Research shows that approximately 80% of premature bearing failures are due to incorrect installation. Proper bearing installation can not only extend bearing life and reduce costs, but also significantly improve production efficiency. Therefore, learning correct bearing installation knowledge is urgent.
Bearings are components used for support, specifically to support rotating parts on a shaft. By friction type, bearings are classified as sliding bearings and rolling bearings; by load direction, they include radial bearings, thrust bearings, and radial-thrust bearings. So how to install them correctly?
Sliding Bearing Assembly
Sliding bearings are characterized by sliding friction, offering smooth operation, low noise, and the ability to withstand heavy loads and significant impact. They are classified into integral, split, and block types based on structural design.
1) Integral Sliding Bearing Assembly
Commonly called bushings, integral sliding bearings are the simplest form, primarily assembled via pressing or hammering. In special cases, thermal installation is used. Most bushings are made of copper or cast iron. Care is required during assembly: use a wooden hammer or a hammer with a wooden block for striking, or a press for larger interference fits. Tilting must be avoided, and oil grooves/holes must align precisely.
Post-assembly, if deformation occurs, recondition the inner bore. Small bores are reamed, while larger ones are scraped. Maintain the shaft-bushing clearance within tolerance. To prevent rotation, install positioning pins or set screws on the contact surface. Due to material hardness differences, drilling may cause bit deflection. Solutions:
Pre-punch hard material before drilling.
Use a shorter drill bit to increase rigidity.
2) Assembly of Split Bearings
Split bearings, also known as two-piece bearings, are characterized by simple structure, convenient adjustment, and disassembly. Two bearing liners are inlaid on the bearing shell, and a reasonable clearance is adjusted with shims at the joint.
① Assembly of Bearing Liner and Bearing Body
The contact between the upper and lower bearing liners and the inner hole of the bearing body must be good. If it does not meet the requirements, use the inner hole of the bearing body of the thick-walled bearing liner as a benchmark, scrape the back of the bearing liner, and at the same time, the steps at both ends of the bearing liner should tightly against the ends of the bearing body. For thin-walled liners, it is sufficient that the split surface of the liner is about 0.1mm higher than the split surface of the bearing body, and scraping is not necessary.
② Installation of Bearing Liner in Bearing Body
The bearing liner installed in the bearing body is not allowed to have displacement either radially or axially. Usually, the steps at both ends of the bearing liner are used for positive positioning or positioning pins are used.
③ Fitting and Scraping of Bearing Liner
Split bearing liners are generally matched with their corresponding shaft for spotting. Usually, the lower liner is scraped first, then the upper liner. To improve efficiency, when scraping the lower liner, the upper bearing liner and cover may not be installed. When the contact points of the lower liner basically meet the requirements, then press the upper liner and upper cover tightly, and when scraping the upper liner, further correct the contact points of the lower liner. During fitting and scraping, the tightness of the shaft can be adjusted by changing the thickness of the shims as the number of scraping times increases. When the bearing cover is tightened, the shaft can rotate easily without significant clearance, and the contact points meet the requirements, indicating the fitting and scraping is completed.
④ Measurement of Bearing Clearance
The size of the bearing clearance can be adjusted by shims at the split surface, or obtained by directly scraping the bearing liner. The bearing clearance is usually measured by the lead wire compression method. Take several sections of lead wire with a diameter larger than the bearing clearance, place them on the journal and the split surface, then tighten the nuts to compress the split surface. Then unscrew the nuts, remove the bearing cover, carefully take out the flattened lead wires, measure the thickness of each section with a micrometer, and the bearing clearance can be known based on the average thickness of the lead wires. Generally, the bearing clearance should be 1.5‰-2.5‰ (mm) of the shaft diameter. When the diameter is large, a smaller clearance value is taken. For example, for a shaft diameter of 60mm, the bearing clearance should be between 0.09-0.15mm.
II. Assembly of Rolling Bearings
Rolling bearings offer advantages such as low friction, compact axial dimensions, easy replacement, and simple maintenance.
1) Technical Requirements for Assembly
① The end face of the rolling bearing marked with a code should be installed in a visible direction for easy reference during replacement.
② The fillet radius at the shoulder of the shaft neck or housing hole must be smaller than the corresponding radius on the bearing.
③ After assembly, the bearing must not be skewed on the shaft or in the housing hole.
④ Among two bearings on the same shaft, one must allow axial movement during thermal expansion of the shaft.
⑤ Strictly prevent contaminants from entering the bearing during assembly.
⑥ After assembly, the bearing should operate flexibly with low noise, and the working temperature should generally not exceed 65°C.