Bearings, as the core components of mechanical products, bear the heavy responsibility of supporting the rotating shaft. According to the differences in the friction characteristics of bearings, bearings can be divided into two categories: rolling friction bearings (rolling bearings for short) and sliding friction bearings (sliding bearings for short). These two types of bearings have their own advantages and disadvantages in structure and performance. In practical applications, the selection of bearings requires comprehensive consideration of many factors.

Comparative analysis of rolling bearings and sliding bearings

• Comparison of structure and movement mode

  The most significant difference between rolling bearings and sliding bearings is whether they are equipped with rolling elements. Rolling bearings, such as balls, cylindrical rollers, tapered rollers or needle rollers, support the shaft through their rotation, so that the contact area is limited to a few points, and the more rolling elements there are, the more contact points there are. Sliding bearings, on the other hand, do not have such rolling elements and rely on a smooth surface to support the shaft, and their contact area is a single surface. This structural difference directly leads to the rolling movement of rolling bearings and sliding movement of sliding bearings, which in turn leads to fundamental differences in friction forms.

• Comparison of load-bearing capacity

  In general, plain bearings usually have better load-bearing capacity than rolling bearings due to their larger pressure-bearing area. At the same time, rolling bearings are relatively weak in their ability to withstand shock loads. However, if rolling bearings are fully lubricated by liquid, the cushioning and vibration absorption effects of the lubricating oil film can significantly improve their ability to withstand shock loads. It is worth noting that at high speeds, the centrifugal force of the rolling elements in rolling bearings increases, which reduces their load-bearing capacity and may cause noise. In contrast, the load-bearing capacity of hydrodynamic plain bearings increases with increasing speed.

• Comparison of friction coefficient and starting friction resistance

  Under normal working conditions, the friction coefficient of rolling bearings is usually lower than that of sliding bearings, and its value is more stable. In contrast, the lubrication state of sliding bearings is easily affected by external factors such as speed and vibration, resulting in a larger range of friction coefficient variations. During the startup phase, since sliding bearings have not yet established a stable oil film, their starting friction resistance is often greater than that of rolling bearings. However, the starting friction resistance and operating friction coefficient of hydrostatic sliding bearings remain at a low level.

• Comparison of operating speed applicability

  The operating speed of rolling bearings is limited by the centrifugal force of the rolling elements and the temperature rise of the bearings. Therefore, they are not suitable for high-speed working conditions and are mostly suitable for medium and low speed environments. Incompletely liquid-lubricated bearings are also affected by heat and wear, and their operating speed cannot be too high. In contrast, fully liquid-lubricated bearings, especially hydrostatic sliding bearings that use air as a lubricant, can achieve high-speed rotation of up to 100,000 r/min.

• Power loss comparison

  Rolling bearings usually have lower power loss due to their lower friction coefficient, which is better than incompletely liquid-lubricated bearings. However, if lubrication and installation are not done properly, their power loss may increase significantly. Fully liquid-lubricated bearings have lower friction power loss, but hydrostatic sliding bearings may have higher total power loss than hydrostatic sliding bearings due to the oil pump power loss.

• Service life comparison

  The service life of rolling bearings is affected by material pitting and fatigue, and the design life is usually 5 to 10 years or replaced during overhaul. The bearings of incomplete liquid lubrication bearings wear quickly and need to be replaced regularly. The service life of fully liquid lubricated bearings is theoretically unlimited, but in actual use, due to the influence of stress cycles, especially hydrodynamic sliding bearings, the bearing material may suffer fatigue damage.

• Comparison of rotational accuracy

  Rolling bearings usually have high rotational accuracy due to their small radial clearance. Incompletely liquid-lubricated bearings are unstable and severely worn under boundary lubrication or mixed lubrication conditions, so their accuracy is low. Completely liquid-lubricated bearings have high buffering and vibration absorption capabilities due to the presence of oil film, thus ensuring high rotational accuracy, among which hydrostatic sliding bearings have better rotational accuracy.

• Comparison in other aspects

  Rolling bearings use oil, grease or solid lubricants in small quantities. When working at high speeds, the amount of lubricant used will increase, and the requirements for oil cleanliness are also high, so good sealing performance is required. Sliding bearings, especially fully liquid-lubricated sliding bearings, use a large amount of lubricant and have equally strict cleanliness requirements. In addition, the bearing bushings of sliding bearings need to be replaced frequently, and sometimes even the journals need to be repaired.

Selection of rolling bearings and sliding bearings

Under actual working conditions, there is no uniform standard for the selection of rolling bearings and sliding bearings, because the actual working conditions are very complex and diverse. Rolling bearings are widely favored for their small friction coefficient, small starting resistance, high sensitivity, high efficiency, excellent interchangeability and versatility. They are quite convenient to use, lubricate and maintain, so they have become the first choice in many machines. However, sliding bearings also have their unique application occasions.

Sliding bearings are often used in certain specific occasions, such as when the radial space size is limited or the installation must be split. Due to the structural characteristics of rolling bearings, their radial dimensions are relatively large, so in these occasions, sliding bearings may be more suitable. For those equipment that require high precision, such as precision grinders and various precision instruments, sliding bearings are also more widely used because their lubricating oil film can provide buffering and vibration absorption functions.

Of course, sliding bearings also have their specific application occasions, such as extremely high working speed, extremely large impact and vibration, and need to work in water or corrosive media. In these cases, the reasonable selection of sliding bearings can give full play to their advantages.

In summary, for different machines and equipment and actual working conditions, the selection of rolling bearings or sliding bearings requires comprehensive consideration of various factors. In the past, large crushers often used sliding bearings cast with babbitt alloy to withstand impact loads and wear resistance requirements; while small jaw crushers used more rolling bearings to improve transmission efficiency and sensitivity. With the advancement of rolling bearing manufacturing technology, large jaw crushers are now gradually using rolling bearings as the mainstream choice.

In addition, heavy load occasions are also common applications for sliding bearings. Under heavy load conditions, rolling bearings are prone to heat and fatigue, while sliding bearings can better withstand such loads. For example, sliding bearings play an important role in rolling mills, steam turbines, aircraft engine accessories, and mining machinery.