Angular contact ball bearings
Angular contact ball bearings are rolling bearings capable of supporting both radial and axial loads. Their inner and outer ring raceways have a specific axial contact angle (typically 15°, 30°, or 40°). The larger the contact angle, the greater the axial load bearing capacity. These bearings are widely used in high-speed, precision transmission systems such as machine tool spindles, automotive transmissions, and aircraft engines. They offer high speed, high precision, and a high maximum speed, meeting the stringent requirements for rotational accuracy (radial runout ≤ 0.005mm) and smooth operation (vibration velocity ≤ 1.8mm/s). The performance of angular contact ball bearings depends on factors such as contact angle, clearance, cage structure, and material. Proper selection and installation are crucial to ensuring their functionality.
The structural characteristics of angular contact ball bearings determine their unique load-bearing performance. Based on the contact angle, they can be divided into three basic types: α = 15° (Type C), α = 30° (Type AC), and α = 40° (Type B). Derivative types include double-row angular contact ball bearings and four-point contact ball bearings. Bearings with a 15° contact angle primarily support radial loads, with relatively weak axial load capacity. They are suitable for high-speed, light-load applications, such as front-end supports for precision machine tool spindles. They have a maximum speed of over 8,000 rpm and a rotational accuracy of P4 (GB/T 307.1). Bearings with a 30° contact angle offer balanced radial and axial load capacity and are the most widely used, such as automotive generator bearings and centrifugal pump main shaft bearings. They can operate stably under conditions with a radial to axial load ratio of 2:1. Bearings with a 40° contact angle primarily support axial loads, with relatively low radial load capacity. They are suitable for applications with heavier axial loads, such as crane drum bearings and vertical turbine main shaft bearings. Double-row angular contact ball bearings can withstand bidirectional axial loads through the symmetrical arrangement of two rows of rolling elements, reducing the axial size of the bearing combination and are suitable for space-constrained occasions, such as the Z-axis screw support of CNC machine tools.
The materials and heat treatment processes of angular contact ball bearings directly impact their precision and lifespan. Rings and rolling elements are typically made of high-carbon chromium bearing steel (such as GCr15). After quenching (oil quenching at 830-860°C) and low-temperature tempering (160-180°C), the hardness reaches HRC61-65, ensuring high wear resistance and contact fatigue strength (contact fatigue life L10 ≥ 1000 hours). For bearings used in high-temperature environments (150-250°C), heat-resistant bearing steel (such as Cr4Mo4V) with a hardness of HRC58-62 is used, maintaining excellent mechanical properties even at 200°C. Cage material selection depends on the rotational speed and operating environment: Steel cages (such as 08 steel stamped cages) are suitable for low to medium speeds (≤3000 r/min) and general environments; copper alloy cages (such as H62 brass machined cages) are suitable for medium to high speeds (3000-6000 r/min) and good lubrication conditions; polyamide (nylon 66) cages are suitable for high speeds (>6000 r/min) and corrosive environments, but their operating temperature must be below 120°C. Bearing accuracy grades are divided into P0, P6, P5, P4, and P2. Bearings graded P4 and above have strictly controlled ring tolerances, rotational accuracy, and surface quality, making them suitable for high-end equipment such as precision machine tools. Their radial runout is ≤0.008mm and their axial runout is ≤0.01mm.
The mounting method of angular contact ball bearings is crucial to their performance. Common mounting methods include back-to-back (DB), face-to-face (DF), and tandem (DT). Each mounting method offers different stiffness and load-bearing characteristics. Back-to-back mounting (with the narrow sides of the two bearing outer rings facing each other) provides a large pivot distance, high rigidity, and the ability to withstand overturning moments, making it suitable for supporting machine tool spindles. For example, a DB arrangement of the front and rear spindle bearings in a horizontal machining center can achieve a radial stiffness exceeding 1000 N/μm. Face-to-face mounting (with the wide sides of the two bearing outer rings facing each other) provides a small pivot distance and can withstand bidirectional axial loads, making it suitable for applications requiring high axial precision, such as supporting the output shaft of a gearbox. Tandem mounting (with the two bearings arranged in the same direction) can withstand large unidirectional axial loads, with a load capacity 1.5-2 times that of a single bearing, making it suitable for equipment such as propeller shafts and rolling mills. Bearing preload must be controlled during installation. Too little preload will result in excessive play and vibration, while too much preload will increase frictional heat and shorten bearing life. The preload force is usually adjusted by the amount of shoulder grinding or the thickness of the spacer sleeve. For P4 grade precision bearings, the preload force is generally 1%-2% of the bearing’s rated dynamic load. For example, the preload force of model 7206AC bearing (rated dynamic load 19.2kN) is controlled at 192-384N.
Lubrication and maintenance of angular contact ball bearings are crucial to ensuring their long-term stable operation. The lubrication method should be selected based on the speed and operating conditions. Grease lubrication is suitable for medium and low speeds (≤6000 rpm). Use lithium-based grease (such as No. 2 lithium-based grease). Fill 1/3-1/2 of the bearing’s internal space . Too much grease will cause stirring heat, while too little will result in insufficient lubrication. Oil lubrication is suitable for high speeds (>6000 rpm). Use oil spray or oil mist lubrication. The lubricant viscosity should be 20-40 cSt at 40°C (such as No. 32 machine oil). The spray pressure should be 0.1-0.3 MPa to ensure that the lubricant fully penetrates the raceway and rolling element contact areas. During operation, regularly check the bearing temperature (≤80°C), vibration (≤2.8 mm/s), and abnormal noise. Abnormally high temperature may indicate poor lubrication or excessive preload. Increasing vibration may indicate bearing wear or loose installation, which requires prompt attention. The life of a bearing is closely related to the operating conditions. Under rated load and speed, the L10 life can reach more than 10,000 hours. However, in actual use, it is necessary to avoid overload (≤120% of the rated dynamic load), overtemperature (≤120°C) and contaminant intrusion (IP65 or above protection level is required). Through proper use and maintenance, the service life of the bearing can be extended to the design life.
