NACHI precision bearings have the requirements of ● large load capacity ● low friction ● smooth and quiet rotation ● high precision ● high rigidity, and these functions must be sustained at the same time. These functions are called bearing durability (grease life, acoustic life, fatigue life, etc.), that is, life in a broad sense. But durability affects its continuance due to various damage and deterioration. In addition, there are other damages such as cracking, seizure, etc. that can also affect bearing life, but these damages should be distinguished from bearing life. The reasons for these damages, in addition to bearing selection errors, also include factors such as bearing peripheral design and bearing installation. On the other hand, the repeated stress caused by the load will cause damage to the bearing material itself due to rolling fatigue. Even if the bearing is used correctly, the life of the bearing in the narrow sense will eventually be reached. Generally speaking, once there are signs of metal fatigue, it can be immediately judged that the bearing can no longer be used, and the life of the bearing will come to an end at this time. The life of the bearing can be expressed by the total number of rotations since the bearing started running or the total running time of the bearing at a certain speed. Even under the same load conditions, the life of the bearing varies according to the size and type of the bearing used. When selecting bearings, recalculate bearing life. The fatigue life (narrow life) of a bearing is originally different for each bearing, and is usually described by the statistical results of the operation of a group of identical bearings under the same conditions. Therefore, when selecting a bearing, the calculated life of the bearing cannot be understood as the average life of all bearings, but can only be understood as the expected life that most of the NACHI bearings can reach. Therefore, we define the rating life and basic load rating Cr or Ca as follows. ●Basic rating life The total number of revolutions that a group of identical bearings can rotate under the same conditions without material damage due to rolling fatigue. ● The basic dynamic load rating (Cr or Ca) can reach the bearing load with the same direction and magnitude of bearing life of 1 million revolutions. The basic rating life of the bearing is calculated according to equations 2.1 and 2.2. (Formula 2.1) (Formula 2.2) L : Basic rating life (rev) Lh : Basic rating life (hours) C : Basic dynamic load rating (N) (Cr for radial bearings, Ca for thrust bearings)P : Bearing load (equivalent dynamic load) (N) (Pr for radial load, Pa for thrust bearing) p : 3 (ball bearing), 10/3 (roller bearing) N : Speed: (min- 1) The basic dynamic load rating when radial ball bearings are assembled in multiple rows is calculated by multiplying the dynamic load rating of single-row bearings by the following coefficients. 2-column with 3-column with 4-column with 1.62 2.16 2.64.