Abstract: This article focuses on the assembly process and scraping requirements of the bearing for our 25MW and 50MW units, and discusses the construction methods, requirements, and quality control points during the construction process.

Keywords: Bearing; Assembly; requirement; Scraping and scraping; essentials

Introduction: Split type radial sliding bearings are mainly used in heavy-duty large and medium-sized machines, such as metallurgical mining machinery, large generators, steel ball coal mills, piston compressors, and transportation vehicles. Its material is mainly Babbitt alloy, and in some cases, copper based bearing alloys are used. During assembly, the scraping method is generally used to achieve its accuracy requirements and ensure its performance. The standards are implemented according to the manufacturer's regulations and personal accumulated experience.

Project Overview: Units # 1, # 2, # 3, and # 4 of the first phase of our factory's project are N25-35-1 medium pressure condensing steam turbines produced by Wuhan Steam Turbine Generator Factory. The basic bearing are Wu Tao, which are elliptical and made of Babbitt alloy. The requirements and assembly methods for the clearance between the bearing at different sizes of shaft necks are as follows:

1. Requirements for bearing, seats, and covers

(1) Load bearing shell. The contact area between the back of the load-bearing bearing and the bearing seat should be greater than 70%, and it should be evenly distributed. The contact range angle a should be greater than 150 °, and the clearance B of the remaining allowable clearance parts should not exceed 0.05mm, as shown in Figure 1.

Figure 1

(2) The contact area between the bearing shell and the bearing cover should be greater than 60% and evenly distributed. The contact range angle a should be greater than 120 °, and the allowable gap amount b in the gap area should not exceed 0.05mm.

(3) If the above requirements cannot be met, the contact between the tile seat and tile cover should be checked by coloring and applying red lead powder. The tile back should be filed with a fine file for grinding until the requirements are met. Contact the spot road at 3-4 points every 25mm2.

(4) When assembling the bearing shell, bearing seat, and bearing cover, the gasket at the joint between the two halves of the bearing should have the same shape as the bearing mouth, and its width should be less than 1mm measured inside the bearing. The gasket should be flat and free of burrs, and the thickness of the gasket at both ends of the bearing mouth should be consistent. The connecting bolts of the tile base and tile cover should be tightened and evenly stressed. All items should be cleaned thoroughly.

2. Several key elements required for the performance of the scraping surface of the bearing shell

(1) Contact range angle and contact surface requirements.

The contact angle of the bearing shell is generally 120 °, and for heavy-duty equipment it is generally 90 °. In the case of body technology, the contact range angle a is also required to be 60 °. The size of the contact range angle a and the requirements for the contact spot are usually clearly specified in the drawing. If there is no annotation, the general technical standards can be implemented according to the requirements of the business technical documents.

(2) Oil line and tile mouth oil groove belt

A. At the beginning of the sliding bearing, strong lubrication is used, and the oil groove is usually opened on the upper tile that is not under force (the upper tile is under less force). The cross-section is a semi-circular arc, distributed 180 degrees along the circumference of the upper tile, and is machined by mechanical processing. The oil hole in the middle of the oil groove is the same as the center position of the upper bearing, and the two ends are connected to the oil groove belt of the bearing mouth. Due to the gap between the upper bearing and the shaft, lubricating oil can easily enter the surface of the upper bearing and the shaft. Its main function is to smooth the lubricating oil, such as the oil groove belt of the bearing mouth on the inner side (radial) of the bearing.

B. The oil groove belt is distributed at the junction of the upper and lower bearing  (on both sides). As shown in Figure 1. The oil groove belt is formed into a circular arc wedge shape, which is a strip-shaped oil groove that can store a large amount of lubricating oil, facilitating lubrication and cooling of the bearing and shaft. The oil groove belt is usually machined by machinery, but also manually machined by fitters.

(3) Lubricating oil wedge; The lubricating oil wedge is located at the connection between the oil groove belt and the bearing shell within the contact range angle a. It is manually scraped (commonly known as the scraping mouth) and has two main functions: one is to store oil and cool the bearing shell and shaft, and the other is to use its circular wedge angle to continuously suck lubricating oil from the axial width of the shaft to the bearing part, so that the bearing shell and shaft have sufficient and good lubrication. The lubricating oil wedge part is a circular arc wedge angle composed of irregular arcs at both ends. It smoothly connects the oil groove belt and the working contact surface of the bearing shell. The connection part with the oil groove belt needs to be scraped more, and the edges and corners of the oil groove belt connection should be machined and scraped off. At the transition from the middle of the lubricating wedge angle to the contact surface, it is scraped into a circular arc wedge angle shape to scrape the lubricating wedge angle. It should be done when the fine scraping of the bearing shell is basically completed, and it is not easy to scrape in advance.

(4) The top clearance and side clearance of the bearing shell

A. The top clearance of the bearing shell can be taken as 1.5% -2% of the shaft diameter based on experience, and should be selected within this range according to the speed, load, and lubricating oil viscosity.

B. When there is no specific requirement for side inspection on the drawing, the side clearance should be 1/2 of the top clearance. The side clearance needs to be scraped out as needed. The side clearance should not be too large, as this will cause a large amount of lubricating oil to flow away from the side clearance and reduce the amount of lubricating oil required for the bearing. This should be particularly noted. The width b at Z is the planned surface of the tile mouth, and the size is the maximum value of Z for the specified side gap. The sharp corners at the side clearance and tile mouth plane should be chamfered, depending on the size of the bearing shell, generally ranging from 1 × 45 ° to 3 × 45 °. The side gap is basically composed of irregular arcs at both ends.

3. Scraping process of bearing shell

(1) Rough scrape the bearing shell.

A. Gently scrape the machining marks of the upper and lower tiles once, ensuring that the tile surface is completely scraped and evenly scraped, and the machining marks are removed.

B. Paint on the shaft, roughly scrape with the grinding points of the upper and lower tiles several times, then insert the upper and lower tiles into the tile seat and tile cover respectively, paint on the tile, roughly scrape with the grinding points of the shaft, and after the contact area and grinding points are evenly distributed, 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.

(2) Fine scrape the bearing shell. When fine scraping the axle tile, the upper and lower tiles should be cushioned (tile joint surface), assembled, and the two ends of the bearing  should be scraped, painted on the tiles, and polished with a shaft. When starting to tighten the assembly, the clamping force should be uniform, and the shaft should not be pressed too tightly. It should be able to rotate, and the pad should be removed and tightened as needed. At this time, attention should also be paid not to scratch the tile mouth. After multiple scraping, the spots on the tile contact surface should be evenly and densely distributed.

(3) Fine scraping of bearing . The purpose of precision scraping is to scrape the contact spots and contact area according to the requirements specified in the pattern. The grinding method is the same as rough scraping, with the points increasing from large to small and from deep to shallow. At the end of precision scraping, the lubricating oil wedge (opening) and side clearance are scraped out to achieve the performance of the bearing, which is very important.

When scraping the bearing shell, consideration should be given to the condition of the shaft related components, such as center distance deviation, regardless of the contact condition of the tooth surface, in order to accurately position the shaft. The small accumulated errors caused by mechanical processing can be further eliminated by scraping. Large errors cannot be solved by scraping.

2025 December 1st Week Marginal Product Recommendation:

Material Specification Sheet–MG-6:

Material specification sheet – MG-6 is Ball and roller bearing steel according to EN ISO 683-17. Ball and roller bearing steel for balls and rollers of any dimension,rings and discs up to 30mm effective thickness.