| | | Life of a Linear System: If a linear system reciprocates when it is under a load, a continuous stress acts on it, ultimately causing flaking of its rolling elements and/or rolling surfaces due to material fatigue, making it inoperable. The distance a linear system travels before this flaking condition first occurs is called the life of the system. A linear system can also become inoperable due to sintering, cracking, pitting, or rusting. These factors are differentiated from those affecting the life because they are related to installation accuracy, operating environment, or the selected lubrication method of the installer. Rated Life: Even when two linear systems are manufactured at the same time, have the same part number, and are used under identical conditions, their lifetimes can differ due to differences in their fatigue failure characteristics. This prevents determining the life of any particular linear system. Therefore, the rated life is determined statistically and is defined as the distance 90% of linear systems travel before experiencing flaking. Rated Basic Dynamic Load(compliant with ISO14728-1*2) and Rated Basic Dynamic Torque: The life of a linear system is expressed in terms of the distance traveled. Therefore, the life of a linear system is calculated using the allowable load that corresponds to a certain distance traveled. This allowable load is a measure of the system's performance relative to the applied load and is called the rated basic dynamic load. It is defined as a constant-direction load with a magnitude corresponding to a life of 50x103 m. In some cases or linear systems, the basic dynamic load rating may vary depending on the direction of the applied force. In the NB Linear System catalog, the value of the basic dynamic load rating is assumed when a force is applied from directly above and is indicated in the dimension tables. For ball splines, the linear motion may involve torque loading, so the basic dynamic torque rating is defined in a similar fashion. *2: This does not apply to some products. | | Rated Life Estimation: The rated lifetime estimation depends on the type of rolling element used. Both Equations (3) and (4) are used for ball and roller elements respectively. In cases when torque loading is applied, Equation (5) is to be used. When a ball is used as the rolling element, L = (-f - )3 ' 50 (3) When a roller is used as the rolling element, (C \10'3 When torque loading is applied, L = (-^ )3 ' 50 (5) L : rated life(km) C : basic dynamic load rating(N) P : applied load(N) Ct : basic dynamic torque rating(N-m) T : applied torque(N-m) Numerous variables, such as guide rail accuracy, mounting conditions, operating conditions, vibration and shock while under linear motion affect an actual application. Therefore, calculating the actual applied load accurately is extremely difficult. In general, the calculation is simplified by using coefficients representing these effects. These coefficients include hardness (fh), temperature (f-), contact (fc), and applied load (fW). By using these coefficients, Equations (3) ~ (5) can be expressed by Equations (6) ~ (8). When a ball is used as the rolling element, L=(fT • p ) •50(6) When a roller is used as the rolling element, L = ( fH-fT'fc . C )103 . 50 ..................(7) I fw P ' When torque loading is applied, L = (JF^._Ct)3. 50 ........................ fw T L : rated life(km) fH : hardness coefficient fC: contact coefficient fW : applied load coefficient P : applied load(N) C : basic dynamic load rating (N) Ct : basic dynamic torque rating(N-m) T : applied torque(N-m) | | |