Failure analysis of the hottest roller bearing

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Failure analysis of roller bearing

Abstract: starting with the fracture shape of the failed bearing, the internal inclusions, microstructure and crack morphology of the roller and the outer ring of the bearing are analyzed, and the causes of bearing failure are put forward

the excavator used in the construction of the Three Gorges dam is imported from South Korea. During the use, the bearing often breaks, causing the excavator to fail to work normally. Through the analysis of the metallographic structure and microhardness of the failed roller and bearing outer ring, this paper puts forward the causes of bearing failure

1 macroscopic inspection of failed parts

1.1 roller

shows that pits of different sizes can be seen on the cylindrical surface after the surface layer is peeled off, and the end face is seriously damaged and worn away. After the roller is cut longitudinally along the diameter in the pit, it is observed that there is an inverted triangle cavity in the lower right corner of the section, which is caused by the peeling of the original crack at the beginning. In the upper right corner, there is a crack extending from the end face to the column, about 4.5mm long. The crack has branches in the middle. The crack is thin, straight and rigid, and the tail end is thin (see Figure 2), with obvious stress crack characteristics

1.2 bearing outer ring fragments

part of the fatigue fracture can be seen on the outer ring fragments to eliminate the gap shape. A crack parallel to the surface can be seen at the place 0.7mm away from the surface. The crack is intermittent, zigzag and thin at the end. As a part of the crack, the crack also has the characteristics of stress crack

2 rating of non-metallic inclusions

(1) roller: sulfide grade 1, point and spherical oxide grade 1.5

(2) bearing outer ring: sulfide grade 1, point like, spherical oxide grade 1.5

3 microstructure examination

3.1 roller

3.1.1 heart structure

heart structure is composed of tempered cryptoneedle martensite, granular carbide and residual austenite

roller original tissue 4% slightly etched with acid and alcohol × 500

3.1.2 the structure around the surface pit

when observing the metallographic structure at the pit formed by the peeling off of the roller surface, it is found that there is a white bright layer at the bottom of the pit, with a width of about 0.18 ~ 0.5mm and a length of 15mm. There are three transverse cracks in the white bright layer. There is a dark area with a width of about 0.40 ~ 0.50mm close to the white bright layer at the bottom of the pit, and the original structure of the roller is behind the dark area. The microstructure of white bright zone and dark zone is quenched martensite, and the dark zone is tempered hidden needle fine needle martensite + a small amount of granular carbide + residual austenite

3.1.3 microhardness

in order to reflect the difference in hardness of three different colored tissues, we tested the microhardness of the roller profile from the outside to the inside, which directly reflected the change of microhardness indentation size: the indentation in the white bright layer was the smallest, the indentation in the dark area was the largest, and the indentation of the slightly lighter original tissue was in the middle. The average hardness values of the three areas are: white bright area hv0.11264, dark area hv0.1551, original tissue hv0.1800

white bright area, dark area, original structure and microhardness indentation at the bottom of roller pit × 200 4% slightly acid alcohol etching

3.2 microstructure of bearing outer ring

What are the test methods of impact testing machine? The microstructure of the outer ring is tempered cryptoneedle martensite + a small amount of granular carbides and retained austenite

3.3 surface hardness

3.3.1 roller

the hardness of most points on the roller surface is between HRC60 and 61, but in some places, the hardness of a longitudinal line is between hrc56 and 57

3.3.2 hardness of bearing outer ring fragments

after testing, the inner surface hardness of bearing outer ring fragments is hrc58 ~ 59

4 analysis of the causes of roller surface pits

from the quenching martensite structure in the white bright area, we can infer that the rollers are pressed too tightly with each other during operation, and a lot of heat is generated due to friction. The extruded part forms a high-temperature area. Due to the existence of lubricating oil, the high-temperature part on the surface is re quenched, After quenching is basically in a state of holding goods and waiting to rise, huoma will definitely want the power battery enterprise to reduce the cost of the power battery (white and bright after corrosion). Due to the effect of local high temperature, the sub surface layer close to the surface received another tempering, so the tempering temperature is higher than the tempering temperature of the roller during the original heat treatment, resulting in the decrease of the hardness of the sub surface layer, which is very easy to peel off. After peeling off, a pit is formed. The white bright area at the bottom of the pit we see is actually left after the surface layer peels off

from this, it is not difficult for us to draw a conclusion: the cracks on the rollers are due to the roller assembly being too tight and bumping against each other during operation, resulting in local tissue transformation, which is produced under the action of huge tissue stress, so they have the characteristics of stress cracks. Due to the structural transformation, the volume of the roller in the bearing becomes larger, which makes the inner surface of the outer ring of the bearing bear great compressive stress, so it is finally cracked

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