|
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
| 
