With the development of the market economy and the implementation of national energy policies, equipment in industries such as mining, cement, steel, and electricity are all moving towards large-scale development, and the demand for large motors is also increasing. Most of the bearings used in large motors are split type radial sliding bearings, which are mainly made of Babbitt alloy material. During assembly, the scraping and grinding method is generally used to achieve its accuracy requirements and ensure its performance. Therefore, the quality of scraping is crucial for the normal operation of the motor and directly affects its service life. Poor quality of scraping and grinding can easily cause the bearing bushing to develop from local adhesion to majority adhesion during motor testing in a very short period of time, until it cannot be used due to shaft burning. So when scraping and grinding the bearing bushing, it is operated by experienced technicians.
The following introduces the scraping method of split sliding bearings (bushings).
1. Requirements for the fit between the bearing bushing, bearing seat, and bearing cover
(1) The contact area between the back of the lower bearing bushing and the bearing seat should be greater than 70%, and it should be evenly distributed. The contact range angle should be greater than 150 °, and the clearance of the remaining parts with clearance should not exceed 0.05mm.
(2) The contact area between the back of the upper bearing bushing and the bearing cover should be greater than 60%, and evenly distributed. The contact range angle should be greater than 120 °, and the clearance in the allowable clearance area should not exceed 0.05mm.
2. Technical requirements for scraping and grinding of bearing bushing
2.1 Requirements for Contact Angle and Contact Spot
The contact angle of the bearing bushing is within the range of 60 °~120 °. Choose the small value for light load and the large value for heavy load; Generally, it is required to have two or more contact points evenly distributed per square centimeter within a 60 ° (or 120 °) arc, and one or more lower bearing bushing and one or more upper bearing bushing.
2.2 Oil tank and tile mouth oil tank belt
(1) Split sliding bearings generally have oil grooves located on the upper bearing with less stress. The cross-section is a semi-circular arc, distributed 180 degrees along the circumference of the upper tile, and is machined by mechanical processing. Due to the presence of clearance on the upper bearing, lubricating oil can easily enter between the upper bearing surface and the shaft. Its main function is to smoothly inject lubricating oil into the oil groove on the inner side (radial) of the bearing bushing.
(2) The oil groove belt is distributed at the junction of the upper and lower bearing bushing (on both sides). The oil groove belt is formed into a circular arc wedge shape, with a depth of generally 1mm to 3mm towards the outer side at the joint surface of the tile mouth. The width of the oil groove belt is generally 8mm to 40mm, and the size of the oil groove belt from one side to the end face of the bearing bushing is generally 8mm to 25mm. The length of the oil groove belt is about 85% of the axial length of the bearing bushing, and it is a strip-shaped oil groove that can store a large amount of lubricating oil, facilitating lubrication and cooling of the bearing bushing and shaft.
2.3 Lubricating oil wedge
The lubricating oil wedge is located at the connection between the oil groove belt and the bearing bushing within the contact angle, and is manually scraped and ground (commonly known as the scraping groove). Its main functions are twofold: one is to store oil and cool the bearing and shaft; The second is to use its circular wedge angle, driven by the rotation of the shaft, to continuously attract lubricating oil towards the bearing part, forming an oil film, so that the bearing bushing and shaft are fully lubricated. The lubricating oil wedge part is a circular arc wedge angle composed of two irregular arcs, which smoothly connects the oil groove belt and the working contact surface of the bearing bushing. Scraping and grinding the lubricating oil wedge should be carried out when the precision scraping of the bearing is basically completed, and it is not advisable to scrape and grind it in advance.
2.4 Top clearance and side clearance of bearing bushing
(1) When there are no special requirements, the top clearance of the bearing can be taken as 1 ‰ to 2 ‰ of the shaft diameter based on experience, and should be selected within this range according to the speed, load, and lubricating oil viscosity.
(2) The side clearance of the bearing bushing, unless otherwise specified, is 1/2 of the top clearance on each side; For those with smaller top clearance, the clearance on each side is equal to the top clearance. The side clearance of the bearing bushing is manually scraped and ground as needed. The side clearance extends from the joint surface of the bearing mouth to the specified working contact angle zone, and is axially connected to the oil groove belt and lubrication wedge angle. This part should not be in contact with the shaft, and attention should be paid to this during scraping. The sharp corners at the side clearance and tile mouth plane should be chamfered, generally ranging from 1 × 45 ° to 3 × 45 ° depending on the size of the bearing bushing.
3. Scraping and Grinding Process of Split Bearing
3.1 Scratching and grinding of tile back
The contact between the upper and lower bearing bushing should be checked by coloring the tile seat and tile cover with red lead powder, and the back of the tile should be polished with a fine file until it meets the requirements.
3.2 Rough scraping of bearing bushing
(1) Gently scrape the machining marks on the upper and lower bearing bushing, ensuring that the entire surface of the bearing is scraped and evenly ground, and remove the machining marks.
(2) Apply a thin layer of display agent (red lead powder or other) on the shaft neck, and roughly scrape the grinding points of the upper and lower bearing bushing several times. After the contact area is evenly distributed with the grinding points, it can be transferred to fine scraping. When rough scraping, attention should be paid not to scrape off the tile mouth, and it is required to have full contact within a 180 ° range.
3.3 Fine scraping of bearing bushing
When finely scraping the bearing pads, pads should be added to the upper and lower bearing pads (at the joint surface of the pad mouth). After assembly, scrape and grind the bearing pads at both ends, apply red lead powder to the pads, and use shaft grinding points. When starting to tighten the assembly, the clamping force should be uniform, and the shaft should not be pressed too tightly. It can rotate and be scraped, removed, and tightened as needed. At this point, attention should also be paid not to scrape the tile mouth off. After multiple scraping and grinding, the spots on the contact surface of the bearing bushing should be evenly distributed and dense.
3.4 Fine scraping of bearing bushing
The purpose of precision scraping is to scrape and grind the contact spots and contact area to the specified technical requirements. At this point, there is no need to use a display agent. Just add a little turbine oil, and the grinding method is the same as fine scraping. The dots start from large to small, from deep to shallow, and from sparse to dense. During the grinding process, the large dots can be broken open with a scraper and become dense small dots. After multiple scraping and grinding, gradually scrape until they meet the requirements. Is the precision scraping about to end?, It is very important to scrape and grind out the side clearance of the lubricating oil wedge (opening) to achieve the performance of the bearing bushing.
2024 December 3rd Week Marginal Product Recommendation:
MG-090 Bronze Wrapped Bushings:
MG-090 bronze self-lubricating bearings use a kind of high density bronze alloy of special compositions as backing, the surface of alloy is rolled with diamond pattern of the oil indents or half ball oil indents, this kind of bearing has a higher density, a higher load capacity.
https://www.marginalbearings.com/bronze-wrapped-bushings/mg-090-bronze-wrapped-bushing.html
