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Analysis of failure of roller bearings
Source: Bearing network time: 2013-01-17
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The excavator used in the construction of the Three Gorges Dam is imported from South Korea; the bearing cracking often occurs during use; the excavator cannot work normally. This article has the metallographic arrangement and microhardness of the failed roller and bearing outer ring. Anatomy; the cause of bearing failure.
1 Microscopic view of the failed parts 1. The roller shows; on the cylindrical surface, the uneven pits which occur after the surface layer falls off are visible; and the end face is damaged severely; the grinding is gone a lot. The roller is along the pit The diameter is longitudinally cut and investigated; the lower right corner of the section has an inverted triangle; this is where the original crack falls off at the beginning. The upper right corner has a crack extending from the end to the column; the length is about 4.5 mm; the crack is There are branches in the middle; the crack is thin and straight. The trap is considered (see Figure 2); it has significant stress crack characteristics.
1.2 The outer ring fragments of the bearing can see some fatigue fracture shape on the outer ring fragments. A crack parallel to the outer surface can be seen at the distance of 0. 7mm from the outer surface of the debris; the crack is intermittent, curved, and the tail end is tapered. One of the same; the crack has the same characteristics of stress cracking.
2 Non-metallic inclusion rating (1) Roller: Sulfide grade 1; point and globular oxide scale 1. 5 grade.
(2) bearing outer ring: sulfide grade 1 point, spherical oxide 1. 5 level.
3 Microscopic arrangement view 3. 1 Roller 3.1.1 The heart arrangement is arranged for tempering needle martensite; granular carbide and residual austenite composition.
Roller original arrangement 4% slightly acid alcohol etch × 500
3.1.2 The outer dimples are arranged around the pits formed by the outward appearance of the roller. When the metallographic arrangement is investigated, it is found that the bottom of the pit is a white bright layer; its width is about 0. 18 to 0.5 mm; the length is 15 mm. There are three transverse cracks in the white bright layer. The bottom outer layer of the pit is close to the white bright layer and has a dark area of ​​about 0. 40 to 0.50 mm; the dark area is the original arrangement of the roller. The white and dark areas are arranged. It is quenched martensite; the dark area is tempered needle fine martensite + a few granular carbides + residual austenite.
3.1.3 Microhardness In order to reflect the difference in hardness between the three different color arrangements; we performed a microhardness test on the roller profile from the outside to the inside; visually reflected the microhardness indentation size change Status: The most indentation in the white layer is the most important hardness value of the three areas: white light area HV0. 11264, dark area HV0. 1551, original arrangement HV0.1800.
White bright area, dark area, original arrangement and microhardness indentation at the bottom of the roller pit × 200 4% slightly acid alcohol etching 3. 2 Bearing outer ring microscopic arrangement bearing outer ring microscopic arrangement for tempering hidden needle Markov Body + minority granulated carbide and residual austenite.
3. 3 Appearance hardness 3.3.1 The hardness of most points on the outer surface of the roller roller is between HRC60 and 61; however, some local longitudinal line hardness is between HRC56 and 57.
3.3.2 The hardness of the outer ring of the bearing is tested; the hardness of the inner and outer parts of the bearing outer ring is HRC58～59.
4 The appearance of the external crater of the roller is analyzed. From the quenching martensite arrangement in the Bailiang area, we can infer that the rollers are pressed too tightly during the working process; a lot of heat is generated due to the conflict; the kneaded part constitutes a high temperature. Zone; because there is lubricating oil; therefore, the high temperature part of the surface is quenched from the head; it constitutes quenched martensite (white color after corrosion). Because of the high temperature effect; the subsurface layer close to the exterior receives another tempering Therefore, the secondary tempering temperature is higher than the tempering temperature of the original heat treatment of the roller; the hardness of the subsurface layer is lowered; it is easy to fall off; the pit is formed after falling off; the white light area at the bottom of the pit seen by us is practiced after the surface layer falls off. Remaining.
Therefore, it is not difficult to conclude that the cracks on the rollers are due to the tight installation of the rollers; they collide with each other during operation; the arrangement is partially changed; it occurs under the macroscopic arrangement of stress effects; therefore, it has stress crack characteristics. Because the arrangement changes the volume of the roller inside the bearing becomes larger; the inner and outer surfaces of the bearing outer ring are subjected to great compressive stress; therefore, the end is cracked.
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