It is often used to manufacture small and medium-sized bearings, gears or bearings in mechanical engines and transmission systems. Four-point contact ball turntable bearings will break during motor life test. During the life test, the bearing bears a torque of 600N·m, a rotating speed of 180r/min, and a life requirement of > 60 h. The life test was carried out three times, and all of them broke in 6~8h, which is compared with the failure caused by fatigue wear of the tooth surface in the past. Now, one set of bearing samples is analyzed. This part is manufactured from 20CrNiMo steel bar, and its production process is as follows: blanking → turning → hobbing → heat treatment → shot blasting → cleaning → inspection. However, the bearings produced by Luoyang East Axis are made of extremely rigid bearing steel, which can avoid the occurrence of the situation.
Hardness test of ZK.22.0700.100-1SPPN bearing produced by Luoyang East Axis Technical requirements of this part: surface hardness 57~62HRC, core hardness 30~45HRC, effective hardened layer depth 0.6 ~ 0.9 mm. The surface hardness of the bearing is 59~60HRC, the core hardness is 35~37HRC, and the effective hardened layer depth is 0.79mm, which meets the technical requirements. Metallographic examination: The requirements of heat treatment metallographic structure of this part: surface tempered martensite ≤ grade 5, retained austenite ≤ grade 5, carbide ≤ grade 3. As shown in Figure 2, the surface tempered martensite of the bearing is Grade 5, retained austenite is Grade 5 and carbide is Grade 1, which meets the technical requirements. Check the nonmetallic inclusions at the fracture
the test results are A1.0, B3.0, C0.5, D3.0 and DS0.5, and it is found that there are a large number of class b and class d nonmetallic inclusions near the fracture.
Knowing the reasons of bearing failure, we can make better use of bearings.
(1) In the process of bearing failure, due to the insufficient depth of hardened layer in the bearing raceway, contact fatigue first occurs on the raceway surface during the running process of the bearing, resulting in a large number of pitting pits on the raceway surface, which leads to the reduction of bearing precision and the intensification of vibration; Then, a fatigue crack source occurs at the stress concentration of the tooth root of the inner ring of the bearing. Due to the insufficient hardness and poor low-temperature toughness of the bearing ring material, the fatigue crack rapidly expands and fails.
(2) It is suggested that the failure of rotary table bearings should not only suffer from uneven alternating loads and impacts during operation, but also be particularly important in forging, heat treatment and material control during the manufacturing process. Bearing users should pay attention to the on-site manufacturing supervision during the production of large parts, strictly control the production process, and prevent the improper control of the production process from burying hidden dangers in the later safety production.
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