For kinematically complex bearings like axial cylindrical roller bearings with high sliding friction the kf factor can reach values up to 90. In turn, mixing grease types at a machine can be long-term fatal and should be avoided. As the conditions become more severe the factor value becomes smaller, which shortens the grease life calculation. Lubrication, whether it is through the use of oils or grease, plays a vital role in the performance and life of rolling element bearings. Often, the only features needed are grease supply holes and an external grease nipple for replenishment. Grease is normally applied with special lubricating equipment with a head that deposits the grease between the balls forcing it into, and around, the ball or roller raceway interface. Correction factors can be applied for the impact of load.
This stored volume strongly determines the remaining lubrication process in the bearing. A more severe test method is to replace the distilled water with salt water following the standard test procedure. This note provides some comments on the paper by Booser and Baker and presents the results of a brief investigation of the performance of partly evaporated greases in the rolling four-ball test. Today, the typical diameter of the nearly circular craters present in most common failures ranges from 1 to 4 µm. This book reviews the physical and chemical aspects of grease lubrication, primarily directed toward lubrication of rolling bearings. Lubricating systems can be used to provide the bearing occasionally with fresh grease. The roller tilt angle increases with the increase of the plastic viscosity.
Lithium: Higher temperature, high speeds. After the initial filling or during relubrication, the grease will be located between the rolling elements, leading to high churning losses during start-up or running-in. The sucked oil can be used again after filtration. Spherical roller bearings as a category tend to apply the greatest stress on greases. The same consistency prevents an optimal lubrication performance.
As the grease reaches its dropping point, irreversible and spontaneous oil bleeding occurs and the grease loses its properties. The replenishment interval depends on the type of bearing, dimensions, bearing's rotating speed, bearing temperature, and type of grease. Typical grease systems are much simpler than oil systems and do not cost as much. Pictures of the film thickness profile across the contact area were also registered. The designation of lubricant grease is indicated by the grade of needle penetration.
Like the oil bath method, the oil pick-up ring uses the bearings movement to distribute oil, but instead of having the bearing itself move through a static pool of oil, a separate ring acts as the oil catch. Bearing Failures One can observe strong oxidation and hardening of the grease that occurs following high-temperature stress, which is produced through electrical grounding arcing. The bearing alternates during a defined test cycle between standstill and rotation at 80 rpm. For applications running at higher speeds and temperatures, the oil pick-up ring may be a more affective method than the oil bath. As the speed increases, the roller tilt and skew and the bearing slip become more serious. Additionally, if the lubricating device dose not seal well and tightly, some oil mist may leak out and pollute the environment.
. Two flow types are distinguished, depending on the shape of the lubricated surfaces. But when and how should relubrication be triggered? Baker suggested that evaporation of base oil from a grease is a significant factor in determining the service life of the grease. Mineral oil without any additive could be used in normal conditions. Preface xvii List of Abbreviations xix 1 Introduction 1 1.
Experimental validation is shown for centrifugal force driven free surface flow, and layer thickness film thickness decay in single elastohydrodynamically lubricated contacts. By addressing a number of influencing factors, grease service life can be greatly reduced. In addition, the grease will form pockets in multiple-lip seals where the flow of contaminant particles will be very slow. Practical implication will be introduced through the issue of electric continuity bearing currents or bearing spark erosion and the effect on the grease and rolling bearings. Some comments on relubrication are included. If relubrication has not taken place, severe film breakdown will result, called the end of grease life, which subsequently leads to bearing damage and failure.
With the increase of sliding speed, the enhancement of tribological properties of graphene nanoparticles can open the door for titanium alloys to be used as cutting tools and other high speed friction applications. Grease Lubrication in Rolling Bearings provides an overview of the existing knowledge on the various aspects of grease lubrication including lubrication systems and the state of the art models that exist today. Some applications require a specific kind of lubrication method, such as oil mist. This is accomplished through the formation of a thin oil or grease film on the contact surfaces. With the advent of modern frequency converting techniques, an additional negative influence on bearing life time has been discovered and continues to cause failures: bearing currents. In recent years, increased failures due to electrical arcing highfrequency alternating current passing between the rotor and the frame through the bearing in high-frequency drives have added to these issues. An exact calculation of the grease service life is consequently of particular importance.
Users are advised to not only inspect the condition of the old grease, but to send samples to a laboratory that specializes in analyzing used lubricants. The reduction factor ranges must be selected from a range. Using the Arrhenius aging principle and applying it to the test temperature enables an estimation of the grease life at other temperatures. Its disadvantages are grease-life limitations and a limited cooling ability. This may lead to starvation, especially in sealed bearings where the grease reservoirs are smaller. The needed sealing devices are comparatively simple, therefore, the lubricant grease itself has a certain sealing function, so it is suitable to be used in dusty situations where it is difficult to refill greases. This information can then be used to determine the relubrication intervals for an application.