In the field of modern mechanical engineering, bearings, as key components, are of paramount importance. They are like the “joints” of mechanical equipment, supporting mechanical rotating bodies, reducing the friction coefficient of mechanical loads during transmission, and ensuring the stable and efficient operation of the equipment. There are many types of bearings, each with its unique design, performance characteristics, and applicable scenarios. Choosing the right bearing is crucial for improving the performance of mechanical equipment, extending its service life, and reducing maintenance costs. Next, we will delve into the selection and application scenarios of different types of bearings.
Common Bearing Types and Their Characteristics
Deep Groove Ball Bearings
Deep groove ball bearings are one of the most common types of bearings. They have a simple structure, consisting of an outer ring, an inner ring, a set of steel balls, and a set of cages. The raceway of the bearing ring is in the shape of a continuous deep groove, and the projection of the contact point between the steel ball and the raceway in the radial plane is approximately circular. This structure enables deep groove ball bearings to mainly bear radial loads and also a certain amount of axial loads. When the radial clearance of the bearing increases, it has the properties of an angular contact ball bearing and can bear alternating axial loads in both directions. Deep groove ball bearings have a small friction coefficient, high limiting speed, high precision, and relatively affordable prices.
Angular Contact Ball Bearings
There is a contact angle between the rings and balls of angular contact ball bearings, and the standard contact angles are generally 15°, 30°, and 40°. The size of the contact angle directly affects the performance of the bearing. A larger contact angle means stronger axial load capacity; a smaller contact angle is more conducive to high-speed rotation. Single-row angular contact ball bearings can bear radial loads and unidirectional axial loads, while double-row angular contact ball bearings can bear radial loads and bidirectional axial loads. In terms of structural design, such bearings usually consider how to better cope with combined loads and can operate stably at higher speeds.
Self-Aligning Ball Bearings
Self-aligning ball bearings have a unique structure with double rows of steel balls and the outer ring raceway is of an inner spherical type. This special design allows them to automatically adjust for misalignment caused by deflection or eccentricity of the shaft or housing, having good self-aligning performance. Self-aligning ball bearings mainly bear radial loads, and the tapered bore bearings can be conveniently mounted on the shaft using fasteners, making installation and disassembly relatively easy.
Spherical Roller Bearings
Spherical roller bearings are equipped with spherical rollers between the outer ring with a spherical raceway and the inner ring with double raceways. According to different internal structures, they are divided into four types: R, RH, RHA, and SR. Due to the fact that the arc center of the outer ring raceway is consistent with the bearing center, they have self-aligning performance and can automatically adjust for misalignment caused by deflection or eccentricity of the shaft or housing. Spherical roller bearings can not only bear large radial loads but also bidirectional axial loads, with strong load-carrying capacity.
Tapered Roller Bearings
Tapered roller bearings are equipped with frustum-shaped rollers, and the rollers are guided by the large rib of the inner ring. Their design feature is that the vertices of the conical surfaces of the inner ring raceway surface, outer ring raceway surface, and roller rolling surface intersect at a point on the bearing centerline. Single-row tapered roller bearings can bear radial loads and unidirectional axial loads, while double-row tapered roller bearings can bear radial loads and bidirectional axial loads. This type of bearing is suitable for bearing heavy loads and impact loads, with line contact between the rollers and the raceways, resulting in high load-carrying capacity.
Cylindrical Roller Bearings
The rollers of cylindrical roller bearings are usually guided by two ribs of one bearing ring. The cage, rollers, and guiding ring form an assembly, which can be separated from the other bearing ring, belonging to separable bearings. This kind of bearing is relatively convenient to install and disassemble, especially when the inner and outer rings are required to have interference fits with the shaft and housing, its advantages are more obvious. Cylindrical roller bearings generally mainly bear radial loads, and only single-row bearings with ribs on both inner and outer rings can bear small constant axial loads or large intermittent axial loads.
Thrust Ball Bearings
Thrust ball bearings are composed of a washer-shaped raceway ring with a raceway, balls, and a cage assembly. The raceway ring matched with the shaft is called the shaft ring, and the raceway ring matched with the housing is called the seat ring. Single-direction thrust ball bearings can bear unidirectional axial loads, and double-direction thrust ball bearings can bear bidirectional axial loads, but neither can bear radial loads. Thrust ball bearings have a compact structure, occupy small space, and are suitable for occasions with large axial loads.
Thrust Roller Bearings
Thrust roller bearings are used to bear axial loads as the main shaft and radial combined loads, but the radial load shall not exceed 55% of the axial load. Compared with other thrust roller bearings, this type of bearing has a lower friction coefficient, higher speed, and a certain degree of self-aligning ability. The rollers of type 29000 bearings are asymmetric spherical rollers, which can reduce the relative sliding between the rollers and the raceways during operation. Moreover, the rollers are long, have a large diameter, and a large number of rollers, resulting in a large load capacity. They are usually lubricated with oil, and in individual low-speed cases, grease lubrication can be used.
Bearing Selection Principles
Considering Load Type and Magnitude
This is the primary factor in bearing selection. If mainly bearing radial loads, roller bearings such as cylindrical roller bearings and spherical roller bearings are good choices because the line contact between their rollers and raceways can bear large radial forces. For example, in rolling mills, the huge rolling force makes the rolls need to bear strong radial loads, and at this time, cylindrical roller bearings can exert their advantage of strong load-carrying capacity. When axial loads are dominant, thrust ball bearings and thrust roller bearings are more suitable. For instance, in ship propulsion systems, the propeller shaft mainly bears axial thrust, and thrust roller bearings can effectively cope with this working condition. In the case of combined radial and axial loads, angular contact ball bearings or tapered roller bearings can meet the requirements. In automobile transmissions, gear shafts bear both radial forces from gear meshing and axial forces caused by operations such as gear shifting, and tapered roller bearings can well adapt to this combined load environment.
Paying Attention to Speed Requirements
Different bearing types have different performances in terms of limiting speed. For high-speed rotating equipment, such as machine tool spindles and high-speed motors, angular contact ball bearings are ideal choices. Their design features enable them to maintain stable operation at high speeds, reducing vibration and noise. Angular contact ball bearings have a small contact angle, and the friction between the balls and the raceways is relatively small, which is conducive to high-speed rotation. However, bearings such as spherical roller bearings, due to their structure and roller characteristics, have relatively low speeds and are not suitable for high-speed working conditions. In some applications of electric spindles that require high precision and high speed, angular contact ball bearings can meet the strict requirements of the equipment for running precision and speed.
Adapting to the Working Environment
The working environment has an undeniable impact on bearings. In humid environments or environments with corrosive media, such as chemical equipment and food processing machinery, bearings with good corrosion resistance should be selected, such as deep groove ball bearings made of stainless steel or bearings with special coatings. In high-temperature environments, such as heating furnace rollers in the metallurgical industry and turbochargers of internal combustion engines, high-temperature resistant bearings are essential. These bearings can maintain stable performance at high temperatures, preventing problems such as material performance degradation and lubrication failure caused by excessive temperatures. In dusty environments, such as mining machinery and construction machinery, bearings with good sealing performance can effectively prevent dust from entering, protect the internal structure of the bearings, and extend their service life. Deep groove ball bearings with dust covers or seals are commonly used in such environments.
Considering Installation and Maintenance
The convenience of installation and maintenance of bearings is also a factor to be considered during selection. Some separable bearings, such as cylindrical roller bearings, are relatively easy to install and disassemble, which can save time and labor costs when the equipment needs to be repaired or parts replaced. For equipment that requires regular maintenance, it is more appropriate to choose bearing types that are easy to add lubricants and inspect. Some bearings with oil injection holes or that can be installed with lubrication devices can facilitate lubrication operations, ensuring that the bearings operate under good lubrication conditions. In some large mechanical equipment, such as wind turbines, due to the high difficulty and cost of maintenance, selecting bearings with high reliability and low maintenance requirements, such as spherical roller bearings, can reduce equipment downtime and improve overall operating efficiency.
Bearing Selection Examples in Different Application Scenarios
Automotive Industry
- Engine: During the operation of an automobile engine, the crankshaft needs to bear complex loads, including periodic gas pressure, inertial force of the piston connecting rod, etc. These loads include both radial and axial forces, and the engine speed is relatively high. Therefore, a combination of sliding bearings and cylindrical roller bearings is usually used for the engine crankshaft. Sliding bearings can provide good anti-friction performance and load-carrying capacity, adapting to the high-load and high-speed working requirements of the engine; cylindrical roller bearings are used to bear part of the radial load, ensuring the stable operation of the crankshaft.
- Transmission: The gear shafts in the transmission need to bear both radial and axial loads, and are subject to impact loads during gear shifting. Tapered roller bearings are widely used in automobile transmissions due to their ability to bear combined loads and impact loads. They can effectively support the gear shafts, ensure correct meshing between gears, and transmit power.
- Wheel Hub: Automobile wheel hub bearings need to bear the weight of the vehicle (radial load) and the axial force generated during braking. A combination of deep groove ball bearings and angular contact ball bearings is commonly used for automobile wheel hubs. Deep groove ball bearings mainly bear radial loads, while angular contact ball bearings are used to bear axial loads. They work together to ensure the stable rotation of the wheel hub and meet various working conditions of the automobile during driving.
Industrial Machinery
- Machine Tools: Machine tool spindles have extremely high requirements for precision and speed. Angular contact ball bearings, with their characteristic of maintaining high precision at high speeds, have become the preferred bearing type for machine tool spindles. Multiple angular contact ball bearings are usually installed in pairs to improve the rigidity and load-carrying capacity of the spindle, meeting the requirements for high precision and high speed during cutting processing of machine tools. For example, in precision CNC machining centers, the spindle speed can reach tens of thousands of revolutions per minute, and angular contact ball bearings can ensure that the runout accuracy of the spindle during high-speed rotation is controlled within a very small range, thereby ensuring the high precision of machined parts.
- Cranes: When cranes lift heavy objects, components such as hooks and boom arms bear huge loads, which are mainly axial loads. Thrust roller bearings are suitable for bearing such working conditions where axial loads are dominant. Their large load capacity and good self-aligning performance can ensure the stability and reliability of cranes during operation. In large port cranes, thrust roller bearings can support huge lifting mechanisms, realizing the stable lifting and lowering of heavy objects.
- Conveyor Belts: The rollers in the conveyor belt system mainly bear the weight of the conveyor belt and materials, which is a radial load. Deep groove ball bearings are widely used in conveyor belt rollers due to their simple structure, low cost, and ability to bear a certain radial load. They can make the rollers rotate smoothly, reduce the frictional resistance between the conveyor belt and the rollers, and ensure the efficient operation of the conveyor belt system.
Home Appliance Field
- Washing Machines: During the washing and dehydration process of washing machines, the motor drives the inner tub to rotate, and the inner tub shaft needs to bear a certain radial and axial load, and the speed is relatively high. Deep groove ball bearings with rubber seals are commonly used in washing machine motors and inner tub shafts. Deep groove ball bearings can meet their requirements for speed and radial load, and rubber seals can prevent liquids such as water and detergents from entering the interior of the bearings, avoiding rust and damage to the bearings, and extending their service life.
- Air Conditioner Compressors: When air conditioner compressors are working, the crankshaft needs to bear high pressure and speed, and the load is relatively complex. A combination of sliding bearings and rolling bearings is more common. Sliding bearings are used to bear the main radial and axial loads, providing good anti-friction performance; rolling bearings are used for auxiliary support and improving the operating efficiency of the compressor. In some high-efficiency and energy-saving air conditioner compressors, high-precision rolling bearings are used, which can reduce friction power consumption and improve the energy efficiency ratio of the compressor.
Aerospace
- Aircraft Engines: Aircraft engines are in extreme working conditions of high temperature, high pressure, and high speed during flight. Angular contact ball bearings and cylindrical roller bearings play a key role in aircraft engines. Angular contact ball bearings are used to bear the axial and radial loads of the engine rotor, ensuring the high-speed rotation accuracy of the rotor; cylindrical roller bearings are used to support certain components of the engine, bearing large radial loads. These bearings are usually made of special high-temperature resistant and high-strength materials, and undergo precision processing and strict quality inspection to ensure the safe and reliable operation of the engine under complex working conditions.
- Aerospace Instruments: Aerospace instruments have extremely high requirements for precision and reliability. Small deep groove ball bearings and miniature angular contact ball bearings are commonly used in rotating components of aerospace instruments, such as gyroscopes and accelerometers. These bearings can provide precise rotational support in a small space, ensuring the accuracy and stability of instrument measurements, and providing pilots with accurate flight data.
