This article describes the technologies of grease lubrication which contribute to the reduction of rolling bearing torque. The bearing torque consists of the viscous drag force, the rolling friction and the sliding friction. The drag force has correlation with the fluidity of lubricants. Reduction of viscosity and grease volume relating to the generation of rotating resistance can decrease bearing torque. It is reported that the rheological properties of grease cause channeling or churning phenomenon in the bearing and the grease volume is decreased by the channeling. Large yield stress and thixotropic property is thought to improve channeling property. It is also reported that the rolling friction reduces with the inlet distance at the contact area, and the decrease of sliding friction between rolling elements and the cage has possibility of further reduction of bearing torque.
In this article, latest research developments of the dynamics (the carriage drift and sticking) of linear bearings are outlined. First,carriage drift (which is the differences of the carriage displacements or angular displacements at a certain position on a rail during a back-and-forth process) in linear guideway type roller bearings is explained, and it is pointed out that the carriage drift is caused by roller skewing. Secondly, sticking (which is the significant increase in the required driving force when a carriage is driven back-and-forth with a short stroke length) of the linear guideway type ball bearing is explained, and it is shown that the sticking is caused by the sliding friction between the rolling-load balls in the load zone.
A foil bearing is one of self-acting gas-lubricated bearings, constructed of a set of flexible thin metal foils. The feature is high dynamic stability under high-speed operation over a wide range of temperature, however the rotational accuracy is not always guaranteed. As is always the case with self-acting gas-lubricated bearings, the stiffness and the load capacity are not so high. Accordingly, the potential application is high-speed and small rotational machinery but not limited to micro gas turbines and centrifugal compressors. This article describes the structures of radial and thrust foil bearings and the recent technology trends.
The actual service life of component is often below the desired life. One of the prevalent failure modes in bearing raceways is hydrogen-induced rolling contact fatigue (RCF) with associated microstructural change called white etching constituent. Despite these failures having been observed for a long time in various industries, the detailed reasons and mechanisms for their formation are not fully understood. In this review, experimental methods for hydrogen-induced RCF are discussed, specifically hydrogen charging, hydrogen content measurement in steel and various types of RCF testers. The review also highlights the surface and subsurface observation technique. Beneficial surface treatment and enhanced lubrication with additives are shown as countermeasures to prevent diffusion of hydrogen into the metal.
The ever increasing requirements for energy savings, environmental protection and high efficiency from the industry lead to ever more severe operating conditions for rolling bearings, such as higher rotation speeds, higher loads, and better corrosion resistance. Engineering ceramics, such as silicon nitride, zirconia, silicon carbide and alumina have superior characteristics to meet these requirements. Silicon nitride, in particular, has excellent balance of properties for rolling bearing applications, such as light weight, high hardness, electrical insulation and corrosion resistance. This paper describes the manufacturing method and material characteristics of silicon nitride, its basic performance and examples of applications in rolling bearings.
The bearings installed in railway vehicles play an important role in securing their stable high-speed traveling performance and are also responsible for the safety and reliability in train operations. The bearings, therefore, have to ensure sufficient durability against the variations in the bearing load and rotational speed under any meteorological conditions. In addition, the maintenance-free for them has to be realized between their overhaul inspections. To achieve these requirements, a great deal of effort has been made to develop and introduce new technologies. This article describes an overview of the technological trends on the rolling bearings for railway vehicles, especially the bearings used for axle journals, gear units and traction motors of which the bogie consists, including the use conditions and performance requirements for their bearings.
Nonlinear rotor vibration of a turbo compressor with saturated water journal bearings was analyzed by using bifurcation diagrams. Bifurcation analysis can be utilized to study the nonlinear vibration phenomena, such as whip, with large amplitude for which linear perturbation theories cannot be applied. The combination of synchronous vibration and rigid rotor whip resulted in chaotic behaviors, including Hopf bifurcation, intermittent chaos, and a period-3 window of broadband frequency. Many windows were found at frequencies whose ratios to the rotational frequency were rational numbers. To study these chaotic behaviors, the rotor dynamics was numerically analyzed considering the stiffness and damping of the hydrodynamic bearing and its elastomeric supporting structure. Even though nonlinearity was considered only for the stiffness of the hydrodynamic bearing, the results showed spontaneous Hopf bifurcation, and its frequency agreed with the experiment results. However, the broadband window and the intermittent chaos were not reproduced in this analysis. Other dynamical models should be considered to realize greater agreement between the analytical and experimental results.
In this study, in order to clarify the influence of contact pressure on the wear characteristics of LIGA-Ni (Lithographie,Glvanoformung, Abformung-Nickel) and the difference between wear characteristics of LIGA-Ni and rolled Ni, the wear characteristics of the LIGA-Ni and the rolled Ni against the contact pressure were investigated. The wear mechanism was discussed from the standpoints of crystalline structure. Furthermore, the cause of crystalline alteration was discussed. Experimental result has shown that the LIGA-Ni specimen and the rolled Ni specimen have different wear characteristics with respect to the contact pressure. The wear amount of the rolled Ni specimen increased in proportion to the contact pressure. On the other hand, the wear amount of some of the LIGA-Ni specimen deviated greatly from the proportionate increase at the contact pressure around 4500 MPa, and it increased abruptly. It became clear that this cause was the difference of crystalline alteration during the wear process. In the rolled Ni specimen, the crystal refined gradually as the contact pressure increased, and the wear increased proportionately. On the other hand, in the LIGA-Ni specimen, the crystal changed from coarsening to refining as the contact pressure increased, whereby the amount of wear increased disproportionately.