Allowance of abrasion for oil-less bearing depends on its dimension and accuracy, which directly leads to its lifetime. Since abrasion amount can be changed due to other conditions such as speed, load, inflow of foreign substance, temperature, axis processing status, and tolerance, it is difficult to accurately anticipate the abrasion amount and life time without using it. Also, oil-less bearing is mostly used in complex and special conditions compared to ball and roller bearing, so it is difficult to anticipate the life time using calculation formula. However, the wear amount is estimated by the following formula.
W = K.P.V.T
specific wear amount K
| Lubrication | mm/kgf/cm2 · m/min · hr |
|---|---|
| Dry | 1 X 10-3 ~ -5 |
| Boundary lubrication under low speed | 1 X 10-5 ~ -7 |
| Periodic lubrication | 1 X 10-6 ~ -8 |
| Continuous lubricaiton under water application | 1 X 10-8 ~ -10 |
PV value is a value that has multiplied surface pressure per unit area P (kgf/cm2, unit area for bearing is internal diameter x length) and speed per unit time V (m/min), which is used as important criteria for selecting bearing. Therefore, PV value should be calculated and selected as indicated below so that it does not exceed allowable PV value for each bearing. Calculation formula is indicated as below.
PV value calculation formula
| Bushing | P(kgf/㎠) | V(m/min) | PV(kgf/cm2·m/min) |
|---|---|---|---|
Radial journal rotation  |
102 W / ød X L | π ød n / 103 | π W n / 10 X L |
Oscillation  |
102 W / ød X L | π ød c θ / 180 X 103 | π W c θ / 18 X 102 X L |
Reciprocation  |
102 W / ød X L | 2 c S / 103 | W c S / 5 X ød X L |
| Washer | P(kgf/㎠) | V(m/min) | PV(kgf/cm2·m/min) |
Thrust motion  |
Rotation | Rotation | Rotation |
| 400 W / π X (øD2 - ød2) | π øD n / 103 | 4 W øD n / 103 X (øD2 - ød2) | |
| Oscillation | Oscillation | Oscillation | |
| 400 W / π X (øD2 - ød2) | π øD θ / 180 X 103 | 4 W øD c θ / 180 X 103 X (øD2 - ød2) | |
| Plate | P(kgf/㎠) | V(m/min) | PV(kgf/cm2·m/min) |
Reciprocation  |
102 W / B X L | 2 c S / 103 | W c S / 5 X B X L |
| Item | Unit | Item | Unit | Item | Unit |
|---|---|---|---|---|---|
| Inner diameter | Ød mm | Width | B mm | Stroke distance | S mm |
| Outer diameter | ØD mm | Rotating speed | n rpm | Oscillating angle | θ ° |
| Length | L mm | Oscillating cycle | c cpm | Load | W kgf |