Industrial gearboxes are the workhorse of modern manufacturing. These machines are oftentimes difficult to find, as they are so well integrated into plant operations. Industrial gearboxes drive a wide variety of manufacturing operations: sugar mills, steel manufacturing, cement manufacturing, water treatment, paper and textile mills, automotive manufacturing, power generation, plastic manufacturing and the mining industry, to name a few.
All of these industries have something in common: They all need to produce more in less time in a smaller space with equipment that is efficient, reliable and long-lasting. Even though these applications may be different, they all operate to the same set of industry standards for industrial gear lubricants.
These specifications have remained fairly static over the past 20 years. Based on evolving end-user demands, however, a few global original equipment manufacturers are coming to the forefront and establishing new and tougher requirements for industrial gear lubricants to reflect modern, real-world conditions.
In the 1950s, a typical large-scale industrial gearbox may have been about the size of the average sport utility vehicle. Today, it would be roughly the size of a wine refrigerator. This size reduction comes with new challenges. Modern gearboxes have much smaller sump sizes, which means less oil is available to lubricate and cool the system. Higher power density in gearboxes leads to an increased operating temperature, which further stresses gearbox components like bearings, gears and seals.
According to Lubrizols market research, end users recognize that higher stress on their equipment is driving the need for higher-performing industrial gear lubricants. Bearings and gears can fail due to fatigue or wear, or a combination of both.
Fatigue failures include pitting, spalling, white etching corrosion, and other failure mechanisms.
Wear failures include metal removal due to heavy loading or inadequate lubricant protection.
A properly formulated industrial gear lubricant is crucial to protect gearbox components from both types of damage.
Climbing Expectations
Years ago, basic industrial gear lubricants were required to meet US Steel 224, which addressed gearboxes in steel mills. This specification includes requirements for extreme pressure, corrosion inhibition, yellow-metal protection and the ability of the lubricant to separate water. Another specification, AGMA 9005-E02 from the American Gear Manufacturers Association, built on the basic US Steel 224 with additional requirements for rust and oxidation performance, load carrying as shown in FZG testing, demulsibilty and foam testing.
Lubricants formulated to meet the European DIN 51517 specification are more advanced. This specification requires the lubricant to provide a level of bearing protection and seal compatibility.
Premium gear lubricants meeting the specific needs of major OEMs, such as SEW Eurodrive, Siemens MD (formerly known as the Flender specification), Hansen Industrial Transmissions and others, go many steps further in protecting critical gearbox components. These OEMs have specifications requiring advanced bearing protection, gear micropitting resistance, and compatibility with the many different materials found in a modern gearbox, such as paints and liquid and elastomeric seals.
Balancing New and Old
How are lubricant and additive manufacturers responding to these evolving needs? As noted above, in order to meet the requirements of the industry specifications and the realities of modern gearbox operating conditions, lubricants need to provide:
Superior bearing protection.
Greater oxidative/thermal stability.
Increased fatigue/micropitting resistance.
Extended drain intervals.
Improved seal/elastomers compatibility.
Better demulsibility and foam control.
Enhanced paint/coating compatibility.
As formulators work to meet multiple evolving OEM specifications, they also have to ensure that new fluids simultaneously meet the older legacy specifications. They must also consider the needs of the industrial manufacturing shop owner who wants to simplify the number of different fluid types kept in inventory, so that one fluid can cover a range of equipment.
Along with the introduction of new specifications comes new tests. This can present scheduling delays in situations in which these new tests are not widely established in the industry, thereby creating bottlenecks in obtaining product approvals.
Today, the biggest challenge a formulator faces is finding chemistry that not only provides protection for bearings and gears under the difficult conditions of high speed, pressure and temperature, but does so without compromising the paints, adhesives and elastomers in the system.
Down in the Micropits
To illustrate this point, we will present two case studies: one with a focus on micropitting protection, and the other with a focus on paint/coating compatibility.
In Case Study 1, to increase the micropitting protection and extend the breadth of base oil coverage, a new phosphorus chemistry was synthesized and tested in key antiwear and micropitting tests.
Starting with the thinnest ISO viscosity grade, tribological tests were run to establish minimum extreme pressure, antiwear and friction modifier contents. Once an optimal wear additive package was developed and validated across various base oils, it was checked to ensure that it had no detrimental effects on key compatibility tests.
The rest of the additive package was developed around the antiwear core and run through all of the specification tests in API Group I, Group II and synthetic base stocks.
The new chemistry performed well in important legacy tests such as Timken and Four-ball Wear tests, as well as in the tests of more modern OEM requirements: gear scuffing, bearing wear, micropitting and corrosion protection (see photos page 62).
Preserving Paint
New environmental regulations encourage the use of water-based paints. Unfortunately, these types of coatings are more susceptible to damage when exposed to lubricants than traditional solvent-based types. For the industrial gear oil formulator, this presents another challenge, since the formulations of most paints are proprietary to their respective manufacturer. In addition, tests that need to be run to confirm coating compatibility often have very limited capacity. This puzzle led to Case Study 2.
By working closely with the coatings division of a major company, researchers developed an internal screening test to deepen understanding of paints and paint testing. From there, a matrix of controlled tests was statistically designed to maximize the number of tests that could be run in a short timeframe.
Test results led to the development of a robust synthetic-based industrial gear oil that did not affect surfaces coated in water-based paints, as seen in the photos above.
While focusing on solving one challenge, the formulators needed to simultaneously consider the impact their approach would have on the other challenge. This ultimately resulted in a lubricant formulation that met and surpassed two (potentially divergent) requirements and was compatible in a myriad of global base stocks.
Look Ahead, Not Back
After many years of relative stability (or stagnation), industrial gear oil specifications have recently entered a phase of significant upgrade. The methods and materials used to build gearboxes in the 1950s are very different from today. Advances in the composition and surface finishing of gear teeth and bearing metallurgy require corresponding advances in lubricant formulations.
Adding to the demands placed on the lubricant today are changes in other gearbox components, such as interior protective coatings, shaft seals composed of newer elastomers, and tighter bearing tolerances to facilitate greater precision, quieter operation and efficiency.
With the introduction of new, more robust specifications containing test methods that reflect modern equipment needs, our industry needs to reconsider maintenance of the outdated heritage specifications.
Should the old specifications be modified or declared obsolete?
Should the old tests be replaced with more technically relevant ones?
Considering the diminishing relevance to modern equipment, does our industry recognize the financial burden the old tests carry?
Has our industry considered the impact these heritage specifications have on the time required to bring new technologies to market?
OEMs recognize that a higher-performing lubricant helps ensure their gearboxes can operate closer to the design parameters they intended. Its a brave new world for industrial gear technology, and OEMs are leading the way in aligning their specifications with modern real-world conditions.
Lubricant and additive companies are working quickly to meet these new and evolving specifications, but need help to simplify the lubricant development and testing process.
Our industry needs to embrace and evolve higher-tier specifications rather than relying on legacy standards. This will enable higher-performing lubricants to be brought to market faster, with less wasted cost in outdated testing. New specifications could result in delivery of dedicated lubricants with balanced performance attuned specifically for todays industrial gearbox designs.
David Hobson is technology manager – industrial additives, at Lubrizol Ltd. in Hazelwood, U.K., and Tim Cooper is the companys industrial product manager for Europe, Africa and the Middle East. For information about this article, e-mail David.Hobson@Lubrizol.com orTim.Cooper@Lubrizol.com.