Ⅰ. Rolling Bearings and Sliding Bearings
What is a rolling bearing
Rolling bearings refer to bearings in which the friction between the mechanical shaft and the shaft seat is rolling friction. Rolling bearings are composed of inner rings, outer rings, rolling elements, and cages. Among them, the outer ring is fixed as a support; the inner ring rotates with the shaft; the rolling element is the most important, which is related to the performance and service life of the bearing; the cage assists the rolling element to work and makes it evenly distributed. Sliding bearings do not have the above structure, and the key role here is the material used to make the sliding bearings.
In addition, the main function of bearings is to reduce friction. Among them, the magnitude of the friction of rolling bearings is related to the level of its manufacturing process, that is, whether it is accurate. However, the magnitude of the friction of sliding bearings is related to its manufacturing material. Usually, the discussion is about metal sliding bearings and non-metallic sliding bearings (mostly plastic).
What is a sliding bearing?
Bearings that use the sliding motion of shafts and bearings to bear loads are called sliding bearings. Sliding bearings are bearings that work under sliding friction. They also have another name called bearing bushings. This type of bearing has high reliability and will not lock immediately when worn! The rolling bearing is very stable and reliable during operation, and there is not much noise.
Ⅱ. Comparison Between Roller Bearings and Sliding Bearings
1. Structural Differences
Rolling bearings have a clear and structured design, consisting of four parts: inner ring, outer ring, rolling elements, and a cage. The inner ring, which cooperates with the central shaft and rotates together, is matched with the outer ring, which supports the entire bearing on the bearing base. The role of the rolling elements is facilitated by the cage, which evenly distributes them between the inner and outer rings. The performance and lifespan of rolling bearings are directly influenced by the shape, size, and quantity of the rolling elements. The cage's essential role includes evenly distributing the rolling elements and preventing them from falling off, while also facilitating lubrication during rotation. Rolling bearings are relatively easy to maintain, and the maintenance steps are convenient and quick. Therefore, medium working speeds are one of the conditions under which rolling bearings can work stably.
The structure of sliding bearings is less apparent. Compared to the structure of sliding bearings, the choice of materials is more critical for their production. Sliding bearings exhibit stability and low noise during rotation, thanks to the support of a sliding surface rather than a point, which increases the contact area and enhances stability. However, this contact surface also leads to some drawbacks, such as the need for additional power to overcome initial resistance when starting rotation.
Due to the larger contact area, sliding bearings require the application of lubricating oil during operation. The presence of lubricating oil forms a thin oil film between the sliding bearing and the sliding contact surface, effectively reducing friction and surface wear.
Sliding bearings can be applied in areas where applying lubricating oil is challenging or for routine maintenance. They are also more widely used in situations with heavy loads and low-speed operations.
2. Different Types of Movement
As the names suggest, sliding and rolling are the respective modes of operation for sliding bearings and rolling bearings, indicating different forms of friction during operation.
3. Different Friction Forces
Reducing friction between contact points is the main function of bearings. However, for rolling bearings, the size of the friction force is closely related to the structure and manufacturing level of sliding bearings. For sliding bearings, the influence of raw materials on the size of the friction force is more critical. In general, sliding bearings can be classified into metal and non-metal categories.
Under normal working conditions, the friction coefficient of rolling bearings is lower than that of sliding bearings, and the value is relatively stable. However, the lubrication of sliding bearings is easily affected by external factors such as rotation speed and vibration, and the friction coefficient varies widely.
At startup, since the sliding bearing has not yet formed a stable oil film, the resistance is greater than that of the rolling bearing, but the starting friction resistance and working friction coefficient of the hydrostatic sliding bearing are very small.
4. Applicable working speed
Due to the limitations of the centrifugal force of the rolling elements and the temperature rise of the bearings, the speed of rolling bearings cannot be too high, and they are generally suitable for medium and low speed working conditions. Due to the heating and wear of the bearings, the working speed of incomplete liquid lubrication bearings cannot be too high. The high-speed performance of fully liquid lubricated bearings is very good, especially when the hydrostatic sliding bearing uses air as a lubricant, its speed can reach 100,000r/min.
5. Power Loss
Due to the small friction coefficient of rolling bearings, their power loss is generally not large, less than that of incomplete liquid lubricated bearings, but it will increase dramatically when lubrication and installation are improper. The friction power loss of fully liquid lubricated bearings is low, but for hydrostatic sliding bearings, due to the oil pump power loss, the total power loss may be higher than that of hydrodynamic sliding bearings.
6. Comparison of service life
Due to the influence of material pitting and fatigue, rolling bearings are generally designed to last 5 to 10 years, or they are replaced during overhaul. The bearing bushes of incomplete liquid lubrication bearings are severely worn and need to be replaced regularly. The life of fully liquid lubricated bearings is theoretically unlimited. In fact, due to stress cycles, especially hydrodynamic sliding bearings, fatigue damage may occur to the bearing bush material.
7. Rotation accuracy
Due to the small radial clearance, the rotation accuracy of rolling bearings is generally high. Incomplete liquid lubrication bearings are in a state of boundary lubrication or mixed lubrication, and the operation is unstable, and the wear is severe, and the accuracy is low. Due to the existence of oil film, fully liquid lubrication bearings can buffer and absorb vibration, and the accuracy is higher. Hydrostatic sliding bearings have higher rotation accuracy.
8. Comparison of other aspects
Rolling bearings use oil, grease or solid lubricants, and the amount used is very small. The amount used is large at high speeds, and the cleanliness of the oil quality is high, so they require sealing, but the bearings are easy to replace and generally do not need to repair the journal. For sliding bearings, except for incomplete liquid lubricated bearings, the lubricant is generally liquid or gas, the amount used is large, the oil cleanliness requirements are also very high, the bearing bushings need to be replaced frequently, and sometimes the journals need to be repaired.
Ⅲ. Advantages and disadvantages of sliding bearings and rolling bearings.
The most basic structure of a sliding bearing is divided into a bearing shell and a journal.
Sliding friction and rolling friction are essentially different (one is point contact, the other is surface contact), which also has essential advantages and disadvantages.
Advantages and disadvantages of roller bearing
Advantages:
(1) High Speed Capability: Due to the design of rolling elements, rolling bearings can provide lower friction at high rotational speeds, making them suitable for applications requiring rapid rotation, such as mechanical transmission systems and motors.
(2) High Load-Carrying Capacity: Roller bearings effectively distribute loads, making them suitable for high-load applications, such as automotive wheel hubs bearing the weight of vehicles.
(3) Precision and Rigidity: Rolling bearings typically have high precision, offering good axial and radial rigidity. This makes them popular in applications that demand high accuracy and stability.
(4) Maintainability: Roller bearings are generally relatively easy to maintain due to their design, allowing for easy replacement of rolling elements and extending bearing life.
Disadvantages:
(1) High noise
(2) The structure of the bearing seat is relatively complex
(3) High cost
(4) Large radial dimensions and poor vibration reduction ability
(5) Low life and high noise at high speed.
Advantages and disadvantages of sliding bearing
Advantages:
(1) Low Noise: Sliding bearings typically generate less noise due to lower sliding friction during operation. They are suitable for noise-sensitive applications, such as household appliances.
(2) Simple Design: The design of sliding bearings is relatively simple, often composed of fewer components. This simplicity makes them suitable for special designs or applications with limited space.
(3) Low Cost: Due to their simple structure, sliding bearings have relatively low manufacturing costs, making them suitable for applications with tight budgets.
(4) Low-Speed and High Torque Applications: Sliding bearings are commonly used in low-speed rotation and high-torque applications, such as door hinges, skateboards, and hand-crank generators.
Disadvantages:
(1) Complex maintenance, requiring high lubrication conditions;
(2) Boundary lubrication bearings have high friction and wear. (This is also a disadvantage of large contact area)
In summary, the application occasions of sliding bearings are: high speed, high precision, heavy load, and in machines with low speed impact. In addition, rolling bearings are widely used in most occasions. Any product has advantages and disadvantages, and we need to make choices based on our needs.
Ⅳ. Contact Us
If you need to know more about our YIHEDA bearing series plastic structural parts, you can contact our sales manager at any time. We can provide: product selection, technical support, free proofing and other services.