Cylindrical roller bearings
Cylindrical roller bearings are one of the most widely used types of rolling bearings. Composed of an inner ring, outer ring, cylindrical rollers, and a cage, they feature high load capacity, high radial stiffness, high maximum speed, and a simple structure. They are widely used in machine tool spindles, automotive transmissions, electric motors, and other mechanical equipment. The performance of cylindrical roller bearings depends on factors such as their structural design, material selection, manufacturing precision, and installation and use. Understanding their structural characteristics, operating principles, and performance parameters is crucial for their proper selection and use.
The structural characteristics of cylindrical roller bearings determine their unique operating performance. Both the inner and outer rings have cylindrical raceways, and the cylindrical rollers are in line contact with the raceways. Therefore, they have a large radial load capacity and can withstand large radial loads and certain axial loads (primarily unidirectional axial loads). Cylindrical roller bearings are available in two configurations: with or without a cage. Cage-equipped cylindrical roller bearings prevent friction and collisions between the rollers, increasing the bearing’s maximum speed and making them suitable for high-speed rotation. Cage-equipped cylindrical roller bearings (full complement roller bearings) have a greater load capacity but a lower maximum speed, making them suitable for low-speed, heavy-load applications. Depending on their structural form, cylindrical roller bearings can be divided into single-row, double-row, and multi-row cylindrical roller bearings. Single-row bearings offer a simple structure and are easy to use; double-row and multi-row bearings can withstand greater radial loads and are suitable for heavy-load applications. In addition, the inner ring or outer ring of some cylindrical roller bearings can be separated, which is called separable cylindrical roller bearings. This type of bearing is easy to install and disassemble, easy to install on the shaft or in the bearing seat, and the clearance can be adjusted to meet different usage requirements.
The material choice for cylindrical roller bearings significantly impacts their service life and performance. Inner and outer rings, as well as rollers, are typically constructed from high-carbon chromium bearing steel (such as GCr15 and GCr15SiMn). This steel offers high hardness (HRC 60-65), excellent wear resistance, and good contact fatigue strength, ensuring a long bearing life over extended periods of use. For cylindrical roller bearings subjected to impact loads or operating in high-temperature environments, carburized bearing steel (such as 20CrNiMo) can be used. Carburizing treatment achieves a surface hardness of HRC 58-62, while the core possesses excellent toughness, enabling it to withstand impact loads. The cage material varies depending on the application. For low-speed applications, steel cages (such as 08F steel) offer high strength and rigidity; for high-speed applications, copper alloy cages (such as H62 brass) offer excellent wear resistance and lubricity; and for corrosive environments, plastic cages (such as polyamide 66) offer excellent corrosion resistance. In addition, the rolling elements and raceway surfaces of the bearings need to be precisely machined and heat treated to improve surface quality and contact fatigue strength. The surface roughness is generally controlled at Ra0.025-0.1μm, and the roundness error does not exceed 0.001mm.
The main performance parameters of cylindrical roller bearings include rated dynamic load, rated static load, limiting speed, and clearance. These parameters are important criteria for selecting and using bearings. The rated dynamic load refers to the maximum load a bearing can withstand at a rated life of 106 revolutions. It reflects the bearing’s resistance to fatigue damage. The larger the rated dynamic load, the greater the bearing’s load-bearing capacity. The rated static load refers to the maximum load a bearing can withstand when stationary or rotating slowly. It reflects the bearing’s resistance to plastic deformation. The larger the rated static load, the less likely the bearing will deform plastically under static load. The limiting speed refers to the maximum speed a bearing can reach under certain load and lubrication conditions. It is affected by factors such as the bearing’s structure, material, and lubrication method. Exceeding the limiting speed will cause the bearing to heat up, intensify wear, and shorten its service life. Clearance refers to the gap between the inner ring, outer ring and rollers of the bearing, which is divided into radial clearance and axial clearance. Appropriate clearance can ensure the normal operation of the bearing and reduce vibration and noise. Too small clearance will cause serious heating of the bearing, and too large clearance will increase the vibration and noise of the bearing. Therefore, it is necessary to select the appropriate clearance group (such as C2, C0, C3, C4) according to the use conditions.
The installation and maintenance of cylindrical roller bearings have a significant impact on their service life and performance. During installation, ensure that the fit between the bearing’s inner ring and shaft, and between the outer ring and bearing seat, meets the design requirements. Excessive interference fit will reduce the bearing’s internal clearance, while too small an interference fit will cause the bearing to slip during operation, causing wear and heat. Avoid striking the bearing during installation. Use a special tool to evenly press the bearing into the shaft or bearing seat. For separable bearings, install the inner and outer rings separately, then install the rollers and cage. Lubrication is key to ensuring the proper operation of the bearing. Lubricants reduce friction and wear between the rolling elements and raceways, remove heat, and prevent rust. Commonly used lubricants include grease and oil. Grease is suitable for low-speed, high-temperature applications, while oil is suitable for high-speed, high-temperature applications. The grease filling volume is generally 1/3-1/2 of the bearing’s internal space. Too much or too little will affect the lubrication effect. During the maintenance process, the operation of the bearings needs to be checked regularly, including temperature, vibration, noise, etc. If any abnormality is found, the machine should be stopped for inspection in time and the damaged bearings should be replaced. At the same time, the lubricant should be replaced regularly to keep the bearings clean and well lubricated.
Cylindrical roller bearings can fail primarily due to fatigue spalling, wear, burns, cracks, and plastic deformation. Understanding the causes of failure and implementing appropriate preventive measures can effectively extend bearing service life. Fatigue spalling is the most common failure mode. It is primarily caused by fatigue cracks on the raceway and rolling element surfaces under alternating loads. Crack propagation leads to material spalling. Preventive measures include selecting the appropriate bearing model and material, ensuring accurate installation, and enhancing lubrication. Wear is caused by impurities within the bearing, poor lubrication, or improper fit. Preventive measures include keeping the bearing clean, using the appropriate lubricant, and ensuring accurate fit. Burns are caused by bearing overheating, primarily due to poor lubrication, insufficient clearance, or excessive speed. Preventive measures include improving lubrication conditions, selecting appropriate clearance, and controlling the speed within the specified range. Cracks and plastic deformation are primarily caused by overload, shock loads, or material defects. Preventive measures include avoiding overload, selecting tough materials, and strengthening material quality inspection. By properly selecting, installing, and maintaining cylindrical roller bearings, and implementing effective failure prevention measures, you can maximize their performance and extend their service life.
