Every year, The Timken Company tests numerous greases to determine the best blends for optimal bearing performance. Be it a high-revving race car or hard-working machine, the right grease can reduce wear, extend bearing life and keep maintenance costs from mounting. Whether you manage a steel mill or a motorsports team, grease testing can identify the properties that are most important to your bearings, making it possible to select a formulation that outperforms all others.
At the highest levels of stock car competition, many teams lean on Timken as a lubrication resource, trusting the company’s expertise in bearings and tribology to keep them running all weekend long. This requires a special grease specifically formulated for the extreme operating conditions experienced by bearings in racing hubs. However, as loads, speeds and temperatures on the track have increased over the years, Timken has observed greater wear and discoloration in the wheel end assemblies it regularly inspects and rebuilds for professional racers.
To help teams prevent hub damage and maintain a competitive edge, Timken recently conducted new rounds of testing to identify the best grease for use in its popular RacePac wheel end assemblies.
And while many different greases were put through the paces, only one formulation managed to cross the finish line before excessive heat caused an early break down.
It is important to note that every grease has limiting properties, and there is no universal antifriction bearing grease. Identifying the optimal grease requires a thorough understanding of each specific application, particularly the operating load, speed, temperature and ambient conditions. To help customers meet their most challenging requirements, Timken operates a world-class lubricant testing facility at its global headquarters in North Canton, Ohio, that is equipped with the finest talent, tools and technologies for accurately predicting the impact of different greases on bearing performance. By closely analyzing greases, Timken can recommend better solutions to customers that make sense for their unique needs.
While Timken is best known for bearings, the company has always emphasized the selection of proper lubricants, thus Timken OK Load, a special test machine that was manufactured by Timken from 1935 to 1972 to indicate the possible performance of extreme pressure (EP) additives in a lubricating grease or oil. Today, Timken OK Load remains an industry-recognized standard test to compare the extreme pressure resistance of greases and oils in a reproducible way.
Currently, Timken houses numerous application-relevant test machines at its headquarters facility that not only compare the performance of various lubricants with high resolution, but also identify performance gaps that can help in developing better lubrication solutions for different applications, including wheel hub RacePac assemblies.
And as RacePac testing shows, the right grease can often go the extra mile, equating to less bearing damage and more victory laps.
A Bit About Grease
Grease is used in roughly 80 percent of all bearings in the world. It is typically composed of a base-oil, a thickening agent and additives. Specific base-oils are designed to handle certain applications and environments, while the thickener acts like a sponge to retain and appropriately release the oil. Additives, meanwhile, are used to enhance the various properties of grease including viscosity, load-carrying capacity and resistance to oxidation, corrosion and wear.
Compared to oil, grease tends to stay put within the bearing and requires less maintenance. It can also act as an effective sealant, keeping out contaminants and debris. The downside to grease, compared to oil, is that grease generates higher friction and has poor heat dissipation, making high-speed applications a challenge for greases.
Every grease is a unique formulation having different functional properties. While the manufacturing of grease is not complicated, the ingredients and quantities used in the process can exert considerable influence on the behavior of the final product. Take a closer look at grease, and you will find that:
- Base-oils account for 60 percent to 90 percent of grease composition. Petroleum-based mineral oil, the most commonly used base-oil (about 90 percent global share), is inexpensive and suitable for a wide range of applications. Synthetic oils, meanwhile, can yield wider operating temperatures and longer life. These tend to include polyalphaolefins (PAO), esters, perfluoropolyethers (PFPE), polyglycol (PAG) and silicone-based oils;
- Thickening agents constitute 3 percent to 40 percent of grease formulation and can be of different types: soaps, complexes, mixed soaps and nonsoap. Soap greases (including soda, sodium, calcium, lithium and aluminum) are an economical choice for applications with operating temperatures up to 121°C. For greater temperature demands, complex greases such as calcium-complex, aluminum-complex or lithium-complex are often used. Lithium calcium, meanwhile, is one example of a mixed soap ideal for high-temperature applications where good water resistance is also required, such as rail bearings for locomotives and rolling stock. There are also nonsoap greases (thickened with polyurea, clay and Teflon) that are suited for very high operating temperatures due to their excellent resistance to temperature change;
- Additives make up the remaining 1 percent to 10 percent of most greases. There are many types of additives, including rust inhibitors that provide a barrier to water. Oxidation inhibitors are another common additive used to disrupt the oxidation process. There are also antiwear additives that prevent metal-to-metal contact between the bearing surfaces and extreme-pressure additives―including sulfur- and phosphorous-based additives as well as solid lubricants like molybdenum disulfide (MoS2) and graphite―that reduce the likelihood of scuffing wear or shock loading. In addition, polymers are frequently used to modify the viscosity of grease or to make greases tackier.
Prior to grease selection, the most critical characteristics to review are the viscosity and consistency of the grease, its shear, work and roll stability, the oxidation and corrosion properties of the grease, as well as its wear, extreme pressure and water washout resistance. Consulting with a bearing expert is the best way to learn about the characteristics most pertinent to your application―even one phone call or plant visit can result in recommendations for a smoother-running operation.
Testing All Greases
Within its motorsports program, Timken focuses on proving new technologies on the track, and that starts in the lab with extensive analysis of specific grease formulations. For testing the performance of different greases in its RacePac assemblies, Timken selected from numerous manufacturers of automotive lubricants the one formulation that most closely matched its criteria for a premium racing grease.
Timken also modified its hub test rig to crank up the heat on its bearings. Historically, track loads, speeds and temperatures were such that bearings able to survive 12 hours on the test rig were shown to have good service life in the field.
However, as more teams began to report bearing burnups, Timken saw a need to set a higher standard. This time, a programmable heat gun was affixed to the test rig to apply 740°F air directly to the hub, replicating the heat generated by the brake rotor of an 800-horsepower stock car racing around the track at up to 200 miles per hour.
The test was conducted under loads and speeds identical to those observed at the track, with no heat being applied to the hubs for the first six hours. For the final six hours, the heat gun was activated and left to run. Teams have reported to Timken that it is not uncommon for hubs to reach 350°F or even 400°F during a race (where the brake rotors become glowing cherry-red going into a corner, with the heat sinking directly into the hub and the bearings).
A better bearing grease can reduce the amount of cooling that must be routed to the wheel hubs, enabling additional aerodynamic adjustments to race cars.
One Blend Stands Above Others
Timken tested both front- and rear-wheel hubs to compare different greases against the baseline grease traditionally used in its RacePac assemblies. The 12-hour test simulated more than 2,500 miles of intense driving conditions, and in the end, only one grease―Grease A―clearly showed improved performance over the baseline grease.
Testing revealed that many of the greases failed to operate at a lower temperature than the baseline grease and did not maintain their stability. Trace elemental analysis, illustrated in Table 1, also showed that less bearing wear occurred in both the front and rear hubs when Grease A was used versus other blends (indicated by lower levels of iron and chromium, measured in parts per million, where metal is worn away from the bearing surfaces, leading to grease contamination and reduced bearing life):
Several greases also exceeded the maximum bearing operating temperature of 400°F (the flashpoint of the grease), triggering automatic shutoff of the test rig. Conversely, as seen in Table 2, bearings using Grease A operated much cooler and never exceeded 300°F even after heat was applied. Compared to the baseline grease, Grease A provided up to a 13 percent reduction in average operating temperature in the front hub and up to an 8 percent reduction in the rear hub, equating to less wear and greater durability when bearings are properly serviced.
Race teams already using their new RacePac hubs with Grease A say they are pleased with the results, and many have requested to learn even more about grease testing. In the months ahead, Timken tribologists plan to take a closer look at the role of lubricant selection on improving other efficiencies in the wheel end assemblies, considering preliminary test results show a simultaneous reduction in bearing operating temperatures and average torque are theoretically achievable.
At the same time, Timken is seeing significantly less discoloration and staining in the RacePac bearings it refurbishes, confirming Grease A as the right choice for a more robust and reliable lubricant solution.
All racers and MRO pros are aware of the benefits of bearing grease, but less understood is the positive impact the optimal blend can have on machine performance. There are endless options available to customers, and that’s why Timken, with a fundamental knowledge of grease selection and decades of testing expertise, can help you narrow in on the best formulations for your application. If you’re ready to identify the ideal lubricant, contact your local Timken expert to start a conversation about better greases and improving bearing reliability.
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