Tried and tested: How the right questions can unlock gear oil performance

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INDUSTRIAL

Tried and tested: How the right questions can unlock gear oil performance Chris Pether, Industrial CTS Specialist, Afton Chemical and Paul Norris, Senior R&D Scientist, Afton Chemical

Developing the next generation of gearbox lubricants demands a fresh look at how gear oil is evaluated.

External testing tells only half the story – whether a lubricant has passed or failed.

But what we really want (and need) to know is: Why? And how can we improve on that?

Additive companies with in-house and bespoke test rigs are uniquely positioned to bring together expert insights from OEMs, part suppliers and formulators and improve understanding of how oil, additives and hardware interact. Afton Chemical argues that collaboration offers the most flexible and direct route to reliable next generation gear oils, even for the most severe applications.

The combination of engineering changes as well as the more severe operational use puts more stress on the gearbox and the lubricants that protect it.

It’s no small feat for a single lubricant to deliver balanced performance across a range of operating conditions, while providing focused protection on critical elements such as bearings, seals and material compatibility.

Evolving equipment design:

Challenging times Industrial OEMs are tasked with reducing the physical size and weight of the gearbox while increasing the torque output. Amplified torque density demands improved gear and bearing wear protection from the lubricant under higher loads, extreme pressure and even shock loading, depending on the application.

New bearing types Roller bearings come under considerable stress when the input shaft is rotating faster. Larger-diameter steel roller bearings can handle higher loads but have reduced speed capacity, so many OEMs are moving towards the use of journal bearings instead. These space-saving bearings can handle greater loads and higher speeds but present a challenge due to the different metallurgy. The gear oil must ensure that all metals in a journal bearing are protected from any chemically corrosive elements, and that an effective tribo layer is present to prevent wear damage from start-up to fully operational temperature and speeds.

Consumers expect gearboxes to last longer while also running them for extended periods of time or even continuously. Lengthier operation at higher temperatures requires excellent thermal and oxidative stability to stop the by-products of lubricant breakdown, such as acids, from building up and attacking sensitive gear, bearing and seal surfaces.

Seal performance at speed Higher operating speeds place huge demands on seals, which are designed to keep the lubricant contained within the gearbox and keep external contaminants such as dust and moisture out. Multiple seals comprising different elastomers are used depending on the task they must do and the environment they Continued on page 12

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work in. The challenge for the lubricant is to be fully compatible with a broad range of elastomer materials to help preserve the flexibility and function of seals under static and dynamic conditions, often for extended durations.

applications, such as wind turbines. Long-term partnerships with equipment builders, parts suppliers and materials manufacturers have resulted in proven additive technology that performs reliably in operation.

Material compatibility As well as seals, lubricants must also be compatible with many other materials, from the paint inside the gearbox casing to an array of sealants and component coatings. Compatibility issues can cause sealants to harden or paints and coatings to flake off. This can remove functional or protective layers and contaminate the lubricant, limiting gearbox performance and longevity. New paints, coatings and sealants are often introduced by OEMs, so a focus on compatibility early in the lubricant development program is essential for minimising the risk of component failure in the field.

Lubricant testing capabilities

Diverse applications: Gearboxes are used in an array of applications from power generation to mining, materials processing to production and warehousing, and marine propulsion to port operations. In addition to the overarching trends of increased torque and reduction in gearbox footprint, each OEM will also consider specific application needs which can give rise to conflicting OEM fluid specifications.

For oil companies who are looking for broad coverage lubricants, these conflicts must be resolved within the additive chemistry. Improving the performance and longevity of all gearbox components including lubricant is a shared objective for OEMs, elastomer manufacturers and lubricant suppliers.

Insight-driven development The bringing together of appropriate engineering expertise, in-depth additive understanding and fluid evaluation capabilities at the earliest stage of development generates the most useful and actionable insights. Additive systems offering the right performance, longevity, and compatibility with innovative new materials are most likely to be achieved successfully through collaborative development.

This has certainly been the case when developing lubricant additives for extremely demanding

Whenever hardware and lubricant specifications are evolving, especially when this is happening rapidly as it is for industrial gearboxes, fluid evaluation capability becomes integral to success.

In-house test rigs provide early access and setup flexibility to run both standard and bespoke test procedures, offering an opportunity to gain a deeper understanding of exactly which factors are influencing gearbox and lubricant performance, and why.

Being able to explore these factors to improve fluid formulation and equipment reliability helps OEMs to bring new gearbox developments to market with greater speed and confidence.

Recognising this, installing test equipment for all the latest gear oil specifications is a logical step to take. This enables teams of mechanical engineers and chemists to work even more productively with gearbox OEMs, parts suppliers and oil companies to resolve specific hardware and lubricant challenges.

Next generation gearbox fluids can be developed faster, as bespoke tests can be devised to better predict real world lubricant performance at an earlier stage. Given current hardware trends, the focus areas for testing should include seal and bearing compatibility.

Figure 1: Gearbox

Seal testing Conventional sealing rings have a maximum service life that depends on several factors: how much strain the operating cycle places on the seals – speed, starts and stops, dynamics – and how long the gearbox is Continued on page 14

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operating for. Higher fluid specifications for the latest seal materials has led to a doubling of the testing time in the classic dynamic seal test, from 1008 to 2016 hours. Being able to conduct and evaluate these results enhances our understanding of this area and prepares us for the next step change in performance requirements.

Bearing testing Testing effective wear protection for journal bearings has also come under the microscope. Journal bearings have a greater area of surface contact than roller bearings, but involve a softer metal (often copper alloy, nickel or aluminium alloy) moving against a harder metal – steel.

The challenge is to ensure that the lubricant film forms just as effectively on the softer metal as on the steel, and that this protection is in place from start-up.

Being able to examine this closely has helped the understanding of the best chemistries for protecting journal bearings – especially at high temperatures and in the presence of water.

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Today and tomorrow It is a demonstrable fact that technology that stands the test of time in the field is ultimately what counts.

Winning the reliability battle is as much about looking ahead to future requirements as meeting current needs. Close collaboration between gearbox OEMs, part suppliers and oil companies is a vital step towards understanding those changing needs and to quickly build new test capability as required. This enables finished lubricants to be developed with greater speed and confidence.

Whether top tier synthetics with outstanding longevity or mineral fluids with excellent dynamic seals performance, a tried and tested collaborative development approach is crucial if next generation fluids are to get the market’s seal of approval.

LINK www.aftonchemical.com