Rolling bearing type selection-06

The required service life L is determined based on the total accumulated time that the equipment is expected to work. The common unit is the number of working hours. The calculation of life can also be expressed by the total number of revolutions of the bearing. In the process of calculating the service life, various working states are Must be considered. Is the equipment working on an eight-hour shift or a working day? Is it used continuously throughout the day? Does it start and stop frequently or does it work for a long time once it is started?

Maintenance costs, probabilistic life and scrap must also be considered. Is it more cost-effective to replace the equipment after long-term use or to perform regular repairs (including bearing replacements)? Of course, the reliability of the bearing is a major consideration when determining the required life L. The standard reliability level in the bearing industry is usually stipulated as 90%, that is, based on a large number of bearings working in the same application Among them, 90% of the bearings remain intact when reaching the selected bearing working life (L life). If the failure rate is required to be low, the required life L needs to be corrected.

Improving the reliability of the bearing to make it higher than 90% reliability can be solved by reducing the service life of the standard bearing with a 10% failure rate. In other words, if greater reliability is to be achieved, the life of the standard bearing must be reduced. For example: for a bearing with a reliability of 96%, the bearing life must be defined as L, not L. Without increasing the bearing size, you must reduce the life of the original L bearing.

Later we will give the design dynamic load carrying capacity of a given bearing as a function of speed, actual bearing load and design life. In a given application, the speed and actual load are given, so the dynamic load capacity is a function of the design life. In order to increase the reliability to 96%, you can increase the outer dimensions of the bearing to achieve the same level as when the operating reliability is 90%, which means you can increase its dynamic load capacity so that it is higher than 90% reliable. The required value for performance requires selecting a larger bearing.

For example, if you require a bearing with a load capacity failure rate of 4% and an operating life of more than 1,000 hours, to achieve these requirements, the life correction percentage given in the table is 53% of the normal L bearing life. Divide the required life by the correction percentage, so L is: 1000/0. 53 = 1887 (h). This result shows that in order to obtain the required 1000-hour life of 96% reliability, it is valuable to introduce the bearing life corresponding to 90% reliability into the dynamic load capacity equation to calculate the bearing size.