Cause analysis of 4106 bearing needle spalling
Rolling bearings are important basic components and are widely used in industry. Needle roller bearings are one of the main types of rolling bearings. They are characterized by small cross-sectional radial dimensions, good bearing rigidity, and high radial load carrying capacity, so they are particularly suitable for limited space and large carrying capacity at radial installation positions. Therefore, it is widely used in variable speed transmission systems, steering systems, motorcycle engine connecting rods, etc. of automobiles and construction machinery. However, if the needle roller bearing fails, it will inevitably cause major losses of corresponding important engineering equipment, and even cause safety accidents. Therefore, it is necessary to conduct failure analysis on its operation status and common failure modes and failure mechanisms in order to better adopt Precaution.
There are many factors influencing the failure of needle roller bearings, from the metallurgical quality of the bearing material to the bearing manufacturing process (cold and hot processing, heat treatment, grinding), final assembly and any steps during the later service period will affect the quality of the needle roller bearing, and thus affect its use life. Many literatures have carried out failure analysis on rolling bearings and believe that the causes of bearing failure are fatigue wear, material hole defects, forging defects, grinding burns, improper maintenance (environmental corrosion) and assembly problems. At the same time, the literature summarizes the problem of aviation bearing failure and believes that there are some problems in bearing design, manufacturing (including the quality of raw materials), assembly, lubrication, use and maintenance, among which the design and manufacturing are particularly prominent. However, for needle roller bearings, the literature believes that there are three main reasons for their failure, as shown in Figure 1. In fact, the failure of needle roller bearings is often caused by the coupling of multiple factors, so it is difficult to completely classify the causes of their failure.
Therefore, it is necessary to analyze the failure of the failed needle roller bearing and seek the most important factor leading to its failure in order to better take improvement measures. Unfortunately, there are few literatures on the failure analysis of needle roller bearings. Therefore, this paper uses the 4106 needle roller bearing needle spalling example for failure analysis, in order to provide reference for needle roller bearing design and preventive measures.
Figure.1 The main failure modes of needle roller bearings
Test process and results
The existing set of model 4106 needle roller bearings (see Figure 2), the material is GCr15. The rated dynamic load of the bearing is 5500N, the rated static load is 5000N, and the life requirement is L10=150h. The bearing’s test load is 2500N, the test speed is 3000r/min, and it is lubricated with N32# oil. The needle roller peeled off during the test, and the actual life of the bearing was only 90h. The reason for the failure of the needle roller bearing is analyzed.
Figure 2 Overall morphology of the failed needle roller bearing
Macroscopic morphology analysis
The macroscopic morphology of the failed 4106 needle roller bearing was observed.
Overall appearance: This needle roller bearing is partially scratched on the outer diameter surface (see Figure 2); both ends of the bearing are sealed intact, and one of the surfaces is scratched, as shown in Figure 3.
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Figure 3 Overall morphology of both ends of 4106 bearing
Outer ring appearance: the color of the bearing area of the inner diameter surface of the outer ring is dark gray, the inner raceway is seriously worn out, and there are spalling pits of different sizes in some parts, as shown in Figures 4 and 5; There are two wear scars in the direction, one of which is wider and dark in color (see Figure 4).
Figure 4 4106 bearing outer ring inner diameter surface appearance
Figure 5 The enlarged morphology of the spalling area of the inner raceway of the outer ring
The shape of the cage: the cage is relatively complete, and there are wear marks on the side where the side contacts the needle roller (see Figure 6); the end of the cage and the needle roller contact is severely worn, and the dents are large, as shown in Figure 6 and Figure 7.
Figure 6 4106 bearing cage shape
Figure 7 Partially enlarged morphology of 4106 bearing cage
Needle morphology: 9 needles are gray and dull, 5 of them are worn and 3 are severely worn. The wear area is about 2/3 of the entire needle surface, and the other two have peeling at one end, as shown in Figure 8. As shown in Figure 9; there are no obvious signs of wear on both ends of the 9 needle rollers (see Figure 8).
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Figure 8 Overall morphology of 4106 bearing needle roller
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Figure 9 The enlarged morphology of the 4106 bearing peeling needle roller
Lubrication status: The grease is gray-black, indicating that it has been oxidized. The needle bearing and grease are filtered and cleaned, and no obvious foreign matter is seen, as shown in Figure 10.
Figure 10 Needle bearing cleaning dross
Chemical composition inspection
The SPECTOR M9 direct-reading spectrometer was used to check the chemical composition of the needle and outer ring. The results are shown in Table 1. From the inspection results in Table 1, it can be seen that the chemical composition of the needle rollers and the outer ring are in compliance with the relevant regulations of the standard GB/T18254-2002 “High Carbon Chromium Bearing Steel” and is qualified.
Table 1 Chemical composition (mass fraction) inspection results of needle roller and outer ring (%)
Hardness inspection
According to JB/T1255—2014 “Technical Conditions for Heat Treatment of Rolling Bearing High Carbon Chromium Bearing Steel Parts“, the hardness test of needle rollers and outer rings of failed needle roller bearings is carried out. The test results are shown in Table 2. From the inspection results in Table 2, it can be seen that the hardness of the needle roller and outer ring of the failed needle roller bearing meets the requirements of the JB/T1255-2014 standard.
Table 2 Hardness test results of needle roller and outer ring (HRC)
| Name | Test point 1 | Test point 2 | Test point 3 |
| Roller pin | 62.7 | 62.3 | 62.7 |
| Outer ring | 60.7 | 60.4 | 60.4 |
| standard requirement | 60～63 | ||
Metallographic inspection
According to the GJB18254-2016 “High-carbon chromium bearing steel” standard, the material quality of the needle and outer ring of the failed needle roller bearing is inspected, and the rolling is tested according to the JB/T1255-2014 “Technical conditions for heat treatment of rolling bearing high-carbon chromium bearing steel parts” The quenched and tempered structure of the needle and outer ring was inspected, and the results are shown in Table 3. It can be seen from the inspection result that the material quality of the needle roller and outer ring meets the standard requirements; the quenched and tempered structure of the needle roller and outer ring meets the standard requirements.
Cut the spalling pit along the outer ring and grind it into a metallographic sample. Observe: the spalling pit depth is about 0.05mm, and cracks at the bottom of the pit extend into the base, as shown in Figure 11. Observe the metallographic structure of the radial surface in the bearing area of the outer ring, and there is no burn on the inner diameter surface, as shown in Figure 12.
Table 3 Inspection results of quenched and tempered structure of needle roller and outer ring
| Name | Martensite structure/grade | Network carbide/grade |
| Roller pin | 3 | 2 |
| Outer ring | 4 | 2 |
| Standard requirement | 1~4 | 1~2.5 |
Figure 11 Sectional morphology of spalling pits in the outer ring
Figure 12 Metallographic structure of the inner diameter surface of the outer ring
Scanning Electron Microscope Analysis
In order to observe the wear morphology in more detail, a JSM-6380LV scanning electron microscope was used to observe a needle with a severely worn surface, a needle with a worn end and the outer ring, as shown in Figure 13-15.
By observing the spalling pits on the raceway surface of the outer ring, it is found that the spalling pits on the inner diameter surface of the outer ring are of different sizes, and there are micro-cracks and broken matrix at the edge of the pit; there are obvious rolling marks in the pit, indicating that the inner diameter of the outer ring bears larger Exfoliation due to fatigue.
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Figure 13 The spalling pits and enlarged morphology of the outer ring raceway surface of the submitted bearing
By observing the worn-out roller needle, it is found that one end of the roller needle is severely worn and peeled off, and the other surface is intact, and there are debris and micro-cracks on the edge of the spalling pit, and there are obvious rolling traces in the spalling pit.
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Figure 14 Worn roller pin at one end and magnification electron microscope appearance
By observing the severely worn roller needle, it is found that both ends of the roller needle have spalling pits, one end is severely worn, and even secondary spalling occurs; there are debris and micro-cracks on the edge of the spalling pit, and there are obvious rolling traces in the spalling pit.
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Figure 15 The appearance of severely worn needle roller and magnifying electron microscope
Results and discussion
As mentioned earlier, the entire process of needle roller bearings from raw materials to manufacturing process, assembly, post-maintenance service and lubrication will affect their quality and cause early failure of needle roller bearings. The characteristic of needle roller bearings is that needle roller bearings are equipped with thin and long rollers and the bearing still has a high and uniform radial bearing capacity. Through the above inspection and analysis, it can be known that the failure mode of the needle roller bearing is surface-originated spalling and the chemical composition, hardness and uniformity of the needle roller bearing, the metallurgical quality of the material, and the quenched and tempered structure have not been found to be abnormal, which meets the requirements of relevant standards. Eliminate the possibility of needle roller bearing parts (needle roller and outer ring) material quality and heat treatment quality causing its failure; 4106 bearing cleaning filter slag does not find foreign matter, and eliminate the factors that affect the lubricating oil contamination by foreign matter; 4106 bearing uses oil lubrication, although The color of the non-load-bearing area of the inner diameter surface of the needle roller and the outer ring changed to gray-black, but the metallographic examination found that there was no burned tissue on the inner diameter surface of the outer ring, so the influencing factors of insufficient lubrication can be excluded.
4106 needle roller bearings are characterized by a fixed outer ring, and the needles rotate with the shaft. For needle roller bearings, the surface of the needle roller should bear a uniform radial load. The failed needle roller bearing outer ring raceway surface is severely worn on one side, and the needle roller surface on this side has a large area of circumferential peeling (the other side has no peeling), and the side cage is also relatively severely worn. These morphological characteristics indicate There is eccentric load phenomenon during the operation of the bearing. During the operation of the needle roller bearing, the uneven load caused the load to be uneven, which changed the state of the lubricating oil film, so that the temperature of the needle roller and the inner diameter surface of the side bearing the larger load increased, thereby changing the surface structure performance.As the bearing continues to run, the surface structure peels off and breaks. Cracks, leading to early bearing failure. Therefore, it is concluded that the eccentric load in the operation of the 4106 needle roller bearing is the main reason for its early failure.
Conclusion
The failure mode of 4106 needle roller bearing is surface-originated spalling, and the eccentric load phenomenon during operation is the main reason for its early failure.
Author: Guo Hao, Hu Lin Zhuang, Wang Shanshan, Lei Jianzhong (Institute of Luoyang Bearing Co., Ltd., Henan Province, high performance Laboratory bearing technology)
Source: China Flanges Supplier: www.epowermetals.com
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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