Abstract: In order to study the morphology changes of the bearing ring surface after enhanced grinding and verify the existence of micro "oil pockets", combined with experiments, the surface morphology of the bearing ring before and after processing was analyzed, and the micro "oil pockets" on the surface were quantitatively analyzed. The results show that after strengthened grinding processing, there are obvious wrinkles and a large number of small pits on the surface of the ring, which verifies the existence of micro "oil pockets" and analyzes that "oil pockets" have strong oil storage capacity, which can achieve self-lubricating effect.
Keywords: Strengthening grinding; Surface morphology; Micro oil pocket; Oil storage capacity
0 Introduction
Lubrication is very important for bearings, and good lubrication can greatly reduce friction coefficient and reduce wear. For complex and harsh working environments, traditional grease lubrication methods have significant limitations, while bearing self-lubrication can achieve oil-free or low oil lubrication of bearings, effectively improving work efficiency, ensuring bearing performance, and extending bearing life.
The bearing strengthening grinding technology is a new composite machining method that combines "strengthening plastic machining" and "grinding micro cutting" technologies. During the process of strengthening grinding, the abrasive material sprayed out under high pressure will cause wrinkles and depressions on the surface of the bearing ring. Therefore, this article will explore the existence of micro "oil pockets" on the surface of the bearing ring by observing the micro morphology, and analyze the oil storage performance of the "oil pockets", providing new processing technology ideas for achieving self-lubrication of the bearing ring.
1 Test
1.1 Test Equipment and Test Objects
The processing equipment used in this experiment is a bearing ring coreless strengthening grinder independently developed by Professor Liu Xiaochu from Guangzhou University. Its main structure includes an electromagnetic coreless fixture system, a high-pressure spraying and recycling device for strengthening the grinding material, and an automatic control system.
The test machining object is 6207 Deep Groove Ball Bearing ring after heat treatment and finishing, which is made of GCr15 bearing steel, with an outer diameter of 72.00mm and a width of 10.00mm.
1.2 Preparation of experimental strengthening abrasives
The strengthened grinding material in the experiment is mainly composed of grinding powder (mainly composed of brown corundum), grinding strengthening liquid, cast steel shot, and bearing steel shot in proportion to their mass fraction. The components of the strengthened abrasive are shown in Table 1.
Table 1 Composition of Reinforced Grinding Materials
1.3 Test Plan
The processing parameters are set as follows:
(1) The distance between the nozzle and the surface of the collar is 45mm;
(2) The spraying angle is 45 °;
(3) The workpiece speed is 150r/min;
(4) The processing pressure is 0.4MPa;
(5) The processing time is 5 minutes.
After processing, wire cutting technology is used to cut and sample the bearing rings that have not been strengthened and ground, and the bearing rings that have been strengthened and ground. The ideal area is selected, and the surface microstructure of the two bearing ring samples is observed using a field emission scanning electron microscope (FESEM) with model JSM-7001F.
2. Test results and analysis
2.1 Comparison of Surface Micromorphology
The surface microstructure of the bearing ring sample without strengthened grinding, magnified 1000 times by a field emission scanning electron microscope, is shown in Figure 1.
Figure 1: Micromorphology of the Surface of the Ring Sample without Enhanced Grinding
From the figure, it can be seen that the surface morphology of the bearing ring is relatively regular, and it is flat, smooth, and free from obvious wrinkles and pits. The texture is clear and regular. The reason is that the bearing rings that have not been strengthened and ground are processed by precision machining, so the texture direction is consistent, the surface roughness is small, but there are no obvious small pits "oil pockets", which is not conducive to storing lubricating oil.
The surface microstructure of the strengthened ground bearing ring sample, magnified 1000 times by a field emission scanning electron microscope, is shown in Figure 2.
Figure 2: Micromorphology of the surface of the strengthened ground ferrule sample
From the figure, it can be seen that the micro morphology of the bearing ring surface has become disorderly, with disordered and blurry textures, and obvious wrinkles and pits appear on the surface. During the strengthening grinding process, the abrasive material is high-pressure sprayed onto the surface of the ring, causing it to undergo elastic-plastic deformation, causing surface texture to become disordered, and a large number of small pits to appear. Due to the existence of small pits, the bearing is more conducive to storing oil molecules during the lubrication process, achieving the goal of self lubrication. This indicates that after strengthened grinding processing, micro "oil pockets" appear in the bearing ring that are conducive to storing oil molecules, which can greatly reduce the friction coefficient during bearing movement and reduce bearing wear.
2.2 Quantitative analysis of the size of microscopic "oil pockets" on the surface
After strengthening the grinding process, there are many "oil pockets" appearing on the surface of the bearing ring, and their shapes and sizes vary. Therefore, the surface microstructure map after being scanned and magnified by a field emission scanning electron microscope at 5000 times is selected, and six different areas of "oil pockets" are selected on the map, as shown in Figure 3.
Figure 3 "Oil sacs" in six different regions
Estimate the actual area of the "oil sac" based on the image ratio, and use the single molecule oil film method to estimate the diameter of the oil molecule, resulting in a diameter of d=3.0 × 10-10m, and using the circular area formula S=π d2/4, the cross-sectional area of the oil molecule center can be calculated as S oil=7.07 × 10-20m2. From this, the number of oil molecules contained in a single microscopic "oil pocket" can be calculated, as shown in Table 2.
Table 2 "Oil Sack" Area and Number of Oil Molecules Contained in Six Regions
From Table 2, it can be seen that the wrinkles and small pits on the surface of the bearing ring after strengthened grinding processing, namely the micro "oil pocket", all have strong oil storage capacity. Among them, the area with the smallest area is S4, where the "oil pocket" accommodates approximately 6.36 × 107 oil molecules; The area with the largest area is S3, where the "oil pocket" contains approximately 1.62 oil molecules × 108; The average number of oil molecules that can be accommodated in the microscopic "oil sacs" of six different regions is about 1.17 × 108. Therefore, compared with bearing rings that have not undergone enhanced grinding processing, the bearing rings that have undergone enhanced grinding processing have stronger oil storage capacity. The micro "oil pockets" generated on the surface after processing can effectively store oil molecules, achieving self-lubricating effect during bearing operation, reducing friction, reducing wear, and extending the service life of the bearing.
3 Conclusion
The surface morphology of the bearing ring after enhanced grinding processing is disordered, with unclear textures and obvious wrinkles and pits, creating a microscopic "oil pocket" that is conducive to storing oil molecules.
(2)The micro "oil pocket" on the surface of the bearing ring after strengthening grinding processing has strong oil storage capacity, which can reduce the friction coefficient, reduce wear, improve fatigue life of the bearing, achieve less oil lubrication, reduce the number of lubricant additions, improve work efficiency, and provide a reference for achieving the self-lubricating function of the bearing.
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