Cylindrical roller bearing ring fracture cause analysis, illustrated

Cylindrical roller bearing used in medium-sized machinery more of its use in the process of cylindrical roller bearing ring fracture accident is also one of a common problem. In the following 崋 bearing network (for short ） Share out the failure of cylindrical roller bearing ring, the picture mainly introduces bearing ring fracture analysis of concrete conditions. A graphic introduction, some of cylindrical roller bearing ring fracture macroscopic reason: 1, as shown in figure 1, the outer wall of cylindrical roller bearing ring have severe pitting and extrusion deformation. Figure 1 2 outer wall fatigue pitting and deformation, as shown in figure 2, figure 3, cylindrical roller bearing ring fracture with transverse fracture and longitudinal fracture. By the shape of known ( As shown in figure 2, figure 3 arrow) , the cracking from the outer wall, extended to the lining of tear, and are located in the outer wall cracking was fatigue pitting or fall off, shown in figure 3 pieces of fatigue spalling, outside wall also found widespread pitting. Therefore, the contact stress caused by fatigue pitting and fall off, is probably bearing ring crack source point. In addition, the guard place due to axial thrust, plus processing relief groove deeper, stress concentration is bigger, is easy to fracture the guard. Figure 2 transverse fracture figure 3 longitudinal fracture 3, as shown in figure 4, in only 1 pieces found on a macroscopic crack, the crack of surface crack, the contact stress is produced by fatigue crack, is a sign of fatigue peeling. Experiment, we use the metallographic cutting machine cutting sampling on bearing ring fragments, due to the vibration and the impact of the external load, makes further rupture, or crack of debris, rupture or crack at the rim, it shows that hard and brittle materials, shock resistance is poor, due to the structure stress of the guard, easier to rupture. Figure 4 pieces of the superficial to the longitudinal crack on the 4, as shown in figure 5, the cylindrical roller bearing ring inner surface also found several wear grooves and the peeling, and macro visible cracks. This suggests that relative sliding friction bearing ring on the shaft. According to the working principle of bearing, bearing ring interference fit should be on the shaft, shaft turns, bearing ring with shaft rotation, roller between the bearing ring and outer ring rolling, in order to reduce the vibration of the shaft. If the clearance between the shaft and bearing ring is too big, the shaft and bearing ring relative sliding friction, will cause the roller can't normal rolling, ring directly under a lot of contact stress and bearing overload work, leading to pitting corrosion fatigue and fatigue. Figure 5 grooves of the inner surface of bearing ring wear, spalling and macroscopic crack, damage to the bearing fatigue damage analysis 1, pitting corrosion and fatigue peeling for high vice ( The high pressure) Contact mechanical parts, are theoretically contact point, line, but in fact material after elastic deformation under load, theory of point and line contact becomes very small surface contact, the contact part will produce very high stress, the stress is called the surface contact stress. High parts of the contact stress of actual change cycle, in contact under the action of cyclic stress, the micro cracks on the metal surface to form a small first, then the direction of crack along with surface into acute Angle, when arrived at a certain depth, and the out surface of parts, finally, there are small pieces of metal peeling off, on the surface of parts to form a small pit, this phenomenon is called fatigue pitting ( 'Pitting') 。 Pitting is under the action of contact stress failure forms, belongs to fatigue failure. After bearing pitting failure happens, in operation, is usually a strong vibration noise and fever phenomenon. Cylindrical roller bearing ring and rolling fatigue pitting on the surface of the body surface rolling bearing is one of the most basic and common failure forms and is usually used as the basis for rolling bearing life calculation. When the contact stress is very big, the metal surface may form a macroscopic visible cracks, makes large metal flake, namely fatigue peeling. According to the result of macro examination, ring surface pitting and falls off phenomenon is serious, See figure 1) , belong to the service life of the early failure ( Only 7 months) 。 2, fall off fatigue pitting corrosion and fatigue cracking in ring from a macro analysis shows that the influence of except near the collar of the fracture, the position of most of the freedom of fracture surface are associated with fatigue pitting corrosion and fatigue peeling, pitting and chipped for fracture fracture source location ( As shown in figure 3, figure 4) That ring of brittle fracture and fatigue pitting there is intrinsic relationship and fall off. Pitting in transverse section microscopic observation macro and micro cracks found that the surface crack ( See figure 4) In the cause of pitting and spalling at the same time, effective bearing area is greatly reduced, the ring can also be a source of fracture, under the action of vibration, the ring of brittle fracture. Three, the conclusion cylindrical roller bearing ring fatigue pitting and loss is the direct cause of the bearing ring fracture. Macro analysis that ring surface falls off fatigue, severe and appear show ring contact stress is too large, this is the reason why ring accelerated fatigue, that's what led to the contact stress of ring is too big? Macro check found in the inner wall of the bearing ring is different from the sharp grinding crack and spalling of the pitting ( See figure 5) , the individual position also found that the macro crack. The clearance between the shaft and bearing inner ring is too big, relative sliding friction and cause can't normal rolling roller, inner ring directly under a lot of contact stress and bearing overload work, leading to pitting corrosion fatigue and fatigue. So the bearing inner ring and shaft assembly bad ( Should be interference fit) And the root cause of the bearing clearance is too large is ring fracture. In addition, in the process of cutting piece of damage to the bearing samples for processing, the fragments appear rupture, crack, and further illustrate the bearing steel after quenching shock and vibration performance is poorer. It is understood that machine in the process of running under certain shock load, so also can't rule out the possibility of ring fracture due to the impact.