Full definition
The speed factor (n·dm) is a critical parameter in evaluating the operational demands placed on a bearing due to its rotational speed and size. It is calculated using the formula n·dm = n (RPM) × dm, where dm is the mean bearing diameter, calculated as (d + D) / 2, with d being the inner diameter and D the outer diameter of the bearing, both measured in millimeters. The speed factor serves as an essential guideline in the selection of the appropriate lubrication type for bearings, ensuring optimal performance and longevity under varying operational conditions.
Typical speed factor ranges assist engineers in determining the most suitable lubrication system for their applications. For speed factors below 150,000, general-purpose lubricants, such as NLGI 2 grease, are often adequate. When the speed factor falls within the range of 150,000 to 400,000, it is advisable to utilize specialized high-speed greases or oils that can better withstand the demands of increased rotational speeds. For speed factors exceeding 400,000, advanced lubrication methods such as oil jet lubrication are recommended, along with the use of precision bearings classified as P4 or P5, which provide a higher level of accuracy and durability due to their design features, such as polyamide cages or ceramic hybrid materials.
Understanding the speed factor helps in selecting the right bearing for specific applications. For instance, in high-speed machinery, using a bearing with a suitable speed factor alongside the correct lubrication can significantly improve performance and reduce the risk of premature failure. ISO 15 provides guidance on the viscosity grades of lubricants, ensuring that the selected grease or oil matches the operational requirements of the bearing system.