What is bearing selection? What information do you need to provide for bearing selection?
Bearing selection: Select the type and size of bearings based on the required rated life, space and lubrication conditions, and of course include installation and removal recommendations.
Selection can be simple, based on the general bearing catalog, and experienced application engineers can complete it in ten minutes.
Selection can also be complex, using advanced computer programs and verification tests.
Either way, the basic information required to complete the bearing selection is the same. Perhaps not all information is required in some equipment applications, but the more complete the information provided, the more beneficial it is for the selection practice.
1. Number of bearings
Quantity and cost have a direct impact. If bearings are used in large quantities, the number of bearings required or the annual consumption of bearings will be very important.
Try to choose conventional, standard, and suitable bearings for large-scale selection.
2. Drawing information
Detailed drawings containing bearing dimensions, tolerances, and bearing arrangements are important sources of information, as well as drive equipment and drive connection methods. Through drawings, bearing application engineers can see things that customers think are unimportant.
A bearing assembly drawing that is only partially visible may mean that important factors that affect bearing life are not visible to the application engineer.
3. Load information
The information provided should be sufficient so that the bearing application engineer can have a good understanding of the changes in load direction.
A common mistake is to only give the maximum load, thinking that if the bearing can withstand the highest load, it must be able to withstand lower loads. This is not absolute, and under certain conditions, the rolling elements may slide instead of rolling. Therefore, the maximum and minimum loads should always be given.
Providing only the maximum load may also lead to the use of oversized bearings or not finding bearings that meet the requirements. Some equipment is variable load and variable speed operation, and at the maximum load and speed, the bearing has a life of only a few thousand hours or less. To avoid this, it is best to provide a load diagram that estimates the load change and duration.
4. Impact information
Impact is also a load that is usually high but short-lived. It needs to be compared with the static load capacity of the bearing. Impact will cause the rolling elements to impact the bearing cage, so repeated impact loads will affect the choice of cage.
5. Vibration information
Vibration will have an impact on the bearing, especially when it is stationary. Because of the risk of false brinelling failure (fretting wear caused by rolling elements vibrating in the same position). Vibration can also affect lubricants. For example, under vibration, grease may lose consistency and move away from the bearing.
6. Acceleration information
Bearing selection requires consideration of more than just rotational acceleration, which can cause rolling elements to slide rather than roll. Centrifugal acceleration also needs to be considered. Bearing components rotate around an axis, such as vibrating screens or planetary gearboxes. Centrifugal acceleration affects the choice of bearing cage.
7. Speed information
Speed and load are key parameters, so speed curves or histograms are very useful information. Knowing only the maximum speed can lead to lubrication problems. For example, a lubricant selected based only on the maximum speed may not be able to establish an adequate oil film at lower speeds.
Long stationary times should also be noted. Bearings may fail due to false brinelling due to vibration or stationary corrosion in adjacent equipment.
8. Rated life requirements
Required rating life that is too high may lead to the selection of expensive bearings, seals and lubrication systems. In addition, oversized bearings are more difficult to lubricate, have higher friction torques, and are more sensitive to minimum loads.
According to practice, once L10h exceeds 100,000 hours, the bearing begins to be too large and will fail for reasons other than normal fatigue.
9. Available space
Providing the available space dimensions at the beginning of the selection will allow us to select the right bearing faster. Preliminary preselection of bearings based on the available space and existing shafts.
10. Running accuracy
Standard running accuracy bearings are suitable for most applications. However, some precision-running equipment or equipment running at high speeds will require improved running accuracy.
Note: Overestimating and increasing the need for running accuracy will pay a higher cost.
11. Maximum deformation
Equipment components will deform under load, so the design engineer is likely to require maximum deformation.
For example: The pinion shaft in a bevel gear will bend under high torque, causing the supporting bearing and adjacent components to deform, thereby changing the contact position between the gear teeth.
One way to increase stiffness is to preload the bearing. In most cases, a slight bearing preload will theoretically increase bearing life, but increasing the preload may also cause uncontrolled operation.
12. Friction torque requirements
Some applications may have special requirements for rotational friction torque.
13. Lubrication Method and Lubricant
Sometimes a device requires a specific lubrication method, or a specific lubricant. For example, a gearbox requires a high viscosity gear oil. With the preferred lubrication method and lubricant information, the application engineer will be able to evaluate the operating conditions and whether the bearings are compatible.
14. Temperature
The ambient and operating temperatures will affect the selection of bearings. It is very important to provide the true maximum and minimum temperatures. If only the maximum temperature of the device is given, it may cause problems.