Advanced Bearing Selection and Precision Grade Q&A

1. What is the core classification standard of bearing precision grades? Which scenarios are suitable for different precision grades?
Bearing precision grades are mainly divided based on dimensional tolerance, rotation accuracy, and surface roughness. The common standard is the ISO standard, which is divided into five grades from low to high: P0 (ordinary grade), P6, P5, P4, and P2. Grade P0 has the lowest precision and low cost, suitable for general machinery with low requirements on rotation accuracy, such as agricultural machinery, ordinary motors, and conveying equipment; Grades P6/P5 are precision grades, suitable for scenarios with certain precision requirements, such as machine tool feed shafts, small and medium-sized motors, and automobile hubs; Grades P4/P2 are high-precision grades with minimal rotation error, suitable for high-end equipment such as machine tool spindles, high-speed centrifuges, and precision instruments, which can meet the precise positioning requirements under high-speed operation.

2. What is the definition of bearing internal clearance? Why adjust the clearance according to working conditions?

Bearing internal clearance refers to the gap between the inner and outer rings of the bearing and the rolling elements, divided into radial clearance and axial clearance. Its size directly affects bearing operation accuracy, temperature, and service life. The core reason for adjusting the clearance is to adapt to the working condition temperature and load: under high-temperature conditions, thermal expansion of bearing components will reduce the clearance; if the initial clearance is too small, it is easy to cause jamming and overheating, so a larger clearance needs to be reserved; under heavy-load conditions, contact deformation between rolling elements and raceways will consume the clearance, so a smaller clearance should be selected to ensure load-bearing stability; under high-speed conditions, appropriate clearance can reduce vibration and noise, avoiding increased wear due to friction between components.

3. For bearings of the same size, what are the differences in load-bearing capacity and rotation speed between roller bearings and ball bearings?

The differences mainly come from the contact area and friction form: in terms of load-bearing capacity, roller bearings (such as cylindrical roller, tapered roller bearings) have line contact with the raceway, with a large contact area, so their radial load-bearing capacity is much higher than that of ball bearings of the same size, making them more suitable for heavy-load scenarios; ball bearings (such as deep groove ball, angular contact ball bearings) have point contact with a small contact area, resulting in weak load-bearing capacity but slightly better impact resistance. In terms of rotation speed, ball bearings have a smaller friction coefficient, low running resistance, and their limit speed is higher than that of roller bearings of the same size, suitable for high-speed operation scenarios; while roller bearings have obvious frictional heating, so their maximum speed is relatively low.

4. What is the difference between the basic dynamic load rating and basic static load rating of bearings? How to refer to them during selection?

The basic dynamic load rating refers to the maximum load that a bearing can bear when its service life reaches 1 million revolutions at the rated speed. It is mainly used for life calculation under rotating working conditions and is a core parameter for selecting high-speed, continuous operation equipment; the basic static load rating refers to the maximum load that a bearing can bear when it is stationary or rotating slowly (rotational speed ≤10 rpm). Exceeding this load will cause permanent deformation of rolling elements and raceways, suitable for intermittent operation and static load-bearing scenarios. During selection, for rotating equipment, the actual load must not exceed the basic dynamic load rating, and the service life should be calculated using the life formula; for stationary or low-speed equipment, the basic static load rating is the key check point to avoid plastic deformation.

5. What is the significance of the contact angle of angular contact ball bearings? How to select different contact angles?

The contact angle of an angular contact ball bearing is the angle between the normal line of the contact point between the rolling element and the raceway and the bearing axis. It determines the ratio of the bearing's axial and radial load-bearing capacities. The larger the contact angle, the stronger the axial load-bearing capacity and the weaker the radial load-bearing capacity, and vice versa. Common contact angles are 15° (Type C), 25° (Type AC), and 40° (Type B): 15° contact angle is suitable for high-speed, light-load scenarios, focusing on radial load-bearing, such as the front bearing of machine tool spindles; 25° contact angle is a general type, balancing radial and axial load-bearing, suitable for motors, water pumps and other equipment; 40° contact angle has the strongest axial load-bearing capacity, suitable for scenarios with a large proportion of axial load, such as crane hooks and machine tool tailstocks.

6. How does bearing material affect its performance? What are the common bearing materials?

Material directly determines the hardness, wear resistance, corrosion resistance, and high-temperature resistance of the bearing: ordinary bearings mostly use high-carbon chromium bearing steel (such as GCr15), which has high hardness and good wear resistance after heat treatment, suitable for conventional working conditions; under high-temperature conditions (temperature ＞150℃), heat-resistant bearing steel (such as GCr15SiMn) should be selected, which has stronger oxidation resistance and high-temperature stability; under corrosive conditions (such as chemical and marine environments), stainless steel bearings (such as SUS440C) are selected, which can resist acid-base and water vapor erosion, but their hardness and wear resistance are slightly lower than ordinary bearings; high-end precision equipment can use ceramic rolling element bearings, which have a small friction coefficient, high limit speed, good wear resistance, and anti-magnetic interference, suitable for special high-end scenarios.