Roller bearings are divided into ball bearings and roller bearings according to the rolling elements.
Roller bearings rely on the rolling contact between the main parts to support the rotating parts.
Different roller bearings can withstand different radial and axial forces.
When choosing roller bearings, the choice should be made according to specific working conditions.
Roller bearings mainly include CARB Toroidal Roller Bearings, Cylindrical Roller Bearing, Needle Roller Bearing, Spherical Roller Bearing, Tapered Roller Bearing, Thrust Roller Bearing and other structural types.
Roller bearings extend the working life of wheels, pulleys, fans, pumps, compressors, and other rotating parts by reducing friction and enabling parts to move smoothly.
They have a wide range bearing to provide stability in high-speed applications with high radial loads, radial loads exert force across the diameter (radius) of the shaft, such as those exerted by the load supported by a pulley or wheel.
Tapered roller bearings, cylindrical bearings, and combination bearings support axial and radial loads, such as those encountered on vehicle axels where their force is both through the wheel and along the wheel axis.
Needle roller bearings support high speed, high radial loads in confined spaces.
Spherical roller bearings support heavy shock loads where misalignment is a risk, such as wind turbines, pumps, paper processing, and fans.
Tapered roller bearing cones and cups support high radial and axial loads and are used for such things as axels and gearboxes.
Main Types of Roller Bearings
1)Cylindrical Roller Bearings have high radial load capacity and moderate thrust loads. They contain rollers that are cylindrically shaped but crowned or end-relieved to reduce stress concentrations. Cylindrical roller bearings are similar in design to needle roller bearings but the dimensions of diameter and roller length are closer in magnitude.
2)Spherical Roller Bearings are self-aligning, double row, combination radial and thrust bearings. They use a spherical or crowned roller as the rolling element.
3)Tapered Roller Bearings consist of an inner ring (cone), an outer ring (cup), a cage and rollers, which are profiled to distribute the load evenly across the roller. During operation, tapered roller bearings create a line contact between the raceway and rolling element, distributing loads across a larger area.
4)Needle Roller Bearings are a type of cylindrical roller bearing where the length of the roller is much larger than than the diameter. Needle roller bearings are designed for radial load applications where a low profile is desired.
5)Thrust Bearings are designed for pure thrust loads and can handle little or no radial load. Roller thrust bearings use rollers similar to other types of roller bearings
Why Select the Roller Bearings?
The main considerations are as follows:
The size, direction and nature of the load on the bearing are the main factors for selecting the bearing.
When selecting the bearing according to the size of the load, compared to the point contact of the ball bearing, the main components in the roller bearing are in line contact, which is easy to bear the load and the deformation after the load is small.
When selecting bearings according to the load direction, for pure axial loads, thrust bearings are generally selected. For larger axial forces, choose thrust roller bearings. Choose thrust ball bearings for smaller axial forces. For pure radial loads, deep groove ball bearings, cylindrical roller bearings or needle bearings are generally used. When bearing a radial load while still bearing a small axial load, deep groove ball bearings or tapered roller bearings can be selected; when the axial load is large, angular contact balls with larger contact angles can be selected Bearings or tapered roller bearings.
Under normal circumstances, the speed will not have any influence on the choice of bearing type, but when the speed is large, the speed should be included in the standard of bearing selection.
1) Compared with roller bearings, ball bearings have a higher limit speed, so in the case of high speed, ball bearings are given priority.
2) In the case of the same inner diameter, the smaller the outer diameter, the smaller the rolling elements, so the centrifugal force added to the outer ring by the rolling elements is smaller, so it is more suitable for working at high speeds. According to the properties given in Table 1, needle roller bearings are more suitable for working at high speeds.
3. Bearing’s Self-aligning Performance
When the center line of the shaft does not coincide with the center line of the bearing seat and there is an angular error, or when the shaft is bent or tilted due to force, the axis of the inner and outer rings of the bearing will be deflected. At this time, a self-aligning bearing with a certain degree of self-aligning performance or an outer spherical ball bearing with a seat should be used.
Roller bearings are most sensitive to the deflection of the bearing, and the load carrying capacity of this type of bearing may be lower than that of ball bearings under deflection. Therefore, when the shaft stiffness and the support stiffness of the bearing seat hole are low, or when there is a large deflection moment, the use of such bearings should be avoided as much as possible.
4.Bearing Installation and Removal
When the bearing seat has no split surface and components must be installed and removed in the axial direction, bearings with separable inner and outer rings (such as N0000, NA0000, 30000, etc.) should be preferred.
Lubrication is of great significance to bearings. The lubricant in the bearing can not only reduce friction resistance, but also play a role in heat dissipation, reducing contact stress, absorbing vibration, and preventing rust.
Commonly used lubrication methods for bearings are oil lubrication and grease lubrication. In addition, it is lubricated with solid lubricants. The choice of lubrication method depends on the speed of the bearing. Generally, the dn value of the bearing (d is the inner diameter of the bearing, mm; n is the speed of the bearing, r/min) indicates the speed of the bearing. Figure 5 shows the dn limit for grease lubrication and oil lubrication.
Applications of Roller Bearings
As different types of roller bearings offer different combination of properties like performance, speed, reliability, load capacity, durability and precision, they are used in a wide range of devices and in several different industries. Some of the widely used applications of roller bearings are aviation cargo systems, engines, agriculture industry, heavy equipments and machinery, solar panels, medical equipments, automobile industry, power houses and many others.