Purpose and methods of bearing shell scraping

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The purpose of dressing the bearing shells is to ensure a tight fit within the appropriate contact angle, while also leaving a certain gap as required by the usage conditions. This gap allows for the formation of a proper oil film, which ensures that the bearing shells can function properly during use. 　　Methods for scraping bearing shells 1: Grooving Use small tools to create grooves in the metal surface, then treat it with a scraper. 　　2: Corner scraping Apply some colored powder to the journal, then use bearing shells to grind it back and forth. The number of grinding passes should be 15 or more; after 15 passes, dot-like particles of powder will appear on its surface. Use a scraper to remove these dots, and then continue grinding. Approximately 25 grinding passes in total are sufficient. 　　3: Clearance The size of the clearance is checked using a feeler gauge; if it does not meet the requirements for use, it is necessary to repeat the two procedures mentioned above. At the same time, the thrust clearance of the bearing shells must also be checked. For the thrust clearance, it is required that both the shell and the contact angle be adjusted so as to maintain uniformity at the contact points, with the vertical heights of the thrust surface and the radial surface remaining consistent. 　　4: Scraping the surface Use a triangular scraper to thoroughly treat the areas where gaps exist. It is necessary to ensure that the surface of these gaps is smooth and even, and it is also important to check the dimensions to determine whether they meet the requirements for use. 　　Shaving bearing bushings requires certain practical experience; if it is the first time performing this task, it is necessary to learn more about the relevant techniques before proceeding, and one should not carry out the operation blindly. 　　Requirements for replacing bearing shells As a critical wear-prone component in mechanical equipment, bearing shells need to be replaced at least twice a year. What are the requirements when selecting and replacing such bearing shells? 　　1: Dimension requirements When replacing bearing shells, it is necessary to select shells of the same grade and with consistent dimensions, based on the repair dimensions of the crankshaft journals. The inner and outer diameters of the bearing shells, as well as the tolerances for cylindricity and roundness, and the actual thickness of the shells must meet the technical specifications; the dimensions of the bearing shells must not be altered arbitrarily. 　　2: Material requirements The material of the newly installed bearing shells must be the same as that of the original bearing shells. Parameters such as the melting point, hardness, toughness, corrosion resistance, and deformation capacity of the metal should all remain similar. If conditions permit, it is possible to use products manufactured by the same manufacturer. 　　3: Fit of the bearing seat The fit between the bearing bush and the bearing seat should be tight enough to prevent the bearing bush from loosening or shifting during operation. When the bearing bush is connected properly, there should be a sense of resistance, and it should be possible to push it in smoothly; if this is the case, it indicates that the fit between the bearing bush and the seat is good. 　　4: Installation height 　　When the bearing shells are in a free state, their end surfaces should be above the base of the bearing. When the bearing shells are pressed to the center of the shaft seat, their end surfaces should be at an appropriate height above the dividing plane of the bearing seat. Either too high or too low a height can affect the proper transmission of forces by the bearing; the appropriate range for this height can be determined by comparing it with the height of the shaft seat.