, higher
operating temperatures increase sludge and varnish formation, which can damage equipment by forming deposits that
can block filters, oil passageways and valves. On the other
hand, less viscous lubricants generate less heat, minimizing
the chance of exceeding recommended operating temperatures or damaging equipment.
Lubricants play a critical role in removing contaminants
such as dirt, water, wear particles and other foreign matter
that can damage gears and bearings and impact efficient,
smooth running of the gears. As the lubricant travels through
the filter system, contaminants, which can originate outside
the system or from wear inside, should be removed. Even
other lubricating fluids that find their way into the system
can cause contamination if they are incompatible, thereby
reducing performance.
Changes in
industrial gearboxes
Lubricant attributes
Oil property retention
Oxidative, viscosity,
thermal stability
Improved lubrication
Micropitting resistance
Bearing protection
Improved performance
Demulsibility
Seal performance
• Power increased
• Weight and size reduced
• Oil volume lowered
• Greater reliability and
durability required
• Cost to produce lowered
• New materials and surface
finishing used
• Teeth and bearing
loadings increased
• Gearbox temperatures
increased
Industrial gearbox changes are key drivers for improved industrial gear oils
Figure 1. Industrial Gear Oil Trends
2 November - December 2008
Because they don’t move easily through the filtration
system, highly viscous lubricants can be difficult to filter.
Pressure at the filter can increase and, if sufficiently high, will
trigger a system bypass, allowing contaminant-laden lubricant to circumvent the filters. Equipment damage can follow.
Worn gears and higher levels of iron in the lubricant are signs
of an ineffective filtration system.
Less viscous lubricants can flow more easily through the
filtration system. Contaminants are effectively removed,
reducing the likelihood of gear and bearing damage, and
increasing equipment life. Another benefit is that the lubricant may need to be changed less frequently, resulting in less
downtime and cost.
Fluid Durability
Industrial gear oils must be durable enough to withstand
in-service conditions and to retain that performance over
time. Although many fluids may meet the industry specification when new, they rapidly lose performance while in
service. Industrial gear oils formulated for extended durability will keep gears operating properly and protect
equipment investment by extending life, reducing downtime, maximizing productivity and lowering maintenance
costs.
Industrial gears often operate under heavy loads and
require extreme-pressure protection for gear components.
Typical industrial gear oils do not always provide high
extreme-pressure performance at low viscosity grades. This
challenges the notion that industrial gears performing in
harsh environments must have highly viscous lubricants to
be adequately protected.
Fluid Demulsibility
It would seem easy enough to keep a gearbox dry, but
water can creep into the system, particularly the reservoir,
in a variety of ways. Mist from water used in routine plant
maintenance can enter the reservoir breather, forming
condensation in the reservoir after hot-running equipment
cools after shutdown. Or, water may enter in some other
way. In any case, it can lead to corrosion and decrease
performance.
It is vital for the gear oil to be formulated to quickly separate water at both the high and the low temperatures found
in industrial gearboxes. The ability to rapidly drain water
from the system helps extend the life of both the component and the oil.
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Universal vs. Dedicated Fluids
There are two types of industrial gear lubricants. The first,
so-called universal gear oils, are formulated so they may also
be used in automotive gear applications. Universal fluids may
contain components that are both unnecessary for and
harmful to industrial gear performance. Or, they may not
contain components that are necessary in industrial applications. For example, water separation is not necessary in
automotive gear oil applications. However, water separation
is critical in industrial gear oil applications; therefore, demulsibility additives must be incorporated.
The second type of gear oil lubricant is called a dedicated
fluid. These fluids are tailored for industrial applications by
carefully formulating the lubricant with additive components
specifically designed for such applications.
The Right Additives
Additives used to enhance extreme-pressure properties in
gear oil can be prone to thermal instability, resulting in sludge
formation. However, technology is available that provides the
optimum balance of thermal stability for sludge-free gearboxes and also extreme-pressure protection for heavy-duty
durability.
The combination prolongs gearbox life, maximizes efficiency and eliminates downtime. But most important, high
extreme-pressure performance and cleanliness are maintained across a full spectrum of viscosity grades, down to ISO
VG 68. Using a lower-viscosity grade can improve efficiency
while maintaining durability for optimum performance.
In industrial settings, equipment downtime significantly
impacts the bottom line. A lower-viscosity lubricant with
optimized additive technology effectively protects geardriven equipment and ensures its operation at maximum
performance.
About the Author:
Tim Cooper is The Lubrizol Corporation’s industrial additives product
manager for Europe, Africa and the Middle East. He is responsible for the
industrial additives product line, which encompasses hydraulic, turbine,
industrial gear and grease additives. Tim has worked at Lubrizol for 23
years in a variety of technical and commercial positions in both the United
Kingdom and the United States. These roles have covered a broad spectrum of activities including additives for industrial lubricants, paints and
coatings, specialty monomers and surfactants. He earned an honor’s
degree in applied chemistry from Trent Polytechnic in 1985. For more information, visit www.lubrizol.com.
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