Linear Bearings: Load/Life Calculation  
Linear bearings undergo reciprocating rather than rotary motion so that accelerations are much higher than typically experienced by rotary bearings. Since linear bearings have become important primarily as a result of robotic automation, one must often refer to manufacturer's literature for load/life formulas. What follows is one way to calculate the life of a linear slide bearing. The symbol L is used to represent the rated life. It is defined as the length of travel endured by the slide under a specified condition. In reality, slide life varies from one slide to another, so that a rating referred to as L10 is typically used in industry. The L10 rating is defined as the length of travel that 90% of all slides (of the same model) will complete before the first sign of failure. The following factors are used in the calculation of load/life predictions: 1. Factor for Speed
 
2. Factor for Temperature Excessive temperature can reduce the hardness of loadbearing slide components and lower the life of the slide due to wear and fatigue. We define the factor for temperature of the slide as "ft" and values are tabulated in the following table. Please note that ft is listed assuming that polymer ball separators are not used. Delrin separators can typically only withstand temperatures less than 180ºF.
 
3. Factor for Load Type The load endured by a linear slide bearing is a combination of variable forces, vibrations, impacts, occasional loads, etc. We use the load type factor "fw" to account for these varying forces. The values for "fw" are tabulated in the following table.
Using the factors just defined, the L10 life rating can be expressed as follows:
 
4. Factor for other than 90% Reliability If other than the 90% reliability is required, the known value of L10 shall be multiplied by a reliability factor "fr" such that:
Ln = fr × L10
where Ln = rated life at the reliability of K% (n = 100  K). The values of the factor "fr" are presented in the following table.
 
Adding the "fr" factor in front of the previous equation, the L10 life rating can be expressed as follows, with each factor remaining as before.
