EPEN Technology Knowledge: How to Choose Rolling Bearings and Sliding Bearings?

  • Rolling bearings and sliding bearings have their own characteristics in structure and advantages and disadvantages in performance. When selecting them, they should be comprehensively considered in combination with the actual situation

Rolling bearings and sliding bearings have their own characteristics in structure and advantages and disadvantages in performance. When selecting them, they should be comprehensively considered in combination with the actual situation

 

As an essential part of mechanical products, bearing plays an important role in supporting the rotating shaft. According to the different friction properties in bearings, bearings are divided into rolling friction bearings (hereinafter referred to as rolling bearings) and sliding friction bearings (hereinafter referred to as sliding bearings). The two types of bearings have their own characteristics in structure and advantages and disadvantages in performance. When selecting them, they should be comprehensively considered in combination with the actual situation. The following is a comparative analysis of the specific performance of rolling bearings and Sliding Bearings.

 

 

1 Comparison of structure and movement mode

The most obvious difference between rolling bearings and Sliding Bearings is whether there is a rolling element.

 

Rolling bearing: there are rolling elements (ball, cylindrical roller, tapered roller and needle roller) to support the rotating shaft by its rotation, so the contact part is a point. The more rolling elements, the more contact points.

 

Sliding bearing: there is no rolling element, and the rotating shaft is supported by a smooth surface, so the contact part is a surface.

 

The difference between the two structures determines that the motion mode of the rolling bearing is rolling, and the motion mode of the sliding bearing is sliding, so the friction situation is completely different.

 

 

2 Bearing capacity comparison

In general, the bearing capacity of sliding bearings is generally higher than that of rolling bearings due to their large bearing area, and the ability of rolling bearings to withstand impact loads is not high. However, fully liquid lubricated bearings can withstand large impact loads due to the buffer and vibration absorption effect of lubricating oil film. When the rotating speed is high, the centrifugal force of the rolling element in the rolling bearing increases, and its bearing capacity should be reduced (noise is easy to occur at high speed). For the hydrodynamic sliding bearing, its bearing capacity increases with the increase of rotating speed.

 

 

3 Comparison of friction coefficient and starting friction resistance

Under general working conditions, the friction coefficient of rolling bearing is lower than that of sliding bearing, and the value is relatively stable. However, the lubrication of sliding bearings is easily affected by external factors such as speed and vibration, and the friction coefficient changes widely.

 

During start-up, 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 Comparison of applicable operating speeds

Due to the restriction of the centrifugal force of the rolling element and the temperature rise of the bearing, the rotating speed of the rolling bearing can not be too high. It is generally suitable for medium and low speed working conditions. Due to the heating and wear of the bearing, the working speed of the bearing with incomplete liquid lubrication should not be too high. The fully liquid lubricated bearing has very good high-speed performance, especially when the hydrostatic sliding bearing uses air as lubricant, its speed can reach 100000r/min.

 

 

Figure (a) composition of rolling bearing; (b) Composition of sliding bearing

 

5 Power loss comparison

As the friction coefficient of rolling bearings is small, the power loss is generally small, which is less than that of incomplete liquid lubricated bearings, but it will increase sharply when the lubrication and installation are not correct. The friction power loss of fully liquid lubricated bearing is low, but for hydrostatic sliding bearing, the total power loss may be higher than that of hydrodynamic sliding bearing due to the power loss of oil pump.

 

6 Service life comparison

Due to the influence of material pitting and fatigue, the rolling bearing is generally designed for 5-10 years or replaced during overhaul. The bearing bush of incomplete liquid lubricated bearing is seriously worn and needs to be replaced regularly. Theoretically, the life of fully liquid lubricated bearings is infinite. In fact, due to the stress cycle, especially the dynamic pressure sliding bearings, the bearing material may be fatigue damaged.

 

7 Rotation accuracy comparison

Due to the small radial clearance, the rotation accuracy of rolling bearings is generally high. The incompletely liquid lubricated bearing is in the state of boundary lubrication or mixed lubrication, with unstable operation, serious wear and low accuracy. The fully liquid lubricated bearing has high precision due to the existence of oil film, which can buffer and absorb vibration. Hydrostatic sliding bearing has higher rotation accuracy.

 

8 Comparison in other aspects

The rolling bearing uses oil, grease or solid lubricant in a small amount, but in high speed, the amount is large, and the cleanliness of the oil is high. Therefore, it is required to be sealed. However, the bearing is easy to replace, and the journal generally does not need to be repaired. For sliding bearings, except for bearings that are not fully lubricated with liquid, the lubricant is usually liquid or gas, with a large amount of lubricant and high requirements for oil cleanliness. Bearing pads need to be replaced frequently, and sometimes the journal is repaired.

 

More about EPEN Multi-layer Sliding Bearings

Jiashan Epen Bearing Co., Ltd. is a professional manufacturer of sliding bearings, metal plastic composite bearings business, specializing in adhering to do fine, the better for our customers continue to create value concept, is committed Sliding Bearings, new composite materials research, development, promotion and applications. Company's existing main products for metal-plastic composite series Sliding Bearings, bimetal bearings, sliding bearings single metal series, are widely used in automotive, metallurgy, engineering machinery, construction machinery, plastics machinery, machine tool industry, water conservancy and hydropower 30 a number of areas.

 

 

 

Epen Multi-layer Sliding Bearings include EU Bushing, EX Bushing, EU PTFE lined Steel base Bearing, EU PTFE lined Stainless Steel base Bearing, EUB PTFE lined Copper base Bearing, EX POM lined Steel base Bearing, EV PVDF lined Steel base Bearing, EV PVDF lined Copper base Bearing, EK PEEK lined Steel base Bearing, EXB POM lined Copper base Bearing.

 

For example, EU tri-layer maintanence-free bushing have a base of lower carbon steel, onto which a porous bronze layer is sintered. PTFE mixtures are impregnated into the intersice of this bronze layer after rolling process completed. Eu has good physical & mechanical properties, also has certainly chemical properties. It is suitable for rotary, oscillating movement with performance of self-lub. Anti-wear, lower firction, lower noise.