Rolling Bearing Failure Modes - Wear

Bearing failures are best classified according to the root cause of the failure, but it is not always easy to map causes to characteristics (symptoms) or failure mechanisms to failure modes. references). GB/T 24611-2020/ISO 15243:2017 classifies failure modes into six major categories and different sub-categories based on the apparent characteristic appearance visible in use (Figure 1). Figure 1 Failure Mode Wear refers to the continuous loss of material caused by the interaction of two sliding or rolling/sliding contact surfaces during use. Abrasive wear (particle wear; three-body wear) is the loss of material due to sliding in the presence of hard particles, removed from one hard surface or particle by cutting or furrowing as it slides over another surface Material. A certain degree of darkening occurs on the surface after wear, and the degree of darkening varies according to the thickness and characteristics of the abrasive grains (Figure 2). Due to the material on the rotating surface and possibly the cage (Fig. 3) being abraded away, the number of abrasive particles gradually increases, and eventually the wear enters an accelerated process, which leads to bearing failure. Fig. 2 Abrasive wear on the inner ring of a spherical roller bearingFig. 3 Abrasive wear further developed on the pockets of a metal solid cage Although the surface is generally darkened to a certain extent, polishing occurs when the abrasive particles are very fine Abrasive wear on the surface of the large end face of the roller and the large rib surface of the inner ring and the raceway of the tapered roller bearing and the raceway Note: The 'running-in' of rolling bearings is a natural short-term process, After this process, the operating state (such as noise or operating temperature) will be stabilized or even improved. From this, the running track is visible, but this does not mean that the bearing is damaged. Adhesive wear is the transfer of material from one surface to another with frictional heating and sometimes surface tempering or requenching. This process creates localized stress concentrations and can lead to cracking or spalling in the contact area. In the case of insufficient lubrication, smearing (slip, sticking, scratching, roughening) occurs when sliding occurs and the local temperature rise caused by friction causes the contact surfaces to stick, resulting in material transfer. Smearing often occurs between the rolling elements and the raceway if the rolling elements are under loaded and are strongly accelerated when they re-enter the load zone (Fig. 5, Fig. 6). Seizure can occur with heavy application. Smearing often occurs suddenly, as opposed to the gradual accumulation process of abrasive wear. Fig.5 Coating on outer ring raceway of cylindrical roller bearingFig.6 Coating on outer ring raceway of spherical roller bearing Due to insufficient lubrication, smearing will also occur on the rib surface and roller end surface (Figure 7). For full complement rolling element (without cage) bearings, smearing can also occur at the contact between the rolling elements due to lubrication and rotating conditions. Fig. 7 Coating of the roller end face of cylindrical roller bearing If the bearing ring is installed on the shaft or in the housing, the clamping force is insufficient and the ring moves (creep) relative to its bearing surface, and the bearing inner diameter surface, outer Coating (also known as gluing) occurs on the radial surface or on the bearing surface of the shaft and housing bore. Due to the small difference between the diameters of the two parts, there is also a small difference in the circumference of the two parts. Therefore, the radial load relative to the rotation of the ferrule causes the two parts to come into contact at a series of consecutive points, and the two contact parts rotate relative to each other with a slight differential speed. This rolling motion of the ferrule relative to its bearing surface with a small rotational speed difference is called 'creep'. When creeping occurs, the rough peaks in the contact area between the ferrule and the bearing surface are rolled down, giving the ferrule surface a shiny appearance. Rolling occurs frequently during creep, but is not always accompanied by slippage at the contact of the ferrule and bearing surface, so other damage such as scratch marks, fretting and wear can also be seen. Under certain load conditions, when the interference between the ferrule and the bearing surface is not large enough, fretting wear is the main problem. In addition, when the radial clearance is used, creep will also occur between the end face of the ferrule and its axial abutment surface, which will lead to transverse thermal cracks in severe cases, and eventually cause the ferrule to crack. Explanation of related terms: wear: The gradual loss of material from a solid surface during use, generally caused by relative motion between the surface and a contacting object or objects. Abrasive wear: Gradual loss of material due to insufficient lubrication and intrusion of (external) particles. The surface will be darkened to some extent, and the degree of darkening will vary depending on the size and characteristics of the abrasive grains. Three-body wear: A type of abrasive wear that occurs when particles are not confined and are free to roll on a surface, slide and interact with two contact surfaces simultaneously. Hard particles: such as sand and particles from grinding processes such as grinding wheels. Ploughing: A groove formed by plastic deformation of the softer of two opposing surfaces. Polishing: A smoothing effect that makes the original machined surface appearance of a bearing part brighter.