The trend toward energy-efficient bearings has produced a shift in the traditional design focus of increasing capacity to a higher priority on reducing friction. For specific bearing types and key applications, the goal is lower friction bearings designed for operating energy efficiency.
"The change in focus has made energy efficiency goal number one for certain bearing types," says William Bonis, an applications engineer for SKF. In the past, designs have targeted increased service life, power density or machine downsizing using ultra-clean steel and optimized internal geometries with a primary focus on capacity.
"But now we are taking an alternate approach with an environmental focus and the impact bearing energy consumption has on industrial applications since bearings impact nearly all types of rotating machinery," says Bonis.
One bearing type, the deep groove ball bearing, is used in nearly all electrical motor-driven equipment including pumps, fans and compressors. Since this equipment accounts for a large portion of consumed industrial power, even a small improvement in bearing energy efficiency can account for huge benefits to annual energy savings, not to mention the total cost of equipment ownership over the life of an electric motor.
With its E2 deep groove ball bearing, SKF achieved the target of 30 percent less power consumption from the perspective of the bearing losses in small electric motors. This is accomplished using internal design changes, a special polymer cage and a low-friction, long-life grease. The end result is lower energy consumption and reduced bearing temperatures resulting in extended grease and bearing service life. For equipment end users, this translates to an overall lower cost of ownership.
E2 tapered roller bearings are targeting a different series of applications with a focus on large industrial transmissions in applications such as wind energy, railway and mining equipment. The initial size range includes tapered roller bearings with an outside diameter from 220 to 600 mm. The E2 tapered roller bearings' reduced energy consumption of 30 percent is accomplished through an optimized roller count, roller and flange guidance topography, raceway profile and a special polymer cage.
Since surface topography and raceway profile is critical to roller bearing performance under loaded conditions, significant analytical work using internally developed software was performed to help define the profiles and finishes of the rolling contact area that contributes to bearing friction. Experimental testing has validated the improvement predicted through analysis. These internal modifications do not affect boundary dimensions of the bearing, enabling direct replacement of an existing bearing by an E2 bearing.
It's important for design engineers to realize there are specific target applications for each type of E2 bearing, as well as available sizes depending on the bearing type. The intention is to achieve the reduced bearing friction while meeting the application requirements specific to the particular application. The E2 bearings are not replacing SKF's standard product line, rather they are intended as a complement for targeted markets.
SKF continues to focus on alternate bearing types such as the spherical roller bearing, cylindrical roller bearing, CARB and angular contact ball bearing for energy efficiency. These E2 designs will also target specific application parameters such as higher speed and/or lighter loading.
"From a design engineer's perspective, one needs to have those intended application conditions in mind," says Bonis. "You would not apply this technology to extremely high-load or slow-speed applications as those design requirements can be better met with the standard range of bearings."
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