Service Life of OilLess Bushes, Bush Bearings & Wear Plates
The service life of Sleeve type Bearing, which depends on the amount of wear, is greatly affected by friction conditions, regardless if it is dry, boundary lubrication or fluid film lubrication. The ratio of bearing length to shaft diameter has an important effect on the coefficient of friction. For a bearing with a ratio of one (bearing length equal to shaft diameter), the coefficient is generally lowest. Wear amount can be estimated by the following experimental formula.
Theoretical estimation becomes almost useless when a rapid change in wear amount occurs due to lack of lubricant supply or invasion of foreign matter.
W = K · P · V · T
W = Wear Amount (mm)
P = Bearing Pressure N/mm2 {kgf/cm2}
V = Velocity m/s {m/min}
T = Running Time (hr) and
K = Specific Wear Amount mm/(N/mm2·m/s·hr) {mm/(kgf/cm2·m/min·hr)}
If the Specific Wear amount K is known, the Wear Amount W for a given Running Time T is determined and hence, the life of a Bearing is calculated from an allowable Wear Amount of the Bearing. Note that the estimated life given by the above formula should be used only as a reference because other factors, which also affect the Bearing life, have not been taken into consideration. These factors include the Velocity and Load, different modes of operation, type of lubricant used, clearance surface roughness of mating material, invasion of foreign materials, etc. Experiment values of Specific Wear Amount K for Journal Radial Sleeve Bearings under different lubrication conditions are given here for reference:
| Typical Specific Wear Conditions |
Wear Amount (K) |
| No lubrication; lack of oil… |
1 x 10-3 ~ -5 |
| Boundary lubrication condition due to low speed, etc… |
1 x 10-5 ~ -7-5 ~ -7 |
| Relatively good condition due to greasing, etc… |
1 x 10-6 ~ -8 |
| Fluid film lubrication condition… |
1 x 10-8 ~ -10 |
Bearings #ZA 500 under low speed, non-lubricating and high load operation show Specific Wear Amount K of 1 x 10-7
The invasion of foreign particles or the lack of lubrication will lead general oil lubricated bearings to a sudden rise in Specific Wear Amount K, followed by seizure. In contrast OilLess Grade are not sensitive to foreign particles and lack of lubrication and stand longer on such conditions. Their excellent reliability and safety have been verified by R&D and experience over an extended period of time
