Technical Requirements and Methods for Scratching and Grinding of Sliding Bearings of Large Motors

With the development of the market economy and the implementation of the national energy policy, the equipment in industries such as mines, cement, steel and electric power are all developing in the direction of large-scale, and the demand for large-scale motors is also increasing. Most of the large motor bearings are split radial sliding bearings, and their materials are mainly Babbitt alloys. When assembling, the method of scraping and grinding is generally used to meet its precision requirements and ensure its performance. Therefore, the quality of scraping is very important to the normal operation of the motor, and directly affects the service life of the motor. The quality of scratching is not good. During the test run of the motor, it is easy to cause the bearing pad to develop from local sticking loss to most of the sticking loss in a very short period of time, until the bearing pad burns out and cannot be used. Therefore, when scraping and grinding the bearing bush, it is operated by a fitter with rich technical experience.

 

The scraping method of the split sliding bearing (bearing bush) is introduced below.

1 Coordination requirements of bearing bush, bearing seat and bearing cover

(1) The contact area between the pad back of the lower bearing bush and the bearing seat should be greater than 70%, and the distribution should be uniform. The contact range angle should be greater than 150°, and the gap between the rest of the allowable gap should not be greater than 0.05mm.

(2) The contact area between the pad back of the upper bearing pad and the bearing cap should be greater than 60%, and the distribution should be uniform. The contact range angle should be greater than 120°, and the gap between the allowable gap parts should not be greater than 0.05mm.

2 Technical requirements for bearing pad scraping

2.1 Contact angle and contact spot requirements

The contact angle of the bearing pad is within the range of 60°~120°, the small value is selected for light load, and the large value is selected for heavy load; it is generally required that the number of contact points uniformly distributed on each square centimeter area within a 60° (or 120°) arc, There should be more than two lower bearing bushes, and more than one upper bearing bush.

2.2 Oil groove and tile mouth oil groove belt

(1) For split sliding bearings, the oil groove is generally opened on the upper tile with less stress. The cross-section is semicircular, distributed along the inner circumference of the upper tile at 180°, and is machined. Because there is a gap in the upper pad, the lubricating oil can easily enter between the upper pad surface and the shaft, and its main function is to smoothly inject the lubricating oil into the inner (radial) pad oil groove of the bearing pad.

(2) The oil groove belt of the tile mouth is distributed at the junction of the upper and lower bearing bushes (both sides). The oil groove is in the shape of a circular wedge, the outer depth of the joint surface of the tile mouth is generally 1mm to 3mm, the width of the oil groove is generally 8mm to 40mm, and the size of the single side of the oil groove from the end face of the bearing bush is generally 8mm to 25mm. The length of the oil groove belt is about 85% of the axial length of the bearing pad. It is a strip-shaped oil groove that can store a large amount of lubricating oil, which is convenient for the lubrication and cooling of the bearing pad and the shaft.

2.3 Lubricating oil wedge

The lubricating oil wedge is located at the connection between the oil groove belt and the bearing bush within the contact angle, and is made by manual scraping (commonly known as the scraping tile mouth). It has two main functions: one is to store oil to cool the bearing pad and the shaft; the other is to use its arc wedge angle to continuously attract the lubricating oil to the bearing part under the drive of the shaft rotation to form an oil film, so that the bearing pad and the shaft be well lubricated. The lubricating oil wedge part is a circular wedge angle composed of two irregular circular arcs, which smoothly connects the oil groove belt and the working contact surface of the bearing bush. The scraping and grinding of the lubricating oil wedge should be carried out when the fine scraping of the bearing bush is basically completed, and it is not suitable to scrape and grind in advance.

2.4 Top clearance and side clearance of bearing pad

(1) The top clearance of the bearing bush, when there is no special requirement, can be selected from 1‰ to 2‰ of the shaft diameter according to experience, and should be selected within this range according to the speed, load and viscosity of the lubricating oil.

(2) The side clearance of the bearing bush, if there is no special requirement, the clearance on each side is 1/2 of the top clearance; for the smaller top clearance, the clearance on each side is equal to the top clearance. The side clearance of the bearing pad is scraped manually according to the needs. The side clearance part extends from the joint surface of the joint to the specified working contact angle area, and axially connects with the oil groove belt and the lubricating wedge angle. This part should not be If there is contact with the shaft, this should be paid attention to when scraping. The sharp angle between the side clearance and the joint plane should be chamfered, depending on the size of the bearing bush, generally 1×45°～3×45°.

3 Scraping process of split bearing

3.1 Scratching of tile back
The tile seat and tile cover should be used as the benchmark, and the contact between the upper and lower bearing bushes should be checked by applying red lead powder by the coloring method, and the back of the tile should be repaired with a fine file until it meets the requirements.

3.2 Coarse scraping bearing
(1) Gently scrape the machining tool marks of the upper and lower bearing bushes once, and it is required to scrape all the tile surfaces, scrape and grind evenly, and scrape off the processing marks.

(2) Apply a thin layer of display agent (red lead powder or other) on the journal, and scrape roughly with the grinding points of the upper and lower bearing bushes several times. After the contact area and the grinding points are evenly distributed, it can be transferred to fine scraping. . When rough scraping, care should be taken not to scratch the part of the tile mouth, and full contact within 180° is required.

3.3 Fine scraping bearing
When finely scraping the bearing pads, the upper and lower bearing pads should be padded (the joint surface of the pad mouth), and the bearing pads at both ends should be scraped after assembly, and red lead powder should be applied to the pads, and the points should be grinded with a shaft. When starting to press the assembly, the pressing force should be uniform, and the shaft should not be pressed too tightly, as long as it can rotate, scrape, remove the mat, and press it. At this time, care should also be taken not to scrape the tile mouth. After repeated scraping and grinding, the spots on the contact surface of the bearing bush can be evenly distributed.

3.4 Fine scraping bearing
The purpose of fine scraping is to scrape and grind the contact spots and contact area to the specified technical requirements. At this time, there is no need to show the agent, just add a little turbine oil, the grinding method is the same as fine scraping, the spots are from large to small, from deep to shallow, from sparse to dense, and the large spots can be broken with a scraper during the scraping process. Into dense small ideas, after many times of scraping and grinding, gradually scraping until it meets the requirements. When the fine scraping is about to end, it is very important to scrape out the side clearance of the lubricating oil wedge (opening tile opening) so that it can achieve the performance of the bearing bush.


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