Types of Bearings and Their Applications

Do you know what kind of mechanical component a bearing is? Bearings are often referred to as the “food of the machinery industry”, they are critical components widely used in various types of machines.

What is a Bearing?

A bearing is a component that assists in the rotation of an object. As the name suggests, a bearing supports the rotating shaft within a machine. Machines that use bearings include automobiles, airplanes, and generators. Common household appliances, such as refrigerators, vacuum cleaners, and air conditioners, also utilize bearings. In these machines, bearings support shafts equipped with wheels, gears, turbines, rotors, and other parts, helping the shaft to rotate smoothly.

Function of Bearing

Bearing reduces friction and makes rotation smoother. Friction inevitably occurs between a rotating shaft and the part that supports the rotation. Bearings are used between the rotating shaft and the support mechanism. By reducing friction, bearings enable smoother rotation and lower energy consumption. This is the primary function of a bearing.

They protect the rotation support part and keep the rotating shaft in the correct position. The rotating shaft and the support part are subjected to significant forces. Bearings prevent the support part from being damaged by these forces and maintain the rotating shaft in its correct position. It is precisely because of these functions that we can use machines repeatedly over long periods.

Different Types of Bearing

The following sections explain the types, differences, and specific applications of common bearings.

Angular Contact Ball Bearing

Angular contact ball bearings can support both radial and axial loads simultaneously. They can operate at relatively high speeds. The larger the contact angle, the higher the axial load-carrying capacity. The contact angle is the angle between the line connecting the contact points of the ball and raceways in the radial plane and the perpendicular line to the bearing axis. High-precision and high-speed bearings typically use a 15-degree contact angle. The contact angle increases under the action of the axial force.

Features

Universally Matchable Bearings: These are specially processed so that when bearings are installed adjacent to each other, any combination can achieve a predetermined internal clearance or preload, as well as an even load distribution, without the use of shims or similar devices. They are used when the load-carrying capacity of a single bearing is insufficient or when the bearing must support combined loads or axial loads in both directions.

Basic Design Bearings: These are intended for single bearing arrangements. Single-row angular contact ball bearings of the basic design are mainly used in configurations where there is only one bearing at each position. Their width and protrusion tolerances are standard grade. Therefore, they are not suitable for mounting two single-row angular contact ball bearings immediately adjacent to each other.

Self-Aligning Ball Bearing

Self-aligning ball bearings come in two structures: cylindrical bore and tapered bore. Cage materials include steel plate and synthetic resin. Their defining feature is that the outer ring raceway is spherical, providing self-aligning properties. This can compensate for errors caused by concentricity issues and shaft deflection, although the relative inclination of the inner and outer rings must not exceed 3 degrees.

They mainly withstand radial loads but can also withstand small axial loads. The axial displacement of the shaft is limited within the clearance limits. Due to their self-aligning performance, they allow for normal operation under conditions where the inner and outer rings are slightly inclined relative to each other, making them suitable for components where strict coaxiality of the housing bore cannot be guaranteed.

Features

• The outer ring raceway of a self-aligning ball bearing is part of a sphere, with the center of curvature lying on the bearing axis. Therefore, the bearing has a self-aligning function; it can automatically adjust when the shaft or housing deflects, without increasing the burden on the bearing. 
• It can withstand radial loads and a moderate amount of axial load in both directions. However, it cannot withstand moment loads.  Because the contact angle is small, it remains almost unchanged under axial load, resulting in low axial load capacity but high radial load capacity. It is suitable for situations with heavy loads or impact loads.
• Double-row self-aligning ball bearings with adapter sleeves and lock nuts can be installed at any position on a smooth shaft, eliminating the need for positioning shoulders.

Spherical Roller Bearing

Spherical roller bearings feature double rows of rollers, a common spherical raceway on the outer ring, and two inner ring raceways inclined at an angle relative to the bearing axis. This ingenious construction provides self-aligning performance, making them less susceptible to errors in the angle between the shaft and the bearing housing, as well as to shaft bending. They are suitable for occasions where angular errors are caused by installation errors or shaft deflection. In addition to radial loads, this bearing can also withstand bidirectional axial loads. Spherical roller bearings are available with cylindrical and tapered bores. The tapered bore has a taper of either 1:30 or 1:12. These tapered bore bearings can be easily and quickly mounted on smooth or stepped shafts using adapter sleeves or withdrawal sleeves.

Applications

• Stamped steel reinforced cages, stamped steel cages, glass fiber reinforced polyamide 66 cages, machined brass two-piece cages, machined brass integral cages, and stamped steel cages for vibration applications. Codes on the bearings may differ for the same structure.
• Paper-making machinery, reduction gears, railway vehicle axles, rolling mill gearbox bearing seats, rolling mill rollers, crushers, vibrating screens, printing machinery, woodworking machinery, various industrial reducers, and vertical self-aligning bearings with seats.

Spherical Roller Thrust Bearing

Spherical roller thrust bearings are roughly similar to spherical roller bearings. The housing washer raceway surface is spherical with its center at a point consistent with the bearing’s central axis. The rollers are spherical, providing an automatic self-aligning function, making them less sensitive to coaxiality and shaft deflection. These bearings are mainly used in oil drilling rigs, iron and steel making machinery, hydroelectric generators, vertical motors, marine propeller shafts, tower cranes, and extruders.

Features

Interference fits should not be used for the outer ring and the bearing housing bore, nor should the fit between the inner ring and the journal be too tight. It is required that the bearing can produce flexible axial displacement when adjusted using a nut during installation. If an interference fit is used with spherical roller bearings, it is easy to alter the contact angle, causing uneven load distribution and high temperature rise. Therefore, the installation fit for the inner/outer rings with the journal and housing bore is generally best when the bearing can be pushed into the journal and housing bore just by using both thumbs.

For the axial installation clearance of spherical roller bearings, adjustment can be made using adjustment nuts on the journal, shims, threads in the bearing housing bore, or preloading springs. The size of the axial clearance depends on the arrangement during installation, the distance between bearings, and the materials of the shaft and housing, and can be determined according to working conditions.

For high-load and high-speed spherical roller bearings, the effect of temperature rise on axial clearance must be considered when adjusting clearance; the reduction in clearance caused by temperature rise must be estimated, meaning the axial clearance should be adjusted to be slightly larger.

For low-speed bearings subject to vibration, installation with no clearance or with preload should be adopted. The purpose is to ensure good contact between the rollers and raceways of the spherical roller bearing, distribute the load evenly, and prevent damage to the rollers and raceways from vibration and impact.

After adjustment, the size of the axial clearance is checked with a dial indicator. The method involves fixing the dial indicator to the machine body or bearing housing, having the indicator tip rest against the smooth surface of the shaft, and pushing the shaft left and right axially; the maximum swing of the needle indicates the axial clearance value.

Tapered Roller Bearing

Tapered roller bearings are separable bearings; both the inner and outer rings have tapered raceways. Depending on the number of roller rows, they are divided into single-row, double-row, and four-row tapered roller bearings. Single-row tapered roller bearings can withstand radial loads and axial loads in a single direction. When the bearing is subjected to a radial load, an axial component force is generated, so another bearing capable of withstanding the reverse axial force is needed to balance it.

Feature

The angle of the outer ring and the diameter of the outer raceway are standardized. Changes are not allowed during design and manufacturing to ensure that the outer ring and inner assembly of tapered roller bearings are universally interchangeable worldwide.

Tapered roller bearings are mainly used to withstand combined radial and axial loads, dominated by radial loads. They have a larger load-carrying capacity but a lower limit speed. Tapered roller bearings can withstand axial loads in one direction and can limit the axial displacement of the shaft or housing in one direction. The load-carrying capacity of the bearing depends on the raceway angle of the outer ring; the larger the angle, the greater the load-carrying capacity.

This type of bearing is a separable bearing. The clearance of single-row tapered roller bearings needs to be adjusted by the user during installation; the clearance of double-row and four-row tapered roller bearings is set at the factory according to user requirements and does not need adjustment by the user.

Tapered roller bearings have tapered inner and outer ring raceways with tapered rollers arranged between them. The projection lines of all tapered surfaces meet at the same point on the bearing axis. This design makes tapered roller bearings particularly suitable for bearing compound (radial and axial) loads.

The axial load capacity of the bearing is largely determined by the contact angle alpha, the larger the angle alpha, the higher the axial load capacity. The size of the angle is represented by the calculation coefficient e; the larger the e value, the larger the contact angle, and the greater the applicability of the bearing to withstand axial loads.

Tapered roller bearings are usually separable, meaning the cone assembly (consisting of the inner ring with rollers and cage) can be installed separately from the cup (outer ring). Tapered roller bearings are widely used in automobiles, rolling mills, mining, metallurgy, plastic machinery, and other industries.

Deep Groove Ball Bearing

Deep groove ball bearings are the most widely used type of rolling bearing. They have low friction resistance and high speed. They can be used on parts that bear radial loads or combined radial and axial loads, as well as on parts that bear axial loads, such as low-power motors, automobile and tractor gearboxes, machine tool gearboxes, and general machines and tools.

When the radial clearance of the bearing is increased, it possesses certain performance characteristics of angular contact ball bearings and can bear combined radial and axial loads.

Compared with other types of bearings of the same size, these bearings have a smaller friction coefficient and a higher limit speed. However, they are not impact-resistant and are not suitable for bearing heavy loads.

After being mounted on the shaft, deep groove ball bearings can limit the axial displacement of the shaft or housing in both directions within the range of the bearing’s axial clearance, so that they can be used for bidirectional axial positioning.

In addition, this type of bearing has a certain self-aligning ability. When inclined 2′ to 10′ relative to the housing hole, it can still work, but it will have a certain impact on the bearing life.

For deep groove ball bearings, if the load is too small during operation, sliding will occur between the balls and the raceway, which can cause scratches. This tendency is particularly present in large deep groove ball bearings, where the balls and cage are heavy.  In many cases, bearings will corrode. There are many reasons for bearing corrosion. The most common factors are as follows:

• Intrusion of moisture, dirt, etc., due to poor sealing devices.
• The bearing has not been used for a long time, exceeding the rust prevention period, and lacks maintenance.
• Large surface roughness of the metal.
• Contact with corrosive chemical media; the bearing was not cleaned properly and has dirt on the surface, or the bearing was touched with sweaty hands. After cleaning, the bearing was not packaged or installed in time and was exposed to the air for a long time, subjected to moisture intrusion and contamination.
• Ambient temperature and humidity and contact with various environmental media; failure of the rust inhibitor or quality not meeting requirements.

Thrust Ball Bearing

Thrust ball bearings are designed to withstand thrust loads during high-speed operation and consist of washer-shaped rings with raceway grooves for ball rolling. Because the rings are cushion-shaped, thrust ball bearings are divided into flat-base cushion types and self-aligning spherical cushion types. Additionally, this bearing can withstand axial loads but cannot withstand radial loads.

Features

• Available in single-direction and double-direction types.
• To allow for installation errors, both single-direction and double-direction types can be selected with spherical self-aligning seat cushions or with spherical seat rings.
• High-quality steel — Utilizing ultra-clean steel that can extend bearing life by up to 80%.
• Advanced Grease Technology — NSK’s lubricant technology can extend grease life and improve bearing performance.
• High-grade Steel Balls — Quiet and smooth during high-speed rotation.
• Installation errors can be accommodated by using the rings found in the options.

Thrust ball bearings are only suitable for parts that bear axial loads on one side and have relatively low speeds, such as crane hooks, vertical pumps, vertical centrifuges, jacks, low-speed reducers, etc. The shaft ring, seat ring, and rolling elements of the bearing are separable and can be mounted and dismounted separately.

Thrust roller bearings are used to bear combined axial and radial loads dominated by axial loads, but the radial load must not exceed 55% of the axial load. Compared with other thrust roller bearings, this bearing has a lower friction factor, higher speed, and self-aligning performance. Thrust cylindrical roller bearings are mainly used in heavy machine tools, high-power marine gearboxes, oil drilling rigs, vertical motors, and other machinery.

Cylindrical Roller Bearing

These are radial rolling bearings where the rolling elements are cylindrical rollers. The internal structure of cylindrical roller bearings adopts a parallel arrangement of rollers, and spacers or spacer blocks are installed between the rollers to prevent the rollers from tilting or rubbing against each other, effectively preventing an increase in rotational torque.

Large and medium-sized electric motors, rolling stock, machine tool spindles, internal combustion engines, generators, gas turbines, reduction gearboxes, rolling mills, vibrating screens, and lifting and transport machinery.

Features

• The rollers and raceway are in line contact or modified line contact, providing large radial load capacity, suitable for bearing heavy loads and impact loads.
• Small friction coefficient, suitable for high speeds, with a limit speed close to that of deep groove ball bearings.
• N-type and NU-type can move axially, able to adapt to changes in the relative position of the shaft and housing caused by thermal expansion or installation errors and can be used as free-end supports.
• High processing requirements for the shaft or seat bore; the relative deflection of the outer ring axis after bearing installation must be strictly controlled to avoid contact stress concentration.
• The inner or outer ring can be separated, facilitating installation and disassembly.

Four-Point Contact Ball Bearing

A four-point contact ball bearing is a separable bearing, it can also be said to be an angular contact ball bearing set that can withstand bidirectional axial loads.  Its inner and outer ring raceways have a peach-shaped cross-section. When there is no load or a pure radial load, the steel ball and the ring appear to have four points of contact, which is the origin of the name.

Four-point contact ball bearings have a separable structure, and a single bearing can replace angular contact ball bearings combined in a face-to-face or back-to-back arrangement.

They can withstand radial loads and bidirectional axial loads, and can limit axial displacement in two directions, but they occupy less axial space than double-row angular contact ball bearings of current specifications.

Compared with other ball bearings, four-point contact ball bearings have smaller axial clearance and higher limit speed when the radial clearance is the same.

Four-point contact ball bearings are suitable for bearing pure axial loads or combined axial and radial loads dominated by axial loads. Because of the double-half inner ring (or outer ring), the number of balls is increased, resulting in a larger load-carrying capacity. 

Under normal working conditions, when this type of bearing bears an axial load in any direction, a contact angle can be formed. The steel ball contacts the inner and outer raceways at one point each, avoiding large sliding friction in the contact area. Therefore, the bearing is not suitable for bearing loads dominated by radial force.

Cylindrical Roller Thrust Bearing

Cylindrical roller thrust bearings are often combined into high-stiffness bearing configurations and can withstand heavy loads and vibration loads without difficulty. They are only suitable for components bearing axial loads on one side and operating at lower speeds, such as crane hooks, vertical pumps, vertical centrifuges, jacks, and low-speed reducers. The shaft washer, housing washer, and rolling elements of the bearing are separable and can be mounted and dismounted separately.

Needle Roller Thrust Bearing

Needle roller thrust bearings have a thrust-stopping function, bear axial loads, have low speeds, and can allow for deflection.

Tapered Roller Thrust Bearing

Tapered roller thrust bearings can form very compact axial bearing configurations. Such bearings can withstand heavy axial loads, are insensitive to impact loads, and have good rigidity. LYTBZ produces single-direction tapered roller thrust bearings and double-direction tapered roller thrust bearings. Screw-down bearings constitute specially designed single-direction tapered roller thrust bearings and contain a full complement of rollers. This type of bearing is used for screw-down bearing configurations in rolling mills. LYTBZ tapered roller thrust bearings have a logarithmic contact profile between the raceway and the rollers, ensuring optimal stress distribution in the bearing, thereby extending bearing life.

Insert Bearing with Housing

An insert bearing with housing is a bearing unit that combines a rolling bearing with a bearing housing. Most insert bearings have a spherical outer diameter and are installed together with a bearing housing that has a spherical inner bore. They come in various structural forms and have good versatility and interchangeability. At the same time, this type of bearing also has a certain degree of self-aligning capability in its design, is easy to install, and has a dual-structure sealing device, allowing it to work in harsh environments.

Structure of Bearing and Their Function

Bearings reduce friction through rolling motion. When the “shaft” begins to rotate, multiple “rolling elements” (“balls” or “rollers”) inside the bearing will begin to roll. Bearings reduce friction through this “rolling motion.” Compared with the “sliding motion” of plain bearings (sliding bearings), bearings with “rolling motion” can reduce friction more effectively and reduce the consumption of rotational energy.

Although there are many types of modern bearings, their basic structure is roughly the same as that conceived by Leonardo da Vinci about 500 years ago. The components of a bearing are:

• Rings: Ring-shaped parts
• Rolling Elements: Parts that roll between the raceway rings (rolling elements include balls and rollers)
• Cage: A part that prevents rolling elements from contacting each other and maintains a certain interval between them.

Rings

The bearing shown in Figure 2 is called a “radial bearing,” which supports forces perpendicular to the shaft.  Ball bearings use “balls” as rolling elements, while roller bearings use “rollers.” Rings are used for such radial bearings.  The inner one assembled onto the shaft is called the inner ring. The outer one is called the outer ring, and it is assembled into the housing.

Rolling Elements

Rolling elements include “balls” and “rollers.” There are various types of rolling elements available for selection based on bearing usage conditions such as the magnitude of support required and rotation speed.

Cage

When the bearing inner ring rotates, the rolling elements will also begin to roll. At this time, if there is no cage in the bearing, adjacent rolling elements will contact each other. The rolling directions of the two rolling elements at the contact surface are opposite, which would form an obstacle to the rolling motion of the rolling elements. To prevent this, a cage is used to separate adjacent rolling elements, allowing them to roll smoothly. Depending on the bearing usage conditions, such as the magnitude of the support force and rotation speed, various types of cages are available for selection.

Raceway rings, rolling elements, and cages each play different roles. Only when these roles are coordinated can the bearing rotate smoothly.  However, with just these components, the bearing still cannot continue to rotate smoothly. Next, we will introduce another important item for bearings.

Lubricant

To ensure that the bearing can rotate smoothly, it is necessary to reduce the friction of the rolling motion and prevent wear of the parts. Lubricant can play this role. Semi-solid grease and liquid lubricating oil are mostly used as bearing lubricants. In addition, “lubricants” also function to reduce internal heat generation in rotating bearings and extend bearing life. Therefore, “lubricant” is also an “important item” for ensuring the “stable” and smooth rotation of bearings.