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BY TIM COOPER, THE LUBRIZOL CORPORATION

I t would be great if industrial gears ran in cool, clean anddry environments. However, conditions in gear-driven

operations such as steel mills, manufacturing plants andother strenuous industrial applications are anything but cool,clean and dry. That’s why lubricant selection can be so chal-lenging.

Changes Impacting Gear Oil LubricantsHarsher Environments

Even with regular lubricant maintenance, heat, higherloads and pressures, and contaminants such as water cancompromise a gear system. Today’s gear-driven equipment,and the lubricants that protect and allow them to performwell over the long haul, must withstand increasingly harshenvironments that also cause quick consumption of essen-tial gear oil additives. This is partly due to the trend towardsmaller machines and exposure to diverse applications and

punishing operating conditions. In addition, maintenanceand plant managers expect higher performance, less down-time and more productivity to decrease costs and improveprofits.

Gearbox Size Today’s gearboxes typically are smaller and made from

newer, lighter-weight materials than before. But, thesesmaller, lighter pieces of equipment are pushed to producemore power and, at the same time, be more durable and reli-able than before.

Downsizing gearboxes means less oil and additive to lubri-cate and protect gears. However, at the same time,equipment loads are increasing. That translates into highertemperatures and more rapid oxidation. Oxidation harmsindustrial gear oils because it can form sludge that canshorten both oil and gear life. The results are expensive down-time, repair or replacement costs.

Selecting the Right OilTo handle increased demands, today’s industrial gear oils

must contain high-performance additive chemistry. The goalis to keep the lubricant thermally stable and robust enoughto ensure that it lasts longer, protects better and performsmore efficiently, while at the same time keeping the systemclean and carrying away heat and contaminants. This is noeasy task. Consider industrial gear oils that at one time werewidely acceptable for a given application. Even if these oilsmeet minimum industry specif ications, which can remainunchanged for up to 10 years, they may not be durableenough to protect your equipment.

There are f ive factors to keep in mind when selectingindustrial gear oil that will provide you optimum perform-ance and profitability. Each is discussed in this article.

Selecting the Right Industrial Gear Oil

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Fluid CleanlinessSmaller gearboxes must do the same amount of work as,

or even more than, their larger predecessors. But spaces aresmaller and tolerances are tighter. That translates to higherspeeds and loads. The trend toward smaller reservoirs meansthe system must cycle the fluid more often with less time todissipate heat, release foam, settle out contaminants anddemulsify water.

Constant gear rolling and sliding produces friction andheat. The heavier operating loads common in today’s indus-trial settings increase metal-to-metal contact or boundarylubrication, producing even more heat and pressure. To meetlonger drain intervals for environmental and cost reasons, thefluid stays in the system longer. Therefore, fluid cleanlinessand performance retention becomes critical.

Highly viscous lubricants generate heat from internal fluidfriction and also may consume more power to turn the gears.The rate of oxidation in the f luid can increase, whichdecreases the fluid’s effectiveness and life. In addition, higheroperating temperatures increase sludge and varnish forma-tion, which can damage equipment by forming deposits thatcan block filters, oil passageways and valves. On the otherhand, less viscous lubricants generate less heat, minimizingthe chance of exceeding recommended operating tempera-tures or damaging equipment.

Lubricants play a critical role in removing contaminantssuch as dirt, water, wear particles and other foreign matterthat can damage gears and bearings and impact eff icient,smooth running of the gears. As the lubricant travels throughthe filter system, contaminants, which can originate outsidethe system or from wear inside, should be removed. Evenother lubricating fluids that f ind their way into the systemcan cause contamination if they are incompatible, therebyreducing performance.

Because they don’t move easily through the f iltrationsystem, highly viscous lubricants can be diff icult to f ilter.Pressure at the filter can increase and, if sufficiently high, willtrigger a system bypass, allowing contaminant-laden lubri-cant to circumvent the filters. Equipment damage can follow.Worn gears and higher levels of iron in the lubricant are signsof an ineffective filtration system.

Less viscous lubricants can flow more easily through thef iltration system. Contaminants are effectively removed,reducing the likelihood of gear and bearing damage, andincreasing equipment life. Another benefit is that the lubri-cant may need to be changed less frequently, resulting in lessdowntime and cost.

Fluid DurabilityIndustrial gear oils must be durable enough to withstand

in-service conditions and to retain that performance overtime. Although many f luids may meet the industry specif i-cation when new, they rapidly lose performance while inservice. Industrial gear oils formulated for extended dura-bility will keep gears operating properly and protectequipment investment by extending life, reducing down-time, maximizing productivity and lowering maintenancecosts.

Industrial gears often operate under heavy loads andrequire extreme-pressure protection for gear components.Typical industrial gear oils do not always provide highextreme-pressure performance at low viscosity grades. Thischallenges the notion that industrial gears performing inharsh environments must have highly viscous lubricants tobe adequately protected.

Fluid DemulsibilityIt 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 plantmaintenance can enter the reservoir breather, formingcondensation in the reservoir after hot-running equipmentcools after shutdown. Or, water may enter in some otherway. In any case, it can lead to corrosion and decreaseperformance.

It is vital for the gear oil to be formulated to quickly sepa-rate water at both the high and the low temperatures foundin industrial gearboxes. The ability to rapidly drain waterfrom the system helps extend the life of both the compo-nent and the oil. Figure 1. Industrial Gear Oil Trends

Changes inindustrial gearboxes

• 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

Lubricant attributesOil property retention Oxidative, viscosity, thermal stabilityImproved lubrication Micropitting resistance Bearing protectionImproved performance Demulsibility Seal performance

Universal vs. Dedicated FluidsThere are two types of industrial gear lubricants. The first,

so-called universal gear oils, are formulated so they may alsobe used in automotive gear applications. Universal fluids maycontain components that are both unnecessary for andharmful to industrial gear performance. Or, they may notcontain components that are necessary in industrial applica-tions. For example, water separation is not necessary inautomotive gear oil applications. However, water separationis critical in industrial gear oil applications; therefore, demul-sibility additives must be incorporated.

The second type of gear oil lubricant is called a dedicatedfluid. These fluids are tailored for industrial applications bycarefully formulating the lubricant with additive componentsspecifically designed for such applications.

The Right AdditivesAdditives used to enhance extreme-pressure properties in

gear oil can be prone to thermal instability, resulting in sludgeformation. However, technology is available that provides theoptimum balance of thermal stability for sludge-free gear-boxes and also extreme-pressure protection for heavy-dutydurability.

The combination prolongs gearbox life, maximizes eff i-ciency and eliminates downtime. But most important, highextreme-pressure performance and cleanliness are main-tained across a full spectrum of viscosity grades, down to ISOVG 68. Using a lower-viscosity grade can improve efficiencywhile maintaining durability for optimum performance.

In industrial settings, equipment downtime signif icantlyimpacts the bottom line. A lower-viscosity lubricant withoptimized additive technology effectively protects gear-driven equipment and ensures its operation at maximumperformance.

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 theindustrial additives product line, which encompasses hydraulic, turbine,industrial gear and grease additives. Tim has worked at Lubrizol for 23years in a variety of technical and commercial positions in both the UnitedKingdom and the United States. These roles have covered a broad spec-trum of activities including additives for industrial lubricants, paints andcoatings, specialty monomers and surfactants. He earned an honor’sdegree in applied chemistry from Trent Polytechnic in 1985. For more infor-mation, visit www.lubrizol.com.

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