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Analysis of Mating Surface Condition of Failed Bearings

by:JNSN     2022-03-14
By the condition of the failed bearing mating surface can reflect the support of the bearing ring in the shaft and the bearing seat, we can draw a lot of inferences. Rotation of the ferrule relative to the mating surface can cause abnormal noise. They can also cause fretting corrosion and wear, which further contaminates the lubricant with corrosive and abrasive particles. In addition, as the support of the ferrule deteriorates further, fretting corrosion can make disassembly difficult. A few examples are given below. Fretting corrosion phenomenon: There are dark brown drag marks on the mating surface, and occasionally brown wear substances can be found near the bearing or in the lubricant. Wear of the mating surfaces (inner hole, outer surface of the outer ring) may cause fatigue fracture for rotating parts (usually shafts), and may destroy the function of floating bearings for stationary parts (usually bearing seats), see Figure 13. From these fretting corrosion conditions, it is usually possible to infer the location and size of the load bearing zone and the creep of the ferrule, see Figure 14. Reason: When the fit is too loose relative to the acting force, there will be fretting between the fitting parts, and the machining quality of the synchronously rotating mating surface will not be realized. The deflection of the shaft, the deformation of the bearing seat model, and the ring bearing the circumferential load bear the floating bearing. Remedies for floating function: Rings that are subjected to point loads provide the floating function of floating bearings Use a tight fit on the bearing mating surface as much as possible Improve the stiffness of the shaft (bearing seat) Coating the bearing mating surface Use a ring with high temperature dimensional stability (To prevent the expansion of the ferrule due to the change of the material structure and the loose fit) Improve the roundness of the mating surface If necessary, check and improve the surface quality of the mating surface 3.2.2 Bearing scars or sliding wear. Phenomenon: There is cold welding on the mating surface (the inner hole of the inner ring, the outer surface of the outer ring) and the axial mating surface, or in the bright area with good surface roughness, see Figures 15 and 16. Wear on the mating and end faces will reduce the preload or increase the clearance, see Figure 17. Cause: Rotation of loosely fitted inner and shaft/outer rings and housings under circumferential load; also with static load and imbalances Insufficient axial support of the rings Use a tight fit on the bearing mating surface to increase the axial contact area, ensure axial support, ensure the drying of the mating surface, and improve the function of the floating bearing. The mating surfaces are worn in some areas and completely uncontacted in others, see Figures 18, 19. Fatigue failure and fracture due to uneven load distribution and bending of the ferrule. Rib fracture (fig. 20) due to too little inner ring support in tapered roller bearings, plastic deformation due to too small contact surface. Reason: Inappropriate design Insufficient machining accuracy Remedy: Replace the fitting and ensure the rigidity of the bearing seat, if necessary, use another bearing to check the fitting 17 Evaluate the running characteristics and damage of the removed bearing Fretting corrosion of the outer surface occurs at rigid point contact with the housing (eg stiffeners) 19: Only half the width of the outer diameter of the outer ring is supported 3.2.4 Face scratching phenomenon: circumferential scratches/bearing rings Face or seal worn, see Figures 21, 22. Causes: Bearings are not positioned enough in the housing or on the shaft There are a lot of impurities in the narrow gap between the mating surfaces of the bearing and the fittings The fit is too loose The axial clearance is too large Remedy: Correctly adjust the fit to ensure the cleanliness of the lubricant Check Axial play, as far as possible to make it more suitable.
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