Bearings - 2021-04-30
Drive-train solutions for vehicles and machines in the agriculture industry must meet a variety of performance demands that typically centre on high torque and high loads. Bearings for transmissions, differentials and prop shafts must therefore offer the highest levels of reliability and service life. NSK, based on decades of experience in supplying bearings for automotive drive trains, has successfully transferred its knowledge and experience to applications in the agriculture industry, bringing a number of distinct advantages to OEMs and end users alike.
There are numerous emerging trends in the agriculture sector, which is now starting to follow the lead set by automotive. By way of example, there are growing calls for increased levels of downsizing to improve fuel economy, while EU legislation on CO2 emissions is constantly tightening. However, by sourcing bearings that offer attributes such as a high load rating and low-friction running, it is possible to meet these challenges head-on.
While experience in automotive is advantageous, there are a number of important differentiations when it comes to applications for the agriculture sector. Whereas road vehicles demand good acceleration/speed performance and travel on smooth surfaces, farm vehicles must cope with rugged terrain and carry/pull high loads, which means that high torque replaces high speed as the primary drive-train requirement.
Many pitfalls can arise if drive trains use poorly specified or incorrectly selected bearings. Common failures of transmission bearings include flaking, fretting, cage damage and creep, all of which have undesirable consequences. With modern agriculture so dependent on high productivity through maximised vehicle uptime, the potential costs and lost operational hours due to a failed bearing are little short of catastrophic. For the OEM, it could mean warranty call-outs and damage to professional reputation.
In drive trains, flaking occurs when bearing material fragments chip away from the smooth surface of the raceway or rolling elements due to rolling fatigue, subsequently creating regions with a coarse texture. This failure mechanism can result from a variety of sources, including excessive load and penetration by foreign matter.
To overcome the potential for flaking, NSK solutions include HR series high-load bearings, which provide excellent performance in drive-train applications for the agriculture sector. Offering a higher load-carrying capacity and longer operating life not only prevents flaking, but adds value through its ability to support downsizing initiatives. HR series tapered roller bearings use conical rollers guided by a back-face rib on the cone. These bearings are capable of taking high radial and axial loads in one direction as the rollers are larger in both size and number.
The HR series is also available as a deep-groove ball bearing, which offers 7-19% higher dynamic load rating and a 22-68% increase in ISO L10 life.
To help counter the ingress of contamination, which is another common cause of flaking in drive-train bearings, NSK’s TM series is proving popular. The seal is particularly effective in the transmission systems of vehicles for agriculture applications, where it can facilitate 2.5 times more service life than open bearings.
The innovative design of the seal lip structure prevents contaminants such as gear dust from entering, while simultaneously allowing the passage of lubricating oil. In addition, the sealed-in grease has a high affinity for transmission oil to aid initial lubrication. Poor or improper lubrication is yet another contributor to flaking.
Further NSK solutions that are ideal for gearbox manufacturers serving the agriculture sector include NSKHPS spherical roller bearings and HST thrust ball bearings. The former use state-of-the-art material technology that provides suitability for applications necessitating high loads. In fact, as NSK’s highest load-rating spherical roller bearing (25% higher), it is possible to downsize in some applications.
HST high-reliability cage-equipped thrust bearings are specifically for applications in hydraulic static transmissions (HST), found commonly in machines/vehicles for the agriculture sector. The bearing provides twice the life of conventional thrust bearings, thanks in part to the use of EP steel supported by a special heat treatment that resists sub-surface fatigue of the inner and outer races.
NSK not only offers an extensive range of proven products for drive-train applications in the agriculture industry, but can provide added-value solutions for initiatives that include downsizing, lower friction and reduced CO2. Through innovations such as special materials, advanced heat treatment and innovative manufacturing processes, NSK has been benefitting the automotive sector with its expertise in transmission bearings for many decades, with growing numbers in agriculture also now gaining from this industry-proven resource.
Picture 1): NSK HR series tapered roller bearings can take high radial and axial loads in one direction
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