BEARING LIFE B020
The anticipated life of a ball bearing is determined by the bearing user not the bearing manufacturer. This life once determined is called the L10 life of the bearing and it is based on a fatigue life. Since the manufacturer of the equipment that uses the bearing is the only one that know the operating conditions he sets the L10 life.
What do we mean by good bearing life? Most of us change the bearings every time we disassemble the equipment to replace the mechanical seal or the packing sleeve. Is this really a sensible thing to do? If you think about it for a minute there is nothing in a bearing to wear out, there are no sacrificial parts.
Bearing life is determined by the number of hours it will take for the metal to fatigue. That is a function of the load on the bearing, the number of rotations, and the amount of lubrication that the bearing receives.
Pump companies predict bearing life measured in years. As an example, the Duriron Pump Company anticipates a three hundred-year life for the radial bearing on their MK II Group II 3 x 2 x 10 pump (75 mm x 50 mm x 250 mm) when pumping a liquid with a specific gravity of “one” (fresh water).
Please look at the following diagram for a reproduction of Durco’s data:
Ball bearings fail for two main reasons:
- High heat caused by over lubrication and overloading. Over lubrication is the larger problem.
- Contamination of the bearing lubrication from moisture and solids. Moisture is the biggest problem.