Year: 2024
Type: editorial
Abstract: In recent years, a considerable body of research has been dedicated to enhancing bearings through the utilization of novel manufacturing processes. One notable example is the use of deep rolling processes to significantly extend the service life of bearings [1]. This approach has been coupled with hard turning, taking into account the impact of induced residual stresses and improved surface roughness. Moreover, emerging manufacturing techniques, such as tailored forming, have demonstrated the ability to conserve valuable raw materials and reduce the weight of bearings [2]. Surface modifications applied to bearing surfaces have been explored as a means to decrease frictional losses. The application of coatings on bearings is particularly noteworthy, as it serves to prevent damage to bearing surfaces in the event of conventional lubricant failure during operation. Furthermore, the integration of sensors has been investigated to enable more effective monitoring of bearing conditions [3]. Notably, self-regenerative coatings like molybdenum oxide with a molybdenum reservoir exhibit intriguing properties in this context [4]. Ongoing research is also placing emphasis on developing additional optimized surfaces and surface textures for further advancements in bearing performance. Three exciting contributions have been submitted in the field of bearings. Jaeil Hwang presents a method to more accurately predict bearing life under complex operating conditions, such as oscillation, while considering surface residual stresses. In the standardized calculation method, material properties, such as fatigue limit stress, were taken into account by introducing the fatigue limit stress proposed by Ioannides and Harris. This standard calculation method provides a reasonable range for fatigue life, aligning well with experimental results under ideal test conditions, such as constant external load. However, complex operating conditions of bearings, such as fluctuating loads and oscillating movements, are not considered. Nevertheless, this is essential for the application of bearings in machinery, such as wind turbines. Hence, there is a need for a new analytical calculation model that can predict the fatigue life of bearings under these complex conditions In the proposed approach, fatigue life is determined based on the Palmgren-Miner linear damage rule by evaluating subsurface stresses below the rolling contact using the S-N curve according to the fatigue criterion of Lundberg and Palmgren. Hwang's work confirmed that the analytically determined fatigue life according to ISO 281 still remains close to the results of bearing life tests. Furthermore, the results obtained with the proposed approach show good agreement with the calculation results obtained with ISO 281 [5].In another article, tapered roller bearings are optimized concerning lubrication. Li et al. investigate the contact between the roller end and the rib of tapered roller bearings. This contact significantly influences the lubrication state and performance loss. To enhance the lubrication performance of the inner ring rib and the large roller end in tapered roller bearings used in railway wagons, a thermal elastohydrodynamic lubrication model was created based on the structural analysis of the inner rib and the large roller end. This considers spin-slide effects between the rib and the large roller end, using a Carreau rheological model in a tapered roller bearing. Under various conditions, variations in the friction coefficient were compared to the ratio of the curvature radii of the large roller end to the rib, and the film thickness and film temperature varied with the speed, while the effect of the load between the two rib structures was compared. The results showed that rotational movement has little influence on the lubrication at the contact point between the inner ring rib and the large roller end of the tapered roller bearing. There exists an optimal ratio of curvature radii between the large roller end and the spherical or conical rib; furthermore, the friction coefficient corresponding to this optimal ratio value is the lowest. With increasing inner ring speed, both the film thickness and temperature increase for the two rib structures. In contrast to the spherical rib, the difference between the minimum and central film thickness is nearly constant, and the conical rib shows a slight temperature increase. With increasing load, the difference between the minimum and central film thickness becomes larger, and the temperature in the contact zone gradually rises for both ribs. In contrast to the conical rib, due to the higher film temperature, the spherical rib exhibits a lower friction coefficient and a smaller minimum film thickness [6]. Kelley et al. pursue an alternative approach to enhance lubrication conditions by using micro textures on bearing surfaces. Microtextures are employed to mitigate friction in start-stop cycles, under mixed lubrication conditions, and during sliding in a rolling element bearing, as well as at the contact between a roller and a bearing rib. The selection of the microstructure geometry is crucial, ensuring that individual depressions in the contact area between the ball or roller and the bearing surface act as reservoirs for the lubricant. Initial applications involving microstructured angular contact ball bearings under oscillating motion conditions demonstrated friction-reducing effects during reciprocating motion, where the microstructures functioned as lubricant reservoirs. This concept is extended to the sliding contact for tapered roller bearings, exploring whether the observed reductions in friction can be attributed to the microstructures acting as lubricant reservoirs or if there is a positive hydrodynamic effect due to the microstructures. Through a calculation approach and some illustrative bench test measurements, the behavior of microstructured tapered roller bearings is investigated. An examplarly micro dimple is shown in Fig. 1. It is obvious, that small dimples help to increase the central film thickness [7].
Language: English
Subfield: Mechanical Engineering
Field: Engineering
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $2,125
OpenAlex ID: W4390540914