Operating temperature and speed
They influence many performance characteristics of an application and its parts, and do so in various ways depending on the operational state, such as at start-up or in normal operation, when steady-state conditions have been reached.
Estimating the operating temperature and verifying speed limitations is a critical aspect of the analysis of an application.
This section provides details of these primary relationships, and guidance on what to consider.
Bearing operating temperature and heat flow
Temperature has a major influence on many performance characteristics of an application. The heat flow to, from and within an application determines the temperature of its parts.
The operating temperature of a bearing is the steady state temperature it attains when running and in thermal equilibrium with its surrounding elements. The operating temperature results from (diagram 1):
- the heat generated by the bearing, as a result of the combined bearing and seal frictional power loss
- the heat from the application transferred to the bearing via the shaft, housing, foundation and other elements in its surroundings
- the heat dissipated from the bearing via the shaft, housing, foundation, lubricant cooling system (if used) and other cooling devices
The bearing operating temperature depends as much on the application design as on the bearing generated friction. Therefore, the bearing, its adjacent parts and the application should all be thermally analysed.
Bearing size, operating temperature and lubrication conditions
For a given bearing type, the bearing size, operating temperature and lubrication conditions are interdependent as follows (diagram 2):
- Bearing size is selected based on bearing load, speed and lubrication conditions.
- Operating temperature is a function of the bearing load, size, speed and lubrication conditions.
- Lubrication conditions depend on the operating temperature, the viscosity of the lubricant and the speed.
These interdependencies are dealt with by taking an iterative approach to the analysis, in order to achieve an optimum design for a bearing arrangement and select the most appropriate components for it.