Roller bearing failure analysis

pick? to: failure of the bearing from the shape of the fracture analyzes the roller and the bearing outer ring of the internal inclusions, microstructure and crack form, the reasons put led perimeter displays a bearing failure.
excavators used in construction of Three Gorges Dam is imported from South Korea, often occur in the course of the bearing fracture, resulting excavator does not work. Based on the failure of the roller and the bearing outer ring of the microstructure, hardness and other GMC car dvd gps of analysis, the cause of bearing failure.
1? Invalid parts of macro-check
1.1 roller
shown in the cylindrical surface can be seen peeling off the surface resulting from the pits of various sizes , and the face badly damaged, rubbed off a lot. In the pit at the roller along the longitudinal diameter was observed after cut open, inverted triangle bottom right corner of an empty profile, which is where the original crack caused by falling off in the beginning. The upper right corner there is a column extending from the side facing the cracks, about 4.5mm, cracks in the middle, with branches, thin crack direct energetic, tapering tail (see Figure 2), has obvious characteristics of stress cracks.
1.2 bearing outer ring fragments
debris on the outer ring to see some form of fatigue fracture. 0.7mm from the surface of the debris can be seen at a parallel with the surface cracks, cracks intermittent, tortuous, tapering tail. Part of the crack, the crack also has the characteristics of stress cracks.
2? Non-metallic inclusions rating
(1) roller: sulfide l-level, point-like and globular oxides 1.5.
(2) the bearing outer ring: led light power supply a point-like, globular oxides 1.5.
3? Microstructure examination
3.1 roller
3.1.1 Heart Ministry
Ministry of temper hidden heart needle martensite and austenite grain carbide composition.
roller 4% of the original organization of alcohol slightly acid etching? × 500
3.1.2 surface pits surrounding tissue
formed in the roller surface of the peeling Microstructure observation pits found at: pit bottom is a white layer, its width is about 0.18 ~ 0.5mm, length 15mm. White layer has three transverse cracks. Pit close to the bottom of times the outer white layer with a width of 0.40 ~ 0.50mm dark area, dark area is the roller after the original organization. White light and dark intervals organizations quenched martensite, tempered dark hidden needle for the needle a small amount of granular martensite + carbide + retained austenite.
3.1.3 microhardness
three different colors to reflect the lady's handbag of the hardness difference, we conducted a cross-section outside to the inside of the roller hardness test, directly reflects the changes in microhardness indentation size: white layer in the indentation minimum, maximum indentation area dark, slightly lighter color of the original tissue indentation center. Three areas, the average hardness values ​​were: white light district HV0.11264, dark areas HV0.1551, the original organization HV0.1800.
roller pit at the bottom of the white light zone, dark zone, the original organization and microhardness indentation? × 200 4% alcohol, slightly acid etching
3.2 Microstructure bearing outer ring
bearing outer ring of the microstructure of tempered martensite needles hidden a small amount of granular carbides and residual austenite.
3.3 surface hardness
3.3.1 Roller
most point on the roller surface hardness of HRC60 ~ 61 between the vertical but also in some places a line between hardness are HRC56 ~ 57.
3.3.2 bearing outer debris hardness
tested, the inner surface of the bearing outer ring of debris hardness HRC58 ~ 59.
4? Roller surface of the pit Cause Analysis
white light from the quenched martensite zone we can deduce, roller during operation because the weight of each other tight, because Friction generated a lot of heat, extruded parts to form a high temperature, because oil is, therefore, the surface area was re-quenching temperature, quenching to form martensite (white corrosion was bright). As the local temperature effect, so close to the surface of the sub-surface has accepted a temper, so the second roller is higher than the original tempering temperature tempering heat treatment temperature, resulting in sub-surface hardness decreased, easy to peel off, peel off after the formation of the pit, we see the bottom of the pit area is actually a bright white surface residue after peeling down.
As a result, we can conclude: roller on the roller assembly is due to tight crack, hit each other when the pressure of operation, so that local organizational changes have taken place in the great stress under the action of the organization , and therefore has a stress crack cosmetic bag. As the organizational changes made within the roller bearing size larger, outer circle of the bearing surface to withstand a great deal of stress, which eventually split support.