Part 1 of this article dealt with some important parameters that are required to be known by the designer or the selector of the rolling bearings. A through knowledge of all these parameters will benefit a lot to the designer in selecting the proper bearing. The other parameters that a designer or selector should know are discussed in detail below.
Parameters required for the Selection of a Bearing:
5. Type of Bearing: The designer should have a clear idea on the type of bearings needed for the application. A wrong selection of the type of bearing can lead to premature and abnormal failure of the selected bearing. For example an application that calls for the use of a bearing to carry axial load (thrust bearing), a radial load carrying bearing (Cylindrical Roller bearing –NU type) cannot be selected, since the principle of application of the bearings differ from one to another.
6. Shaft Diameter: The diameter of the shaft on which the bearing needs to be mounted on has to be decided upon by the designer. The bearing bores are normally available in sizes that are divisible by 5 for example the bore sizes like 25,30,35,40,45, etc. in the metric series. There also exists a series for the inches series where the bearing sizes are measures in inches. TIP: The inside diameter of the bearing can be know from its number. Simply multiply the last two digits of the bearing with ‘5’. Or the other way around divide the diameter of your shaft by ‘5’ to know the last two digits of the bearing number.
7. Presence of Errors in the shaft: The designer should know about the presence of errors in the shaft like static angular misalignment, dynamic angular misalignment, etc. Because it is quite impossible to have all application to run without these errors. Certain types of bearings can accommodate these types of errors to a minimum extent possible like in the case of spherical roller bearings which can accommodate angular misalignments up to 3 Deg.
8. Expected Life of the bearing: This is an important criterion that every designer must have in mind before the selection of a rolling element bearing. The bearing in majority of the cases forms the heart of the equipment. Just think about the bearings used in the engine of a plane, the designer must really consider the amount of life he expects out of the bearing. This data will help a lot in selecting the right kind of bearing.
9. Severity in operation: This relates to the type of operation the bearing is going to be subjected to. For example a bearing used in the water pump in our homes has a lesser severity of operation compared to a pump pumping sewage. The amount of shock loads tends to be high in the pump that pumps sewage. This is accounted for during the selection by the introduction of a application factor. The value of the application factor varies from manufacturer to manufactures and has to be consulted only with the selection data of the respective manufacturer.