For formulators of industrial gear oils, there are more moving parts than ever. Lubricants for gearboxes must meet test requirements for lingering legacy specifications as well as a proliferating number of new standards that are evolving rapidly and demanding increasingly higher performance. In addition, there are tougher field conditions to surmount, more materials to be compatible with, and stricter raw material regulations.
Its tough to keep up, said David Hobson, a Derbyshire, United Kingdom-based technology manager for Lubrizol. Following about a decade of relative stability, specifications for industrial gear oils began undergoing massive changes around 2010, said Hobson, speaking at the UNITI Mineral Oil Technology Congress in Stuttgart, Germany, earlier this year.
Adhere to the Tiers
Fifteen years ago, two types of gear oil requirements dominated the market: a lower, fit-for-purpose tier and a higher-quality second tier (that had yet to require micropitting resistance). Tons of government, industry and original equipment manufacturer specifications – such as U.S. Steel 224, DIN 51517 and Fives Cincinnati – also were in effect that formulators, using various base oil grades and viscosities, needed to meet to be competitive.
By 2005, micropitting resistant requirements were introduced, creating a niche Tier 3 of products shepherded by specifications such as Siemens MD, Moventas, Hansen and Renk. Around the same time, top-tier wind turbine oil challenges began to emerge, bringing with them a plethora of various compliance standards, such as Winergys and Moventas Winds.
The updates have not been without reason, Hobson noted. Changes in oil characteristic requirements have been driven primarily by harsher field conditions that call for products with greater complexity, increased severity resistance and broader base oil coverage.
Now, all four tiers are prominent, and many formulators need to meet requirements across the board, which makes for dozens of specifications, said Hobson. Its not possible to formulate one lubricant for each specification; we have to consolidate. So, a typical Tier 3 product will meet between 10 and 15 specifications, and it will do that over a broad range of base oils and viscosity grades.
There are also massive contrasts among the various specifications. For example, U.S. Steel 224 requirements have not changed since before 1990, but one particular original equipment manufacturer (OEM) has altered its requirements five times in the past five years.
Another OEM has made eight changes to its compliance criteria since 2002. Widely recognized industry standards such as ISO 12925-1, Chinese GB 5903 and DIN 51517 Part 3 have evolved at different times and to different degrees – some mandating a few rapid changes within the span of a year.
Additive packagers need to develop new formulations to meet new requirements; yet, they also need to test whether their refreshed chemical compositions throw them out of favor with the legacy specifications – which are sometimes completely divergent. For example, many customers still command U.S. Steel 224 compatibility, which requires Timken and 4-ball extreme pressure tests, along with the FZG scuffing test. Timken, for example, is a block-on-ring test that has no relevance to modern gearboxes, yet many products are still forced to pass it, Hobson added.
Tier 3 products today must pass these and many other tests, including micropitting tests such as FVA54 and bearing fatigue assessments including FAG FE-8. Meeting the requirements of these varying performance challenges involves incorporating a broad spectrum of tribological protection qualities. Thats asking a lot from a single lubricant, Hobson pointed out.
The same formulation that needs to satisfy Timken requirements also needs to be state-of-the-art and pass the 600-hour bearing test. Whats quite challenging is the fact that chemicals often used to boost the Timken test hurt the results of a 600-hour bearing test, and vice versa, he noted
Things get even more complicated. In terms of contaminant-handling attributes, while AGMA 9005-EO2 and DIN 51517-3 may require only demulsification and defoaming tests, Tier 2 oils ask for those as well as air release limitations. And each calls for quite different lubricant compositions, he continued.
Defoaming is the collapse of foam on the surface of the lubricant, while air release is release of air from the bulk of the lubricant. Most antifoam agents actually make air release qualities worse. So formulation requires precise attention to base oil composition changes and careful tweaks to an additive package.
Pressed by Tests
Determining the right colloidal composition of a particular additive package is not the biggest challenge, Hobson said. Coming up with a new formulation and testing it in a limited time is.
When a new test is incorporated into a specification, the first thing we do is benchmark our existing technology, he explained. It may pass that test, but if it doesnt, thats when a formulator needs to do a deeper dive. It is important to know which of our components brings positive performance to the test. Depending on whether we have to synthesize new chemistry, how difficult the test is and the availability of the test (which is often a problem), it can take many months to complete that investigation.
Once formulators adjust the technology platform by adding a new component and rebalancing the rest of the elements in the formulation, they must then redo the test programs. If a formulator has 50 specifications to cover, and each specification has at least 10 tests, for example, a typical complete formulation would take more than four years, which no longer aligns with the pace of change in requirements, Hobson said.
A formulator is often in the early stages of development on one specification when the next one is announced, and must stop development to examine the requirements of the new specification and analyze whether to continue on the current path as is, modify the formulation development, or start all over. To further intensify the race against the clock, formulators sometimes may be ready long before the test is. In some cases, a specification is launched, and the tests it calls for arent available for another six months.
Dont Taint the Paint
The change that has the most drastic impact for formulators, he noted, is material compatibility testing. In 2015, a much wider range of materials is used in sealants, paints and adhesives that interact with oils in gearboxes. And the lubricant must play well with them all. Gearboxes contain static seals, dynamic seals, various elastomers and all types of paints and adhesives, and the challenge for formulators comes in making sure the formulation is benign to them all.
Most gearbox oils are packed with surface-active chemistries that improve its performance, such as corrosion inhibitors, demulsifiers, detergents, antifoaming agents and more. They are attracted to a metal-to-oil interface, Hobson said, but they are also attracted to a paint-to-oil interface or water-oil interface.
Gearboxes are often painted both on the inside and the outside to protect the surfaces. If the paint is corroded or chipped, it no longer protects the surface, and paint residue can start to block filters and lead to all sorts of significant oil starvation issues.
On the other side, however, paint manufacturers just like [oil additive formulators], are under pressure to make more environmentally friendly products. Therefore, they are moving from traditional, solvent-based paints to water-based types, which are more susceptible to damage from lubricants. He mentioned that aqueous-based paints seem to be particularly prone to incompatibility with lubricants formed with synthetic base stocks.
What makes it even more challenging, he continued, is not knowing ahead of time what a formulation will need to be compatible with. There are probably 10 or 15 surface-active components in a paint and the same number in a lubricant. We know what we put in our lubricants and [paint makers] know what they put in their paints, but thats as far as it goes. Its all very proprietary, black box knowledge.
Understandably, he went on, the responsibility to make sure the products work well together falls primarily on the lubricants side of the equation. Paint manufacturers are under pressure to deliver cost-effective components that meet environmental regulations. At the development level, there is no formal requirement for paint formulas to be compatible with oil at this time.
Lubrizol set out to develop an industrial gear oil in a synthetic base stock that was compatible with aqueous-based paints and needed a way of determining what was causing paint compatibility issues in real time. The company surmounted this particular challenge by collaborating with its own internal coatings division and paint laboratory to understand paints and paint testing, and thus developed an internal screen test.
Hobson said the company was able to dramatically improve its synthetic-based industrial gear oils compatibility with aqueous paints.
Pit Your Wits against Micropitting
Micropitting is fatigue failure on gears and bearings that results in micron-sized pits in the surface. It is one of the most prevalent adversaries of a gear oil, Hobson espoused.
Lubrizols API Group I formulations provided successful micropitting resistance, but with Group I refineries closing and the severity of most applications increasing, more and more customers began calling for Group II, Group III and synthetic base oils. Lubrizol knew that its additives needed to perform in a broader range of base stocks, Hobson said. We needed to optimize our additive technology to specifically address micropitting and simultaneously satisfy new material compatibility requirements.
The team had already internalized the FVA54 test, but needed to balance chemistry for a number of other tribological trials, including extreme pressure, antiwear and friction modification. Lubrizol built an additive package that resulted in an enhanced industrial gear oil formulation that performed better in key industry and OEM tests that measure wear resistance, material compatibility and corrosion protection.